EFFECTS OF GIBBERELLIC-ACID AND UNICONAZOLE ON THE ACTIVITIES OF SOMEENZYMES OF ANTHOCYANIN BIOSYNTHESIS IN CARROT CELL-CULTURES

Gibberellic acid (GA3) inhibition of anthocyanin accumulation by carro t cell-suspension cultures was reversed by supplying dihydroquercitin or naringenin to the culture and not by supplying 4-coumaric acid or m alonic acid. This suggested that gibberellic acid was inhibiting chalc one synthase, chalcone isomerase, or acetyl CoA carboxylase. Acetyl-Co A-carboxylase specific activity was the same in GA3-treated and untrea ted cultures and was not detected in cultures treated with uniconazole , an inhibitor of gibberellic acid biosynthesis. Chalcone-isomerase sp ecific activity was lower in GA3-treated cultures than in untreated cu ltures and was lower in uniconazole-treated cultures than in the GA3-t reated cultures. The total chalcone synthase activity in extracts from GA3- and from uniconazole-treated cells was not significantly differe nt from that in extracts of untreated tissue. When these extracts were chromatographed on a Mono Q column, three peaks of chalcone synthase activity were found in extracts of nontreated cells, whereas only two of these peaks were detected in extracts of GA3-treated cells. The ext racts from GA3-treated cells did not contain the peak of chalcone synt hase activity that, in untreated cells, preceded the main peak. The co rrelation between the absence of this peak and the inhibition of antho cyanin accumulation suggests that this form of chalcone synthase is re sponsible for anthocyanin synthesis and that GA3 prevents this form fr om appearing in the cells.