SENESCENCE OF RICE LEAVES .32. EFFECTS OF ABSCISIC-ACID AND BENZYLADENINE ON POLYAMINES AND ETHYLENE PRODUCTION DURING SENESCENCE

The effects of abscisic acid (ABA) and benzyladenine (BA) on polyamines and ethylene production during senescence of detached rice leaves under light were investigated. The senescence of rice leaves was followed by measuring the decrease of protein. BA (0.01 mM) significantly retarded and ABA (0.1 mM) markedly promoted senescence of detached rice leaves. Putrescine and spermine levels were increased (30 to 50%) by ABA and decreased (30 to 50%) by BA. However, spermidine level was found to be decreased (50%) by ABA and increased (25%) by BA. BA treatment had no effect on the activities of ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMDC), but resulted in 20 to 50% lower activity of arginine decarboxylase (ADC) when compared with the water controls. Both the activities of ODC and SAMDC were increased about 2-3 times by ABA during the 3rd and 4th day of incubation. ABA treatment resulted in a peak of ADC activity during the first 24 h of incubation. ABA inhibited but BA promoted ethylene production during senescence. It is concluded that (a) endogenous polyamine levels and polyamine biosynthetic enzyme activities are not correlated with rice leaf senescence, (b) the effect of ABA of BA on senescence are separated from that on polyamine levels or polyamine biosynthesis, and (c) polyamine and ethylene biosynthesis in rice leaves do not compete for the substrate, S-adenosylmethionine.