ABSTRACT
Components of the cholinergic system—acetylcholine, acetylcholinesterase, and acetylcholine receptors—are the principal components of the nerve transmission in animals. Plants, though nerveless, have long been known to possess most of the components of the cholinergic system. Plants also have a repertoire of chemicals that inhibit various components of the acetylcholine system. A hitherto overlooked fact is that many of these anticholinergic chemicals present in some plants act as allelochemicals and help the plants to dominate their habitat by affecting the growth of other plants in their vicinity. Since the target sites of most of the allelochemicals in victim plants are unknown, the possibility of cholinergic chemicals as allelochemicals opens new areas of research in plant biology. We have shown earlier that the extract of Cyperus rotundus inhibits acetylcholinesterase activity in electric eel, wheat, and tomato and that it also inhibits germination and growth of root and shoot in tomato and wheat. Now, we present evidence that the methanolic extracts of 45 weeds, including invasive weeds like Lantana camara, Ageratum conyzoides, Argemonemexicana, Ranunculus sceleratus, and Prosopis juliflora contain very high levels of anticholinesterases. Anticholinesterases block the enzyme acetylcholinesterase, resulting in an increase in the levels of acetylcholine in the system. We propose that cholinergic chemicals act as allelochemicals in plants.
