Evolutionary and biogeographic studies in the genus Kniphofia moench (Asphodelaceae)
- Authors: Ramdhani, Syd
- Date: 2007
- Subjects: Asphodelaceae Asphodelaceae -- Genetics Cladistic analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4220 , http://hdl.handle.net/10962/d1003789
- Description: Kniphofia, a genus of approximately 71 species, is almost entirely African with two species occurring in Madagascar and one in Yemen. Commonly known as ‘red hot pokers’ they are popular among horticulturists. The genus is also well known for its complex alpha taxonomy. To date, no studies have examined the phylogenetic relationships among species or the evolutionary history of the genus, and little work has been done on their biogeography. The main focus of this study was (i) to review the alpha taxonomy, (ii) to assess diversity and endemism in Kniphofia, (iii) to use DNA sequence data to reconstruct a specieslevel phylogeny to understand intra-generic species relationships and evolutionary processes (iv) to use phylogeographic approaches to study the biogeography and evaluate biogeographical patterns, and (v) to assess anatomical variation and determine if anatomical characters are useful for species delimitation. It was found that the genus has six centres of diversity, five of which are centres of endemism. The South African Centre is the most speciose and is also the largest centre of endemism. Kniphofia shows a strong Afromontane grassland affinity in Tropical and East Africa. In South Africa, it is found from high altitudes to coastal habitats, with the most speciose regions being Afromontane grasslands. It is thus not considered to be an Afromontane element, but rather an Afromontane associate. Five major evolutionary lineages were identified using cpDNA sequence data (trnT-L spacer), four of which are southern African. The fifth lineage is represented by material from Madagascar, East and Tropical Africa. The nuclear ITS region failed to provide resolution, as many sequences were identical. The five lineages recovered using cpDNA showed some congruence with geographic origin rather than the taxonomic arrangement based on morphology. All of the species with multiple samples were non-monophyletic. This could be due to hybridisation and/or incomplete lineage sorting. The nested clade analysis, although preliminary, did not completely agree with the phylogenetic analyses. One of the three third level nested clades appears to show fragmentation between the Cape Region, KwaZulu-Natal and northern parts of southern Africa. Furthermore, another nested clades recovered suggest a range expansion and radiation from the Drakensberg into the adjacent Drakensberg-Maputoland-Pondoland transition. Morphological species of Kniphofia exhibited substantial leaf anatomical variation and anatomical characters do not cluster samples into their morphological species. The anatomical results do not fit any geographic pattern, nor do they correspond to the lineages recovered using molecular markers or the nested clades. Leaf anatomical variation does not appear to be influenced by geographical or environmental factors. However, hybridisation may play a role but was not tested in this study. In light of the above findings it is proposed that the evolutionary and biogeographic history of Kniphofia is strongly linked to tectonic events, and Quaternary climatic cycles and vegetation changes. Tectonic events (viz. uplifts) may have resulted in vicariance events that may account for the five cpDNA lineages recovered in phylogenetic analyses, while Quaternary climatic cycles and vegetation changes may have had a more recent impact on evolution and biogeography. It is hypothesised that the ancestral area for Kniphofia was much more widespread when Afromontane grasslands were more extensive during cooler and drier glacial episodes. Kniphofia on the high mountains of Tropical and East Africa would have tracked Afromontane grasslands as they expanded their ranges in cooler periods. While during wetter and warmer interglacial periods Kniphofia would have retreated into refugia on the mountains of Tropical and East Africa, with no gene flow possible between these refugia. In South Africa, where latitude compensates for altitude, Kniphofia may have maintained a distribution that extended into the lowlands even during interglacials. A cyclic climate change hypothesis implies that populations of Kniphofia (at different phases of the climatic cycle) would have experienced periods of contractions and fragmentation followed by periods of range expansion and coalescence or secondary contact. Altitudinal shifting is proposed to be the most likely mechanism for fragmentation and range expansion, and would would possibly promoted hybridisation. Within the five lineages there is evidence for recent differentiation as the branch lengths are short, there are numerous nonmonophyletic species and numerous identical haplotypes (cpDNA and ITS) which collectively indicate a recent radiation in southern Africa. A recent radiation would also account for the taxonomic confusion and difficulty in differentiating morpho-species. These climatic events may also account for the substantial anatomical variation in southern African Kniphofia species.
- Full Text:
- Date Issued: 2007
- Authors: Ramdhani, Syd
- Date: 2007
- Subjects: Asphodelaceae Asphodelaceae -- Genetics Cladistic analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4220 , http://hdl.handle.net/10962/d1003789
- Description: Kniphofia, a genus of approximately 71 species, is almost entirely African with two species occurring in Madagascar and one in Yemen. Commonly known as ‘red hot pokers’ they are popular among horticulturists. The genus is also well known for its complex alpha taxonomy. To date, no studies have examined the phylogenetic relationships among species or the evolutionary history of the genus, and little work has been done on their biogeography. The main focus of this study was (i) to review the alpha taxonomy, (ii) to assess diversity and endemism in Kniphofia, (iii) to use DNA sequence data to reconstruct a specieslevel phylogeny to understand intra-generic species relationships and evolutionary processes (iv) to use phylogeographic approaches to study the biogeography and evaluate biogeographical patterns, and (v) to assess anatomical variation and determine if anatomical characters are useful for species delimitation. It was found that the genus has six centres of diversity, five of which are centres of endemism. The South African Centre is the most speciose and is also the largest centre of endemism. Kniphofia shows a strong Afromontane grassland affinity in Tropical and East Africa. In South Africa, it is found from high altitudes to coastal habitats, with the most speciose regions being Afromontane grasslands. It is thus not considered to be an Afromontane element, but rather an Afromontane associate. Five major evolutionary lineages were identified using cpDNA sequence data (trnT-L spacer), four of which are southern African. The fifth lineage is represented by material from Madagascar, East and Tropical Africa. The nuclear ITS region failed to provide resolution, as many sequences were identical. The five lineages recovered using cpDNA showed some congruence with geographic origin rather than the taxonomic arrangement based on morphology. All of the species with multiple samples were non-monophyletic. This could be due to hybridisation and/or incomplete lineage sorting. The nested clade analysis, although preliminary, did not completely agree with the phylogenetic analyses. One of the three third level nested clades appears to show fragmentation between the Cape Region, KwaZulu-Natal and northern parts of southern Africa. Furthermore, another nested clades recovered suggest a range expansion and radiation from the Drakensberg into the adjacent Drakensberg-Maputoland-Pondoland transition. Morphological species of Kniphofia exhibited substantial leaf anatomical variation and anatomical characters do not cluster samples into their morphological species. The anatomical results do not fit any geographic pattern, nor do they correspond to the lineages recovered using molecular markers or the nested clades. Leaf anatomical variation does not appear to be influenced by geographical or environmental factors. However, hybridisation may play a role but was not tested in this study. In light of the above findings it is proposed that the evolutionary and biogeographic history of Kniphofia is strongly linked to tectonic events, and Quaternary climatic cycles and vegetation changes. Tectonic events (viz. uplifts) may have resulted in vicariance events that may account for the five cpDNA lineages recovered in phylogenetic analyses, while Quaternary climatic cycles and vegetation changes may have had a more recent impact on evolution and biogeography. It is hypothesised that the ancestral area for Kniphofia was much more widespread when Afromontane grasslands were more extensive during cooler and drier glacial episodes. Kniphofia on the high mountains of Tropical and East Africa would have tracked Afromontane grasslands as they expanded their ranges in cooler periods. While during wetter and warmer interglacial periods Kniphofia would have retreated into refugia on the mountains of Tropical and East Africa, with no gene flow possible between these refugia. In South Africa, where latitude compensates for altitude, Kniphofia may have maintained a distribution that extended into the lowlands even during interglacials. A cyclic climate change hypothesis implies that populations of Kniphofia (at different phases of the climatic cycle) would have experienced periods of contractions and fragmentation followed by periods of range expansion and coalescence or secondary contact. Altitudinal shifting is proposed to be the most likely mechanism for fragmentation and range expansion, and would would possibly promoted hybridisation. Within the five lineages there is evidence for recent differentiation as the branch lengths are short, there are numerous nonmonophyletic species and numerous identical haplotypes (cpDNA and ITS) which collectively indicate a recent radiation in southern Africa. A recent radiation would also account for the taxonomic confusion and difficulty in differentiating morpho-species. These climatic events may also account for the substantial anatomical variation in southern African Kniphofia species.
- Full Text:
- Date Issued: 2007
Comparative study of the feeding damage caused by the South African biotypes of the Russian wheat aphid (Diuraphis noxia Kurdjumov) on resistant and non-resistant lines of barley (Hordeum vulgare L.)
- Authors: Jimoh, Mahboob Adekilekun
- Date: 2011
- Subjects: Aphids Russian wheat aphid -- Research -- South Africa Barley -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4201 , http://hdl.handle.net/10962/d1003770
- Description: Cereal crop productivity is hampered when these plants are infested by phloem feeding aphids. A great deal of research has been carried out with the direct aim of a clearer understanding of the mechanism involved in the interaction between aphids and their host plants. Research has directly or indirectly been geared towards enhanced plant productivity and achieving sustainable agriculture. Barley (Hordeum vulgare L.) is an important small grain crop in South Africa, whose crop performance is negatively affected by fluctuations in weather patterns as well as by agricultural pests. One of the insect pests infesting barley is the Russian wheat aphid, Diuraphis noxia Kurdjumov (RWA), of which the two South African biotypes, codenamed RWASA1 and RWASA2, were studied in this thesis. During dry spells, RWA infestation becomes a more serious threat to barley productivity. Resistant plants have been used to combat RWA infestation of small grains. In South Africa, 27 RWA-resistant wheat cultivars are currently used in commercial cultivation, but no resistant barley lines have, unfortunately, been developed, in spite of this grain’s significant economic importance. This informed the study in this thesis, and this interest particularly focussed on three RWA-resistant lines developed by the USDA, testing their performance against South African RWA biotypes, for possible adaptation to South Africa. The aim was thus to examine the plant-aphid interactions, aphid breeding rates, plant damage and sustainability, evidence of resistance or tolerance and finally potential performance under elevated CO2 (a very real climate change threat). Two major avenues of research were undertaken. The first aspect involved examination of structural and functional damage caused by RWASA1 and RWASA2 on the three resistant and a non-resistant line. Aphid population growth and damage symptoms (chlorosis and leaf roll) of infestation by these aphid biotypes were evaluated. This was followed by a structural and functional approach in which the effects of feeding on the transport systems (phloem and xylem) of barley were investigated. Fluorescence microscopy techniques (using aniline blue fluorochrome, a specific stain for callose and 5,6-CFDA, a phloem-mobile probe) were applied to investigate the feeding-related damage caused by the aphids, through an examination of wound callose formation and related to this, the resultant reduction in phloem transport capacity. Transmission electron microscopy (TEM) techniques provided evidence of the extent of the feeding-related cell damage. The second aspect involved a study of the effect of changing CO2 concentrations ([CO2]) on the resistant and susceptible barley cultivars to feeding by the two RWA biotypes. Leaves of plants grown at ambient and two elevated levels of [CO2] were analysed to investigate the effect of changing [CO2] on biomass, leaf nitrogen content and C:N ratio of control (uninfested) and infested plants. The population growth studies showed that the populations of the two RWA biotypes as well as bird cherry-oat aphid (BCA, Rhopalosiphum padi L.) increased substantially on the four barley lines. BCA was included here, as it had been the subject of several previous studies. RWASA2 bred faster than RWASA1 on all lines. The breeding rates of the two RWA biotypes were both suppressed and at near-equivalent levels on the three resistant lines, compared to the non-resistant PUMA. This suggests that the resistant lines possessed an antibiosis resistance mechanism against the feeding aphids. Feeding by the aphids manifested in morphological damage symptoms of chlorosis and leaf roll. The two biotypes inflicted severe chlorosis and leaf roll on the non-resistant PUMA. In the resistant plants, leaf rolling was more severe because of RWASA2 feeding compared to RWASA1 feeding. In contrast, chlorosis symptoms were more severe during RWASA1 feeding than was the case with RWASA2 feeding. Investigation of the effect of aphid feeding on the plants showed that callose was deposited within 24h and that this increased with longer feeding exposure. Wound callose distribution is more extensive in the non-resistant PUMA than in the resistant plants. RWASA2 feeding on the resistant lines caused deposition of more callose than was evident with RWASA1 feeding. During long-term feeding, it was evident that variation in the intensity and amount of wound callose was visible in the longitudinal and transverse veins of the resistant plants. Of the three STARS plants, STARS-9301B had the least callose. Interestingly, wound callose occurred in both resistant and non-resistant plants, in sharp contrast to what has been reported on resistant wheat cultivars that were developed in South Africa. The relative reduction in the wound callose deposited in the resistant line, when compared to the non-resistant lines, suggests the presence of a mechanism in the resistant lines, which may prevent excessive callose formation. Alternatively, the mechanism may stimulate callose breakdown. RWASA2 feeding on the resistant lines deposited more wound callose than RWASA1 feeding. This evidence supports the hypothesis that RWASA2 is a resistance breaking and more aggressive feeder than RWASA1 is; and further underscores the urgent need for development of RWA-resistant barley cultivars. The ultrastructural investigation of the feeding damage showed that the two biotypes caused extensive vascular damage in non-resistant plants. There was extensive and severe cell disruption and often obliteration of cell structure of the vascular parenchyma, xylem and phloem elements. In sharp contrast, among the resistant plants, feeding-related cell damage appeared to be substantially reduced compared to the non-resistant PUMA. Low frequency of damaged cells indicated that majority of the cell components of the vascular tissues were intact and presumed functional. There was evidence of salivary material lining the secondary walls of the vascular tissue, which resulted in severe damage. Within xylem vessels, saliva material impregnated half-bordered pit pairs between the vessels and adjacent xylem parenchyma. This is believed to prevent solute exchange through this interface, thereby inducing leaf stress and vi leaf roll. A notable finding is that RWASA2 effectively induced more cell damage to vascular tissues in the resistant lines than did RWASA1. In general the experimental evidence (see Chapter 5) suggests that the resistant lines are possibly more tolerant (or able to cope with) to RWA feeding. Evidence for this is the reduction of wound callose and at the TEM level, a comparatively less obvious cell damage in the resistant lines, which suggests that they possess antibiosis and tolerance capacity. The apparent reduction of feeding-related cell damage from the TEM study confirmed the disruptive action of the feeding aphids in experiments using the phloem-mobile probe, 5,6-CF. Results showed that feeding by RWASA1 and RWASA2 reducedthe transport functionality of the phloem in all cases, but that RWASA2 feeding caused a more obvious reduction in the rate and distance that 5,6-carboxyfluorescein was transported, than did RWASA1. Investigation of the effect of changing [CO2] on the barley cultivars showed that in the absence of aphids and under elevated CO2 conditions, the plants grew more vigorously. In this series of experiments, the infested plants suffered significant reduction in biomass under ambient (as was expected) and under the two elevated CO2 regimes. Biomass loss was greater at elevated CO2 than under ambient [CO2]. The infested nonresistant PUMA plants showed a more significant biomass loss than did the resistant cultivars. Clearly, the benefits derived from elevated CO2 enrichment was thus redirected to the now-advantaged aphids. Uninfested vii plants showed an increase in leaf nitrogen under the experimental conditions. However, feeding aphids depleted leaf nitrogen content and this was more apparent on plants exposed to RWASA2 than was the case with RWASA1. The end result of this was that C:N ratio of infested plants were higher than uninfested plants. Clearly, the faster breeding rates of the aphids at elevated CO2 caused depletion of N and a resultant deficiency exacerbated chlorosis as well as leaf rolling due to the higher aphid population density under elevated CO2 than at ambient. By 28 days after infestation (DAI), majority of the plants exposed to enriched CO2 treatments had died. A major finding here was thus that although this study demonstrated that elevated CO2 resulted in an increase in biomass, this was detrimentally offset in plants infested by the aphids, with a decline in biomass and loss of functionality leading to plant death at 28DAI. The overriding conclusion from this study is a clear signal that the twin effects of CO2 enrichment (a feature of current climate change) and aphid infestations may precipitate potential grain shortages. A disastrous food security threat looms.
