Morphogenesis in germinating Fusarium graminearum macroconidia

Fusarium graminearum (teleomorph Gibberella zeae) is a significant pathogen of wheat and corn. F. graminearum forms multicellular macroconidia that play an important role in dissemination of the disease. The spatial pattern of morphogenesis in germinating macroconidia is described. Germ tubes preferentially emerge from the apical cells in a bipolar pattern that appears to be common to filamentous fungi. Chitin deposition occurs at two locations: the spore apices and cortical regions of macroconidial cells that subsequently produce a germ tube. The spatial pattern of morphogenesis requires the presence of functional microtubules, which may be responsible for the transport of key polarity factors to specific sites. These observations suggest that F. graminearum possesses a regulatory system that marks germ tube emergence sites. Perturbation of this system may represent an effective approach for inhibiting colonization of host plant surfaces.     

Ultrastructural studies on the cell walls in Fusarium sulphureum.

The cell walls of Fusarium sulphureum have a microfibrillar component that is randomly arranged. X-ray-diffraction diagrams of the microfibrils are consistent with a high degree of crystallinity and show that they are chitin. The chitin microfibrils of the peripheral walls envelop the hyphal apex and extend across the septae. During the first 8h in culture, the conversion of conidial cells to chlamydospores is evidenced by a swelling of the cells and the original microfibrils remain randomly arranged. Within 24h new wall material is deposited as the cells expand and the wall thickens. The new microfibrils are indistinguishable from those of the original conidial cells. After 3 days in culture, the chlamydospores are fully developed and have the characteristic thick wall which is a continuous layer of randomly arranged microfibrils. Chlamydospores maintained in a conversion medium for 8 days have microfibrils identical with those in 3-day-old cultures; thus a further change in the microfibril orientation did not occur during that period. Alkaline hydrolysis of the walls removes most of the electron-dense staining constituents from the inner wall layer and leaves the outer wall layer intact. This treatment also reveals some of the wall microfibrils. An additional treatment of the walls with HAc/H2O2 completely removes the wall components that react positively to heavy metal stains. The results are discussed in relation to the structure of other fungal cell walls.     

Transport of phenylalanine by conidia of Fusarium sulphureum.

L-Phenylalanine was actively transported by conidia of Fusarium sulphurenum Schlect (isolate 1). Uptake was optimal at pH 7, 30 degrees C; respiration-dependent; and was unaffected by relatively high internal concentrations of phenylalanine. The Km for transport was 1-3 X 10(-5) M and the Vmax was 2.5-4 nmol/min per milligram dry weight. Phenylalanine is transported by a general transport system for basic and neutral amino acids. Sucrose repressed uptake of phenylalanine and this repression was largely negated by cycloheximide. Efflux of accumulated phenylalanine was influx-dependent; this transport system deteriorated slowly with aging of the conidial culture.     

Differentiation inside multicelled macroconidia of Fusarium culmorum during early germination

Multicelled conidia are formed by many fungal species, but germination of these spores is scarcely studied. Here, the germination and the effects of antimicrobials on multicompartment macroconidia of Fusarium culmorum were investigated. Germ-tube formation was mostly from apical compartments. The intracellular pH (pH(in)) of the different individual cells of the macroconidia was monitored during germination. The pH(in) varied among different compartments and during different stages of germination. The internal pH was lowest in ungerminated cells and rose during germ-tube formation and was highest in new germ tubes. Antifungal compounds affect the pH(in) and differentiation of the conidia. The pH(in) inside the macroconidial compartments was lowered very fast in the presence of nystatin (1 and 4 microg/ml). At sublethal doses (0.3 microg/ml), the apical compartments were preferentially targeted showing lower pH(in) values. The reduced germination capacity of apical compartments under these conditions was compensated by an increased germination capacity of middle compartments.     

The effect of ionic surface-active agents on macroconidial plasma membrane of Fusarium sulphureum.

A method was developed for direct assessment of changes in cytoplasmic volume and permeability of plasma membranes of intact cells to divalent cations. This technique, which ultilized an amphipathic spin label partitioning between intracellular aqueous and hydrophobic environments, allowed estimates of the proportion of cells in a homogenous population sustaining membrane damage associated with Ni+2 and water permeability and the rate at which such damage was induced. Several specific effects of cationic and anionic surfactants on the macroconidial plasma membranes of Fusarium sulphureum Schlect (isolate 1) were distinguished on the basis of detergent concentration and charge. The induction of water uptake by the cells was found to be an effect of dodecylguanidine acetate (Dodine), a cationic fungicide, at low concentration. At higher concentrations (greater than 5 X 10(-5) M) both the impermeability of the plasma membrane to divalent cations and the ability to accumulate actively L-phenylalanine were lost irreversibly and cell lysis occurred above 5 X 10(-4) M. Sodium dodecyl sulfate eliminated divalent cation impermeability more rapidly than Dodine but was less effective in inhibiting active transport function. An antagonistic effect between cationic and anionic detergents was observed.     

