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 (Vignaradiata 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.