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Respiratory and Nitrogenase Activities of Soybean Nodules Formed by Hydrogen Uptake Negative (Hup^–) Mutant and Revertant Strains of Rhizobium japonicum Characterized by Protein Patterns ¹

Laboratory for Nitrogen Fixation Research, Oregon State University, Corvallis, Oregon 97331

Rates of respiratory CO₂ loss and nitrogenase activities of H₂ uptake-negative mutant strains and H₂ uptake-positive revertant strains of Rhizobium japonicum have been investigated. Two-dimensional gel protein patterns of bacteroids formed by inoculation of soybeans (Glycine max L.) with these two strains show that they are closely related and revealed only one obvious difference between them. On the basis of molecular weight standards, it was concluded that the missing protein spot in the H₂ uptake-negative mutant strain could be caused by a failure of the mutant to synthesize hydrogenase. Nodules formed by the H₂ uptake-negative mutant strain evolved respiratory CO₂ at a rate of about 10% higher than that of nodules formed by the H₂ uptake-positive revertant strain. During short-term experiments employed, rates of both C₂H₂ reduction and ¹⁵N₂ fixation varied considerably among replicate samples and no statistically significant differences between mutant and revertant strains were observed. It was observed that increasing the partial pressure of O₂ over nodules significantly decreased the proportion of nitrogenase electrons allocated to H⁺.

¹ Supported by National Science Foundation Grants PCM 77-08784 and PCM 81-18148; National Institute of Health Biomedical Research Support Grant RR07079; and the Oregon Agricultural Experiment Station from which this is Technical Paper 6358. J.J.D. was supported by the Institut National de la Recherche Agronomique.