Browsing by Author "Linder, Peter"

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    Chemical modelling of urine
    (1984) Little, John Charles; Linder, Peter
    A urine model has been developed. The model is used in the computation of chemical speciation and degree of precipitation by means of equilibrium constants and solubility products. The urine model was developed in order to investigate some of the factors associated with urolithiasis. A specific model development procedure was used. This procedure was based on iterative construction, validation, refinement and usage of the model. One refinement stage involved the potentiometric characterisation of the solution equilibria of the Mg-P0 4-NH 3-H system. Whereas the subsystems; H-P0 4 , H-NH 3 and Mg-P0 4 -H, were rigorously characterised, the overall system was only tentatively explored. The results obtained, however, indicate that the characterisation of the three subsystems is likely to be sufficient for the purposes of the urine model. The validation of the basic urine model was achieved by comparing the model's predicted precipitation with experimental observations in another project currently being pursued in this department. This validation has indicated that the kinetics of precipitation should be taken into account for some of the important urinary so 1 id. The urine mode 1 was nevertheless successfully used to investigate the effect of pH on urinary precipitation, the influence of some urinary components on calcium oxalate precipitation and the role of cadmium in urolithiasis. The results obtained were in general agreement with other observed and predicted results. Finally, a coherent procedure for investigating the problems of urolithiasis by means of such a model is proposed.
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    The embryology, seed coat, and conservation of some Kenyan species of the orchidaceae
    (2000) Ochora, John; Stock, WD; Linder, Peter; Newton, Len
    Aspects of embryology, seed morphological features and symbiotic seed germination of the Kenyan orchid species of the subfamily Epidendroideae were examined critically in order to elucidate their development and importance in conservation. The embryology of ca. 70 species was studied by clearing-squash techniques and differential-interference-contrast optics and seeds of ca. 50 species were studied by scanning electron microscopy to determine their variations.
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    A morphological-anatomical classification of growth forms in monocotyledons
    (2000) Munro, Sioban Lucille; Linder, Peter
    This thesis examines the morphology and anatomy of monocots from the standpoint of both taxic and growth form diversity and attempts to address the problems encountered in classifying and naming the structures which comprise the axial system of monocots. The morphology and anatomy of the growth habits of a variety of monocots were described using standard sectioning and light microscope procedures.
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    Phylogenetic and functional growth from diversification in the Cape grass genus Ehrharta Thunb
    (2000) Verboom, George Anthony; Linder, Peter; Stock, WD
    This thesis uses phylogenetic and comparative data to test an hypothesis of adaptive radiation in the Cape grass genus Ehrharta Thunb. sensu stricto. Morphological data and sequence data from two noncoding regions of DNA (lTS1 and trnL-F) are used to produce a phylogenetic hypothesis for the tribe Ehrharteae. Combined analysis of these data sets resolves four principal clades that approximate the genera Ehrharta s. s., Micro/aena, Tetrarrhena and Zotovia and this result thus supports a four-genus classification. Poor resolution and a reduction in branch length at the base of a clade nested within Ehrharta s. s. suggests past radiation. Parsimony-based reconstruction of ancestral habitats and growth form attributes indicates that such radiation is associated with a historical transition to seasonallydrier but more fertile habitats, and the coincident or subsequent evolution of several growth form novelties (e.g. buried and swollen culm bases and annualness). These traits are interpreted to reflect divergent strategies for surviving seasonal drought (Le. via seed or storage). Much higher transpiration rates in summer-deciduous leaves than in perennating culms of two species suggest that the evolution of summer-deciduous foliage was important in the occupation of seasonally-arid habitats. Controlled growth experiments are used to test the hypothesis that divergence in persistence traits is associated with differences in seedling biomass allocation and relative growth rate (RGR). Ehrharta s. s. shows wide variation in seedling RGR and regressions based on phylogenetically independent contrasts suggest that differences are better explained by early biomass allocation than leaf area indices. Species with a high allocation to leaves grow faster and flower sooner, so these traits are typical of seeding species.
