Hormonal Regulation of Gene Expression m the Aleurone Layers of Cereal Grains

The aleurone layers of cereal grains offer a convenient system for studies of the molecular action of two plant hormones, gibberellins (GA) and abscisic acid (ABA). Gibberellins induce the synthesis of ix-amylase and several other hydrolytice enzymes. The action of GA is essentially at the transcriptional level, it enhances the level of steady-state levels of ix-amylase mRNAs, the rate of transcription of ᴕ-amylase genes and the activity of a trans-acting factor which interacts with specific regions of ix-amylase genes. Abscisic acid antagonizes the effect of GA by inhibiting the induction of hydrolytic enzymes, yet the effect of ABA itself is dependent on transcriptional and/or translational process. Abscisic acid inhibits the transcription of ix-amylase genes, destabilizes ᴕ-amylase mRNA and reduces ix-amylase activities. Several ABA induced proteins have been studied including an ix-amylase inhibitor, a lectin and a basic protein with long repeats. These proteins can also be induced by drought stress, apparently due to the drought-enhanced accumulation of ABA