Showing papers on "Ultrastructure published in 1979"
TL;DR: Cultured diploid human skin fibroblasts were fractionated by a procedure that maximizes recovery of particles containing acid hydrolases to suggest that the dense and buoyant lysosomal organelles originate primarily from residual bodies and the GERL network, respectively.
324 citations
TL;DR: Improved preservation by a modified freeze-substituted hyphal tip cells of Fusarium acuminatum resulted in an extensive system of smooth membrane cisternae with electron-dense contents and a smooth profile of all cellular membranes and most organelles.
188 citations
Journal Article•
TL;DR: The observations suggest that MBs in livers of griseofulvin-treated mice, and probably also of human alcoholic hepatitis, contain large amounts of prekeratin-like polypeptides which are assembled into a special form of fimbriated rods of 14- to 20-nm filaments.
108 citations
Journal Article•
TL;DR: Light microscopy indicates that avian and mammalian growth plates have very different structures, electron microscopy finds many similarities, suggesting that the physiological control mechanisms in these two vertebrate classes have much in common.
Abstract: The ultrastructure of the proximal tibial growth plate of the 7 weeks old chicken has been described. Little ultrastructural difference could be ascertained between growth plates examined from normal white leghorn and commercial broiler chickens. The growth plate may be divided into five zones: interstitial, proliferating, prehypertrophic, hypertrophic, and degenerating hypertrophic. These zones reflect a maturation of chondrocytes, beginning with a stage of high mitotic and cytoplasmic activity passing through a stage of active secretion of matrical components (prehypertrophic and hypertrophic) and ending with degeneration of the cells and calcification of the matrix. Mineralization of the matrix appears to be initiated within matrical dense bodies, as in the mammal. Single hydroxyapatite crystals are first encountered about 0.1 mm proximal (i.e. towards the knee) to the limit of metaphyseal blood vessel ingrowth, while dense calcification is observed 0.1 mm distal to the tips of these metaphyseal vessels. The diameter of microfibrillary collagen in the growth plate matrix ranges from approximately 9 nm in the proximal zones to 19 nm in the distal zones. Many of the fibrils in the distal zones have a more or less distinct periodicity. Other major elements of the growth plate matrix are the ruthenium red-stained syncytial aggregates of mucopolysaccharides which are probably derived from the granules within the large intracellular Golgi vesicles. These findings have led the author to conclude that, while light microscopy indicates that avian and mammalian growth plates have very different structures, electron microscopy finds many similarities, suggesting that the physiological control mechanisms in these two vertebrate classes have much in common.
107 citations
Journal Article•
TL;DR: Using the internal perfusion technique, it is confirmed that organelles which had been attached to the fibrils by decreasing the internal concentration of ATP moved along thefibrils after ATP was introduced, and the role of such components of the organelle in cytoplasmic streaming is discussed.
Abstract: Previous investigators have proposed that cytoplasmic streaming in Chara internodal cells results from the interaction between an endoplasmic factor and fibrils composed of microfilaments in the stationary cortex. Using the internal perfusion technique, we confirmed the observation that organelles which had been attached to the fibrils by decreasing the internal concentration of ATP moved along the fibrils after ATP was introduced. Thin-sectioned specimens revealed that endoplasmic organelles of various shapes were linked to microfilament bundles in the absence of ATP. Linkage was effected by regularly arranged electron-dense materials with a spacing of 100 -- 130 nm at definite regions on each organelle. The organelles in question were studied in negatively stained preparations of endoplasm. The organelles had some common features. (1) They were all membrane-limited.(2) Their sizes and configurations varied largely. (3) One or more protuberances were present on them. (4) The protuberances were usually rod- or horn-like. (5) Small globular bodies 20--30 nm in diameter were found in ordered array with the same spacing as those in thin sections at the surface of the protuberances. (6) Many fine filaments were always attached to the surface of the protuberances. These fine filaments differed from F-actin in diameter (less than 4 nm) and inability to react with heavy meromyosin from rabbit skeletal muscle. The role of such components of the organelles in cytoplasmic streaming is discussed. A paracrystalline array of microfilaments with a transverse periodicity of about 38 nm is presented, together with its optical diffraction pattern.
