bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of covalency on the deformation mechanisms in intermetallic compounds
Authors: Fraser Hamish L.
Published: June 2020

It has been found that the effects of covalency on the anisotropy of Peierls stresses plays a significant role on the mobilities of dislocations in intermetallic compounds, and therefore influences the ductility exhibited by these materials especially at room temperature. In way of example, brief notes are given for the cases of TiAl and Ti3AL For TiAl, the microstructure of samples deformed at room temperature consists mainly of dislocations of the type b=<011], with the attendant superlattice extrinsic stacking-faults, see Fig.l; also, in some grains twinning has occurred. The density of dislocations with Burgers vectors parallel to <110] is extremely low; their line directions tend to be fairly close to screw orientation. For compression at 600°C, the deformation microstructure tends to be dominated by dislocations with b=1/2<110], as shown in Fig.2(a), and most of the dislocations observed of this type were found to be lying in screw orientation. In agreement with previous work, at the higher temperatures dislocations with b=<101] were observed to be dissociated partly on the {100} planes, the two inclined sets of straight dislocations in Fig.2(b), corresponding to Kear-Wilsdorf locks. These various results, including the line directions of the dislocations, are interpreted on the basis of the effect of covalent bonding on the anisotropy of the Peierls stresses (following) and therefore dislocation mobilities in this compound. The lack of ductility exhibited at room temperature is attributed to a lack of mobility of dislocations with b=1/2<110] caused by covalency, and the formation of sessile configurations by dissociation of dislocations with b=<101]. The increase in ductility of TiAl at higher temperatures is attributed to the operation of the slip systems 1/2<110]{111}, where dislocations with b=1/2<110] become significantly more glissile because of thermal activation, and also to an increased amount of twinning (apparently above 600°C) since the twinning dislocations (with b=1/6<112]) also are expected to be more glissile. When samples of this compound are produced containing 0.4at.%Er, the action of the rare earth addition is to internally getter the interstitial impurities. In this case, the deformation microstructure is dominated by dislocations with Burgers vectors with b=1/2<110], a typical area being shown in Fig.3. This is consistent with a reduced anisotropy of charge density about the Ti atoms, and therefore reduced effects of covalency.
Phase distribution in rapidly solidified TiAl alloys
Authors: Hall Ernest L. , Huang Shyh-Chin
Published: June 2020

There is at present a great deal of interest in the intermetallic compound γ-TiAl, particularly with regard to its use as an aircraft engine or aerospace structural material. This compound possesses an attractive combination of properties, including high melting temperature, low density, high modulus, and good oxidation and creep resistance, but is somewhat deficient in room temperature ductility due to its crystal structure, which is the Ll0 face-centered tetragonal structure consisting of alternating (002) planes of Ti and Al. The Ti-Al equilibrium phase diagram in the vicinity of γ-TiAl shows that γ-TiAl forms via a peritectic reaction and thus, in order to minimize segregation and to insure maximum homogeneity, it is desirable to produce γ-TiAl alloys by rapid solidification. It is then useful, in order to establish a baseline for advanced alloy design, to have an understanding of the microstructures resulting from rapid solidification. In this paper, we report the results of microstructural studies of binary Ti-Al alloys varying in stoichiometry from 46 to 70 at. % Al which were rapidly solidified into the form of ribbon using melt spinning.
Ultrathin silicon membrane thickness determination by CBED and measurement of plasmon mean free path
Authors: Xu Peirong
Published: June 2020

The lower limit of accurate thickness measurement using two beam CBED patterns is usually about one extinction distance for the reflection used. We have used (111) symmetric CBED patterns to measure thin silicon membrane thicknesses as low as 130 Å by comparing experimental patterns with computer simulated CBED patterns. The silicon plasmon mean free path was also measured using these thickness values.

Symmetric convergent beam diffraction patterns of (111) silicon in the thickness range of 130 Å to 1300 Å were obtained in a VG HB501A STEM with a 5 Å probe (8 mrad convergence angle) scanning a 100 Å × 100 Å area. The sample was made by ion implantation, anodic etching and annealing. Subsequent photolithography and reactive ion etching thinned the specimen down further to as thin as 100 Å. The sample was chemically cleaned by the Shiraki method before being loaded into the microscope.
The relaxation of compressive biaxial strains in SOS via microtwins
Authors: Twigg M. E. , Richmond E. D. , Pellegrino J. G.
Published: June 2020

For heteroepitaxial systems, such as silicon on sapphire (SOS), microtwins occur in significant numbers and are thought to contribute to strain relief in the silicon thin film. The size of this contribution can be assessed from TEM measurements, of the differential volume fraction of microtwins, dV/dν (the derivative of the microtwin volume V with respect to the film volume ν), for SOS grown by both chemical vapor deposition (CVD) and molecular beam epitaxy (MBE).

