Entry of Oxygen and Nitrogen into Intact Soybean Nodules

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Abstract
The apparent nitrogenase activity of soybean root nodules is reduced approximately 70% upon nodul detachment. By increasing the partial pressure of oxygen in the assay vessel from approximate∧ 0.2 to 0.5 atm, the nitrogenase activity of detached nodules is restored to the original attached level. Oi the other hand, maximal assayable nitrogenase activity of nodules attached to the intact soybean plan is achieved in the presence of 0.2–0.3 atm of oxygen. Exposure of attached nodules to 0.5 atm oxygei causes a decrease in nitrogenase activity seemingly due to in activation of nitrogenase. These and othe data suggest that, upon detachment, the entry of oxygen into the nodules is impaired. A model for th regulation of airflow into attached and detached nodules is presented. This model is also consisten with response of nodule activity to water stress.