Ethylene-Induced Polyamine Accumulation in Rice (Oryza sativa L.) Coleoptiles

Effects of ethylene on free polyamine biosynthesis in rice (Oryza sativa L. cv Taichung Native 1) coleoptiles were investigated in sealed and aerobic conditions. In sealed conditions, putrescine increased significantly and coincided with ethylene accumulation. Application of ethylene in sealed containers promoted putrescine accumulation over that in sealed controls. This ethylene-enhanced putrescine accumulation was inhibited by the ethylene action inhibitor 2,5-norbornadiene at 4000 muL/L. In aerobic conditions, ethylene and 1-aminocyclopropane-1-carboxylic acid also induced putrescine accumulation. Activity of arginine decarboxylase (EC 4.1.1.19) and S-adenosylmethionine decarboxylase (EC 4.1.1.50) increased on exposure to ethylene in aerobic conditions. Ornithine decarboxylase (EC 4.1.1.17) activity, however, remained unchanged. The ethylene-induced putrescine accumulation was inhibited by 5 x 10(-4)m alpha-difluromethylarginine, but not by 5 x 10(-4)m alpha-difluromethylornithine. Apparently, arginine decarboxylase, not ornithine decarboxylase, mediates the ethylene-induced putrescine accumulation. The increased S-adenosylmethioinine decarboxylase activity, however, did not result in a significant spermidine/spermine accumulation. In ethylene-treated coleoptiles, the accumulation of putrescine paralleled the increase of coleoptile length in both sealed and aerobic conditions. alpha-difluromethylarginine inhibited ethylene induced putrescine accumulation and coleoptile elongation. It seems that putrescine biosynthesis might be involved in the ethylene-induced elongation of rice coleoptiles.