Evidence for the Regulation of Phytochrome-mediated Processes in Bean Roots by the Neurohumor, Acetylcholine

Using pharmacological and chromatographic techniques, it was shown that acetylcholine was present in all organs of both light- and dark-grown mung bean seedings (Phaseolus aureus). The highest concentrations were found in tissues containing active growing points: buds and secondary roots. Within 4 minutes, red light caused an increase in the efflux of acetylcholine from secondary root tips as well as a significant increase in the endogenous titer. Four minutes of subsequent far red light reduced the latter to a level comparable to that in the dark.Acetylcholine, given for 4 minutes in the dark, was able to substitute for red light in reducing the formation of secondary roots, inducing increased H(+) efflux, and causing the root tips to adhere to a negatively charged glass surface. Acetylcholine-esterase and atropine inhibited the latter phenomenon, whereas eserine inhibited the far red-induced release from glass. THESE AND OTHER DATA SUPPORT THE CONCLUSION THAT ACETYLCHOLINE FUNCTIONS IN MUNG BEAN ROOTS AS IT DOES IN ANIMAL SYSTEMS: by mediating changes in ion flux across cell membranes. It also seems probable that acetylcholine acts as a local hormone which regulates these phytochrome-mediated phenomena.