Cell wall of Fusarium sulphureum: I. Chemical composition of the hyphal wall

The hyphae wall of Fusarium sulphureum Schlect. (Isolate 1) was isolated and purified. Electron microscopy studies showed that the isolated cell wall consisted of two distinct layers, an outer electron dense layer and a broader electron transparent inner layer. Chemical analysis revealed that the cell wall contained 66% carbohydrate, 7.3% protein, 5.5% lipid and 1.8% ash.The major cell wall component N-acetylglucosamine (39%) was shown by X-ray diffraction analysis to be present as chitin. Glucose constituted 14% of the cell wall, while mannose, galactose, and glucuronic acid, accounted for 15% of the cell wall. Glucorunic acid appears to be predominantly linked to galactose in the intact wall.     

Evaluation of selective media for the isolation of Fusarium solani var. coeruleum and Fusarium sulphureum from soil and potato tuber tissue

A new selective medium containing pentachloronitrobenzene and 2-aminobutane (the PAB medium) was developed for soil-dilution plate enumeration of fungal propagules of Fusarium solani var. coeruleum and F. sulphureum from field soil. Growth of ‘weed-fungi’ was less on the PAB medium than on the previously developed F. solani var. coeruleum isolation medium (the PM70 medium) and significantly more propagules of F. solani var. coeruleum were detected. Propagule counts (x) of F. solani var. coeruleum and F. sulphureum from the PAB medium, after log₁₀ (x/10 + 1) transformation, were linearly related to the angular transformation of measurements of soil infectivity from the tuber bait method using the susceptible cv. Catriona. Slopes from disease-inoculum regressions for F. solani var. coeruleum and F. sulphureum in November and May were similar and this suggests that the mode of pathogenic action of F. solani var. coeruleum and F. sulphureum was similar. Recently harvested tubers, inoculated in November, however, were more resistant to infection by both pathogens than stored tubers inoculated in May. Storage of air dry soil at 4°C for 6 months reduced the population of F. sulphureum but not the population of F. solani var. coeruleum. Whereas the PAB medium is recommended primarily for use in the isolation of F. solani var. coeruleum and F. sulphureum from field soil, the PM70 medium appears to be more suitable for recovery of these pathogens and others, including Phoma exigua var. foveata from diseased tuber tissue.     

Transmission of Fusarium solani var. coeruleum and F. sulphureum from seed potatoes to progeny tubers in the field

In experiments in three years, seed tubers were inoculated before planting with either Fusarium solani var. coeruleum or F. sulphureum to initiate a rot, or were contaminated by dipping in soil slurries containing spore suspensions of one or other of the pathogens. Transmission to progeny tubers was tested by uniformly wounding and incubating tubers and by dilution plating of soil samples. In two years, transmission of F. sulphureum was greater from highly contaminated than from rotting seed and was greater on cv. Pentland Crown than on cvs Desiree and Maris Piper. F. solani var. coeruleum appeared to be transmitted most readily from rotting seed and Maris Piper was the cultivar most extensively contaminated. In experiments with different harvest dates, transmission of both fungi from highly contaminated seed could be detected by late June or mid-July. More progeny tuber wounds rotted in F. sulphureum than in F. solani var. coeruleum plots and in one year, F. sulphureum caused more rots on cv. Record than on cv. Maris Piper. These differences between the pathogens may be related to their differing abilities to sporulate underground on the surface of seed tubers and on stem bases.     

Studies on the macroconidia of Microsporum canis

The characteristics of an in vitro polyuridylic acid dependent amino acid incorporating system prepared from germinating macroconidia of Microsporum canis are described. The incorporation of ¹⁴C-phenylalanine into polyphenylalanine is dependent on S-30 extract, adenosine triphosphate, magnesium ions and polyuridylic acid. Incorporation is slightly enhanced by yeast transfer ribonucleic acid and pyruvate kinase. The system is highly sensitive to ribonuclease, puromycin and miconazole (an antifungal agent), moderately sensitive to sodium fluoride and much less sensitive to phenethylalcohol, cycloheximide, chloramphenicol and deoxyribonuclease. Cell-free extract from ungerminated conidia has less capacity to synthesize the protein and during germination a marked increase in the protein synthetic activity is observed. The results from experiments wherein ribosomes and S-100 fraction from germinated and ungerminated spores are interchanged, revealed that the defect in the extract from the ungerminated spore is in the ribosomes.Abbreviations Poly(U) polyuridylic acid - tRNA transfer ribonucleic acid - ATP adenosine triphosphate - GTP guanosine triphosphate - BSA bovine serum albumin - RNase ribonuclease - DNase deoxyribonuclease - POPOP 1,4-bis-2(5-phenyl oxazolyl)benzene - PPO 2,5-diphenyl oxazole - TCA trichloracetic acid     

