Nitrate Assimilation Function of Yellow Lupine Root Nodules?

Low nitrate assimilation activity of the root nodules was demonstrated by assaying the activities of nitrate reductase, glutamate synthetase, glutamate dehydrogenase, and asparagine synthetase as well as the kinetics of 14C-labeled sucrose incorporation in the amino acids and amides of the cortex and the bacteroid-containing root nodule zones. Irrespective of the exogenous nitrogen concentration (0, 11.2, or 25 mM NO-3), nitrate concentration in the nodules was low as compared to the plant roots, leaves, and stems. This allowed us to propose the presence of structural and/or metabolic barriers in the nodules limiting nitrate transport and assimilation in the nodule.