In a (001) silicon thin film subjected to compressive stress along the [100] axis , this stress can be relieved by four twinning systems: a/6[211]/( lll), a/6(21l]/(l1l), a/6[21l] /( l1l), and a/6(2ll)/(1ll).3 For the a/6[211]/(1ll) system, the glide of a single a/6[2ll] twinning partial dislocation draws the two halves of the crystal, separated by the microtwin, closer together by a/3.
A comparative HVEM study of ICB-deposited aluminum films
Authors: Westmacott K.H. , Dahmen U.
Published: June 2020

The Ionized Cluster Beam (ICB) technique pioneered by Takagi and colleagues in Kyoto is an exciting new method for depositing thin films possessing novel microstructures and unusual properties, (see for example Ref. 1 for a review of recent work). These materials are of interest not only for their potential use in electronic applications but also because of their eminent suitability for fundamental high resolution studies of grain boundary structure

The HVEM's at the National Center for Electron Microscopy are employed in a complementary fashion to characterize fully the microstructure of ICB deposited Al films. In-situ annealing studies of the films are conducted in the 1.5 MeV Kratos HVEM taking advantage of its heating stage, excellent specimen chamber vacuum (10-8 torr), and high resolution video camera. The increased penetration at 1.5 MeV allows different film thicknesses of Al film to be examined as well as the regions of the foil where the silicon substrate remains backing the Al film. High resolution studies of the atomic structure of grain boundaries are performed on the 1 MeV JEOL ARM using its unique tilting stage and ability to image structures at the 0.15 nm level.
Analyzing kinesin and cytoplasmic-dynein driven movement with nanometer precision
Authors: Schnapp B.J. , Gelles J. , Steuer E. , Sheetz M. P.
Published: June 2020

Kinesin and cytoplasmic dynein are microtubule-based, force-generating ATPases thought to be involved in the bidirectional transport of vesicular organelles along microtubules. In vitro, kinesin and dynein promote movement of 0.1 - 0.2μm plastic beads toward the plus and minus ends, respectively, of microtubules. In these systems, the proteins are thought to remain fixed, by nonspecific absorption, to the bead surface. The motion of the bead on the microtubule is detected by video enhanced, DIC microscopy, and reflects the movement of the motor protein along the microtubule.

To quantitate bead motion, a method was devised for tracking the position of kinesin or dynein coated beads moving along microtubules. The method involves 1) cross-correlation of a template bead image (the kernal) with each of the frames in a video sequence, followed by 2) calculation of the centroid of the cross-correlation function for each of the frames in the sequence. The centroid provides a measure of bead position. Application of this method to the measurement of the relative position of two stationary beads adsorbed nonspecifically to the glass surface indicates that the standard deviation of the measured horizontal and vertical coordinates can be less than 0.5 nm. More recently, we have determined that centroid calculation of the unprocessed bead image (i.e. without cross-correlation) can provide a measure of bead position with standard deviations in the horizontal and vertical directions of less than 2 nm. The latter method is faster, but more sensitive to the contrast and magnification of the video image.
Correlative light, scanning and Transmission Electron Microscopy of polyethylene glycol (PEG) embedded and subsequently de-embedded tissues
Authors: Kondo Hisatake
Published: June 2020

Our understanding of the detailed morphology of bioloqical specimens often requires the correlation between images of the surface by scanning electron microscopy (SEM) and of the underlining interior structure by light microscopy (LM) or transmission electron microscopy (TEM). In order to accomplish the correlation with high quality, the polyethylene glycol (PEG) embedding and subsequent deembedding has been revealed to be a simple and quite reliable procedure.

Tissue or cell samples are fixed and dehydrated in ethanol according to the conventional procedures. Vials containing the specimens in 100% ethanol are warmed in an oven at about 60°C and approximately equal amount of pure molten PEG-4000 is added in the vials. PEG is easily dissolved by gentle agitation. Thereafter the specimens are transferred to pure molten PEG contained in well-dried gelatin capsules. After the specimens have been sunk to the bottom of the capsule, each capsule is immersed in liquid nitrogen to solidify PEG. Portions of the solidified PEG including the specimens are cut out with a razer blade and mounted with dental wax on supporting stubs fitting the collet of the microtome. The specimen blocks are sectioned with a well-dried glass or diamond knife. Wrinkle-free sections, 200-300 nm thick, can be easily obtained with some practice unless the room atmosphere is humid. The sections are picked up with a platinum loop filled with 2.5 % sucrose and mounted on glass slides for LM or formvar-coated grids for TEM, both of which have previously been treated with 0.1 % poly-L-lysine. For LM sections may be processed for immunohistochemistry. For TEM, sections on grids are put into a submerged grid holder in 90 % ethanol. The holder is transferred to 100 % ethanol and subsequently to a critical point apparatus with carbon dioxide. For SEM, the specimen blocks with its mirror-smooth face, after taking sections, is removed from the stubs and immersed in warm water to get rid of PEG. The blocks are then dehydrated in ethanol and critical point dried with carbon dioxide.
Scanning and Transmission Electron Microscopic correlates of sulfur mustard (HD) toxicity
Authors: Petrali J.P. , Oglesby S.B. , Mills K.R.
Published: June 2020

In spite of the many reports, since World War I no the pathology of mustard injury,
no ultrastructural studies were performed until our laboratory published a report on the ultrastructure of the pathogenesis of blister formation following exposure to sulfur mustard of human–skin grafted to congenitally athymic nude mice. This study afforded us the opportunity for the first time to focus on several objectives: 1) to further delineate the histopathology which had been noted at light microscopy levels; 2) to identify possible early mustard-induced morpho- logical changes which may occur during the latent asynptcamtic phase; and 3) to prcmote our understanding of the temporal features of mustard pathology with the expectation that prophylactic and therapeutic strategies might be morphologically predictable. We now have the opportunity to describe HD-induced pathology in cells-in-culture and compare them with that of the skin lesion of a human skin grafted model and a hairless guinea pig model.

