Hormonal Regulation of α-Amylase Expression in Barley Aleurone Layers

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Abstract
The expression of .alpha.-amylase isozymes in barley (Hordeum vulgare L.) aleurone layers is known to be maximally induced between 12 and 20 hours after addition of the phytohormone, gibberellic acid (GA3). Addition of another hormone, abscisic acid (ABA), or its metabolite, phaseic acid, during this time period resulted in reduced .alpha.-amylase expression. Expression of the high isoelectric point .alpha.-amylase isozyme group was affected much more by both of these treatments than was expression of the low isoelectric point .alpha.-amylase isozyme group. Addition of either the translation inhibitor cycloheximide or the transcription inhibitor cordycepin prevented the decrease in .alpha.-amylase mRNA levels after ABA treatment. Cordycepin also prevented the decreases in .alpha.-amylase expression that resulted from phaseic acid treatment. Midcourse GA3 removal experiments were performed to determine whether ABA treatment and the removal of GA3 have analogous effects on .alpha.-amylase expression. It was found that cordycepin treatment also prevented decreases in .alpha.-amylase mRNA levels resulting from GA3 removal. We conclude that the suppression of .alpha.-amylase expression caused by ABA or midcourse GA3 removal is dependent on continuous RNA and protein synthesis.