Effects of gibberellic acid and uniconazole on the activities of some enzymes of anthocyanin biosynthesis in carrot cell cultures

Abstract

Gibberellic acid (GA₃) inhibition of anthocyanin accumulation by carrot cell-suspension cultures was reversed by supplying dihydroquercitin or naringenin to the culture and not by supplying 4-coumaric acid or malonic acid. This suggested that gibberellic acid was inhibiting chalcone synthase, chalcone isomerase, or acetyl CoA carboxylase. Acetyl-CoA-carboxylase specific activity was the same in GA₃-treated and untreated cultures and was not detected in cultures treated with uniconazole, an inhibitor of gibberellic acid biosynthesis. Chalcone-isomerase specific activity was lower in GA₃-treated cultures than in untreated cultures and was lower in uniconazole-treated cultures than in the GA₃-treated cultures. The total chalcone synthase activity in extracts from GA₃- and from uniconazole-treated cells was not significantly different 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 extracts from GA₃-treated cells did not contain the peak of chalcone synthase activity that, in untreated cells, preceded the main peak. The correlation between the absence of this peak and the inhibition of anthocyanin accumulation suggests that this form of chalcone synthase is responsible for anthocyanin synthesis and that GA₃ prevents this form from appearing in the cells.