- Full Text:
- Date Issued: 2011
- Authors: Jimoh, Mahboob Adekilekun
- Date: 2011
- Subjects: Aphids Russian wheat aphid -- Research -- South Africa Barley -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4201 , http://hdl.handle.net/10962/d1003770
- Description: Cereal crop productivity is hampered when these plants are infested by phloem feeding aphids. A great deal of research has been carried out with the direct aim of a clearer understanding of the mechanism involved in the interaction between aphids and their host plants. Research has directly or indirectly been geared towards enhanced plant productivity and achieving sustainable agriculture. Barley (Hordeum vulgare L.) is an important small grain crop in South Africa, whose crop performance is negatively affected by fluctuations in weather patterns as well as by agricultural pests. One of the insect pests infesting barley is the Russian wheat aphid, Diuraphis noxia Kurdjumov (RWA), of which the two South African biotypes, codenamed RWASA1 and RWASA2, were studied in this thesis. During dry spells, RWA infestation becomes a more serious threat to barley productivity. Resistant plants have been used to combat RWA infestation of small grains. In South Africa, 27 RWA-resistant wheat cultivars are currently used in commercial cultivation, but no resistant barley lines have, unfortunately, been developed, in spite of this grain’s significant economic importance. This informed the study in this thesis, and this interest particularly focussed on three RWA-resistant lines developed by the USDA, testing their performance against South African RWA biotypes, for possible adaptation to South Africa. The aim was thus to examine the plant-aphid interactions, aphid breeding rates, plant damage and sustainability, evidence of resistance or tolerance and finally potential performance under elevated CO2 (a very real climate change threat). Two major avenues of research were undertaken. The first aspect involved examination of structural and functional damage caused by RWASA1 and RWASA2 on the three resistant and a non-resistant line. Aphid population growth and damage symptoms (chlorosis and leaf roll) of infestation by these aphid biotypes were evaluated. This was followed by a structural and functional approach in which the effects of feeding on the transport systems (phloem and xylem) of barley were investigated. Fluorescence microscopy techniques (using aniline blue fluorochrome, a specific stain for callose and 5,6-CFDA, a phloem-mobile probe) were applied to investigate the feeding-related damage caused by the aphids, through an examination of wound callose formation and related to this, the resultant reduction in phloem transport capacity. Transmission electron microscopy (TEM) techniques provided evidence of the extent of the feeding-related cell damage. The second aspect involved a study of the effect of changing CO2 concentrations ([CO2]) on the resistant and susceptible barley cultivars to feeding by the two RWA biotypes. Leaves of plants grown at ambient and two elevated levels of [CO2] were analysed to investigate the effect of changing [CO2] on biomass, leaf nitrogen content and C:N ratio of control (uninfested) and infested plants. The population growth studies showed that the populations of the two RWA biotypes as well as bird cherry-oat aphid (BCA, Rhopalosiphum padi L.) increased substantially on the four barley lines. BCA was included here, as it had been the subject of several previous studies. RWASA2 bred faster than RWASA1 on all lines. The breeding rates of the two RWA biotypes were both suppressed and at near-equivalent levels on the three resistant lines, compared to the non-resistant PUMA. This suggests that the resistant lines possessed an antibiosis resistance mechanism against the feeding aphids. Feeding by the aphids manifested in morphological damage symptoms of chlorosis and leaf roll. The two biotypes inflicted severe chlorosis and leaf roll on the non-resistant PUMA. In the resistant plants, leaf rolling was more severe because of RWASA2 feeding compared to RWASA1 feeding. In contrast, chlorosis symptoms were more severe during RWASA1 feeding than was the case with RWASA2 feeding. Investigation of the effect of aphid feeding on the plants showed that callose was deposited within 24h and that this increased with longer feeding exposure. Wound callose distribution is more extensive in the non-resistant PUMA than in the resistant plants. RWASA2 feeding on the resistant lines caused deposition of more callose than was evident with RWASA1 feeding. During long-term feeding, it was evident that variation in the intensity and amount of wound callose was visible in the longitudinal and transverse veins of the resistant plants. Of the three STARS plants, STARS-9301B had the least callose. Interestingly, wound callose occurred in both resistant and non-resistant plants, in sharp contrast to what has been reported on resistant wheat cultivars that were developed in South Africa. The relative reduction in the wound callose deposited in the resistant line, when compared to the non-resistant lines, suggests the presence of a mechanism in the resistant lines, which may prevent excessive callose formation. Alternatively, the mechanism may stimulate callose breakdown. RWASA2 feeding on the resistant lines deposited more wound callose than RWASA1 feeding. This evidence supports the hypothesis that RWASA2 is a resistance breaking and more aggressive feeder than RWASA1 is; and further underscores the urgent need for development of RWA-resistant barley cultivars. The ultrastructural investigation of the feeding damage showed that the two biotypes caused extensive vascular damage in non-resistant plants. There was extensive and severe cell disruption and often obliteration of cell structure of the vascular parenchyma, xylem and phloem elements. In sharp contrast, among the resistant plants, feeding-related cell damage appeared to be substantially reduced compared to the non-resistant PUMA. Low frequency of damaged cells indicated that majority of the cell components of the vascular tissues were intact and presumed functional. There was evidence of salivary material lining the secondary walls of the vascular tissue, which resulted in severe damage. Within xylem vessels, saliva material impregnated half-bordered pit pairs between the vessels and adjacent xylem parenchyma. This is believed to prevent solute exchange through this interface, thereby inducing leaf stress and vi leaf roll. A notable finding is that RWASA2 effectively induced more cell damage to vascular tissues in the resistant lines than did RWASA1. In general the experimental evidence (see Chapter 5) suggests that the resistant lines are possibly more tolerant (or able to cope with) to RWA feeding. Evidence for this is the reduction of wound callose and at the TEM level, a comparatively less obvious cell damage in the resistant lines, which suggests that they possess antibiosis and tolerance capacity. The apparent reduction of feeding-related cell damage from the TEM study confirmed the disruptive action of the feeding aphids in experiments using the phloem-mobile probe, 5,6-CF. Results showed that feeding by RWASA1 and RWASA2 reducedthe transport functionality of the phloem in all cases, but that RWASA2 feeding caused a more obvious reduction in the rate and distance that 5,6-carboxyfluorescein was transported, than did RWASA1. Investigation of the effect of changing [CO2] on the barley cultivars showed that in the absence of aphids and under elevated CO2 conditions, the plants grew more vigorously. In this series of experiments, the infested plants suffered significant reduction in biomass under ambient (as was expected) and under the two elevated CO2 regimes. Biomass loss was greater at elevated CO2 than under ambient [CO2]. The infested nonresistant PUMA plants showed a more significant biomass loss than did the resistant cultivars. Clearly, the benefits derived from elevated CO2 enrichment was thus redirected to the now-advantaged aphids. Uninfested vii plants showed an increase in leaf nitrogen under the experimental conditions. However, feeding aphids depleted leaf nitrogen content and this was more apparent on plants exposed to RWASA2 than was the case with RWASA1. The end result of this was that C:N ratio of infested plants were higher than uninfested plants. Clearly, the faster breeding rates of the aphids at elevated CO2 caused depletion of N and a resultant deficiency exacerbated chlorosis as well as leaf rolling due to the higher aphid population density under elevated CO2 than at ambient. By 28 days after infestation (DAI), majority of the plants exposed to enriched CO2 treatments had died. A major finding here was thus that although this study demonstrated that elevated CO2 resulted in an increase in biomass, this was detrimentally offset in plants infested by the aphids, with a decline in biomass and loss of functionality leading to plant death at 28DAI. The overriding conclusion from this study is a clear signal that the twin effects of CO2 enrichment (a feature of current climate change) and aphid infestations may precipitate potential grain shortages. A disastrous food security threat looms.
- Full Text:
- Date Issued: 2011
Plastochron index - an indicator of plant structure and function a case study using Pisum sativum L
- Ade-Ademilua, Omobolanle Elizabeth
- Authors: Ade-Ademilua, Omobolanle Elizabeth
- Date: 2006
- Subjects: Plant anatomy Plant physiology Peas -- Anatomy Peas -- Physiology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4183 , http://hdl.handle.net/10962/d1003751
- Description: The use of chronological age for example, using days after sowing (DAS), or days after germination (DAG) as a time variable may result in the inherent variability between plants resulting in differences which can be large enough to obscure subtle developmental trends that become evident among plants sown at the same time. An alternative to DAS or DAG is the plastochron index (PI), first used by Erickson and Michelini (1957) as a morphological time scale and numerical index; which to according to the authors suggested and represented a more accurate reflection of the developmental status of a plant. The research presented in this thesis was therefore aimed specifically at utilizing the index in qualitative and quantitative analyses, to confirm its usefulness in analyzing and predicting plant growth and development. Specifically this research focused on investigating various morphological and physiological events that together, hopefully, would serve as a template for the prediction of the growth, development and reactions of Pisum sativum L. to different growth conditions. In Chapter 3, the use of the average length of the first pair of leaflets on each node as a suitable parameter for calculating PI in P. sativum is suggested. The results presented in Chapter 3 suggest that plant age is best expressed using the plastochron index, as this reflects the time interval between the initiations of successive pairs of leaflets. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2005) A re-evaluation of plastochron index in peas - a case for using leaflet length. South African Journal of Botany 71: 76-80”. The PI formula developed was subsequently used in this research to conduct qualitative and quantitative investigations of plant growth and development in which all data and observations were related directly to the plastochron index. In Chapter 4, the sink to source transition in Pisum sativum L. leaves at different plastochron ages in nodulating plants was investigated using the phloem-mobile fluorescent marker, 5,6-carboxyfluorescein (5,6-CF). The results demonstrated that young leaves remained strong sinks up until LPI 0, after which sink-source transition occurred up to LPI 1.8 and leaflets transitioned to strong source systems by LPI 2.0. A well-developed cross-connected phloem system between paired leaflets in peas, and the petiole and the stem vascular supply was observed. The data presented in the second part of Chapter 4 suggest that the phloem transport between leaflet pairs is independent of the sink/source state of the leaflets, or of movement along the source to sink gradient. The data support the presence of a modular transport system which may ensure re-allocation and balancing between leaflets of the same physiological age and photosynthetic and transport status, thereby load-balancing the local transport system, before exporting to other younger (sink) regions. The investigation of leaf development using the plastochron index (Chapter 5) revealed that the formation of air spaces in the palisade and spongy mesophyll, one of the preparatory events for transition from sink to source state in developing leaves, occurs between LPI 0 and LPI 1 in pea leaflets. Results of the anatomical and ultrastructural study related to PI are presented in Chapter 5. The density of wall ingrowths in transfer cells of minor veins increased with LPI and appeared to be associated with the probable transition to source state and the related potential increase in the production of assimilates for export. The onset of wall ingrowth development in leaflets at LPI 0 provided evidence that sink-to-source transition commences at LPI 0 in P. sativum. Presumably-functional plasmodesmata as well as a few mature sieve elements were evident in class IV veins in the apical region of young and older leaflets at LPI 0. The number of mature sieve elements per vein however, increased with increasing LPI. Most class V veins were still undergoing division at LPI 0 and their sieve elements did not show signs of maturity until LPI 1. The increase in the number of mature metaphloem sieve elements in young, supposedly importing tissue at LPI 0 to older, supposedly exporting tissues at LPI 2 is evidence of the association between phloem maturation and transition from importing to exporting status. In Chapter 6, I report on the effects of elevated CO[subscript 2] on the growth and leaf development of nodulating and non-nodulating Pisum sativum L var. Greenfeast grown under controlled environment of the same nitrogen (6mM) and nitrogen- free nutrient solution conditions. Shortterm exposure to elevated CO[subscript 2] induced rapid plant growth, irrespective of treatment. However, long-term elevated CO[subscript 2] treatment did not affect rate of leaf appearance (RLA) in nodulated plants, irrespective of mineral N supply but enhanced RLA in non- nodulating plants supplied with mineral N. Supplied N resulted in a significant increase in leaflet elongation rate (LfER) under both ambient and elevated CO[subscript 2], but LfER was not significantly affected by nodulation but was increased by high CO[subscript 2]. This suggested that the growth of nodulating P. sativum L may not be significantly affected under CO[subscript 2] levels as high as 1000 μmol mol[superscript -1]. The data suggest that elevated CO[subscript 2] will enhance canopy size, provided adequate soil N is available and more so in non-nodulating plants. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2004) The effects of elevated CO[subscript 2] and nitrogen availability supersedes the need for nodulation in peas grown under controlled environmental conditions. South African Journal of Botany 70: 816 – 823”. This thesis demonstrates that the similarity in the qualitative analyses results obtained from plants from different CO[subscript 2], nitrogen and nodulation treatment conditions, highlights the fact that plants of same PI value are at the same developmental state, irrespective of the growth condition. Furthermore, changes in plant structure and function observed under different growth conditions can be related simply to changes in plastochron index. The work presented in this thesis demonstrate that changes in plant structure and function analyzed are related to changes in PI. An important finding of this thesis is that with the use of PI, results can be compiled as a template for predicting the structure- function state of pea plants at any plastochron age, under any growth conditions, before using small representative sample populations.
- Full Text:
- Date Issued: 2006
- Authors: Ade-Ademilua, Omobolanle Elizabeth
- Date: 2006
- Subjects: Plant anatomy Plant physiology Peas -- Anatomy Peas -- Physiology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4183 , http://hdl.handle.net/10962/d1003751
- Description: The use of chronological age for example, using days after sowing (DAS), or days after germination (DAG) as a time variable may result in the inherent variability between plants resulting in differences which can be large enough to obscure subtle developmental trends that become evident among plants sown at the same time. An alternative to DAS or DAG is the plastochron index (PI), first used by Erickson and Michelini (1957) as a morphological time scale and numerical index; which to according to the authors suggested and represented a more accurate reflection of the developmental status of a plant. The research presented in this thesis was therefore aimed specifically at utilizing the index in qualitative and quantitative analyses, to confirm its usefulness in analyzing and predicting plant growth and development. Specifically this research focused on investigating various morphological and physiological events that together, hopefully, would serve as a template for the prediction of the growth, development and reactions of Pisum sativum L. to different growth conditions. In Chapter 3, the use of the average length of the first pair of leaflets on each node as a suitable parameter for calculating PI in P. sativum is suggested. The results presented in Chapter 3 suggest that plant age is best expressed using the plastochron index, as this reflects the time interval between the initiations of successive pairs of leaflets. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2005) A re-evaluation of plastochron index in peas - a case for using leaflet length. South African Journal of Botany 71: 76-80”. The PI formula developed was subsequently used in this research to conduct qualitative and quantitative investigations of plant growth and development in which all data and observations were related directly to the plastochron index. In Chapter 4, the sink to source transition in Pisum sativum L. leaves at different plastochron ages in nodulating plants was investigated using the phloem-mobile fluorescent marker, 5,6-carboxyfluorescein (5,6-CF). The results demonstrated that young leaves remained strong sinks up until LPI 0, after which sink-source transition occurred up to LPI 1.8 and leaflets transitioned to strong source systems by LPI 2.0. A well-developed cross-connected phloem system between paired leaflets in peas, and the petiole and the stem vascular supply was observed. The data presented in the second part of Chapter 4 suggest that the phloem transport between leaflet pairs is independent of the sink/source state of the leaflets, or of movement along the source to sink gradient. The data support the presence of a modular transport system which may ensure re-allocation and balancing between leaflets of the same physiological age and photosynthetic and transport status, thereby load-balancing the local transport system, before exporting to other younger (sink) regions. The investigation of leaf development using the plastochron index (Chapter 5) revealed that the formation of air spaces in the palisade and spongy mesophyll, one of the preparatory events for transition from sink to source state in developing leaves, occurs between LPI 0 and LPI 1 in pea leaflets. Results of the anatomical and ultrastructural study related to PI are presented in Chapter 5. The density of wall ingrowths in transfer cells of minor veins increased with LPI and appeared to be associated with the probable transition to source state and the related potential increase in the production of assimilates for export. The onset of wall ingrowth development in leaflets at LPI 0 provided evidence that sink-to-source transition commences at LPI 0 in P. sativum. Presumably-functional plasmodesmata as well as a few mature sieve elements were evident in class IV veins in the apical region of young and older leaflets at LPI 0. The number of mature sieve elements per vein however, increased with increasing LPI. Most class V veins were still undergoing division at LPI 0 and their sieve elements did not show signs of maturity until LPI 1. The increase in the number of mature metaphloem sieve elements in young, supposedly importing tissue at LPI 0 to older, supposedly exporting tissues at LPI 2 is evidence of the association between phloem maturation and transition from importing to exporting status. In Chapter 6, I report on the effects of elevated CO[subscript 2] on the growth and leaf development of nodulating and non-nodulating Pisum sativum L var. Greenfeast grown under controlled environment of the same nitrogen (6mM) and nitrogen- free nutrient solution conditions. Shortterm exposure to elevated CO[subscript 2] induced rapid plant growth, irrespective of treatment. However, long-term elevated CO[subscript 2] treatment did not affect rate of leaf appearance (RLA) in nodulated plants, irrespective of mineral N supply but enhanced RLA in non- nodulating plants supplied with mineral N. Supplied N resulted in a significant increase in leaflet elongation rate (LfER) under both ambient and elevated CO[subscript 2], but LfER was not significantly affected by nodulation but was increased by high CO[subscript 2]. This suggested that the growth of nodulating P. sativum L may not be significantly affected under CO[subscript 2] levels as high as 1000 μmol mol[superscript -1]. The data suggest that elevated CO[subscript 2] will enhance canopy size, provided adequate soil N is available and more so in non-nodulating plants. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2004) The effects of elevated CO[subscript 2] and nitrogen availability supersedes the need for nodulation in peas grown under controlled environmental conditions. South African Journal of Botany 70: 816 – 823”. This thesis demonstrates that the similarity in the qualitative analyses results obtained from plants from different CO[subscript 2], nitrogen and nodulation treatment conditions, highlights the fact that plants of same PI value are at the same developmental state, irrespective of the growth condition. Furthermore, changes in plant structure and function observed under different growth conditions can be related simply to changes in plastochron index. The work presented in this thesis demonstrate that changes in plant structure and function analyzed are related to changes in PI. An important finding of this thesis is that with the use of PI, results can be compiled as a template for predicting the structure- function state of pea plants at any plastochron age, under any growth conditions, before using small representative sample populations.
- Full Text:
- Date Issued: 2006
Ammophila arenaria (L.) Link (marram grass) in South Africa and its potential invasiveness
- Authors: Hertling, Ursula Margret
- Date: 1998
- Subjects: Grasses -- South Africa Alien plants -- South Africa Sand dune plants -- South Africa Grasses -- Ecology -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4198 , http://hdl.handle.net/10962/d1003767
- Description: Ammophila arenaria (L.) Link is a European sand binding plant which was introduced to South Africa in the 1870's for the purpose of dune stabilisation. Because of its known invasiveness along the west coast of North America, and the problems South African ecosystems experience with alien invader plants, it was deemed necessary to study the biology and ecology of this species in South Africa. The aim of this thesis is to establish the potential invasiveness of A. arenaria on Cape coastal dunes and assess whether its use for dune stabilisation is still justifiable. A. arenaria occurs nowadays between the Langebaan area on the west coast and Gonubie in the Eastern Cape. Although widespread, the grass appears to occur only in areas where it has been planted. Its unaided spread may be prevented by adverse climatic conditions. Studies on the community biology of South African A. arenaria communities as compared to indigenous dune plant communities and natural A. arenaria communities in Europe cannot confirm the aggressive behaviour that A. arenaria shows in California and Oregon. In South Africa, A. arenaria does not exert strong floristic control over other species or outcompete and replace them, neither does it alter the topography of South African beaches and dunes. It forms weaker species associations and tends to develop communities of little species variability along the coast, thereby proving its alienness in South Africa, but this does not imply its invasiveness. Studies on succession of A. arenaria stabilisation areas show that monospecific A. arenaria plantings can be succeeded by a species-rich indigenous dune scrub or dune fynbos within a few decades. Plant-parasitic nematodes have been recorded, which may play an important role in the succession of A. arenaria stands in South Africa as was observed in Europe. Monitoring of A. arenaria communities and indigenous communities over nearly three years shows that A. arenaria is not spreading and replacing indigenous plants but in fact rather being replaced by the latter. A. arenaria profits from a superior sand burial tolerance but is affected by adverse climatic factors, mostly the lack of rainfall and strong radiation. In comparison to the indigenous dune grasses Thinopyrum distichum and Ehrharta villosa, it does not show any superior demographic traits such as an unusually high growth rate or large aboveground biomass production. Although A. arenaria produces viable seed in South Africa, the indigenous grasses show better germination and seedling establishment in the field. This study indicates that A. arenaria is not invasive in South Africa, nor likely to become an invader species in the near future. However, more research is required to confirm these results and more caution recommended regarding the further use of this alien grass for dune stabilisation.
