摘要:

An increasing number of fungi are being collected and screened for the biological control of pests, but nomenclature, taxonomy, and correct identification of many of them remain problematic.Trichodermaspp. and the rust fungi are promising candidates for biocontrol agents, yet they present serious taxonomic problems. Several groups of entomopathogenic fungi are also potential biocontrol sources of agents. Genera such asCordyceps,Aschersonia,Verticillium,Beauveria, andMetarhiziumare in need of urgent revision. Before their release can be considered, all details of their complex life cycles and taxonomy have to be elucidated to satisfy quarantine authorities. Formerly, the taxonomy and identification of biocontrol fungi has been based largely on morphological structures, but molecular techniques have been introduced to provide more objective criteria.BeauveriaandMetarhiziumspp. have been subjected to several molecular techniques that have resolved phylogeny and species concepts. InMetarhizium, a high degree of genetic diversity is present. Incorrect typification, lack of holotypes, and poorly resolved life cycles and unclear teleomorph – (syn)anamorph connections are serious taxonomic contraints. Only a small fraction of the fungi that can be used for biological control has been examined. The destruction of habitats and ecosystems for these fungi will result in the disappearance of fungal germ plasm of potential value, not only for biological control but also as a source of novel metabolites. This loss and the decline of taxonomic expertise in the fungi are major problems.Key words: biocontrol, taxonomy,Trichoderma,Beauveria,Metarhizium,Cordyceps.

ISSN:0008-4026    

DOI:10.1139/b95-229

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Many reviews in the past decade outline the need to understand the complex interactions between fungal pathogens of roots, mycorrhizal fungi, mycorrhizosphere associates, and various climatic and edaphic factors to develop stable mycorrhizal biocontrol strategies. Cylindrocarpon root rot caused byCylindrocarpon destructansis a good example of a replant disorder that is amenable to this type of control in nurseries and new or renovated orchard sites. Cylindrocarpon root rot was reduced by endomycorrhizal colonization of potted peach rootstocks withGlomus aggregatumunder controlled environment conditions using Turface or natural, untreated orchard soils. Several mechanisms of suppression are discussed including tolerance to the pathogen through increased host vigor and reduced exudation, competition for space and nutrients, and induced host resistance. Technical innovations and new concepts of fungal community ecology are improving the odds of developing effective biocontrols with mycorrhizae. Exploitation of natural and integrated disease management using multiple mechanisms of pathogen inhibition may offset the difficulties in inoculum preparation.Key words:Cylindrocarpon destructans, antagonism, competition, rhizosphere, mycorrhizosphere.

ISSN:0008-4026    

DOI:10.1139/b95-230

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This article explores the relationship between cellular turgor pressure and mechanisms used by fungi to invade solid substrates. In the oomyceteSaprolegnia ferax, the rate of hyphal growth through solid medium decreases as turgor is reduced and the effect is most pronounced at high agar concentrations. This is the first clear evidence that turgor provides the force for invasive hyphal growth. Among pathogenic fungi, the role of turgor in plant infection has been established by experiments on the rice blast fungusMagnaporthe grisea, which can punch through the surface of rice leaves and a variety of synthetic membranes. In common with other walled organisms, fungal growth hinges on an interplay between turgor and the resistance offered by the wall; irrespective of turgor, no cellular expansion or substrate deformation can occur unless the wall yields. Turgor is the only logical source of the necessary force when fungi penetrate plastics, lift the lids of Petri dishes, or burst through asphalt paving. In other cases, fungi use exoenzymes to soften the substrate in advance of the invading cells. This process is particularly significant in plant infection, which involves a combination of physical force and the secretion of cuticle- and wall-degrading enzymes.Key words: hyphae, osmotic stress, Oomycetes,Magnaporthe,Saprolegnia, turgor pressure.

