A comparison of the mechanisms of action of vinclozolin, procymidone, iprodione and prochloraz againstBotrytis cinerea

Iron and copper on Botrytis cinerea: new inputs in the cellular characterization of their inhibitory effect

Certain metals play key roles in infection by the gray mold fungus, Botrytis cinerea. Among them, copper and iron are necessary for redox and catalytic activity of enzymes and metalloproteins, but at high concentrations they are toxic. Understanding the mechanism requires more cell characterization studies for developing new, targeted metal-based fungicides to control fungal diseases on food crops. This study aims to characterize the inhibitory effect of copper and iron on B. cinerea by evaluating mycelial growth, sensitivity to cell wall perturbing agents (congo red and calcofluor white), membrane integrity, adhesion, conidial germination, and virulence. Tests of copper over the range of 2 to 8 mM and iron at 2 to 20 mM revealed that the concentration capable of reducing mycelial growth by 50% (IC50) was 2.87 mM and 9.08 mM for copper and iron, respectively. When mixed at equimolar amounts there was a significant inhibitory effect mostly attributable to copper. The effect of Cu50, Fe50, and Cu50-Fe50 was also studied on the mycelial growth of three wild B. cinerea strains, which were more sensitive to metallic inhibitors. A significant inhibition of conidial germination was correlated with adhesion capacity, indicating potential usefulness in controlling disease at early stages of crop growth. Comparisons of the effects of disruptive agents on the cell wall showed that Cu, Fe, and Cu-Fe did not exert their antifungal effect on the cell wall of B. cinerea. However, a relevant effect was observed on plasma membrane integrity. The pathogenicity test confirmed that virulence was correlated with the individual presence of Cu and Fe. Our results represent an important contribution that could be used to formulate and test metal-based fungicides targeted at early prevention or control of B. cinerea.

Enantioselective synthesis of 3-hydroxy- and 3-amino-3-alkynyl-2-oxindoles by the dimethylzinc-mediated addition of terminal alkynes to isatins and isatin-derived ketimines

A common protocol for enantioselective alkynylation of isatins and isatin-derived ketimines using terminal alkynes and Me2Zn in the presence of a catalytic amount of a chiral perhydro-1,3-benzoxazine with moderate to excellent enantioselectivity under mild reaction conditions is described. The additions to ketimines present a novel approach to chiral amines being derivatives of oxindoles. The reaction is broad in scope with respect to aryl- and alkyl-substituted terminal alkynes and isatin derivatives. In isatins, the alkynylation occurs at the Si face of the carbonyl group, whereas in the ketimine derivatives it occurs at the Re face of the imine.

Investigation of the antifungal activity of the dicarboximide fungicide iprodione against Bipolaris maydis

Southern corn leaf blight (SCLB), mainly caused by Bipolaris maydis, is a destructive disease of maize worldwide. Iprodione is a widely used dicarboximide fungicide (DCF); however, its antifungal activity against B. maydis has not been well studied until now. In this study, the sensitivity of 103 B. maydis isolates to iprodione was determined, followed by biochemistry and physiology assays to ascertain the fungicide's effect on the morphology and other biological properties of B. maydis. The results indicated that iprodione exhibited strong inhibitory activity against B. maydis, and the EC₅₀ values in inhibiting mycelial growth ranged from 0.088 to 1.712 μg/mL, with a mean value of 0.685 ± 0.687 μg/mL. After treatment with iprodione, conidial production of B. maydis was decreased significantly, and the mycelia branches increased with obvious shrinkage, distortion and fracture. Moreover, the expression levels of the osmotic pressure-related regulation genes histidine kinase (hk) and Ssk2-type mitogen-activated protein kinase (ssk2) were upregulated, the glycerin content of mycelia increased significantly, the relative conductivity of mycelia increased, and the cell wall membrane integrity was destroyed. The in vivo assay showed that iprodione at 200 μg/mL provided 79.16% protective efficacy and 90.92% curative efficacy, suggesting that the curative effect was better than the protective effect. All these results proved that iprodione exhibited strong inhibitory activity against B. maydis and provided excellent efficacy in controlling SCLB, indicating that iprodione could be an alternative candidate for the control of SCLB in China.

