The role of calcium ions in phytochrome-controlled swelling of etiolated wheat (Triticum aestivum L.) protoplasts

Protoplasts from dark-grown wheat (Triticum aestivum L.) maintained at a constant osmotic potential at 22°C, were found to swell upon red irradiation (R) and the effect was negated by subsequent far-red light (FR), indicating phytochrome involvement. Swelling only occurred when Ca²⁺ ions were present in the surrounding medium, or were added within 10 min after R. Furthermore, Mg²⁺, Ba²⁺ or K⁺ could not replace this requirement for Ca²⁺. The presence of K⁺ did not enhance the Ca²⁺-dependent swelling response. When the Ca²⁺-ionophore A 23187 was added to the medium, protoplasts swelled in the dark to the same extent as after R. Both the Ca²⁺-channelblocker Verapamil and La³⁺ inhibited R-induced swelling. It is proposed that R causes the opening of Ca²⁺-channels in the plasma membrane. Boyle-van't Hoff analyses of protoplast volume after R and FR are consistent with the conclusion that R irradiation causes changes in membrane properties.Abbreviations EDTA ethylenediaminetetraacetic acid - FR far-red light - nov non-osmotic-volume - Pfr FR-absorbing form of phytochrome - Pr R-absorbing form of phytochrome - R red light