ISSN:0008-4026    

DOI:10.1139/b95-231

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Wall structure has been analysed by a process of careful demolition, in which chemical extradants are used to remove specific polymers for sugar and linkage analysis, gel-permeation or ion-exchange chromatography, and nuclear magnetic resonance spectroscopy. Sequence-dependent endoglycanases cleave certain polysaccharides into oligomers that can be sequenced completely and give a clear picture of the repetitive units used to make fundamental polymers. We have also developed and adapted new chemical procedures and pulse-labelling techniques to give more information on the ways that wall polymers are subtly modified during growth. In this report, we review these conventional means of carbohydrate analyses together with newer methods of selective enzymic hydrolysis, separation of large oligosaccharides by high pH anion-exchange chromatography, and detection of molecular mass of several thousand daltons by electrospray mass spectrometry. These new technologies have already given much valuable information about the polymeric building blocks, but little information on how these polymers are arranged in space. For this, we adapted new cryopreservation techniques for electron microscopy that can image the wall in as close to the in vivo state as possible. In addition to defining anomeric linkages and linkage structures in preparations of native polymers, nuclear magnetic resonance spectroscopy can also determine the relative mobility of particular polymers within the structure of hydrated cell walls. The generation of antibodies to particular cell wall epitopes has enabled us to define architectural differences among species, among tissue types, and even among domains within a single wall. Our awareness of the diversity and complexity of primary cell wall architecture has driven a search for methodologies such as Fourier transform infrared and Fourier transform Raman microspectroscopies, which are suitable for analysis at the single cell wall level.Key words: cell walls, polysaccharides, gas – liquid chromatography – mass spectrometry, Fourier transform infrared microspectroscopy, nuclear magnetic resonance spectroscopy, immunocytochemistry.

ISSN:0008-4026    

DOI:10.1139/b95-232

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Apical hyphal extension involves very localized apical deposition of newly synthesized wall skeletal material, notably chitin. A branch forms where a new localized site of chitin deposition occurs in the lateral wall. Key enzymes involved are the chitin synthases. Their activity must be under tight regulation to achieve the orderly deposition of chitin. There is evidence that inactive chitin synthase is distributed throughout the hyphal plasma membrane and activated at the apex and at an incipient branch site. At these sites, the wall is plastic. We have investigated the hypothesis that physical stressing of the membrane, a consequence of the cell's turgor pressure acting at these weaker points, may locally activate the chitin synthase. Results show that cells that have been subjected to hypoosmotic stress have raised native chitin synthase activities. It is suggested that stressing the membrane may cause a conformational change in chitin synthase molecules in the membrane or changes in the interactions between chitin synthase and associated polypeptides, leading to activation. This process may act along with other regulatory mechanisms discussed here, such as post-translational modification and availability of allosteric effectors, to restrict the enzymic activity to sites where chitin synthesis is required.Key words: chitin synthase, zymogen, turgor pressure, membrane stress,Candida albicans, hyphal growth.

ISSN:0008-4026    

DOI:10.1139/b95-233

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Independent nuclear motility is involved in many important aspects of fungal life cycles, including the following: nuclear division; population of hyphal tip cells, branches, and spores with nuclei; dikaryotization; and karyogamy. Spindle pole bodies are almost constantly in motion during all phases of the nuclear cycle, and they have been linked to most instances of independent nuclear motility. A role for microtubules in this process is now well established, and research is being focused on which set of them, astral or cytoplasmic, is utilized as well as on the microtubule-associated motor proteins that may generate the force. In some cases, F-actin may interact with the microtubules or even provide an alternative cytoskeleton supporting nuclear migration. Hyphal tip growth and independent nuclear motility are coordinated and interrelated processes, making the elucidation of the signals, processes, and structures involved an attractive area for further research.Key words: actin, microtubule, microtubule associated protein, microtubule organizing center, motility, nucleus.

ISSN:0008-4026    

DOI:10.1139/b95-234

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The role of cytosolic pH (pHc) in determining the growth site and in tip elongation has been investigated by measuring and manipulating pHc. pHcacidifies by 0.1–0.2 units as the growth axis is established. Concomitantly, cells accumulate KCl, which increases the cellular osmotic pressure, resulting in the generation of turgor pressure. The K+taken up is apparently compartmentalized as the free cytosolic K+activity remains constant. At present, the relation between pHc, K+, and turgor pressure is not well understood. A small but statistically significant cytosolic pH gradient, acid at the future growth site, is also detectable during axis establishment. As growth is initiated the intensity of the gradient increases to approximately 0.3 pH units. The magnitude of the pH gradient correlates with the rate of tip elongation. The gradient may regulate tip elongation in a number of ways, including local control of the assembly and stability of cytoskeletal elements.Key words: cytosolic pH gradients, tip growth, turgor pressure, weak acids and bases, SNARF 1, pH-sensitive microelectrodes.

