Rapid modulation of nitrate reductase in leaves and roots: Indirect evidence for the involvement of protein phosphorylation/dephosphorylation

Nitrate reductase activity (NRA; NADH-nitrate reductase, E.C.1.6.6.1) has been measured in extracts from leaves of spinach (Spinacia oleracea L.) in response to rapid changes in illumination, or supply of CO 2 or oxygen. Measured in buffers containing magnesium, NRA from leaves decreased in the dark and increased again upon illumination. It decreased also, when CO 2 was removed in continuous light, and was reactivated when CO 2 was added. Nitrate reductase (NR) from roots of pea (Posum sativum L.) was also rapidly modulated in vivo. It increased under anaerobiosis and decreased in air or pure oxygen