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1.
A number of sterol biosynthesis-inhibiting (SBI) fungicides and plant growth regulator analogs were applied as root drenches to barley seedlings and their effect on the total sterol composition of the roots and shoots was measured by gas-liquid chromatography. Prochloraz was found to be inactive in this system, probably because of poor uptake, while the other compounds could be divided into two groups according to their mode of action as assessed by sterol profiling. The morpholines tridemorph and fenpropimorph inhibited the enzyme cycloeucalenol—obtusifoliol isomerase whereas triadimenol, nuarimol, paclobutrazol, and triapenthenol (RSW 0411) inhibited the enzyme responsible for the removal of the C-14 methyl group. Effects of individual diastereo-isomers and enantiomers of some compounds on sterol profiles were compared with their known fungicidal and anti-gibberellin properties. Shoot growth was reduced by all the compounds tested, paclobutrazol, nuarimol, and triapenthenol being the most effective. As well as inducing accumulation of abnormal sterols, SBI fungicide treatment changed the ratio of campesterol to stigmasterol and sitosterol. It is hypothesized that this may reflect changes in membrane architecture and may offer an explanation for the increased frost hardiness sometimes observed with SBI fungicide-treated plants.  相似文献   

2.
Metabolism of the triazolylmethane fungicides triadimefon, triadimenol, and diclobutrazol by Aspergillus niger was studied using a replacement culture technique and 14C substrates. Components of metabolite mixtures were characterized by TLC, GLC, radio-GC, and GC-MS analyses of the free materials and their trifluoroacetate and trimethylsilyl ether derivatives. The three compounds underwent a common metabolic change involving oxidation of C(CH3)3 to C(CH3)2CH2OH. In this work the isopropyl analog of triadimefon, previously reported as a metabolite, was an artifact and resulted from nonbiological oxidation of the corresponding primary alcohol. The fungus also reduced triadimefon to triadimenol, giving a mixture of 1R2S, 1S2R and 1R2R, 1S2S diastereoisomers. The less fungitoxic 1R2S, 1S2R triadimenol predominated, so that this conversion may be directly associated with the relative insensitivity of A. niger to triadimefon. Implications of oxidative and reductive metabolism of these fungicides are suggested with particular reference to the differing fungitoxicities of diastereoisomers and enantiomers.  相似文献   

3.
An enzymatic assay system has been developed to measure the relative potency of fungicides such as triadimefon, triarimol, triforine, and buthiobate as inhibitors of sterol 14-demethylation. The enzyme preparation used is the 8000g supernatant derived from a homogenate of an aerobically adapted, anaerobically grown, high sterol strain of Saccharomyces cerevisiae. After incubation of the enzyme with [2-14C]mevalonic acid and the fungicide the ratio, radioactivity in 4,4-dimethyl sterols/radioactivity in 4-demethyl sterols is determined. The higher this ratio is, the more efficient is the fungicide as an inhibitor of fungal sterol 14-demethylation. The ratio has been determined for a number of commercial fungicides and two series of triazole compounds. A similar assay system based on the 10,000g supernatant from a rat liver homogenate was also tested but gave an inaccurate assessment of the relative potency of fungicides as inhibitors of fungal sterol 14-demethylation.  相似文献   

4.
An assay for measuring ergosterol synthesis in cell-free extracts of the filamentous plant pathogen Botrytis cinerea is described. The extracts capable of synthesizing C4-desmethyl sterols from [2- 14 C]mevalonate were derived by mechanical disruption of young conidial germlings in a Bead-Beater apparatus. The C4-desmethyl sterol fraction consisted of three distinct compounds and totalled 39% of the non-saponifiable lipids formed. Ergosterol accounted for 63% of the C4-desmethyl sterols. Only small amounts of C4-monomethyl sterols were synthesized, while C4, 4-dimethyl sterols made up 29% of the non-saponifiable lipids. The latter fraction mainly consisted of lanosterol (54%) and eburicol (28%). The cell-free system had a narrow pH optimum for synthesis of C4-desmethyl sterols of pH 7.3–7.4. Cell-free synthesis of C4-desmethyl sterols was inhibited by the imidazole fungicide imazalil, concomitant with an accumulation of eburicol. The IC50 value (concentration of fungicide which inhibited cell-free synthesis of C4-desmethyl sterols by 50%) was 9.1 × 10 ?9 M. These results are consistent with the hypothesis that imazalil is a potent inhibitor of the cytochrome P450-dependent sterol 14x-demethylase of B. cinerea. The method described may be used to screen compounds biochemically for inhibition of sterol synthesis in an agriculturally important plant pathogen.  相似文献   

