Increase in permeability to oxygen and in oxygen uptake of soybean nodules under limiting phosphorus nutrition

Abstract

The O2 uptake of soybean roots nodulated with Bradyrhizobium japonicum strain PJ 17 and its response to external oxygen pressures (pO2) were measured in situ, 40–45 days after sowing (DAS). on plants grown hydroponically with either limiting (low‐P) or non‐limiting (control) orthophosphate (P1) supplied weekly. At this age. school mass, nodule mass and number of nodules of low‐P plants were respectively 35. 14 and 26% of those of control plants, whereas root mass was not significantly affected by P nutrition. The mean individual mass and size of nodules were also lower in low‐P plants. The rate of O2 or growth and maintenance of root and nodule tissue of low‐P plants was 35% of control values. By contrast. the nodule nitrogenase‐linked O2 uptake and the nodule permeability to O2 of low‐P plants were respectively 210 and 190% of those of control plants at ambient pO2 However. P deficiency did not significantly affect the specific acetylene reducing activity of nodule nitrogenase at 45 DAS nor the ratio of whole plant N fixed to nodule mass at 75 DAS. It is argued that P deficiency induces an increase in nodule O2 uptake per electron transfered by nitrogenase and an alteration in the structural features of nodules that are related to permeability to O2.