Showing papers on "Ultrastructure published in 1997"

Oocyte ultrastructure in bovine primordial to early tertiary follicles.

Abstract: The aim of the present study was to describe in detail the changes occurring in the cytoplasmic ultrastructure of the bovine oocyte from the onset of growth in the primordial follicle until the completion of growth in the tertiary follicle. Bovine oocytes from primordial, primary, secondary and early to mid-antral follicles were processed and analysed by light and transmission electron microscopy. The primordial follicular oocyte was characterized by numerous coated pits on the oolemma and the accumulation of free and organelle-related smooth (SER) and rough (RER) endoplasmic reticulum, round mitochondria and Golgi complexes around the nucleus, which was located slightly off centre. Up to the secondary follicular stage the oocyte displayed an increase in the number of microvilli, elongated mitochondria and Golgi complexes. During the secondary follicular stage, formation of the zona pellucida, development of gap junctions between the oocyte and the granulosa cells, formation of the cortical granules in the oocyte and reduction in the number of coated pits on the oolemma were seen. In the tertiary follicular oocyte up to 100 μm in diameter, the number of Golgi complexes and lipid droplets increased and the organelles were dislocated to the deep cortical region. During the final growth of the oocyte up to >120 μm, the organelles were dislocated further to the peripheral region, the extent of the free SER and RER compartments were reduced, the number of individual cortical granules increased, hooded mitochondria became abundant and the perivitelline space developed. In conclusion, the growth of the bovine oocyte is associated with the relocation and modulation of a number of cytoplasmic organelles as well as the development of oocyte specific structures such as the zona pellucida and cortical granules.

Growth and ultrastructure of Arabidopsis root hairs: the rhd3 mutation alters vacuole enlargement and tip growth

Abstract: The root hairs of plants are tubular projections of root epidermal cells and are suitable for investigating the control of cellular morphogenesis. In wild-type Arabidopsis thaliana (L.) Heynh, growing root hairs were found to exhibit cellular expansion limited to the apical end of the cell, a polarized distribution of organelles in the cytoplasm, and vesicles of several types located near the growing tip. The rhd3 mutant produces short and wavy root hairs with an average volume less than one-third of the wild-type hairs, indicating abnormal cell expansion. The mutant hairs display a striking reduction in vacuole size and a corresponding increase in the relative proportion of cytoplasm throughout hair development. Beadlabeling experiments and ultrastructural analyses indicate that the wavy-hair phenotype of the mutant is caused by asymmetric tip growth, possibly due to abnormally distributed vesicles in cortical areas flanking the hair tips. It is suggested that a major effect of the rhd3 mutation is to inhibit vacuole enlargement which normally accompanies root hair cell expansion.

Light and dark cells of rat vallate taste buds are morphologically distinct cell types.

Abstract: Cells of mammalian taste buds have been classified into morphological types based on ultrastructural criteria, but investigators have disagreed as to whether these are distinct cell types or the extremes of a continuum. To address this issue, we examined taste buds from rat vallate papillae that had been sectioned transversely, rather than longitudinally, to their longest axis. In these transverse sections, dark (Type I) and light (Type II) cells were easily distinguished by their relative electron density, shape and topological relationships. Cells with electron-lucent cytoplasm (light cells) were circular or oval in outline, while those with electron-dense cytoplasm (dark cells) had an irregular outline with sheetlike cytoplasmic projections that separated adjacent light cells. A hierarchical cluster analysis of 314 cells across five morphological parameters (cell shape and area, and nuclear ellipticity, electron density and invagination) revealed two distinct groups of cells, which largely corresponded to the dark and light cells identified visually. These cells were not continuously distributed within a principal components factor solution. Differences in the means for dark and light cells were highly significant for each morphological parameter, but within either cell type, changes in one parameter correlated little with changes in any other. These analyses all failed to reveal cells with a consistent set of intermediate characteristics, suggesting that dark and light cells of rat vallate taste buds are distinct cell types rather than extremes of a continuum. Sections of taste buds were stained with antibodies to several carbohydrates, then observed by indirect immunofluorescence. Optical sections taken with a confocal laser-scanning microscope showed that the Lewis antigen was present only on spindle-shaped cells with circular or oval outlines and lacking transverse projections; these characteristic shapes matched those of light cells seen by electron microscopy. The H blood group antigen and the 2B8 epitope appeared at most cell-cell interfaces in the bud and are present on dark cells and possibly on some light cells. These findings relate molecular markers to morphological phenotypes and should facilitate future studies of taste cell turnover, development and regeneration.

