Studies on the Genetic Control of a Nitrogenase Component in Leguminous Root Nodules

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Abstract
An attempt was made to determine whether Rhizobium or the host legume carries genetic information required for synthesis of the enzyme complex nitrogenase. No rhizobial mutants were found which could reduce N2. Anaerobically‐grown rhizobial cells contained neither component of nitrogenase. Rhizobium strain 32H1 was used to produce root nodules on Vigna sinensis and Phaseolus aureus. Other V. sinensis plants were inoculated with Rhizobium strain 29C2. The iron‐molybdenum component of nitrogenase (fraction I) from these three combinations was purified by DEAE‐cellulose chromatography and preparative electrophoresis. The final sample formed a single band after analytical electrophoresis on polyacrylamide gel. No differences in mobility were observed between the three nitrogenase samples during short periods of analytical electrophoresis. Longer periods of electrophoresis produced degradative products with similar electrophoretic mobilities from each nitrogenase sample. Amino acid analysis of fraction I samples from the three host‐symbiont combinations suggested that the protein from the V. sinensis‐Rhizobium 29C2 combinations was different from the other two samples. These results are interpreted as preliminary evidence that Rhizobium carries the genetic information for fraction I of nitrogenase.