Exposure to iprodione induces ROS production and mitochondrial dysfunction in porcine trophectoderm and uterine luminal epithelial cells, leading to implantation defects during early pregnancy

Iprodione is a well-known fungicide used in the cultivation of strawberries, tomatoes, grapes, and green beans. In recent studies, neurotoxicity, cardiotoxicity, and endocrine toxicity of iprodione have been reported. Although reproductive toxicity of iprodione has been identified in animal studies, its effects are limited to male fertility. Also, the toxic effects of iprodione on pregnancy, especially the implantation process, have not been elucidated. This study demonstrated a series of cytotoxic responses of iprodione along with the alteration of implantation-related gene expression in porcine trophectoderm (pTr) and luminal epithelium (pLE) cells. In this study, iprodione suppressed cell viability, proliferation, and migration of these cells. Iprodione induced G1 phase arrest and attenuated spheroid formation by pTr and pLE cells. Furthermore, iprodione caused mitochondrial dysfunction and excessive reactive oxygen species generation, which resulted in an increase in mitochondrial calcium levels. Consequently, DNA damage and apoptotic cell death were induced by iprodione treatment in pTr and pLE cells. This stress-induced cell death was mediated by alterations in intracellular signal transduction, including the PI3K/AKT and MAPK signaling pathways. This finding suggests the potential of iprodione to impair the implantation capacity by exerting cytotoxic effects on fetal and maternal cells.

Detection and Fitness of Dicarboximide-Resistant Isolates of Alternaria alternata from Dendrobium officinale, a Chinese Indigenous Medicinal Herb

Black spot, caused by Alternaria alternata, poses a severe threat to the industry of Dendrobium officinale, a Chinese indigenous medicinal herb. Dicarboximide fungicides (DCFs) have been intensively used to control this disease for decades in China, and offer excellent efficacy. The resistance of phytopathogenic pathogens against DCFs are reportedly selected in fields; however, the DCF resistance of A. alternata from D. officinale is not well understood. The isolates of A. alternata with low procymidone resistance (Pro^LR) were detected in the commercial orchards of D. officinale in China in 2018 and biochemically characterized in this study. The result showed that the Pro^LR isolates were selected in the commercial orchards with a resistance frequency of 100%, and no significant difference in mycelial growth, sporulation, and virulence was observed among the Pro^LR and procymidone-sensitive (Pro^S) isolates. A positive cross-resistance pattern was exhibited between procymidone and iprodione. Results of amino acid sequence alignment of AaOS-1 from the tested isolates showed that all of the Pro^LR genotypes could be categorized into two groups, including group I (mutations at AaOs-1) and group II (no mutation). Under procymidone (5.0 µg/ml) treatment conditions, the AaOs-1 expression levels increased in the Pro^S isolates and ranged from approximately 2.94- to 3.69-fold higher than those under procymidone-free conditions, while the AaOs-1 expressions of the Pro^LR isolates were significantly lower than those in the Pro^S isolates under the same conditions. The data indicated that the mutations at AaOs-1 are involved in the DCF resistance of A. alternata selected in the D. officinale orchards.