5.
Strains of Pseudocercosporella herpotrichoides collected in France on winter wheat give either fast-growing mycelial colonies with regular margins or slow-growing mycelial colonies with irregular margins. Most of the fastgrowing isolates were sensitive to triadimenol (EC50 below 2mg litre?1), but some of them were resistant to this inhibitor of sterol C-14 demethylation. In contrast, all the slow-growing strains were highly resistant to triadimenol (EC50 greater than 100 mg litre?1). This resistance was also expressed in inhibition of germ-tube elongation. Positive cross-resistance was observed between most of the inhibitors of sterol C-14 demethylation, with the exception of some imidazole derivatives (clotrimazole, prochloraz). All the fast-growing strains were tolerant to fenpropimorph and fenpropidin whereas the slow-growing ones were susceptible; the reverse was true with piperalin and tridemorph. All the field isolates were inhibited to the same extent by the inhibitors of squalene-epoxidase, nafifine and terbinafine. Two types of mutant resistant to triadimenol have been induced under laboratory conditions from sensitive fast-growing strains. The most common mutants were resistant to all the inhibitors of sterol C–14 demethylation and also in some conditions to fenpropimorph, tridemorph and the inhibitors of squalene-epoxidase. The other mutants were characterised by a reduced spectrum of cross-resistance between triadimenol and the other inhibitors of sterol biosynthesis. The field isolates and laboratory mutants resistant to triadimenol and propiconazole were also resistant to each of the four enantiomers of these two fungicides.  相似文献   

6.
Isolates of Erysiphe graminis f. sp. hordei and tritici with decreased sensitivity to triadimefon showed cross-resistance to other inhibitors of sterol C-14-demethylation, such as triadimenol, propiconazol, diclobutrazol, prochloraz and nuarimol. The isolates exhibited a moderate degree of resistance to these compounds. No cross-resistance was detected to tridemorph, fenpropimorph and pyrazophos. The resistant hordei isolates were more sensitive to ethirimol than the sensitive isolate. The competitive abilities of resistant hordei and tritici isolates were inferior to that of the sensitive isolates. In the presence of the fungicides no differences in germination, appressorium formation and penetration between the sensitive and resistant isolates were observed; 48 h after inoculation the sensitive isolate showed several morphological alterations and further fungal development was arrested. At four to five times higher doses of triadimefon, similar morphological alterations were detected in the resistant isolate. Low concentrations of triazole fungicides which slightly affected mycelium growth of both the sensitive and the resistant isolate of f.sp. hordei severely inhibited development of conidiophores of the sensitive isolate whereas that of the resistant isolate was hardly affected.  相似文献   

7.
Thirty single-spore isolates of Rhynchosporium secalis were assayed in vitro to assess relative sensitivities to the fungicide triadimenol. Minimum inhibitory concentrations ranged from 0.2 to 3.2 μg/ml. Isolates collected in 1981 from winter barley crops treated with triadimenol + tuberidazole, triadimefon, or prochloraz were as sensitive as those from untreated crops, and four isolates collected prior to the widespread use of these fungicides were not especially sensitive. All isolates tested in the greenhouse on winter and spring barley were controlled by Baytan (triadimenol and fuberidazole).  相似文献   