- Full Text:
- Date Issued: 1998
- Authors: Hertling, Ursula Margret
- Date: 1998
- Subjects: Grasses -- South Africa Alien plants -- South Africa Sand dune plants -- South Africa Grasses -- Ecology -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4198 , http://hdl.handle.net/10962/d1003767
- Description: Ammophila arenaria (L.) Link is a European sand binding plant which was introduced to South Africa in the 1870's for the purpose of dune stabilisation. Because of its known invasiveness along the west coast of North America, and the problems South African ecosystems experience with alien invader plants, it was deemed necessary to study the biology and ecology of this species in South Africa. The aim of this thesis is to establish the potential invasiveness of A. arenaria on Cape coastal dunes and assess whether its use for dune stabilisation is still justifiable. A. arenaria occurs nowadays between the Langebaan area on the west coast and Gonubie in the Eastern Cape. Although widespread, the grass appears to occur only in areas where it has been planted. Its unaided spread may be prevented by adverse climatic conditions. Studies on the community biology of South African A. arenaria communities as compared to indigenous dune plant communities and natural A. arenaria communities in Europe cannot confirm the aggressive behaviour that A. arenaria shows in California and Oregon. In South Africa, A. arenaria does not exert strong floristic control over other species or outcompete and replace them, neither does it alter the topography of South African beaches and dunes. It forms weaker species associations and tends to develop communities of little species variability along the coast, thereby proving its alienness in South Africa, but this does not imply its invasiveness. Studies on succession of A. arenaria stabilisation areas show that monospecific A. arenaria plantings can be succeeded by a species-rich indigenous dune scrub or dune fynbos within a few decades. Plant-parasitic nematodes have been recorded, which may play an important role in the succession of A. arenaria stands in South Africa as was observed in Europe. Monitoring of A. arenaria communities and indigenous communities over nearly three years shows that A. arenaria is not spreading and replacing indigenous plants but in fact rather being replaced by the latter. A. arenaria profits from a superior sand burial tolerance but is affected by adverse climatic factors, mostly the lack of rainfall and strong radiation. In comparison to the indigenous dune grasses Thinopyrum distichum and Ehrharta villosa, it does not show any superior demographic traits such as an unusually high growth rate or large aboveground biomass production. Although A. arenaria produces viable seed in South Africa, the indigenous grasses show better germination and seedling establishment in the field. This study indicates that A. arenaria is not invasive in South Africa, nor likely to become an invader species in the near future. However, more research is required to confirm these results and more caution recommended regarding the further use of this alien grass for dune stabilisation.
- Full Text:
- Date Issued: 1998
Genetic studies on collagenolytic achromobacter strains and their bacteriophages
- Authors: Thomson, Jennifer Ann
- Date: 1974
- Subjects: Bacteriophages -- Genetics Bacterial genetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4246 , http://hdl.handle.net/10962/d1007291
- Description: From Summary: A survey of collagenolytic aerobic bacteria from cured hides yielded three strains of Bacillus and eight of Achromobacter which degraded collagen at 0.4 M NaCl. Achromobacter sp. 2 was chosen for genetic studies due to its high collagenolytic activity and the lack of genetic information on Achromobacter. Four temperate bacteriophages specific for Achromobacter sp. 2 were isolated and their relationships studied. The phages caused lysogenic conversion resulting in the inability of lysogens to adsorb phage. Achromobacter sp. 2 was shown to be a cryptic lysogen as it was not immune to superinfection but had a very low rate of spontaneous induction which could be increased with mutagens. It is proposed that the cryptic lysogeny of this strain is maintained by a defective excision mechanism and the mode of prophage integration in the host chromosome. DNA extracted from phage α3a was used to transfect spheroplasts. The optimal conditions for the development of competence for transfection were determined. The presence of nuclease-attack on phage DNA under conditions of prolonged incubation of DNA and spheroplasts was proposed. A method for extracting Achromobacter DNA was devised which yielded purified, undegraded DNA, but it was not possible to transform Achromobacter sp. 2 with this DNA. The a phages were used to transduce a number of genetic markers into Achromobacter auxotrophs. The transduct ants had the ability to release the cryptic α3 prophage at a high rate while maintaining their sensitivity to homologous phage infection. It is proposed that this is due to complementation between the cryptic prophage and the residual phage functions in the transducing particles. The transductants segregated auxotrophs with a probability of 10⁻³ per cell per generation. It appears that an unusual system of generalised transduction is operating whereby the transducing particles contain both phage and bacterial DNA which is incorporated into the recipient genome by a single recombination event yielding unstable transductants. In a study on induction of Escherichia coli (λ), carcinogenic nitrosamines were shown to be inducers of phage development. This provides a screening system for potentially harmful nitrosamines.
- Full Text:
- Date Issued: 1974
- Authors: Thomson, Jennifer Ann
- Date: 1974
- Subjects: Bacteriophages -- Genetics Bacterial genetics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4246 , http://hdl.handle.net/10962/d1007291
- Description: From Summary: A survey of collagenolytic aerobic bacteria from cured hides yielded three strains of Bacillus and eight of Achromobacter which degraded collagen at 0.4 M NaCl. Achromobacter sp. 2 was chosen for genetic studies due to its high collagenolytic activity and the lack of genetic information on Achromobacter. Four temperate bacteriophages specific for Achromobacter sp. 2 were isolated and their relationships studied. The phages caused lysogenic conversion resulting in the inability of lysogens to adsorb phage. Achromobacter sp. 2 was shown to be a cryptic lysogen as it was not immune to superinfection but had a very low rate of spontaneous induction which could be increased with mutagens. It is proposed that the cryptic lysogeny of this strain is maintained by a defective excision mechanism and the mode of prophage integration in the host chromosome. DNA extracted from phage α3a was used to transfect spheroplasts. The optimal conditions for the development of competence for transfection were determined. The presence of nuclease-attack on phage DNA under conditions of prolonged incubation of DNA and spheroplasts was proposed. A method for extracting Achromobacter DNA was devised which yielded purified, undegraded DNA, but it was not possible to transform Achromobacter sp. 2 with this DNA. The a phages were used to transduce a number of genetic markers into Achromobacter auxotrophs. The transduct ants had the ability to release the cryptic α3 prophage at a high rate while maintaining their sensitivity to homologous phage infection. It is proposed that this is due to complementation between the cryptic prophage and the residual phage functions in the transducing particles. The transductants segregated auxotrophs with a probability of 10⁻³ per cell per generation. It appears that an unusual system of generalised transduction is operating whereby the transducing particles contain both phage and bacterial DNA which is incorporated into the recipient genome by a single recombination event yielding unstable transductants. In a study on induction of Escherichia coli (λ), carcinogenic nitrosamines were shown to be inducers of phage development. This provides a screening system for potentially harmful nitrosamines.
- Full Text:
- Date Issued: 1974
Ecology and degree of specialization of South African milkweeds with diverse pollination systems
- Authors: Coombs, Gareth
- Date: 2010
- Subjects: Milkweeds -- South Africa Milkweeds -- South Africa -- Ecology Milkweeds -- South Africa -- Pollination Allee effect Self-pollination Pollination by insects
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4189 , http://hdl.handle.net/10962/d1003758
- Description: Like orchids, the complexity of flowers found in asclepiads (Asclepiadoideae, Apocynaceae) and the fact that pollen is presented as pollinaria, offers excellent opportunities to study various aspects of plant-pollinator interactions. In this thesis I investigated two broad themes: ecological aspects of the pollination biology of hymenopteran and fly-pollinated asclepiads as well as the degree of specialization to certain pollinators in these species. Colonizing plants often reproduce through self-pollination, or have highly generalized pollination systems, or both. These characteristics facilitate establishment in small founding populations and generates the prediction that reproductive success should be independent of population size in these species. Chapter one examines the pollination biology of Gomphocarpus physocarpus, an indigenous, weedy species and investigates the relationship between reproductive success and population size. In this species, there is no evidence of an Allee effect and reproductive success is not correlated with population size. In addition G. physocarpus is not capable of self-pollination, suggesting it is completely reliant on pollinators for seed set. The lack of a relationship between pollination success and population size is therefore likely explained by the generalized wasp pollination system of this species. Several milkweeds are invasive outside of their native ranges. Invasive species either need to co-opt native pollinators in order to reproduce or reduce their reliance on pollinators through having the ability to self-pollinate. Co-opting native pollinators is expected to be easier in species that have generalized pollination systems, alternatively species with specialized flower morphologies need to rely on similar functional groups of pollinators to be present within the invaded range. Chapter two investigates the pollination biology and pollination success of the invasive milkweed, Araujia sericifera, and finds that in South Africa, this species is visited mainly by native honeybees and nocturnal moths. Moths however contribute little to pollen removal, and deposition. Based on the apparent morphological mismatch between the flower of A. sericifera and native honeybees, I propose that the native pollinators of this species are likely to be larger Hymenoptera (e.g. Bumblebees). Data from a breeding system study, indicated that this species is not capable of automatic self-pollination, but could set fruit from geitonogamous self-pollinations pointing to the importance of native pollinators for successful reproduction. The pollinaria of milkweeds can accumulate on pollinators to form pollen masses large enough to physically interfere with the foraging behaviour of pollinating insects. In chapter three I describe the pollination biology of Cynanchum ellipticum and find that this species is mainly pollinated by honeybees although this species is visited by several other members of Hymenoptera, Lepidoptera and Diptera. Due to the structure of the pollinaria, these chain together relatively efficiently and frequently form large pollinarium loads on the mouthparts of honeybees. However there is little evidence that these pollinarium loads influence the foraging times of pollinators and only a few individual honeybees exhibited longer foraging times and most honeybees were unaffected by the presence of large pollinarium loads. Within the genus Cynanchum there is large variation in the gynostegium structure that may influence the pattern of pollinarium loading on pollinators as well as pollen reception as shown in chapter three. In Chapter four, the pollination biology of Cynanchum obtusifolium is examined, and like that of C. ellipticum, this species is visited by a wide diversity of pollinators but honeybees appear to be the primary pollinators. More importantly this species is shown to be andromonoecious and produces two morphologically different flower types, that may be distinguished based on differences in the gynostegium structure. These two types of flower could mainly be distinguished by the length of the anther wings. I found that flowers with short anther wings function as male flowers by only exporting- and rarely receiving pollinia. Flowers with longer anther wings function as hermaphrodite flowers and can both export and receive pollinia. The ratio of male to hermaphrodite flowers varied at different times during the flowering season, but preliminary data suggested that this was not related to levels of pollination success. The genera Stapelia and Ceropegia are well known for their intricate floral adaptations that mimic the brood and feeding substrates of pollinating flies. Despite several studies that have documented the various adaptations to fly pollination in different species, there is a lack of natural history studies documenting different flower visitors, pollen loads and long term levels of pollination success in these species. In Chapter six I document the pollination biology of Ceropegia ampliata by documenting different pollinators and quantifying average levels of pollination success and the nectar reward. I also experimentally manipulated the trapping hairs of this species to determine whether trapping hairs influence average levels of pollen export and receipt. I show that Ceropegia ampliata is pollinated by a generalist guild of flies (mainly Tachinidae, Sarcophagidae, Muscidae and Lauxaniidae) and produces minute quantities of relatively dilute nectar as a reward. Pollination success was generally low in this species and increases periodically suggesting that the abundance of pollinators is patchy. I found that flowers with trapping hairs that had already wilted had higher levels of pollinarium removal than flowers with erect hairs, however experimentally removing the hairs had no significant effect on pollen export and receipt. In Chapter seven, I document the pollinators, pollen loads and long term levels of pollination success in Stapelia hirsuta var. bayllissi, a rare sapromyiophilous stapeliad. I find that, in contrast to C. ampliata, this species was specialized to pollination by small flies of the family Anthomyiidae. Similar to the results from Chapter seven, I find that long term levels of pollination success were typically low but could increase periodically, although such increases were generally unpredictable. There are currently very few records documenting pollinator interactions in the Periplocoideae. Many species within this subfamily exhibit open-access flowers suggestive of pollination by short-tongued insects. I investigated the pollination biology of Chlorocyathus lobulata, a rare species with a highly localized distribution. I aimed to determine the pollinators, average levels of pollination success and demography of this species in order to determine whether this rare species is suffering from the collapse of a highly specialized pollinator mutualism. I also quantified the high incidence of flower herbivory caused by larvae of the moth, Bocchoris onychinalis. I find that C. lobulata has a highly generalized fly pollination system and average levels of pollination success suggested that a large proportion of flowers had pollen removed and deposited suggesting that this species is not experiencing pollination failure. The large numbers of juveniles present also indicated that recruitment is taking place.
- Full Text:
- Date Issued: 2010
- Authors: Coombs, Gareth
- Date: 2010
- Subjects: Milkweeds -- South Africa Milkweeds -- South Africa -- Ecology Milkweeds -- South Africa -- Pollination Allee effect Self-pollination Pollination by insects
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4189 , http://hdl.handle.net/10962/d1003758
- Description: Like orchids, the complexity of flowers found in asclepiads (Asclepiadoideae, Apocynaceae) and the fact that pollen is presented as pollinaria, offers excellent opportunities to study various aspects of plant-pollinator interactions. In this thesis I investigated two broad themes: ecological aspects of the pollination biology of hymenopteran and fly-pollinated asclepiads as well as the degree of specialization to certain pollinators in these species. Colonizing plants often reproduce through self-pollination, or have highly generalized pollination systems, or both. These characteristics facilitate establishment in small founding populations and generates the prediction that reproductive success should be independent of population size in these species. Chapter one examines the pollination biology of Gomphocarpus physocarpus, an indigenous, weedy species and investigates the relationship between reproductive success and population size. In this species, there is no evidence of an Allee effect and reproductive success is not correlated with population size. In addition G. physocarpus is not capable of self-pollination, suggesting it is completely reliant on pollinators for seed set. The lack of a relationship between pollination success and population size is therefore likely explained by the generalized wasp pollination system of this species. Several milkweeds are invasive outside of their native ranges. Invasive species either need to co-opt native pollinators in order to reproduce or reduce their reliance on pollinators through having the ability to self-pollinate. Co-opting native pollinators is expected to be easier in species that have generalized pollination systems, alternatively species with specialized flower morphologies need to rely on similar functional groups of pollinators to be present within the invaded range. Chapter two investigates the pollination biology and pollination success of the invasive milkweed, Araujia sericifera, and finds that in South Africa, this species is visited mainly by native honeybees and nocturnal moths. Moths however contribute little to pollen removal, and deposition. Based on the apparent morphological mismatch between the flower of A. sericifera and native honeybees, I propose that the native pollinators of this species are likely to be larger Hymenoptera (e.g. Bumblebees). Data from a breeding system study, indicated that this species is not capable of automatic self-pollination, but could set fruit from geitonogamous self-pollinations pointing to the importance of native pollinators for successful reproduction. The pollinaria of milkweeds can accumulate on pollinators to form pollen masses large enough to physically interfere with the foraging behaviour of pollinating insects. In chapter three I describe the pollination biology of Cynanchum ellipticum and find that this species is mainly pollinated by honeybees although this species is visited by several other members of Hymenoptera, Lepidoptera and Diptera. Due to the structure of the pollinaria, these chain together relatively efficiently and frequently form large pollinarium loads on the mouthparts of honeybees. However there is little evidence that these pollinarium loads influence the foraging times of pollinators and only a few individual honeybees exhibited longer foraging times and most honeybees were unaffected by the presence of large pollinarium loads. Within the genus Cynanchum there is large variation in the gynostegium structure that may influence the pattern of pollinarium loading on pollinators as well as pollen reception as shown in chapter three. In Chapter four, the pollination biology of Cynanchum obtusifolium is examined, and like that of C. ellipticum, this species is visited by a wide diversity of pollinators but honeybees appear to be the primary pollinators. More importantly this species is shown to be andromonoecious and produces two morphologically different flower types, that may be distinguished based on differences in the gynostegium structure. These two types of flower could mainly be distinguished by the length of the anther wings. I found that flowers with short anther wings function as male flowers by only exporting- and rarely receiving pollinia. Flowers with longer anther wings function as hermaphrodite flowers and can both export and receive pollinia. The ratio of male to hermaphrodite flowers varied at different times during the flowering season, but preliminary data suggested that this was not related to levels of pollination success. The genera Stapelia and Ceropegia are well known for their intricate floral adaptations that mimic the brood and feeding substrates of pollinating flies. Despite several studies that have documented the various adaptations to fly pollination in different species, there is a lack of natural history studies documenting different flower visitors, pollen loads and long term levels of pollination success in these species. In Chapter six I document the pollination biology of Ceropegia ampliata by documenting different pollinators and quantifying average levels of pollination success and the nectar reward. I also experimentally manipulated the trapping hairs of this species to determine whether trapping hairs influence average levels of pollen export and receipt. I show that Ceropegia ampliata is pollinated by a generalist guild of flies (mainly Tachinidae, Sarcophagidae, Muscidae and Lauxaniidae) and produces minute quantities of relatively dilute nectar as a reward. Pollination success was generally low in this species and increases periodically suggesting that the abundance of pollinators is patchy. I found that flowers with trapping hairs that had already wilted had higher levels of pollinarium removal than flowers with erect hairs, however experimentally removing the hairs had no significant effect on pollen export and receipt. In Chapter seven, I document the pollinators, pollen loads and long term levels of pollination success in Stapelia hirsuta var. bayllissi, a rare sapromyiophilous stapeliad. I find that, in contrast to C. ampliata, this species was specialized to pollination by small flies of the family Anthomyiidae. Similar to the results from Chapter seven, I find that long term levels of pollination success were typically low but could increase periodically, although such increases were generally unpredictable. There are currently very few records documenting pollinator interactions in the Periplocoideae. Many species within this subfamily exhibit open-access flowers suggestive of pollination by short-tongued insects. I investigated the pollination biology of Chlorocyathus lobulata, a rare species with a highly localized distribution. I aimed to determine the pollinators, average levels of pollination success and demography of this species in order to determine whether this rare species is suffering from the collapse of a highly specialized pollinator mutualism. I also quantified the high incidence of flower herbivory caused by larvae of the moth, Bocchoris onychinalis. I find that C. lobulata has a highly generalized fly pollination system and average levels of pollination success suggested that a large proportion of flowers had pollen removed and deposited suggesting that this species is not experiencing pollination failure. The large numbers of juveniles present also indicated that recruitment is taking place.
