Physiological responses of soybean plants grown in a nitrogen-free or energy limited environment

Soybean (Glycine max L.] Merr.) seedlings grown in the absence of combined N and in an Ar:O₂ (79:21, volume/volume) atmosphere had greater seedling and nodule mass, threefold higher acetylene reducing activity per gram fresh weight nodules, no observable increase in nitrogenase Fe-protein, and a higher energy charge than did control plants. A sharp fall in acetylene reducing activity and energy charge accompanying stem-girdling was prevented by exogenous succinate, a result consistent with a path from the roots to the nodule other than via the phloem.