Cytogenotoxic activity of the pesticides imidacloprid and iprodione on Allium cepa root meristem

Effects of imidacloprid and iprodione, isolated and in mixture, were assessed by using seed germination and root growth test, flow cytometry, and chromosomal aberrations test on Allium cepa root meristem. The highest concentrations of imidacloprid, including field concentration, increased the frequency of sub-G₁ particles, decreased the frequency of nuclei in G₂/M, increased the coefficient of variation of G₁ (CVG₁) and the frequency of aberrant cells, and inhibited the mitotic index culminating in the reduction in root length. All doses of iprodione also presented cytogenotoxic action. The highest concentration of the fungicide affected the growth of A. cepa roots. In response to exposure to pesticide mixtures, the cell cycle of A. cepa was blocked in the G₁ phase. The mixtures with low doses of the pesticides significantly decreased the mitotic index, and as a consequence, the genotoxicity was reduced. In the mixtures with the highest doses of the agrochemicals, the blockage of the cell cycle was insufficient for damage repair, resulting in a significant increase of chromosomal aberrations. The results suggest caution in the use of pesticides doses that induce cytological abnormalities in non-target organisms.

The fungicide iprodione affects midgut cells of non-target honey bee Apis mellifera workers

The honey bee Apis mellifera is an important pollinator of agricultural crops and natural forests. Honey bee populations have declined over the years, as a result of diseases, pesticides, and management problems. Fungicides are the main pesticides found in pollen grains, which are the major source of protein for bees. The objective of this study was to evaluate the cytotoxic effects of the fungicide iprodione on midgut cells of adult A. mellifera workers. Bees were fed on iprodione (LD₅₀, determined by the manufacturer) for 12 or 24 h, and the midgut was examined using light and transmission electron microscopies. The expression level of the autophagy gene atg1 was assessed in midgut digestive cells. Cells of treated bees had signs of apoptosis: cytoplasmic vacuolization, apical cell protrusions, nuclear fragmentation, and chromatin condensation. Ultrastructural analysis revealed some cells undergoing autophagy and necrosis. Expression of atg1 was similar between treated and control bees, which can be explained by the facts that digestive cells had autolysosomes, whereas ATG-1 is found in the initial phases of autophagy. Iprodione acts by inhibiting the synthesis of glutathione, leading to the generation of reactive oxygen species, which in turn can induce different types of cell death. The results indicate that iprodione must be used with caution because it has side effects on non-target organisms, such as pollinator bees.

Synergistic Inhibition of Mycotoxigenic Fungi and Mycotoxin Production by Combination of Pomegranate Peel Extract and Azole Fungicide

Fungal plant pathogens cause considerable losses in yield and quality of field crops worldwide. In addition, under specific environmental conditions, many fungi, including such as some Fusarium and Aspergillus spp., are further able to produce mycotoxins while colonizing their host, which accumulate in human and animal tissues, posing a serious threat to consumer health. Extensive use of azole fungicides in crop protection stimulated the emergence of acquired azole resistance in some plant and human fungal pathogens. Combination treatments, which become popular in clinical practice, offer an alternative strategy for managing potentially resistant toxigenic fungi and reducing the required dosage of specific drugs. In the current study we tested the effect of pomegranate peel extract (PPE) on the growth and toxin production of the mycotoxigenic fungi Aspergillus flavus and Fusarium proliferatum, both alone and in combination with the azole fungicide prochloraz (PRZ). Using time-lapse microscopy and quantitative image analysis we demonstrate significant delay of conidial germination and hyphal elongation rate in both fungi following PPE treatment in combination with PRZ. Moreover, PPE treatment reduced aflatoxin production by A. flavus up to 97%, while a combined treatment with sub-inhibitory doses of PPE and PRZ resulted in complete inhibition of toxin production over a 72 h treatment. These findings were supported by qRT-PCR analysis, showing down-regulation of key genes involved in the aflatoxin biosynthetic pathway under combined PPE/PRZ treatment al low concentrations. Our results provide first evidence for synergistic effects between the commercial drug PRZ and natural compound PPE. Future application of these findings may allow to reduce the required dosage of PRZ, and possibly additional azole drugs, to inhibit mycotoxigenic fungi, ultimately reducing potential concerns over exposure to high doses of these potentially harmful fungicides.