- Full Text:
- Date Issued: 2010
The life history of selected coastal foredune species of South Africa
- Authors: Knevel, Irma Cornelia
- Date: 2002
- Subjects: Sand dune plants -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4207 , http://hdl.handle.net/10962/d1003776
- Description: South African dune fields are severely threatened by human expansion and in the long run the stabilisation of many dunes will be necessary. The alien grass Ammophila arenaria is the most important drift sand stabiliser at present in South Africa. Although not invasive, the current impact of A. arenaria on the dune systems of South Africa is considerable, and thus the stabilising benefit of the grass seemed to may be outweighed by its negative consequences. It is therefore preferable to use indigenous sand stabilising species. In order to define guidelines for the application of indigenous plants for stabilisation, their autecology should be studied first to enhance the chance of successful stabilisation results. The main aim of the present thesis was to gather information on the life history processes of selected indigenous, sand stabilising foredune species. To investigate the growth of foredune pioneer species, the common pioneer Scaevola plumieri was followed over a three-year period to determine the growth season and leaf phenology. Soil-borne pathogens are known to influence the growth and vegetation dynamics of foredune species. To examine this effect on the South African foredunes the rhizosphere soil and the roots of several species were studied. To test the effect of the nematode fauna on succeeding plant species a transplantation experiment was carried out. The seed stage is the only life-cycle stage that can survive unfavourable conditions. Therefore, the seed ecology of several foredune species was studied extensively to determine the reproductive season, the seed production, the fate of seeds after shedding (germination, seawater dispersal), germination requirements and seed bank strategy. Seeds of the species Arctotheca populifolia, Ipomoea pes-caprae, Myrica cordifolia, and Scaevola plumieri were subjected to germination trials, field observations on seedling survival, and scarification and stratification experiments. This was done to obtain information about the germination requirements and to determine the reproductive season and growth season. The seed bank strategy of the foredune species, as well as the seed bank density, was determined by extensive sampling along the Cape coast. The species S. plumieri thrived under sand accretion situations, which makes it a good candidate for stabilisation purposes. The growth of S. plumieri was seasonal, with the highest leaf production during spring and summer. The stem position on the foredune had a strong effect on the overall performance of S. plumieri , with the stems situated on the landward face of the foredune showing higher leaf and seed production. Theiii nematode survey of soil and roots of several foredune species showed that all plant species featured a specific nematode fauna in the rhizosphere soil and the roots. The specific nematode fauna affected the growth of foreign plant species in the transplantation experiment, resulting in a lower root and/or shoot biomass production. Most of the foredune species produce seeds from spring to late summer. For S. plumieri the position of the stem on the dunes, as well as the predation of unripe seeds affected the number of seeds produced. The highest production was found for the landward faced stems. The S. plumieri seeds were able to float on seawater for at least three months without losing viability, as was observed for seeds of I. pes-caprae. The seeds of M. cordifolia, however, sank after a few days, but their viability was not affected. The rhizome fragments of A. arenaria and S. virginicus floated for 120 days, whereas the fragments of E. villosa sunk after one day. The viability of S. virginicus fragments was affected by the duration in seawater by an increase in sprouting time. The seeds of all species tested germinated readily under controlled conditions, except S. plumieri seeds which required a long lag-phase before germination. In the field the seeds of A. populifolia, I. pes-caprae and S. plumieri germinated, producing many seedlings. Only the seedlings of A. populifolia and S. plumieri survived. Of the species found in the foredunes 57% was represented in the soil seed bank. For most species, the seeds that were found in the seed bank showed viability of at least 40%. Many of the seeds found were older than one year, suggesting a short-term persistent seed bank. The present study is a start in filling the gap in information on dune pioneer and foredune species. The conclusion was that in general all species in the present study were easy to grow under controlled conditions, and thus could be used for stabilisation purposes. When the more rapidly growing pioneer species are planted in combination with succeeding foredune species, a functional and aesthetic ecosystem could be created.
- Full Text:
- Date Issued: 2002
- Authors: Knevel, Irma Cornelia
- Date: 2002
- Subjects: Sand dune plants -- South Africa Sand dune ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4207 , http://hdl.handle.net/10962/d1003776
- Description: South African dune fields are severely threatened by human expansion and in the long run the stabilisation of many dunes will be necessary. The alien grass Ammophila arenaria is the most important drift sand stabiliser at present in South Africa. Although not invasive, the current impact of A. arenaria on the dune systems of South Africa is considerable, and thus the stabilising benefit of the grass seemed to may be outweighed by its negative consequences. It is therefore preferable to use indigenous sand stabilising species. In order to define guidelines for the application of indigenous plants for stabilisation, their autecology should be studied first to enhance the chance of successful stabilisation results. The main aim of the present thesis was to gather information on the life history processes of selected indigenous, sand stabilising foredune species. To investigate the growth of foredune pioneer species, the common pioneer Scaevola plumieri was followed over a three-year period to determine the growth season and leaf phenology. Soil-borne pathogens are known to influence the growth and vegetation dynamics of foredune species. To examine this effect on the South African foredunes the rhizosphere soil and the roots of several species were studied. To test the effect of the nematode fauna on succeeding plant species a transplantation experiment was carried out. The seed stage is the only life-cycle stage that can survive unfavourable conditions. Therefore, the seed ecology of several foredune species was studied extensively to determine the reproductive season, the seed production, the fate of seeds after shedding (germination, seawater dispersal), germination requirements and seed bank strategy. Seeds of the species Arctotheca populifolia, Ipomoea pes-caprae, Myrica cordifolia, and Scaevola plumieri were subjected to germination trials, field observations on seedling survival, and scarification and stratification experiments. This was done to obtain information about the germination requirements and to determine the reproductive season and growth season. The seed bank strategy of the foredune species, as well as the seed bank density, was determined by extensive sampling along the Cape coast. The species S. plumieri thrived under sand accretion situations, which makes it a good candidate for stabilisation purposes. The growth of S. plumieri was seasonal, with the highest leaf production during spring and summer. The stem position on the foredune had a strong effect on the overall performance of S. plumieri , with the stems situated on the landward face of the foredune showing higher leaf and seed production. Theiii nematode survey of soil and roots of several foredune species showed that all plant species featured a specific nematode fauna in the rhizosphere soil and the roots. The specific nematode fauna affected the growth of foreign plant species in the transplantation experiment, resulting in a lower root and/or shoot biomass production. Most of the foredune species produce seeds from spring to late summer. For S. plumieri the position of the stem on the dunes, as well as the predation of unripe seeds affected the number of seeds produced. The highest production was found for the landward faced stems. The S. plumieri seeds were able to float on seawater for at least three months without losing viability, as was observed for seeds of I. pes-caprae. The seeds of M. cordifolia, however, sank after a few days, but their viability was not affected. The rhizome fragments of A. arenaria and S. virginicus floated for 120 days, whereas the fragments of E. villosa sunk after one day. The viability of S. virginicus fragments was affected by the duration in seawater by an increase in sprouting time. The seeds of all species tested germinated readily under controlled conditions, except S. plumieri seeds which required a long lag-phase before germination. In the field the seeds of A. populifolia, I. pes-caprae and S. plumieri germinated, producing many seedlings. Only the seedlings of A. populifolia and S. plumieri survived. Of the species found in the foredunes 57% was represented in the soil seed bank. For most species, the seeds that were found in the seed bank showed viability of at least 40%. Many of the seeds found were older than one year, suggesting a short-term persistent seed bank. The present study is a start in filling the gap in information on dune pioneer and foredune species. The conclusion was that in general all species in the present study were easy to grow under controlled conditions, and thus could be used for stabilisation purposes. When the more rapidly growing pioneer species are planted in combination with succeeding foredune species, a functional and aesthetic ecosystem could be created.
- Full Text:
- Date Issued: 2002
Changes in carbohydrate concentration and amylolytic activity in germinating maize
- Authors: Breen, C M
- Date: 1969
- Subjects: Corn -- Research Corn -- Analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4251 , http://hdl.handle.net/10962/d1007680
- Description: Changes in the concentration of some carbohydrates and in amylolytic activity have been followed during germination of Zea. Mays L. var. Hickory King and var. Early Pearl. Assay techniques have been developed which permitted assay of individual grains. Thus during the investigation both groups and individual grains were used as samples. The use of groups permitted control of assay technique. Length of radicle, coleoptile and lateral roots were recorded in order to permit quantitative estimation of correlation between growth and the concentration of the various carbohydrates. Initially, during the study of changes in the carbohydrate concentration in Hickory King grains, total reducing sugar, sucrose and dextrin concentrations were estimated. However, the results obtained for changes in dextrin concentration, although reproduceable, thereby indicating reliable assay technique, presented a confusing picture and, in view of the apparent importance of sucrose and reducing sugar concentration, assay of dextrin concentration was discontinued in a subsequent study of Early Pearl. Instead changes in total reducing sugar, sucrose and glucose concentrations were followed. The results revealed that there is very considerable variability in physiological activity between grains subjected to the same germination conditions. However, all, irrespective of variety, follow the same basic metabolic pattern during germination. The trends observed were: (i) Reducing sugar accumulates slowly during the first 72-96 hours germination, but thereafter accumulation is very rapid, although concentration may decrease towards the end of the gestation period. (ii) Glucose follows a similar pattern to reducing sugar, accumulating slowly during the early stages of germination, followed by a period of rapid increase in concentration, which may decrease towards the end of the germination period. (iii) Sucrose concentration in dormant grains is fairly high, but it decreases markedly during the first 96 hours germination. This is followed by a phase of sucrose accumulation. (iv) Dextrin concentration shows two peaks. Initial level is low, but it accumulates rapidly during the first 72 hours. The level decreases between 72 and 120 hours but increases when the germination period is increased to 192 hours, after which there is a marked decrease. It was impossible, from the data relating to the study of individual grains, to discern a trend in dextrin concentration. With the exception of dextrin, about which there is little information, the results are in general agreement with the literature. Investigation of correlation between the various carbohydrates and between these and growth revealed that: (i) reducing sugar concentration and growth are positively correlated ; (ii) glucose concentration and growth are positively correlated; (iii) sucrose and reducing sugar concentrctions are negatively correlated during the initial stages of germination; (iv) sucrose and glucose concentrations are negatively correlated during early germination; (v) glucose and reducing sugar are positively correlated; (vi) in general, correlation between growth and concentration of the carbohydrates studied, decreases during the later periods of germination. These observations suggested that growth was, at least during the early stages of germination, dependent on the level of reducing sugar, and more particularly on the level of glucose, and that sucrose is the principal source of reducing sugar during this period. The relationship between amylase activity (total alpha- and beta-amylase activity) and reducing sugar concentration tends to be curvilinear, which suggests that amylolytic activity produces relatively little reducing sugar during early gennination, even though amylase activity and growth may be positively correlated. The results suggest, contrary to the observations of previous workers, that alpha-amylolytic activity may be present in dormant grains and that maize is not characterised by low levels of beta-amylase activity during germination. From the observations it is concluded that the initinl accumulati on of reducing sugar is the result of sucrose hydrolysis, and therefore sucrose is an importnnt metabolite durjng early germination. Amylolytic activity contributes little reducing sugar durlng the initia1 stages of germinatIon but that after approximately 72 hours it represents the major source of reducing sugar.
- Full Text:
- Date Issued: 1969
- Authors: Breen, C M
- Date: 1969
- Subjects: Corn -- Research Corn -- Analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4251 , http://hdl.handle.net/10962/d1007680
- Description: Changes in the concentration of some carbohydrates and in amylolytic activity have been followed during germination of Zea. Mays L. var. Hickory King and var. Early Pearl. Assay techniques have been developed which permitted assay of individual grains. Thus during the investigation both groups and individual grains were used as samples. The use of groups permitted control of assay technique. Length of radicle, coleoptile and lateral roots were recorded in order to permit quantitative estimation of correlation between growth and the concentration of the various carbohydrates. Initially, during the study of changes in the carbohydrate concentration in Hickory King grains, total reducing sugar, sucrose and dextrin concentrations were estimated. However, the results obtained for changes in dextrin concentration, although reproduceable, thereby indicating reliable assay technique, presented a confusing picture and, in view of the apparent importance of sucrose and reducing sugar concentration, assay of dextrin concentration was discontinued in a subsequent study of Early Pearl. Instead changes in total reducing sugar, sucrose and glucose concentrations were followed. The results revealed that there is very considerable variability in physiological activity between grains subjected to the same germination conditions. However, all, irrespective of variety, follow the same basic metabolic pattern during germination. The trends observed were: (i) Reducing sugar accumulates slowly during the first 72-96 hours germination, but thereafter accumulation is very rapid, although concentration may decrease towards the end of the gestation period. (ii) Glucose follows a similar pattern to reducing sugar, accumulating slowly during the early stages of germination, followed by a period of rapid increase in concentration, which may decrease towards the end of the germination period. (iii) Sucrose concentration in dormant grains is fairly high, but it decreases markedly during the first 96 hours germination. This is followed by a phase of sucrose accumulation. (iv) Dextrin concentration shows two peaks. Initial level is low, but it accumulates rapidly during the first 72 hours. The level decreases between 72 and 120 hours but increases when the germination period is increased to 192 hours, after which there is a marked decrease. It was impossible, from the data relating to the study of individual grains, to discern a trend in dextrin concentration. With the exception of dextrin, about which there is little information, the results are in general agreement with the literature. Investigation of correlation between the various carbohydrates and between these and growth revealed that: (i) reducing sugar concentration and growth are positively correlated ; (ii) glucose concentration and growth are positively correlated; (iii) sucrose and reducing sugar concentrctions are negatively correlated during the initial stages of germination; (iv) sucrose and glucose concentrations are negatively correlated during early germination; (v) glucose and reducing sugar are positively correlated; (vi) in general, correlation between growth and concentration of the carbohydrates studied, decreases during the later periods of germination. These observations suggested that growth was, at least during the early stages of germination, dependent on the level of reducing sugar, and more particularly on the level of glucose, and that sucrose is the principal source of reducing sugar during this period. The relationship between amylase activity (total alpha- and beta-amylase activity) and reducing sugar concentration tends to be curvilinear, which suggests that amylolytic activity produces relatively little reducing sugar during early gennination, even though amylase activity and growth may be positively correlated. The results suggest, contrary to the observations of previous workers, that alpha-amylolytic activity may be present in dormant grains and that maize is not characterised by low levels of beta-amylase activity during germination. From the observations it is concluded that the initinl accumulati on of reducing sugar is the result of sucrose hydrolysis, and therefore sucrose is an importnnt metabolite durjng early germination. Amylolytic activity contributes little reducing sugar durlng the initia1 stages of germinatIon but that after approximately 72 hours it represents the major source of reducing sugar.
- Full Text:
- Date Issued: 1969
The anatomy and distribution of the cyperaceae in the Eastern Cape region of South Africa
- Authors: Sonnenberg, Bernd Jürgen
- Date: 2005
- Subjects: Cyperaceae Cyperaceae -- Anatomy Cyperaceae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4228 , http://hdl.handle.net/10962/d1003797
- Description: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C₃ species would predominate in more mesic environments and habitats, whilst the C₄ species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C₃ and forty percent were C₄. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C₃, a C₄ and a potential C₃-C₄ intermediate group. The C₃ group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C₄ group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C₄ species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C₃ anatomy have anatomical characteristics that are similar to the species with C₄ anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C₄ grass species. However, no biochemical data exists to see whether they are C₃-C₄ intermediates or whether the Hattersley and Watson (1975) C₄ criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C₃, C₄ and C₃-C₄ intermediate groups. The C₃ and the potential C₃-C₄ intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C₄ species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C₄ anatomical type within the C₄ Cyperaceae. As a result of this observation, it is possible that the C₄ syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C₃ Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C₄ species, similar to the C₃ grasses. The only C₄ species that occur at high elevations are those with three sheaths. The C₃ and C₄ species within the region occur in similar low rainfall habitat ranges, where the C₄'s are more dominant in xeric habitats on drier soils than the C₃ species, similar to the grasses. Where more C₃ species occur in higher rainfall habitats than the C₄ species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C₄ species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C₄ Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C₃ and more especially C₄ Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C₃ species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C₃ species are mostly present in halophytic habitats. The C₄ species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C₄ Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C₄ anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.
- Full Text:
- Date Issued: 2005
- Authors: Sonnenberg, Bernd Jürgen
- Date: 2005
- Subjects: Cyperaceae Cyperaceae -- Anatomy Cyperaceae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4228 , http://hdl.handle.net/10962/d1003797
- Description: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C₃ species would predominate in more mesic environments and habitats, whilst the C₄ species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C₃ and forty percent were C₄. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C₃, a C₄ and a potential C₃-C₄ intermediate group. The C₃ group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C₄ group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C₄ species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C₃ anatomy have anatomical characteristics that are similar to the species with C₄ anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C₄ grass species. However, no biochemical data exists to see whether they are C₃-C₄ intermediates or whether the Hattersley and Watson (1975) C₄ criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C₃, C₄ and C₃-C₄ intermediate groups. The C₃ and the potential C₃-C₄ intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C₄ species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C₄ anatomical type within the C₄ Cyperaceae. As a result of this observation, it is possible that the C₄ syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C₃ Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C₄ species, similar to the C₃ grasses. The only C₄ species that occur at high elevations are those with three sheaths. The C₃ and C₄ species within the region occur in similar low rainfall habitat ranges, where the C₄'s are more dominant in xeric habitats on drier soils than the C₃ species, similar to the grasses. Where more C₃ species occur in higher rainfall habitats than the C₄ species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C₄ species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C₄ Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C₃ and more especially C₄ Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C₃ species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C₃ species are mostly present in halophytic habitats. The C₄ species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C₄ Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C₄ anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.
- Full Text:
- Date Issued: 2005
The effect of elevated CO₂ on Phaseolus vulgaris L. cv Contender
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: The response of Phaseolus vulgaris L. cv. Contender grown in controlled environmental conditions, at either ambient or elevated (360 and 700 μmol mol ̄¹, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), dry weight (DW) accumulation and specific leaf area (SLA). All of these were significantly increased by elevated [CO₂] with the exception of SLA, which was significantly reduced. Except for higher initial relative growth rates (RGR) in CO₂-enriched plants, RGR did not differ significantly between the two CO₂ treatments throughout the remainder of growth period. While growth parameters clearly differed between CO₂ treatments, the effects of CO₂ on many physiological processes including net assimilation rate (NAR), Rubisco activity, and some foliar nutrient concentrations were largely transient. For example, CO₂ enrichment significantly increased NAR, but from 20 DAG onward, NAR declined to levels measured on plants grown under ambient CO₂. Similarly, the decline in both foliar N concentration and Rubisco activity in CO₂-enriched plants after 20 DAG was significantly greater than the decline observed for ambient CO₂ plants. Soluble leaf protein and total chlorophylls (a+b) were also significantly reduced in plants grown under elevated CO₂. Chlorophyll (a/b) ratios increased with time underelevated CO₂, indicating that the rate of decline of chlorophyll b was higher than that of chorophyll α. No significant changes in total carotenoid (x+c) levels were observed in either CO₂ treatment. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly, while P, Ca, Fe and Zn were reduced significantly. However, changes in Mg and Cu concentrations were not significant. High CO₂-grown plants also exhibited pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity. The levels of non-structural carbohydrates (sucrose, glucose, fructose and starch) and nitrogenous compounds (nitrogen, total soluble proteins and free amino acids) were determined for leaves and developing seeds of P. vulgaris. Leaf tissue of elevated CO₂-grown plants accumulated significantly higher levels of both soluble sugars and starch. Leaf ultrastructure revealed considerable erilargement of starch grain sizes with surface areas more than five times larger compared to those of control plants. No apparent differences in structure and membrane integrity of chloroplasts in both CO₂ treatments were noted. Although ambient CO₂-grown plants had comparatively low levels of non-structural carbohydrates (NSC), they accumulated significantly higher levels of nitrogenous compounds. The levels of NSC were consistently higher in seeds of plants grown under elevated CO₂. In comparison to plants grown at elevated [CO₂], pods and seeds of ambient CO₂-grown plants had significantly larger pools of free amino compounds and N. Stomatal conductance (gs) declined significantly, as expected for plants grown under elevated CO₂. This was accompanied by a decline in transpiration rates (E). Reduced gs and E led to high AlE ratio, which meant improved water use efficiency (WUE) values for CO₂-enriched bean plants. Leaf carbon isotope discrimination (∆) against the heavier isotope of carbon (¹³C), has been used to select for high WUE in C₃ plants. In plants grown at elevated CO₂ concentration, ,1 was significantly reduced. Although ∆ was negatively correlated with WUE in both CO₂ treatments, the correlation was steeper and highly negative for CO₂-enriched plants. These results indicate underlying differences in gas-exchange physiology, including stomatal responses between ambient and elevated CO₂-grown plants. Photosynthetic acclimation was investigated using the response of assimilation to internal carbon dioxide concentration (A/C₁ curves). At early stages of growth, the initial slope of the A/C₁ response curve did not differ with CO₂ treatment. In contrast, CO₂-saturated photosynthetic rate (Amax) was significantly higher in plants grown under elevated versus ambient CO₂ at 15 DAG. However, at subsequent stages of growth both the initial slope and Amax declined in bean plants grown in elevated CO₂. Apparent carboxylation efficiency (ACE, estimated from the initial slope of A/C₁ response) values followed a similar trend and were significantly reduced in CO₂-enriched plants. These results indicate that acclimation or negative adjustment of photosynthesis may have been caused by a combination of both stomatal and biochemical limitations. Bean plants grown under conditions of elevated atmospheric CO₂ flowered 3 to 4 days earlier, and produced significantly more flowers and pods than plants grown at ambient conditions. Plants grown at elevated CO₂ aborted 22 and 20% more flowers and pods, respectively, than plants grown at ambient CO₂. Elevated CO₂ also significantly increased the number of tillers or lateral branches produced by plants, which contributed to a significant increase in pod number and seed yield in these plants. Although plants grown at elevated CO₂ produced on average 8 seeds per pod, while plants grown under ambient CO2 conditions produced 5 seeds per pod, the greater number of seeds was offset by lower seed weights in plants grown under _ elevated CO₂. Thus, despite high seed yield in beans grown under elevated CO₂, the harvest index (HI) did not change significantly between CO₂ treatments.
