Induction of NADH-dependent nitrate reductase activity in cucumber cotyledons by de novo synthesis of the enzyme

Abstract

Summary Under non-inducing conditions, nitrate reductase (EC 1.6.6.1, NADH: nitrate oxidoreductase) is not detectable by enzymatic and immunological methods in cotyledons of cucumber (Cucumis sativus L.). Nitrate reductase activity induced by nitrate or pR stress is due to de novo synthesis of nitrate reductase apoprotein, as was shown by inhibition assays using antibodies directed against nitrate reductase of tobacco (Nicotiana tabacum). During the fast induction by ammonium nitrate, enzymatically inactive nitrate reductase apoprotein is accumulated in the middle phase of the induction curve. There is no accumulation of inactive nitrate reductase during the retarded induction by citrate at pR 2.5.