Senescence of Rice Leaves XXX Levels of Endogenous Polyamines and Dark-Induced Senescence of Rice Leaves

The role of endogenous polyamines in the control of dark-induced senescence of detached rice leaves was investigated by quantitating levels of various polyamines by HPLC. Putrescine, spermidine and spermine were all present throughout senescence. Neither cadaverine nor 1,3-diaminopropane was detected. During dark-induced senescence, there was a marked decrease in levels of putrescine and an increase in those of spermidine and spermine. The rate of production of ethylene increased markedly upon excision of leaves. α-Difluoromethylarginine (DFMA) and α-difluoromethylornithine (DFMO) caused a reduction in levels of putrescine, yet had no effect on levels of spermidine and spermine. Neither DFMA nor DFMO had any effect on senescence or on the production of ethylene. Treatment with dicyclohexylamine (DCH) and methylglyoxal bis-(guanylhydrazone) (MGBG) reduced levels of spermine and increased those of putrescine in detached leaves. After treatment with DCH or MGBG, both senescence and the production of ethylene were significantly promoted. The current results suggest that endogenous polyamines may not play a significant role in the control of dark-induced senescence of rice leaves. This conclusion is supported by the further observations that (a) benzyladenine, which is known to retard senescence, decreased levels of putrescine but had no effect on those of spermidine and spermine; and (b) ABA, which promoted senescence, increased levels of putrescine and had no effect on those of spermidine and spermine.