The Ultrastructural Architecture of the Walls of Some Hyphal Fungi
TL;DR: From observations, the co-axial distribution of polymers such as β1, 3-3, 6-glucans, glycoproteins, proteins, chitin and cellulose in the walls of each species is inferred, which has both similarities and differences between the species.
Abstract: SUMMARY: The appearance of the walls of apical and sub-apical regions of hyphae of predominantly 5 day cultures of Neurospora crassa, Schizophyllum commune and Phytophthora parasitica as seen with the electron microscope, employing shadowed or sectioned material, is illustrated and described in detail. The appearance of untreated or control material in buffer is compared with that exposed to various single and sequential treatments with enzymes, including laminarinase, Pronase, cellulase and chitinase, as well as various chemical treatments.
From these observations is inferred the co-axial distribution of polymers such as β1, 3-, β1, 6-glucans, glycoproteins, proteins, chitin and cellulose in the walls of each species. The distributions have both similarities and differences between the species. The significance of all these features for the growth, mechanical rigidity and integrity of a hypha is briefly discussed.
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TL;DR: The known cases of secondary thickening in recent Pteridophyta have been brought together by HILL23 in a useful resume and Botrychium and Ophioglossum, which lacks a definite layer, are described.
Abstract: Secondary thickening in pteridophytes.-The known cases of secondary thickening in recent Pteridophyta have been brought together by HILL23 in a useful resume. After stating the criteria for secondary growth, Botrychium, which has a distinct cambium, and Ophioglossum, which lacks a definite layer, are described, followed by Angiopteris and Marattia, in which a cambium forms a few xylem elements. CORMACK'S observations on the secondary wood in the nodes of Equisetum are cited, though no reference is made to the cambium in the young cone as reported by J]FFREY.24 The other cases of secondary growth include Psilotum, Selaginella spinulosa, and several species of Isoetes, especially I. hystrix, which may show a cambium outside the vascular cylinder.-M. A.
578 citations
26 Oct 2015
TL;DR: Soil is undoubtedly the most complex of all microbial habitats and there is insufficient information on how and where most microbial events occur in soil in situ and which microbes are the major and, physiologically, the most important participants in these events.
Abstract: Soil is undoubtedly the most complex of all microbial habitats. Primarily because of this complexity, there is insufficient information on how and where most microbial events occur in soil in situ and which microbes are the major and, physiologically, the most important participants in these events. Soil differs from most other microbial habitats in that it is dominated by a solid phase consisting of particulates of different sizes and which is surrounded by aqueous and gaseous phases that fluctuate markedly in time and space. The solid phase is a tripartite system composed of finely divided minerals (both primary and secondary); plant, animal, and microbial residues in various stages of decay; and a living and metabolizing microbiota. These particulates exist as both independent entities and mixed conglomerates. The aqueous phase surrounding the particulates is normally discontinuous, except when soil is saturated, and this restricts the movement of microbes, especially of bacteria and other nonfilamentous forms, and results in local accumulations of nutrients and toxicants, escape of cells from grazing predators, a low probability for genetic transfer, etc. These particulate-aqueous associations constitute the "microhabitats" wherein microbes reside and function in soil. The abiotic components of soil have been relatively well defined, both qualitatively and quantitatively. However, the microgeographic distribution and the geometric relations of abiotic components to each other-and to the microbiotic components-and the interactions among and between the abiotic and microbiotic components are not clearly defined. Most of what is known about the composition of the abiotic components has been obtained by dispersing soil-either chemically or physi-
318 citations
TL;DR: A basic proteinase (Prb1) is identified which is induced by either autoclaved mycelia, fungal cell wall preparation or chitin; however, the induction does not occur in the presence of glucose.
Abstract: Summary
The soil fungus Trichoderma harzianum is a mycoparasitic fungus known for its use as a biocontrol agent of phytopathogenic fungi. Among other factors, Trichoderma produces a series of antibiotics and fungal cell wall-degrading enzymes. These enzymes are believed to play an important role in mycoparasitism. Among the hydrolytic enzymes, we have identified a basic proteinase (Prb1) which is induced by either autoclaved mycelia, fungal cell wall preparation or chitin; however, the induction does not occur in the presence of glucose. The proteinase was purified and biochemically characterized as a serine proteinase of 31 kDa and pl 9.2. Based on the sequence of three internal peptides, synthetic oligonudeotide probes were designed. These probes allowed subsequent isolation of a cDNA and its corresponding genomic clone. The deduced amino acid sequence indicates that the proteinase is synthesized as a pre-proenzyme and allows its classification as a serine proteinase. Northen analysis shows that the induction of this enzyme is due to an increase in the corresponding mRNA level.
254 citations
TL;DR: This chapter discusses the cell wall synthesis in apical hyphal growth and reveals a cytoskeletal organization of the cytoplasm at the apex, which may be crucial to its polarized activity.
