Acetylcholine as a Signaling System to Environmental Stimuli in Plants : I. Contribution of Ca²⁺ in heat-stressed Zea mays seedlings

Abstract

Plant growth is influenced by transport of water, ions and hormones under various environmental stresses. If acetylcholine (ACh) mediates the opening and/or closing of ion channels in plants just as in animal systems, it is important to detect such evidence. The effect of heat stress on the acetylcholinesterase (AChE) activity and Ca²⁺ as a trigger of ACh release can be determined in selected organs of dark grown Zea mays seedlings. The enzyme activity in the coleoptile node was 3-7 fold higher than that of other organs. By heat stress, the AChE activity increased about 20% in the node. Cytochemical evidence for AChE activity was found only in the node. This reaction appeared in the cortical cells around the vascular system. After heat stress, the localization of AChE was radicaly changed in the node. AChE activity was detected in all endodermal cells surrounding the vascular system. Further, fluorescent labeled Ca²⁺ in the node was identified in cortex cells around the vascular system, epidermis and adhering peripheral cortical cells with a laser scanning confocal microscope. Following heat stress, Ca²⁺ was found more in the cortical cells and whole endodermal cells between the cortex and stele. The appearance of AChE and Ca²⁺ in endodermal cells after heat stress seems to be correlated with ACh function controlling ion channels.