Inhibition of flavonoid biosynthesis by gibberellic acid in cell suspension cultures of Daucus carota L.

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Abstract
In carrot cells (Daucus carota L.), cultured in the presence of gibberellic acid, anthocyanin synthesis is blocked at the level of chalcone synthase. By feeding suitable precursors for anthocyanins (naringenin, eriodictyol, dihydroquercetin) biosynthesis of cyanidin glycosides can be restored. After addition of these substrates to the culture medium in the presence of gibberellic acid, the activity of chalcone synthase remained as low as in the control without precursors. The highest increase in anthocyanin content was achieved using dihydroquercetin as the added precursor. The time course of this supplementation showed a rapid response; within 4 h a substantial increase in anthocyanin could be observed. In contranst, the flavonol quercetin is not a precursor for cyanidin. The fact that naringenin was also accepted for cyanidin synthesis leads to the conclusion that hydroxylation in 3′-position of ring B in Daucus carota takes place at the flavonoid stage.