Towards reconciliation of structure with function in plasmodesmata—who is the gatekeeper?
- Authors: Botha, Christiaan E J , Cross, Robin H M
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6497 , http://hdl.handle.net/10962/d1004493
- Description: Whilst the structure of higher plant plasmodesmata was first described by Robards (1963. Desmotubule—a plasmodesmatal substructure. Nature 218, 784), and despite many subsequent intensive investigations, there is still much that remains unclear relating to their ultrastructure and functioning in higher plants. We have examined chemically fixed plant material, and suggest that the conformational changes seen in plasmodesmatal substructure, particularly the deposition of electron-dense extra-plasmodesmal material, is linked to either manipulation of the hormonal balance (as in Avocado fruit), or of osmotic potential in leaf blade material. These changes result in the deposition of β 1,3-glucan (callose) at the neck region of these plasmodesmata. This electron-dense material is deposited at the neck region of plasmodesmata, and forms a collar-like structure. The formation of a collar is shown to be coupled with loss of lucence within the cytoplasmic sleeve. The formation of a collar at the plasmodesmatal orifice thus results in encapsulation and closure of the plasmodesmatal orifice. Closure of the orifice coincides with a loss of electron-lucence and a lack of resolution of the desmotubule. These ultrastructural changes are potentially significant and could contribute to, result in, or assist in the down-regulation of cell to cell trafficking via plasmodesmata.
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- Date Issued: 2000
Phloem loading in the sucrose-export-defective (SXD-1) mutant maize is limited by callose deposition at plasmodesmata in bundle sheath-vascular parenchyma interface
- Authors: Botha, Christiaan E J , Cross, Robin H M , Van Bel, A J E , Peter, Craig I
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6503 , http://hdl.handle.net/10962/d1005926
- Description: Using Lucifer Yellow we have demonstrated that the phloem-loading pathway from the mesophyll to the bundle sheath-vascular parenchyma interface in Zea mays source leaves follows a symplasmic route in small and intermediate vascular bundles in control as well as in the green sections of mutant sucrose-export-defective (SXD-1) plants. In the anthocyanin-rich mutant leaf sections, Lucifer Yellow transport was prohibited along the same path, at the bundle sheath-vascular parenchyma interface in particular. Plasmodesmata at the latter interface in SXD-1 anthocyanin-rich leaf sections appear to be structurally altered through callose deposition at the plasmodesmal orifices. We suggest that a transport bottleneck at the bundle sheath-vascular parenchyma interface is thus orchestrated and regulated through callose formation, preventing symplasmic transport across this important loading interface.
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- Date Issued: 2000
Multiple metaphors in an understanding of academic literacy
- Authors: Boughey, Chrissie
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6088 , http://hdl.handle.net/10962/d1008587
- Description: This article describes understandings derived from work in a first year Systematic Philosophy class at a historically black South African university which challenge the assumptions on which the writer has based her practice as a teacher of English as a second language for many years. These assumptions focus on the perception of problems related to the production and reception of academic texts as solely, or even mainly, linguistic in origin. Analysis of writing and interviews with students suggests that the problems in the writing stem mainly from their unfamiliarity with academic discourses in spite of the fact that all are speakers of English as an additional language.
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- Date Issued: 2000
Palynology and palaeo-environment of Pleistocene hyaena coprolites from an open-air site at Oyster Bay, Eastern Cape coast, South Africa
- Authors: Carrion, J S , Brink, J S , Scott, Lucy E P , Binneman, J N F
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:7000 , http://hdl.handle.net/10962/d1008357
- Description: Hyaena coprolites in a soil horizon at Oyster Bay, Eastern Cape coast, South Africa, were found associated with abundant, early Last Glacial vertebrate faunal remains that were apparently accumulated by brown hyaenas and prehistoric humans. Artefacts of the Howieson's Poort sub-stage of the Middle Stone Age occur in the same soil. Although direct association between the different finds cannot be demonstrated, there is evidence to suggest that they are broadly contemporaneous. Pollen assemblages in the coprolites were dominated by Myrica and, to a lesser extent, Stoebe-Elytropappus type and Poaceae. Comparison with the modern pollen spectrum suggests that the past environment differed markedly from the current. The presence of Stoebe-Elytropappus, in particular, is considered to indicate a displacement of vegetation zones to lower altitudes. Both fossil pollen and fauna suggest a landscape with a complex mosaic of vegetation indicative of overall cooler, more inland conditions than today.
