TITLE	Ethylene biosynthesis in sweet-potato root tissue induced by infection with black rot fungus (Ceratocystis fimbriata)
AUTHOR	Hiroshi Hyodo* Department of Biological Sciences, Faculty of Agriculture, Shizuoka University, Ohya, Shizuoka 422-8529, Japan Seijiro Yoshioka Department of Biological Sciences, Faculty of Agriculture, Shizuoka University, Ohya, Shizuoka 422-8529, Japan Yoshifumi Imai Department of Biological Sciences, Faculty of Agriculture, Shizuoka University, Ohya, Shizuoka 422-8529, Japan Hiroko Nakane Department of Biological Sciences, Faculty of Agriculture, Shizuoka University, Ohya, Shizuoka 422-8529, Japan Fumie Nishikawa Department of Biological Sciences, Faculty of Agriculture, Shizuoka University, Ohya, Shizuoka 422-8529, Japan
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ABSTRACT	Ethylene production rapidly increased in sweet potato (Ipomoea batatas Lam.) root tissue in response to infection by black rot fungus (Ceratocystis fimbriata Ell. & Halst). Ethylene production increased in the surface layer (0-0.5 mm) of the root inoculated with endoconidia of C. fimbriata, reaching a maximum 1 day after inoculation and declining thereafter. The rise in the surface layer was followed by a subsequent increase in the inner, second (0.5-1.0 mm), and third (1.0-1.5 mm) layers as the fungus penetration progressed. Discs 10 mm in diameter and 0.5 mm thick excised from the surface of the infected root slices were used for the experiments. Our previous study demonstrated that ethylene synthesis in the infected tissue may occur via a pathway independent of the methionine-ACC (1-aminocyclopropane-1-carboxylic acid) pathway. Ethylene synthesis in the infected tissue was significantly suppressed by the inhibitors that interfere with NADPH oxidase, phospholipase A2 and lipoxygenase, by metal ion chelators, and by scavengers of reactive oxygen species. The inhibition of metal ions was restored by the addition of cupric ion. These results suggest that in the infected sweet potato root tissue, polyunsaturated fatty acids are released from membrane phospholipids followed by peroxidation by lipoxygenase. The hydroperoxides could be decomposed in the presence of copper ion or copper enzyme and reactive oxygen species such as hydroxyl radical, leading to ethylene generation. De novo protein synthesis was required for ethylene synthesis to be induced in response to the fungal infection.
KEYWORD	Ceratocystis fimbriata; Copper ion; Ethylene biosynthesis; Infected tissue; Ipomoea batatas; Lipoxygenase; Membrane lipids; Reactive oxygen species; Unsaturated fatty acids;
ARTICLE INFO	Botanical Bulletin of Academia Sinica, Volume 44 Number 3 July 2003, page 179-186, 8 pages
PUBLISHER	Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, Republic of China