Lithium inhibits phytochrome-stimulated nitrate reductase activity and transcript level in etiolated maize leaves

Our earlier work indicated an involvement of signals generated via polyphos phoinositide turnover in phytochrome (Pfr) mediated light stimulation of ni trate reductase (NR) activity. We now show that lithium, an inhibitor in th e cycling of inositol phosphates, inhibits red-right stimulated nitrate ind uced NR activity. The effect of lithium was more pronounced if it was given immediately after red light irradiation than if supplied 1 h after. The in hibition of NR activity by lithium was partially reversed by myo-inositol a nd totally reversed by calcium. Red light stimulated NR transcript level wa s also inhibited by lithium, however, calcium could only partially reverse this effect. In the present system we show that lithium decreased the level of phosphoinositide-bis-phosphate as well as other phosphoinositides in re d light irradiated tissues. These results further suggests an involvement o f calcium and signals produced via turnover of polyphosphoinositides in sig nal transduction in Pfr regulation of NR transcript level and NR activity. (C) 1998 Elsevier Science ireland Ltd. All rights reserved.