Thesis (Ph. D.)--University of Sydney, 2008. / Includes graphs and tables. Includes list of publications: p. iv. Title from title screen (viewed May 5, 2008). Thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Chemical and Biomolecular Engineering. Includes bibliographical references. Also available in print form.

Thesis--University of Florida. / Description based on print version record Typescript. Vita. Includes bibliographical references (leaves 88-95).

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xiii, 104 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 70-73).

Exocyst positive organelle (EXPO) is a newly discovered double membrane organelle involved in exocytosis and likely other vesicle trafficking processes. EXPO is likely generated from the ER, fused with plasma membrane and released a single membrane vesicle to cell exterior. The Arabidopsis protein Exo70E2 was found to be associated with EXPO and therefore is considered as a marker of EXPO and might play a role in EXPO-mediated vesicle trafficking. Understanding the biological function of AtExo70E2 (abbreviated as E2 in this thesis) will be very helpful in unraveling the function of EXPO. The aim of this work was to use various molecular, genetic and physiological approaches to determine the possible role of Arabidopsis Exo70E2 in biological pathways. By using the Exo70E2pro:GUS line, the expression pattern of Exo70E2 was determined. Exo70E2 was expressed mainly in roots, especially in root tips and epidermal cells in the division and elongation zones of roots. Its expression level was induced when the seedlings were treated with Flg22, a peptide derived from bacterial flagillin protein that induces the plant defense response. The tissue subcellular localization of Exo70E2 was also studied using the 35S:Exo70E2-eYFP and Exo70E2pro:Exo70E2-GFP reporter lines. The GFP fusion protein was found primarily in the epidermal cells of roots even in the 35S:Exo70E2-eYFP lines. For phenotypic analysis resulting from mutations of the Exo70E2 gene, I obtained three T-DNA insertion mutant lines and generated its overexpression lines. The two mutant alleles, e2-2 and e2-3 are in the Columbia ecotype background and further characterized. e2-2 which has a T-DNA insertion in an exon is likely a knock out line as Exo70E2 gene transcript could not be detected. e2-3, which carries a T-DNA insertion in its promoter region, was found to accumulate a higher level of the transcript, suggesting that the insertion causes its enhanced expression of Exo70E2. There was no obvious difference between wild type and e2-2 in their phenotypes under different conditions tested in this study. However, e2-3 had a retarded growth phenotype when grown in soil or on MS medium. The seedlings of e2-3 on MS medium also had a yellowish color although such a phenotype was not obvious when they were grown in soil. When supplementing the MS medium with sucrose, glucose or mannitol, the growth of e2-3 was more reduced compared to wild type under these conditions. However, on the medium with NaCl or under phosphate deficiency, the yellowish phenotype of e2-3 was rescued and the mutant seedlings became relatively healthier than the seedlings under the regular MS medium. A proteomics approach was taken to compare protein secreted from the seedlings of wild type and the mutants. Proteins secreted by seedlings to the liquid medium were collected, concentrated and subjected to MS analysis. Comparison of the profiles of secreted proteins between the wild type and the mutants leaded to identification of candidate proteins whose secretion might be affected by the mutation. My study indicates that Exo70E2 and EXPO are involved in transporting proteins (likely also metabolites) to the exterior of cells and the rhizosphere and might play an important role in stress responses.

M.Sc. / An increasing problem in subtropical regions, such as South Africa, is the susceptibility of various banana varieties to Fusarium wilt by the soil borne pathogen Fusarium oxysporum tsp. cubense (FOC). In this study the problem of fungal susceptibility of banana was addressed by investigating the biochemical aspects of cell wall strengthening in banana roots. Defence responses were induced in both adult and tissue culture tolerant Goldfinger and susceptible Williams banana cultivars by treatment of the plants with a heat-released elicitor preparation from the mycelial cell walls of FOC race 4 and the crude filtrate. Banana plants were maintained in a hydroponic system, before being inoculated with the elicitor and crude filtrate preparation. Differences in lignin content, callose deposition, phenolics and the enzymes involved in cell wall strengthening; (PAL, CAD, POD and PPO) between the tolerant and susceptible banana cultivars were investigated. Differences in defence responses after treatment with elicitor and with crude filtrate were observed, but it was shown that the former is a more efficient experimental system for the characterisation of susceptible and tolerant responses in banana cultivars. An elicitor concentration of 45 4g/m1 greatly induced cellular POD, PPO, PAL and CAD activity in Goldfinger, whereas no significant increase was observed for Williams. Lignin content increased significantly in Goldfinger compared to Williams. The quantitative determination of induced total phenolics, phenolic glycosides, phenolic esters and cell wall-bound phenolic acids were higher in Goldfinger than in Williams. These increases in the four phenolic subfractions were clearly confirmed by reverse phase HPLC. No significant increase in callose accumulation was observed for both cultivars. The obtained results indicate an important role for cell wall strengthening as an inducible defence mechanism of banana roots against FOC race 4.

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Although dynamic interactions between plant cells and their environment require adhesion between the cell wall (CW) and the plasma membrane (PM), few plant adhesion molecules have been identified. Therefore, the seed coat mucilage secretory cells (MSCs) of Arabidopsis thaliana (which undergo developmentally regulated changes in adhesion) were developed into a novel model system to study PM-CW adhesion. Twenty-seven candidate genes were identified using data from publicly available and seed-specific microarrays. Mutant plants for these genes were screened for defects in adhesion via plasmolysis, and for changes in MSC morphology that may result from defective adhesion (Chapter 1). Two fasciclin-like arabinogalactan proteins were isolated in this screen. One of these, SOS5, was characterized in detail (Chapter 2). sos5 mutants are sensitive to hyperosmotic conditions and show defects in PM-CW adhesion and MSC mucilage structure. Interestingly, these phenotypes may be attributed to defects in adhesion or to defects in cell wall deposition.