Ammonium inactivation of nitrate reductase in Lemna minor L.

The addition of ammonium to nitrate induced plants of Lemna minor L. brings about a rapid loss in extractable nitrate reductase activity. This inactivation is reversible both in vivo and in vitro. Inhibitors of RNA and protein synthesis do not protect nitrate reductase against ammonium inactivation. It is suggested that factors, in addition to ammonium ions, are components of the inactivating system. Inactivation may involve some form of protein-protein interaction. The physiological significance of rapid ammonium inactivation of nitrate reductase is discussed.