Effect of temperature on h(2) evolution and acetylene reduction in pea nodules and in isolated bacteroids.

Nitrogenase (EC 1.7.99.2) activity in pea (Pisum savitum) nodules formed after infection with Rhizobium leguminosarum (lacking uptake hydrogenase) was measured as acetylene reduction, H(2) evolution in air and H(2) evolution in Ar:O(2). With detached roots the relative efficiency, calculated from acetylene reduction, showed a decrease (from 55 to below 0%) with increasing temperature. With excised nodules and isolated bacteroids similar results were obtained. However, the relative efficiency calculated from H(2) evolution in Ar:O(2) was unaffected by temperature. Measurements on both excised nodules and isolated bacteroids showed a marked difference between acetylene reduction and H(2) evolution in Ar:O(2) with increased temperature, indicating that either acetylene reduction or H(2) evolution in Ar:O(2) are inadequate measures of nitrogenase activity at higher temperature.