Compatible and Incompatible Interactions Between Callus Tissue and Mycorrhizal or Pathogenic Fungi

Tissue cultures of Nicotiana tabacum were utilized to investigate the mechanisms associated with host specificity and non-host incompatibility in mycorrhizal and pathogenic fungi. They were tested for expression of resistance to different species of mycorrhizal fungi and to a fungal pathogen of tobacco, Thielaviopsis basicola , by monitoring the production of callose, phenolic compounds and peroxidases in dual cultures. Tobacco cells reacted to the presence of all the mycorrhizal fungi with callose deposits, whereas callose was nearly always absent in tobacco cells inoculated with their pathogen T. basicola. The broad-host range ectomycorrhizal fungi Hebeloma crustuliniforme, Lac-caria laccata and Suilhis granulatus elicited less intense responses than did Hymenoscyphus ericae. The results obtained for phenolic production and peroxidase activity were consistently similar to those obtained for callose deposition. They showed that H. ericae , an endomycorrhizal symbiont of Ericaceae, was highly incompatible with tobacco cells and that the tobacco pathogen T. basicola did not elicit strong reactions in the cells of its host. In this paper, the possibility of utilizing callus cultures as a simple model system to study both the different degrees of compatibility and the early events of recognition between mycorrhizal fungi and their host or non-host plants is discussed.     

Signalling between Pathogenic Rust Fungi and Resistant or Susceptible Host Plants

Rust fungi are obligately biotrophic plant parasites that obtaintheir nutrients from living host cells. The initiation of thetwo parasitic phases of these fungi generally requires topographicsignals from the plant surface followed, for the dikaryoticphase, by a successive sequence of signals to control furtherfungal development within the plant. During the fungal lifecycle, three types of intracellular structures (invasion hyphae,M-, and D-haustoria) are formed and each may differently affectthe host membrane that surrounds it, as well as affecting othercellular components. Each intracellular structure also preventsnon-specific plant defences triggered by fungal activities,possibly by interfering with the signalling system rather thandefence expression. In resistant host cultivars, cellular invasiontriggers a rapid cell death (the hypersensitive response) thatshares some features with developmentally programmed cell deathin animal and plant tissues, and is controlled by parasite-specificresistance genes that resemble those that defend plants againstother types of pathogens. Evidence from one system suggeststhat this response is specifically elicited by a fungal peptideand does not involve the oxidative burst typical of resistanceexpression in other plant-pathogen interactions. However, overall,few of the molecules involved in any of these plant-rust fungiinteractions have been completely characterized and much isleft to be discovered, particularly with respect to how cellularsusceptibility to rust fungi is conditioned.Copyright 1997 Annalsof Botany Company Apoptosis; biotrophy; elicitor; hypersensitive response; oxidative burst; suppressor; Uromyces vignae     

Side-Effects of Field Applications of 'Propiconazol' and 'Captafol' on the Composition of Non-target Soil Fungi in Spring Barley

The results show great seasonal variation in number and composition of the fungi isolated from the upper soil layer, especially owing to an increased isolation of primary saprophytic fungi during the late growing season. Before fungicide treatment no statistically significant difference was measured between the number of isolated fungi from the examined soils. During the treatment period significantly fewer fungi were isolated from plots treated with ‘captafol’ or ‘propiconazol’ than from the untreated plots. The differences between untreated and treated plots were not statistically significant 30 days after the last treatment. The ecotoxicological effect on the total isolated fungal flora thus seems negligible. However the fungi responded differen, tly to treatment with ‘captafol’ and ‘propiconazol’. None of the fungi were significantly affected for more than a month when treated with ‘propiconazol’. The number of primary saprophytic fungi (Cladosporium spp., Alternaria spp., Epicoccum purpurascens, and Stemphylium sp.) and Sphaeropsidales, however, was significantly reduced for more than a month when treated with ‘captafol’.     

Effect of Cadmium on Fungi and on Interactions Between Fungi and Bacteria in Soil: Influence of Clay Minerals and pH

