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Environmental and Stress Physiology

Effects of Compounds Affecting Calcium Channels on Phytochrome- and Blue Pigment-Mediated Pulvinar Movements of Cassia fasciculata¹

University of Poitiers, Station Biologique de Beau-Site, 25 Faubourg Saint-Cyprien, F-86000, Poitiers, France

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<sub>3</sub> 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.