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Involvement of oxidative stress and autointoxication in leaf senescence of Amomum villosum

Abstract To clarify whether oxidative stress and autointoxication were involved in leaf senescence of Amomum villosum, the successive leaf maturation and senescence were characterized first, and then the effects of potential autointoxicants on attached mature leaf were determined in this study. Maximum photosynthetic rates (P max) decreased greatly in senescent leaves, which were associated with the decreases in the contents of soluble proteins and chlorophyll (Chl), chlorophyll a/b and stomatal conductance. Maximum efficiency of photosystem (PS) II photochemistry (F v/F m), photochemical quenching coefficient and quantum yield of PS II (Φ PSII) decreased much less in senescent leaves than P max, leading to high PS II excitation pressures. The activities of peroxidase, ascorbate peroxidase and superoxide dismutase increased in senescent leaves, while catalase activity and non-photochemical quenching coefficient decreased. The high PS II excitation pressures in senescent leaves were not effectively dealt with, leading to oxidative stress, as indicated by high malondialdehyde content. Aqueous extracts of leaves and roots of A. villosum and topsoils under this plant inhibited P max more greatly than F v/F m and Φ PSII, leading to high PS II excitation pressures in mature leaves of A. villosum grown in nutrient solution containing the aqueous extracts, and therefore to oxidative stress. Our results indicate that oxidative stress is involved in leaf senescence in A. villosum and autointoxication exacerbates leaf senescence by increasing oxidative stress.