Hormonal Control of Enzyme Synthesis: On the Mode of Action of Gibberellic Acid and Abscisin in Aleurone Layers of Barley

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Abstract
Gibberellic acid (GA) enhances the synthesis of a-amyl-ase and ribonuclease in isolated aleurone layers and this process is inhibited by abscisin. Removal of gibberellic acid in mid-course of [alpha]-amylase production results in a slowing down of [alpha]-amylase synthesis, suggesting a continued requirement of GA for enzyme synthesis. This is a paralleled by a continuous requirement for RNA synthesis. Addition of 6-methylpurine or 8-azaguanine in mid-course results in an inhibition of [alpha]-amylase synthesis within 3 to 4 hours. However, actinomycin D added in mid-course is almost without effect. This is not due to its failure to enter the cells, because it does inhibit 14C-uridine incorporation at this stage. Addition of abscisin to aleurone layers which are synthesizing [alpha]-amylase results in an inhibition of this synthesis within 2 to 3 hours. Cyxcloheximide on the other hand inhibits enzyme synthesis immediately upon its addition. These data are consistent with the hypothesis that the expres -sion of the GA effect requires the synthesis of enzyme-specific RNA molecules. The similarity in the kinetics of inhibition between abscisin on the one hand and 8-azaguanine or 6-methylpurine on the other suggests that abscisin may exert its action by inhibiting the synthesis of these enzyme-specific RNA molecules by preventing their incorporation into an active enzyme-synthesising unit.