Sugar-dependent gibberellin-induced chalcone synthase gene expression in Petunia corollas

The induction of anthocyanin synthesis and anthocyanin biosynthetic gene expression in detached petunia (Petunia hybrida) corollas by gibberellic acid (GA₃) requires sucrose. Neither sucrose nor GA₃ alone can induce these processes. We found that GA₃ enhances sucrose uptake by 20 to 30%, and we tested whether this is the mechanism by which the hormone induces gene expression. Changing the intracellular level of sucrose with the inhibitors p-chloromercuribenzenesulfonic acid and vanadate did not inhibit the induction of chalcone synthase gene (chs) expression by GA₃. Growing detached corollas in various sucrose concentrations did not affect the induction of the gene but did affect its level of expression and the level of anthocyanin accumulated. Only metabolic sugars promoted GA₃-induced anthocyanin accumulation. Mannitol and sorbitol had no effect and 3-O-methylglucose only slightly promoted chs expression and anthocyanin accumulation. Our results do not support the suggestion that sugars act as specific signals in the activation of anthocyanin biosynthetic gene expression during petunia corolla development. We suggest that sugars are essential as general sources of carbohydrates for carbon metabolism, upon which the induction of pigmentation is dependent.