Changes in acetylcholine levels following leaf wilting and leaf recovery by heat stress in plant cultivars

To study for physiological role of acetylcholine (ACh) in plant cultivars of yard-long bean, cucumber and radish, the relationship between ACh levels and leaf response with leaf wilting and its recovery by heat stress was compared between cultivars adapted to the tropical zone (tropical evergreen lowland rain forest zone) and to the temperate zone. Potted-plants were exposed to a jet air of warm (30°C) air for 2 min or 3 min using a hair-dryer. Acetylcholine content was determined by a pyrolysis gas chromatograph equipped with a flame ionization detector. Cultivars from the tropical zone were distinguished by low degree of wilting and a rapid recovery from wilting. And then, the amount of ACh in tissues was more than 2-10 fold in leaf, stem, node, root than that of cultivars from the temperate zone without stress. Futhermore, ACh content after heat stress changed significantly in leaf, stem, pulvini, node, leaf-blade, petiole and root of plants. Little to no change in ACh content following leaf wilting and recovery by stress was found in cultivars adapted to the temperate zone. Thus, a quick leaf response with leaf wilting and its recovery in cultivars from the tropical zone may be controlled by a rapid ACh movement resulting the enzyme activity of ACh hydrolysis in pulvini, node or root of plants.