- Full Text: false
- Date Issued: 2000
Replication of maximal work output levels in able-bodied workers and candidates for disability assessments: benchmark data and guidelines
- Authors: Charteris, J , James, Jonathan P
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6752 , http://hdl.handle.net/10962/d1009332
- Description: [From the introduction]: Injured-at-work employees, when the impairments are musculo-skeletal, and the injury beyond dispute, may be faced with formal rehabilitation or informal recuperation, sometimes preceded by surgical intervention, or they may be exposed to a process of application for compensation, part of which may involve medico-legal assessments. Questions that need to be addressed somewhere in this process will determine whether the impairment is of short duration, chronic or irreparable, and will involve determination also of the severity of the impairment and the issue of the workers’ capacity to return to the former occupation versus the need to find a new employment niche commensurate with the disabled workers’ capabilities. Inevitably in this process, if it is formal, someone will need to assess the musculoskeletal strength of the injured employee and make pronouncements as to physical capacity and work-readiness. In the absence of clinical ergonomists in South Africa this task falls to a variety of professionals, some well and others poorly trained to make these determinations. Most often the assessments of work-readiness are crude, amounting to little more than unsubstantiable value judgements of supervisors or health professionals not well versed in human performance capabilities. Increasingly however, better qualified professionals are making themselves available to meet the growing demands of a more employee-centred working ethos in this country. This paper is targeted at those medical, paramedical and ergonomics professionals who already have the facilities and the expertise to make use of the technique outlined herein, to further enhance their already sound means of job-related disability assessment.
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- Date Issued: 2000
The role of ‘African Chemists’ in the health care system of the Eastern Cape province of South Africa
- Authors: Cocks, Michelle L , Dold, Anthony P
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:7105 , http://hdl.handle.net/10962/d1010675
- Description: Self-medication is documented as an integral part of health care therapy in developing countries such as Ethiopia, Cameroon, Uganda and Mexico. In South Africa the types of illnesses and health problems that are referred to both traditional healers and biomedical practices have been well documented. However, very little literature exists on self-diagnosis, self-medication or sources of the medicines used for self-medication. This bias in the literature has come about largely because anthropological studies have focused on the later stages of the illness referral system when treatment is sought from a specialist for symptoms which have not responded to forms of self-medication. As a result of this, health care studies have documented the more exceptional exotic healing rituals and culturally bound syndromes of a particular society or community, and not discussed the more ordinary practices of self-medication of everyday illness. Self-medication is however an important initial response to illness and many illnesses are successfully managed at this stage. Amayeza stores (singular-iyeza store) — or ‘African chemists’ — are an important source of medicines for self-diagnosed illnesses. The current discussion focuses on the types of medicines and treatments that are obtained from amayeza stores without professional consultation in the Eastern Cape province of South Africa.
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- Date Issued: 2000
Stuffed birds on trees: an historical review of avian systematics in southern Africa
- Authors: Craig, Adrian J F K
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6931 , http://hdl.handle.net/10962/d1011949
- Description: Avian systematics in southern Africa has been heavily dependent on a small number of museum-based specialists. They produced bird checklists which prescribed the names to be used by other scientists. After an initial phase of cataloguing the avifauna, a major preoccupation was the description of geographical variation, which was documented in an extensive subspecific nomenclature. Until recent years, few African ornithologists have been involved in systematics as a biological discipline. This historical overview considers the contribution of particular individuals from Andrew Smith to Phillip Clancey.
- Full Text: false
- Date Issued: 2000
The medicinal use of some weeds, problem and alien plants in the Grahamstown and Peddie districts of the Eastern Cape, South Africa
- Authors: Dold, Anthony P , Cocks, Michelle L
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6514 , http://hdl.handle.net/10962/d1005942
- Description: A List of 33 medicinal plants of exotic or indigenous origin, listed as problem plants or declared weeds, is presented. The cultural uses of these plants should be taken into account when weed legislation in South Africa is considered. Of these species, six have no previous medicinal uses recorded in the literature surveyed and 21 species have additional, previously unrecorded uses. Nine previously unrecorded Xhosa names for plants are documented. Plant use categories and indigenous knowledge is discussed regarding the recorded species. The use of alien plants shows that African traditional healing is not static, but dynamic and adaptive.
