Oxalis reclinata Jacq., is a dicotyledonous plant. O. reclinata belongs to the family Oxalidaceae. This plant produced callus which accumulated red coloured anthocyanin pigments when cultured in vitro. The levels of anthocyanin accumulated by O. reclinata callus were higher than in the intact plant. The major pigment was isolated and identified as cyanjdin-3-glucoside (CROUCH, VAN STADEN, VAN STADEN, DREWES & MEYER, 1993). In nature, anthocyanins are responsible for orange, red, purple and blue colouration of certain tissues of higher plant s. Due to the toxicity of many synthetic red colouring agents, anthocyanins are regarded as potential substitutes for synthetic food colourants. This research was aimed at investigating mechanisms which induce pigment production as well as to optimize anthocyanin yield from callus cultures of O. reclinata, once anthocyanin production was stimulated. Pigmented and non-pigmented callus lines were generated from O. reclinata (CROUCH & VAN STADEN, 1994) and maintained on MURASHIGE & SKOOG (1962) agar medium (O.8% [w/v], pH 5.7) supplemented with 0.5 mgℓ ¯¹ BA, 5 mgℓ ¯¹ NAA, 30 gℓ ¯¹ sucrose and 0.1 gℓ ¯¹ myo-inositol. Plant tissue culture studies were conducted on red and white lines of O. reclinata to optimize callus yield and anthocyanin production in vitro. This involved manipulating contributory factors of the culture environment (carbohydrates, nitrates, phosphates, phytohormones, light and temperature). In vitro studies showed that, light played an inductive role in anthocyanin production in callus cultures of O. reclinata. The auxin, 2,4- dichlorophenoxyacetic acid (2,4-D) reduced pigment production but increased callus biomass. This hormone probably exerted its effect by reducing the pool of anthocyanin precursors, such as phenylalanine, resulting in increased primary metabolic activity. Suspension cultures were shown to be a viable means of propagating pigmented callus cells of O. reclinata. The growth curves for red and white callus cells were determined using the settled cell volume (SCV) method. Pigmented cell cultures grew for longer periods compared to nonpigmented cells of O. reclinata. White callus cells reached the stationary phase after 18 days. Red callus cells continued growing exponentially for an extra three days compared to white callus cells. The vacuole was identified as the organelle where anthocyanins accumulate using the light microscope. The molecular techniques of two-dimensional electrophoresis and in vitro translation were utilized to analyze differences in gene expression between white and red callus cultures of O. reclinata. Thus far, two-dimensional electrophoresis has shown that the red callus of O. reclinata had more polypeptides compared to the white callus. The level of gene expression was higher in the red callus compared to white callus, as revealed by nonradioactive in vitro translation. With optimization of radioactive in vitro translation, identification of specific structural anthocyanin genes which are under regulatory control should be possible. Future research should aim at acquiring a better understanding about the genetic control of anthocyanin biosynthesis in order to manipulate this pathway effectively. / Thesis (M.Sc.)-Univesity of Natal, Pietermaritzburg, 1996.

