Assessment of the potency of 1-substituted cyclopropenes to counteract ethylene-induced processes in plants

A study was undertaken to assess the potency of 1-methylcyclopropene (1-MCP) analogues to block the ethylene receptor and thereby inhibit ethylene action. Eight structural analogues of 1-MCP with substitution in the 1-position and a side chain containing 2–10 carbons were synthesized and their potency to inhibit ethylene-induced plant processes was tested on climacteric fruit like avocado, and tomato, on ethylene-induced growth modification in etiolated pea seedlings and on abscission in citrus leaf explants. High concentrations of ethylene were used under conditions which hasten ethylene-induced processes. The results showed differences in the responses of the various tissues tested as related to the concentrations of the inhibitors. Some required much higher concentration to exert the same effect, while some, when applied at the same concentration, blocked the receptor for a longer period of time than the others. Fruits responded differently than other plant organs to the same inhibitor, indicating possible differences in characteristics and availability of the ethylene receptors in the various tissues. The potency of the inhibitors was greatly affected by their molecular structure and size. The highest potency of a given inhibitor was obtained when the treatment was applied before the onset of ethylene action. The relationship between ethylene and the inhibitors was found to be of an apparent non-competitive nature. All the fruits treated with the various inhibitors resumed normal ripening after recovery from the inhibition which is crucial when considering the putative inhibitors for practical use.