Spermiogenesis and spermatozoon of Echinostoma caproni (Platyhelminthes, Digenea): transmission and scanning electron microscopy, and tubulin immunocytochemistry

Abstract: Spermiogenesis and the spermatozoon of Echinostoma caproni (from experimentally infested laboratory mice) were investigated by several methods. Transmission electron microscopy shows that spermiogenesis consists of proximo-distal fusion of three processes followed by elongation of the spermatid. Scanning electron microscopy shows that the spermatozoon is a filiform cell, 235 microns in length, with a cylindrical anterior extremity and a broader posterior extremity. Epifluorescence microscopy, including immunocytochemistry of tubulin and labelling of nucleus with specific dyes, has provided valuable additional information. Migration of the nuclei from the common cytoplasmic mass of spermatids to the distal part of the elongating spermatids is visualized, and centrioles demonstrated in the proximal, anterior region, and the nucleus in the distal, posterior region of the spermatozoon. One axoneme has a distal extremity which in the mature spermatozoon extends 30 microns more distally than the other, with the result that the posterior part of the spermatozoon contains a single axoneme and nucleus. Immunocytochemistry experiments show that a region, 15 microns in length, not labelled by the anti-tubulin antibodies with certain fixation-permeabilization procedures, corresponds to a region which, by transmission electron microscopy, shows external ornamentation on the membrane. This region has a bilaterally asymmetric pattern (in TEM), forms angles or coils according to the fixation used, and marks the boundary between two distinct patterns of movement. Spermiogenesis and the spermatozoon in E. caproni correspond to the general pattern found in the digeneans, with the exception of this asymmetric region. It is emphasized that the use of various methods provides a better understanding of sperm structure than transmission electron microscopy alone, particularly in the case of long, filiform spermatozoa.

Developmental changes in calcium content of ultrastructurally distinct subcellular compartments of preimplantation human embryos.

Abstract: The ultrastructural localization of mobilizable Ca2+ in different subcellular compartments of human oocytes and preimplantation embryos was studied using the potassium-pyroantimonate technique and transmission electron microscopy; the specificity was confirmed by chelation experiments and X-ray microanalysis In unfertilized oocytes, Ca2+ was detected in small vesicles beneath the plasma membrane as well as in other forms of smooth endoplasmic reticulum (SER) and in mitochondria but not in cortical granules In pronuclear zygotes and blastomeres of cleaving embryos, Ca(2+)-rich vesicles were no longer present close to the plasma membrane, and the entire periphery was poor in Ca(2+)-containing organelles which, however, were abundant in the perinuclear region The uneven Ca2+ loading of SER and mitochondria from the pronuclear stage onwards suggests that Ca2+ release from both these types of organelle contributes to the embryonic Ca2+ signals During mitosis, less Ca2+ was detected with organelles, but the antimonate reaction product was more abundant in the cytosol These data suggest that, in addition to different forms of SER, mitochondria also act as a source of mobilizable Ca2+ in preimplantation human embryos The previously described developmental and cell cycle related changes in the characteristics of Ca2+ signals are associated with the redistribution and structural reorganization of these organelles

Morphological Specializations of the Digestive Tract of Zacryptocerus rohweri (Hymenoptera: Formicidae)

Abstract: Light, scanning, and transmission electron microscopy are used to examine the morphology and ultrastructure of the peculiar digestive tract of the turtle ant, Zacryptocerus rohweri. The proventriculus is heavily sclerotized and covered with clusters of small spines. Narrow spine-lined channels converging at the opening to the midgut act as a fine filter of food; particles .12.5 µm are unable to pass through the proventriculus. In the midgut, ultrastructural study reveals bacteria among the microvilli of midgut epithelial cells. The hindgut of Z. rohweri consists of an enlarged, dark- colored pouch filled with masses of bacteria of three major morphotypes. A thick layer of circular muscle and deep infoldings of the epithelium greatly increase surface area for absorption. Newly emerged individuals appear to acquire these microorganisms by soliciting material from the abdomen tip of other older workers in the colony. Whether or not the hindgut bacteria are true symbionts is unknown; their acquisition and presence suggest that they may supplement the ants' limited, liquid diet by supplying essential amino acids and other nutrients. J. Morphol. 234:253-262, 1997. r 1997 Wiley-Liss, Inc.

