Light-Affected Ca2+ Fluxes in Protoplasts from Vallisneria Mesophyll Cells

In Vallisneria gigantea Graebner mesophyll cells, red light irradiation induces cytoplasmic streaming by decreasing the Ca(2+) concentration in the cytoplasm, while far-red light irradiation inhibits it by increasing the concentration (S Takagi, R Nagai 1985 Plant Cell Physiol 26: 941-951). To examine the effects of light irradiation on Ca(2+) fluxes across the cell membrane, protoplasts are isolated from the mesophyll cells. Changes in Ca(2+) concentration in a solution bathing the protoplasts are monitored by spectrophotometry, using the Ca(2+) -sensitive dye murexide. Red light irradiation induces an increase in Ca(2+) concentration, which means an efflux of Ca(2+) from the protoplasts. Subsequent far-red light irradiation produces a rapid decrease in Ca(2+) concentration down to the dark control level; however, this is not observed in the presence of the Ca(2+) -channel blocker nifedipine. Vanadate inhibits both the streaming and the Ca(2+) efflux induced by red light irradiation. The results suggest that red light and far-red light control Ca(2+) movements across the cell membrane, which in turn regulate the streaming.