Effects of Compounds Affecting Calcium Channels on Phytochrome- and Blue Pigment-Mediated Pulvinar Movements of Cassia fasciculata.

Verapamil and nifedipine, known as calcium channel blockers, inhibited the phytochrome-mediated movements induced on Cassia fasciculata leaflets by a light-off signal, whereas they had no effect on the ;blue' pigment-mediated movements induced by a light-on signal. LaCl(3) inhibited both types of reactions, but the inhibition of light-induced opening needed a 10 times higher concentration than that of dark-induced closure. Bay K 8644, an activator of calcium channels, increased the rate of dark-induced closure, whereas it had no effect on the light-induced opening. These data suggest that calcium ions are not mobilized in the same way in the two types of movements: possibly from external stores in the phytochrome-mediated reaction and from internal stores in the ;blue' pigment-mediated reaction.