- Full Text: false
- Date Issued: 2000
Assessing the potential for biological invasion - the case of Ammophila arenaria in South Africa
- Authors: Hertling, Ursula M , Lubke, Roy
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6518 , http://hdl.handle.net/10962/d1005947
- Description: Many plants, especially woody species, introduced into South Africa for ornamental or commercial purposes, have become invasive in a number of habitats. Because of the risk of an invasion of coastal dunes by yet another species, the European dune grass Ammophila arenaria, used as a dune stabilizer, is assessed using lists of attributes of invasive species and invasible ecosystems. It is impossible to predict plant invasions, but both invasive species as well as invaded ecosystems are often characterized by certain attributes which facilitate invasions. Many of the species attributes connected with invasion appear to apply to A. arenaria. Above all, the grass is characterized by ecological tolerance and vigorous rhizomatous reproduction. An important site attribute connected with invasion is an evolutionary history with isolation patterns, which applies to the South African Cape coast. We conclude also on the basis of the overseas experience, that the potential for A. arenaria to become invasive needs urgent investigation in the South African context.
- Full Text: false
- Date Issued: 2000
An estimation of the standing stock and population structure of Upogebia africana (Crustacea: Thalassinidae) in the Knysna Estuary
- Authors: Hodgson, Alan N , Allanson, Brian R , Cretchley, Robyn
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6923 , http://hdl.handle.net/10962/d1011907
- Description: Within the Knysna Estuary Upogebia africana has an extensive distribution from north of Leisure Isle to the Red Bridge, occupying 62% of the available intertidal zone. Six sites were surveyed within the above distributional range. U. africana was found from the high-water level (Spartina zone) to the shallow subtidal zone (to about 1.5 m depth). The density, biomass and population structure of the mud prawns were found to be highly variable within the estuary. Only small animals (carapace length –× = 10.9 mm) were found in the upper estuary at the Red Bridge. Although large animals were present, the Invertebrate Reserve had a low density and biomass of U. africana (– × = 11.7 m–2; 3.9 g.m–2 dry weight). By contrast a relatively inaccessible centre mud bank (Oyster Bank) in the middle reaches of the estuary had much larger populations (–× = 176.5 m–2; 65.3 g.m–2 dry weight). This site is, therefore, a natural mud prawn reserve. Within the intertidal zone, mud prawn density (74–76 m–2) and biomass (26–27 g.m–2 dry weight) was usually greatest in the Spartina and lower Zostera zones. Sex ratios throughout the estuary did not deviate significantly from 1:1.
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- Date Issued: 2000
The exploitation of Upogebia africana (Crustacea: Thalassinidae) for bait in the Knysna Estuary
- Authors: Hodgson, Alan N , Allanson, Brian R , Cretchley, Robyn
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6924 , http://hdl.handle.net/10962/d1011911
- Description: The activities of people collecting Upogebia africana for bait at six popular collecting sites in the Knysna Estuary were monitored from February 1995 until April 1996. Three groups of bait harvesters were identified on the basis of their source of income: subsistence fishers who rely on bait collecting and fishing for their income; supplementary fishers who catch fish to supplement their income; leisure anglers who draw no income from fishing. Two groups of collectors were identified based on methods of collecting bait and fishing: leisure anglers who collect bait using a prawn pusher or pump and fish using a rod and tackle; non-leisure fishers who collect using tin cans and fish with hand or planted lines. The average harvest of bait per collecting trip by leisure anglers was 59 mud prawns, whereas non-leisure fishers took 101 animals, twice the legal limit. The numbers of bait collectors present per mud bank were found to be highest on public holidays ([horizontal bar over]X = 43.5) and higher during the summer holidays ([horizontal bar over]X = 16.5) than during the spring/summer ([horizontal bar over]X = 8.6) and autumn/winter ([horizontal bar over]X = 4.6) periods. Most collectors spent 11-30 minutes on the mud banks. It was estimated that 1.86 x 10[superscript 6] U. africana or about 740 kg (dry mass) was removed by bait collectors annually from the six bait-collecting sites studied. This represented about 8.5% of the mud prawn stocks at these sites and about 0.9% of the entire estuary stock. 85% of the mud prawns taken as bait was removed by 77% of the bait collectors who were the non-leisure fishers.
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- Date Issued: 2000
A Scottish bellfounder (letter)
- Authors: Lewis, Colin A
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6180 , http://hdl.handle.net/10962/d1012374 , http://www.ringingworld.co.uk
- Description: Colin Lewis was Professor of Geography at Rhodes University, Grahamstown, South Africa from 1989 until his retirement at the end of 2007. In 1990, with the strong support of the incumbent Vice-Chancellor, Dr Derek Henderson, he instigated the Certificate in Change Ringing (Church Bell Ringing) in the Rhodes University Department of Music and Musicology - the first such course to be offered in Africa. Since that date he has lectured in the basic theory, and taught the practice of change ringing. He is the Ringing Master of the Cathedral of St Michael and St George, Grahamstown, South Africa.
