Mode of Action of (E)-1-(2, 4-dichlorophenyl)-4, 4-dimethyl-2-(1, 2, 4-triazol-1-yl)-1-penten-3-ol (S-3308) in Ustilago maydis

Abstract

The new fungicide, S-3308 [(E)-1-(2, 4-dichlorophenyl)-4, 4-dimethyl-2-(1, 2, 4-triazol-1-yl)-1-penten-3-ol] inhibited sporidial multiplication and caused morphological changes in Ustilago maydis. Sporidia were branched, swollen and multicellular in the presence of 2μg/ml fungicide. Increase in dry weight was inhibited 66% during 8hr incubation. Both endogenous and exogenous respirations were inhibited by S-3308 but a high concentration (100μg/ml) was required for complete inhibition. Syntheses of protein, DNA and RNA were only slightly affected by the fungicide. A relative amount of ergosterol severely decreased in the treated sporidia and the concomitant accumulation of 24-methylenedihydrolanosterol, obtusifoliol and 14α-methyl-Δ^{8, 24(28)}-ergostadienol was observed. Incorporation of ¹⁴C-acetate into C-4-desmethyl sterols and sterol esters was inhibited more than 80%. On the contrary, the accumulation of radioactivities in the fractions of 4, 4-dimethyl sterols and C-4-methyl sterols was observed. These results indicate that S-3308 particularly inhibits the demethylation at the C-14 position of 24-methylenedihydrolanosterol in the sterol biosynthetic pathway.