5-Hydroxytryptamine affects turnover of polyphosphoinositides in maize and stimulates nitrate reductase in the absence of light.

Incubation of etiolated maize leaves for 5 min in 5-hydroxytryptamine increased phosphatidylinositol-4,5-bisphosphate levels but on longer incubation its level decreased and a corresponding increase in inositol-trisphosphate was observed. The increase in phosphatidylinositol-4,5-bisphosphate by 5-hydroxytryptamine was similar to that obtained after short irradiation of leaves with red light. Nitrate-inducible and phytochrome-stimulated enzyme nitrate reductase could be stimulated in darkness if the leaves were incubated in the presence of nitrate and 5-hydroxytryptamine. These results indicate that one of the initial events in phytochrome-mediated enzyme stimulation could be through the generation of 'signals' from the turnover of the phosphoinositide cycle.