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 Ca(2+) ions were present in the surrounding medium, or were added within 10 min after R. Furthermore, Mg(2+), Ba(2+) or K(+) could not replace this requirement for Ca(2+). The presence of K(+) did not enhance the Ca(2+)-dependent swelling response. When the Ca(2+)-ionophore A 23187 was added to the medium, protoplasts swelled in the dark to the same extent as after R. Both the Ca(2+)-channelblocker Verapamil and La(3+) inhibited R-induced swelling. It is proposed that R causes the opening of Ca(2+)-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.
Department of Plant Physiological Research, Agricultural University, Generaal Foulkesweg 72, NL-6703 BW, Wageningen, The Netherlands.
M E
ME
Bossen
H H
HH
Dassen
R E
RE
Kendrick
W J
WJ
Vredenberg