93 citations
TL;DR: During most phases of the disease, hyphae bridged the intercellular spaces or were attached to and followed the contours of host cell walls, but only late in the Disease, long after host cells were necrotic, were hyphAE observed within largely disintegrated host cell Walls.
Abstract: The fungus Cercospora beticola Sacc. incites a leaf spot disease of sugarbeet ( Beta vulgaris L.). Lesion formation was studied by electron microscopy. One week after inoculation, the fungus was established in the intercellular spaces of the mesophyll and degenerative changes had occurred in cells near infection sites. Visible necrotic spots were produced as these lesions enlarged. During the degenerative sequence cell membrane systems and organelles were disrupted; affected cells quickly collapsed and became necrotic. After 3 weeks a boundary zone with two regions separated the central necrotic tissue from apparently unaffected, healthy tissue outside the lesion. Two types of cell wall apposition occurred, one a localized callose-type in the lesion center, and the second a generalized wall thickening in the inner boundary zone. Electron-dense material occluded intercellular spaces in the outer boundary zone. During most phases of the disease, hyphae bridged the intercellular spaces or were attached to and followed the contours of host cell walls. Only late in the disease, long after host cells were necrotic, were hyphae observed within largely disintegrated host cell walls.
89 citations
TL;DR: This chapter discusses the membrane-coating granules (MCGs), which represent a specific secretory product of almost all stratified squamous epithelia and contain lysosomal enzymes, but this probably reflects their origin rather than their function.
Abstract: Publisher Summary This chapter discusses the membrane-coating granules (MCGs) MCGs represent a specific secretory product of almost all stratified squamous epithelia In keratinized epithelia they contain lysosomal enzymes, but this probably reflects their origin rather than their function Their contents are extruded from the cells so as to fill the intercellular spaces where it probably provides the efficient permeability barrier found in most such epithelia The work on these granules has been almost entirely structural Definitive information on the composition of MCGs awaits their isolation, presumably by differential centrifugation Epithelia have always been difficult subjects for this procedure because of the massive quantity of insoluble fibrous protein present in the cells The outstanding ultrastructural problem is the origin of MCGs A spatial association with the Golgi apparatus is not convincing evidence of their origin from this structure
81 citations
TL;DR: Open lung biopsies from three patients with Legionnaires' disease were examined by light and transmission electron microscopy, suggesting that the tissue changes are potentially capable of reverting to normal structure and function.
Abstract: Open lung biopsies from three patients with Legionnaires' disease were examined by light and transmission electron microscopy. The patients had serious underlying disease. All developed a rapidly progressive pneumonia unresponsive to penicillin, oxacillin, and gentamicin. One patient, who received erythromycin, survived. Light microscopy in all three showed severe acute bronchopneumonia. The Legionnaires' disease bacterium was seen in tissue sections and confirmed by direct immunofluorescence. Transmission electron microscopy showed numerous rod-shaped intracellular organisms that were morphologically similar to other gram-negative bacteria and the Rickettsieae. They were within phagolysosomes, free in the cytoplasm, and rarely within structures resembling dilated rough endoplasmic reticulum. Lung tissue changes included marked detachment and necrosis of alveolar pneumocytes, septal and alveolar exudate with lysis, and prominent endothelial cell swelling and degeneration. Capillary and epithelial basement membranes were consistently intact, suggesting that the tissue changes are potentially capable of reverting to normal structure and function.
72 citations
70 citations
TL;DR: Glandular trichomes on the inflorescence of Chrysanthemum morifolium cv.
