Evidence for the involvement of plasma-membrane-bound nitrate reductase in signal transduction during blue-light stimulation of nitrate uptake in Chlorella saccharophila

Research paper by Christine Stöhr, Ulrich Glogau, Michael Mätschke, Rudolf Tischner

Indexed on: 01 Nov '95Published on: 01 Nov '95Published in: Planta


Nitrate uptake in Chlorella saccharophila (Krüger) Nadson was found to be stimulated by blue light, leading to a doubling of the rate. In the presence of background red light (300 μmol photons · m-2 · s-1), only 15–20 μmol photons · m-2 · s-1 of blue light was sufficient to saturate this increased uptake rate. Incubation of Chlorella cells with anti-nitrate-reductase immunoglobulin-G fragments inhibited blue-light stimulation. However, ferricyanide (10 μM) doubled and dithiothreitol (100 μM) inhibited the stimulatory effect of blue light. Among the protein-kinase inhibitors used, only staurosporine (10 μM) prevented the blue-light stimulation. Phosphatase inhibitors were without effect and sodium vanadate totally inhibited nitrate uptake, pointing to an involvement of the plasma-membrane ATPase. Preincubation of the cells with calmodulin antagonists or calcium ionophores did not significantly reduce blue-light stimulation of nitrate uptake. The data are discussed with regard to transduction of the signal for blue-light stimulation of nitrate uptake and the possibility that the plasma-membrane-bound nitrate reductase is the blue-light receptor.