No abstract available. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

This study was conducted to determine if, and how, over storey proteoid shrubs affect the species richness of a southern Cape mountain fynbos community. Protea eximia, P. lorifolia and P. repens were the dominant overstorey shrubs in the community studied. The percentage canopy cover and density of overstorey protea shrubs before a fire were regressed against the a-diversity of understorey species after a fire, for spatial scales ranging from 1 - 100m². High canopy cover percentages (≥ 50%) and high densities (≥ 30 plants per 100m²) of overstorey proteas before a fire enriched the a-diversity levels of understorey species after a fire. The spatial scale at which α-diversity was measured affected results. The number of understorey species at a site, where overstorey proteas were absent for several fire-cycles, was compared with those where overstorey proteas persisted. The number of understorey species was least where the overstorey proteas were lacking for several fire-cycles, but results also depended on the spatial scale at which α-diversity was measured. The basal cover percentage and density of sprouting understorey species of two sites, burned at several short (6 year) fire-cycles and where overstorey proteas were lacking, were compared with those of an adjacent site which was not burned for 28 years and where the overstorey proteas persisted. Where several short fire-cycles eliminated the overstorey proteas, the basal cover percentage of understorey sprouters was approximately 32% higher than where the overstorey shrubs persisted. The number of understorey species in dense clumps of understorey sprouters was contrasted against those on 0.25m² quadrats located in the open and under burned skeletons of overstorey protease In dense clumps of sprouters the mean number of understorey species was less than half of that for quadrats located in the open, or for quadrats located under the burned protea skeletons. Species specific competitive interactions amongst overstorey protea and understorey sprouter species were examined for several pyric successional stages. Competitive interactions between overstorey proteas and understorey sprouters were evident in all pyric successional stages. Results indicate that the overstorey proteoid shrubs are important to restrain the competitive ability of understorey sprouters, to prevent homogeneity in post-fire regeneration niches and to amplify within-community patchiness of understorey species, which ultimately enhances the species richness of fynbos communities. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

The use of genetic markers that are linked to specific traits in sugarcane has the potential to increase the efficiency of the selection of improved varieties. Conventionally, markers are identified by analysing the segregation of potential markers and traits in the progeny of single crosses. However, this approach is not practical for sugarcane breeding programmes where replicated, well characterized progenies do not exist. The objective of this project was to investigate the potential of using commercial varieties for identifying markers associated with some of the important traits in sugarcane. This approach would be far more effective than dealing with single progenies since the traits of commercial varieties have already been characterized. The DNA of fifty commercial varieties of sugarcane was amplified by RAPD PCR using forty-one arbitrary decamer primers. Analysis of the resulting banding profiles, obtained by agarose gel electrophoresis, yielded fifty-four reliable polymorphic fragments. Two approaches were used to identify putative markers linked to the traits of resistance to eldana, sugarcane mosaic virus, and smut: (1) a correlation approach which attempted to identify whether the presence of any polymorphisms could be used to imply the existence of a particular phenotypic state, and (2) multiple regression analysis, in order to determine whether polymorphisms could be used to predict the performance of the varieties for each of the traits. Both approaches appeared to identify associations between polymorphisms and the traits, although multiple regression analysis yielded the most informative results and was able to assign statistical values to the associations. Using multiple regression, the best predictive model was obtained for sugarcane mosaic virus resistance. This model consisted of four polymorphisms and had an r² of 0.40l. By dividing the resistance ratings into three groups (resistant, intermediate and susceptible), 52% of the varieties were correctly classified and only 2% of the varieties were predicted in opposite groups (i .e. predicted susceptible when actually resistant, and vice versa). The predictive model for eldana resistance consisted offour polymorphisms and had an r² of 0.347. This model classified 30% of the varieties in the correct group of three while none of the varieties were predicted in opposite groups. The predictive model for smut resistance consisted of three polymorphisms and had an r² of 0.316. This model classified 30% of the varieties in the correct group of three while 2% of the varieties were predicted in opposite groups. Further analysis of sugarcane varieties using additional polyrnorphisrns has the potential to identify markers linked to important traits. These markers could be used for marker-assisted selection to increase the efficiency of selecting for improved sugarcane genotypes for commercial release. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.

