Microsomal fractions derived from suspension-cultured chickpea (Cicer arietinum L.) cells induced for phytoalexin biosynthesis catalyzed the monohydroxylation of 4′-methoxyisoflavones (biochanin A and formononetin) in the 2′- and 3′-positions. The reactions depended on NADPH and molecular oxygen. Post-microsomal supernatants or microsomes from non-induced cells are without detectable activity in the hydroxylase assay. 4′-Hydroxyisoflavones (genistein and daidzein) were not hydroxylated to any significant extent. The occurrence of these hydroxylases proceeds concomitantly with the accumulation of two pterocarpan phytoalexins, medicarpin and maackiain, by induced cell cultures. The results are discussed with regard to the biosynthetic sequences in the conversion of isoflavones to pterocarpans.
