| Abstract: | Diclobutrazol (2RS, 3RS)-1-(2, 4-dichlorophenyl)-4, 4-dimethyl-2-(1,2, 4-triazol-1-yl)pentan-3-ol] decreased the rate of growth of Ustilago maydis during the log phase. Marked changes in sterol composition were observed with a decrease in ergosterol and an increase in methyl-sterols, indicating a block in the removal of the 14-methyl group. The inhibition was of rapid onset (<4 h). Changes in other lipid constituents were minor and there was no build up of unsaturated fatty acids. The fungicidal activity resides in the (2R, 3R)-isomer, which is known to be more potent in blocking a yeast 14-demethylase enzyme than the (2S, 3S)-isomer. This relationship held in the 4-chlorophenyl homologues, which as a group were less fungicidal and less potent inhibitors than the 2, 4-dichlorophenyl compounds. The evidence presented indicates that the primary lesion caused by the fungicide was a build up of membrane sterols containing extra methyl groups; this, in combination with a loss of ergosterol, is believed to prevent proper membrane ordering and thus to cause a loss of membrane function. |