Abstract: Glandular trichomes on the inflorescence of Chrysanthemum morifolium cv. Dramatic are initiated from a single epidermal cell outgrowth and develop through an anticlinal division and a series of periclinal divisions to form a biseriate multicellular structure. Cells of the young trichome contain a large nucleus with prominent nucleoli and few small cellular organelles. Prior to the secretory stage, numerous ribosomes, polyribosomes, and dictyosomes are present in a dense cytoplasm but most of the dictyosomes are lost as secretion commences. Plastids in the stalk cells senesce but in a different manner than those in the upper tiers of secretory cells. Lipoidal substances form in the degenerating plastids. Cell wall ingrowths and the deposition of a flocculent material in the primary cell wall characterize secretory hairs. In very old hairs cellular lysis takes place with mitochondria being the last cellular organelle to remain intact. The secreted material, which collects in a subcuticular space, appears to...
61 citations
TL;DR: Observations of later developmental stages revealed the major events of capsulogenesis, valvogenesis, and sporoplasm maturation, which occurred concomitantly during spore construction.
Abstract: SYNOPSIS
Ultrastructure of the plasmodium wall and of sporogenesis were studied in Myxosoma funduli Kudo infecting the gills of Fundulus kansae (Garman). Plasmodia were located within the lamellar tissues adjacent to sinuses and capillaries. The plasmodium wall consisted of a single unit membrane which was continuous with numerous pinocytic canals extending into the parasite ectoplasm. The plasmodium membrane was covered by a surface coat of almost uniform thickness which prevented direct parasite-host cell contact. Numerous generative cells and cell aggregates, representing early stages of spore development, were seen in immature plasmodia. Later stages of spore development, including mature spores, were observed in older plasmodia. Sporogenesis was initiated by envelopment of one generative cell, the sporont, by a 2nd, nondividing cell, the envelope cell. The sporont and its progeny proceeded through a series of divisions until there were 10 cells, all compartmentalized within the envelope cell. Subsequently, the 10 cells became structurally differentiated and arranged into two 5-celled spore-producing units, each consisting of 1 binucleate sporoplasm and 2 capsulogenic cells, all surrounded by 2 valvogenic cells. Observations of later developmental stages revealed the major events of capsulogenesis, valvogenesis, and sporoplasm maturation, which occurred concomitantly during spore construction.
TL;DR: In lung tissue and yolk sac membranes, the organisms replicated within the cytoplasm of infected cells and in the intercellular spaces and were specifically identified in thin sections by immunoferritin techniques.
Abstract: Eleven lung samples positive for Legionnaires' disease, 12 strains of Legionella pneumophila cultured on various bacteriological media, and one strain growth in the yolk sac of fertile hens' eggs were examined by negative staining, thin sectioning, and scanning electron microscopy. All organisms studied were ultrastructurally similar irrespective of strain, source, or method of cultivation, presenting mainly as short rods, 0.6 x 1.5 micrometer, with tapered ends, though long forms and filaments were also evident. In this they resembled typical Gram-negative organisms. Division was by non-septate binary fission, and the cell wall was composed of two triple-unit membranes with morphological evidence of a peptidoglycan layer. The bacterial cytoplasm was rich in ribosomes and nuclear elements and often contained vacuoles. No acid polysaccharides or bacterial appendages were detected surrounding the organisms. In lung tissue and yolk sac membranes, the organisms replicated within the cytoplasm of infected cells and in the intercellular spaces and were specifically identified in thin sections by immunoferritin techniques.
TL;DR: The ultrastructure of Spirulina platensis, a cyanobacterium with a helical morphology, has been studied in relation to temperature and light intensity and cylindrical bodies have been observed with a somewhat different ultrast structure from those found in other species of cyanobacteria.
Abstract: The ultrastructure of Spirulina platensis, a cyanobacterium with a helical morphology, has been studied in relation to temperature and light intensity. An increase in temperature gives rise to a more tightly coiled trichome, an increase in sheath material formation and a decrease in cyanophycin (above 17°C) and polyglucan (above 20°C) granule concentration. An increase in light intensity leads to an increase in gas vesicle concentration while the phycobilisome content decreases. Furthermore, cylindrical bodies have been observed with a somewhat different ultrastructure from those found in other species of cyanobacteria. The occurrence, size and ultrastructure of polyhedral bodies, photosynthetic lamellae, mesosomes, lipid deposits and an unknown kidney-shaped inclusion in relation to temperature and light intensity are described.