We used standardized ultrastructural technology to study by transmission and scanning electron microscopy the subcellular effects of HD on human skin grafted to athymic mice, human lyrrphocytes and human keratinocytes in culture, and, the hairless guinea pig model. While doses of mustard differed according to the dictates of individualized protocols, all specimens were gathered at 24-48 hours following exposure and were aldehyde fixed, dehydrated in graded ethanols and either embedded in epoxy resin for transmission electron microscopy or critical-point dried and sputter coated with gold-palladium for scanning electron microscopy.
Molecular architecture and functions of the neuronal cytoskeleton
Authors: Hirokawa Nobutaka
Published: June 2020

In this symposium I will present our studies about the molecular architecture and function of the cytomatrix of the nerve cells. The nerve cell is a highly polarized cell composed of highly branched dendrites, cell body, and a single long axon along the direction of the impulse propagation. Each part of the neuron takes characteristic shapes for which the cytoskeleton provides the framework. The neuronal cytoskeletons play important roles on neuronal morphogenesis, organelle transport and the synaptic transmission. In the axon neurofilaments (NF) form dense arrays, while microtubules (MT) are arranged as small clusters among the NFs. On the other hand, MTs are distributed uniformly, whereas NFs tend to run solitarily or form small fascicles in the dendrites Quick freeze deep etch electron microscopy revealed various kinds of strands among MTs, NFs and membranous organelles (MO). These structures form major elements of the cytomatrix in the neuron. To investigate molecular nature and function of these filaments first we studied molecular structures of microtubule associated proteins (MAP1A, MAP1B, MAP2, MAP2C and tau), and microtubules reconstituted from MAPs and tubulin in vitro. These MAPs were all fibrous molecules with different length and formed arm like projections from the microtubule surface.
Scanning sensor microscopy of biological membranes
Authors: Engel A. , Stemmer A. , Lezius M. , Aebi U.
Published: June 2020

The attractive features of nm-sized sensors scanned over a surface by piezoceramic elements and kept in close contact by a servo system are their high spatial resolution and sensitivity as well as the possiblity to operate them in different environments. The first sensor ever used is a sharp metal tip which picks up a tunnel current iT when approached towards the surface of a conductor. As iT changes by an order of magnitude for a variation of the tunnel gap s by 0.1 nm, a precise control of s is possible and used in the scanning tunneling microscope (STM) to map surface topographies at atomic scale. The possibility to probe atomic dimensions in this way led to the development of the scanning force microscope (SFM) which determines the deflection of a flexible cantilever while scanned over a surface. Measuring this deflection by a light optical system then provided a SFM that can be operated in buffer solutions.
Structure and function of nonorthodox chromatins: I. aggregation sensitivity of DNA is correlated to the Protein content of chromosomal material
Authors: Pelzer J. , Bohrmann B. , Johansen R. , Maeder M. , Gyalog R. , Arnold-Schulz-Gahmen B. , Villiger W. , Kellenberger E.
Published: June 2020

Aggregation insensitive eukaryotic chromatin in which DNA is associated with histones can be crosslinked by all fixatives commonly used in electron microscopy. By crosslinking it becomes protected from aggregation during dehydration with organic solvents. This is not the case with most nonorthodox chromatins, where the ratio of protein to DNA is estimated to be 5 to 10 times lower and where the basic, acid-soluble proteins are rather different from the histones. The aggregation sensitivity of different chromatins is summarized in table 1.

Nonorthodox aggregation sensitive chromatins were found in Eubacteria, bacteriophage- pools (fig. 1a,b), Cyanobacteria, mitochondria, and Dinoflagellates (fig. 2a,b). The latter organisms are of particular interest because of morphologic similarities to other flagellates like Euglena with its aggregation insensitive histone-containing chromosomes (fig. 3a,b). With respect to the distribution over the living world, nonorthodox chromatins might be more frequent than the histone-containing ones.
Structural analysis of ribosomal particles from Escherichia coli by STEM
Authors: Boublik M. , Mandiyan V. , Tumminia S. , Hainfeld J.F. , Wall J.S.
Published: June 2020

Presently, dedicated scanning transmission electron microscopy (STEM) is the most direct, most versatile and least destructive electron microscopic technique for high resolution studies of biological specimens. Apart from the morphology (shape, characteristic dimensions) of biological macromolecules, STEM can provide quantitative information on their molecular mass, the mass distribution within individual particles (for calculation of the radius of gyration), and the topography of their individual macromolecular components and functional sites. Deposition of nucleic acid molecules under non-denaturing conditions opened the EM field for studies of their conformation under various ionic conditions, their interactions with other macromolecules, proteins in particular, and ultimately to the visualization of the total reconstitution process of macromolecular complexes from their constituents.