8.
The effects of the sterol biosynthesis inhibitor (SBI) fungicides fenarimol, fenpropimorph, imazalil, prochloraz, propiconazole and triadimenol on growth and sterol composition of Ustilago maydis, Botrytis cinerea and Pyrenophora teres, grown from spores or sporidia in liquid culture, were determined. Growth of U. maydis was only slightly inhibited by SBI fungicides at concentrations which caused considerable changes in both sterol content and composition. Conversely, in B. cinerea and P. teres, growth was strongly inhibited under conditions where ergosterol was still the predominant sterol, suggesting that, in these two fungi, growth may be more sensitive to SBI fungicides than overall sterol production. Demethylase inhibitor fungicides behaved as a homogeneous group in their effects on growth and on sterol profiles of the three fungi studied.  相似文献   

9.
In Ustilago avenae sporidia, following the first doubling period of about 4 h, triadimenol (2 μg ml?1) affected sporidial multiplication more severely than other growth processes; daughter cells failed to separate from the parent sporidia resulting in chains of interconnected cells. Triadimenol incubated with the fungus for 8 h interfered neither with respiration nor with protein and nucleic acid synthesis but after 6 h the toxicant had induced a higher content of free fatty acids. Triadimenol markedly altered, both quantitatively and qualitatively, the sterols in sporidia of U. avenae. Incorporation of [14C]acetate (in the form of sodium acetate) into lipid fractions for a period of 2 h revealed that the toxicant powerfully inhibited the synthesis of the 4-demethyl sterol fraction (predominantly ergosterol), whilst the 4,4-dimethyl sterol fraction rapidly accumulated. This was confirmed by g.1.c. analysis of the sterols after 6 and 8 h incubation which showed that the amount of ergosterol, the major sterol in untreated sporidia, was diminished while simultaneously 4,4-dimethyl, 4-methyl and 14-methyl sterols increased. The accumulation of 14-methyl sterols suggests that triadimenol acts as a potent inhibitor of one of the metabolic steps involved in the demethylation at the 14-position during ergosterol biosynthesis.  相似文献   

10.
The inhibitory activity of commercial and experimental triazole fungicides on the target enzyme, sterol 14α-demethylase (P45014DM), was studied in a cell-free sterol synthesis assay of Botrytis cinerea Pers. ex Fr. In order to assess structure-activity relationships, the inhibitory activities of the compounds on radial growth of the fungus were tested as well. The EC50 values (concentrations of fungicide inhibiting radial growth of B. cinerea on PDA by 50%) of all triazoles tested ranged between 10?8 and 10?5 m. IC50 values (concentrations of fungicide inhibiting incorporation of [2-14C]mevalonate into C4-desmethyl sterols by 50%) generally ranged between 10?9 and 10?7 M and correlated with inhibition of radial mycelial growth. However, differences in IC50 values did not reflect quantitatively the observed differences in EC50 values, since the ratio between EC50 and IC50 increased with decreasing fungitoxicity. For a limited number of compounds the correlation between intrinsic inhibitory activity and fungitoxicity was low. Both in-vitro tests were used to investigate structure-activity relationships for stereoisomers of cyproconazole, SSF-109 and tebucona-zole. Fungitoxicity and the potency to inhibit cell-free C4-desmethyl sterol synthesis correlated for all stereoisomers tested. Mixtures of isomers of tebucona-zole or cyproconazole were slightly less active than the most potent isomer. The high activity of several commercial triazoles in both experiments implies that poor field performance of triazole fungicides against B. cinerea is due neither to insensitivity of the P45014DM nor to low in-vitro sensitivity of the fungus.  相似文献   

