Acetylcholine in plants: Presence,metabolism and mechanism of action

Acetylcholine (ACh) has been detected in representatives of many taxonomic groups throughout the plant kingdom. The site of its synthesis in plants is probably young leaves. In some plant species choline acetyltransferase (ChAT) activity has been found. This enzyme showing properties similar to animal ChAT, probably participates in ACh synthesis from its precursors, choline and acetyl-Coenzyme A. Acetylcholinesterase (AChE) activity has also been found in many plant tissues. This enzyme decomposes ACh and exhibits properties similar to animal AChE. The presence of both ChAT and AChE in plant tissues suggests that ACh undergoes similar metabolism in plants as it does in animals. Exogenous ACh affects phytochrome-controlled plant growth and development. Mimicking red light (R), ACh stimulates adhesion of root tips to a glass surface and influences leaf movement and membrane permeability to ions. It also affects seed germination and plant growth. Moreover, ACh can modify some enzyme activity and the course of some metabolic processes in plants. Acetylcholine in the presence of calcium ions (Ca²⁺), like R stimulates swelling of protoplast isolated from etiolated wheat leaves. It is proposed that the primary mechanism of action of ACh in plant cells is via the regulation of membrane permeability to protons (H⁺), potassium ions (K⁺), sodium ions (Na⁺) and Ca²⁺.