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Oxidative stress enzyme activities and desiccation tolerance in seeds of two rainforest species, Afzelia africana Sm. and Gambeya albida (G. Don) Aubrev. and Pellegr.
Abstract
Plants when exposed to stress generate reactive oxygen species (ROS), which are detoxified through antioxidant defense systems involving enzymatic and non-enzymatic components. This research studied the impact of desiccation on the activities of some oxidative stress enzymes: Peroxidase (POD), Catalase (CAT), Polyphenol oxidase (PPO), and Glucose-6-phosphate dehydrogenase (G6PDH) in seeds of Afzelia africana and Gambeya albida. Mature seeds were collected directly from parent trees and desiccated under ambient laboratory conditions for 0, 3, 7, 10, 13, 15, 22 and 35 days, after which enzyme activities were assayed. In A. africana, maximum germination (90.00%) occurred after 15 days of desiccation at 4.86% moisture content, whereas germinability of G. albida declined by more than 50% after 7 days at 9.02% moisture. G6PDH activity in A. africana increased appreciably during early desiccation, while G. albida showed a momentary peak followed by decline. Peroxidase activity decreased initially in A. africana but increased in G. albida during early desiccation, whereas catalase activity increased at later stages in both species. PPO activity showed no significant differences between the species. Overall, the orthodox seeds of A. africana maintained stronger antioxidant enzyme responses during desiccation while the recalcitrant seeds of G. albida exhibited reduced enzymatic activity. These findings highlight the role of antioxidant enzymes in cellular stability during water loss and provide insight into the physiological basis of desiccation tolerance in tropical tree seeds.