Development and early differentiation of gonad in the european eel (Anguilla anguilla [L.], Anguilliformes, Teleostei): A cytological and ultrastructural study.

Abstract: The structure of the gonad of the European eel (Anguilla anguilla [L.]), an "undifferentiated" gonochoristic teleost, was investigated by transmission electron microscopy from 6-8 cm elvers to 22 cm yellow eels with juvenile hermaphroditic gonads. The pear-shaped gonads of 6-8 cm elvers assume, in 12-15 cm eels, a lamellar shape and enlarge by migration of germ cells, which we refer to as primary primordial germ cells. In the gonads of ∼ 16 cm eels, the primary primordial germ cells multiply, giving rise to clusters of germ cells that have ultrastructural characteristics of the primary primordial germ cells but show giant mitochondria, enlarged Golgi complexes, and round bodies not limited by membranes. We refer to these as secondary primordial germ cells. In 16-18 cm eels, syncytial clones of oogonia interconnected by cytoplasmic bridges are also observed. In 18-22-cm-long eels, the gonads contain primordial germ cells, oogonial clones, early oocyte cysts, single oocytes in early growth stages, and primary spermatogonia. Such germ cells are present in the same cross section where they are either intermingled or are in areas of predominantly female germ cells close to areas with predominantly male germ cells. These gonads are juvenile hermaphroditic and should be considered ambisexual because in larger eels they differentiate either into an ovary or into a testis. Somatic cells always envelop the germ cells following their migration into the gonad. These somatic cells first show similar ultrastructural features and then differentiate either into early Sertoli cells investing spermatogonia, or into early follicular (granulosa) cells investing the early previtellogenic oocytes. In eels ∼ 14 cm long, primitive steroid-producing cells also migrate into the gonad. In the ambisexual gonad they differentiate either into immature Leydig cells in the male areas, or into early special cells of the theca in the female areas. Nerve fibers are joined to the steroid-producing cells. Gonad development and differentiation are also associated with structural changes of the connective tissue characterized by the progressive appearance and deposition of collagen fibrils first in the mesogonadium, then in the gonad vascular region, and then in the germinal region. The collagen-rich areas are massive in the male areas and reduced in the female ones. J. Morphol. 231:195-216, 1997. © 1997 Wiley-Liss, Inc.

Uranyl nitrate-induced proximal tubule alterations in rabbits : A quantitative analysis

Abstract: Naturally occurring uranium in drinking water is a significant health concern in several areas of North America. Because the kidney is a known target organ to examine the effects of uranium or its compounds, the objective of this study was to determine whether kidney repair occurs after exposure to, and withdrawal of, uranyl nitrate (UN). This work, part of a larger study to establish safe levels of uranium in drinking water supplies, examined the ultrastructural changes in proximal tubule cells of New Zealand white rabbits following subchronic exposure to UN in water and for 91 days after exposure ended. The rabbit was chosen as the experimental animal because of its high sensitivity to uranium. Animals were exposed to 24 or 600 mg UN per liter (UN/L) in drinking water for 91 days, with no recovery or recovery periods of 45 or 91 days. Ultrastructural changes, quantified by a stereological image analysis system based on point counting, were observed in renal proximal tubules (PTs). Each electron micrograph was statistically considered an experimental unit. The severity of lesions was directly proportional to the dose. Animals exposed to 600 mg UN/L had the most severe lesions; nevertheless, alterations were remarkable in animals exposed to the low dose. At both recovery periods, the lesions were significantly more severe than those in animals of the no-recovery group, which may result from the kidney's ability to store uranium. The PT cells had increased lysosomal and vacuolar mass as well as variations in mitochondrial mass. In addition, there was epithelial cell degeneration with a focal loss of brush borders, thickening and splitting of tubular basement membrane, and occasionally cell necrosis. Interstitial fibrosis of the renal cortex persisted as the recovery period increased in the animals of UN-dosed groups. Alterations may be due to disturbed fluid transport across the PT and other cells and decreased cell respiration resulting from damaged cell constituents. Cell damage caused by UN in drinking water persisted throughout the 91-day recovery period. By eventually determining the no observable effect level for the kidney by UN, this study may assist in devising a model to ascertain the safe levels of uranium in water.

