Regulation of the accumulation of mRNA for alpha-amylase in barley aleurone.

The effect of gibberellic acid and Ca(2+) on the accumulation of alpha-amylase mRNAs in aleurone layers of barley (Hordeum vulgare L. cv Himalaya) was studied using cDNA clones containing sequences of mRNAs for the high and low isoelectric point (pI) alpha-amylases. There is no significant hybridization between the two alpha-amylase cDNA clones under the hybridization and washing conditions employed. These clones were therefore used to monitor levels of mRNAs for high and low pI alpha-amylases. It is shown that although the synthesis of the high pI alpha-amylase proteins depends on the presence of Ca(2+) in the incubation medium, the accumulation of mRNA for this group occurs to the same degree in the presence or the absence of Ca(2+). The accumulation of low pI alpha-amylase mRNA is also not affected by the presence or absence of Ca(2+) in the incubation medium. These results establish gibberellic acid, not Ca(2+), as the principal regulator of alpha-amylase mRNA accumulation in barley aleurone, while Ca(2+) controls high pI alpha-amylase synthesis at a later step in the biosynthetic pathway.