11.
With three plant pathogens,Botrytis cinerea, Venturia inaequalis and Puccinia graminis f. sp.tritici, the time course of sterol biosynthesis during spore germination was examined by labeling experiments along with the question whether this pathway could be inhibited by triazole fungicides. Conidia ofB. cinerea andV. inaequalis are able to synthesize sterols immediately after the beginning of the germination process when the germ tubes have not yet emerged. On the contrary uredospores ofP. graminis start sterol biosynthesis after 6 to 8 h germination time almost at the end of the germ tube phase, indicating that sterol reserves of the spores are likely to be used for the germ tube growth.The sterol C-14 demethylation appeared to be the rate limiting step within the sterol biosynthetic pathway: the half life of 24-methylenedihydrolanosterol was less than 1 h forB. cinerea. It was more than 1 h forV. inaequalis and 3 h forP. graminis. Independent of these differences in the time course of sterol biosynthesis and in the C-14 demethylation rate, the synthesis of sterols in germinating spores was strongly inhibited by triazole fungicides in all three pathogens examined. In contrast toP. graminis, this inhibition could be demonstrated withB. cinerea andV. inaequalis even in ungerminated conidia, indicating that the fungicides were rapidly taken up and reached their target within 1 or 2 h. These results are discussed along with the question whether spore germination can be used as a bioassay for the estimation of sensitivities of triazole fungicides.  相似文献   

12.
Wheat caryopses were treated with racemic fenpropimorph. As shown previously in other plant species, 9(β,19-cyclopropyl sterols were found to accumulate markedly. A distinctive feature was a remarkable accumulation of 31 -norcyclobranol, a very rare sterol in nature. A8-sterols were also identified. The ratio A8-sterols: cyclopropyl sterols was shown to depend greatly on the configuration of the methyl substituent in position 2 of fenpropimorph. Whereas cyclopropyl sterols predominated in the case of seedlings treated with the (2S)-2-methyl enantiomer, A8-sterols were shown to be very abundant in plants treated with the (2R)-2-methyl enantiomer. A8-sterols were shown also to be more abundant in leaves than in roots. Experiments were conducted to find out whether the phytotoxic response of plants to fenpropimorph could be ascribed to its action on sterol biosynthesis. From the results obtained it appears that this is not the case and thus the phytotoxic effect is probably related to a cellular target other than sterol biosynthesis.  相似文献   

13.
ABSTRACT Single-conidial isolates of Uncinula necator from (i) a population representing two vineyards with no previous exposure to sterol demethylation inhibitor (DMI) fungicides ("unexposed," n = 77) and (ii) a population representing two vineyards in which powdery mildew was poorly controlled by triadimefon after prolonged DMI use ("selected," n = 82) were assayed to determine distributions of sensitivities to the DMI fungicides triadimenol (the active form of triadimefon), myclobutanil, and fenarimol. Median 50% effective dose (ED(50)) values (micrograms per milliliter) in the selected versus unexposed populations were 0.06 versus 1.9 for triadimenol, 0.03 versus 0.23 for myclobutanil, and 0.03 versus 0.07 for fenarimol, respectively. Isolates were grouped into sensitivity classes according to their ED(50) values, and those from the selected population were categorized as resistant if the frequency of their sensitivity class had increased significantly relative to levels found in the unexposed population (ED(50) values exceeding 0.56, 0.18, and 0.18 mug/ml for triadimenol, myclobutanil, and fenarimol, respectively). Of the 76 isolates defined as resistant to triadimenol, 64% were classified as cross-resistant to myclobutanil, 18% were classified as cross-resistant to fenarimol, and 17% were classified as resistant to all three fungicides; 25% of the isolates classified as resistant to myclobutanil also were classified as resistant to fenarimol. Similar cross-resistance relationships were revealed when all isolates were examined by regressing log ED(50) values for each fungicide against those for the remaining two fungicides to determine the correlation coefficients (e.g., r = 0.85 for triadimenol versus myclobutanil and 0.56 for triadimenol versus fenarimol). The restricted levels of cross-resistance indicated by these data, particularly between fenarimol and the other two fungicides, is in sharp contrast to the high levels of cross-resistance among DMIs reported for some other pathogens and has significant implications with respect to programs for managing grapevine powdery mildew and DMI resistance.  相似文献   

