The effects of polyamines (putrescine, spermidine, spermine and diaminopropane) on the production of ethylene in detached rice leaves were investigated. Polyamines effectively promoted the production of ethylene in detached rice leaves under both light and dark conditions. Putrescine stimulated the production of ethylene within 4 hours of its application, a result suggests that putrescine enhances the production of ethylene directly. Putrescine also stimulated the production of ethylene in detached leaves that had been aged for 2 and 4 days. The stimulatory effect of putrescine resulted from the enhancement of the synthesis of 1-aminocyclopropane-l-carboxylic acid (ACC) and the conversion of ACC to ethylene. The activity of S-adenosylmethio-nine decarboxylase in segments of rice leaves was inhibited by the application of putrescine. Thus, the enhancement of the synthesis of ACC by putrescine seems to be mediated by increases in the activity of ACC synthase and in the level of the substrate (S-adenosylmethionine) for ACC synthase.
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