- Full Text:
- Date Issued: 1997
- Authors: Mjwara, Jabulani Michael
- Date: 1997
- Subjects: Plants -- Effect of carbon dioxide on Kidney bean
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4215 , http://hdl.handle.net/10962/d1003784
- Description: The response of Phaseolus vulgaris L. cv. Contender grown in controlled environmental conditions, at either ambient or elevated (360 and 700 μmol mol ̄¹, respectively) CO₂ concentrations ([CO₂]), was monitored from 10 days after germination (DAG) until the onset of senescence. Elevated CO₂ had a pronounced effect on total plant height (TPH), leaf area (LA), dry weight (DW) accumulation and specific leaf area (SLA). All of these were significantly increased by elevated [CO₂] with the exception of SLA, which was significantly reduced. Except for higher initial relative growth rates (RGR) in CO₂-enriched plants, RGR did not differ significantly between the two CO₂ treatments throughout the remainder of growth period. While growth parameters clearly differed between CO₂ treatments, the effects of CO₂ on many physiological processes including net assimilation rate (NAR), Rubisco activity, and some foliar nutrient concentrations were largely transient. For example, CO₂ enrichment significantly increased NAR, but from 20 DAG onward, NAR declined to levels measured on plants grown under ambient CO₂. Similarly, the decline in both foliar N concentration and Rubisco activity in CO₂-enriched plants after 20 DAG was significantly greater than the decline observed for ambient CO₂ plants. Soluble leaf protein and total chlorophylls (a+b) were also significantly reduced in plants grown under elevated CO₂. Chlorophyll (a/b) ratios increased with time underelevated CO₂, indicating that the rate of decline of chlorophyll b was higher than that of chorophyll α. No significant changes in total carotenoid (x+c) levels were observed in either CO₂ treatment. Under enhanced CO₂, the foliar concentrations of K and Mn were increased significantly, while P, Ca, Fe and Zn were reduced significantly. However, changes in Mg and Cu concentrations were not significant. High CO₂-grown plants also exhibited pronounced leaf discoloration or chlorosis, coupled with a significant reduction in leaf longevity. The levels of non-structural carbohydrates (sucrose, glucose, fructose and starch) and nitrogenous compounds (nitrogen, total soluble proteins and free amino acids) were determined for leaves and developing seeds of P. vulgaris. Leaf tissue of elevated CO₂-grown plants accumulated significantly higher levels of both soluble sugars and starch. Leaf ultrastructure revealed considerable erilargement of starch grain sizes with surface areas more than five times larger compared to those of control plants. No apparent differences in structure and membrane integrity of chloroplasts in both CO₂ treatments were noted. Although ambient CO₂-grown plants had comparatively low levels of non-structural carbohydrates (NSC), they accumulated significantly higher levels of nitrogenous compounds. The levels of NSC were consistently higher in seeds of plants grown under elevated CO₂. In comparison to plants grown at elevated [CO₂], pods and seeds of ambient CO₂-grown plants had significantly larger pools of free amino compounds and N. Stomatal conductance (gs) declined significantly, as expected for plants grown under elevated CO₂. This was accompanied by a decline in transpiration rates (E). Reduced gs and E led to high AlE ratio, which meant improved water use efficiency (WUE) values for CO₂-enriched bean plants. Leaf carbon isotope discrimination (∆) against the heavier isotope of carbon (¹³C), has been used to select for high WUE in C₃ plants. In plants grown at elevated CO₂ concentration, ,1 was significantly reduced. Although ∆ was negatively correlated with WUE in both CO₂ treatments, the correlation was steeper and highly negative for CO₂-enriched plants. These results indicate underlying differences in gas-exchange physiology, including stomatal responses between ambient and elevated CO₂-grown plants. Photosynthetic acclimation was investigated using the response of assimilation to internal carbon dioxide concentration (A/C₁ curves). At early stages of growth, the initial slope of the A/C₁ response curve did not differ with CO₂ treatment. In contrast, CO₂-saturated photosynthetic rate (Amax) was significantly higher in plants grown under elevated versus ambient CO₂ at 15 DAG. However, at subsequent stages of growth both the initial slope and Amax declined in bean plants grown in elevated CO₂. Apparent carboxylation efficiency (ACE, estimated from the initial slope of A/C₁ response) values followed a similar trend and were significantly reduced in CO₂-enriched plants. These results indicate that acclimation or negative adjustment of photosynthesis may have been caused by a combination of both stomatal and biochemical limitations. Bean plants grown under conditions of elevated atmospheric CO₂ flowered 3 to 4 days earlier, and produced significantly more flowers and pods than plants grown at ambient conditions. Plants grown at elevated CO₂ aborted 22 and 20% more flowers and pods, respectively, than plants grown at ambient CO₂. Elevated CO₂ also significantly increased the number of tillers or lateral branches produced by plants, which contributed to a significant increase in pod number and seed yield in these plants. Although plants grown at elevated CO₂ produced on average 8 seeds per pod, while plants grown under ambient CO2 conditions produced 5 seeds per pod, the greater number of seeds was offset by lower seed weights in plants grown under _ elevated CO₂. Thus, despite high seed yield in beans grown under elevated CO₂, the harvest index (HI) did not change significantly between CO₂ treatments.
- Full Text:
- Date Issued: 1997
The autecology of Azolla filiculoides Lamarck with special reference to its occurrence in the Hendrik Verwoerd Dam catchment area
- Authors: Ashton, Peter John
- Date: 1983
- Subjects: Azolla filiculoides -- South Africa -- Gariep Dam Azollaceae Azolla -- South Africa -- Gariep Dam Water ferns -- South Africa -- Gariep Dam Aquatic weeds -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4181 , http://hdl.handle.net/10962/d1003732
- Description: An autecological study of the heterosporous fern Azolla filiculoides Lamarck and its endosymbiotic blue-green alga Anabaena azollae Strasburger, based on a combination of field and laboratory studies, is presented. The taxonomy, morphology and anatomy of the fern-alga association were studied as well as nutritional and physiological aspects of the symbiosis. These studies have defined the habitat and nutritional requirements of the fern and have provided new insights into its reproductive biology, nitrogen metabolism and the nature of the association between the fern and alga. In the catchment area of the Hendrik Verwoerd Dam the availability of suitably sheltered habitat limits the distribution of A. filiculoides while the availability of nutrients, in particular calcium, phosphorus and iron, limits the growth of the fern. The multilayered mats formed by A. filiculoides are essential for spore production, cause dramatic changes in the hydrochemistry of the underlying waters and confer a great competitive advantage on the plant. Methods for the isolation of the fern and algal components of the symbiosis have been developed but recombination of the individual organisms to reform the symbiosis was unsuccessful. The development of the fern is closely linked to that of the alga and the association is maintained throughout the life cycle of the fern. Because of its specific habitat and nutritional requirements, A. filiculoides is unlikely to colonize the open waters of the Hendrik Verwoerd Dam.
- Full Text:
- Date Issued: 1983
- Authors: Ashton, Peter John
- Date: 1983
- Subjects: Azolla filiculoides -- South Africa -- Gariep Dam Azollaceae Azolla -- South Africa -- Gariep Dam Water ferns -- South Africa -- Gariep Dam Aquatic weeds -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4181 , http://hdl.handle.net/10962/d1003732
- Description: An autecological study of the heterosporous fern Azolla filiculoides Lamarck and its endosymbiotic blue-green alga Anabaena azollae Strasburger, based on a combination of field and laboratory studies, is presented. The taxonomy, morphology and anatomy of the fern-alga association were studied as well as nutritional and physiological aspects of the symbiosis. These studies have defined the habitat and nutritional requirements of the fern and have provided new insights into its reproductive biology, nitrogen metabolism and the nature of the association between the fern and alga. In the catchment area of the Hendrik Verwoerd Dam the availability of suitably sheltered habitat limits the distribution of A. filiculoides while the availability of nutrients, in particular calcium, phosphorus and iron, limits the growth of the fern. The multilayered mats formed by A. filiculoides are essential for spore production, cause dramatic changes in the hydrochemistry of the underlying waters and confer a great competitive advantage on the plant. Methods for the isolation of the fern and algal components of the symbiosis have been developed but recombination of the individual organisms to reform the symbiosis was unsuccessful. The development of the fern is closely linked to that of the alga and the association is maintained throughout the life cycle of the fern. Because of its specific habitat and nutritional requirements, A. filiculoides is unlikely to colonize the open waters of the Hendrik Verwoerd Dam.
- Full Text:
- Date Issued: 1983
The coastal grasslands of the Eastern Cape west of the Kei River
- Authors: Judd, Rachel Anne
- Date: 1999
- Subjects: Grassland ecology -- South Africa -- Eastern Cape Grasslands -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4203 , http://hdl.handle.net/10962/d1003772
- Description: The grasslands of South Africa are the foundation of commercial and subsistence agriculture yet they are being degraded at an alanning rate. The coastal grasslands of the Eastern Cape are no exception and they suffer added pressure of coastal resort development because of their proximity to an attractive coastline. In order to determine the degree of conservation necessary for any area it is essential to know what species occur there in order to determine if protection from habitat destruction is required. Four aims were defined for this studv. The initial aim was a phytogeographical classification of the grasslands in the coastal region west of the Kei River. This was done by vegetation sampling followed by computer based analysis with TWINSPAN. This analysis defined ten grassland associations. five being located in the area west of the Keiskamma River and five occurring east of it. The associations in the eastern half are termed mesic while those in the western balf are xeric. The second aim was to determine the presence of any underlying ecological gradients affecting the distribution of tbe associations. Indirect gradient analysis was carried out where samples are analysed irrespective of environmental factors. Direct gradient analysis was then carried out using scores per sample of various environmental factors. Environmental factors whicb migbt produce such gradients are both naturally-ocurring and man-induced. Natural factors which were recorded in the field include depth of soil at sample site, soil family, aspect and distance from the shore. An important factor is the land / sea interface. Natural factors analysed in the laboratory include soil pH. conductivity. percent organic matter, calcium, magnesium, phosphate and potassium. Man-induced factors are land use history e.g. Ploughing and grazing. Both direct and indirect gradient analysis were carried out with the computer based programme CANOCO. The third aim of the study was to determine the presence of any successional trends between the ten defined associations. This was done using several characteristics of the associations. Alpha and beta diversity were the first factors compared between associations. The percentage contribution of the Cyperaceae, Fabaceae, Asteraceae and Poaceae to each association was assessed and compared. The presence of various life forms of the species occurring in each association was determined together with the cover abundance of different classes of grass species. These results were then combined and analysed in the light of the results from CANOCO analvsis. They show that the mesic Themeda Iriandra - Anthospermum herhoceum, association which occurs closest to the shore and with the least disturbance is a depauperate form of the mesic climax Themeda triandra association. The mesic Hyparrhenia hirta - Dtheteropogon amplectens association may be a secondary grassland on account of phosphate and potassiun poor soils and land-use. The mesic Hyparrhenia hirta - Themedo triandra association is a slightly degraded form of the climax association due to grazing. The severely disturbed Stenotaphrum secundatum - C'entella coriacea association, which is located close to the shore, is a secondary grassland. Analysis of the xeric associations indicates a clearly defined ordination of associations on the basis of land-use. The Cynodon daclylon - Helictolrichon hirtulum and Sporobolis africanus - Setaria sphacelata associations which occur where ploughed lands have been left to lie fallow are secondary in nature. The Themeda triandra - Ehrharta calycina association is thought to be the closest representati ve of a climax xeric association but the presence of E. calycina indicates that some disturbance has occurred. The vegetation is subject to moderate grazing. The Cynodon dactylon - Ehrharla calycina and Diheleropogon filifolius - Ehrharla calycina associations are subject to varying intensities of trampling and grazing and are degraded forms of the Themeda triandra - Ehrharla calycina association. Because of tbe overriding influence of the land-use gradient separation along gradients of the remaining eight factors was limited. The effect of fire and temporal change in the mesic Themeda triandra and Hyparrhenia hirta - Themeeia trianda associations was assessed via long-term studies at Potter's Pass outside East London. The results show a quick response to burning with a return to 100% cover within six months by both associations. During spring the two associations could not be separated by either TWINSPAN or DECORANA. indicating a temporal shift from the Hyparrhenia hirta - Themeda triandra association to the Themeda triandra association. The fourth and final aim was to identify plants requiring protection from habitat destruction and to make recommendations for further conservation areas and management of the coastal grasslands. Through the collection and identification of as many plants as possible a species checklist was prepared and the status of each was determined through reference to the Red Data Book of threatened and endangered species. Kniphofia rooperi is vulnerable in the Cape and Euphorbia hupleuroides is considered rare in kwazulu-Natal. Ten species are endemic to the Cape and / or South Africa. The richness of the vegetation lies in the presence of species representative of the four major floras which converge in the eastern Cape. i.e. The Cape, NamaKarroo, Tongoland-Pondolaod floras and the Kalahari Highveld Regional Transitional Zone. Suggestions are made for the conservation of the grassland associations at various sites within the study area based on the present area conserved. Less than 2% of the coastline in the study area is conserved and it is felt that the area under conservation should be increased. Management suggestions based on the available literature are given for both farmed and conserved areas. There is a great potential for further studies on grassland dmamics within the areas surveyed. In terms of management, the grasslands require careful examination to determine the most effective season in which to burn if at all. As with most agricultural systems in South Africa. grazing strategies will benefit from further research. Any additional research on the dynamics of these grasslands can only be of benefit to the sustained utilisation of this vital resource.
- Full Text:
- Date Issued: 1999
- Authors: Judd, Rachel Anne
- Date: 1999
- Subjects: Grassland ecology -- South Africa -- Eastern Cape Grasslands -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4203 , http://hdl.handle.net/10962/d1003772
- Description: The grasslands of South Africa are the foundation of commercial and subsistence agriculture yet they are being degraded at an alanning rate. The coastal grasslands of the Eastern Cape are no exception and they suffer added pressure of coastal resort development because of their proximity to an attractive coastline. In order to determine the degree of conservation necessary for any area it is essential to know what species occur there in order to determine if protection from habitat destruction is required. Four aims were defined for this studv. The initial aim was a phytogeographical classification of the grasslands in the coastal region west of the Kei River. This was done by vegetation sampling followed by computer based analysis with TWINSPAN. This analysis defined ten grassland associations. five being located in the area west of the Keiskamma River and five occurring east of it. The associations in the eastern half are termed mesic while those in the western balf are xeric. The second aim was to determine the presence of any underlying ecological gradients affecting the distribution of tbe associations. Indirect gradient analysis was carried out where samples are analysed irrespective of environmental factors. Direct gradient analysis was then carried out using scores per sample of various environmental factors. Environmental factors whicb migbt produce such gradients are both naturally-ocurring and man-induced. Natural factors which were recorded in the field include depth of soil at sample site, soil family, aspect and distance from the shore. An important factor is the land / sea interface. Natural factors analysed in the laboratory include soil pH. conductivity. percent organic matter, calcium, magnesium, phosphate and potassium. Man-induced factors are land use history e.g. Ploughing and grazing. Both direct and indirect gradient analysis were carried out with the computer based programme CANOCO. The third aim of the study was to determine the presence of any successional trends between the ten defined associations. This was done using several characteristics of the associations. Alpha and beta diversity were the first factors compared between associations. The percentage contribution of the Cyperaceae, Fabaceae, Asteraceae and Poaceae to each association was assessed and compared. The presence of various life forms of the species occurring in each association was determined together with the cover abundance of different classes of grass species. These results were then combined and analysed in the light of the results from CANOCO analvsis. They show that the mesic Themeda Iriandra - Anthospermum herhoceum, association which occurs closest to the shore and with the least disturbance is a depauperate form of the mesic climax Themeda triandra association. The mesic Hyparrhenia hirta - Dtheteropogon amplectens association may be a secondary grassland on account of phosphate and potassiun poor soils and land-use. The mesic Hyparrhenia hirta - Themedo triandra association is a slightly degraded form of the climax association due to grazing. The severely disturbed Stenotaphrum secundatum - C'entella coriacea association, which is located close to the shore, is a secondary grassland. Analysis of the xeric associations indicates a clearly defined ordination of associations on the basis of land-use. The Cynodon daclylon - Helictolrichon hirtulum and Sporobolis africanus - Setaria sphacelata associations which occur where ploughed lands have been left to lie fallow are secondary in nature. The Themeda triandra - Ehrharta calycina association is thought to be the closest representati ve of a climax xeric association but the presence of E. calycina indicates that some disturbance has occurred. The vegetation is subject to moderate grazing. The Cynodon dactylon - Ehrharla calycina and Diheleropogon filifolius - Ehrharla calycina associations are subject to varying intensities of trampling and grazing and are degraded forms of the Themeda triandra - Ehrharla calycina association. Because of tbe overriding influence of the land-use gradient separation along gradients of the remaining eight factors was limited. The effect of fire and temporal change in the mesic Themeda triandra and Hyparrhenia hirta - Themeeia trianda associations was assessed via long-term studies at Potter's Pass outside East London. The results show a quick response to burning with a return to 100% cover within six months by both associations. During spring the two associations could not be separated by either TWINSPAN or DECORANA. indicating a temporal shift from the Hyparrhenia hirta - Themeda triandra association to the Themeda triandra association. The fourth and final aim was to identify plants requiring protection from habitat destruction and to make recommendations for further conservation areas and management of the coastal grasslands. Through the collection and identification of as many plants as possible a species checklist was prepared and the status of each was determined through reference to the Red Data Book of threatened and endangered species. Kniphofia rooperi is vulnerable in the Cape and Euphorbia hupleuroides is considered rare in kwazulu-Natal. Ten species are endemic to the Cape and / or South Africa. The richness of the vegetation lies in the presence of species representative of the four major floras which converge in the eastern Cape. i.e. The Cape, NamaKarroo, Tongoland-Pondolaod floras and the Kalahari Highveld Regional Transitional Zone. Suggestions are made for the conservation of the grassland associations at various sites within the study area based on the present area conserved. Less than 2% of the coastline in the study area is conserved and it is felt that the area under conservation should be increased. Management suggestions based on the available literature are given for both farmed and conserved areas. There is a great potential for further studies on grassland dmamics within the areas surveyed. In terms of management, the grasslands require careful examination to determine the most effective season in which to burn if at all. As with most agricultural systems in South Africa. grazing strategies will benefit from further research. Any additional research on the dynamics of these grasslands can only be of benefit to the sustained utilisation of this vital resource.