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    Phylogenetic relationships of the African species of the genus Merxmuellera Conert (Poaceae: Danthonioideae)
    (2001) Mafa, Paseka; Linder, Peter; Barker, N P
    This study expands on existing molecular (rpoC2 and ITS) and morphological data sets to further test the hypothesis of non-monophyly of Merxmuellera sensu lato. The results reveal that despite high levels of resolution, the morphological data yield poorly supported phylogenies due to high levels of homoplasy in the dataset.
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    Physiological responses of soybean seeds (Glycine Max L. Merr.) to metal pollutants
    (1999) Malan, Heather Louise; Farrant, Jill; Linder, Peter
    Seeds, especially cereals and legumes are a vital component of the human diet and as a result of elevated levels of environmental pollution, seed-bearing crop plants are grown increasingly on contaminated soils. Although several studies have looked at seeds as potential sources of metals that may enter the food chain, very little research has been carried out to examine the effect of such toxicants on the physiology of these plant parts. This study examines the effect of two metal pollutants, namely Cd and Ni, on the development and functioning of soybean seeds. Cadmium was chosen because it is considered to be the most serious of the metal pollutants, is highly toxic to mammals and easily enters the food chain. Nickel, is relatively mobile within plants compared to other metal pollutants and also represents a potential threat to the environment. Soybean plants (cv Crawford) were grown to maturity in a circulating nutrient solution system, which in the case of treatment plants, was amended with either Cd or Ni. From the results of preliminary trials in which the effect of metal pollutant concentration on plant growth and pod production were examined, nutrient solution concentrations of 0.05 mg Cd/litre or 1 mg Ni/litre were used for routine cultivation of the plants (termed metal-treatment plants). Seeds were harvested at four (initially five) different growth stages and the effect of the metal pollutants on size and other developmental parameters investigated. Accumulation and distribution of Cd, Ni and other elements within the seeds was examined. Firstly, by using inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and secondly, at a finer resolution utilising a nuclear rnicroprobe, coupled with proton induced X-ray emission (PIXE). The anatomy and ultra-structure of metal pollutant-treatment seeds was compared with that of control seeds using light as well as transmission electron microscopy (LM and TEM). Possible structural aberrations caused by the presence of Cd or Ni were identified. In another set of experiments, seeds were germinated in solutions of different concentrations of Cd or Ni (termed metal-germinated seeds). The LCso and ECso values for germination and radicle extension respectively, were derived. The effect of metal pollutants on seedling establishment was also examined by cultivating the plants further in nutrient solution containing different concentrations of the metal pollutants. Other seedlings (termed recovery seedlings), subsequent to germination in the metal pollutant, were transferred to the standard control nutrient solution. Uptake of metal pollutant, concentration of photosynthetic pigments and photosynthetic functioning were examined in metal-germinated, recovery and control seedlings. In the final section of the study, chemical speciation in the nutrient solution used for cultivation of metal-treatment plants was modelled using the speciation software MINTEQA2. Percentage bioavailability of the metal pollutants as well as of four nutritionally important metals, Fe, Mn, Mg and Zn was examined. Furthermore, computer simulations were also carried out to model the effect of pH and increasing metal pollutant concentration, on the bioavailability of the abovementioned metals. Addition of even low concentrations of Cd or Ni to the nutrient solution resulted in reduction in root biomass and pod (and hence seed) production. This effect increased with metal pollutant concentration. Cadmium appeared to be more phytotoxic than Ni and lower concentrations of the former were required elicit an equivalent response. Visual toxicity symptoms noted, included red pigmentation in the petioles, chlorosis of the trifoliate leaves followed by the appearance of necrotic areas. In addition, Ni-toxicity symptoms included terminal deformed pods, as well as red spots in the inter-veinal areas of leaves. Both Cd and Ni accelerated plant senescence. Leaf abscission was promoted and in the case of the older growth stages, the rate of pod development was increased relative to that of control pods. Nonetheless, the presence of metal pollutants did not appear to enhance pod abscission during the developmental period examined. In metal-treatment plants, pollutant loads in roots were much higher than in shoots. Cadmium levels in the seeds harvested from these plants were extremely low (approximately 1µg/g.dm) indicating that the metal is excluded from these tissues to a great extent. Nickel was more mobile than Cd, reaching higher levels than the latter in all plant parts and a concentration of approximately 50 µg/g.dm in mature treatment seeds. Pods did not appear to exclude entry of metal pollutants into the seeds and contained similar concentrations as the seeds in the case of Cd and lower concentrations in the case of Ni. Seed concentration of both metal pollutants (when expressed as µg/g.dm) was highest in the youngest growth stages and then decreased with age. Cadmium was found to decrease mean seed size relative