Fungi (Rhizopus stolonifer, Trichoderma viride, Fusarium oxysporum f. sp. conglutinans, Cunninghamella echinulata, and several species of Aspergillus and Penicillium) tolerated higher concentrations of cadmium (Cd) when grown in soil than when grown on laboratory media, indicating that soil mitigated the toxic effects of Cd. In soil amended with clay minerals, montmorillonite provided partial or total protection against fungistatic effects of Cd, whereas additions of kaolinite provided little or no protection. Growth rates of Aspergillus niger were inhibited to a greater extent by 100 or 250 μg of Cd per g in soil adjusted to pH 7.2 than in the same soil at its natural pH of 5.1. However, there were no differences in the growth rates of Aspergillus fischeri with 100 or 250 μg of Cd per g in the same soil, whether at pH 5.1 or adjusted to pH 7.2. Growth of A. niger and A. fischeri in a soil contaminated with a low concentration of Cd (i.e., 28 μg/g), obtained from a site near a Japanese smelter, did not differ significantly from growth in a soil collected some distance away and containing 4 μg of Cd per g. Growth of A. niger in sterile soil amended with 100 μg of Cd per g and inoculated with Bacillus cereus or Agrobacterium tumefaciens was reduced to a greater extent than in the same soil containing 100 μg of Cd per g but no bacteria. The inhibitory effects of Agrobacterium radiobacter to A. niger were slightly reduced in the presence of 100 μg of Cd per g, whereas the inhibitory effects of Serratia marcescens were enhanced.     

Identification of New Sphingomyelinases D in Pathogenic Fungi and Other Pathogenic Organisms

Sphingomyelinases D (SMases D) or dermonecrotic toxins are well characterized in Loxosceles spider venoms and have been described in some strains of pathogenic microorganisms, such as Corynebacterium sp. After spider bites, the SMase D molecules cause skin necrosis and occasional severe systemic manifestations, such as acute renal failure. In this paper, we identified new SMase D amino acid sequences from various organisms belonging to 24 distinct genera, of which, 19 are new. These SMases D share a conserved active site and a C-terminal motif. We suggest that the C-terminal tail is responsible for stabilizing the entire internal structure of the SMase D Tim barrel and that it can be considered an SMase D hallmark in combination with the amino acid residues from the active site. Most of these enzyme sequences were discovered from fungi and the SMase D activity was experimentally confirmed in the fungus Aspergillus flavus. Because most of these novel SMases D are from organisms that are endowed with pathogenic properties similar to those evoked by these enzymes alone, they might be associated with their pathogenic mechanisms.     

Induced Resistance to Pathogenic Fungi in Norway Spruce

Norway spruce (Picea abies) trees (approximately 16 m high) of a single clone were used to study the effects of fungal infection and wounding on induction of resistance to the bark beetle-associated bluestain fungus Ceratocystis polonica. A dose-response experiment was designed involving three different dosages of fungal (fungus and wound) and sterile agar (wound) pretreatment inoculations (10, 50, or 100 inoculations/m² on the stem between 0.8 and 2.0 m high). Three weeks after pretreatment, trees were challenged with a massive C. polonica inoculation (400 inoculations/m²). Control trees that received no pretreatment were heavily colonized and killed by the challenge inoculation. The high and medium fungal pretreatments reduced subsequent fungal colonization success by 76% to 97% relative to the control, and fungal pretreatments protected the trees much more efficiently than sterile agar pretreatments. The protection was demonstrated to be local and not systemic in a subsequent experiment, where trees were pretreated with the medium fungal dosage on the lower bole and challenge inoculated further up the stem. Protection was also demonstrated to be pathogen nonspecific, as trees that had been pretreated with a medium dosage of the root rot fungus Heterobasidion annosum showed enhanced resistance to challenge inoculation with C. polonica.     

Large-Scale Chromosomal Changes and Associated Fitness Consequences in Pathogenic Fungi

Pathogenic fungi encounter many different host environments to which they must adapt rapidly to ensure growth and survival. They also must be able to cope with alterations in established niches during long-term persistence in the host. Many eukaryotic pathogens have evolved a highly plastic genome, and large-scale chromosomal changes including aneuploidy, and loss of heterozygosity (LOH) can arise under various in vitro and in vivo stresses. Both aneuploidy and LOH can arise quickly during a single cell cycle, and it is hypothesized that they provide a rapid, albeit imprecise, solution to adaptation to stress until better and more refined solutions can be acquired by the organism. While LOH, with the extreme case of haploidization in Candida albicans, can purge the genome from recessive lethal alleles and/or generate recombinant progeny with increased fitness, aneuploidy, in the absence or rarity of meiosis, can serve as a non-Mendelian mechanism for generating genomic variation.     