- Full Text:
- Date Issued: 1999
Coastal dune ecology and management in the Eastern Cape
- Authors: Avis, Anthony Mark
- Date: 1993
- Subjects: Sand dune ecology -- South Africa Shore protection -- South Africa Coastal zone management -- South Africa Sand dunes -- South Africa Sand dune plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4185 , http://hdl.handle.net/10962/d1003753
- Description: The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape.
- Full Text:
- Date Issued: 1993
- Authors: Avis, Anthony Mark
- Date: 1993
- Subjects: Sand dune ecology -- South Africa Shore protection -- South Africa Coastal zone management -- South Africa Sand dunes -- South Africa Sand dune plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4185 , http://hdl.handle.net/10962/d1003753
- Description: The importance of understanding the ecological functioning of coastal dune systems is emphasized as being fundamental to the correct management of the dune landscape. Dune vegetation along the Eastern Cape coastline, from Cape St Francis in the west to Kei Mouth in the east was described in terms of the distribution and phytochorological affinities of the taxa. At a regional scale species distribution was strongly influenced by both the climate, particularly rainfall, and the phytochorological affinities of the taxa. Seven communities were defined using TWINSPAN, and the interrelationships between these communities in anyone area appeared to be linked to a successional gradient. Dune Slacks are thought to play a key role in this successional sequence, and a temporal study of this community led to a conceptual model of plant succession in these dunefields. Climate, particularly rainfall and wind, are major factors influencing plant succession. Wind-borne sand causes the slacks to migrate in an easterly direction under the influence of the predominantly westerly winds, although easterly winds, mainly in summer months may reverse these trends. Autogenic changes appeared to be important in this succession, and a comparative study of a good example of a primary succession at Mtunzini in Natal was undertaken to elucidate the main mechanism of change. Eight communities that were identified here were concluded to be distnbuted along a gradient of increasing age, with successional changes predictable, linear and directional. Species were grouped in distinct zones along the continuum and edaphic changes (decrease in soil pH, increase in organic matter and exchangeable bases) were related to the community based changes in species composition. The mechanism of change supported the facilitation model of plant succession which is a modification of the original Clementsian concept. Similar results were found in the Eastern Cape, but due to the harsh environment, multiple pathways of succession exist. Data from this study lent support to the model of plant succession developed earlier, and confinned that the dune slacks played an important role in this facilitation by acting as centres of diversity. The foredunes were found to have an indirect role in protecting these slacks from salt spray and sand movement. The central theme of the management studies was to investigate the ecological consequences of recreational pressure within the dune environment. Current levels of beach utilization at East London were lower than other beaches in South Africa, but a general trend of increasing utilization due to sociopolitical changes can be expected. The suitability of questionnaire surveys to assess aspects such as the adequacy of facilities, perceptual carrying capacity and the beach users opinion of natural vegetation and preference for particular beaches was demonstrated. The dune vegetation was found to be sensitive to human trampling, but at current levels, the ecological carrying capacity will not be exceeded since results of the aerial census counts and questionnaire survey revealed that few people entered sensitive zones such as the coastal forest. More detailed long term studies on the susceptibility of dune vegetation to both trampling and off-road vehicle impacts revealed a low resilience of dune plant communities to these effects. Although susceptibility differed between the three communities tested, generally the greatest amount of damage occurred after the first few passages, and vehicles caused a more significant decrease in height when compared to trampling. Recovery rates were slow and low levels of repeated damage were sufficient to retard or prevent the recovery of the plants. Stricter control of vehicle use on beaches is therefore required, and in high use zones the ecological carrying capacity should be increased by providing access tracks if possible, or if not possible, by restricting access. A historical account of the process of dune stabilization showed that although first initiated in 1845, indigenous species were only used in the past three decades. The use of alien species has resulted in problems such as a reduction in the ecological integrity and aesthetic appeal of coastal systems. The techniques applied in the stabilization of drift sands with indigenous vegetation have been successful, as revealed by a quantitative survey of 17 sites in the Eastern Cape. Sites were grouped by multivariate analysis on the basis of their species composition, and variability between sites was dependent on the types of species planted. Selection of suitable species is therefore important and is discussed with respect to their natural distribution along the coast. The long term objective of stabilization should be the creation of functional, diverse, aesthetic ecosystems, since the intrinsic and economic value of the dune landscape for tourism lies therein. However, detailed studies should be undertaken prior to implementing a manipulative process such as dune stabilization, since ecological processes may be disrupted. An understanding of such processes is therefore important if one wishes to effectively manage the dune landscape.
- Full Text:
- Date Issued: 1993
Vegetation ecology of the Camdebo and Sneeuberg regions of the Karoo biome, South Africa
- Authors: Palmer, Anthony Riordan
- Date: 1989
- Subjects: Plants -- South Africa -- Great Karoo Great Karoo (South Africa)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4173 , http://hdl.handle.net/10962/d1002021
- Description: An hierarchical syntaxonomic classification of the vegetation of the Camdebo and Sneeuberg regions of the karoo biome is presented as a second approximation after the earlier work by Acocks (1953). Details on the geomorphology, geology, climate, and early vegetation history of the area are given. The vegetation of the study area was stratified with the aid of Landsat imagery and the community classification was generated using two-way indicator species analysis (Twins pan) which produced ordered phytosociological tables. Tabular comparisons and final sorting of tables are according to the methods and techniques of the ZiirichMontpellier school of phytosociology. Syntaxonomic ranks are defined as five classes, nine orders and seventeen communities. The classes are Grasslands, Karoo Shrublands, Karoo Dwarf Shrublands, Sub-tropical Transitional Thicket, and Riparian Thicket. The distribution of syntaxa corresponds with the steep precipitation gradient experienced in the study area. These vegetation concepts are applied to the description of the flora of the Karoo Nature Reserve and an analysis of the total flora of the reserve is provided. The communities of the pediments, which contain the highest number of endemics, are poorly conserved. I test the validity of the vegetation classification by interpreting the results of an analysis of soils within the hypothesized vegetation units. There is a gradient of increasing Na, silt and pH levels from the Shrublands and Grasslands to the Succulent and Grassy Dwarf Shrublands of the pediments. A qualitative model of the vegetation history during the glacial-interglacial sequence in the Graaff-Reinet region of the eastern Cape is presented. Using a descriptive approach, the distribution patterns of 68 taxa, which are differential species for Karoo Shrublands, Succulent Thicket and Karoo Dwarf Shrublands, are investigated relative to major southern African biomes. The results indicate that a large proportion of the differential species in the phytosociological classification show affinity with Grassland and Savanna Biomes. Three species groups encountered in the Dwarf Shrublands show affinity with the Nama-Karoo biome. The differential species of the Succulent Thicket have a predominantly subtropical distribution. Using an historical approach, the palaeoenvironment of the region during the past 20 000 years is discussed briefly. On the basis of the descriptive and historical perspectives, a qualitative model of vegetation history is presented. The Succulent Thicket may have become established on edaphically favourable sites in the ameliorating conditions of the warmer, wetter Holocene subsequent to the Last Glacial Maximum. The Dwarf Shrubland and Succulent Dwarf Shrubland are depauperate in relation to ccmmunities in other southern African biomes, but the relatively large number of endemics suggests a long history in the region. Their differential species groups occur under arid conditions, accompanied by soils with high base and fertility status. The Dwarf Shrublands may have been more extensive during the drier glacial times on those sites currently occupied by Shrubland. The Shrublands display the expected affInity with the Grassland and Savanna Biomes. The small number of endemics suggest that these communities may have occupied the region in the period since the Last Glacial Maximum. Species with Succulent Karoo Biome affInity are poorly represented. The reliability of using Landsat products to detect and map the vegetation of the region is assessed. The manual classification of Landsat standard products provides a poor reflection of the vegetation of the arid, sparsely-vegetated bottomlands and pediments. The products provide good representation of the boundaries of thicket vegetation, but this uni-temporal approach does not distinguish between floristically different thicket communities. After analyzing digital Landsat data, I suggest that the multi-spectral scanner detects the boundaries of broad soil pedons and geological formations in areas of low vegetative cover. I describe and map the vegetation categories of the region after manual interpretation of six Landsat scenes. This is an effIcient, cost-effective method of mapping vegetation in extensive regions. The mapping units do not reflect the syntaxonomic classification, representing rather an integration of physiographic, pedological, geological and floristic information. With the view to improving the classification of these units, I develop a qualitative model of the natural resources of the region using an expert system
- Full Text:
- Date Issued: 1989
- Authors: Palmer, Anthony Riordan
- Date: 1989
- Subjects: Plants -- South Africa -- Great Karoo Great Karoo (South Africa)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4173 , http://hdl.handle.net/10962/d1002021
- Description: An hierarchical syntaxonomic classification of the vegetation of the Camdebo and Sneeuberg regions of the karoo biome is presented as a second approximation after the earlier work by Acocks (1953). Details on the geomorphology, geology, climate, and early vegetation history of the area are given. The vegetation of the study area was stratified with the aid of Landsat imagery and the community classification was generated using two-way indicator species analysis (Twins pan) which produced ordered phytosociological tables. Tabular comparisons and final sorting of tables are according to the methods and techniques of the ZiirichMontpellier school of phytosociology. Syntaxonomic ranks are defined as five classes, nine orders and seventeen communities. The classes are Grasslands, Karoo Shrublands, Karoo Dwarf Shrublands, Sub-tropical Transitional Thicket, and Riparian Thicket. The distribution of syntaxa corresponds with the steep precipitation gradient experienced in the study area. These vegetation concepts are applied to the description of the flora of the Karoo Nature Reserve and an analysis of the total flora of the reserve is provided. The communities of the pediments, which contain the highest number of endemics, are poorly conserved. I test the validity of the vegetation classification by interpreting the results of an analysis of soils within the hypothesized vegetation units. There is a gradient of increasing Na, silt and pH levels from the Shrublands and Grasslands to the Succulent and Grassy Dwarf Shrublands of the pediments. A qualitative model of the vegetation history during the glacial-interglacial sequence in the Graaff-Reinet region of the eastern Cape is presented. Using a descriptive approach, the distribution patterns of 68 taxa, which are differential species for Karoo Shrublands, Succulent Thicket and Karoo Dwarf Shrublands, are investigated relative to major southern African biomes. The results indicate that a large proportion of the differential species in the phytosociological classification show affinity with Grassland and Savanna Biomes. Three species groups encountered in the Dwarf Shrublands show affinity with the Nama-Karoo biome. The differential species of the Succulent Thicket have a predominantly subtropical distribution. Using an historical approach, the palaeoenvironment of the region during the past 20 000 years is discussed briefly. On the basis of the descriptive and historical perspectives, a qualitative model of vegetation history is presented. The Succulent Thicket may have become established on edaphically favourable sites in the ameliorating conditions of the warmer, wetter Holocene subsequent to the Last Glacial Maximum. The Dwarf Shrubland and Succulent Dwarf Shrubland are depauperate in relation to ccmmunities in other southern African biomes, but the relatively large number of endemics suggests a long history in the region. Their differential species groups occur under arid conditions, accompanied by soils with high base and fertility status. The Dwarf Shrublands may have been more extensive during the drier glacial times on those sites currently occupied by Shrubland. The Shrublands display the expected affInity with the Grassland and Savanna Biomes. The small number of endemics suggest that these communities may have occupied the region in the period since the Last Glacial Maximum. Species with Succulent Karoo Biome affInity are poorly represented. The reliability of using Landsat products to detect and map the vegetation of the region is assessed. The manual classification of Landsat standard products provides a poor reflection of the vegetation of the arid, sparsely-vegetated bottomlands and pediments. The products provide good representation of the boundaries of thicket vegetation, but this uni-temporal approach does not distinguish between floristically different thicket communities. After analyzing digital Landsat data, I suggest that the multi-spectral scanner detects the boundaries of broad soil pedons and geological formations in areas of low vegetative cover. I describe and map the vegetation categories of the region after manual interpretation of six Landsat scenes. This is an effIcient, cost-effective method of mapping vegetation in extensive regions. The mapping units do not reflect the syntaxonomic classification, representing rather an integration of physiographic, pedological, geological and floristic information. With the view to improving the classification of these units, I develop a qualitative model of the natural resources of the region using an expert system
- Full Text:
- Date Issued: 1989
Studies in the South African Bulbous liliaceae
- Authors: Jessop, John Peter
- Date: 1973
- Subjects: Bulbs (Plants) -- South Africa Liliaceae -- South Africa Lilies -- South Africa Liliaceae -- Classification -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4261 , http://hdl.handle.net/10962/d1012563
- Description: The work comprises two principal sections; an attempt at ellucidating generic relationships in the South African bulbous Liliaceae, and a revision of the species of selected genera. In the first section the approaches investigated were: 1) A re-evaluation of the nature of the bulb apex, showing a likelihood that certain groups possess axillary and other groups terminal inflorescences. 2) An investigation of leaf anatomy, showing that most genera have very similar leaf structure, but that a few genera do differ from this norm. Scilla (Euscilla) generally possesses a distinctly lignified bundle sheath and the Urginea-Drimia group show a great range in structures - including a palisade. 3) An impression technique to determine patterns in the surface of the leaf cuticle. A close correlation appears to exist between these patterns and leaf shape. 4) Scanning Electron Microscope pictures of pollen revealed a considerable uniformity within the group and between this group and most other members of the Liliaceae. 5) Scanning Electron Microscope pictures of seeds revealed two main groups in the bulbous Liliaceae determined on the appearance of the cell walls of the testa. 6) A simple chromatographic technique was not found to be useful. 7) An investigation of chromosome numbers of. 44 samples of 15 species supplemented published data in allowing an analysis to be made of the application of chromosome numbers to generic concepts. Many genera of the Liliaceae - especially in the bulbous group - have extremely variable chromosome numbers. It is considered that numbers are more applicable to tribal than to generic concepts. Few indications of meiotic abnormalities were detected. Phylogenetic and taxonomic aspects of the genera of the bulbous Liliaceae are discussed and a key to the South African bulbous Liliaceae genera constructed. The following generic alterations are proposed: Ledebouria to be split off Scilla. Schizocarphus to be placed in Scilla. Resnova to be placed in Drimiopsis. The Astemme section (= Neobakeria) to be removed from Polyxena and placed in Massonia. The Cape species of Hyacinthus to be placed in Polyxena. Thuranthos, Urgineopsis and Urginea to be placed in Drimia. It is suggested that Schizobasis and Bowiea are of great importance in explaining the origin of Asparagus - possibly even directly from this group. In the generic revisions, thirteen genera are dealt with including typification, synonymy, distribution, field notes, species descriptions and keys. 67 species are dealt with, of which three are new (all in Ledebouria), and 31 new combinations are proposed.
- Full Text:
- Date Issued: 1973
- Authors: Jessop, John Peter
- Date: 1973
- Subjects: Bulbs (Plants) -- South Africa Liliaceae -- South Africa Lilies -- South Africa Liliaceae -- Classification -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4261 , http://hdl.handle.net/10962/d1012563
- Description: The work comprises two principal sections; an attempt at ellucidating generic relationships in the South African bulbous Liliaceae, and a revision of the species of selected genera. In the first section the approaches investigated were: 1) A re-evaluation of the nature of the bulb apex, showing a likelihood that certain groups possess axillary and other groups terminal inflorescences. 2) An investigation of leaf anatomy, showing that most genera have very similar leaf structure, but that a few genera do differ from this norm. Scilla (Euscilla) generally possesses a distinctly lignified bundle sheath and the Urginea-Drimia group show a great range in structures - including a palisade. 3) An impression technique to determine patterns in the surface of the leaf cuticle. A close correlation appears to exist between these patterns and leaf shape. 4) Scanning Electron Microscope pictures of pollen revealed a considerable uniformity within the group and between this group and most other members of the Liliaceae. 5) Scanning Electron Microscope pictures of seeds revealed two main groups in the bulbous Liliaceae determined on the appearance of the cell walls of the testa. 6) A simple chromatographic technique was not found to be useful. 7) An investigation of chromosome numbers of. 44 samples of 15 species supplemented published data in allowing an analysis to be made of the application of chromosome numbers to generic concepts. Many genera of the Liliaceae - especially in the bulbous group - have extremely variable chromosome numbers. It is considered that numbers are more applicable to tribal than to generic concepts. Few indications of meiotic abnormalities were detected. Phylogenetic and taxonomic aspects of the genera of the bulbous Liliaceae are discussed and a key to the South African bulbous Liliaceae genera constructed. The following generic alterations are proposed: Ledebouria to be split off Scilla. Schizocarphus to be placed in Scilla. Resnova to be placed in Drimiopsis. The Astemme section (= Neobakeria) to be removed from Polyxena and placed in Massonia. The Cape species of Hyacinthus to be placed in Polyxena. Thuranthos, Urgineopsis and Urginea to be placed in Drimia. It is suggested that Schizobasis and Bowiea are of great importance in explaining the origin of Asparagus - possibly even directly from this group. In the generic revisions, thirteen genera are dealt with including typification, synonymy, distribution, field notes, species descriptions and keys. 67 species are dealt with, of which three are new (all in Ledebouria), and 31 new combinations are proposed.
- Full Text:
- Date Issued: 1973
Plants, people, and place: complex, mutualistic, and co-evolving global patterns through time
- Authors: Van Wijk, Yvette Ethné
- Date: 2019
- Subjects: Ethnobotany -- South Africa -- Western Cape , Khoisan (African people) -- Ethnobotany , Human-plant relationships -- South Africa -- Western Cape , Plants -- Classification -- South Africa -- Western Cape , Plant remains (Archaeology) -- South Africa -- Western Cape , Ethnoscience -- South Africa -- Western Cape , Regression analysis
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/76575 , vital:30609
- Description: My thesis studies and analyses the suite of distinctive plant taxa which persist in small patches of vegetation growing in close association with archaeological habitation sites in the southern Cape, South Africa. The unexpected correlation and overlap between botanical taxa collected at 75 site complexes, and ethnobotanical data collected in collaboration with modern Khoi-San communities in the same area, is explored and interrogated. Although sparse, reports of the same suite of taxa recovered from archaeological excavations in the Cape provinces provides depth of time to the study, linking the past to the present. The three-way correlation of a suite of plants closely associated with humans and habitation sites through time, allows for triangulation of the data in order to validate and cross verify the results using more than one frame of reference. Both the plants and the knowledge about their uses have persisted in spite of historical attrition, and alienation of land and language, suffered by the Khoi-San over the past 300 years. Drawing on a large body of primary and secondary data, and using an interdisciplinary, abductive and pragmatic mixed methods approach, a pattern can be traced throughout Africa and globally. Regression analysis strongly indicates that the most ubiquitous taxa were selected for a purpose and are not randomly present in association with humans. Botanical, anthropological, and archaeological studies seldom focus on the inter-connectedness of people and plants at the sites they inhabited. Very little research into modern vegetation in close association with the sites has been undertaken, and vegetation mapping has not captured the occurrence of these site-specific small vegetation patches recorded during my surveys. The topographically, geologically, and vegetatively complex and varied southern Cape, and greater Cape area, is extremely rich in archaeological sites and history. This study suggests that the value of site-specific plant taxa to humans throughout the aeons of pre-agricultural history, persists into the present. Due to tolerance of a broad range of climatic and environmental variables, there is value in the study of these ancient and neglected useful plants in the face of climate change. That this vegetation is so closely associated with archaeological sites of cultural and historic importance confers an urgency to recognising the existence and significance of the distinctive and possibly anthropogenic vegetation surrounding the sites.