Abstract: Publisher Summary This chapter discusses the cell wall synthesis in apical hyphal growth. It appears that the hyphal apex is best viewed as a highly polarized system of exocytosis. Wall materials, extracellular enzymes, and probably other substances are excreted at the growing end of a tubular cell. The most obvious cellular features that accompany this polarized system are (1) the unidirectional flow of vesicles in the cytoplasm fusing with the plasma membrane at the apex, (2) the gradients in wall synthesis at the apex, and (3) the cytoplasmic gradients in ion distribution that are maintained at the apex. New microscopic techniques reveal a cytoskeletal organization of the cytoplasm at the apex, which may be crucial to its polarized activity. Growth of the wall at the hyphal apex requires that the wall in this region has plastic properties, which contrast with the requirement of rigidity elsewhere in the hypha. A widely held view involves the participation of wall-lytic enzymes in plasticizing the wall at the apex and in allowing new wall material to be inserted. A critical evaluation of the evidence presented to support this view makes this hypothesis less attractive. As an alternative a steady-state model is discussed based on recent observations in the author's laboratory. This model holds that the assemblage of polymers synthesized at the apex is inherently plastic. However, this assemblage develops rigidity by interactions, in the wall, between and among the various individual polymers present while the wall segment moves in subapical directions during elongation. This model seems to fit many of the original observations made on living hyphae.
252 citations
TL;DR: Before biocontrol can become an important component of plant-disease management, it must be effective, reliable, consistent and economical and to meet these criteria, superior strains exhibiting improved biocOntrol activity as well as an expanded host range must become available.
Abstract: Molecular mechanisms of lytic enzymes involved in the biocontrol activity of Overview The many achievements of modern agriculture notwithstanding , certain cultural practices have actually enhanced the destructive potential of crop diseases caused by fungi. These practices include the use of genetically uniform crop plants in continuous monoculture, the use of plant cultivars susceptible to pathogens, .and the use of nitrogenous fertilizers at concentrations that increase disease susceptibility. Plant-disease control has thus become heavily dependent on fungicides to combat the wide variety of fungal diseases that threaten agricultural crops (Vliaard e t al., 1993). Studies aimed at replacing pesticides with environmentally safer methods are currently being conducted at many research centres. Biological control is a potent means of reducing the damage caused by plant pathogens and is environmentally nonhazardous. Although commercialized systems for the biological control of plant diseases are few, intensive activity is currently being geared towards the development of an increasing number of biocontrol agents. Potential agents for biocontrol activity are rhizosphere-compatible fungi and bacteria which exhibit antagonistic activity towards plant pathogens. Before biocontrol can become an important component of plant-disease management , it must be effective, reliable, consistent and economical. To meet these criteria, superior strains exhibiting improved biocontrol activity as well as an expanded host range must become available (Goldman e t al., 1994; Harman et a/., 1989). This goal requires extensive study of the molecular and cellular biology of the antagonistic interactions between the biocontrol agent and the phytopathogenic fungi. The acquired knowledge can be used for genetic manipulations to improve existing biocontrol agents. Tricho&rrncr spp. are common fungi, found in almost any soil. Members of this genus are antagonistic to other fungi, including plant-pathogenic species. Possible mechanisms involved in Trichoderma antagonism are : (a) antibiosis, whereby the fungi produce volatile or nun-Trzchoderma attacks another fungus by excreting lytic enzymes (such as proteases, glucanases and chitinases) that enable it to degrade the latter's cell walls and utilize and have been shown to have a direct antifungai effect (Lorito e l al., 1993). Via these mechanisms, Tri~hoderma antagonizes other fungi, thereby serving as a potential biological control agent of plant harzianum involved in mycoparasitism Chitinases Chitin, an unbranched homopolymer of 1,4-Blinked AT-acetyl-D-glucosamine (GlcNAc), is the second most abundant polymer in nature, after cellulose. It does not occur in plants, vertebrates or prokaryotes, but is abundant as a structural polymer in most fungi and insects, including those …
245 citations
References
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TL;DR: The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present, and is less likely to contaminate sections.
