Phytochemical and Immunocytochemical Evidence for the Accumulation of 2'-Hydroxylupalbigenin in Lupin Nodules and Bacteroids. Hubert Gagnon. Department of Biology, Concordia University, 1455 De Maisonneuve Boulevard W., Montreal, Quebec, Canada H3G 1M8. Jacques Grandmaison, and Ragai K. Ibrahim. Department of Biology, Concordia University, 1455 De Maisonneuve Boulevard W., Montreal, Quebec, Canada H3G 1M8. MPMI 8:131-137. Accepted 31 October 1994. Copyright 1995 The American Phytopathological Society.

Symbiotic interaction between Rhizobium lupini and Lu-pinus albus promotes both qualitative and quantitative changes in the isoflavonoids of root and nodule tissues. These changes were determined by high-pressure liquid chromatography and radiolabeling with L-[U-l4C]phenyl-alanine. Root nodules from mature lupin plants accumulate prenylated derivatives of both genistein and 2'-hydroxy-genistein, with the predominance of 2'-hydroxylupalbi-genin, a diprenylated isoflavone. Immunogold localization, using specific polyclonal immunoglobulin Gs, revealed an association of 2'-hydroxylupalbigenin with the establishment of early symbiotic structures, as well as with the bacteroids themselves. These results, together with the fact that prenylated isoflavonoids significantly reduce the in vitro growth rate of a number of Rhizobium species, suggest that 2'-hydroxylupalbigenin may be involved in the symbiotic association of L. albus and R. lupini. This hypothesis is discussed in relation to the putative biological significance of prenylated isoflavonoids