Ethylene biosynthesis in sweet potato root tissue infected by black rot fungus (Ceratocystis fimbriata).
Kyoko Okumura, Hiroshi Hyodo, Masaya Kato, Yoshinori Ikoma and Masamichi Yano
Postharvest biology and technology.Oct 1999. v. 17 (2) Pages: 117-125.
1999
บทคัดย่อ
The rate of ethylene production in sweet potato (Ipomoea batatas Lam) root tissue greatly increased in response to infection by black rot fungus (Ceratocystis fimbriata Ell. & Halst.). Ethylene evolved rapidly in the first layer of root cells (0-0.5 mm) 24 h after inoculation with the endoconidia of the fungus. In this layer, the host-parasite interactions were very strong. Ethylene production rate reached a peak (up to 300 nl g(-1) h(-1)) 24 h after inoculation, and then declined to a low level. This was followed by an increase in ethylene production in the second layer of cells (0.5-1.0 mm) following continuing invasion by the fungus. Incorporation of L-[(14)C(U)]methionine into ethylene 24 h after inoculation occurred at a lower rate in the first cell layer than in the second, where the ethylene production rate was about 15-fold less. When ACC (1-aminocyclopropane-1-carboxylic acid) was supplied externally, the rate of ethylene production in the first layer was not enhanced, and neither was [(14)C]methionine incorporation into ethylene diluted. The activity of ACC oxidase extracted from the first layer was extremely low (less than 10 nl g(-1) h(-1)) when compared with the ethylene production rate, although ACC oxidase protein was weakly detected by Western blot analysis in the extract from the infected tissue using antibodies raised against ACC oxidase purified from recombinant Escherichia coli. These results indicate that the predominant ethylene generated in the site adjacent to the invaded region of sweet potato root tissue may originate from a pathway independent of ACC. However, it is possible that the methionine-ACC pathway may operate in tissue internal to the above active site.