- Full Text:
- Date Issued: 2019
- Authors: Van Wijk, Yvette Ethné
- Date: 2019
- Subjects: Ethnobotany -- South Africa -- Western Cape , Khoisan (African people) -- Ethnobotany , Human-plant relationships -- South Africa -- Western Cape , Plants -- Classification -- South Africa -- Western Cape , Plant remains (Archaeology) -- South Africa -- Western Cape , Ethnoscience -- South Africa -- Western Cape , Regression analysis
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/76575 , vital:30609
- Description: My thesis studies and analyses the suite of distinctive plant taxa which persist in small patches of vegetation growing in close association with archaeological habitation sites in the southern Cape, South Africa. The unexpected correlation and overlap between botanical taxa collected at 75 site complexes, and ethnobotanical data collected in collaboration with modern Khoi-San communities in the same area, is explored and interrogated. Although sparse, reports of the same suite of taxa recovered from archaeological excavations in the Cape provinces provides depth of time to the study, linking the past to the present. The three-way correlation of a suite of plants closely associated with humans and habitation sites through time, allows for triangulation of the data in order to validate and cross verify the results using more than one frame of reference. Both the plants and the knowledge about their uses have persisted in spite of historical attrition, and alienation of land and language, suffered by the Khoi-San over the past 300 years. Drawing on a large body of primary and secondary data, and using an interdisciplinary, abductive and pragmatic mixed methods approach, a pattern can be traced throughout Africa and globally. Regression analysis strongly indicates that the most ubiquitous taxa were selected for a purpose and are not randomly present in association with humans. Botanical, anthropological, and archaeological studies seldom focus on the inter-connectedness of people and plants at the sites they inhabited. Very little research into modern vegetation in close association with the sites has been undertaken, and vegetation mapping has not captured the occurrence of these site-specific small vegetation patches recorded during my surveys. The topographically, geologically, and vegetatively complex and varied southern Cape, and greater Cape area, is extremely rich in archaeological sites and history. This study suggests that the value of site-specific plant taxa to humans throughout the aeons of pre-agricultural history, persists into the present. Due to tolerance of a broad range of climatic and environmental variables, there is value in the study of these ancient and neglected useful plants in the face of climate change. That this vegetation is so closely associated with archaeological sites of cultural and historic importance confers an urgency to recognising the existence and significance of the distinctive and possibly anthropogenic vegetation surrounding the sites.
- Full Text:
- Date Issued: 2019
Systematics and biogeography of forest snails, chondrocyclus (mollusca: gastropoda: caenogastropoda: cyclophoridae) in Southern Africa
- Authors: Cole, Mary Louise
- Date: 2017
- Subjects: Chondrocyclus , Mollusks -- South Africa , Cyclophoridae -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/4356 , vital:20651
- Description: This study presents a molecular phylogeny and systematic revision of Chondrocyclus, the major South African group of the large family of operculate terrestrial molluscs, the Cyclophoridae. Chondrocyclus snails are small gastropods found in forest and moist thicket throughout South Africa. This is the first detailed systematic treatment of a group of Cyclophoridae in mainland Africa and the first to provide molecular data. This study complements regional studies on the systematics of the family in Asia and provides comparative data for studies of higher level relationships within the Cyclophoridae. Phylogenetic reconstruction by BI and ML methods of combined and single gene datasets of 16S and CO 1 all showed Chondrocyclus to be monophyletic and recovered five well-supported clades that corresponded to groups of populations identifiable on the basis of combinations of morphological characters. Species were diagnosed morphologically and were shown to be genetically distinct lineages. Informative morphological features include shell dimensions, protoconch, periostracum, operculum, radula and penis. Two species in Afromontane regions of Zimbabwe and Malawi respectively are excluded from Chondrocyclus based on morphology and tentatively placed in Cyathopoma. Diversity recognised within the genus more than doubled, from a previous seven South African species to seventeen. Re-descriptions of established species and descriptions of new species are provided, together with photographs of morphological characteristics. New taxon names and nomenclatural acts within it are disclaimed and are therefore not available in the sense of the International Code of Zoological Nomenclature until validly published elsewhere. Several cryptic species within previously widespread “species” and unrecorded narrowly endemic species were documented. The clade consisting of populations of “Chondrocyclus isipingoensis”, now considered to be a species complex, was sister to a group containing the other four clades. The “Isipingoensis” clade occurs widely in Afromontane regions, along the Great Escarpment, and on the south-east coast. The other four clades occur from Zululand to the Cape Peninsula with a pattern of east-west lineage turnover. The biogeography of Chondrocyclus is interpreted by comparison with concordant patterns in other terrestrial molluscs and unrelated taxa with poor dispersal ability. This study complements other research on composition, spatial distribution and phylogenetic diversity of low-vagility invertebrates and expands the data available for biodiversity conservation in South Africa.
- Full Text:
- Date Issued: 2017
- Authors: Cole, Mary Louise
- Date: 2017
- Subjects: Chondrocyclus , Mollusks -- South Africa , Cyclophoridae -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/4356 , vital:20651
- Description: This study presents a molecular phylogeny and systematic revision of Chondrocyclus, the major South African group of the large family of operculate terrestrial molluscs, the Cyclophoridae. Chondrocyclus snails are small gastropods found in forest and moist thicket throughout South Africa. This is the first detailed systematic treatment of a group of Cyclophoridae in mainland Africa and the first to provide molecular data. This study complements regional studies on the systematics of the family in Asia and provides comparative data for studies of higher level relationships within the Cyclophoridae. Phylogenetic reconstruction by BI and ML methods of combined and single gene datasets of 16S and CO 1 all showed Chondrocyclus to be monophyletic and recovered five well-supported clades that corresponded to groups of populations identifiable on the basis of combinations of morphological characters. Species were diagnosed morphologically and were shown to be genetically distinct lineages. Informative morphological features include shell dimensions, protoconch, periostracum, operculum, radula and penis. Two species in Afromontane regions of Zimbabwe and Malawi respectively are excluded from Chondrocyclus based on morphology and tentatively placed in Cyathopoma. Diversity recognised within the genus more than doubled, from a previous seven South African species to seventeen. Re-descriptions of established species and descriptions of new species are provided, together with photographs of morphological characteristics. New taxon names and nomenclatural acts within it are disclaimed and are therefore not available in the sense of the International Code of Zoological Nomenclature until validly published elsewhere. Several cryptic species within previously widespread “species” and unrecorded narrowly endemic species were documented. The clade consisting of populations of “Chondrocyclus isipingoensis”, now considered to be a species complex, was sister to a group containing the other four clades. The “Isipingoensis” clade occurs widely in Afromontane regions, along the Great Escarpment, and on the south-east coast. The other four clades occur from Zululand to the Cape Peninsula with a pattern of east-west lineage turnover. The biogeography of Chondrocyclus is interpreted by comparison with concordant patterns in other terrestrial molluscs and unrelated taxa with poor dispersal ability. This study complements other research on composition, spatial distribution and phylogenetic diversity of low-vagility invertebrates and expands the data available for biodiversity conservation in South Africa.
- Full Text:
- Date Issued: 2017
The conservation, ecology, and distribution of the critically endangered Encephalartos latifrons Lehm
- Authors: Swart, Carin
- Date: 2019
- Subjects: Encephalartos , Cycadaceae , Cycads -- Conservation -- South Africa , Botany, Economic -- South Africa , Rare plants -- South Africa , Endangered plants -- South Africa , Wild plant trade -- Law and legislation -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/94483 , vital:31049
- Description: Cycads have attracted global attention both as horticulturally interesting and often valuable plants; but also as some of the most threatened organisms on the planet. In this thesis I investigate the conservation management, biology, reproductive ecology and distribution of Encephalartos latifrons populations in the wild and draw out conclusions on how best to conserve global cycad biodiversity. I also employ computer-modelling techniques in some of the chapters of this thesis to demonstrate how to improve conservation outcomes for E. latifrons and endangered species in general, where information on the distribution, biology and habitat requirements of such species are inherently limited, often precluding robust conservation decision-making. In Chapter 1 of this thesis I introduce the concept of extinction debt and elucidate the importance of in situ cycad conservation. I explain how the concept of extinction debt relates to single species, as well as give details on the mechanisms causing extinction debt in cycad populations. I introduce the six extinction trajectory threshold model and how this relates to extinction debt in cycads. I discuss the vulnerability of cycads to extinction and give an overview of biodiversity policy in South Africa. I expand on how national and global policies contribute to cycad conservation and present various global initiatives that support threatened species conservation. I conclude Chapter 1 by explaining how computer-based models can assist conservation decision-making for rare, threatened, and endangered species in the face of uncertainty. Chapter 2 of this thesis illustrates how a modelling approach, using limited available historical and present day locality information, is a feasible method to determine areas of suitable habitat for E. latifrons and other critically endangered cycad species where locality information is inherently uncommon. Results from this chapter show that conservation planning through structured decision-making may be improved by the use of computer models, even when locality data are limited. These results may be incorporated into biodiversity conservation plans or used to assist conservation-decision makers when undertaking recovery efforts for E. latifrons and may provide guidance to conservation planners and policy makers when undertaking conservation plans to improve cycad biodiversity both nationally and globally. There was limited information available in the biology and ecological requirements of E. latifrons. This information is important when making policy decisions such as the publication of non-detriment findings and compiling biodiversity management plans for this and other cycad species. Chapter 3 investigates the life-history, population structure, fire response and survival of an in situ E. latifrons population. A demographic census was undertaken between 2013 and 2017 on a previously undiscovered population. Population characteristics of the “new” population were compared to the demographics of a well-known and intensively managed population. Results of this chapter show that at least one in situ E. latifrons population is stable and increasing under current environmental conditions. Importantly, the population is naturally recruiting seedlings without the need for artificial pollination. Demographic information described in this chapter is a necessary precursor to undertaking a Population Viability Assessment for the species. This will assist conservation decision-makers when determining the best conservation management strategy for E. latifrons. It may also be useful to apply generalisatons to other cycad species (with similar life-histories and habitat requirements) where there is limited information available on the species biological and ecological requirements, restricting robust policy conservation decision-making. It was important for this study to determine the extent and variety of cone fauna within existing E. latifrons wild populations. Previous anecdotal evidence suggested that E. latifrons is functionally extinct as a species, but evidence to the contrary was found when a healthy, self-sustaining wild population was discovered to be naturally recruiting. It was important to establish the existence and diversity of male cone faunal species (an important breeding site for weevil pollinators) within wild populations. Chapter 4 set out to determine if potential pollinators exist in the wild and if so, how diverse are they and in what numbers. This is the first comprehensive analysis of cone fauna present in wild E. latifrons populations. Equally important was the need to determine if wild populations are capable of producing viable seeds under conditions conducive to natural pollination. Results of this chapter show that there is a relatively high diversity of insect fauna in the male cones of some wild E. latifrons populations. Furthermore, some wild populations are capable of producing viable seeds through natural pollination; even though they may not be naturally recruiting seedlings into the population. A staggered germination pattern displayed by one of the wild E. latifrons populations was studied, suggesting the evolution of an adaptive trait given the stochastic environment (climatically and disturbances such as fire) within which E. latifrons populations may be found. Species recovery (restoration and/or population augmentation) may be the only conservation solution remaining to save endangered species such as E. latifrons from extinction in the wild. Chapter 5 involves the return of 25 seedlings germinated as part of a seed viability experiment (see Chapter 4) back into a wild population from where they originated. The primary threat to seedling survival at the site was livestock activity (grazing/trampling). The population was subsequently fenced off to mitigate this threat and seedlings planted both inside and outside a fenced area to establish if there was a difference in seedling survival between the unprotected and protected sites. A high percentage (92%) of seedlings planted perished in total. None of the seedlings planted outside the fenced area survived over the monitoring period, while only two seedlings planted within the fenced area survived. Survival of the seedlings inside the fenced area was only after placing individual cages on the seedlings to prevent further losses. The primary causes of death for all seedlings included uprooting, and defoliation with some of the seedlings missing completely. This chapter found that the lack of natural seedling recruitment at the site was as a result of livestock activity. Grazing by livestock poses a significant threat to natural recruitment in some E. latifrons populations. Alternative restoration methods are suggested and protection of seedlings while undertaking a restoration/augmentation programme is emphasised. Developing conservation management plans for rare and/or endangered species is often met with high levels of uncertainty, particularly if there is limited information available on the biology and ecological requirements for the species concerned. Population viability analysis (PVA) is often suggested as a tool to determine conservation management scenarios that may enhance wild population persistence. The standard PVA approach is however problematic as it is a time-consuming process requiring the collection of demographic data over long time periods. In addition, the PVA approach does not take in to account non-biological factors which may impede the effective implementation of conservation plans. Chapter 6 of this thesis makes use of a Multi-Criteria Decision Making (MCDM) approach called the Analytical Hierarchy Process (AHP) to decide on the best conservation management strategy for an E. latifrons population. Sensitivity analysis was completed to test the robustness of the decision and to identify which criteria influenced the original results. In this study, the development of the decision tree and criteria judgements, were made solely by the researcher. It is emphasised that the decision outcome may be biased if not conducted as part of a multi-stakeholder workshop using the same approach. Nevertheless, it is recommended that a Population Viability Risk Management (PVRM) assessment be undertaken for E. latifrons using an MCDM approach such as AHP as a prestudy, before the revision of the Biodiversity Management Plan (BMP) for E. latifrons. This method is particularly useful when non-biological criteria are to be incorporated into the decision-making process. It is also a viable and holistic alternative to the standard PVA approach when developing conservation management plans for rare and endangered species. In Chapter 7 I review the concept of extinction debt in cycads using E. latifrons as an example. I assimilate historical information to understand mechanisms that may have impacted on E. latifrons populations in the past. This was done to understand the scale of extinction time lags on E. latifrons and to relate this to its present position on the exitinction trajectory. I recommend aligning South African policies and biodiversity assessments with international initiatives and draw out general conclusions for the conservation of global cycad biodiversity. I conclude by recommending further research for E. latifrons.
- Full Text:
- Date Issued: 2019
- Authors: Swart, Carin
- Date: 2019
- Subjects: Encephalartos , Cycadaceae , Cycads -- Conservation -- South Africa , Botany, Economic -- South Africa , Rare plants -- South Africa , Endangered plants -- South Africa , Wild plant trade -- Law and legislation -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/94483 , vital:31049
- Description: Cycads have attracted global attention both as horticulturally interesting and often valuable plants; but also as some of the most threatened organisms on the planet. In this thesis I investigate the conservation management, biology, reproductive ecology and distribution of Encephalartos latifrons populations in the wild and draw out conclusions on how best to conserve global cycad biodiversity. I also employ computer-modelling techniques in some of the chapters of this thesis to demonstrate how to improve conservation outcomes for E. latifrons and endangered species in general, where information on the distribution, biology and habitat requirements of such species are inherently limited, often precluding robust conservation decision-making. In Chapter 1 of this thesis I introduce the concept of extinction debt and elucidate the importance of in situ cycad conservation. I explain how the concept of extinction debt relates to single species, as well as give details on the mechanisms causing extinction debt in cycad populations. I introduce the six extinction trajectory threshold model and how this relates to extinction debt in cycads. I discuss the vulnerability of cycads to extinction and give an overview of biodiversity policy in South Africa. I expand on how national and global policies contribute to cycad conservation and present various global initiatives that support threatened species conservation. I conclude Chapter 1 by explaining how computer-based models can assist conservation decision-making for rare, threatened, and endangered species in the face of uncertainty. Chapter 2 of this thesis illustrates how a modelling approach, using limited available historical and present day locality information, is a feasible method to determine areas of suitable habitat for E. latifrons and other critically endangered cycad species where locality information is inherently uncommon. Results from this chapter show that conservation planning through structured decision-making may be improved by the use of computer models, even when locality data are limited. These results may be incorporated into biodiversity conservation plans or used to assist conservation-decision makers when undertaking recovery efforts for E. latifrons and may provide guidance to conservation planners and policy makers when undertaking conservation plans to improve cycad biodiversity both nationally and globally. There was limited information available in the biology and ecological requirements of E. latifrons. This information is important when making policy decisions such as the publication of non-detriment findings and compiling biodiversity management plans for this and other cycad species. Chapter 3 investigates the life-history, population structure, fire response and survival of an in situ E. latifrons population. A demographic census was undertaken between 2013 and 2017 on a previously undiscovered population. Population characteristics of the “new” population were compared to the demographics of a well-known and intensively managed population. Results of this chapter show that at least one in situ E. latifrons population is stable and increasing under current environmental conditions. Importantly, the population is naturally recruiting seedlings without the need for artificial pollination. Demographic information described in this chapter is a necessary precursor to undertaking a Population Viability Assessment for the species. This will assist conservation decision-makers when determining the best conservation management strategy for E. latifrons. It may also be useful to apply generalisatons to other cycad species (with similar life-histories and habitat requirements) where there is limited information available on the species biological and ecological requirements, restricting robust policy conservation decision-making. It was important for this study to determine the extent and variety of cone fauna within existing E. latifrons wild populations. Previous anecdotal evidence suggested that E. latifrons is functionally extinct as a species, but evidence to the contrary was found when a healthy, self-sustaining wild population was discovered to be naturally recruiting. It was important to establish the existence and diversity of male cone faunal species (an important breeding site for weevil pollinators) within wild populations. Chapter 4 set out to determine if potential pollinators exist in the wild and if so, how diverse are they and in what numbers. This is the first comprehensive analysis of cone fauna present in wild E. latifrons populations. Equally important was the need to determine if wild populations are capable of producing viable seeds under conditions conducive to natural pollination. Results of this chapter show that there is a relatively high diversity of insect fauna in the male cones of some wild E. latifrons populations. Furthermore, some wild populations are capable of producing viable seeds through natural pollination; even though they may not be naturally recruiting seedlings into the population. A staggered germination pattern displayed by one of the wild E. latifrons populations was studied, suggesting the evolution of an adaptive trait given the stochastic environment (climatically and disturbances such as fire) within which E. latifrons populations may be found. Species recovery (restoration and/or population augmentation) may be the only conservation solution remaining to save endangered species such as E. latifrons from extinction in the wild. Chapter 5 involves the return of 25 seedlings germinated as part of a seed viability experiment (see Chapter 4) back into a wild population from where they originated. The primary threat to seedling survival at the site was livestock activity (grazing/trampling). The population was subsequently fenced off to mitigate this threat and seedlings planted both inside and outside a fenced area to establish if there was a difference in seedling survival between the unprotected and protected sites. A high percentage (92%) of seedlings planted perished in total. None of the seedlings planted outside the fenced area survived over the monitoring period, while only two seedlings planted within the fenced area survived. Survival of the seedlings inside the fenced area was only after placing individual cages on the seedlings to prevent further losses. The primary causes of death for all seedlings included uprooting, and defoliation with some of the seedlings missing completely. This chapter found that the lack of natural seedling recruitment at the site was as a result of livestock activity. Grazing by livestock poses a significant threat to natural recruitment in some E. latifrons populations. Alternative restoration methods are suggested and protection of seedlings while undertaking a restoration/augmentation programme is emphasised. Developing conservation management plans for rare and/or endangered species is often met with high levels of uncertainty, particularly if there is limited information available on the biology and ecological requirements for the species concerned. Population viability analysis (PVA) is often suggested as a tool to determine conservation management scenarios that may enhance wild population persistence. The standard PVA approach is however problematic as it is a time-consuming process requiring the collection of demographic data over long time periods. In addition, the PVA approach does not take in to account non-biological factors which may impede the effective implementation of conservation plans. Chapter 6 of this thesis makes use of a Multi-Criteria Decision Making (MCDM) approach called the Analytical Hierarchy Process (AHP) to decide on the best conservation management strategy for an E. latifrons population. Sensitivity analysis was completed to test the robustness of the decision and to identify which criteria influenced the original results. In this study, the development of the decision tree and criteria judgements, were made solely by the researcher. It is emphasised that the decision outcome may be biased if not conducted as part of a multi-stakeholder workshop using the same approach. Nevertheless, it is recommended that a Population Viability Risk Management (PVRM) assessment be undertaken for E. latifrons using an MCDM approach such as AHP as a prestudy, before the revision of the Biodiversity Management Plan (BMP) for E. latifrons. This method is particularly useful when non-biological criteria are to be incorporated into the decision-making process. It is also a viable and holistic alternative to the standard PVA approach when developing conservation management plans for rare and endangered species. In Chapter 7 I review the concept of extinction debt in cycads using E. latifrons as an example. I assimilate historical information to understand mechanisms that may have impacted on E. latifrons populations in the past. This was done to understand the scale of extinction time lags on E. latifrons and to relate this to its present position on the exitinction trajectory. I recommend aligning South African policies and biodiversity assessments with international initiatives and draw out general conclusions for the conservation of global cycad biodiversity. I conclude by recommending further research for E. latifrons.
