The effects of abscisic acid on senescence in leaf discs of radish, Raphanus sativus L.

After a 6 day incubation period, abscisic acid (ABA) at 10(-4) M retarded the decline in pigment levels and promoted the decline in protein levels of radish leaf discs. ABA treatment also retarded the rise in the specific activity of the RNA fraction (calculated by counts per minute incorporated of (14)C-8-adenine as a fraction of optical density at 260 nm) observed in water-treated control discs. The results indicated that ABA was primarily effective in enhancing senescence in the early stages following leaf excision. Thus the increase in RNA specific activity during an initial 24 h incubation period was especially pronounced with ABA treatment although there was no effect of the hormone on RNA level. Moreover, in contrast to control discs, the pigment levels declined markedly in ABA-treated discs in this period. When the discs had been incubated in water ("preaged") for 3 or 5 days prior to ABA treatment, however, the hormone then had little effect on RNA metabolism and protein and pigment levels relative to the water control.Data are collated from different experiments to show the changes in RNA, pigment and protein with ABA treatment during a 6 day senescence period.It is considered that ABA is speeding up the natural changes in RNA metabolism possibly by affecting both RNA synthesis and degradation.