FLAVONOID PROBES FOR RHIZOBIUM/LEGUME NODULATION STUDIES

NITROGEN IS A LIMITED MINERAL NUTRIENT IN MANY AGRONOMIC SYSTEMS. LEGUMINOUS CROPS SUCH AS SOYBEAN AND ALFALFA USE BOTH SOIL NITROGEN AND, WHEN SUITABLE STRAINS OF THE NITROGEN-FIXING MICROSYMBIONTS BRADYRHIZOBIUM AND RHIZOBIUM ARE AVAILABLE, ATMOSPHERIC NITROGEN. IT HAS BEEN ESTIMATED THAT THE 50 MILLION HECARES OF CULTIVATED GRAIN AND FORAGE LEGUMES IN THE UNITED STATES OBTAINED MORE THAN 6 MILLION METRIC TONS OF NITROGEN ANNUALLY FROM RHIZOBIAL NITROGEN REDUCTION EVEN THOUGH THE INDIGENOUS RHIZOBIA ARE FREQUENTLYINEFFICIENT NITROGEN REDUCERS. THE SYMBIOTIC RHIZOBIA/HOST NITROGEN-FIXING RELATIONSHIP IS CHARACTERIZED BY MICROSYMBIONT COLONIZATION OF HOST DERIVED ROOT NODULES. THESE NODULES DEVELOP IN A COMPLEX SERIES OF STEPS WHICH AREBELIEVED TO BE INITIATED BY THE ACTION OF PLANT-DERIVED FLAVONOIDS ON THE BACTERIUM THROUGH ITS NODULATION GENES ANDGENE PRODUCTS. THE SIGNIFICANCE OF THE FLAVONOIDS IN SYMBIOSIS SUGGESTS THAT THEY MAY BE OF VALUE IN THE MANIPULATION OF THE SYMBIOTIC PROCESS TO IMPROVE NITROGEN- REDUCTION EFFICIENCY AND, AS A CONSEQUENCE, CROP YIELD. THIS PROJECT IS DIRECTED TO DEVELOPMENT AND APPLICATION OF THE BICHEMICAL TOOLS REQUIRED TO DEVELOP A MORE COMPLETE MODEL OF THE FLAVONOID/SYMBIOSIS RELATIONSHIP. THE PROPOSED RESEARCH HAS CURRENT POTENTIAL FOR USE BY BOTH THE PUBLIC AND PRIVATE SECTOR RESEARCH COMMUNITIES IN THE ELUCIDATION OF THE SYMBIOTIC RHIZOBIUM/LEGUME NITROGEN- FIXING PROCESS. THE POTENTIAL POST APPLICATIONS OF THIS PROJECT ARE THE DESIGN AND DEVELOPMENT OF PRACTICAL AGRICULTURAL METHODS FOR INCREASING THE EFFICIENCY OF NITROGEN-FIXATION THROUGH MODIFICATION OF THE RHIZOBIUM/ MESSENGER/LEGUME INTERACTION AND DEVELOPMENT OF A GREATER UNDERSTANDING OF MICROBE/PLANT INTERACTIONS. THIS LINE OF RESEARCH COULD HAVE A SIGNIFICANT IMPACT ON THE AGRICULTURALCONTROL OF CROP DISEASES.