Being the third most cultivated crop in South Africa, potatoes are of great economic importance. As potatoes originated from cooler areas in the world, they do not easily adapt to South African conditions. The main objective of potato breeding is, therefore, to extend the crop's limited genetic base. Progress in crop improvement is slow due to dominance, segregation and other factors caused by the tetraploid character of cultivated potatoes. A new breeding program for rapid progress has been initiated at the Vegetable and Ornamental Plant Institute, Roodeplaat, South Africa, which comprises the combination of conventional and unconventional breeding techniques. The program is based on the reduction of the ploidy level from the tetraploid to the dihaploid level to facilitate crossings with diploid wild species. Anther culture is the preferred technique for the rapid reduction of the ploidy level and has been successfully applied on different members of the Solanaceae. Cultivated potato, Solanum tuberosum is, however, an important exception. In this study various potato genotypes (tetraploid cultivars, dihaploid breeding lines and a diploid wild species) were used in experiments concerning microtechniques, alternative culture methods and medium manipulation. The main objectives were to evaluate and compare the androgenetic ability of the various genotypes used and to try and identify the factors limiting their in vitro response. Regarding microtechnique, the study focussed on the investigation of the frequency of androgenesis - as a function of plant age - and the determination of defined flower bud lenqths representative of the correct microspore developmental stage for optimal androgenetic response. Combined with an extensive histological study on the microspore development within anthers, from the time of flower selection, after a cold-pretreatment and at various time-intervals during the culture period of 42 days, the following conclusions were reached: In vitro androgenetic response proved optimal when flowers of responsive genotypes were selected during the first seven to 21 days of the flowering period. Both microspore derived embryoid- and callus development were visible within responsive anthers after a culture period of only seven days. The flower bud length required for anthers to be in the optimal stage of microspore development, e.g. the uninucleate stage, varied between the different genotypes but could readily be determined with the DAPI (4,6-diamidino-2- phenylindole) technique. It was also concluded that anthers of the tetraploid cultivar Atzimba should be selected later, between the late-uninucleate and the early-binucleate developmental stages. This suggested a limited selection period for Atzimba anthers, as starch depositioning - which prevent embryogenesis - occurs within anthers during the binucleate stage. Histologically, Atzimba showed limited embryoid development with no embryoid release, while the diploid wild species, S. canasense, proved androgenetically unresponsive. Alternative culture methods were applied to study the effect of different culture phases (liquid, double layered and agar solidified) and anther orientations (lateral, dorsal and ventral) on the androgenetic response of the potato genotypes used. Liquid cultures, based on the so-called shed-pollen technique, enhanced the androgenetic response of the tetraploid cultivar Atzimba. Optimal embryogenesis was obtained for responsive breeding line 87.2002/3 with the utilization of agar solidified media, with maximal response when anthers were cultured in the lateral orientation. No response was observed from S. canasense. The effect of medium manipulation on the androgenetic response of the three genotypes was investigated. The utilization of various combinations of different concentrations of indole-3-acetic acid (1M) and benzyladenine (BA), the alteration of the initial time of incubation of anthers on the initiation media and the use of media without growth regulators compared to that containing gibberellic acid (GA[3]), were investigated. BA had to be present in the initiation media and had a major, though not exclusive, effect on embryogenesis compared to 1M. The optimal BA concentration varied between the two trials. IAA also had an increasing effect on anther response, both in the absence of BA and, especially, in addition with relatively high BA concentrations. In this experiment, only breeding line 87.2002/3 responded. The initial culture of anthers, during the first seven to 21 days of the culture period, on media containing growth regulators proved essential for microspore derived embryoid production in the tetraploid cultivar Atzimba. As these growth regulators are metabolized in the culture media, the regular transfer at shorter, two-weekly intervals to media containing metabolically