The gentian flavonoid biosynthesis pathway.

Flavonol synthase (FLS) is not required for pigment production, but is necessary for the synthesis of the three flavonols: kaempferol, quercetin and myricetin. Anthocyanidins (pelargonidin, cyanidin, and delphinidin) are modified by the addition of sugars and other moieties to form anthocyanins in a species-specific manner. Pink-flowered gentians accumulate gentiocyanin anthocyanin in their petals, and blue-flowered gentians accumulate mainly gentiodelphin anthocyanin, whereas orange-flowered gentian accumulates exclusively pelargonidin glycosides in the petals. Abbreviations: ANS, anthocyanidin synthase; CHI, chalcone isomerase; CHS, chalcone synthase; DFR, dihydroflavonol 4-reductase; F3H, flavanone 3-hydroxylase; F3'H, flavonoid 3'-hydroxlase; F3'5'H, flavonoid 3',5'-hydroxlase; FLS, flavonol synthase; FSII, flavone synthase.