The potential of high resolution STEM at Brookhaven National Laboratory (BNL) was applied to the study of structure-function relationships of ribosomal particles of Escherichia coli, minute but complex cellular organelles playing a fundamental role in protein synthesis.
Ultrastructural Localization Study of Carcinoembryonic Antigen (CEA) in Gastric Cancer: Immunoelectron Microscopic Observation
Authors: Yuming Dong , Guanglin Yang , Jifeng Wu , Xiaolin Chen
Published: June 2020

On the basis of light microscopic observation, the ultrastructural localization of CEA in gastric cancer was studied by immunoelectron microscopic technique. The distribution of CEA in gastric cancer and its biological significance and the mechanism of abnormal distribution of CEA were further discussed.

Among 104 surgically resected specimens of gastric cancer with PAP method at light microscopic level, the incidence of CEA(+) was 85.58%. All of mucinous carcinoma exhibited CEA(+). In tubular adenocarcinoma the incidence of CEA(+) showed a tendency to rising with the increase of degree of differentiation. In normal epithelia and intestinal metaplasia CEA was faintly present and was found only in the luminal surface. The CEA staining patterns in cancer cells were of three types--- cytoplasmic, membranous and weak reactive type. The ultrastructural localization of CEA in 14 cases of gastric cancer was studied by immunoelectron microscopic technique.There was a little or no CEA in the microvilli of normal epithelia. In intestinal metaplasia CEA was found on the microvilli of absorptive cells and among the mucus particles of goblet cells. In gastric cancer CEA was also distributed on the lateral and basal surface or even over the entire surface of cancer cells and lost their polarity completely. Many studies had proved that the alterations in surface glycoprotein were characteristic changes of tumor cells. The antigenic determinant of CEA was glycoprotein, so the alterations of tumor-associated surface glycoprotein opened up a new way for the diagnosis of tumors.
Pathologic Calcification and Cell Viability in Rat Allograft Heart Valves
Authors: Walters K.S. , Lupinetti F.M. , Cobb S. , Moore K.C.
Published: June 2020

Aortic valve allografts are employed in the treatment of patients having aortic valve disease with no apparent rejection or need for immuno-suppression. However, it is unknown whether immunologic differences between donor and recipient affect the performance of the allograft. Because calcification is an important cause of allograft failure, this study was designed to observe the effects of histocompatibility on the degree of allograft calcification.

Four groups of ten adult male Lewis rats per group received aortic valve allografts transplanted heterotopically into the abdominal aorta. The aortic valves were obtained from adult male Lewis rats, Brown Norway rats (BN), Fisher rats (F), and Lewis-Brown Norway-Fisher hybrids (LBNF). At 3, 6, 9, and 12 weeks following implantation, the valves were removed, rinsed in saline and washed free of salts using distilled water. They were then mounted to a specimen holder with Tissue-Tek O.C.T. compound and quick frozen in liquid nitrogen. Sections 8um thick, containing leaflet, were cut using a Reichert-Jung cryostat at -20°C and mounted on carbon stubs.
Projection of antennal receptor cell into subesophageal ganglion in insect
Authors: Lee Bong-Hee , Kim Min-Yung , Kim Woo-Kap
Published: June 2020

This investigation has been carried out to observe different types of synaptic organizations in subesophageal ganglion of Pieris rapae, then to examine the ultrastructure of degenerated antennal receptor terminals in ipsilateral subesophageal ganglion following the removal of an left antenna, and finally to identify which type of synapse is constituted in the subesophageal ganglion by the axon terminal of the receptor cell projecting from the antenna.

For electron microscopy of normal synaptic organizations in the subesophageal ganglion, the general anesthesia of the one-day-old cabbage butterflies was performed in keeping them at 4°C for about 30 min. Thereafter, the heads were cut off from the butterflies with a razor blade and prefixed in 1% paraformaldehyde-1% glutaraldehyde at 4°C for 1 h. After being prefixed for 1 h, the heads were dissected under the stereoscope for getting the intact brains. The brains continued to be kept in a new prefixative at 4°C overnight of completing the fixation. They were washed in 0.4M phosphate buffer, pH 7.4, containing 7% glucose and 0.5% CaCl2, and postfixed in 2% OsO4 in phosphate buffer at 4°C for 2 h.
The proventriculus of the worker honeybee and its differentiation
Authors: Anna Pabst Maria , Crailsheim Karl
Published: June 2020

The proventriculus (pv) of the honeybee regulates the flow of food from the crop into the midgut. It is a formation of the foregut intervening between the crop and the midgut and consists of four bulging pv folds forming a x-shaped lumen. At their ends (=lips) the folds bear filiform hairs forming a comb at their inner margins. The pv folds are lined by a sclerotized cuticular intima. Between the basal plates of the pv folds and at the outside of the organ a flexible cuticle is present. By gulping movements (inner longitudinal and outer circular muscle layer) and with the aid of the hairs it can separate liquid food from pollen grains.

Studies were made of 4- and 6-7-day-old pupae and of foragers (Apis mellifera L.) Scanning electron microscopic preparations show that in 4-day-old pupae the pv is already present in its basic form. The lips have filiform hairs which are repeatedly split at their ends and spine-like hairs on the outer side of the lips.
Involvement of GER in Friend leukemia virus assembly in high-pressure frozen cells
Authors: Djaczenko W. , Müller M. , Benedetto A. , Carbone G.
Published: June 2020

A thickening of ER membranes in murine myeloma cells was attributed by de Harven to the assembly of intracisternal virus particles. We observed similar thickening of GER membranes in Friend leukemia cells (FLC) apparently associated with Friend leukemia virus (FLV) assembly. We reinvestigated the problem of GER involvement in FLV assembly using high pressure cryofixed FLC.

