Salt stress induces a decrease in the oxygen uptake of soybean nodules and in their permeability to oxygen diffusion

The effects of short‐term NaCl‐salinity on nodules of soybean (Glycine max L. cv. Kingsoy) were studied on hydroponically‐grown plants. Both acetylene reducing activity (ARA) and nodule respiration (O2 uptake and CO2 evolution) were immediately inhibited, and the stimulation of them by rising the external partial pressure of O2 (pO2) was diminished by the application of 0.1 M NaCl in the nutrient solution. The permeability of the nodule to O2 diffusion, estimated by O2 consumption or CO2 evolution, was significantly lower in the stressed nodules than in the cootrol ones. The respiratory quotient of intact nodules and the ethanol production of excised nodules were increased by low pO2 and by salt stress. These data confirm that in salt‐stressed soybean nodules, O2 availability is reduced and fermentative pathways are stimulated.