TL;DR: In this paper, the pericardial cavity of the marine lamellibranch bivalve mollusc Mytilus edulis (L) has been studied.
Abstract: The morphology and ultrastructure of the heart and excretory system of the marine lamellibranch bivalve mollusc, Mytilus edulis (L.) are described. This paper supports the view that ultrafiltration of the blood occurs in the pericardial cavity. The auricles, pericardial glands and afferent oblique veins contain podocytes which are usually ascribed to the specific function of ultrafiltration. These cells are absent in the ventricle. The pericardial cavity communicates with the exterior via a very short (ca. 1–2 mm) renal tubule. The kidney comprises of a series of highly branched diverticula of this tubule and displays little or no structural differences throughout the organ. The kidney cells form a single layered columnar epithelium with a brush border, basal nuclei, infolded basal membranes and are characterized by the presence of many membrane-limited granules occupying as much as 20% of the cell volume. These granules and those of the podocytes are subsequently shed into the lumen of the kidney tubule and are excreted in the urine which is therefore largely paniculate.
TL;DR: Direct histocytochemical staining methods on undisrupted tissues, stabilized by chemical fixation, potentially offer perhaps the most reliable approach to the study of the enzymes of the cell with relation to its ultrastructure.
TL;DR: A total of 10 strains of Bacteroides melaninogenicus subspecies were examined by transmission electron kicroscopy after conventional processing, and staining with uranyl acetate and lead citrate, finding morphological differences may be useful in differentiating these subspecies from one another.
Abstract: A total of 10 strains of Bacteroides melaninogenicus subspecies were examined by transmission electron kicroscopy after conventional processing, and staining with uranyl acetate and lead citrate. All strains examined had a cell periphery with a basic ultrastructure typical of that reprted for other Gram-negative bacteria. However, only s.s. asaccharolytucus strins exhibited a moderately electron-dense covering layer, 16–19 nm thick, in contact with the outer membrane of the cell wall, and numerous intercellular membranous vesicles. S.s. melaninogenicus strains, in contrast to those of those of other subspecies, had no extramural structures, and exhibited a distinct, intercellular, fibrillar matrix. S.s. intermedius cells featured a 9–14 nm thick, electron-dense extramural layer which was separated by an electron-lucent layer of similar thickness from the outer membrane of the wall. these morphological differences may be useful in differentiating these subspecies from one another. phological differences may be useful in differentiating these subspecies from one another.
TL;DR: This excretory reactivity of the midgut epithelium has been compared to the cycle of the cuticle and degeneration processes can be observed in the old epithelia.
Abstract: The midgut cells of Tomocerus minor (Insecta, Collembola) were examined with the electron microscope and cytochemically. The midgut epithelium consists of a series of cells characterised by numerous mineral concretions scattered throughout the cytoplasm. Mitochondria are abundant; microvilli are well developed at the apical surface of the cell. A zonula continua (continuous junction) characterises the apical contact region of these cells. Polysaccharides, glycoproteins and carbohydrate components have been demonstrated on the surface of microvilli. Peritrophic membranes surround the food bolus and preserve midgut cells from mechanical abrasion. Lysosomes are present during the alimentary period and show strong acid phosphatase activity. During an intermoulting cycle, two stages can be observed: (1) the postexuvial feeding period during which cytoplasmic extrusions appear at the apical part of the cell: lysosomes increase in number and autophagic vacuoles appear. (2) The preexuvial fasting period; a new epithelium grows beneath the old one and pushes it into the lumen. Degeneration processes can be observed in the old epithelium. This excretory reactivity of the midgut epithelium has been compared to the cycle of the cuticle.
01 Oct 1979
TL;DR: Observations suggest that one of the principal functions of the midGut, midgut caeca, and hindgut epithelia is the transport of ions and water.
