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

摘要

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⁺.