ETHYLENE BIOSYNTHESIS IN SWEET POTATO ROOT TISSUE INFECTED BY CERATOCYSTIS FIMBRIATA

Ethylene production in sweet potato (Ipomoea batatas Lam) was greatly enhanced in root tissue infected by the black rot fungus, Ceratocystis fimbriata Ell. & Halst. The rate of ethylene production in the surface layer (0-0.5 mm) increased in response to fungal invasion, reaching a maximum one day after inoculation with endoconidia of C. fimbriata. Radioactive methionine was not effectively converted to ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity in the infected tissue was far below the level of ethylene production (Okumura et al., 1999). Discs of 10 mm diameter and 0.5 mm thickness were taken from the surface of the inoculated root slices and were analyzed for their ethylene production and its inhibition by various compounds. Ethylene production was inhibited by cycloheximide, diethyldithiocarbamate, 1,10-phenanthroline, sodium benzoate, gallic acid, salicylhydroxamic acid and ibuprofen. These results suggest that protein synthesis is required, and metal ions, fatty acid peroxidation by lipoxygenase and free radicals are involved in ethylene biosynthesis in sweet potato root tissue infected by C. fimbriata.