14.
Pimaricin-resistant mutants of Aspergillus nidulans were selected on a medium containing the polyene-antibiotic. Some resistant mutants contained markedly reduced amounts of ergosterol, but others contained almost normal levels of this sterol. Most resistant mutants which lacked ergosterol had a biochemical lesion in sterol C-22 desaturation. Analysis of sterols in one of these isolates showed the presence of 5,7-ergostadienol, 5,7,24(28)-ergostatrienol, and 5,8-ergostadienol. The sterol C-14 demethylation inhibitor, fenarimol, was more toxic to this mutant than to the wild type. On the other hand, mutants inactive in sterol C-22 desaturation were resistant to oligomycin but showed wild type sensitivity to carboxin. Attempts to select sterol C-14-demethylation-deficient mutants of Aspergillus nidulans, Monilinia fructicola, and Pyricularia oryzae on polyene-containing media were unsuccessful. Apparently C-14-methyl sterols do not support growth of these filamentous fungi.  相似文献   

15.
Triarimol and triforine inhibit ergosterol biosynthesis in fungi and cause accumulation of free fatty acids, 24-methylenedihydrolanosterol, obtusifoliol and 14α-methyl-δ8,24(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 14α-methyl group is probably the prime mechanism of inhibition of ergosterol biosynthesis by triarimol. Rates of formation of obtusifoliol and 14α-methyl-δ8,24(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.Free fatty acid accumulation in U. maydis cells treated with inhibitors of sterol synthesis are derived mainly from polar lipid degradation and from de novo synthesis as a consequence of the disproportionality between fatty acid synthesis and utilization. The free fatty acids may play a significant role in the lethality of these inhibitors in this organism.  相似文献   

16.
Triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-(1,2,4-triazol-1-yl)-2-butanone], 1.5–2.0 μ/ml, inhibited the multiplication of sporidia of Ustilago avenae more strongly than it did the increase of dry weight. The treated sporidia appeared swollen, multicellular, and branched. At concentrations of 1.5–100 μg of triadimefon/ml, the oxidation of glucose was not affected. Increase in dry weight and synthesis of protein, RNA, and DNA were inhibited slightly, whereas cell division was acutely arrested. After an incubation period of 9.5 hr, microscopic studies revealed that daughter cells of the treated sporidia also contained one nucleus. In sporidia treated for 6 hr with triadimefon, both the total lipid content and its composition of fatty acids were not appreciably altered. The treated cells, however, differed from control cells by a higher content of free fatty acids. Triadimefon markedly interfered in sterol biosynthesis in Ustilago avenae. Gas chromatographic (glc) analysis and [14C]acetate incorporation studies indicated that ergosterol biosynthesis was almost completely inhibited by triadimefon; on the other hand, sterol compounds representing precursors of ergosterol (probably 4,4-dimethyl and C-4-methyl sterols) accumulated in treated sporidia. As the results indicate, the inhibition of conversion of immediate sterol precursors to ergosterol may be regarded as the primary target for the action of triadimefon in Ustilago avenae.  相似文献   