FLC (745A clone growing in suspension and FF clone growing in monolayer) were immersed in Hexadecene (Fluka, Switzerland) and rapidly frozen in Balzers HPM 010 freezing machine working at 2200 bar. All cells were freeze substituted at -90°C in 2% OsO4 in absolute acetone. Serial sections cut to avoid misinterpretations due to the geometry of sections, were collected on carbon coated 100 mesh grids.
Ultrastructure of mycelial conidia of Paracoccidioides brasiliensis
Authors: Samsonoff William A. , Edwards Mercedes R. , Restrepo-Moreno A.
Published: June 2020

Paracoccidioides brasiliensis, the causative agent of an endemic South American mycosis, displays two growth phases: at 37°C, in infected tissues or in artificial media, it grows as a pleomorphic multi-budding yeast; at 25°C it becomes a mycelium with septate branched hyphae. Both the yeast and mycelial cells have been characterized by light microscopy. Under proper conditions, the mycelia produce a variety of sporogenous cells, for which only light-microscopy descriptions exist. This report details the ultrastructure of these cells (conidia) as seen by scanning (SEM) and transmission (TEM) electron microscopy.

Mycelia of P. brasiliensis were fixed with formaldehyde and glutaraldehyde (1%-3% each) in cacodylate buffer (pH 7.2) at room temperature, stored in buffer at 4°C, and post-fixed with 1% osmium tetroxide.
Ultrastructure of rhinosporidiosis
Authors: Bharati Arumugam Sarasa , Arumugam S. , Sundaram A. , Rajalakshmi Y.
Published: June 2020

Rhinosporidiosis is an unique fungal disease in that it has constantly eluded all efforts to culture the organism in vitro. Thus its exact life cycle is unknown, besides its various other biological characteristics. With this in view a study undertaken of the 54 cases showed the following L.M. and E.M. features.

Light Microscopy: The fungi were seen to produce polypoid formations of fibrovascular connective tissue with a generally hyperplastic lining of squamous epithelium. The fungi themselves were in the form of multiple cysts of varying sizes and shapes. While most cysts appeared to be rounded or oval, tubular forms could also be seen. Sizes varied from 6-500 microns. The cyst wall appeared to have 2 layers, an inner cellulose and outer chitinous. The inner wall appeared associated with young spores and ovoid bodies 0.2 x 0.3 mm.
Immunocytochemical studies on the behavior of RuBisCO and LHCP II during the cell cycle of synchronized Euglena gracilis
Authors: Osafune Tetsuaki , Sumida Shuji , Ehara Tomoko , Hase Eiji , Schiff Jerome A.
Published: June 2020

Changes in the morphology of pyrenoid and the distribution of RuBisCO in the chloroplast of Euglena gracilis were followed by immunoelectron microscopy during the cell cycle in a light (14 h)- dark (10 h) synchronized culture under photoautotrophic conditions. The imrnunoreactive proteins wereconcentrated in the pyrenoid, and less densely distributed in the stroma during the light period (growth phase, Fig. 1-2), but the pyrenoid disappeared during the dark period (division phase), and RuBisCO was dispersed throughout the stroma. Toward the end of the division phase, the pyrenoid began to form in the center of the stroma, and RuBisCO is again concentrated in that pyrenoid region. From a comparison of photosynthetic CO2-fixation with the total carboxylase activity of RuBisCO extracted from Euglena cells in the growth phase, it is suggested that the carboxylase in the pyrenoid functions in CO2-fixation in photosynthesis.
Sectioned rubisco crystals in TEM
Authors: Karlsson Gunnel , Bovin Jan-Olov , Bosma Michael
Published: June 2020

RuBisCO (D-ribulose-l,5-biphosphate carboxylase/oxygenase) is the most aboundant enzyme in the plant cell and it catalyses the key carboxylation reaction of photosynthetic carbon fixation, but also the competing oxygenase reaction of photorespiation. In vitro crystallized RuBisCO has been studied earlier but this investigation concerns in vivo existance of RuBisCO crystals in anthers and leaves ofsugarbeets. For the identification of in vivo protein crystals it is important to be able to determinethe unit cell of cytochemically identified crystals in the same image. In order to obtain the best combination of optimal contrast and resolution we have studied different staining and electron accelerating voltages. It is known that embedding and sectioning can cause deformation and obscure the unit cell parameters.
Where is the prolamine located in rice endosperm?
Authors: Wu Hsin-Kan , Chung Mei-Chu
Published: June 2020

In one of our earlier papers (Wu et al. 1978), we suggested that glutelin is the major composition of the round storage protein bodies although they also contain relatively more prolamine than the angular one does. Immunochemical studies of Krishnan et al. (1986) later showed the presence of glutelin in the irregularly-shaped (angular) protein bodies while the prolamines were found in the round ones. Our recent experiment using protein A-gold technique found that prolamine is mainly deposited into the angular protein bodies.