- Full Text:
- Date Issued: 2019
Studies in leaf domatia-mite mutualism in South Africa
- Authors: Situngu, Sivuyisiwe
- Date: 2018
- Subjects: Insect-plant relationships , Mites , Mutualism (Biology) , Biological pest control agents
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/63334 , vital:28394
- Description: Plants have various traits which allow them to cope and resist their enemies including both insects and fungi . In some cases such traits allow plants to build mutualistic relationships with natural enemies of plant pests. This is the case in many dicotyledonous plants which produce leaf domatia. Leaf domatia are plant cavities usually found in the axils of major veins in the abaxial side of leaves. They are usually associated with mites and often mediate mutualistic relationships with predacious mites. Mites use leaf domatia primarily for shelter, to reproduce, and to develop. In turn, plants benefit from having predaceous mites on their leaves, because mites act as plant “bodyguards” and offer defence against pathogens and small arthropod herbivores. This phenomenon has been well documented all over the world, but Africa remains disproportionally understudied. The aim of this study was to fill the gap that exists in our knowledge of the extent of the distribution of leaf domatia-mite mutualisms and generate a better understanding of the diversity of mites found within leaf domatia from an African perspective. This was done by surveying plant species that bear leaf domatia from different vegetation types in South Africa. The plants with leaf domatia were examined for the presence of mites in order to determine patterns of mite abundance and diversity and, in so doing, address the following questions: • Does each tree species host have a specific mite or mite assemblage? • Do some mites prefer certain types of leaf domatia? • Do mites prefer a specific place in the tree canopy and does the microclimate in the tree canopy affect the distribution of mites? • Do different vegetation sites and types differ in their mite diversity and species composition? • Does mite abundance and diversity vary with seasons? Do coffee plantations have a different suite of mites than the adjacent forest? The anatomical structures of leaf domatia from six selected plant species(Coffea arabica, Gardenia thunbergia, Rothmannia capensis, Rothmannia globosa (Rubiaceae), Ocotea bullata (Lauraceae) and Tecoma capensis (Bignoniaceae) with different types of leaf domatia were also studied. The results from this study suggested that the key futures which distinguish domatia are the presence of an extra layer of tissue in the lower epidermis, a thick cuticle, cuticular folds, the presence of trichomes and an invagination. This study provides a better understating of the structure of leaf domatia. Leaf domatia bearing plants are widely distributed in South Africa, and species and vegetation-specific associations were assessed. Over 250 plant specimens with leaf domatia were collected and examined and more than 60 different mite species were found in association with the sampled plant species. The majority of mites found within the domatia of these tree species were predaceous and included mites from Stigmatidae, Tydeidae and Phytoseiidae. Furthermore, 15 new species were collected, suggesting that mites are understudied in South Africa. This study showed that the different vegetation types sampled did not differ markedly in terms of their mite biota and that similar mites were found across the region, and the association between leaf domatia and mites was found to be opportunistic and that mites had no preference for any particular domatia types. No host specificity relationship was observed between plants and mites. The assessment of mites associated with Coffea arabica showed that indigenous mites are able to colonise and establish a beneficial mutualism on exotic species. This is important as it ascertains that economically important plants that are cultivated outside their area of natural distribution can still benefit from this mutualism. This study also found that mite abundance and diversity in plants with leaf domatia were influenced by factors such as temperature, relative humidity and rainfall. Mite communities found in association with domatia changed as the year progressed and over the seasons. The seasonal fluctuations varied between the sampled plant species. In addition, this study found that mites were sensitive to extreme environmental conditions, and thus, mites preferred leaves found in the lower parts of the tree canopy and avoided exposed leaves. This study provides a better understanding of the distribution of domatia bearing plants in South Africa and their associated mites and contributes to our knowledge of the biodiversity of mites in the region. Furthermore, this study also adds to our understanding of the leaf domatia - mite mutualism in Africa. The applied example looking at the plant-mite mutualism in Coffea arabica highlights the importance of this mutualism in commercial plants.
- Full Text:
- Date Issued: 2018
- Authors: Situngu, Sivuyisiwe
- Date: 2018
- Subjects: Insect-plant relationships , Mites , Mutualism (Biology) , Biological pest control agents
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/63334 , vital:28394
- Description: Plants have various traits which allow them to cope and resist their enemies including both insects and fungi . In some cases such traits allow plants to build mutualistic relationships with natural enemies of plant pests. This is the case in many dicotyledonous plants which produce leaf domatia. Leaf domatia are plant cavities usually found in the axils of major veins in the abaxial side of leaves. They are usually associated with mites and often mediate mutualistic relationships with predacious mites. Mites use leaf domatia primarily for shelter, to reproduce, and to develop. In turn, plants benefit from having predaceous mites on their leaves, because mites act as plant “bodyguards” and offer defence against pathogens and small arthropod herbivores. This phenomenon has been well documented all over the world, but Africa remains disproportionally understudied. The aim of this study was to fill the gap that exists in our knowledge of the extent of the distribution of leaf domatia-mite mutualisms and generate a better understanding of the diversity of mites found within leaf domatia from an African perspective. This was done by surveying plant species that bear leaf domatia from different vegetation types in South Africa. The plants with leaf domatia were examined for the presence of mites in order to determine patterns of mite abundance and diversity and, in so doing, address the following questions: • Does each tree species host have a specific mite or mite assemblage? • Do some mites prefer certain types of leaf domatia? • Do mites prefer a specific place in the tree canopy and does the microclimate in the tree canopy affect the distribution of mites? • Do different vegetation sites and types differ in their mite diversity and species composition? • Does mite abundance and diversity vary with seasons? Do coffee plantations have a different suite of mites than the adjacent forest? The anatomical structures of leaf domatia from six selected plant species(Coffea arabica, Gardenia thunbergia, Rothmannia capensis, Rothmannia globosa (Rubiaceae), Ocotea bullata (Lauraceae) and Tecoma capensis (Bignoniaceae) with different types of leaf domatia were also studied. The results from this study suggested that the key futures which distinguish domatia are the presence of an extra layer of tissue in the lower epidermis, a thick cuticle, cuticular folds, the presence of trichomes and an invagination. This study provides a better understating of the structure of leaf domatia. Leaf domatia bearing plants are widely distributed in South Africa, and species and vegetation-specific associations were assessed. Over 250 plant specimens with leaf domatia were collected and examined and more than 60 different mite species were found in association with the sampled plant species. The majority of mites found within the domatia of these tree species were predaceous and included mites from Stigmatidae, Tydeidae and Phytoseiidae. Furthermore, 15 new species were collected, suggesting that mites are understudied in South Africa. This study showed that the different vegetation types sampled did not differ markedly in terms of their mite biota and that similar mites were found across the region, and the association between leaf domatia and mites was found to be opportunistic and that mites had no preference for any particular domatia types. No host specificity relationship was observed between plants and mites. The assessment of mites associated with Coffea arabica showed that indigenous mites are able to colonise and establish a beneficial mutualism on exotic species. This is important as it ascertains that economically important plants that are cultivated outside their area of natural distribution can still benefit from this mutualism. This study also found that mite abundance and diversity in plants with leaf domatia were influenced by factors such as temperature, relative humidity and rainfall. Mite communities found in association with domatia changed as the year progressed and over the seasons. The seasonal fluctuations varied between the sampled plant species. In addition, this study found that mites were sensitive to extreme environmental conditions, and thus, mites preferred leaves found in the lower parts of the tree canopy and avoided exposed leaves. This study provides a better understanding of the distribution of domatia bearing plants in South Africa and their associated mites and contributes to our knowledge of the biodiversity of mites in the region. Furthermore, this study also adds to our understanding of the leaf domatia - mite mutualism in Africa. The applied example looking at the plant-mite mutualism in Coffea arabica highlights the importance of this mutualism in commercial plants.
- Full Text:
- Date Issued: 2018
Cell-free biosynthesis of abscisic acid (ABA) in extracts of flavedo from Citrus sinensis (L.) osbeck
- Richardson, Gaynor Rose-Marie
- Authors: Richardson, Gaynor Rose-Marie
- Date: 1996
- Subjects: Biosynthesis Abscisic acid Citrus fruits
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4221 , http://hdl.handle.net/10962/d1003790
- Description: The biosynthetic origin of the plant growth regulator abscisic acid remains equivocal and almost nothing is known about the enzymes involved in this process. The present research programme describes the development of a cell-free system, capable of synthesizing abscisic acid and attempts to provide further information about the biochemistry and enzymology of this important biosynthetic pathway. Cell-free extracts were prepared either directly from the flavedo (crude) or from an acetone powder derived from flavedo, of mature coloured fruits of Citrus sinensis L. cv. Midknight and incubated with mevalonic acid, isopentenyl pyrophosphate, famesylpyrophosphate, geranylgeranyl pyrophosphate, ß-carotene and 1',4'-trans-abscisic acid diol. The neutral and acidic products formed were purified by thin-layer chromatography and high performance liquid chromatography, and quantified by high performance liquid chromatography, gas chromatography-electron capture and unequivocally identified by combined gas chromatography-mass spectrometry. Abscisic acid, 1',4'-trans-abscisic acid diol and phaseic acid were unequivocally identified as the major acidic products formed in this cell-free system. The acid fraction also contained xanthoxin acid. Labelled and unlabelled ß-carotene was converted into the neutral compounds xanthoxin and xanthoxin alcohol. In addition. high performance liquid chromatography-photodiode array analYSis of the oxy-carotenoid fraction revealed the complete spectrum of ß, ß-carotenoids induding zeaxanthin, antheraxanthin and violaxanthin with accumulation of an oxygenated carotenoid tentatively identified as 9- cis-violaxanthin. Identification of putative C₁₅ intermediates was achieved by either UV spectrophotometry and combined capillary gas chromatography-mass spectrometry or microchemical analYSis and co-chromatography. Refeeding studies using (±)-[2-¹⁴C]_ abscisic acid diol as substrate revealed that abscisic acid was not metabolized to abscisic acid diol, suggesting that it was/is produced as an intermediate rather than as a catabolite of ABA in this system. Stigmasterol, and to a lesser extent cholesterol reduced conversion of ß-carotene to abscisic acid but did not influence transformation of 1',4'-trans-abscisic acid diol to abscisic acid. AM01618 stimulated fonnation of abscisic acid and appeared to exert its effect at the level of conversion of 1' ,4'-trans-abscisic acid diol. Zeatin and the cytokinin analogue, ancymidol inhibited the biosynthesis of abscisic acid whereas dithiothreitol increased incorporation of label from ß-carotene into abscisic acid suggesting involvement of a cytochrome P450-type mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kD protein with peroxidase activity characteristic of a cytochrome P-450. Abscisic acid biosynthesizing activity was always greater in extracts from acetone powder and abscisic acid biosynthesis was enhanced in the presence of AMO 1618, NAD+, NADH, NADPH, MgCI₂ and Molybdate but was inhibited by FAD. Activity was further enhanced by the addition of (R,S)-abscisic acid as a cold-pool trap and by induding 0.1% w/v of either Tween 20 or Triton X 100 in the extraction buffer. When cis-ß-carotene was used as substrate, no abscisic acid was produced. Conversely when either all-trans-ß-carotene or a mixture of the two isomers was used, incorporation into abscisic acid occurred. Upoxygenase activity in cell-free extracts of Citrus flavedo increased with increasing protein concentration. As the ability of lipoxygenase to make xanthoxin from violaxanthin, had been reported, increased activity in the cell-free system implied that carotenoid deavage was being brought about by a non-haem oxygenase with lipoxygenase-like properties. Reports had implicated phoshorylation in the activation of many catalytic enzymes (Hanks et aI., 1985). Phosphorylation of the enzymes in this cell-free system proved unsuccessful. Further, it had been reported that in vitro phosphorylation of several membrane polypeptides and soluble polypeptides from com, had been promoted by the addition of Ca²₊ In this cell-free system Ca + did not have a stimulatory effect on protein phosphorylation. Dioxygenases generally occur as soluble enzymes, where they catalyse many oxygenation reactions in metabolic pathways. The addition of 2-oxo-glutarate, a requirement of most soluble oxidases, did not affect the activity of the cell-free system.
- Full Text:
- Date Issued: 1996
- Authors: Richardson, Gaynor Rose-Marie
- Date: 1996
- Subjects: Biosynthesis Abscisic acid Citrus fruits
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4221 , http://hdl.handle.net/10962/d1003790
- Description: The biosynthetic origin of the plant growth regulator abscisic acid remains equivocal and almost nothing is known about the enzymes involved in this process. The present research programme describes the development of a cell-free system, capable of synthesizing abscisic acid and attempts to provide further information about the biochemistry and enzymology of this important biosynthetic pathway. Cell-free extracts were prepared either directly from the flavedo (crude) or from an acetone powder derived from flavedo, of mature coloured fruits of Citrus sinensis L. cv. Midknight and incubated with mevalonic acid, isopentenyl pyrophosphate, famesylpyrophosphate, geranylgeranyl pyrophosphate, ß-carotene and 1',4'-trans-abscisic acid diol. The neutral and acidic products formed were purified by thin-layer chromatography and high performance liquid chromatography, and quantified by high performance liquid chromatography, gas chromatography-electron capture and unequivocally identified by combined gas chromatography-mass spectrometry. Abscisic acid, 1',4'-trans-abscisic acid diol and phaseic acid were unequivocally identified as the major acidic products formed in this cell-free system. The acid fraction also contained xanthoxin acid. Labelled and unlabelled ß-carotene was converted into the neutral compounds xanthoxin and xanthoxin alcohol. In addition. high performance liquid chromatography-photodiode array analYSis of the oxy-carotenoid fraction revealed the complete spectrum of ß, ß-carotenoids induding zeaxanthin, antheraxanthin and violaxanthin with accumulation of an oxygenated carotenoid tentatively identified as 9- cis-violaxanthin. Identification of putative C₁₅ intermediates was achieved by either UV spectrophotometry and combined capillary gas chromatography-mass spectrometry or microchemical analYSis and co-chromatography. Refeeding studies using (±)-[2-¹⁴C]_ abscisic acid diol as substrate revealed that abscisic acid was not metabolized to abscisic acid diol, suggesting that it was/is produced as an intermediate rather than as a catabolite of ABA in this system. Stigmasterol, and to a lesser extent cholesterol reduced conversion of ß-carotene to abscisic acid but did not influence transformation of 1',4'-trans-abscisic acid diol to abscisic acid. AM01618 stimulated fonnation of abscisic acid and appeared to exert its effect at the level of conversion of 1' ,4'-trans-abscisic acid diol. Zeatin and the cytokinin analogue, ancymidol inhibited the biosynthesis of abscisic acid whereas dithiothreitol increased incorporation of label from ß-carotene into abscisic acid suggesting involvement of a cytochrome P450-type mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kD protein with peroxidase activity characteristic of a cytochrome P-450. Abscisic acid biosynthesizing activity was always greater in extracts from acetone powder and abscisic acid biosynthesis was enhanced in the presence of AMO 1618, NAD+, NADH, NADPH, MgCI₂ and Molybdate but was inhibited by FAD. Activity was further enhanced by the addition of (R,S)-abscisic acid as a cold-pool trap and by induding 0.1% w/v of either Tween 20 or Triton X 100 in the extraction buffer. When cis-ß-carotene was used as substrate, no abscisic acid was produced. Conversely when either all-trans-ß-carotene or a mixture of the two isomers was used, incorporation into abscisic acid occurred. Upoxygenase activity in cell-free extracts of Citrus flavedo increased with increasing protein concentration. As the ability of lipoxygenase to make xanthoxin from violaxanthin, had been reported, increased activity in the cell-free system implied that carotenoid deavage was being brought about by a non-haem oxygenase with lipoxygenase-like properties. Reports had implicated phoshorylation in the activation of many catalytic enzymes (Hanks et aI., 1985). Phosphorylation of the enzymes in this cell-free system proved unsuccessful. Further, it had been reported that in vitro phosphorylation of several membrane polypeptides and soluble polypeptides from com, had been promoted by the addition of Ca²₊ In this cell-free system Ca + did not have a stimulatory effect on protein phosphorylation. Dioxygenases generally occur as soluble enzymes, where they catalyse many oxygenation reactions in metabolic pathways. The addition of 2-oxo-glutarate, a requirement of most soluble oxidases, did not affect the activity of the cell-free system.
- Full Text:
- Date Issued: 1996