active substances, proved important. GA[3] had no enhancing-effect on embryogenesis in any of the three tetraploid cultivars. The results obtained in this study suggest that the first 21 days is the critical stage in the anther culture period in terms of the optimal time for flower selection, embryoid induction and the increase in embryogenetic response due to growth regulator influence. It is important to pre-determine the developmental stage when most microspores were in the uninucleate stage of development and to correlate this stage with a specific flower bud length. This would assure maximum response of those genotypes amenable to anther culture. It also implies a more practical and economical starting pOint to anther culture experiments. Following the determination of microspore developmental stage and pollen fertility, flowers should be selected from the donor plants only during the first three weeks of the flowering period. The composition of the nutrient media used for potato anther cultures were sufficient with respect to growth regulators. The growth regulators SA, IAA and the amines glutamine and asparagine had to be present in the initiation media, especially during the first three weeks of the culture period. As microspore development within anyone anther was found to be asynchronous, the regular transfer of anthers to fresh media is recommended to assure proper development of all microspores. The use of a slightly higher IAA concentration could be considered, but care should be taken as too-high concentrations would induce callus production. Microspore derived embryoid production is preferred, as the ploidy level of callus derived plantlets normally varies and somaclonal variation can occur. Liquid media should be considered for anther culture of tetraploid genotypes, while embryoid production can be increased by culturing the anthers of responsive genotypes on agar solidified media on the lateral orientation. Finally, the diploid wild species S. canasense seemed androgenetically unresponsive, or the media and culture conditions used did not satisfy the specific requirements of this genotype. Androgenetic amenability should first be transferred by means of interspecific crossings with a responsive dihaploid genotype, such as the breeding line 87.2002/3. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

Potato leafroll virus (PLRV) is one of the most destructive potato viruses in South Africa. In order to establish resistance against PLRV in commercial potato cultivars, the coat protein (CP) gene of the virus was previously isolated, cloned and subcloned into the plant expression vector pBI121 in both the sense and antisense orientations (BURGER, unpublished results). The pBI121 constructs containing the PLRV-CP gene were subsequently transferred to Agrobacterium tumefaciens LBA 4404 in a triparental mating process with the helper plasmid pRK2013. Two A. tumefaciens- mediated transformation methods for potatoes were investigated, viz. vacuum infiltration and leaf disk transformation. In addition, optimal transformation and regeneration conditions were identified for potato cultivars Late Harvest and BP[1] In total, 27 transgenic potato lines containing the PLRV-CP, β-glucoronidase (GUS) and nptII (neomycin phosphotransferase II) trans genes were generated under kanamycin selection. Transgenic plants grown in the glasshouse appeared to be phenotypically normal, and no differences in ploidy level in comparison to non-transformed plants could be established. Stable transgene insertion into the genome of the transgenic plants was verified using PCR and Southern blot analysis. Expression of the GUS transgene was investigated using a fluorometric assay (JEFFERSON et al. 1987), and it was found that orientation of the inserted PLRV-CP gene upstream from the GUS gene had a direct influence on the levels of GUS expression. The expression of the PLRV-CP gene was analysed using DAS-ELISA and immunoblot detection. Coat protein could not be detected in either assay. RNA dot blots were used successfully to show PLRV-CP expression in transgenic potato plants at the mRNA level. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1995.

