SUGAR-DEPENDENT GIBBERELLIN-INDUCED CHALCONE SYNTHASE GENE-EXPRESSIONIN PETUNIA COROLLAS

The induction of anthocyanin synthesis and anthocyanin biosynthetic ge ne expression in detached petunia (Petunia hybrida) corollas by gibber ellic acid (GA(3)) requires sucrose. Neither sucrose nor GA(3) alone c an induce these processes. We found that GA(3) enhances sucrose uptake by 20 to 30%, and we tested whether this is the mechanism by which th e hormone induces gene expression. Changing the intracellular level of sucrose with the inhibitors p-chloromercuribenzenesulfonic acid and v anadate did not inhibit the induction of chalcone synthase gene (chs) expression by GA(3). Growing detached corollas in various sucrose conc entrations did not affect the induction of the gene but did affect its level of expression and the level of anthocyanin accumulated. Only me tabolic sugars promoted GA(3)-induced anthocyanin accumulation. Mannit ol and sorbitol had no effect and 3-O-methylglucose only slightly prom oted chs expression and anthocyanin accumulation. Our results do not s upport the suggestion that sugars act as specific signals in the activ ation of anthocyanin biosynthetic gene expression during petunia corol la development. We suggest that sugars are essential as general source s of carbohydrates for carbon metabolism, upon which the induction of pigmentation is dependent.