Catalyzes the 3'-hydroxylation of the flavonoid B-ring to the 3',4'-hydroxylated state. Convert naringenin to eriodictyol and dihydrokaempferol to dihydroquercetin. a 3'-unsubstituted flavone + O2 + reduced [NADPH--hemoprotein reductase] = a 3'-hydroxyflavone + H(+) + H2O + oxidized [NADPH--hemoprotein reductase] Secondary metabolite biosynthesis; flavonoid biosynthesis. High expression in petals and ovaries and to a lower extent in sepals, pedicels, anthers and stems. Not detected in leaves, style or roots. High expression early in flower development and then declines as the corolla becomes fully pigmented and opened. May act as a membrane anchor for localization of other, soluble, flavonoid enzymes to the endoplasmic reticulum. Belongs to the cytochrome P450 family.