SUGAR REPRESSION OF A GIBBERELLIN-DEPENDENT SIGNALING PATHWAY IN BARLEY EMBRYOS

Increasing evidence shows that sugars can act as signals affecting pla nt metabolism and development. Some of the effects of sugars on plant growth and development suggest an interaction of sugar signals with ho rmonal regulation. We investigated the effects of sugars on the induct ion of alpha-amylase by gibberellic acid in barley embryos and aleuron e layers. Our results show that sugar and hormonal signaling interact in the regulation of gibberellic acid-induced gene expression in barle y grains. The induction of alpha-amylase by gibberellic acid in the al eurone layer is unaffected by the presence of sugars, but repression b y carbohydrates is effective in the embryo, alpha-Amylase expression i n the embryo is localized to the scutellar epithelium and is hormone a nd sugar modulated. The effects of glucose are independent from the ef fects of sugars on gibberellin biosynthesis. They are not due to an os motic effect, they are independent of abscisic acid, and only hexokina se-phosphorylatable glucose analogs are able to trigger gene repressio n. Overall, the results suggest the existence of an interaction betwee n the hormonal and metabolic regulation of alpha-amylase genes in barl ey grains.