Acclimation of Soybean Nodules to Changes in Temperature.

This study examines how O2 status, respiration rate, and nitrogenase activity of soybean (Glycine max) nodules acclimate to short-term (<30 min) temperature change from 20 to 15[deg]C or from 20 to 25[deg]C. Acclimation responses were compared between nodules on uninhibited plants and nodules that were severely O2 limited by exposure to Ar:O2. In uninhibited nodules the decrease in temperature caused a rapid inhibition of nitrogenase activity followed by partial recovery, whereas in Ar:O2-inhibited nodules the temperature decrease caused a minor stimulation followed by a gradual decline in nitrogenase activity. In contrast, the temperature increase caused a gradual increase in nitrogenase activity in uninhibited nodules, and an initial inhibition followed by a rapid rise in Ar:O2-inhibited nodules. In both uninhibited and Ar:O2-inhibited nodules, temperature had only minor effects on the degree to which nitrogenase activity was limited by O2 supply, but nodule permeability to O2 diffusion was greater at 25[deg]C, and less at 15[deg]C, than that measured at 20[deg]C. On the basis of these data, we propose that temperature change alters the nodule's respiratory demand and that the observed changes in nodule permeability occur to maintain control over the infected cell O2 concentration as the O2 demand increases at high temperature or decreases at low temperature.