PHYSIOLOGICAL AND BIOCHEMICAL-CHANGES RELATED TO METHYL JASMONATE-INDUCED CHILLING TOLERANCE OF RICE (ORYZA-SATIVA L) SEEDLINGS

Physiological and biochemical changes related to methyl jasmonate (MeJ A)-induced chilling tolerance of rice (Oryza sativa L. cv. Taichung Na tive 1) seedlings were investigated. Treatment of whole plants with 10 mmol m(-3) MeJA for 48 h before chilling (5 degrees C) was optimal fo r the induction of chilling tolerance. MeJA greatly improved the survi val 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 op ening of stomata and decreasing the root bleeding rate. Putrescine and spermine levels in shoots increased but spermidine levels decreased o n exposure to MeJA. In roots, putrescine levels also increased and spe rmidine levels increased transiently on exposure to MeJA. Activities o f arginine decarboxylase (ADC; EC 4.1.1.19) and S-adenosylmethionine d ecarboxylase (SAMDC; EC 4.1.1.50) in both shoots and roots increased o n exposure to MeJA, while the activity of ornithine decarboxylase (ODC ; EC 4.1.1.17) remained unchanged. The MeJA-induced putrescine increas e was inhibited by 50 mmol m(-3) alpha-difluoromethylarginine (DFMA), an irreversible inhibitor of ADC, but not by 50 mmol m(-3) alpha-diflu oromethylornithine (DFMO), an irreversible inhibitor of ODC. The effec t of MeJA on the induction of chilling tolerance was also reduced by 5 0 mmol m(-3) DFMA. The effects of DFMA were partly prevented by 1 mol m(-3) putrescine. This indicates that putrescine accumulation is requi red for the induction of chilling tolerance of rice seedlings by MeJA.