The role of Ca2+in the action of GA in the barley aleurone

Abstract

The barley aleurone has been widely used as a model system for studying the action of two plant growth regulators, gibberellic acid (GA), and abscisic acid (ABA). In the isolated aleurone layer as well as in the germinating grain, these two substances act in an antagonistic fashion to regulate the production of hydrolases, chiefly a-amylase (Jacobsen et al. 1979), that are important for germination of the grain. Early experiments using isolated aleurone layers revealed that the increase in a-amylase and other hydrolases that is stimulated by GA required millimolar levels of extracellular Ca2+ (Chrispeels and Varner, 1967). Although the role of Ca2+ in ABA action has apparently not been studied in the barley aleurone, it has recently been shown that the expression of proteins induced by ABA in the wheat aleurone also requires Ca2+ (Napier et al. 1989). The goal of our research has been to understand the role of Ca2+ n the action of plant growth regulators. We here report on the ability of GA to regulate Ca2+ levels in the cytosol and in the endoplasmic reticulum (ER), the site of hydrolase production in the barley aleurone.