Sterols inhibitors

Jones, A.L. 1981. Fungicide resistance Past experience with benomyl and dodine and future concerns with sterol inhibitors. Plant Dis. 65 990-992. 

Kudakasseril, G. J. Lam, L. Staba, E. J. Effect of sterol inhibitors on the incorporation of " C-isopentenyl pyrophosphate into artemisinin by a cell-free system from Artemisia annua tissue cultures and plants. Planta Medica, 1987, 53 280-284. 

For tree fruits such as apples (Table IX), low rates of 2-4 grams active ingredient per 100 liters of spray give near-perfect control of both major diseases, scab and powdery mildew excellent cedar apple rust control is also observed at these rates. Standards for these tests include both sterol inhibitors (fenarimol and bitertanol) and non-systemic protectant fungicides (sulfur and captan). 

Since research on the growth and biochemical responses, as well as resistance, to sterol inhibitors has been recently reviewed (8-14) this information will be covered here only insofar as necessary to establish the background for a discussion on the molecular basis for fungal growth inhibition by these substances. Since most of the work has been conducted with C-14 demethylation inhibitors, emphasis will be given to them, particularly the azoles. 

Figure 1. Continued. Structures of representative sterol inhibitors.

Some fungi treated with sterol inhibitors produce approximately twice the amount of sterol of non-treated cells (38,42). 

These alterations In the relative proportions of fatty aH ds have been attributed to adaptive-type responses to changes in the fluid properties of membranes brought about by sterol inhibitor-induced modification of the sterol content... 

TABLE II, Azole sterol Inhibitors and their ED q concentrations for selected sensitive fungi... 

Certain Mucorales examined have shown a relatively high degree of tolerance to the sterol inhibitors. For example, 80 ppm of propiconazole is required for 50% growth inhibition of Mucor rouxii in liquid shake culture (57). Growth inhibition by this relatively high concentration of theTnhibitor is probably due to direct interaction of the triazole with the plasma membrane, and not to... 

As might be expected for cells in which the plasma membrane has been altered, leakage of cellular constituents (5,73,74) and altered substrate uptake (35,51, and cited in 37,75) including an increased permeability to protons (75), have been observed in sterol inhibitor-treated cells. 

There are no plasma membrane-bound enzymes whose activities are known to be specifically and sufficiently altered to account for growth Inhibition by the sterol inhibitors at sub-MIC doses. A likely candidate is chitin synthetase, but the activity of this enzyme is not reduced in fact, sterol inhibitor-treated fungi contain more glucosamine polymers than controls. However, the altered deposition of chitin (see above references) may reflect a discontinuity between cytoskeletal elements which are believed to be involved in cell wall formation and the plasma membrane, but it is unlikely that this is at the root of growth inhibition since a wall-less slime mutant of Neurospora crassa is as sensitive as the wild-type strain to propiconazole (57TI Cytochrome oxidase and microsomal ATPase are inhibited by high concentrations (10 5,... 

Antifungal azoles, names, 270-27It Aphelenchus avenae. ecdysteroids, 214 Apis melllfera. effect of sterols on brood production, 183 Artemisia absinthium, sesquiterpene Inhibitor production, 104 Ascaris. sterol biosynthesis, 202-203 Ascarls suum, ecdysteroids, 214 Aspergillus nldulans, studies of sterol inhibitors, 276-277 Aspergillus nlger. studies of fatty acids, 222,223... 

Deriv. from plant sterols. Inhibitor of cholesterol absorption. Shows lipid lowering and body weight reducing props. Used as the di-Na salt. 

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