to control seeds, but had no effect on the number of seeds per pod. Nickel on the other hand, exerted no effect on size but did reduce the average number of seeds contained in each pod. As a result of reduced mass, the presence of Cd in the nutrient solution reduced the lipid, starch and total N content of seeds harvested from soybean plants grown in such a medium. No significant effect on the quantity of storage reserves could be detected in Ni-treatment seeds. Mature seeds harvested from Cd-treatment plants had lower Fe and Mn, but higher Zn and Mg contents than control seeds. Nickel-treatment seeds also exhibited reduced Fe, Mn and elevated Zn contents, but Mg levels were also reduced. Shifts in seed concentrations of the nutritionally important metals noted above, were also found in pods, most notably a reduction in Fe content. Despite the presence of metal pollutants within the seeds, the extent of germination in metal pollutant-treatment seeds was not impaired compared to control seeds. The rate of germination, however, was depressed slightly in both metal treatments. Examination of metal distribution within seeds using ICP-AES revealed that Cd was localised mainly in the testa and cotyledons, with very little in the axis. Nickel was mainly concentrated in the axis and least in the cotyledons. Cadmium levels in metal-treatment seeds were too low for distribution maps to be made using PIXE and only point analyses were carried out. Overall, these results agreed with those obtained from ICP analysis. Nickel, which accumulated to higher levels within seeds, was mapped successfully using PIXE. The embryo axis appeared to contain the highest concentrations of Ni, particularly in the apical meristem and cortex, but was virtually absent from the root cap area and the central stele. Interesting elemental maps were also obtained for S, Fe and Mn (supplied in the nutrient solution at normal physiological concentrations). Levels of Ni in control seeds were extremely low and could not be mapped. The LC50 and EC50 values for germination and radicle elongation respectively, in the presence of exogenous metal pollutant, were found to be lower for Cd than Ni. This is consistent with the higher phytotoxicity of the former element. Radicle elongation was found to be more sensitive to the presence of exogenous metal pollutants than seed germination. The major effect on seedling establishment was reduction in growth, particularly of the lateral roots. As in the case of mature plants, pollutant loads in the roots of seedlings were higher than in shoots. Recovery seedlings appeared relatively healthy after a period of exposure to metal pollutants, up to a critical concentration of metal pollutant. Nonetheless, although little reduction in the concentration of photosynthetic pigments or the efficiency of photosynthetic functioning was recorded, two weeks after exposure to the metal pollutants, root biomass was still reduced relative to that of control seedlings. The total chlorophyll content of metal pollutant-germinated seedlings decreased at low concentrations of the metal pollutants, but then increased at higher concentrations. It is suggested that this is the result of the combined effects of inhibition of photosynthetic pigment synthesis, coupled to reduced leaf expansion. Metal pollutant-treatment and control seeds did not differ from each other in external appearance nor at the LM level. Slight ultra-structural variations were noted using TEM however, including the presence of vesicles in the nucleoplasm of Cd-treatment cotyledon cells, an increase in the number of crystalloid inclusions in protein bodies (possibly phytate) as well as an increased number of starch grains in the radicle tip cells of Ni-treatment seeds. Further research is needed to confirm these results. Significant ultra-structural changes in metal pollutant-germinated seedlings were noted compared to the controls. From examination of the ultra-structure of such seedlings, both Cd and Ni appeared to affect nuclear functioning, proteolysis, as well as starch grain formation. Cadmium elicited a response at lower concentrations than Ni. It is stressed that these are not necessarily the principal toxic actions of the metals however, as marked structural changes were apparent only at high concentrations. Aberrations to cytoplasm adjacent to the cell wall were also noted in cells from seedlings germinated in the presence of Ni. Computer speciation simulations using MINTEQA2 predicted that in the respective treatment solutions, 87% of Cd, but only 49% of Ni, was in a form suitable for plant uptake. Shifts in seed contents of Mg, Mn and Zn, in response to amendment of the nutrient solution with metal pollutants, could not be explained by changes in chemical speciation in the growth medium. The decrease in Fe content in Ni-treatment seeds on the other hand, may possibly be a consequence of decreased bioavailability of this ion in the nutrient solution. pH was found to exert an effect on the speciation profile of metal pollutants, as well as on that of nutrients. The most marked effect was noted on Nt2. The proportion of metal in this form (the bioavailable form) decreased from 49% to 3% when pH was increased from 6.0 to 7.0. Although plants are able to limit entry of metal pollutants into seeds to some extent, they do still enter these tissues and it is important that the effects on functioning of such plant parts be examined. This study reports preliminary findings on this aspect. Much work remains to be done however particularly with regard to the effect of metal pollutants on the quality of storage reserves, especially proteins. Furthermore, this work should be extended to the seeds of other important crop plants.