外科深部真菌感染的病原学分析

目的分析外科住院患者合并真菌感染状况。方法分离的真菌用API 20C AUX真菌鉴定条,用ATB FUNGUS-2进行药敏试验。结果真菌的种类分布中第1位是白色念珠菌占53%,第2位是热带念珠菌占20%,第3位是光滑念珠菌占14%,第4位是近平滑念珠菌占4%,第5位是其余念珠菌占2%;真菌在外科各区分布中,外科ICU占42%,移植外科占25%;真菌在各类标本分布中,痰占43%,尿液占13%,粪便占10%,引流液占9%,血液占7%;真菌对药物5-氟胞嘧啶、两性霉素B、氟康唑、伊曲康唑的药物敏感性分别是93%、98.9%、90.8%、59.8%。结论外科真菌感染集中在重症病区(ICU),分离的致病真菌主要是白色念珠菌、热带念珠菌、光滑念珠菌,真菌对两性霉素B敏感性最高。     

植物挥发性物质与植物抗病防御反应

植物挥发性物质的许多组分具有抗菌活性,这可能是其抵御植物病原菌侵染的化学防卫因素;其中一些组分为防卫基因表达的高效调节子,是病原菌侵染植物过程中,植株自身或相邻植株间传递信息的信号分子.该文就植物挥发性物质的主要类群、生理作用、病原菌侵染和其他因子诱导对其影响及其在植物抗病防御反应中的作用作了介绍.     

Contrasting Effects of Elevated Temperature and Invertebrate Grazing Regulate Multispecies Interactions between Decomposer Fungi

Predicting the influence of biotic and abiotic factors on species interactions and ecosystem processes is among the primary aims of community ecologists. The composition of saprotrophic fungal communities is a consequence of competitive mycelial interactions, and a major determinant of woodland decomposition and nutrient cycling rates. Elevation of atmospheric temperature is predicted to drive changes in fungal community development. Top-down regulation of mycelial growth is an important determinant of, and moderator of temperature-driven changes to, two-species interaction outcomes. This study explores the interactive effects of a 4 °C temperature increase and soil invertebrate (collembola or woodlice) grazing on multispecies interactions between cord-forming basidiomycete fungi emerging from colonised beech (Fagus sylvatica) wood blocks. The fungal dominance hierarchy at ambient temperature (16 °C; Phanerochaete velutina > Resinicium bicolor > Hypholoma fasciculare) was altered by elevated temperature (20 °C; R. bicolor > P. velutina > H. fasciculare) in ungrazed systems. Warming promoted the competitive ability of the fungal species (R. bicolor) that was preferentially grazed by all invertebrate species. As a consequence, grazing prevented the effect of temperature on fungal community development and maintained a multispecies assemblage. Decomposition of fungal-colonised wood was stimulated by warming, with implications for increased CO₂ efflux from woodland soil. Analogous to aboveground plant communities, increasing complexity of biotic and abiotic interactions appears to be important in buffering climate change effects on soil decomposers.     

Interspecific Interactions among Tropical and Subtropical Freshwater Fungi

Abstract Twenty-seven species of tropical and subtropical fungi isolated from freshwater were examined for evidence of interspecific interactions, which are important in determining the ecological roles of fungi. Evidence for interspecific interactions was examined by inoculating paired fungi 25 mm apart on the surface of agar plates. The antagonistic activities were different among different isolates and even between isolates of the same species, for example, Ophioceras dolichostomum isolated from different origins. Pseudohalonectria longirostrum and Kirschsteiniothelia elaterascus, which produced pigment in culture, were strongly inhibitory species. Several aquatic hyphomycetes seems to be less competitive and less likely to produce antagonistic substances. Competitive abilities were also influenced by the range of enzymes that a fungus produced. For example, Verticillium sp. and Diaporthe sp., which produced only one or two kinds of enzyme, were found to exhibit weak competitive abilities and were easily replaced. The results of competition experiments also showed that slow-extending fungi (e.g., Pseudohalonectria longirostrum and Kirschsteiniothelia elaterascus) were more competitive than early fast-extending fungi (e.g., Ophioceras dolichostomum and Nectria haematococca). Received: 13 October 1998; Accepted: 3 March 1999     

霉克舒对致病性浅部真菌的体外抑菌作用研究

从湛江地区 15 4例癣病患者分离真菌 ,评价一种新的抗真菌药—霉克舒对上述真菌菌株的体外抑菌活性。应用琼脂稀释法测定霉克舒对浅部真菌的最小抑菌浓度 (MIC) ,同时以兰美抒作为对照药物。从 15 4例癣病患者中分离出 14 1株真菌 ,其中以红色毛癣菌和须癣毛癣菌为主 ,分别占 6 6 .7%和 14 .2 %。霉克舒的抑菌作用与兰美抒相比略强或相当 ;对霉克舒各单一成分的初步抑菌效果进行比较 ,复合物的抑菌作用明显强于水杨酸或特比萘芬等单一成分。上述结果显示 ,霉克舒在体外对常见致病性浅部真菌具有较强的抗菌活性。