Sugar sensing and Ca2+-calmodulin requirement in Vitis vinifera cells producing anthocyanins

We have previously reported that sucrose modulates anthocyanin biosynthesis in cell suspension cultures of Vitis vinifera L. The main role of sugar in this response does not seem to be that of general carbohydrate source for the supply of energy. In the present work, a number of pharmacological agen ts were used to further investigate the components of the signal transducti on pathway involved in the induction of anthocyanin biosynthesis by sugar. We found that the phosphorylation of hexose by hexokinase. but not its tran sport, has to be taken into account for the sucrose signal transduction lea ding to anthocyanin accumulation. Indeed, 3-O-methylglucose, a glucose anal og transported into cells but not phosphorylated by hexokinase, has no effe ct on anthocyanin production. Mannose mimics the effect of sucrose in grape cells. and mannoheptulose, a specific inhibitor of hexokinase, reduces the accumulation of anthocyanins in response to sucrose. The results with the two latter analogs are discussed. Ca2+ channel blockers, verapamil and LaCl 3, which were used to investigate the role of extracellular Ca2+, all inhib ited the sugar response. Ca2+ depletion by pretreatment with ethylene glyco l his (beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) also blocked the sugar response, which was partially recovered when Ca2+ was added exog enously after Ca2+ depletion. The use of two potent calmodulin antagonists, N-(6-aminohexyl)-5-chloro-1-naphtalenes (W7) and chlorpromazine. showed th at calmodulin is involved in the sugar signal transduction. A protein kinas e inhibitor, 6-dimethylaminopurine (6-DMAP), and the protein phosphatase in hibitors, endothall and cantharidin, also inhibited the sugar response. The results of the present study suggest the involvement of several components of general signal transduction pathways such as Ca2+, calmodulin, and prot ein kinases/phosphatases in the induction of anthocyanin biosynthesis by su gar. (C) 2000 Elsevier Science Ltd. All rights reserved.