The objective of this research is to characterize the biochemistry and molecular biology of nitrogen assimilation of alfalfa (Medicago sativa) in symbiosis with the bacterium Rhizobium meliloti, and to determine the effect of the plant host in regulation of nodule formation and nitrogen fixation. The proposed research will test the hypothesis that assimilation of ammonia produced during nitrogen fixation involves the the expression of nodule.specific forms of enzymes of the nitrogen assimilation pathway, and will be pursued through analysis of the expression of genes for phosphoenolpyruvate carboxylase, glutamate synthase, and aspartate amino transferase in alfalfa strains that form nitrogen fixing and non.nitrogen fixing nodules. This research will increase knowledge of plant host contributions to nitrogen fixation. It has the potential to identify mechanisms of coordination of plant and bacterial gene expression involved in this agronomically and economically important process and, indirectly, to increase its efficiency.
