Physiological and biochemical changes related to methyl jasmonate‐induced chilling tolerance of rice (Oryza sativa L.) seedlings

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Abstract
Physiological and biochemical changes related to methyl jasmonate (MeJA)‐induced chilling tolerance of rice (Oryza sativa L. cv. Taichung Native 1) seedlings were investigated. Treatment of whole plants with 10 mmol m−3 MeJA for 48 h before chilling (5 °C) was optimal for the induction of chilling tolerance. MeJA greatly improved the survival ratio of chilled seedlings and ameliorated chilling injury such as demolition of membrane structure (estimated by electrolyte leakage). MeJA also prevented water loss in chilled seedlings by reducing the opening of stomata and decreasing the root bleeding rate. Putrescine and spermine levels in shoots increased but spermidine levels decreased on exposure to MeJA. In roots, putrescine levels also increased and spermidine levels increased transiently on exposure to MeJA. Activities of arginine decarboxylase (ADC; EC 4.1.1.19) and S‐adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in both shoots and roots increased on exposure to MeJA, while the activity of ornithine decarboxylase (ODC; EC 4.1.1.17) remained unchanged. The MeJA‐induced putrescine increase was inhibited by 50 mmol m−3α‐difluoromethylarginine (DFMA), an irreversible inhibitor of ADC, but not by 50 mmol m−3α‐difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. The effect of MeJA on the induction of chilling tolerance was also reduced by 50 mmol m−3 DFMA. The effects of DFMA were partly prevented by 1 mol m−3 putrescine. This indicates that putrescine accumulation is required for the induction of chilling tolerance of rice seedlings by MeJA.