INDUCTION OF LEAF UNROLLING BY PHYTOCHROME and ACETYLCHOLINE IN ETIOLATED WHEAT SEEDLINGS

Abstract-Phytochrome regulates the unrolling of primary leaf sections from 8-day-old dark-grown wheat ( Triticum aeslivum L. cv. Arminda) seedlings. Red light (R)-stimulated unrolling of leaf sections pretreated in 1 m M ethylene-bis-(β-aminoethylether)- N,N,N',N' -tetraacetic acid (EGTA) if 1 m M CaCl₂ was added during a 30 min treatment period including and following irradiation. Nifedipine at 1 μ M (a Ca²+-channel antagonist) applied 10 min before R prevented the R stimulation of leaf unrolling. The Ca²+-channel agonist Bay K-8644 (1 μ M ) and acetylcholine (ACh, 1 mY M ) stimulated unrolling of leaf sections prewashed in EGTA in darkness, if 1 m M CaCl₂ was present in the medium during a 30 min treatment period. Acetylcholine also induced leaf unrolling in the absence of Ca²+ when 100 μ M NaCl was present in the medium. Apart from ACh, only carbamylcholine out of the choline derivatives tested was active in induction of leaf unrolling in the presence of 1 m M Ca²+. The ACh receptor antagonists, atropine (10 μ M ) AND D-tubocurarine (10 μ M ), nullified the ACh-induced Ca²+- and Na+-dependent leaf unrolling, respectively. Muscarine and nicotine, agonists of ACh, at 1 μ M stimulated leaf unrolling in the presence of Ca²+ and Na+, respectively. The ACh-induced Ca²+-dependent leaf unrolling was reduced by 1 μ M Nifedipine, 10 μ M Li+ and 10 μ M "calmodulin" inhibitor, trifluoperazine (TFP), whereas only TFP was active in the reduction of the Na+-dependent ACh-induced leaf unrolling response. It is proposed that leaf unrolling of dark-grown primary wheat leaves can be regulated by phytochrome and by activation of two different types of ACh receptors.