Comparative metabolomics of aging in a long-lived bat: Insights into the physiology of extreme longevity

Vespertilionid bats (Mammalia: Order Chiroptera) live 3–10 times longer than other mammals of an equivalent body size. At present, nothing is known of how bat fecal metabolic profiles shift with age in any taxa. This study established the feasibility of using a non-invasive, fecal metabolomics approach to examine age-related differences in the fecal metabolome of young and elderly adult big brown bats (Eptesicus fuscus) as an initial investigation into using metabolomics for age determination. Samples were collected from captive, known-aged big brown bats (Eptesicus fuscus) from 1 to over 14 years of age: these two ages represent age groups separated by approximately 75% of the known natural lifespan of this taxon. Results showed 41 metabolites differentiated young (n = 22) and elderly (n = 6) Eptesicus. Significant differences in metabolites between young and elderly bats were associated with tryptophan metabolism and incomplete protein digestion. Results support further exploration of the physiological mechanisms bats employ to achieve exceptional longevity.

Morphogenetic Alterations of Alternaria alternata Exposed to Dicarboximide Fungicide, Iprodione

Fungicide-resistant Alternaria alternata impede the practical control of the Alternaria diseases in crop fields. This study aimed to investigate cytological fungicide resistance mechanisms of A. alternata against dicarboximide fungicide iprodione. A. alternata isolated from cactus brown spot was cultured on potato-dextrose agar (PDA) with or without iprodione, and the fungal cultures with different growth characteristics from no, initial and full growth were observed by light and electron microscopy. Mycelia began to grow from one day after incubation (DAI) and continued to be in full growth (control-growth, Con-G) on PDA without fungicide, while on PDA with iprodione, no fungal growth (iprodione-no growth, Ipr-N) occurred for the first 3 DAI, but once the initial growth (iprodione-initial growth, Ipr-I) began at 4-5 DAI, the colonies grew and expanded continuously to be in full growth (iprodione-growth, Ipr-G), suggesting Ipr-I may be a turning moment of the morphogenetic changes resisting fungicidal toxicity. Con-G formed multicellular conidia with cell walls and septa and intact dense cytoplasm. In Ipr-N, fungal sporulation was inhibited by forming mostly undeveloped unicellular conidia with degraded and necrotic cytoplasm. However, in Ipr-I, conspicuous cellular changes occurred during sporulation by forming multicellular conidia with double layered (thickened) cell walls and accumulation of proliferated lipid bodies in the conidial cytoplasm, which may inhibit the penetration of the fungicide into conidial cells, reducing fungicide-associated toxicity, and may be utilized as energy and nutritional sources, respectively, for the further fungal growth to form mature colonies as in Ipr-G that formed multicellular conidia with cell walls and intact cytoplasm with lipid bodies as in Con-G.

Dicarboximide resistance in field isolates of Alternaria alternata is mediated by a mutation in a two-component histidine kinase gene

Isolates of Alternaria alternata collected from a field site which had previously been treated with the dicarboximide fungicide iprodione were found to demonstrate a high level of resistance to iprodione and the phenylpyrrole fungicide, fludioxonil in plate assays. In order to determine the genetic basis for this fungicide resistance a partial length clone of a two-component histidine kinase (HK) was isolated from genomic DNA of a fungicide-sensitive A. alternata isolate using degenerate primers by PCR. Analysis of the AaHK1 gene structure indicates the presence of six 90 amino acid repeat domains upstream of a kinase domain as found in the homologous HK genes from other fungal species. Comparison of nucleic acid sequences from the fungicide-sensitive and fungicide-resistant A. alternata isolates confirmed the presence of mutations leading to premature termination of the translated HK protein. The possible role of the two-component HK in the development of dicarboximide resistance in A. alternata is discussed.

