Regulation of Gene Expression by Abscisic Acid in Barley Aleurone Layers

Abstract

The aleurone layers of certain small cereal grains, such as barley, wheat and oat, have been used as a convenient system to study the mode of action of two phytohormones, GA3 and ABA. It has been well documented that GA induces the synthesis and secretion of several hydrolytic enzymes, including α-amylases, proteases, β-1,3; 1,4 glucanase and nuclease in isolated barley aleurone layers [for review see 7, 12]. At least for α-amylases, the GA3 induction of their synthesis is mainly regulated at the transcription level [11]. Essentially all the GA3 effects in barley aleurone layers can be blocked by ABA [7]. However, kinetic studies by Chrispeels and Varner [2] indicate that these two hormones do not directly compete with each other for a common site. This observation seems to suggest that ABA may have a unique mode of action instead of being the mere reversal of GA3 action. As part of our attempt to investigate the mode of action of ABA in barley aleurone layers, we have studied the regulation of ABA metabolism and the effect of ABA metabolites on the synthesis of GA3-induced α-amylase. In addition, we have shown that certain effects of ABA in aleurone layers are dependent on RNA and protein synthesis. We also report here the characterization of several ABA-induced proteins and their potential physiological roles.