ABSTRACT
Acetylcholine (ACh) is a neurotransmitter that also influences a large number of physiological functions in animals as well as plants. Research in recent decades has firmly established that acetylcholine affects regeneration and differentiation in various neuronal and non-neuronal tissues in animals. There are experimental evidences that suggest that ACh plays an important role in root and shoot morphogenesis in tomato. ACh induces rooting in leaf explants of tomato (Lycopersicon esculentum Miller var. Pusa Ruby). It also promotes secondary root formation. The roots originating from the midrib of leaf explants resemble taproot. ACh causes a decrease in shoot and callus formation in leaf explants of tomato when cultured on shoot regeneration medium. The breakdown products, choline and acetate, were ineffective even at 10−3 M concentration. ACh has a natural role in tomato morphogenesis because exogenous application of an inhibitor of ACh hydrolysis (neostigmine) could mimic the effect of ACh. Neostigmine, if applied along with ACh, potentiated the effect of ACh. Inhibitors of enzymatic hydrolysis of ACh, neostigmine and physostigmine, also suppress callogenesis and caulogenesis. The explants cultured on neostigmine-fortified medium showed a decline in the activity of acetycholinesterase (AChE-an ACh-hydrolyzing enzyme) activity. Nicotine, an agonist of nicotinic acetylcholine receptor in animals, simulates ACh action in a plant system, suggesting that a similar molecular mechanism is operative in both animal and plant cells. These results strongly support the role of ACh as a natural regulator of morphogenesis in tomato plants.