Lipid composition of Botrytis cinerea and inhibition of its radiolabelling by the fungicide iprodione

•  Botrytis cinerea is an important plant pathogen that causes grey mould in over 200 hosts. It is often controlled by dicarboximides, which have various proposed mechanisms of action, including effects on lipids. Here we have examined the effect of one dicarboximide, iprodione, on lipid metabolism. •  B. cinerea, cultured in malt extract media, was challenged with iprodione and its lipids extracted, separated by TLC, and analysed by GLC. Lipid metabolism was followed using [1-¹⁴ C]acetate. •  Triacylglycerol was the major nonpolar and phosphatidylcholine the main polar lipid in B. cinerea. Linoleate, followed by α-linolenate, were the major fatty acids and most lipid classes had compositions broadly similar to the total fatty acid pattern. Iprodione, at concentrations causing a cessation of growth (5 µM) caused a decrease in polar lipid but not total nonpolar lipid labelling. Within the nonpolar lipids, DAG was better labelled. •  The data show that iprodione had a selective effect on lipid metabolism. The altered pattern of labelling suggested that choline (ethanolamine) phosphotransferase would be worth investigating as a primary site of action.

Effect of iprodione, a dicarboximide fungicide, on primary cultured rainbow trout (Oncorhynchus mykiss) hepatocytes

As is known from literature, iprodione, a dicarboximide fungicide, has a highly specific action, with a capacity to cause oxidative damage through production of free oxygen radicals (ROS), but it does not appear to be species selective. Since this substance is able to diffuse in water, evaluation of its capacity to induce oxidative damage in an aquatic organism such as the rainbow trout (Oncorhynchus mykiss) was considered of particular interest. A study was, therefore, undertaken to investigate the effect of iprodione on free radicals (ROS) and malondialdehyde (MDA) production, reduced glutathione (GSH) content and catalase activity (CAT), in primary cultured trout hepatocytes, following treatment with 0.2, 0.3 and 0.4 mM concentrations for a 24-h period. The iprodione 0.3 and 0.4 mM concentrations increased both ROS and MDA production and decreased GSH content and CAT activity. These results suggest that iprodione is able to produce oxidative damage in primary cultured fish hepatocytes, thus confirming that its action is specific, but not species selective. It is also well known that ROS production in fungi is due to interaction with the flavin enzyme NADPH cytochrome c reductase to the extent that the normal electron flow from NADPH to cytochrome c is blocked. In contrast, we observed that, in primary cultured trout hepatocytes, iprodione appears to have no effect on NADPH cytochrome c reductase activity. It is, therefore, possible to presume that the mechanism of oxidative damage in trout hepatocytes differs from that observed in fungi. Moreover, our experiments also demonstrate that iprodione is able to induce "in vitro" CYP1A1, leading to the conclusion that the production of ROS is due to this phenomenon.

Adaptation to oxidative stress: effects of vinclozolin and iprodione on the HepG2 cell line

It is well known that the dicarboximide fungicides, vinclozolin and iprodione, induce lipid peroxidation by means of oxygen activation in fungi, but their action on mammalian cells is not yet clear. We therefore investigated the effect of 1- and 24-h treatments with vinclozolin at concentrations of 25, 50, 100 microg/ml and iprodione at concentration of 62.5, 125, 250 microg/ml on malonaldehyde and free radical production and on reduced glutathione levels in the human HepG2 hepatoma cell line. The concentrations were chosen on the basis of neutral red cytotoxicity assays. One-hour treatment with the different concentrations of either vinclozolin or iprodione increased both malonaldehyde and free radical content, and decreased reduced glutathione levels, whereas 24-h treatment decreased malonaldehyde content and free radical production, and increased reduced glutathione concentration. These results suggest that the mammalian cells respond to the initial oxidative damage caused by the two dicarboximide fungicides by means of a characteristic adaptative phenomenon within 24 h. This hypothesis is supported by the antagonized effects caused by treatment with the two dicarboximide fungicides and buthionine sulfoximine 0.5 mM, a specific and irreversible inhibitor of reduced glutathione synthesis. The data confirm that the two dicarboximide fungicides maintain their specific action in mammalian cells, although this action is masked by adaptation.

