Ethylene Production in Sweet Potato Root Tissue Infected by Ceratocystis fimbriata

The rate of ethylene production by sweet potato (Ipomoea batatasLam. cv. Norin No. 1) root tissue infected with Ceratocystisfimbriata Ell. & Halst. increased markedly during incubationat 29?C under high relative humidity. During incubation thefungus progressively invaded root tissue. The rate of ethyleneproduction reached a peak two days after inoculation when thebrowning region that contained the penetrating mycelia had expandedinward about 0.3 mm from the surface, followed by a declinein ethylene production. Apparently, the 1-aminocyclopropane-1-carboxylicacid (ACC) synthase activity was not high enough, and the amountof ACC in the infected tissue was too low to account for thehigh rate of ethylene production throughout the incubation period.Ethylene production by the infected tissue showed scarcely anyinhibition by amino-ethoxyvinylglycine, a specific inhibitorof ACC synthase. These findings suggest that the pathway ofethylene biosynthesis that operates in infected sweet potatoroot tissue may differ from the methionine pathway in whichACC serves as an intermediate. (Received March 24, 1984; Accepted June 27, 1984)