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Doctoral Degrees (Biological Sciences)

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Browsing Doctoral Degrees (Biological Sciences) by Subject "Antioxidant pre-treatments."

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    Physiological and biochemical investigations into the reinvigoration of deteriorated Brassica oleracea L. (Cabbage) and Lactuca sativa L. (Lettuce) seeds with antioxidants and inorganic salt solutions.
    (2021) Adetunji, Ademola Emmanuel.; Varghese, Boby.; Naidoo, Sershen.; Pammenter, Norman William.
    This study focused on reinvigorating deteriorated Brassica oleracea L. (cabbage) and Lactuca sativa L. (lettuce) seeds with antioxidants and inorganic (electrolysed and non-electrolysed) salt solutions. All pre-treatment solutions were applied to fresh (control) and controlled deteriorated (CDd) seeds at 75% viability (P75), 50% viability (P50) and 25% viability (P25). The pre-hydration treatments were compared in terms of their effects on seed germination, seedling vigour, electrolyte conductivity (EC), accumulation of lipid peroxidation products, protein carbonylation (PC), antioxidant enzymes and germination enzymes. The study also investigated the effects of invigorating CDd seeds with selected antioxidants on subsequent seedling growth, gas exchange and photochemistry under greenhouse conditions. Controlled deterioration, in general, resulted in the loss of seed vigour and viability but at higher rates in lettuce than cabbage, and increased EC and PC, and lowered antioxidant and germination enzymes activities in both species. However, significant lipid peroxidation was only recorded in lettuce seeds. Antioxidant pre-treatments enhanced viability of CDd seeds of cabbage at P25 and lettuce at P50 and P25, and improved seedling vigour of fresh, P75 and P50 cabbage, and P50 and P25 lettuce seeds. Antioxidant pretreatments reduced EC and lipid peroxidation in lettuce seeds, while PC was reduced in both species. The treatments also elevated antioxidant and germination enzymes activities in P25 cabbage seeds and P50 and P25 lettuce seeds. The inorganic salt pre-treatments did not enhance percentage seedling production in CDd cabbage seeds. However, in CDd lettuce seeds, Cacontaining solutions and electolysed (cathodic water) treatments promoted percentage normal seedling production and enhanced seedling vigour irrespective of pre-treatment solution pH or seed deterioration level. In the greenhouse studies, certain antioxidants promoted seedling vigour and leaf area in both species and enhanced shoot dry weight and gas exchange in lettuce. In summary, CDd lettuce seeds responded better to both types of invigoration (i.e., antioxidants and inorganic salt solutions) than cabbage seeds, while antioxidants appeared to be relatively more beneficial than inorganic salts in both species. The results suggest that the benefits of certain pre-treatment solutions were based on the enhancement of the activities of key antioxidant and germination enzymes, and the efficiency of photosynthesis at the early stages of growth. The results argue for the use of these seed pre-hydration treatments for mitigating poor stand establishment brought about by seed ageing, and as a useful approach to reinvigorating seeds in long-term storage collections for ensuring global food security.