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- Date Issued: 2000
Evidence of Quaternary glaciation in Southern Africa : moraines on the Bastervoetpad of the eastern Cape Drakensberg, South Africa
- Authors: Lewis, Colin A , Illgner, Peter M
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6710 , http://hdl.handle.net/10962/d1006747
- Description: This volume of Quaternary International comprises the Abstracts from the XVth INQUA Congress held in Durban,South Africa, 3–11 August 1999.
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- Date Issued: 2000
A taxonomic and ecological review of Pseudocloeon glaucum (Agnew)(Ephemeroptera: Baetidae)
- Authors: Lugo-Ortiz, C R , de Moor, Ferdy C , Barber-James, Helen M
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:7007 , http://hdl.handle.net/10962/d1008385
- Description: Pseudocloeon masai (Lugo-Ortiz and McCafferty), P. nadineae (Lugo-Ortiz and McCafferty) and P. quintum (Agnew) are junior subjective synonyms of P. glaucum (Agnew). Larvae of P. glaucum manifest a wide range of variation in mouthpart morphology, particularly with respect to the development of the distomedial process of segment 2 of the labial palps, body size, general body colour and abdominal colour pattern. Such variation is observed in different cohorts and populations, and explains why several names have been applied to the same species. Larvae of P. glaucum also have considerable ecological tolerance, accounting for the abundance and widespread distribution of the species in the Afrotropical Region. New records from Kenya, Lesotho, Namibia and Zimbabwe are provided.
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- Date Issued: 2000
Effect of water temperature on the biogeography of South African estuarine fishes associated with the subtropical/warm temperate subtraction zone
- Authors: Maree, R C , Booth, Anthony J , Whitfield, Alan K
- Date: 2000
- Language: English
- Type: text , Article
- Identifier: vital:7133 , http://hdl.handle.net/10962/d1011776
- Description: Estuarine biogeographical regions along the southeastern coast of South Africa were investigated in terms of fish distribution and abundance patterns, with particular emphasis on the role of water temperature in influencing these patterns. Qualitative and quantitative analyses were conducted upon the ichthyofaunal assemblages to determine whether the location of the subtropical/warm temperate boundary corresponds to that proposed by Whitfield.(n1) Analyses included the distribution ranges of species associated with estuaries according to presence/absence data, cluster analysis of gill net catches in eight estuaries along the southeastern coast and the relative proportion of tropical to temperate marine species within these eight systems. Quantitative analysis indicated that the ichthyofaunal biogeographical regions are indeed a reflection of water temperature regimes and that the subtropical/warm temperate boundary is located between the Great Kei and Mbashe estuaries. A strong negative correlation was found between the number of temperate fish species and the mean of the minimum monthly temperatures recorded in the systems studied. Qualitative analysis revealed that a barrier appears to exist in the vicinity of the Swartkops estuary, which prevents the westward migration of tropical 'vagrants'. The influence of the Agulhas Current along the east coast and its divergence from the coastline in the Algoa Bay region, as well as upwelling phenomena on the southeast and south coasts are identified as major factors that influence marine and estuarine temperature regimes and therefore the ichythyofauna of this region.
- Full Text: false
- Date Issued: 2000
Effect of wave exposure on growth and mortality rates of the mussel Perna perna: bottom up regulation of intertidal populations
- Authors: McQuaid, Christopher D , Lindsay, Tracy L
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6955 , http://hdl.handle.net/10962/d1011994
- Description: The effect of wave exposure on the growth of low-shore populations of Perna perna (Linnaeus) was determined using 3 independent approaches at 6 sites on the south coast of South Africa: (1) Individual marking; notches were filed on the growing edges of mussels in situ. After 111 d, growth from the mark to the new growing edge was measured. (2) Internal shell-growth bands; mussels from the mark recapture experiment were used to establish that growth bands are laid down tidally. Unmarked individuals were then used to measure growth over the last 60 tides. (3) Shepherd¹s length-composition analysis (SLCA); growth rates were determined from length-frequency distributions in 11 samples collected at 6 wk intervals over 15 mo. All 3 approaches showed that growth rate was approximately twice as fast on exposed as on sheltered shores (ANCOVA, p < 0.05 in all cases). Mean length for the first year of growth (averaged for the 3 methods) was 47 and 22 mm, respectively. There were, however, considerable differences among methods. Marking provided the lowest estimates of growth rates, and SLCA the highest. The mean mortality index (Z yr-1) was significantly higher and annual survival rate lower for exposed shores, indicating faster turnover under exposed conditions. Mean longevity on exposed shores (2.6 yr) was only one-third of estimated longevity on sheltered shores (6.7 yr). These findings show that degree of exposure has important interactions with growth and mortality of mussels on the low shore, and that these effects are independent of the effects of exposure on density. The findings also indicate strong bottom up regulation of mussel populations.
