Implications of water stress‐induced changes in the levels of endogenous ascorbic acid and hydrogen peroxide in Vigna seedlings

Vigna cutjang Endl. cv. Pusa Barsati seedlings, subjected to increasing degrees of water stress (−0.5, −1.0, −1,5 MPa), produced an approximately proportional increase in glycolate oxidase activity, hydrogen peroxide (H 2 O 2 ) and proline content but a decrease in catalase activity, ascorbic acid and protein content. Leaf water potential (leaf ψ) and relative water content (RWC) were also lowered with increasing stress. Pretreatment with l ‐cysteine and reduced glutathione (10‐3 M) decreased glycolate oxidase activity, H 2 O 2 content, ascorbic acid oxidase activity, proline content and also slightly improved the water status of leaves stressed (−1.0 MPa) for 2 days. Pretreatment of non‐stressed seedlings with these antioxidants had little or no effect. These studies indicate that treatment with antioxidants makes the plant tolerant against water stress by modulating the endogenous levels of H 2 O 2 and ascorbic acid in stressed tissue.