Rhizobial Purine Metabolism and Nodule Development

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It is well documented that rhizobial purine auxotrophs are incapable of eliciting complete nodule development and symbiotic nitrogen fixation. Recent work in Dr. Noel's laboratory suggests that the underlying cause of the symbiotic defect is inability to produce ribosyl-5-aminoimidazole-4-carboxamide (AICAR), an intermediate in the pathway. The outlined project is to substantiate further the original observations, to test the hypothesis that AICAR is an infection-thread determinant, and to define this role more clearly. The experiments probe the uptake and fate of AICAR in the bacteria and the possibility that AICAR affects the plant directly. They will document the AICAR stimulated enhancement of nodule development by microscopic analysis of anatomy and electrophoretic analysis of proteins. The effect of host roots and root exudate on bacterial purine and AICAR metabolism will be analyzed, mainly by tracer experiments in which labelled compounds are separated by a versatile thin- layer chromatography technique of great resolving power. Metabolic changes in the infectible region of the root will be analyzed after challenging the plant with the most likely bacterial mediator of the AICAR effect. %%% The establishment of the symbiotic association between nitrogen fixing bacteria and the roots of legumes is extremely important to agriculture. It is also of interest for an understanding of how signals are passed from one organism to another.