Photoreversible calcium fluxes induced by phytochrome in oat coleoptile cells

The chromometallic dye murexide was used to measure photoreversible Ca fluxes in apical tips of etiolated oat coleoptiles and in suspension cultures of protoplasts derived from the coleoptile segments. Phytochrome presence in the protoplasts was indicated by a repeatably photoreversible ΔA(725-800 nm) of >0.001 A $\text{centimeters}^{-1}$, recorded on a dual wavelength spectrophotometer. Concentrations of Ca in the solution bathing the cells were observed to change photoreversibly, red irradiation inducing an increase in the medium Ca concentration and subsequent far-red irradiation inducing a decrease down to near dark control levels. These changes could be measured in media with or without exogenously added Ca. Protoplasts from green primary leaves of oat, which had no spectrophotometrically detectable phytochrome, showed no photoreversible Ca fluxes when measured by the same method. These data imply that red light induces an efflux of Ca from phytochrome-containing cells and that far red light can reverse this change by promoting a Ca reentry into these cells.