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Typescript. / Bibliography: leaves [150]-173. / xiii, 173 l illus., table

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Bibliography: leaves 129-151. / xiv, 151 [65] leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1999

Hop cell wall material (CWM) extracted from hop leaves (hamulus lupulus) was purified and characterized. The total sugar content, uronic acid content and monosaccharide composition of the CWM were determined. Galacturonic acid is the major component in the CWM. A mixture of unsaturated oligogalacturonides were released from purified hop CWM by autoclaving. The biological activity of these oligomers was tested for their ability to elicit phytoalexins. The oligomer with hexagalacturonic acid possessed the greatest biological activity. Column chromatography and high-pH anion exchange chromatography were used for the sample separation and purification. Fast-atom-bombardment mass spectrometry (FAB-MS) was used for the structure elucidation. The FAB-MS spectrum showed that the unsaturated galacturonosyl residue was located at the nonreducing terminus of the oligomer. / Graduation date: 1993

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 102-112). Available also in a digital version from Dissertation Abstracts.

Young developing fruits of nasturtium (Tropaeolum majus L.) accumulate large deposits of non-fucosylated "storage" XG in periplasmic spaces of cotyledon cells. The only XG that is clearly fucosylated in these fruits Is the structural fraction (approx. 1% total) integrated into growing primary walk. Storage XG can be fucosylated by a nasturtium transferase in vitro, but this does not happen in vivo, even as a transitory signal required for secretion which would subsequently be cleaved to produce mature non-fucosylated storage XG in the periplasmic space. The two fucosylated subunits that are formed in vitro are identical to those found in structural XG in vivo. A block appears to develop in the secretory machinery of young cotyledon cells resulting in extended galactosylation and diversion of XG traffic to the periplasm without fucosylation. The primary walls buried beneath accretions of storage XG eventually swell and lose cohesion, probably because they continue to extend without incorporating components like fucosylated XG that are needed for maintaining wall integrity.

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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