Fungitoxicity and growth regulation involving aspects of lipid biosynthesis

Abstract

Triarimol and triforine inhibit ergosterol biosynthesis in fungi and cause accumulation of free fatty acids, 24-methylenedihydrolanosterol, obtusifoliol and 14~-methyl-A8,24(28)-ergostadienol. Triparanol also inhibits ergosterol synthesis and causes accumulation of free fatty acids, but not of the latter 3 sterols. Triparanol appears to inhibit prior to lanosterol in the sterol biosynthetic pathway of Ustilago maydis and at unidentified sites subsequent to lanosterol which lead to the accumulation of a sterol which migrates with desmethylsterols on TLC plates. Quantitative abnormalities in sterols and free fatty acids in U. maydis are not produced by the fungicides carbendazim, chloroneb, carboxin and cycloheximide. A deficiency in nitrogen leads to a marked increase in triglycerides, but a normal distribution pattern for other lipids.Inhibition of oxidative demethylation of the sterol 14~-methyl group is probably the prime mechanism of inhibition of ergosterol biosynthesis by triarimol. Rates of formation of obtusifoliol and 14~-methyl-A ,24(28)-ergostadienol in triarimol-treated U. maydis cells suggest that C-4 demethylation occurs along an abnormal pathway which operates effectively only at high substrate concentrations. The growth retardant action of triarimol and ancymidol in higher plants most likely results from inhibition of a reaction in the gibberellin biosynthetic pathway analogous to sterol C-14 demethylation.

Resistance to triforine: A nonexistent problem?

“…Triforine seems to have other advantages: unlike, for instance, triadimefon (Buchenauer and Grossmann, 1977) and triarimol (Sisler and Ragsdale, 1977), triforine does not exert a noticeable growth-retardant action in higher plants by inhibiting gibberellin biosynthesis in a way analogous to inhibiting ergosterol synthesis. Further, in mammals triforine is excreted, after complete metabolic conversion, within 24 h of its being administered (Darda, 1977).…”

Influence of a subinhibitory dose of antifungal atty acids fromSporothrix flocculosa on cellular lipid composition in fungi

“…The modification of the lipidic environment in membranes may therefore be harmful to cell viability (24,25). Several antimicrobial molecules have been found to interfere with lipid metabolism or directly with specific lipid molecules (26,27). Recently, new fatty acids with antifungal activity were isolated and characterized from liquid cultures of the biocontrol agent S. flocculosa (6,7).…”

Mode of Action of the Azasteroid Antibiotic 15-Aza-24-Methylene- d -Homocholesta-8,14-Dien-3β-ol in Ustilago maydis

“…In U. maydis the removal of the C-14 methyl is probably the first step in the reaction sequence from 24-methylenedihydrolanosterol to ergosterol (22). It has been postulated that the removal of the C-14 methyl group results in a C-14 (15) (16) and triforine (22) lead to a large accumulation of the C-4,C-14 methyl sterols (obtusifoliol and 24-methylenedihydrolanosterol) and a gradual buildup of 14a-methylergosta-8,24(28)-dienol. Our data indicate that once the C-14 methyl is removed, C-4 demethylation proceeds rapidly even though the resulting C-14(15) double bond is not reduced.…”