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    Species limits in Cannomois virgata complex (Restionaceae)
    (2000) Mujaju, Claid; Linder, Peter
    The variation in the nut morphology, floral and inflorescence morphology, culm morphology and culm anatomy of the Cannomois virgata complex are described. It is shown that this variation is best expressed by recognising three main clusters: the NW-Swartberg, aledonLangeberg and Coastal. The existence of these clusters was largely influenced by the size of the nuts, bracts, perianths and hollow cavity to culm diameter ratio. These traits were congruent with the overall morphometric variation, shown by the results of the phonetic analysis. The clusters correspond to three species proposed under the operational definition, which recognises species from differentiated clusters in phenetic space whose distinctness was assumed to be the manifestation of underlying fixed and qualitative differences following speciation. These units were considered appropriate as terminals for phylogenetic reconstruction. Empirical comparison of six prevailing species concepts was made by taking advantage of a common operational exigency i.e., the use of phenotypically irreducible clusters of individuals as first order estimates of species. Also, diagnostic characters were found in each of the clusters indicating the existence ofa species complex, rather than a single taxon. I therefore propose that the name Cannomois virgata (Rottb.) Steud. be restricted to the individuals of the Coastal group from which the type was collected. A new species, Cannomois grandis Mujaju, is proposed for the plants belonging to the Caledon-Langeberg group, owing to the giant form exhibited by these plants which are 2 to 3.5 metres tall. The name, Cannomois saundersii Mujaju, was proposed for the NW -Swartberg, in recognition of Mr. Saunders, a seed collector. The distribution of the species were related to the cladogram, suggesting that speciation may have been sympatric for all taxa or somewhat allopatric as shown by the NW -Swartberg taxon which has an overall northern inland distribution within the Cape Floral Region in comparison with the other two.
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    Systematic studies in the tribe Ericeae (Ericaceae-Ericoideae)
    (1999) Oliver, E G H; Linder, Peter
    [P. ii (abstract) missing]Ericaceae, to which the heaths and heathers belong, is a large widespread family comprising some 125 genera with 3000-4000 species (Sleumer 1966, Luteyn 1980). It has been divided up into several subfamilies and tribes and has included several other families, depending on the classification system being followed. The early treatments of genera were based on Linnaeus' Sexual System (Linnaeus 1753, 1754) in which 'Classes', sometimes unnatural groupings, occurred arid no families were defined, although many ericaceous genera were grouped together. The family Ericaceae was first proposed by Jussieu in 1789.
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    Systematics of the genus Cliffortia L. [Rosaceae]
    (2002) Whitehouse, Christopher Maxwell; Linder, Peter
    The Cape Floristic Region is the most diverse of the Mediterranean climate floras. Cliffortia (Rosaceae) is one of the ten largest genera within the Cape Flora with 117 species currently recognised, 104 of which are endemic to the region. I investigate the processes that have driven the diversification of Cliffortia within the Cape Floristic Region by means of comparative analyses based on a phylogenetic hypothesis.