摘要:

AbstractIn order to determine the best conditions to carry out quantitative ultrastructural studies in plant specimens, five different fixation techniques, including some of the most reported electron microscopy fixatives (glutaraldehyde‐paraformaldehyde, osmium tetroxide, potassium permanganate), were assayed in onion root meristems to check their ability to induce morphometric changes in Golgi apparatus ultrastructure. Although the parameters evaluated showed in all cases the same tendency, values obtained after permanganate fixation were always higher than those found after aldehyde techniques (especially aldehyde‐osmium). Aldehyde followed by osmium fixation appears as the most indicated fixation method when accurate quantitative ultrastructural studies are to be develo

ISSN:0741-0581    

DOI:10.1002/jemt.1060110102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractBiological mineralization is a cell‐mediated process which is believed to be triggered by a “nucleating agent.” Various matrix structures, such as matrix vesicles, collagen fibrils and macromolecules, have been claimed to be the source of this substance, since these components have been found by transmission electron microscopy (TEM) of thin sections to be associated with early mineral crystals. Systematic image analysis of the relationships revealed in electron micrographs between specific matrix components and early mineral deposits has shown that unequivocal image interpretation is not possible. This is due principally to the problems posed by overprojection and truncation phenomena, since the structures being analyzed lie within the same dimensional range as thin section thickness. Various examples are illustrated and discussed. The site at which mineral crystals are initially laid down thus cannot be identified with any matrix structure using thin section TEM. Possible technical approaches to resolve this problem of image analysis are disc

ISSN:0741-0581    

DOI:10.1002/jemt.1060110103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA computer graphics system for reconstruction from serial section micrographs was applied to intracellular details of a yeast target cell (Saccharomyces cerevisiaecell) induced by the α factor mating pheromone and was also applied to a periodontal structure of a dog tooth moved orthodontically. In the former, intracellular organelles and a distribution of vesicles could be clearly observed through the cell membrane using the transparent display method in which the smoothing of the reconstructed outer cell membrane surface by computer processing was applied to the transparent display. In the latter case, by cutting through a reconstructed dog tooth and its periodontal tissues, labiolingual and mesiodistal cut surfaces of the tooth and of adjacent alveolar bone could be observed with fine details (232 sections were used)

ISSN:0741-0581    

DOI:10.1002/jemt.1060110104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractC‐peptide and insulin antigenic sites in rat pancreatic β cells were both labeled by the protein A and immunogold techniques. Gold bead density in the secretory granules was correlated with granule size distribution. Our results demonstrate that the distribution patterns of antigenic sites for C‐peptide (which also represents proinsulin sites) and insulin are similar when granule size distribution is correlated to the density of antigenic sites. It was found that the ratio of C‐peptide to insulin in granules is independent of granule size. Examination of frequency histograms by a Kolmogorov‐Smirnov analysis excluded the possibility that the antigenic sites of C‐peptide and insulin are distributed in the same manner. Mean gold bead density for insulin antigen (97 ± 24) was slightly higher than C‐peptide density (64 ± 18). The efficiency of labeling was found to be very low; less than 0.1% of the theoretically estimated antigenic site

ISSN:0741-0581    

DOI:10.1002/jemt.1060110105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractOptimal imaging of complex structures requires proper alignment relative to the optic axis of the electron microscope. This is especially important for high‐voltage and intermediatevoltage microscopes, which form an in‐focus image throughout the entire thickness of the object. As a result, structures at different specimen heights form overlapping and confused images that severely curtail the usefulness of these instruments.The work described here provides a generalized, flexible method for optimizing specimen orientation and eliminating or limiting image overlap by means of a commonly used double‐tilt stage. Analysis of the motion about the two axes provides accurate tilting for any azimuthal direction whether or not it corresponds to a mechanical axis of the stage. An object can be positioned to minimize image overlap, to record stereopairs for any parallax axis, and to record three‐dimensional data sets by the conical collection geometry.Images of muscle paracrystals are shown after tilting about an axis perpendicular to a symmetry direction. The tilted image displays higher‐order symmetry, which is altered by changes of one degree. Precision double‐tilting for optimizing stereopairs is shown for a desmosome recorded using different parallax axes and pretilts. A tomographic conical data‐collection scheme is demonstrated by imaging a microtubule axoneme for a specific cone half‐angle and arbitrary a