Comparative study on the action of S-(+)-carvone, in situ, on the potato storage fungi Fusarium solani var. coeruleum and F. sulphureum

Growth of Fusarium sulphureum was inhibited by S-(+)-carvone administered via the gas phase. Under the same conditions, the related fungus F. solani var. coeruleum was not inhibited. In liquid medium, both fungi were found to convert S-(+)-carvone with the same rate, mainly into isodihydrocarvone, isodihydrocarveol and neoisodihydrocarveol. Only a slight difference in the relative amounts of the bioconversion products was observed. Since the bioconversion products did not inhibit the growth of the fungi to the same extent as S-(+)-carvone, the process can be considered as a detoxification mechanism. The bioconversion as such cannot account for the observed difference in growth inhibition.     

韭菜对香蕉枯萎病菌生长及香蕉枯萎病发生的抑制作用

结合实验室抑菌试验和大棚人工接菌盆栽试验,研究韭菜对香蕉枯萎病菌4号生理小种(Foc4)的拮抗作用及其对香蕉枯萎病发生的防控效果.结果显示:离体条件下,韭菜粗提取液显著抑制Foc4菌丝的生长,造成菌丝变形、细胞的解体;也能显著抑制孢子的萌发并导致孢子失去活性.大棚盆栽试验中,韭菜处理的巴西香蕉苗枯萎病发病率降低70%,病情指数降低86.9%;韭菜处理的广粉1号粉蕉苗枯萎病的发病率降低76.7%,病情指数降低93.4%.研究表明,韭菜对Foc4有很高拮抗效果,而且对香蕉枯萎病有很高的防控作用.     

Effect of thiols on lipid peroxidation in rat liver microsomes

The stimulatory or inhibitory effects of various thiol compounds on in vitro lipid peroxidation by iron-ascorbate in rat liver microsomes were determined. Glutathione had no measurable pro-oxidant capacity, in contrast, it protected against lipid peroxidation. N-Acetyl l-cysteine and S-methyl-glutathione had no effect on in vitro lipid peroxidation. l-Cysteine stimulated lipid peroxidation and also of d-penicillamine and dl-dithiothreitol the pre-oxidant capacity predominated the anti-oxidant capacity. Cysteamine afforded a pronounced protection against in vitro lipid peroxidation. In contrast to the labile character of the glutathione dependent protection, the protection by cysteamine was not affected by heat-pretreatment of the liver microsomes or alkylating protein sulfhydryl groups by N-ethyl maleimide. Again in contrast to glutathione, the protection against in vitro microsomal lipid peroxidation by cysteamine was not reduced after in vivo lipid peroxidation induced by CC14. This suggests that even after the process of lipid peroxidation has been started, administration of cysteamine might still be beneficial.     

Distribution of nuclei in macroconidia ofMicrosporum gypseum

The distribution of nuclei in macroconidia was investigated in 20 strains of the dermatophyteMicrosporum gypseum by fluorescence microscopy. The macroconidia were characterized by the right-left and the central-marginal symmetry indices. In 18 strains the significant majority of the nuclei were situated in the basal part of the macroconidium, the remaining 2 strains showed a more or less uniform distribution of nuclei. All strains had higher numbers of nuclei in the central part of the macroconidium as compared with the periphery.     

Effect of flavonoids on the development of Fusarium oxysporum f. sp. lycopersici

Abstract

In the present study the effect of flavonoid compounds on the germination and fungal growth of the soil-borne tomato pathogen Fusarium oxysporum f. sp. lycopersici was studied. Out of 12 flavonoid compounds only myricetin and luteolin exhibited a low stimulating activity on microconidia germination of Fusarium oxysporum f. sp. lycopersici, whereas the other flavonoids tested were inactive when applied at five different concentrations. In our study the tested flavonoids affect fungal growth differently to microconidia germination. Individual flavonoid concentrations resulted in a small increase of fungal growth, but the lowest flavonoid concentrations showed an inhibiting effect on fungal growth for all flavonoids tested. There is evidence to suggest, that low flavonoid concentrations exhibit slight antimicrobial properties against Fusarium oxysporum f. sp. lycopersici.     

Distribution of nuclei in macroconidia of dermatophytes

The distribution of nuclei in macroconidia was appraised in the following five dermatophyte species:Epidermophyton floccosum, Microsporum cookei, Microsporum gypseum, Trichophyton ajelloi andTrichophyton vanbreuseghemii. In all strains under investigation the number of cells in a macroconidium displays no correlation with the average number of nuclei in a cell of a given macroconidium; cells situated in the central part of the macroconidium tend to have a higher number of nuclei than cells at the periphery. The explored strains mutually differ significantly in the prevalence of nuclei in the left (basal) and right (apical) part of the macroconidium.