Sugars enhance the expression of gibberellin-induced genes in developing petunia flowers

Sugar is essential for the development of detached Petunia hybrida flowers. We have shown that sucrose (Suc) and gibberellic acid (GA₃) are required for anthocyanin accumulation and the expression of various genes in developing petunia corollas. The effect of GA₃ on the expression of the gibberellin-induced gene and chalcone synthase gene, in detached corollas, was promoted by metabolic sugars such as Suc, glucose (Glc) and fructose, but not by the nonmetabolized 3-O-methylglucose and the sugar alcohol, mannitol. Several pieces of evidence support sugars' signaling role in the corollas and the possible involvement of hexokinase as the sugar sensor. Mannose, which is inefficiently metabolized but is phosphorylated by hexokinase at efficiency similar to Glc, was as effective as Glc in promoting gene expression and pigmentation. 2-Deoxyglucose, which is a substrate for hexokinase but is not metabolized in glycolysis, also promoted gene expression. On the other hand, mannoheptulose, a competitive inhibitor of hexokinase, completely abolished the promotive effect of Glc. We suggest that sugar-phosphorylation-related signal transduction interacts with the gibberellin signal to induce gene expression and anthocyanin accumulation in developing petunia corollas.