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 siliques and to a lower extent in stems, flowers and senescing leaves. By UV light treatment. May act as a membrane anchor for localization of other, soluble, flavonoid enzymes to the endoplasmic reticulum. Belongs to the cytochrome P450 family.