Inhibition of Auxin-Induced Ethylene Production by Lycoricidinol

Lycoricidinol, a natural growth inhibitor isolated from bulbsof Lycoris radiata Herb. strongly suppressed auxin-induced ethyleneproduction from the hypocotyl segments of etiolated mung bean(Vigna radiata Wilczek) seedlings. The inhibitor did not significantlyinhibit ethylene formation from its immediate precursor, 1-aminocyclopropane-1-carboxylicacid (ACG), during short-term (up to 4 h) incubation. The ACCcontent in tissue treated with IAA was reduced by lycoricidinolin close parallel with the inhibition of ethylene production.Examination of radioactive metabolites in tissues labeled with3,4-¹⁴C-methionine indicated that reduction of the ACC contentwas not due to any possible promotive effect of lycoricidinolon conjugation of ACC with malonate. Lycoricidinol showed noinhibitory effect on the activity of ACC synthase if appliedin vitro, but it almost completely abolished the increase inthe enzyme activity when applied in vivo during incubation ofthe tissue with IAA. Lycoricidinol also strongly inhibited incorporationof ¹⁴C-leucine into protein in the tissue. The suppression ofthe enzyme induction and, in turn, that, of ethylene productionby lycoricidinol were interpreted as being due to the inhibitionof protein synthesis. (Received September 30, 1983; Accepted December 8, 1983)