Abstract: In Vicia faba L., root excision could cause a gradual decrease of the transpiration rate without affecting the shoot water potential, provided water could be supplied by other means. The lowed transpiration rate could be restored by acetylcholine. To evaluate the role of acetylcholine in this process, endogenous acetylcholine was identified by field desorption spectroscopy coupled with gas chromatography. It is shown that the acetylcholine-like substance isolated from Vicia faba seedlings exhibited a spectroscopic spectrum similar to that of the authentic acetylcholine and an extract of rat brain. These results demonstrated that acetylcholine is an endogenous substance of Vicia faba seedlings. In addition, a method of pyrolysis gas chromatography was established for determining the concentrations of acetylcholine in plants. It was found that acetylcholine contents in the abaxial epidermis exhibited a close relationship with the leaf transpiration rate and the root statues. It is speculated that acetylcholine may play an important role in the regulation of stomatal movement. This hypothesis was confirmed by the finding that acetylcholine has a stimulatory effect on stomatal aperture in the abaxial epidermis and the acetylcholine esterase inhibitor, neostigmine could increase the susceptibility of stomata to acetylcholine.

Key words: Vicia faba, Acetylcholine, Stomatal movement