Hydrogen peroxide-induced chilling tolerance in mung beans mediated through ABA-independent glutathione accumulation

Transient oxidative shock induced by pretreatment of leaves with H2O2 effectively increased chilling tolerance in mung bean and Phalaenopsis. Seedlings of the chilling-tolerant (V3327) cultivar of mung bean (Vigna�radiata L.) were employed to study the mechanism of H2O2-induced chilling tolerance. Pretreatment with 200 mM H2O2 increased survival rates of seedlings chilled at 4°C for 36 h from 30% to 70%. The same treatment also lowered the electrolyte leakage from 86% to 21%. Time-course analysis immediately after the treatment demonstrated that exogenous application of H2O2 did not alter the endogenous H2O2 level of the plants. This observation suggests that the primary receptor for the exogenous H2O2 is localized on the leaf surface or in some other way isolated from the endogenous H2O2 pool. Oxidative shock inhibited the induction of the antioxidant enzymes, ascorbate peroxidase and catalase; however, it substantially increased glutathione content both under chilling and control conditions. Combined pretreatment of mung bean plants with abscisic acid and H2O2 showed no synergistic effect on glutathione content and decreased survival rate relative to treatment with either compound alone. These results suggest that the H2O2-induced chilling tolerance in these plants might be mediated by an elevation of glutathione content and is independent of the ABA mechanism of chilling protection.