Promotive Effect of C18-Unsaturated Fatty Acids on the Abscission of Bean Petiole Explants

摘要

The abscission-promoting effects of C18-unsaturated fatty acids were studied in bean(Phaseolus vulgarisL. cv. Masterpiece) petiole explants with the junction between the petiole and the pulvinus in the primary leaves in the light. Linolenic, linoleic and oleic acids promoted the abscission of the explants in the light. Linolenic acid was the most effective among the compounds tested and its promotive effect was evident without any accompanying increase in the production of ethylene from the explants, as compared with non-treated explants. Linolenic acid is easily converted to its hydroperoxide during the incubation with explants, as indicated by the formation of the conjugated diene and the generation of ethane. The production of ethylene from the explants treated with linolenic acid was completely inhibited by the addition of aminoethoxyvi-nylglycine (AVG), but large amounts of ethane were still generated. The promotive effect of linolenic acid was almost eliminated by the addition of scavengers of free radicals. Hydrogen peroxide andtert-butyl hydroperoxide promoted abscission in the light. From these results, we concluded that the abscission-promoting effect of linolenic acid are not mediated by the effect of ethylene but by the effect of its hydroperoxide, while the well-established pathway for the biosynthesis of ethylene from S-adenosylmethionine to ethylene, via 1-aminocyclopropane-l-carboxylic acid (ACC), was apparently operative.