Gibberellins and gene control in cereal aleurone cells.

The production of hydrolytic enzymes in the germinating cereal grain is considered as a model for plant cell differentiation. Recent literature is reviewed which suggests that gibberellins are involved in this process, but in a less straightforward manner than considered previously. It seems likely that only a subfraction of gibberellin is active and that production of this gibberellin is actually in the hydrolase-producing cells. These include aleurone cells and also the scutellar epithelial cells. At the intracellular level the action of gibberellin results in the accumulation of alpha-amylase mRNA and also mRNA for other unidentified proteins, referred to as gibb-ons. The alpha-amylase mRNAs are transcribed from two distinct gene families. The pattern of expression of alpha-amylase and gibb-on mRNAs is consistent with a common gibberellin-stimulated mechanism of control of for all of these genes. However it seems likely from experiments with ABA and from observations on gibb-on gene expression in non-aleurone cells that gibberellin does not have a role determining the specificity of gene expression, but rather acts as a general stimulator of mRNA accumulation.