Correlation of Lipid Peroxidation in Botrytis cinerea Caused by Dicarboximide Fungicides with Their Fungicidal Activity

Dicarboximide fungicides iprodione, vinclozolin, and procymidone were examined for their capacity to inhibit mycelial growth, to cause cellular leakage, and to cause lipid peroxidation on Botrytis cinerea isolate BC2. All three fungicides effectively inhibited the mycelial growth of the fungi. The IC(50) values were found to be about 2 µM for all three fungicides, indicating that the fungicidal activity of the individual fungicides was almost the same. The fungicides caused significant cellular leakage and lipid peroxidation on the fungi in a concentration-dependent manner. Fungicidal activity of the three individual fungicides on inhibiting mycelial growth of the fungi correlated positively well with both cellular leakage and lipid peroxidation that were caused by the respective fungicides. Positive correlations were also found between the degree of cellular leakage and lipid peroxidation following treatment with the fungicides. Our results support the view that dicarboximide fungicides exert their fungicidal activity mainly through membrane lipid peroxidation and subsequent cellular leakage from the treated fungi.

Morphological and chemical alterations inBotrytis cinereaexposed to the dicarboximide fungicide vinclozolin

Treatment of actively growing Botrytis cinerea hyphae with micromolar concentrations of the dicarboximide fungicide vinclozolin resulted in significant alterations in the growth rate, morphology, and chemical composition of the cells. The addition of vinclozolin resulted in an immediate and severe reduction in the hyphal growth rate and a retardation in the emergence of the second germ tube. Cells treated with vinclozolin had a lower content of pool metabolites than control cells, and this difference increased with time of exposure to the fungicide. In contrast, vinclozolin-treated cells had a higher chitin concentration than control cells. These biochemical alterations were followed by the disorganization and clearing of cells, and by the appearance of dense and dark masses outside the hyphae, presumably composed of cell debris. Hyphae exposed to vinclozolin were more curved and branched and had shorter cells than the controls. The results indicate that vinclozolin causes a slow but generalized leakage of pool metabolites; this release precedes cell lysis and is not the result of a rapid and gross damage to the cytoplasmic membrane.Key words: vinclozolin, Botrytis cinerea, pool metabolites, membrane damage.

Effect of some fungicides on extracellular enzymes of Sclerotium rolfsii sacc

The effect of four fungicides on rot of cocoyam tubers, vegetative growth and extracelluar enzymes of the pathogen was investigated. At 200 ppm concentration, rot was completely prevented by Dithane M45. Benomyl and Iprodione in tubers of Xanthosoma sagittifolium. There was better protection by the fungicides for Cocoyam tubers treated with fungicides before spraying with hyphal suspension than those sprayed first with hyphal suspension of Sclerotium rolfsii sacc. At 600 ppm, Benomyl and Iprodione appreciably inhibited mycelial growth of the pathogen by 100% and 80.2% respectively. Both in vitro polygalacturonase and Cx-cellulase of the pathogen were inhibited by the Iprodione and Benomyl unlike Dithane M45 and Cupravit.

Effect of the fungicides tridemorph and vinclozolin on soil microorganisms and nitrogen metabolism

The effects of tridemorph and vinclozolin were studied on different types of microorganisms, urea hydrolysis and nitrification in soil and in culture. The fungicides adversely affected the population of bacteria, fungi and actinomycetes as a function of time of incubation. Urea hydrolysis both in culture and soil were also inhibited by the fungicides, and tridemorph was more detrimental. In soil, 45 micrograms/g of tridemorph inhibited 50% of ammonification of urea, ID50 for nitrite production was 750 micrograms/g. In urea-hydrolyzing cultures, 80, 75 and 77 mg/L of tridemorph were the ID50 values for urea hydrolysis by Micrococcus sp., Proteus sp. and P. vulgaris respectively.