In Richards Bay Harbour, the mangrove Avicennia marina exhibits a distinct natural productivity gradient. The fringe site, which is regularly inundated twice daily by tides, supports luxuriant adult A. marina trees that are 6-10 m tall and which form a dense, well-developed canopy. The landward site which is only inundated during high spring tides, supports diminutive or dwarf A. marina that are less than 1.5 m in height. In this study we compared leaves from fringe and dwarf sites with respect to morphology, ultrastructure and ecophysiology. Alterations in leaf morphology, ultrastructure and physiology of A. marina were compared at the fringe site (35 ‰) and dwarf site (60 ‰) using morphometric measurements, light (LM), transmission (TEM) and scanning microscopy (SEM). SEM and light microscopy revealed that multicellular salt glands were located on the thick, cutinised adaxial surface from leaves of both sites. The glands appeared to be scattered and protruding from individual crypts in fringe mangrove leaves whilst they appeared sunken and occluded by cuticular material in dwarf mangrove leaves. The salt glands on the abaxial surface were not sunken but obscured by the indumentum of peltate trichomes. Ultrastructural changes observed in dwarf mangrove leaves were associated with cuticle, cell walls, chloroplasts, mitochondria of mesophyll tissue and salt glands. Fringe mangrove leaves had chloroplasts with typical well-developed grana and stroma. Ultrastructural changes of chloroplasts were evident in dwarf mangrove leaves and included swelling and separation of thylakoids, disintegration of granal stacking and integranal lamellae, as well as loss of the integrity of the chloroplast envelope. Multivesicular structures were commonly found in vacuoles and associated with chloroplasts and mitochondria in both leaf types. In fringe mangrove leaves, mitochondria appeared spherical to tubular with a relatively smooth outer membrane and a highly convoluted inner membrane. Swelling and vacuolation of mitochondrial membranes, cristae and mitochondrial clustering in the cytoplasm around the chloroplasts were evident in dwarf mangrove leaves. Extensive lipid accumulation in the form of large, dense plastoglobuli occurred in the chloroplasts of dwarf mangrove leaves. There were characteristic differences in salt gland morphology of fringe and dwarf mangrove leaves, namely in the cell walls, vacuoles, and vesicle formation. In salt glands of dwarf mangrove leaves, a distinct withdrawal of the cytoplasm from the cell wall was observed. This feature was not observed in salt glands of fringe mangrove leaves. Numerous large vacuoles were observed in the secretory cells of glands of dwarf mangrove leaves compared to those of fringe plants. Multivesicular structures, vesicles and mitochondria were common features in both leaf types. Physiological studies involved a comparison of osmotic and ionic relations as well as whole plant responses in fringe and dwarf mangrove leaves. Relative leaf water content decreased by 7.8 % and specific leaf area by 17 % in dwarf compared to those of fringe mangroves. Dwarf mangrove leaves were 27.6 % thicker and leaf cuticle thickness 37.4 % higher than those from fringe mangroves. Fringe mangrove leaves displayed higher total chlorophyll contents by 27 %, with chlorophylls a and b being 22 % and 39.6 % higher, respectively than those of dwarf mangroves. Salt gland frequencies were higher in the apex, mid-lamina and base of fringe than dwarf mangrove leaves by 36 %, 45 % and 51 %, respectively. The concentration of glycinebetaine, a compatible, N-containing osmolyte was significantly higher by 40 % in dwarf than in fringe mangrove leaves. Concentrations of proline were 27 % lower in dwarf than in fringe mangrove leaves. The predominant inorganic ion detected in mature leaves was Na+, which was 19 % higher in dwarf than fringe mangrove leaves. Phosphorus was an element that appeared deficient in dwarf mangrove leaves, being 50 % lower compared to fringe mangrove leaves. The results of this investigation indicated that there were cytomorphological alterations as well as differences in physiological responses in leaves of A. marina at fringe and dwarf sites. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2007.

The two species investigated in this study were Theobroma cacao and Barringtonia racemosa. Theobroma cacao has worldwide economic importance, as cocoa (the main ingredient in chocolate) is produced from the seeds of this tree; while B. racemosa has several applications in herbal medicine. The seeds of both T. cacao and B. racemosa are highly recalcitrant and therefore not amenable to storage for any significant periods. The long-term conservation of the germplasm of these species may only be feasible via cryopreservation. The aims of the present study were to: 1) optimize in vitro regeneration protocols for different types of explants that have the potential to be cryopreserved while maintaining the genetic integrity of these two species; and 2) develop cryopreservation protocols for selected explants. For T. cacao, protocols were established for bud-break and multiplication for both in vitro - and greenhouse-derived nodal explants, as well as a rooting medium for shoots derived from axillary buds. Parameters investigated towards the cryopreservation of axillary shoots, from greenhouse nodal segments, and nodal segments from in vitro plantlets, included the size of the explant and pre-treatments