Role of calcium channels in phytochrome-mediated regulation of gravitropicresponse

The effect of the inhibitors of calcium channels on red-light (R)-mediated inhibition of gravitropic bending was studied in excised wheat (Triticum ae stivum L.) coleoptiles. The effect of a short R pulse (2 min) preceding the gravitropic stimulation was completely alleviated by a similar pulse of fa r-red light (FR), when the latter preceded the gravitropic stimulation and the delay between R and FR pulses did not exceed 20 min. Plant memory of th e R pulse lasted up to 40 min. Neither R nor FR exerted any effect on the g ravitropic reaction when applied after gravitropic stimulation. Treatment w ith 1 muM of verapamil, LaCl3, GdCl3, or ruthenium red before the gravitrop ic stimulation prevented or released the R-exerted suppression of the gravi tropic response (GR). The GR in coleoptiles is apparently regulated by the phytochrome system at the induction phase and involves calcium channels.