Influence of the Starchy Endosperm on α-Amylase Isozyme Levels in Barley

Abstract

α-Amylase activity in malted barley seedlings is composed of the activities of the high-isoelectric point (pI) and low-pI α-amylase isozymes. In intact seedlings, the high-pI isozyme activity is roughly 10-fold greater than low-pI activity. However, in isolated aleurones treated with gibberellin (GA), low-pI activity is equal to or greater than high-pI activity. Therefore, α-amylase expression during malting must be controlled by factors missing from the isolated aleurone system. The objective of this study was to determine the contribution of GA and the starchy endosperm toward producing the α-amylase isozyme levels found in intact seedlings. The possibility that the starchy endosperm could contribute to the prolonged dominance of high-pI expression seen in intact seedlings was explored by incubating isolated aleurones with GA and crude endosperm homogenates from untreated de-embryonated half-seeds. α-Amylase isozyme levels were analyzed with isoelectric focusing activity gels. The levels of the messenger RNAs (mRNAs) that encode them were analyzed by RNA blots. This endosperm treatment reproduced aspects of intact seedling expression by prolonging the rise in high-pI mRNA levels and increasing the secretion of high-pI enzyme. This indicates that the starchy endosperm, by virtue of a resident factor or one created during hydrolytic metabolism, contributes to the expression of the high-pI α-amylase genes in developing seedlings.