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

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Abstract
In Vallisneria gigantea Graebner mesophyll cells, red light irradiation induces cytoplasmic streaming by decreasing the Ca2+ 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 Ca2+ fluxes across the cell membrane, protoplasts are isolated from the mesophyll cells. Changes in Ca2+ concentration in a solution bathing the protoplasts are monitored by spectrophotometry, using the Ca2+ -sensitive dye murexide. Red light irradiation induces an increase in Ca2+ concentration, which means an efflux of Ca2+ from the protoplasts. Subsequent far-red light irradiation produces a rapid decrease in Ca2+ concentration down to the dark control level; however, this is not observed in the presence of the Ca2+ -channel blocker nifedipine. Vanadate inhibits both the streaming and the Ca2+ efflux induced by red light irradiation. The results suggest that red light and far-red light control Ca2+ movements across the cell membrane, which in turn regulate the streaming.