Abstract: Aqueous solutions of lead salts (1, 2) and saturated solutions of lead hydroxide (1) have been used as stains to enhance the electron-scattering properties of components of biological materials examined in the electron microscope. Saturated solutions of lead hydroxide (1), while staining more intensely than either lead acetate or monobasic lead acetate (l , 2), form insoluble lead carbonate upon exposure to air. The avoidance of such precipitates which contaminate surfaces of sections during staining has been the stimulus for the development of elaborate procedures for exclusion of air or carbon dioxide (3, 4). Several modifications of Watson's lead hydroxide stain (1) have recently appeared (5-7). All utilize relatively high pH (approximately 12) and one contains small amounts of tartrate (6), a relatively weak complexing agent (8), in addition to lead. These modified lead stains are less liable to contaminate the surface of the section with precipitated stain products. The stain reported here differs from previous alkaline lead stains in that the chelating agent, citrate, is in sufficient excess to sequester all lead present. Lead citrate, soluble in high concentrations in basic solutions, is a chelate compound with an apparent association constant (log Ka) between ligand and lead ion of 6.5 (9). Tissue binding sites, presumably organophosphates, and other anionic species present in biological components following fixation, dehydration, and plastic embedding apparently have a greater affinity for this cation than lead citrate inasmuch as cellular and extracellular structures in the section sequester lead from the staining solution. Alkaline lead citrate solutions are less likely to contaminate sections, as no precipitates form when droplets of fresh staining solution are exposed to air for periods of up to 30 minutes. The resultant staining of the sections is of high intensity in sections of Aralditeor Epon-embedded material. Cytoplasmic membranes, ribosomes, glycogen, and nuclear material are stained (Figs. 1 to 3). STAIN SOLUTION: Lead citrate is prepared by
24,137 citations
TL;DR: Epoxy embedding methods of Glauert and Kushida have been modified so as to yield rapid, reproducible, and convenientembedding methods for electron microscopy.
Abstract: Epoxy embedding methods of Glauert and Kushida have been modified so as to yield rapid, reproducible, and convenient embedding methods for electron microscopy. The sections are robust and tissue damage is less than with methacrylate embedding.
9,741 citations
1,528 citations
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TL;DR: The known cases of secondary thickening in recent Pteridophyta have been brought together by HILL23 in a useful resume and Botrychium and Ophioglossum, which lacks a definite layer, are described.
Abstract: Secondary thickening in pteridophytes.-The known cases of secondary thickening in recent Pteridophyta have been brought together by HILL23 in a useful resume. After stating the criteria for secondary growth, Botrychium, which has a distinct cambium, and Ophioglossum, which lacks a definite layer, are described, followed by Angiopteris and Marattia, in which a cambium forms a few xylem elements. CORMACK'S observations on the secondary wood in the nodes of Equisetum are cited, though no reference is made to the cambium in the young cone as reported by J]FFREY.24 The other cases of secondary growth include Psilotum, Selaginella spinulosa, and several species of Isoetes, especially I. hystrix, which may show a cambium outside the vascular cylinder.-M. A.
578 citations
"The Ultrastructural Architecture of..." refers background or result in this paper
...those away from the apex in 5 day cultures, does not seem to reside in any one major wall component. Our evidence for this is that (i) hyphal disintegration only occurred following enzymic sequences attacking all the principal components in all three species, and (ii) even when walls of Phytophthora parasitica were reduced to cellulose/protein, removal of either alone was insufficient to cause disintegration. Additional evidence derived from growing fungi in wall-degrading enzymes has been cited by Robertson and his co-workers (Robertson & Rizvi, 1965; Robertson, 1968). Manocha & Colvin (1967) suggest that wall protein may be responsible for the retention of wall morphology in Neurospora crassa after enzymic attack....
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...HUNSLEY AND J. H. BURNETT Fusariurn sp., Polystictus versicolor and Rhizina undulata (D. Hunsley, unpublished) there is clear evidence that when exposed to enzymic, or drastic chemical treatments, hyphal apices still possess microfibrillar components lacking any well-defined angle of orientation. This is important since it has been claimed that hyphal tips either lack microfibrillar components or that they are artefacts of chemical treatment (Marchant, 1966) or that they do not extend to the extreme tip where there is an apical pore free of microfibrils (Strunk 1963, 1968). Since we observed microfibrils after both enzymic and chemical treatments, we reject Marchant’s view. We also concur with Scurfield’s (1967) suggestion that Strunk had been misled by observing a septum with a central pore where a hypha had broken and mistaking it for an hyphal apex....
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TL;DR: This chapter presents data and discusses cell-wall protein from several points of view ranging from the purely enzymic aspects (cell-wall enzymes) to the structural hydroxyproline-rich wall proteins.
Abstract: Publisher Summary The purpose of this chapter is to present data and discusses cell-wall protein from several points of view ranging from the purely enzymic aspects (cell-wall enzymes) to the structural hydroxyproline-rich wall proteins. Although the subject of wall protein is hardly a new field it does begin to look as though the demonstration of wall-bound hydroxyproline has imparted a revivifying stimulus to an old problem-this is more evident from work known to be in progress than from the amount of published material. Physically and chemically, the anisotropic cambial walls contain both cellulose and polyuronides. Electron microscopic studies show that more or less randomly interwoven cellulose microfibrils are recognized as another definitive characteristic of primary cell walls. Isolation of a clean wall fraction from various parts of whole plants is much more difficult than from suspension cultures. An important point is that the primary wall is often contaminated with secondary wall. This increases the difficulty of cell breakage and removal of the cell contents.
357 citations