Comparative acute renal effects of three N-(3,5-dichlorophenyl)carboximide fungicides: N-(3,5-dichlorophenyl)succinimide, vinclozolin and iprodione

A large number of carboximides have been synthesized, tested and, in some cases, marketed as agricultural fungicidal agents. One carboximide fungicide N-(3,5-dichlorophenyl)succinimide (NDPS) proved to be both highly efficacious as a fungicide and a nephrotoxin. The purpose of this study was to compare the acute nephrotoxic potential of three N-(3,5-dichlorophenyl)carboximide fungicides [NDPS, vinclozolin (VCLZ) and iprodione (IPDO)] to determine if nephrotoxic potential correlated with fungicidal efficacy among this class of structurally-related agricultural agents. Male Fischer 344 rats (4 rats/group) received a single intraperitoneal injection of a fungicide (0.4 or 1.0 mmol/kg) or vehicle (sesame oil, 2.5 ml/kg), and renal function was monitored at 24 and 48 h. NDPS (0.4 or 1.0 mmol/kg)-induced renal effects were characterized by marked diuresis, increased proteinuria, elevated blood urea nitrogen (BUN) concentration and kidney weights, decreased organic ion accumulation by renal cortical slices and proximal tubular necrosis. In contrast, IPDO and VCLZ (0.4 or 1.0 mmol/kg) administration resulted in only minor or no alterations in the renal function parameters studied and renal morphology. These results suggest that fungicidal efficacy does not correlate with acute nephrotoxic potential among the N-(3,5-dichlorophenyl)carboximide fungicides.

Biochemical targets for antifungal azole derivatives: hypothesis on the mode of action

The selective interaction of low concentrations of azole derivatives and other nitrogen heterocycles with cytochrome P-450 may be at the origin of the inhibition of ergosterol biosynthesis. From the depletion of ergosterol and the concomitant accumulation of 14 alpha-methylsterols, alterations in membrane functions, the synthesis and activity of membrane-bound enzymes, mitochondrial activities, and an uncoordinated activation of chitin synthase may result. Since chitin synthesis is more important in the hyphal form than in the budding form of C. albicans, the uncoordinated activation of chitin synthesis may be more trouble for the hyphal growth than for yeast budding. The assumption is made that from this difference the greater sensitivity of hyphal growth to azole antifungal agents may originate. It is also assumed that the higher degree of lipid unsaturation may be related to an inhibition of ergosterol biosynthesis. The inhibition of fatty acid desaturation and elongation induced by higher doses of miconazole and ketoconazole and the longer contact times might be related to interference with membrane fluidity, or it might due to chelation of the iron used in the oxidation reduction sequence during desaturation. The decreased availability of ergosterol and the accumulation of 14 alpha-methylsterols also may provide the environment needed to inactivate membrane-bound enzymes; e.g., cytochrome c peroxidase. However, it is still too speculative to correlate effects on membrane components with miconazole-induced changes in properties of all oxidases; e.g., the NADH-dependent, cyanide-insensitive oxidase. The accumulation of toxic concentrations of hydrogen peroxide, resulting from an increased NADH-oxidase activity and disappearance of the peroxidase and catalase activity, may contribute to the degeneration of subcellular structures. The complete disappearance of catalase observed at concentrations of miconazole greater than or equal to 10(-5) M may originate from direct effects on the cell. At these high concentrations reached only by topical application, direct membrane damage resulting from interaction of miconazole with lipids was observed. These direct interactions result in an inhibition of membrane-bound enzyme and mitochondrial activities and in leakage of intracellular components. The direct interactions were much less pronounced in cells treated with ketoconazole. This correlates with the smaller area occupied in the membrane per ketoconazole molecule (30 A2), compared with that occupied in the membrane per miconazole molecule (90 A2).(ABSTRACT TRUNCATED AT 400 WORDS)