ISSN:0741-0581    

DOI:10.1002/jemt.1060110106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe relative sensitivity of an analytical electron microscope and energy‐dispersive x‐ray detector to x‐rays of various elements is investigated through an extensivekASifactor study. Elemental standards, primarily National Bureau of Standards multielement research glasses, were dry‐ground into submicrometer‐sized particles and analyzed at 200 kV accelerating potential. The effect of self‐absorption of x‐rays by the particle has been corrected for, allowing the experimentalkASifactors from this study to approximate those that could be obtained from “infinitely thin” specimens.Whenever possible, elementalk‐factors were determined by the analysis of many (up to a maximum of nine) different standard materials. ExperimentalkASifactors were calculated for a wide range of Kα, Lα, and Mαx‐ray lines. For comparison, theoreticalkASifactors, employing a variety of ionization cross sections, were computed. Good agreement is obtained between several of the theoretical k‐factor models and the experimental results. Mass volatilization of Na and K from the small glass particles during analysis is discussed, as are observations that the grinding and/or dispersing of standard materials in a liquid (such as ethanol) may promote leaching of certain element

ISSN:0741-0581    

DOI:10.1002/jemt.1060110107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA cross‐sectional sample preparation technique is described that relies on lithographic and dry‐etching processing, thus avoiding metallographic polishing and ion milling. The method is capable of producing cross‐sectional transmission electron microscopy samples with a large amount of transparent area (1 μm × 2.5 mm) which allows the examination of many patterned test sites on the same sample from the same chip of a silicon wafer. An example of the application of the technique is given for localized oxidation through

ISSN:0741-0581    

DOI:10.1002/jemt.1060110108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractExperimental conditions for obtaining the optimum signal‐to‐background (S/B) ratio in reflection electron energy‐loss spectroscopy (REELS) are investigated. It is shown that the S/ B ratio can be improved by lowering the incident energy of the electrons. The spectra taken from the GaAs (660) specular reflection spot under the surface resonance condition is demonstrated to have the best S/B ratio and lowest surface plasma excitation, which is capable of providing structural information on the top few atomic l

ISSN:0741-0581    

DOI:10.1002/jemt.1060110109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe designed and built a freeze‐drying device that ensures the protection of the specimens against contaminants during mounting on the cold stage of the freeze‐fracture machine, transferring into the vacuum chamber and deep etching. The device consists of a copper cap that covers the specimen and a thermal connection that ensures thermal transfer between the microtome arm and the copper cap. This device was used to study the ultrastructural features of the erythrocyte membrane skeleton and the immunocytchemical localization of spectrin in an “in situ” approach, by freeze drying and platinum rotary shadowing. Human erythrocytes adhered to polylysine‐coated coverslips and were broken by a stream of buffer that mimics the intracellular ionic environment (“inside buffer”). The samples were prefixed in periodate‐lysine‐paraformaaldehyde fixative, labeled with antispectrin 5‐nm gold particles, fixed in glutaraldehyde, mordanted in tannic acid, postfixed in OsO4, repeatedly washed in water, rinsed quickly in 30% ethanol, freeze‐dried, and rotary‐shadowed. Electron microscopic examination of the replicas revealed the skeletal network on the inner surface of the erythrocyte membrane. Immunocytochemical labeling proved that spectrin represents a fibrillar component of the network. Our data confirm the speculative model of the molecular organization of the erythrocyte skeleton, based on studies on in vitro association of proteic constituents. Both the technique and the device developed by us may lead to a deeper understanding of the spatial organization of the cytoskeletal network of

ISSN:0741-0581    

DOI:10.1002/jemt.1060110110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe use of osmium‐potassium ferrocyanide as the secondary fixative greatly improved chondrocyte preservation and stabilized the cartilage matrix proteoglycan. The proteoglycan was similar in appearance to that seen following fixation in the presence of cationic dyes. Extensive glycogen preservation was noted in these cells, occupying the area prior to and during the formation of the secondary center of ossification. The volume and organization of the glycogen within the cell cytoplasm were greater than that following buffered osmium fixation, and the cellular vacuoles within were greatly reduced.The cells forming the secondary center prior to the onset of mineralization were of greatest interest, because other studies compared them with the primary growth plate and described them as showing signs of hypertrophy as early as 5 days postnatally, as is found in the primary growth plate. Our observations indicate that glycogen is present in these cells, and cellular enlargement was not present. The cells do not resemble the hypertrophic chondrocytes of the primary growth plate, as far as cytoplasmic content is concerned, and we suggest that they may contribute to the development of the secondary center in a different fashio

ISSN:0741-0581    

DOI:10.1002/jemt.1060110111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY