Effects of Abscisic Acid and Ethylene on the Gibberellic Acid-Induced Synthesis of α-Amylase by Isolated Wheat Aleurone Layers

Abstract

Gibberellic acid-induced alpha-amylase synthesis in wheat aleurone layers (Triticum aestivum L. var Potam S-70) escaped from transcriptional control 30 h after addition of the hormone, as evidenced by the tissue's loss of susceptibility to cordycepin. Abscisic acid inhibited the accumulation of alpha-amylase activity when added to the tissue during this cordycepin-insensitive phase of enzyme induction. alpha-Amylase synthesis was not restored by the addition of cordycepin, indicating that the response to abscisic acid was not dependent upon the continuous synthesis of a short lived RNA. When ethylene was added simultaneously or some time after abscisic acid, the accumulation of alpha-amylase activity was sustained or quickly restored. The loss of susceptibility to cordycepin was completely prevented when aleurone layers were incubated with a combination of gibberellic and abscisic acids from the start of the induction period. This effect of abscisic acid was not reversed by ethylene. On the basis of these observations, it is suggested that abscisic acid inhibits both the transcription and translation of alpha-amylase mRNA, and that only the latter site of action is susceptible to reversal by ethylene.The rate of incorporation of [methyl-(14)C]choline into phospholipids was also inhibited by abscisic acid. Ethylene reversed this effect. The effects of abscisic acid and ethylene on phospholipid synthesis were not dependent upon the presence of gibberellic acid. No direct relationship was found between the control of alpha-amylase synthesis and membrane formation by abscisic acid and ethylene.