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 mM ethylene‐bis‐(β‐aminoethylether)‐N,N,N',N'‐tetraacetic acid (EGTA) if 1 mM CaCl2 was added during a 30 min treatment period including and following irradiation. Nifedipine at 1 μM (a Ca2+‐channel antagonist) applied 10 min before R prevented the R stimulation of leaf unrolling. The Ca2+‐channel agonist Bay K‐8644 (1 μM) and acetylcholine (ACh, 1 mYM) stimulated unrolling of leaf sections prewashed in EGTA in darkness, if 1 mM CaCl2 was present in the medium during a 30 min treatment period. Acetylcholine also induced leaf unrolling in the absence of Ca2+ when 100 μM 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 mM Ca2+. The ACh receptor antagonists, atropine (10 μM) AND D‐tubocurarine (10 μM), nullified the ACh‐induced Ca2+‐ and Na+‐dependent leaf unrolling, respectively. Muscarine and nicotine, agonists of ACh, at 1 μM stimulated leaf unrolling in the presence of Ca2+ and Na+, respectively. The ACh‐induced Ca2+‐dependent leaf unrolling was reduced by 1 μM Nifedipine, 10 μM Li+ and 10 μM“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.