Schematic representation of the flavonoid biosynthetic pathway. Enzymes involved in the pathway shown are CHS, chalcone synthase; CHI, chalcone isomerase; F3′H; F3′5′H; F3H, flavanone-3β-hydroxylase; DFR; LDOX; FLS, flavonol synthase; LAR; ANR; and UFGT. Examples for the different hydroxylation patterns of the flavonoid B-ring are given for naringenin (4′-hydroxylated), eriodictyol (3′,4′-hydroxylated), and pentahydroxyflavone (3′,4′,5′-hydroxylated).