No abstract

a-DL-DifluoromethylomUithine (DFMO), a specific enzyme-activated inhibitor of ornithine decarboxylase, at 0.5 to 2.0 millimolar significantly inhibited mycelial growth and especially sporulation of Helminthosporium maydis in the dark; its inhibitory effect on sporulation was greatly increased under light conditions. Putrescine at 0.25 millimolar fully prevented the inhibitory effects of DFMO; the inhibition caused by the latter could not be prevented by cadaverine or CaC12. a-DL-Difluoromethylarginine, a, specific enzyme-activated inhibitor of arginine decarboxylase, at 0.1 to 2.0 millimolar had a weak inhibitory effect on the fungus. The effect was not dependent on the inhibitor concentration and there was no detectable arginine decarboxylase activity in the fungus.Our recent investigation on in vitro activities of ADC2 and ODC from higher plants (4,5) under the same conditions sporulation is three to four times as high as that found in cultures exposed to light (M. 0. Garraway, unpublished data). MATERIALS AND METHODSThe fungus was grown on a synthetic medium containing asparagine described previously (6). The sterilized agar culture media (20 ml per 100 x 20 mm sterile Petri dish) contained glucose, L-asparagine, KH2PO4, and MgSO4 at 0.5, 0.2, 0.3, and 0.15%. Sterilized solutions of Mn, Zn, Fe, and Cu salts at 1 ug/ 1 each were added at 0.2 ml per dish. Solutions of other compounds were filter sterilized prior to application. The pH of the culture media in experiment I was 5.0; in the remaining experiments it was adjusted to 6.0, which proved to be optimal for the fungal growth. Each Petri dish was inoculated at its center with a plug of mycelium 7 mm in diameter. Each experiment was carried out in four replicates. In experiments I and III the Petri dishes were placed in the dark at room temperature. In experiment II, 2 d after inoculation, the plates were transferred from darkness to diffused fluorescent light. Growth was determined by linear extension, and sporulation was expressed on dry weight basis (6).In experiment III the activities of ODC and ADC were determined after the enzymes were extracted with phosphate buffer (pH 7.6) (14) from mycelia exposed to the highest DFMO and DFMA concentrations. Repeated freezing and thawing, sonication, and maceration with glass beads was applied during extraction at 0 to 4°C. The enzymes were assayed as described previously (3,4)

No abstract

No abstract