The metabolism of abscisic acid in higher plant tissues
- Authors: Cowan, Ashton Keith
- Date: 1989
- Subjects: Plants -- Metabolism Plant cells and tissues Abscisic acid -- Metabolism
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4176 , http://hdl.handle.net/10962/d1002024
- Description: The biosynthesis of ABA from R-[2-¹⁴C]-MVA was demonstrated in Persea americana cv. Fuerte mesocarp and in mature seeds of Hordeum vulgare cv. Dyan and cv. Himalaya. Radioactivity from R-[2-¹⁴-C]-MVA was also incorporated into the 1',4'-trans ABA diol in Persea americana mesocarp and a possible role for this metabolite as a precursor of ABA in plants is discussed. The biosynthesis of ABA from MVA could not be demonstrated in either turgid and waterstressed Hordeum vulgare cv. Dyan, Pisum sativum cv. Black-eyed Susan and Phaseolus vulgaris cv. Top-crop or in immature seeds of Pisum sativum and Phaseolus vulgaris. (R,S,)-[2-¹⁴C]-ABA was catabolised to PA, DPA and aqueous conjugates in leaves and mature seeds of Hordeum vulgare cv. Dyan, seedlings and immature seeds of Pisum sativum and Phaseolus vulgaris and in mesocarp from ripening fruits of Persea americana. PA and DPA were identified by either microchemical methods and/or capillary GC-MS. 7'-Hydroxy ABA was characterised as a novel ABA catabolite in light-grown and etiolated leaves of Hordeum vulgare by capillary GC-MS. Circular dichroism analysis revealed that it was derived predominantly from the (R)-enantiomer of ABA. This catabolite was absent in similar studies using the dicotyledons Pisum sativum and Phaseolus vulgaris. Refeeding studies with [¹⁴C]-PA, [C]-DPA and [¹⁴C]-7'-hydroxy ABA were used to confirm the metabolic interrelationship between ABA and its catabolites in both vegetative and non-vegetative tissues from monocotyledonous and dicotyledonous species. The methyl ester of (R,S,)-ABA was hydrolysed efficiently by light-grown leaves of Hordeum vulgare. Older, vegetative tissues catabolised (R,S,)-ABA more efficiently than their younger counterparts. In contrast, small, immature seeds of Pisum sativum catabolised (R,S,)-ABA more effectively than larger, immature seeds of this species. Light did not appear to influence ABA biosynthesis but markedly enhanced ABA catabolism. Light stimulated the overall rate of ABA catabolism in both vegetative and non-vegetative tissue. Water stress reduced ABA catabolism in Hordeum vulgare leaves but had little effect on this process in Phaseolus vulgaris seedlings. Pretreatment of tissues with (R,S,)-ABA retarded the catabolism of (R,S,)-[2-¹⁴C]-ABA, negating ABA-induced conversion to PA. Cycloheximide inhibited ABA biosynthesis and catabolism but did not affect ABA conjugation. Chloramphenicol and lincomycin had little or no effect on ABA metabolism suggesting that the enzymes involved were labile and cytoplasmic in origin. Ancymidol and cycocel inhibited ABA biosynthesis while AM01618 stimulated this process. The cytokinins, benzyladenine, kinetin, isopentenyl adenine and zeatin also inhibited ABA biosynthesis. These results are discussed in relation to the possible involvement of carotenoids in ABA biosynthesis. AM01618, ancymidol andcycocel did not significantly influence the conversion of ABA to PA and DPA while cytokinins appeared to enhance this process only in vegetative tissue. The information derived from these studies was then used in attempts to develop a cell-free system from higher plants capable of metabolising ABA. A cell-free system prepared from imbibed Hordeum vulgare cv. Dyan embryos biosynthesized and catabolised ABA. This is the first demonstration of a cell-free system from non-vegetative tissue capable of metabolising ABA and could prove useful for elucidating its biosynthetic route. This cell-free system generated the terpenyl pyrophosphates IPP, FPP and GGPP from MVA. ABA was produced from both MVA and IPP in the presence of 0₂ and NADPH. The biosynthesis of ABA was stimulated by the addition of the squalene 2,3-oxide cyclase and kaurene synthetase inhibitor, AM01618 and a "cold-pool trap" of (R,S,)-ABA. Ancymidol, cycocel and cytokinins reduced incorporation of label from MVA into ABA. Similar cell-free preparations, in the absence of AM01618, converted (R,S,)-[2-¹⁴-C]-ABA into PA, 7'-hydroxy ABA and water-soluble conjugates. Although the methyl ester of (R,S,)-ABA was efficiently hydrolysed in this cell-free system no DPA was generated. The possible involvement of mixed function oxidase activity and soluble oxidases is discussed in relation to ABA metabolism. While cell-free preparations from Persea americana cv. Fuerte mesocarp and immature seeds of Pisum sativum and Phaseolus vulgaris were unable to synthesize ABA from MVA, these tissue homogenates converted ABA into more polar acidic products. PA and DPA were identified as products of ABA catabolism in extracts from immature seeds of Phaseolus vulgaris and the l',4'-cis diol of ABA in extracts from Pisum sativum immature seeds
- Full Text:
- Date Issued: 1989
- Authors: Cowan, Ashton Keith