for cryopreservation. Nodal segments (6 - 7 mm) and axillary shoots (2 - 4 mm) needed to be soaked in 0.5% (w/v) ascorbic acid for 10 min to minimise phenolic production and subsequent tissue death, and surface-sterilized by soaking in 1% Ca(OCl)2 solution for 5 min to reduce microbial contamination. Subsequent cryopreservation attempts involved only in vitro nodal segments because of the lack of success in achieving elongation of excised axillary buds. Vitrification and slow freezing methods, with or without the application of cryoprotectants, did not achieve successful cryopreservation. Attempts to establish a protocol for producing somatic embryos, as an alternate to axillary shoots and in vitro nodal segments, resulted in the production of globular embryogenic callus for both leaf and cotyledon explants. Cryopreservation of these explants was not investigated in the scope of this study. The study on B. racemosa focused on the development of a somatic embryogenesis protocol. Segments of embryonic axes produced globular-stage embryos when placed on MS medium supplemented with 30 g 1-1 sucrose, 1.0 g 1-1 casein hydrolysate, 2.0 mg 1-1 2,4-D, 0.1 mg 1-1 BAP and 8.0 g 1-1 agar. Various strategies were employed to obtain embryo germination, which included 1) different time intervals on callus initiation medium; 2) the use of different auxins (IAA, NAA and 2,4-D) in combination with the cytokinins BAP and kinetin; 3) desiccation and 4) cold treatments. Although somatic embryo germination was not achieved, globular embryos proceeded with development to the cotyledonary stage when cold-treated for 8 h at 4°C. This study provides some fundamental bases for further investigation towards achieving long-term conservation for both T. cacao and B. racemosa. However, the use of meristems as explants for cryopreservation is suggested to be the way forward for the cryopreservation of both species. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2008.

For the expression of transgenes in plant cells, appropriate promoter sequences have to be introduced upstream of the gene to ensure efficient transcription. Tissue- or signal-responsive promoters are in high demand in practical plant biotechnology. The present study sought to characterise the activities of two promoters in sugarcane, namely the UBI (ubiquitin) promoter and the SUC-1 promoter (UBI linked in tandem to the cauliflower mosaic virus 35S promoter). It was hypothesised that the activity of UBI would be maintained or even increased under conditions of environmental stress, since it is well documented that ubiquitin is a stress-related protein. A further hypothesis was that SUC-1 might enhance overall gene expression since the CaMV 35S component is a constitutive promoter widely and successfully used in plant transformation. Plants of the sugarcane variety NC0310, containing the cry1A(c) (Bt) gene from Bacillus thuringiensis, were used as models in a system in which the plants were stressed by withholding water supply in a controlled manner. Since large numbers of clones of both transgenic and wild-type plants were needed for the water stress and expression experiments, three micropropagation techniques, namely, shoot tip-, callus- and node culture, were optimised and compared. The objective was to propagate genetically stable plants rapidly. Compared to shoot tip culture, node and callus culture proved slow and inefficient. Shoot tip culture was thus chosen as the most suitable for the regeneration of experimental material. Relative Water Content (RWC) determination, leaf elongation measurements and Infra Red Gas Analysis (IRGA) were compared in order to find the most appropriate method of measuring plant water status. In addition to being destructive, no observable differences were evident between the control (non-stressed) and water-stressed plants when using RWC as a measure. Results obtained from leaf elongation measurements compared favourably to the more sophisticated IRGA readings, showing that leaf elongation is as sensitive a measure of water stress. On the basis of preliminary studies with untransformed plants using the latter two techniques, water regimes for stress-induction in the final experiments were designed. Leaf elongation measurements, which are simple and non-destructive, were ultimately chosen to measure plant water status. In the final water stress experiment non-transgenic NCo310 and clonal populations of six transformants were used (three containing the UBI promoter; three the SUC-1 promoter). Exactly half of the plants of each type were stressed by withholding water supply, while the other half (controls) were watered manually twice a day. Leaf elongation measurements were made at the same time daily on the third youngest leaf of 6 plants from each population per treatment. At the same time, leaf