17.
Fluotrimazole [BUE 0620; 1-(3-trifluoromethyltriphenyl) 1,2,4-triazole] (20 μg/ml of nutrient solution) and clotrimazole [Bay b 5097; bisphenyl(2-chlorophenyl)-1-imidazolyl methane] (5 μg/ml) did not inhibit dry weight increase and only slightly reduced multiplication of sporidia of Ustilago avenae during the first doubling period (about 4 hr). After 8 hr, both fluotrimazole and clotrimazole more strongly inhibited sporidia multiplication than dry weight increase. As a consequence of treatment with both fungicides the usually single-celled sporidia appear swollen, multicellular, and branched. Both chemicals at a concentration range of 5–100 μg/ml did not affect oxidation of glucose. The effect of fluotrimazole and clotrimazole on protein, DNA, and RNA synthesis was similar to that on dry weight. Following a 6-hr incubation period total lipid synthesis was quantitatively unaffected by both chemicals. As the analysis of major fatty acids of total lipids revealed fluotrimazole substantially induced the synthesis of 20:4 carbon fatty acids, while in clotrimazole-treated sporidia the pattern of fatty acids did not differ from that of control sporidia. Fluotrimazole and clotrimazole produced a higher quantity of free fatty acids in sporidia of U. avenae. Gas-liquid chromatographic analysis of sterol fractions in treated and control sporidia (6 hr) indicated that both fluotrimazole and clotrimazole seriously inhibited ergosterol biosynthesis and concomitantly caused an accumulation of immediate ergosterol precursors which represent C-4-methyl and 4,4-dimethyl sterols. Incorporation of [14C]acetate for 2 hr into various lipid fractions of sporidia of U. avenae also revealed that radioactivity in C-4-desmethyl sterols in both fluotrimazole- and clotrimazole-treated sporidia was drastically reduced, while the radioactivity of C-4-methyl and 4,4-dimethyl sterols distinctly increased. The data suggest that fluotrimazole and clotrimazole are specific inhibitors of the oxidative demethylation of the C-14-methyl group during ergosterol biosynthesis in U. avenae.  相似文献   

18.
A random sample of conidiospores ofErysiphe graminis f.sp.hordei was obtained from the atmosphere above Cambridge, England, by incubating them on barley seedlings exposed on three dates in 1985. The asexual progeny of each spore was tested for its response to a range of doses of a systemic triazole fungicide, triademenol. Principal components analysis of the data revealed that the majority of isolates had a distinct level of response to triadimenol, being resistant to triadimenol at the rate apoplied to seed commercially. The remaining isolates appeared either to be sensitive to the lowest dose of triadimenol used, or to have one of two intermediate levels of resistance. There was a significant increase in the frequency of isolates with higher levels of resistance to triadimenol during 1985. This is likely to have been a response to the continuing widespread use of demethylation inhibitor (DMI) fungicides by British farmers.  相似文献   

19.
The degradation rates in soil of 1-benzyltriazole together with six analogues having substituents in the phenyl ring and two commercial triazole fungicides, PP450 and triadimefon, were determined at 15°C and 20 % soil water content. The order of degradation rates of the benzyltriazoles was H > 4-OCH3 > 4-F>4-Cl.4-≥tert-C4Hg3,4-diCl>3-CF3. Thus, in general, persistence was enhanced by electron-withdrawing substituents and by lipophilic groups that increased sorption by soil. Of the commercial fungicides, PP450 was degraded very slowly (half-life 578 days) while triadimefon was quickly converted (half-life 15 days) to the corresponding alcohol, triadimenol, which in turn was degraded very slowly. The effects of temperature and soil water content on rate of degradation were studied for 1-benzyltriazole and 1-(4-fluorobenzyl)triazole. The rate of degradation of 1-benzyltriazole was more sensitive to soil temperature and water content than was that of 1 -(4-fluorobenzyl)triazole. The influence of these results on the input data required by models which simulate persistence in field soil is discussed.  相似文献   

20.
The metabolism of triforine, chloraniformethan, the α-(pyrimidin-5-yl)benzhydryl alcohols (fenarimol, nuarimol and triarimol), the trityl-azoles (fluotrimazole and clotrimazole), and the morpholine types of sterol inhibitors is reviewed; the metabolism of the azolyl-alkane derivatives (mainly triadimefon and triadimenol) is discussed in detail. Redox and hydrolytic reactions are of primary importance. Enzymic inactivation may be one factor influencing fungicide selectivity. Metabolism is the dominant factor of selectivity if it represents the activation process, as with triadimefon. Transformations in higher plants do not differ significantly from those occurring in fungi, except that factors such as the formation of conjugates with natural compounds of plant tissues also play a role, as with triforine and triadimenol. The selectivity of fungitoxic action may be influenced by metabolism both in the host plant and the pathogen.  相似文献   

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