Small blocks (1 mm3) of 7 DAF (days after flowering) caryopsis of Orvza perennis were fixed with 3% paraformaldehyde and 3% glutaraldehyde in 0.1M sodium phosphate, pH7.4, dehydrated in a graded ethanol series and infiltrated with Spurr’s resin. Thin sections, after gold labeling, were stained with uranyl acetate and lead citrate. Rabbit antibodies were raised against purified prolamine. Protein A-gold sol complex was prepared based on the technique of Horisberger et al. (1977).
Scanning Electron Microscopy of the gill arch of Plecostomus commersonii (Pisces)
Authors: Fanta E. , Eiras-Stofella D. R.
Published: June 2020

The fish Pleaosomus commersonii occurs in Brazilian rivers and has the whole body covered with shields. It can remain out of the water for long periods without dying and is very resistant to environmental changes. It has 4 U-shaped branchial arches (Fig. 1a) with two special features: the absence of hooks or spines in the gill raker, in the pharyngeal region; and the presence of a second row of filaments, external to the branchial filaments (Fig. 1b).

Through SEM it was possible to describe externally both structures. The branchial filaments have flat secondary respiratory lamellae, which show irregular thickness (Fig. 2). At their tip, buds with one or more openings can be seen. The primary lamellae have an irregular epithelium with many round structures between the flat polygonal epithelial cells. The extra filament has a different aspect: it has no secondary lamellae. The side close to the branchial filament is different from the opposite one; the epithelium resembles that of the primary lamella.
Effects of long-term exposure to modified Karnovsky’s fixative on tissue ultrastructure
Authors: White S. L. , Hoover D. M.
Published: June 2020

In toxicology studies, the potential to store tissues in the primary fixative offers the flexibility to collect selected specimens and hold them for further processing contingent upon findings in other areas such as histopathology and biochemistry. This would allow conservation of resources and time by eliminating the need to duplicate studies specifically for electron microscopy. Previous investigators have dealt primarily with the morphological effects on the tissue produced by various fixatives, buffers, and osmolalities while using optimum processing schedules. However, little information is available on longterm exposure to the primary fixative25. In the present study, we investigated the ultrastructural morphological effects on tissues stored 1 month or 6 months in modified Kamovsky's fixative as compared to tissues given a 3 hr exposure to the primary fixative.

Three male and 3 female Fisher 344 rats ages 6 to 7 weeks were prepared for whole body fixative perfusion by giving an I.V. heparin sodium injection followed by ether anesthesia.
Low-voltage field-emission SEM of polymeric membranes for glucose biosensors
Authors: Mayo Lorna K. , Moore Kenneth C. , Arnold Mark A.
Published: June 2020

An implantable artificial endocrine pancreas consisting of a glucose sensor and a closed-loop insulin delivery system could potentially replace the need for glucose self-monitoring and regulation among insulin dependent diabetics. Achieving such a break through largely depends on the development of an appropriate, biocompatible membrane for the sensor. Biocompatibility is crucial since changes in the glucose sensors membrane resulting from attack by orinter action with living tissues can interfere with sensor reliability and accuracy. If such interactions can be understood, however, compensations can be made for their effects. Current polymer technology offers several possible membranes that meet the unique chemical dynamics required of a glucose sensor. Two of the most promising polymer membranes are polytetrafluoroethylene (PTFE) and silicone (Si). Low-voltage scanning electron microscopy, which is an excellent technique for characterizing a variety of polymeric and non-conducting materials, 27 was applied to the examination of experimental sensor membranes.
Localization of lectin binding sites in the lens of rats: A study by a labeling frozen thin-section method
Authors: Tanaka Toshikazu , Sakai Masahiro , Ihara Nobuo , Honda Yoshihito , Ogawa Kazuo
Published: June 2020

In various tissues, many investigators have reported that sugar residues of cell-membrane proteins participate important functions such as cellular recognition, adhesion and differentiation. As an organ, the lens has distinct polarity from anterior to posterior face as one of its unique structural characteristics. However, a only few studies have been performed about the localization of sugar residues at light-microscope level. The purpose of this study is to detect lectin binding sites in lenses of normal rats and Ihara Cataract Rats (ICR) by utilizing a labeling frozen thin-section method.

The lectins, concanavalin A (Con A) and wheat germ agglutinin (WGA) were used in this study. Wistar rats and ICR rats which develop hereditary cataracts were used as experimental animals. For light microscopy, frozen semi-thin sections were stained with the lectins, using an avidin-biotin-complex procedure and visualized by incubation with 0.1% diaminobenzidine (DAB) and 0.01% H2O2 in PBS.
Ultrastructural localization of secretory glycoconjugates in the gallbladder epithelium of the Richardson’s ground squirrel before and during cholesterol gallstone formation
Authors: MacPherson Brian R.
Published: June 2020

Hypersecretion of mucin is a critical feature of gallbladder epithelial cells in ground squirrels fed a 2% cholesterol-enriched diet for the induction of cholesterol gallstone formation. The timing of this physiological response indicates a potential role for mucin as an initiator of cholesterol crystal nucleation from supersaturated bile. There is little information regarding the specific type of glycoprotein secreted by gallbladder epithelia and routine light microscope histochemistry proved unproductive for detection of specific glycoprotein types being synthesized as the intracellular accumulations were not large enough to permit visualization of a colored precipitate. Ultrastructural histochemistry was utilized to differentiate between the two main mucin types secreted by the gastrointestinal tract - sulphated and sialomucins.