ISSN:0008-4026    

DOI:10.1139/b95-235

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Hyphal tip growth is an exquisitely controlled process that forms developmentally regulated, species-specific, even-diameter tubes at rates of up to about 50 μm/min. The traditional view is that this process results from the balance between the expansive force of turgor pressure and the controlled extensibility of the apical cell wall. While these elements are involved, the model places regulation into either the global domain (turgor pressure) or the extracellular environment (the cell wall), neither of which seem well suited to the level of control evinced. Recent evidence suggests that F-actin-rich elements of the cytoskeleton are important in tip morphogenesis. Our current models propose that tip expansion is regulated (restrained under normal turgor pressure and protruded under low turgor) by a peripheral network of F-actin that is attached to the plasmalemma and the cell wall by integrin-containing linkages, thus placing control in the cytoplasm where it is accessible to normal intracellular regulatory systems. The F-actin system also functions in cytoplasmic and organelle motility; control of plasmalemma-located, stretch-activated, Ca2+-transporting, ion channel distribution; vectoral vesicle transport; and exocytosis. Regulation of the system may involve Ca2+, the concentration of which is influenced by the tip-high gradient of the stretch-activated channels, thus suggesting a possible feedback regulation mechanism.Key words: tip growth, fungi, stretch-activated channels, F-actin, Ca2+, hyphae.

ISSN:0008-4026    

DOI:10.1139/b95-236

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The molecular biology of the high affinity, siderophore-mediated iron uptake system of the basidiomycete fungusUstilago maydisis under investigation.Ustilago maydisproduces two cyclic peptide siderophores, ferrichrome and ferrichrome A. Biosynthesis of both siderophores is initiated by ornithine-N5-oxygenase, the product ofsid1.sid1mRNA accumulates only during growth under iron starvation conditions in wild-type cells or constitutively inurbs1mutants,urbs1encodes a 100-kDa protein with putative Zn finger domains that share sequence identity with those of the GATA family of transcription factors. The promoter region ofsid1was defined by deletion analysis of a 3.0-kb region 5′ to the translational start ofsid1using theEscherichia coliGUS gene as a reporter. Three regions were defined by this analysis to be critical to expression ofsid1. These include (i) a 306-bp region containing two GATA sequences and mapping 2.4 kb from the start of translation; (ii) a 439-bp region immediately 5′ to the start of transcription; and (iii) a region encompassing the first intron ofsid1. Deletion of the GATA sequences resulted in deregulated expression ofsid1, while elimination of the latter two sequences ablated expression of the gene under all circumstances. Current efforts are focused on determining whether Urbsl interacts directly with thesid1promoter via the GATA sequences and whether this interaction is dependent upon iron.Key words: GATA, transcription factor, siderophore, ferrichrome, iron, Urbs1.

ISSN:0008-4026    

DOI:10.1139/b95-237

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The paper of Arst and Cove (Mol. Gen. Genet.126: 111 – 141, 1973) on "Nitrogen metabolite repression inAspergillus nidulans" has influenced studies and perceptions of gene regulation in filamentous fungi during the past 21 years. Here I attempt to appraise the contributions of that paper and assess its role in further developments. Nitrogen metabolite repression, carbon catabolite repression, pathway-specific and integrated induction, as-acting regulatory mutations, a useful class of growth inhibitors, and a homologousNeurospora crassagene are all discussed.Key words:Aspergillus nidulans, carbon catabolite repression, nitrogen metabolite repression.

ISSN:0008-4026    

DOI:10.1139/b95-238

出版商:NRC Research Press    

年代:1995

数据来源: NRC