- Date: 1989
- Subjects: Plants -- Metabolism Plant cells and tissues Abscisic acid -- Metabolism
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4176 , http://hdl.handle.net/10962/d1002024
- Description: The biosynthesis of ABA from R-[2-¹⁴C]-MVA was demonstrated in Persea americana cv. Fuerte mesocarp and in mature seeds of Hordeum vulgare cv. Dyan and cv. Himalaya. Radioactivity from R-[2-¹⁴-C]-MVA was also incorporated into the 1',4'-trans ABA diol in Persea americana mesocarp and a possible role for this metabolite as a precursor of ABA in plants is discussed. The biosynthesis of ABA from MVA could not be demonstrated in either turgid and waterstressed Hordeum vulgare cv. Dyan, Pisum sativum cv. Black-eyed Susan and Phaseolus vulgaris cv. Top-crop or in immature seeds of Pisum sativum and Phaseolus vulgaris. (R,S,)-[2-¹⁴C]-ABA was catabolised to PA, DPA and aqueous conjugates in leaves and mature seeds of Hordeum vulgare cv. Dyan, seedlings and immature seeds of Pisum sativum and Phaseolus vulgaris and in mesocarp from ripening fruits of Persea americana. PA and DPA were identified by either microchemical methods and/or capillary GC-MS. 7'-Hydroxy ABA was characterised as a novel ABA catabolite in light-grown and etiolated leaves of Hordeum vulgare by capillary GC-MS. Circular dichroism analysis revealed that it was derived predominantly from the (R)-enantiomer of ABA. This catabolite was absent in similar studies using the dicotyledons Pisum sativum and Phaseolus vulgaris. Refeeding studies with [¹⁴C]-PA, [C]-DPA and [¹⁴C]-7'-hydroxy ABA were used to confirm the metabolic interrelationship between ABA and its catabolites in both vegetative and non-vegetative tissues from monocotyledonous and dicotyledonous species. The methyl ester of (R,S,)-ABA was hydrolysed efficiently by light-grown leaves of Hordeum vulgare. Older, vegetative tissues catabolised (R,S,)-ABA more efficiently than their younger counterparts. In contrast, small, immature seeds of Pisum sativum catabolised (R,S,)-ABA more effectively than larger, immature seeds of this species. Light did not appear to influence ABA biosynthesis but markedly enhanced ABA catabolism. Light stimulated the overall rate of ABA catabolism in both vegetative and non-vegetative tissue. Water stress reduced ABA catabolism in Hordeum vulgare leaves but had little effect on this process in Phaseolus vulgaris seedlings. Pretreatment of tissues with (R,S,)-ABA retarded the catabolism of (R,S,)-[2-¹⁴C]-ABA, negating ABA-induced conversion to PA. Cycloheximide inhibited ABA biosynthesis and catabolism but did not affect ABA conjugation. Chloramphenicol and lincomycin had little or no effect on ABA metabolism suggesting that the enzymes involved were labile and cytoplasmic in origin. Ancymidol and cycocel inhibited ABA biosynthesis while AM01618 stimulated this process. The cytokinins, benzyladenine, kinetin, isopentenyl adenine and zeatin also inhibited ABA biosynthesis. These results are discussed in relation to the possible involvement of carotenoids in ABA biosynthesis. AM01618, ancymidol andcycocel did not significantly influence the conversion of ABA to PA and DPA while cytokinins appeared to enhance this process only in vegetative tissue. The information derived from these studies was then used in attempts to develop a cell-free system from higher plants capable of metabolising ABA. A cell-free system prepared from imbibed Hordeum vulgare cv. Dyan embryos biosynthesized and catabolised ABA. This is the first demonstration of a cell-free system from non-vegetative tissue capable of metabolising ABA and could prove useful for elucidating its biosynthetic route. This cell-free system generated the terpenyl pyrophosphates IPP, FPP and GGPP from MVA. ABA was produced from both MVA and IPP in the presence of 0₂ and NADPH. The biosynthesis of ABA was stimulated by the addition of the squalene 2,3-oxide cyclase and kaurene synthetase inhibitor, AM01618 and a "cold-pool trap" of (R,S,)-ABA. Ancymidol, cycocel and cytokinins reduced incorporation of label from MVA into ABA. Similar cell-free preparations, in the absence of AM01618, converted (R,S,)-[2-¹⁴-C]-ABA into PA, 7'-hydroxy ABA and water-soluble conjugates. Although the methyl ester of (R,S,)-ABA was efficiently hydrolysed in this cell-free system no DPA was generated. The possible involvement of mixed function oxidase activity and soluble oxidases is discussed in relation to ABA metabolism. While cell-free preparations from Persea americana cv. Fuerte mesocarp and immature seeds of Pisum sativum and Phaseolus vulgaris were unable to synthesize ABA from MVA, these tissue homogenates converted ABA into more polar acidic products. PA and DPA were identified as products of ABA catabolism in extracts from immature seeds of Phaseolus vulgaris and the l',4'-cis diol of ABA in extracts from Pisum sativum immature seeds
- Full Text:
- Date Issued: 1989
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
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