A. Ilan et Dk. Dougall, EFFECTS OF GIBBERELLIC-ACID AND UNICONAZOLE ON THE ACTIVITIES OF SOMEENZYMES OF ANTHOCYANIN BIOSYNTHESIS IN CARROT CELL-CULTURES, Journal of plant growth regulation, 13(4), 1994, pp. 213-219
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.