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- Date Issued: 2000
Rural self-reliance strategies in South Africa : community initiatives and external support in the former black homelands
- Authors: Nel, Etienne L , Binns, Tony
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6716 , http://hdl.handle.net/10962/d1006789
- Description: This paper examines the relevance of the concept of self-reliance in the context of rural community economic development in South Africa. Whilst changing global and local circumstances oblige impoverished communities to become more pro-active in the enhancement of the quality of their lives, they nevertheless cannot ignore basic market forces and the need for an appropriate level of external assistance. Four community-based agricultural ventures in South Africa's former Homelands are examined. A comparison between the four schemes permits an assessment to be made of what such community ventures require if they are to succeed and have a meaningful impact on job creation and poverty alleviation. The role of external support agencies and access to markets in each case features prominently in the assessment.
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- Date Issued: 2000
An empirical formula for estimating the water use of Scaevola plumieri
- Authors: Peter, Craig I , Ripley, Bradford S
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6530 , http://hdl.handle.net/10962/d1005971
- Description: Transpirational water loss of Scaevola plumieri (L) Vahl. (= Scaevola thunbergii Eckl. & Zeyh.) (Goodeniaceae), a dune pioneer plant along the eastern and southern coasts of South Africa, was measured over a wide range of atmospheric conditions and related to the atmospheric vapour pressure deficit (VPD). A plot of leaf transpiration rate (E) against VPD yielded a curvilinear relationship (r[sup 2] = 0.88, P = 0.000). As both leaf and canopy E were found to be closely coupled to atmospheric conditions, this correlation was used to calculate canopy E for entire days. The bulk volumes of water transpired per day were related to the mean daily temperature as recorded at a nearby weather station and were strongly related (r2 = 0.71, P = 0.0037). This correlation allowed the bulk volume of water transpired by one square metre of a S. plumieri-covered dune to be calculated on a daily basis for an entire year. Transpirational losses (566 litres) in 1997 were then compared with rainfall (539 litres), indicating that rainfall was perhaps insufficient to support the plants that year. Similar deficits were calculated for 1996, suggesting that plants were possibly reliant on water stored in the sand or taped ground water. This species showed an unusual positive response of increasing leaf conductance to increasing VPD over the range 0-3 kPa.
- Full Text: false
- Date Issued: 2000
The development of a geomorphological classification system for the longitudinal zonation of South African rivers
- Authors: Rowntree, Kate M , Wadeson, Roy A , O'Keeffe, Jay H
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6722 , http://hdl.handle.net/10962/d1006799
- Description: The recognition of the Reserve by the new South African Water Law poses new challenges for river scientists. The ecological water requirement or environmental flow is recognised by that part of the Reserve known as the ecological Reserve. If the ecological Reserve is to be implemented, it must first be defined and quantified for all river systems subject to water related developments. Standard procedures are being developed through the Resource Directed Measures (RDM) of the Department of Water Affairs and Forestry while monitoring the health of South Africa's rivers is taking place through the National River Health Programme (NRHP). Cost effective methods of developing spatial frameworks for both the RDM and NRHP are required. Concepts of longitudinal river zonation were developed by river ecologists in the 1960s and 1970s to assist in the classification of ecologically uniform stretches of rivers. This paper reviews the different zonation concepts and presents a geomorphological classification of South African river zones that is being applied to the RDM and NRHP. The classification is tested on three rivers, the Sabie, Buffalo and Olifants.
- Full Text: false
- Date Issued: 2000
Cardiac responses under diverse combinations of marching speed and backpack load
- Authors: Scott, Patricia A , Christie, Candice J
- Date: 2000
- Language: English
- Type: Article
- Identifier: vital:6755 , http://hdl.handle.net/10962/d1009457
- Description: Thirty seasoned foot-soldiers were exposed to a total of 16 combinations of marching speed and backpack load, each soldier experiencing 8 of the combinations between 3.5km.h-1 with a 20kg load and 6.5km.h-1 with a 65kg load. Detailed physiological analyses were conducted, of which the heart rate responses are reported here. Steady state was achieved with all combinations under 5.5km.h-1 speed and 35kg load. Excessively elevated heart rates were elicited by all loads over 20kg at 6.5km.h-1 marching speed; by loads over 35kg at 5.5km.h-1 marching speed and by the 65kg load even at 4.5km.h-1 marching speed.
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- Date Issued: 2000