ACCLIMATION OF SOYBEAN NODULES TO CHANGES IN TEMPERATURE

This study examines how O-2 status, respiration rate, and nitrogenase activity of soybean (Glycine max) nodules acclimate to short-term (< 3 0 min) temperature change from 20 to 15 degrees C or from 20 to 25 deg rees C. Acclimation responses were compared between nodules on uninhib ited plants and nodules that were severely O-2 limited by exposure to Ar:O-2. In uninhibited nodules the decrease in temperature caused a ra pid inhibition of nitrogenase activity followed by partial recovery, w hereas in Ar:O-2-inhibited nodules the temperature decrease caused a m inor stimulation followed by a gradual decline in nitrogenase activity . in contrast, the temperature increase caused a gradual increase in n itrogenase activity in uninhibited nodules, and an initial inhibition followed by a rapid rise in Ar:O-2-inhibited nodules. In both uninhibi ted and Ar:O-2-inhibited nodules, temperature had only minor effects o n the degree to which nitrogenase activity was limited by O-2 Supply, but nodule permeability to O-2 diffusion was greater at 25 degrees C, and less at 15 degrees 0, than that measured at 20 degrees 0. On the b asis of these data, we propose that temperature change alters the nodu le's respiratory demand and that the observed changes in nodule permea bility occur to maintain control over the infected cell O-2 concentrat ion as the O-2 demand increases at high temperature or decreases at lo w temperature.