ALFALFA ROOT FLAVONOID PRODUCTION IS NITROGEN REGULATED

Flavonoids produced by legume roots are signal molecules acting both a s chemoattractants and nod gene inducers for the symbiotic Rhizobium p artner. Combined nitrogen inhibits the establishment of the symbiosis. To know whether nitrogen nutrition could act at the level of signal p roduction, we have studied the expression of flavonoid biosynthetic ge nes as well as the production of flavonoids in the roots of plants gro wn under nitrogen-limiting or nonlimiting conditions. We show here tha t growth of the plant under nitrogen-limiting conditions results in th e enhancement of expression of the flavonoid biosynthesis genes chalco ne synthase and isoflavone reductase and in an increase of root flavon oid and isoflavonoid production as well as in the Rhizobium meliloti n od gene-inducing activity of the root extract. These results indicate that in alfalfa (Medicago sativa L.) roots, the production of flavonoi ds can be influenced by the nitrogen nutrition of the plant.