Soybean yields are negatively affected by both natural and stress induced senescence of nodules since it limits nitrogen supply to the plants resulting in nitrogen deficiency. Senescence is due to accelerated and unregulated activity of proteases, specifically cysteine proteases. In this study, transgenic soybean plants expressing a cysteine protease inhibitor (OC-I) specifically in root nodules were characterized under natural and stress-induced tolerance. The hypothesis being that OC-I will delay nodule senescence resulting in prolonged nitrogen supply which will delay leaf degradation for nutrient remobilization thus leading to improved growth. Unlike ectopic expression in previous studies, tissue-specific expression did not lead to reduced growth of the transgenic lines as compared to wild type under normal conditions. Transgenic lines maintained significantly higher photosynthetic machinery (chlorophyll) as well reduced oxidative damage (hydrogen peroxide and malondialdehyde) under natural and stress induced-conditions senescence. The reduced oxidative damage was due to improved antioxidant pool (GST, POD, CAT), osmoprotectant and protective pigment accumulation (proline, anthocyanin, carotene). Ureide content accumulation in root nodules indicated significant nitrogen fixation in transgenic lines as compared to wild type. Metabolite accumulation was also investigated to understand partitioning patterns of the plants. Accumulated data suggest the involvement of OC-I in senescence tolerance.
Dissertation (MSc (Plant Science))--University of Pretoria, 2021.