samples were taken daily for molecular analysis. The stress regime led to marked differences in leaf elongation between control and water-stressed plants. In terms of physiological response (leaf rolling and senescing), plants containing the SUC-1 promoter appeared least affected. The reverse transcription-polymerase chain reaction (RT-PCR) and Northern hybridisation were used to assay UBI and SUC-1 activity. RT-PCR revealed that both promoters drove Bt gene expression in controls and experimentals throughout the stress period, although differences in signal intensity were not observed. The extent of expression occurring in each type of plant was revealed in Northern blots probed with two genic sequences (1) the transgene and (2) sugarcane EST ME42, homologous to heat shock protein 82 in rice. Individual transformants showed overall levels of transgene expression that were variable, possibly due to insert position in the plant genome, as well as variations in relation to the application of stress. SUC-1 seemed superior to UBI in terms of driving transgene expression under stressful environmental conditions, since UBI promoter activity appeared to decrease under stress, while SUC-1 promoter activity remained constant. In addition to the expected 2.0 kb Bt transcript, transcripts of smaller than expected size were also obtained, leading to the suggestion of premature polyadenylation signals in the coding region of the wild-type Bt234 gene. Upon inspection of the transgene sequence, a number of motifs rarely present in plant genes were observed, namely A/T rich sequences, ATTTA motifs and numerous potential polyadenylation sites. / Thesis (M.Sc.)-University of Natal, Durban, 1999.

Rising atmospheric CO2 (Ca) concentrations have generated concern among scientists, mainly because of CO2’s role as a greenhouse gas and its influence on plant growth and development. Previous research has suggested that future CO2 enriched atmospheres may enhance the success of invasive aliens. Chromolaena odorata is an example of an invasive alien proving to be a serious threat to indigenous vegetation in South Africa, and effective control measures are desperately needed to curb infestations in the future. The current study aimed at assessing the response of C. odorata to elevated Ca and interactive factors, and was divided into two trials. During PART A, C. odorata was grown in competition with 2 grass species: Eragrostis curvula and Themeda triandra (selected for their differential preferences to nutrient availability). All three species were potted in a greenhouse at the University of KwaZulu-Natal (Howard College). There were 16 pots in total, and each pot contained four C. odorata plants, four T. triandra seedlings, and four E. curvula seedlings. Eight pots were exposed to elevated Ca (~700ppm), and eight pots were exposed to ambient Ca (~370ppm). The pots at each Ca treatment were further divided: four received high nutrient treatments (3L per addition), while the other four received low nutrient treatments (300 ml per addition). Studies on growth (e.g. plant height, dry weight, etc.), as well as physiology (e.g. Jmax), were undertaken. Results showed that generally, plants responded positively to high nutrient treatments. In contrast, elevated Ca did not affect growth or any of photosynthetic parameters of C. odorata significantly, but did reduce stomatal limitations. During PART B, C. odorata plants were grown monospecifically to assess whether there was a “chamber effect” associated with planting density. Pots at both Ca treatments contained either four C. odorata or two C. odorata seedlings. Growth and physiology were assessed. The fact that elevated Ca did not affect any of the photosynthetic parameters studied, suggests that photosynthetic down-regulation did not occur. This, together with the fact that no increase in stomatal limitations were observed in elevated Ca, implies that enhancement of photosynthetic assimilation could have occurred in C. odorata plants exposed to CO2 enrichment. Results from this study (PART A and PART B), when compared to previous research on this species, suggests that CO2 enrichment may enhance the success of monoculture populations of C. odorata. However, other species may gain competitive advantages over C. odorata occurring in mixed communites, under CO2 enriched environments. In addition, results of this study support the prediction that increasing Ca will reduce the importance of carbon as an external limiting resource, and that the extent of a plant’s response to Ca enrichment will depend on resources other than CO2. If increases in temperature caused by elevated Ca increases nutrient availability in the soil, then Ca could indirectly enhance the success of C. odorata occurring in mixed communities. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2008.