Two ultrastructural methods utilizing the histochemical basis of the high and low iron diamine techniques were used. The high iron diamine (HID) technique imparts density to sulphated complex carbohydrates while the low iron diamine (LID) method imparts density to acidic glycoconjugates.
EM and biochemical determinations of chromaffin cell ecto-ATPase activity
Authors: Kriho V. , Pappas G. D. , Becker R. P.
Published: June 2020

Exocytotic granules of bovine chromaffin cells contain both catecholamines and ATP. Upon stimulation, the granule contents are discharged into the extracellular space. Catecholamines are eventually hydrolyzed. The resultant choline is then taken up by the cell for recycling. The fate of the extracellular ATP has not been determined. Ecto-ATPase activity has been localized at the plasma membrane of the chromaffin cell in the adrenal gland. This ATPase activity may play a role in the local metabolism of the released ATP.

Our present study further investigates this ecto-ATPase activity, using biochemistry and EM cytochemistry, on isolated, intact bovine chromaffin cells. Our biochemical results are seen in the histogram of Fig. 1. ATPase assays show considerable ATPase activity when both Ca++ and Mg++ are present in physiological concentrations in the incubating solution. Even when Ca++ is omitted from the incubating solution, a great deal of ecto-ATPase activity is still demonstrated. Omitting Mg++ from the medium, however, reduced the level of ATPase activity by 91%.
Hydrated cryo-section studies of endocytic structures in cells containing internalized gold markers imaged by TEM
Authors: McDowall Alasdair , Griffiths Gareth
Published: June 2020

A question often raised when interpreting ultrastructural TEM images of sectioned biological material is, “to what degree do the se images reflect structure in vivo?”. It is difficult to unambiguously answer this question by classical electron microscopy alone, due to the necessity to use chemical procedures whose mechanism of action is never completely understood. More commonly, ultrastructural analyses are interpreted from information obtained using a variety of approaches and techniques.

We describe here structures of the endocytic pathway in cultured cells as seen in TEM following two cryo-preparative procedures: 1) Frozen thin sections of chemically fixed and sucrose infused cells (the Tokuyasu technique), and 2) the frozen hydrated technique on non-chemically fixed cells. The Tokuyasu technique offers one of the best methods available for intracellular localization of membrane antigens. In the present study, labelling living cells with colloidal gold conjugates could be complemented by further labelling fixed cryo-sections of the same cells. This was achieved with a range of antibodies and different sizes of protein A gold probes. From this and other data, a current model for the endocytic pathway evolved in which thre e major compartments exist between the plasma membrane-derived clathrin coated vesicles and the degredative lysosomes. Specifically, these compartments are an early endosome, an endosome ‘tran sport’ vesicle and the pre-lysosomal compartment/late endosome.
High resolution mapping of nucleic acid containing complexes in vitro and in situ
Authors: Bazett-Jones D. P. , Hendzel M. J.
Published: June 2020

Structural analysis of combinations of nucleosomes and transcription factors on promoter and enhancer elements is necessary in order to understand the molecular mechanisms responsible for the regulation of transcription initiation. Such complexes are often not amenable to study by high resolution crystallographic techniques. We have been applying electron spectroscopic imaging (ESI) to specific problems in molecular biology related to transcription regulation. There are several advantages that this technique offers in studies of nucleoprotein complexes. First, an intermediate level of spatial resolution can be achieved because heavy atom contrast agents are not necessary. Second, mass and stoichiometric relationships of protein and nucleic acid can be estimated by phosphorus detection, an element in much higher proportions in nucleic acid than protein. Third, wrapping or bending of the DNA by the protein constituents can be observed by phosphorus mapping of the complexes. Even when ESI is used with high exposure of electrons to the specimen, important macromolecular information may be provided. For example, an image of the TATA binding protein (TBP) bound to DNA is shown in the Figure (top panel). It can be seen that the protein distorts the DNA away from itself and much of its mass sits off the DNA helix axis. Moreover, phosphorus and mass estimates demonstrate whether one or two TBP molecules interact with this particular promoter TATA sequence.
Structure of rattlesnake venom lectin determined by single particle high-resolution electron microscopy
Authors: Moisiuk Peter D. , Beniac Daniel R. , Ridsdale Ross A. , Young Martin , Nagar Bhushan , Rini James M. , Harauz George
Published: June 2020

