PHYTOCHEMICAL AND IMMUNOCYTOCHEMICAL EVIDENCE FOR THE ACCUMULATION OF2'-HYDROXYLUPALBIGENIN IN LUPIN NODULES AND BACTEROIDS

Symbiotic interaction between Rhizobium lupini and Lupinus albus promo tes both qualitative and quantitative changes in the isoflavonoids of root and nodule tissues, These changes were determined by high-pressur e liquid chromatography and radiolabeling with L-[U-C-14]phenylalanine , Root nodules from mature lupin plants accumulate prenylated derivati ves of both genistein and 2'-hydroxygenistein, with the predominance o f 2'-hydroxylupalbigenin, a diprenylated isoflavone. Immunogold locali zation, using specific polyclonal immunoglobulin Gs, revealed an assoc iation of 2'-hydroxylupalbigenin with the establishment of early symbi otic structures, as well as with the bacteroids themselves, These resu lts, together with the fact that prenylated isoflavonoids significantl y reduce the in vitro growth rate of a number of Rhizobium species, su ggest that 2'-hydroxylupalbigenin may be involved in the symbiotic ass ociation of L, albus and R, lupini. This hypothesis is discussed in re lation to the putative biological significance of prenylated isoflavon oids.