Fig. 1

Biosynthesis pathway of quercetin in plants. (PAL) Phenylalanine ammonia-lyase. (C4H) Cinnamate 4-hydroxylase. (4CL) 4-coumarate-CoA ligase. (CHS) Chalcone synthase. (CHI) Chalcone isomerase. (F3H) Flavanone 3-hydroxylase. (F3′H) Flavonoid 3′-hydroxylase. (FLS) Flavonol synthetase.