Abstract: The ultrastructure of the alimentary tract lining, excluding the hepatopancreas, of lobsters,Homarus americanus andH. gammarus, and Dungeness crab,Cancer magister, was investigated with transmission electron microscopy. The foregut lining consists of a cuboidal epithelium with extensive interdigitations of the lateral cell membranes and adhering junctions. The ultrastructural organization of the midgut and midgut caeca resembles that of other transporting epithelia. The cells possess a microvillous border, and the basal cytoplasm contains numerous mitochondria and an anastomosing system of smooth endoplasmic reticulum. Hemocytes, presumed neurosecretory axons, and putative endocrine cells occur within the epithelium of the midgut and midgut caeca. Hindgut epithelial cells have numerous mitochondria in the apical cytoplasm, and their basal cell membranes are elaborately infolded. These observations suggest that one of the principal functions of the midgut, midgut caeca, and hindgut epithelia is the transport of ions and water.
TL;DR: Electron microscopy confirmed Enzinger's impression that the cell of origin of the IMM is similar to a fibroblast with features that support the hypothesis that these cells are the source of production of the excessive amount of mucopolysaccharides in the matrix.
Abstract: The clinicopathological data of ten intramuscular myxomas (IMM) and three myxoid liposarcomas (MLS) are presented with emphasis on their ultrastructure. Electron microscopy of three of the IMM demonstrated the principal cell of the IMM to be similar to a fibroblast with prominent R.E.R., well-developed Golgi apparatus and cytoplasmic filaments. Intracytoplasmic lipid droplets were very rare. The matrix was composed of finely granular material, collagen fibers, fibrils and few capillaries. In contrast with the IMM, the cytoplasm of the MLS contained extensive lipid droplets. Capillaries were very abundant and in close proximity to the lipoblasts. The distinction between an IMM and MLS is usually clear-cut by light microscopy. Dissimilar ultrastructural features provide additional data to separate these two tumors. Ultrastructure confirmed Enzinger's impression that the cell of origin of the IMM is similar to a fibroblast with features that support the hypothesis that these cells are the source of production of the excessive amount of mucopolysaccharides in the matrix.
TL;DR: The correlation established between cell staining and function will facilitate exploration of single cell properties, which together constitute hearts and blood vessels, and help to identify isolated muscle cells from nonmuscle cells in mammalian and avian primary cultures.
Abstract: To develop morphological criteria which can be applied systematically for the identification of isolated cardiac and vascular muscle cells in mammalian and avian primary cultures, we have correlated structural and staining properties with excitability, contraction, and norepinephrine sensitivity of isolated muscle cells. The primary cultures of cardiac and vascular muscle contained muscle cells and nonmuscle cells. The muscle cells could be clearly identified by action potentials, contractility, and Masson's trichrome stain characteristics, similar to those of cells from intact source heart and blood vessels. Furthermore, the muscle cells were highly responsive to norepinephrine, showing unequivocal increases in contraction frequency. The sensitivity to norepinephrine was found to be very high (ED50 = 2.3 X 10(-9) M) Phase-contrast observation was sufficient to identify muscle cells only when those cells were contracting. There were no unequivocal morphological characteristics that distinguished between quiescent muscle cells and nonmuscle cells in the absence of histochemical staining. Ultrastructural examination by scanning electron microscopy failed to distinguish between muscle and nonmuscle cells. Histological staining was, therefore, the only reliable nonfunctional identification process that separated muscle cells from nonmuscle cells. Primary cultures, containing nonmuscle as well as muscle cells, are an important experimental preparation because the cellular heterogeneity probably minimizes muscle cell loss of function and phenotypic changes. The correlation we have established between cell staining and function will facilitate exploration of single cell properties, which together constitute hearts and blood vessels.
TL;DR: The results of the investigations concerning the acid phosphatase activity suggest that this enzyme plays a role in the degradation of certain platelets which penetrate into the cytoplasmic zone, and on the other hand in the regulation of VLDL, in the lysis of secretory products elaborated by the cytopsized zone.
