Glutathione reductase (GR) and superoxide dismutase (SOD) enzymes are thought to play an important role in the plant chloroplast antioxidant system. Tobacco plants transformed with E. coli glutathione reductase and superoxide dismutase genes were used to investigate the role of these gene products (enzymes) in the chloroplast antioxidant system. These plants were T1318 (transformants with increased levels of cytoplasmic glutathione reductase activity) and GOR1OT (transformants with increased levels of cytoplasmic' glutathione reductase activity and chloroplastic superoxide dismutase). In addition, 10~M methyl violegen (paraquat), was used to perturb the system experimentally under high light, low light and in darkness. During these experiments GRA (glutathione reductase activity) was assayed and the results expressed as mg-1protein, mg-1 chlorophyll and g-1 tissue, using different types of transgenic plants. T131 B-cytosolic GOR transformants had a higher GRA under high light intensity. Under low light intensity T131B had a small increase in GRA compared to controls (T131 Bs in 1mM CaS04). Also leaf discs in the dark showed similar GRA as did controls. The three treatments had no effect on the GRA of untransformed plants. GOR1OT (cytoplamic GOR and chloroplastic SOD transformants) had a slight increase in GRA under high light intensity and in darkness. At low light intensity GOR10T showed similar results to controls. The results indicate the overall absolute increase in GRA in transgenic plants after methyl violegen treatment. The higher activity than that of nontransgenic controls indicate that bacterial GRA must have also increased following exposure to methyl violegen. / Thesis (M.Sc.)-University of Natal, 1996.

Wheat is one of the most essential food sources in the world. However, there has been serious yield loss of wheat production due to stripe rust disease caused by the fungal pathogen Puccinia striiformis f. sp. tritici. The cost-effective and long-lasting defense to the disease can be achieved by generating genetically resistant crops against the disease forming pathogens. To accomplish this, first step is to acquire knowledge in the plant pathogen interactions of the crop and the pathogen of interests at the cellular and the molecular level. In this thesis research, PstHa2a5 candidate effector gene from Puccinia striiformis f. sp. tritici is investigated to identify its role and interaction between host factors in yellow rust infected Triticum aestivum L. The gene construct was engineered with FLAG-tag fusion at its N-terminus, and synthesized. This construct was cloned into pJL48-TRBO vector for an expression in Nicotiana benthamiana via agrobacterium-mediated gene transformation. The expressed protein structure with FLAG-tag was purified, and immunoprecipitated with one putative N. benthamiana interactor by immunoprecipitation experiments. This candidate interactor protein will be identified with Mass Spectroscopy. In addition to this, subcellular localization of the effector candidate was examined in N. benthamiana plant. This was achieved by cloning PstHa2a5 gene construct in pK7WGF2 gateway destination vector and localization is determined by GFP expression in N. benthamiana after agrobacterium-mediated gene transformation.