INFLUENCE OF THE STARCHY ENDOSPERM ON ALPHA-AMYLASE ISOZYME LEVELS INBARLEY

alpha-Amylase activity in malted barley seedlings is composed of the a ctivities of the high-isoelectric point (pI) and low-pI alpha-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, alpha-amylase expression during malt ing must be controlled by factors missing from the isolated aleurone s ystem. The objective of this study was to determine the contribution o f GA and the starchy endosperm toward producing the alpha-amylase isoz yme levels found in intact seedlings. The possibility that the starchy endosperm could contribute to the prolonged dominance of high-pI expr ession seen in intact seedlings was explored by incubating isolated al eurones with GA and crude endosperm homogenates from untreated de-embr yonated half-seeds. alpha-Amylase isozyme levels were analyzed with is oelectric focusing activity gels. The levels of the messenger RNAs (mR NAs) that encode them were analyzed by RNA blots. This endosperm treat ment reproduced aspects of intact seedling expression by prolonging th e rise in high-pI mRNA levels and increasing the secretion of high-pI enzyme. This indicates that the starchy endosperm, by virtue of a resi dent factor or one created during hydrolytic metabolism, contributes t o the expression of the high-pI alpha-amylase genes in developing seed lings.