Abstract: In contrast to the vitellolysis zone which is involved in the degradation of the yolk, the cytoplasmic zone of the yolk syncytial layer, composed of many cytoplasmic organelles, is implicated in a secretory process. The granular endoplasmic reticulum of the latter is extremely well developed and organized into trabeculae. The yolk nuclei show a RNA positive reaction. The Golgi apparatus is implicated in the elaboration of very low density lipoproteins (VLDL) and of acid phosphatase. The numerous mitochondria seem to suggest an important energy metabolism in the solubilisation area. The appearance of certain special structures (crystalline bodies, pseudovesicular structures, lipochondria) as well as their relation with the organelles of the cytoplasmic zone, re-inforces the impression of a layer with a secretory nature and suggests its participation in the remodelling of the yolk products produced in the vitellolysis zone.
TL;DR: The ultrastructure of the surface of primary human amnion monolayer cells undergoing cytopathology induced by Clostridium difficile toxin was examined and indicated that the type and distribution of cell surface projections were altered dramatically by this toxin.
Abstract: The ultrastructure of the surface of primary human amnion monolayer cells undergoing cytopathology induced by Clostridium difficile toxin was examined by scanning electron microscopy. Our observations indicated that the type and distribution of cell surface projections were altered dramatically by this toxin. The patterns of such surface changes were specific for the two different types of cells found in this cell culture. Cells with demarcated borders showed rearrangement of microvilli into globular chains or ridges which lined up with the branching membrane. Cells without demarcated borders exhibited studlike microvilli, all arranged into ridges or globular chains. These changes were noted after 1 h of toxin exposure and persisted without further progression, in spite of continued toxin exposure, up to 48 h. These data indicate that C. difficile produces a cytolytic toxin and that scanning electron microscopy may be useful in determining toxin-cell interactions.
TL;DR: The gross organization of chromatin is species-specific, but not tissue-specific and function-dependent, and the higher the DNA content the more the euchromatin remains in the condensed state during interphase, but to a lower coiling order than the heterochromatin.
Abstract: In contrast to mammalian cell nuclei those of plants display nearly an identical ultrastructure in all developmental stages and tissues. This indicates that the gross organization of chromatin is species-specific, but not tissue-specific and function-dependent. The species-specific nuclear ultrastructure is determined by the basic nuclear DNA content (2 C value). The higher the DNA content, the more the euchromatin remains in the condensed state during interphase, but to a lower coiling order than the heterochromatin. Some difficulties in the interpretation of electron micrographs of cell nuclei, and the possible role of repetitive DNA sequences in the karyotypical condensation of euchromatin in plants are discussed.
TL;DR: Results from this study indicate that R. thelohani should be considered a member of ApicomplexaUnless definitive evidence is presented to the contrary, it is suggested that the organism moves between cell of epithelial layers and is either released into a lumen intact or passively or actively discharges its contents into aLumen.
Abstract: New fish species and geographic records for Rhabdospora thelohani Laguesse, 1895 (rodlet cells) are presented. Additionally, the ultrastructure of R. thelohani in Alburnoides bipunctatus ohridanus Karaman, Borostomias antarcticus (Lonnberg), Leuciscus cephalus albus Bonaparte and Rutilus rubilio (Bonaparte) is compared with that reported by other authors and with members of Subphylum Apicomplexa. The ultrastructure of R. thelohani was similar in all the fish species examined; however, the organism was not present in all members of any single species and had intertissue density variations. Rhabdospora thelohani is pyriform, averaging in size 7 X 12 micrometer, with a basal nucleus. The surface complex is composed of a layer (0.5 micrometer diameter) formed by microfilaments (9.3 nm) and an outer trilaminar membrane (9.3 nm). The cytoplasm contains structures identical to rhoptries, micronemes and subpellicular microtubules. Mitochondria, Golgi apparatus, and rough endoplasmic reticulum were not observed, althouth free ribosomes were present and arranged in a vesicular pattern. The observations suggest that the organism moves between cell of epithelial layers and is either released into a lumen intact or passively or actively discharges its contents into a lumen. Results from this study indicate that R. thelohani should be considered a member of Apicomplexa unless definitive evidence is presented to the contrary.
Journal Article•
TL;DR: The epidermal ultrastructure of 11 allogeneic bone marrow recipients with chronic graft-versus-host disease (GVHD) was compared with that of 4 recipients without chronic GVHD and revealed three patterns of epidersmal injury typical of chronic GvHD.
