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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Microscopy Research and Technique 31 (1995), S. 63-78 
    ISSN: 1059-910X
    Keywords: Chitinase ; β-1,3-glucanase ; β-fructosidase ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: During the past few years, cyto- and immunocytochemical techniques have been developed and widely used for locating and identifying various molecules in plant cell compartments. The last decade has witnessed tremendous improvements in molecular cytology, thus allowing an accurate in situ detection of various components thought to play important biological functions in the plant metabolism. The use of immunocytochemistry to investigate resistance mechanisms of plants upon pathogen attack has provided key information on the defense strategy that plants elaborate during a host-pathogen interaction. Of the various proteins induced in response to infection, chitinases and β-1,3-glucanases have been the focus of particular attention due to their believed antimicrobial activity through the hydrolysis of the main fungal wall components, chitin and β-1,3-glucans. Attention has also been paid to β-fructosidase, the enzyme that hydrolyzes sucrose into glucose and fructoside. The marked accumulation of this enzyme upon pathogen infection has led to the consideration that infection may greatly infleunce the metabolic activity of colonized tissues by creating alterations of source-sink relationships. Another facet of the plant's defense strategy that has been the focus of considerable interest is related to the accumulation of structural compounds, such as hydroxyproline-rich glycoproteins and callose, to reinforce the wall architecture, thus decreasing vulnerability to microbial enzymes. A number of alternatives designed to improve plant protection towards pathogen invasion have been suggested. Among these, the production of transgenic plants expressing constitutively a foreign resistance gene and the pretreatment of plants with elicitors of defense reactions have been the subject of intensive studies at the molecular, biochemical, and cytological levels. Results of such studies clearly demonstrate the important contribution that cyto- and immunocytochemical approaches can make to our knowledge of how plants defend themselves and how plant disease resistance can be directly enhanced. These approaches will undoubtedly be active areas for future research in the development of biological control alternatives in which the mode of action of the product used is of key importance. © 1995 Wiley-Liss, Inc.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 67-76 
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Cross-linked mixtures of polystyrene and poly(vinyl methyl ether) exhibit a non-vanishing zero-angle intensity in small-angle neutron scattering experiments. A possible explanation is that fluctuations in composition in the mixture may be frozen by the presence of cross-links. Assuming this, we introduce a screening length κ by the condition that the scattered intensity should not be changed by cross-linking. We find κ2 ∼ C/(χ - χi), where C is an elastic constant, χ and χi, respectively, the inverse temperature and that where cross-linking is performed. When the temperature is varied, we find three regimes. In the first one, the scattered intensity is monotonously decreasing. In the second one, it has a finite maximum. In the last one, the maximum eventually diverges.
    Additional Material: 2 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 3 (1994), S. 557-566 
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The phase behavior and scattering properties of crosslinked charged polymer blends in solution are examined. De Gennes' analogy between the effects of crosslinks in a network and electrostatic charges in a dielectric medium on the scattering properties and the phase behavior of crosslinked polymer blends is used. This analogy is extended to include the effects of screening in order to improve its agreement with the experimental data in the small q range. The excluded volume interactions are explicitely introduced through the blob model. The enhancement of compatibility of the mixture and the increase of its rigidity constant are evaluated in certain cases. The limit of neutral polymers is discussed because it corresponds to the case of charged mixtures in the presence of excess salt. The kinetics of the microphase separation transition is briefly discussed. A dynamical model including the long range hydrodynamic interaction is presented. The relaxation frequency of the stable modes and the growth rate of unstable ones are also considered.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 12 (1989), S. 1-10 
    ISSN: 0741-0581
    Keywords: Postfixation ; Colloidal gold particles ; Labeling pattern ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Lactoferrin, a DNA-binding protein, was complexed to colloidal gold and applied on ultrathin sections of resin-embedded plant tissues and bacterial cultures. Optimal results were obtained when lactoferrin was tagged to colloidal gold particles at pH 9.2. Postfixation with osmium tetroxide and embedding with Epon did not prevent the accessibility of the protein towards its corresponding binding sites. In plant nuclei, labeling was observed over the dense chromatin and to a lesser extent over the dispersed chromatin. Nucleolar labeling was preferentially located over the dense fibrillar component. Gold particles were also found to be associated with chloroplasts and mitochondria. In prokaryotic cells, a dispersed labeling was noted over the cytoplasm and, in some cases, the aggregation of few gold particles suggested the presence of packed DNA fibrils. Various control experiments confirmed the specificity of the labeling pattern obtained. Lactoferrin-gold complex appears to be a valuable probe for the intracellular demonstration of DNA molecules in double-fixed and Epon-embedded tissues.
    Additional Material: 14 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 17 (1991), S. 81-94 
    ISSN: 0741-0581
    Keywords: Colloidal gold ; Pathogenesis-related (PR) proteins ; Tobacco plants ; Hypersensitivity ; Tobacco mosaic virus ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: Immunocytochemical techniques are confronted with the problem of obtaining adequate tissue preservation together with retention of protein antigenicity. Various methods, including freeze-drying and freeze-substitution, have been devised to circumvent this problem. In the present study, we report that microwave energy used in combination with low concentrations of glutaraldehyde (0.1%) and paraformaldehyde (2%) preserves the structural integrity of plant tissue and antigenicity of proteins. Tobacco leaf samples fixed in a time as brief as 15-20 s exhibited excellent preservation of fine structures. By contrast, specimens irradiated for shorter (5-10 s) or longer (30-40 s) periods showed poor morphological preservation. Microwave irradiation for 15-20 s was found useful for immobilizing large amounts of soluble antigens. The fast microwave fixation method was successfully used to preserve pathogenesis-related (PR) proteins, which were subsequently localized by a postembedding immunogold procedure. In addition to soluble antigens, cellulose subunits and pectic substances, two major plant cell wall components, were found to be highly preserved in microwave-irradiated tobacco plant tissue. The present study demonstrates that microwave fixation of plant tissue is a simple and inexpensive method that is easy to perform with commercially available microwave ovens. The incubation time for fixation is reduced from 2 h to 15-20 s without loss of fine structural details. This method will undoubtedly acquire increasing applicability and relevance in plant biology.
    Additional Material: 8 Ill.
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