Venom from the rattlesnakeCrotalus atroxcontains a mixture of enzymes that induce a localized effect leading to hemorrhaging, necrosis and edema. As a member of the crotalid family of snake venoms,Crotalus atroxvenom contains a C-type lectin that will agglutinate blood cells in a Ca2+-dependent fashion. The lectin is a hydrophilic protein, consisting of two covalently linked, 135 amino acid residues, identical subunits that are rich in aspartic acid, glutamic acid and lysine. Sequence homology with known carbohydrate recognition domains (CRDs) indicates that rattlesnake venom lectin (RSLV) contains a CRD motif that is not linked to accessory domains. Preliminary X-ray diffraction and sedimentation analysis has indicated that lectin fromCrotalus atroxforms decamers composed of two five-fold symmetric pentamers. Single particles of RSVL imaged at – 171°C displayed two distinct orientations on the specimen support (Figure a) following incubation in a crystallization Teflon well, coated with a lipid monolayer consisting of phosphatidylcholine and monosialoganglioside. When lying in an end-on orientation, the lectin exhibited a “pentagonal ring” with an outer diameter of 6.7 nm and an inner hollow core of 1.7 nm. A side orientation was also seen, whereby a thickness of 5.8 nm was measured for the lectin. Image processing of 2280 single particles placed in 100 classes (Figure b) led to 3D reconstructions of RSVL (Figure c). Density limited 3D reconstructions showed the lectin to be made of two five-fold symmetrical rings covalently linked between the five subunits that constitute each ring of this homodimer. These results are consistent with sedimentation and preliminary X-ray diffraction analysis on the shape of RSVL and provide the framework for structural verification by 2D electron crystallography.
Quantitative Examination of Semicrystalline Polymers Via Atomic-Force Microscopy, Transmission Electron Microscopy, and Small-Angle X-Ray Scattering
Authors: Bischel M. S. , Balijepalli S. , Schultz J. M.
Published: June 2020

The Atomic Force Microscope (AFM) has been used to reliably measure lamellar thickness in semi-crystalline polymers, and to distinguish phases within blends of these polymers.

Traditionally, lamellar thicknesses of semi-crystalline polymers have been determined by (1) measuring structures directly from TEM micrographs or (2) using small angle X-ray scattering (SAXS) spectra. In the first case, the sample must either be etched and replicated, or stained with heavy metals or chlorosulfonic acid to reveal the lamellar structures. Good SAXS measurements require access to a synchrotron, or rotating anode diffractometer. In contrast, the AFM has been used to relaibly measure the lamellar structures in polymer specimens which have undergone minimal sample preparation.

The tapping mode of operation of a Digital Nanoprobe AFM has been used on the free surfaces of polyethylene oxide (PEO) specimens to determine lamellar thicknesses that are in excellent agreement with measurements obtained from both TEM and SAXS. Examples of such comparisons in the existing literature are few.
Characterization of triological sealing system components using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS)
Authors: Shuster Mark , Deis Mick
Published: June 2020

A system approach to solving the tribological problems associated with sealing joints implies comprehensive investigation of all the components. To recognize the root cause of any problem and formulate the required performance for extended reliability we have to evaluate any changes in the system as quantitatively as possible. Any measurable parameters, including geometry, density (porosity), hardness distributions, microstructure and grain size changes observed during routine metallurgical analysis could provide evidence of the root cause of failure. In the head-gasket-block sealing system of the internal combustion engine, the EDS evaluation of the chlorine and sulfur distribution through the head gasket flange fracture in conjunction with analysis of the sludge between the head, block and gasket surfaces pointed to the corrosive nature of the gasket flange cracking.

This approach is even more useful for the closed tribological system of telescopic hydraulic cylinders or rotary axle shaft oil seals.
Low-Voltage, High-Resolution, Scanning Electron Microscopy of Platelet-Bound Fibrinogen
Authors: Simmons S.R. , Albrecht R.M.
Published: June 2020

An essential element in blood clot formation is fibrinogen-mediated platelet aggregation. Fibrinogen is an adhesive plasma protein which binds to the αIIbp3 integrin on activated platelet surfaces. Platelets do not aggregate in the absence of fibrinogen binding, and fibrinogen bound to surfaces of platelets in aggregates is localized to regions of platelet-platelet contact. The fibrinogen molecule is symmetrical and bifunctional and may directly bridge the gap between platelets to bind to receptors on two adjacent platelets. However, the precise mechanism by which fibrinogen links platelets is unclear.

Previously we have utilized colloidal gold labeling with correlative light and electron microscopy to investigate the binding of fibrinogen to receptors on surfaces of spread, substrate adherent platelets. The initial binding of gold-conjugated fibrinogen (FgnAu) and subsequent ligand-triggered receptor movement was followed on living platelets by video-enhanced light microscopy. Fibrinogen receptors initially are dispersed over much of the platelet surface and move centripetally upon fibrinogen binding, ultimately forming a band of bound fibrinogen on the platelet surface overlying a densely woven band of actin filaments surrounding the central granulomere. After preparation for electron microscopy, the same platelets as were followed in the light microscope were located in the high voltage TEM and the low voltage, high resolution, SEM (Hitachi S-900) and the final locations of the gold labeled receptor/ligand complexes were determined relative to internal or surface ultrastructure, respectively. More recently, we have utilized the SEM operated at low (1-2 kV) beam voltage to examine in detail the binding of unlabeled fibrinogen to platelets. With appropriate specimen preparation, individual cell surface macromolecules can be resolved in situ by low voltage SEM. In addition to the centripetal receptor redistribution seen with FgnAu, unlabeled fibrinogen appeared to undergo self-adhesive interactions following binding to platelet fibrinogen receptors, forming small, branched and globular protein aggregates during translocation across the platelet surface.(Fig. 1)