Abstract: The epidermal ultrastructure of 11 allogeneic bone marrow recipients with chronic graft-versus-host disease (GVHD) was compared with that of 4 recipients without chronic GVHD. This electron microscope study revealed three patterns of epidermal injury typical of chronic GVHD. The first type was a nonacantholytic (nondissecting) injury with a prominent cellular infiltrate consisting primarily of lymphocytes accompanied by a few macrophages. The second type was an acantholytic (dissecting) injury with a prominent infiltrate, while the third was a nondissecting injury with a sparse infiltrate. Broad-zone contact was observed between lymphocytes and all epidermal cell types as well as between other lymphocytes and macrophages. Point contact was only observed between lymphocytes and epidermal cells. Lymphocytes appeared to detach desmosomes from adjacent keratinocytes by isolating them with cytoplasmic projections, a phenomenon not previously described. Typical damage to the epidermal cells in the basal and spinous layers consisted of either swelling of the organelles or condensation of the cytoplasm and nucleus. In the keratinocyte, the condensation reaction resulted in the formation of colloid bodies, some of which were phagocytized by macrophages. Besides the cytolytic events, a concurrent stimulatory reaction occurred in the epidermal cells. The number of melanosomes in melanocytes and of Langerhans cell granules and dense bodies in the Langerhans cells all increased. Extensive areas of replication and disruption of the basal lamina were subjacent to areas of necrosis in the basal layer.
TL;DR: In Cyelotella meneghiniana the location of the nucleus in the vegetative cell changes as the cell diameter is decreased by successive cell divisions.
Abstract: In Cyelotella meneghiniana the location of the nucleus in the vegetative cell changes as the cell diameter is decreased by successive cell divisions. Other features of the vegetative cell are ultrastructurally similar to other diatoms: chloroplasts are enveloped by chloroplast endoplasmic reticulum; pyrenoids are traversed by a single thylakoid; mitochondria contain tubular cristae; and dictyosomes are located near the nucleus. The auxospore has one or more large vacuoles that restrict the organelles to a narrow, peripheral band of cytoplasm. The organelles of the auxospore are morphologically similar to those found in the vegetative cells. Peripheral endoplasmic reticulum is present in the auxospore but not in the vegetative cell. The wall of the immature auxospore is composed of an organic component that is supplemented with siliceous scales as the auxospore matures. A metagamic mitosis precedes formation of each of the valves of the initial cell. Both valves of the initial cell are formed insi...
TL;DR: The immunocytological results are consistent with the synthesis of a molecule similar to pro-opiocortin by this type of endocrine cell in human fetuses and the maturation process of this precursor and for the secretory activity of these cells and its possible regulation is presented.
Abstract: Cells immunoreactive with anti-α-(17–39) ACTH, β-(1–24) corticotropin, β-LPH, α- and β-EP were identified in the human fetal anterior pituitary at the ultrastructural level using the peroxidase-antiperoxidase complex method on ultrathin sections. Only one definite cell type was revealed by all these antisera. All granules of each individual immunostained cell reacted regardless of the antiserum used. The immunostained cells occurred in groups and were sometimes located in the wall of the follicle-like structures commonly observed in the fetal anterior pituitary. The cells revealed two main aspects: 1) The largest elements were rich in organelles, and their numerous secretory granules showed significant variations in size (250–500 nm in diameter), electron density of their content and stain-deposit intensity. The ergastoplasm, consisting of irregular tubules, was poorly developed. In the vicinity of the conspicuous Golgi apparatus, organelles related to the GERL complex were commonly observed. Multivesicular bodies were frequent. Some of these cells showed bundles of microfilaments (60 nm in thickness). 2) The smaller cells had an electron-lucent hyaloplasm with sparse organelles; they contained fewer granules and never showed microfilaments. The immunocytological results are consistent with the synthesis of a molecule similar to pro-opiocortin by this type of endocrine cell in human fetuses. Morphological evidence for the maturation process of this precursor and for the secretory activity of these cells and its possible regulation is presented and discussed.