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

Abstract

Our earlier work indicated an involvement of signals generated via polyphosphoinositide turnover in phytochrome (Pfr) mediated light stimulation of nitrate reductase (NR) activity. We now show that lithium, an inhibitor in the cycling of inositol phosphates, inhibits red-light stimulated nitrate induced NR activity. The effect of lithium was more pronounced if it was given immediately after red light irradiation than if supplied1 h after. The inhibition of NR activity by lithium was partially reversed by myo-inositol and totally reversed by calcium. Red light stimulated NR transcript level was 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 red light irradiated tissues. These results further suggests an involvement of calcium and signals produced via turnover of polyphosphoinositides in signal transduction in Pfr regulation of NR transcript level and NR activity.