CONTROL OF THE LIGNIFICATION IN LUPINUS BY GENISTEIN ACTING AS SUPEROXIDE SCAVENGER AND INHIBITOR OF THE PEROXIDASE-CATALYZED OXIDATION OF CONIFERYL ALCOHOL

Peroxidase activity in vascular tissues of lupin (Lupinus albus cv. Multolupa) hypocotyls is mainly located in phloem, cambial initial and xylem cell walls. However, unlike xylem tissues, phloem and cambial cells do not lignify. For this reason, the effect of genistein (5,7,4'-trihydroxyisoflavone), a constitutive lupin isoflavone found in the cell walls of phloem and cambial cells, on the oxidation of coniferyl alcohol by cell wall acidic peroxidases from lupin hypocotyls was studied. The results showed that genistein, used at mu M concentrations, was a potent inhibitor of the peroxidase-catalyzed oxidation of coniferyl alcohol, the first step in lignin biosynthesis. Likewise, genistein also acted as a superoxide scavenger, when the superoxide anions were generated in a phenazin methosulphate-NADH system and determined by the superoxide dismutase-sensitive reduction of nitroblue tetrazolium. These results are discussed in light of a possible integrated control by genistein of cell wall phenolic cross-linking reactions in Lupinus.