The effect of a calcium‐channel antagonist, nifedipine and agonist, Bay K‐8644, on the phytochrome‐controlled swelling of etiolated wheat protoplasts

Abstract

The effect of external Ca2+ and Ca2+‐channel modulators on the phytochrome‐controlled swelling of etiolated wheat (Triticum aestivum L. cv. Arminda) mesophyll protoplasts has been studied. The red light (R)‐stimulated swelling of the protoplasts requires Ca2+ in the surrounding medium and maximum response was observed in a medium containing I mM CaCI2. Far‐red light (FR) irradiation of protoplasts in the presence or absence of Ca2+ does not influence the protoplast volume. The Ca2+‐channel antagonist nifedipine prevents R‐induced protoplast swelling at very low concentrations (0.1 μM). The Ca2+ ‐channel agonist Bay K‐8644 stimulates the swelling of protoplasts incubated in darkness or irradiated with FR. Action of nifedipine depends on whether it is applied before or after the R pulse. The results are compatible with the hypothesis that phytochrome controls the activity of dihydropyridine‐sensitive L‐type Ca2+ channels.