Endomembranes, Cytoskeleton, and Cell Walls: Aspects of the Ultrastructure of the Vascular Cambium of Taproots of Aesculus hippocastanum L. (Hippocastanaceae)

Abstract: The ultrastructure of ray and fusiform cells within the active vascular cambial zone of taproots of Aesculus hippocastanum L. is described. Both cell types are uninucleate and highly vacuolate and contain perinuclear and parietal populations of plastids and mitochondria, abundant rough endoplasmic reticulum, numerous dictyosomes and associated smooth vesicles, coated vesicles, numerous free ribosomes and polysomes, axially oriented microfilament bundles, and randomly oriented cortical microtubules, and they bear unlignified primary cell walls. Oleosomes, microbodies, and amyloplasts are more common within ray cells than in the fusiform cells and provide the main ultrastructural difference between the two. Generally, the ultrastructure of root cambial tissue is similar to the shoot cambium of this species and to the shoot cambia of other hardwood species. On the basis of ultrastructure, it has not been possible to identify true cambial initials in this tissue. Aspects of wall biosynthesis and chemistry wer...

Interaction of a new bis-indol derivative, KAR-2 with tubulin and its antimitotic activity

Abstract: 1. KAR-2 (3"-(beta-chloroethyl)-2",4"-dioxo-3,5"-spiro-oxazolidino- 4-deacetoxy-vinblastine), is a bis-indol derivative; catharantine is coupled with the vindoline moiety which contains a substituted oxazolidino group. Our binding studies showed that KAR-2 exhibited high affinity for bovine purified brain tubulin (Kd-3 microM) and it inhibited microtubule assembly at a concentration of 10 nM. 2. Anti-microtubular activity of KAR-2 was highly dependent on the ultrastructure of microtubules: while the single tubules were sensitive, the tubules cross-linked by phosphofructokinase (ATP: D-fructose-6-phosphate-1-phosphotransferase, EC 2.7.1.11) exhibited significant resistance against KAR-2. 3. The cytoplasmic microtubules of Chinese hamster ovary mammalian and Sf9 insect cells were damaged by 1 microgram ml-1 KAR-2, as observed by indirect immunofluorescence and transmission electron microscopy. Scanning electron microscopy revealed intensive surface blebbing on both types of cells in the presence of KAR-2. 4. KAR-2 was effective in the mouse leukaemia P338 test in vivo without significant toxicity. Studies on a primary cerebro-cortical culture of rat brain and differentiated PC12 cells indicated that the toxicity of KAR-2 was significantly lower than that of vinblastine. The additional property of KAR-2 that distinguishes it from bis-indol derivatives is the lack of anti-calmodulin activity.

Differentiation and ultrastructure of the paruterine organs and paruterine capsules, in the nematotaeniid cestode Nematotaenia dispar (Goeze, 1782) Lühe, 1910, a parasite of amphibians

Abstract: Three types of egg-protecting envelopes of parenchymatic, uterine and embryonic origin have been distinguished in the cyclophyllidean cestode Nematotaenia dispar (Goeze, 1782) Luhe, 1910, a type species for the genus Nematotaenia and the family Nematotaeniidae. The present paper deals with the parenchymatic envelopes, which originate from the modified medullary parenchyma and are represented in this species by the paruterine organs and paruterine capsules. In pregravid proglottids they are composed of elongated myocytons, myofibrils and membranous anucleate cellular processes, containing a large amount of lipid droplets and some calcareous corpuscle cells. These cellular elements (CE) are separated from each other by abundant extracellular matrix (ECM), which consists primarily of an electron lucent ground substance with fine filaments embedded in it. The paruterine capsules of gravid proglottids are surrounded from the outside by a typical medullary parenchyma and are lined by a layer of the connective tissue. The paruterine organs and paruterine capsules show similar ultrastructure. During their histogenesis, all cellular elements undergo extensive flattening, followed by cellular deterioration, with simultaneous reduction in CE/ECM ratio. In the late gravid segments, paruterine capsule walls are very thick and consist of membranous sheets with large amounts of lipid droplets, which cause the cytoplasmic sheets to bulge. Ultrastructure of various types of parenchymatic envelopes in representatives of different cyclophyllidean families, such as paruterine organs in Nematotaeniidae and Mesocestoididae, uterine and parenchymatic egg capsules in Anoplocephalidae (Linstowiinae and Inermicapsiferinae, respectively), is compared.

A new baculovirus of cultured shrimps

Abstract: By means of ultrathin section, negative staining and sucrose gradient ultra-centrifugation, a new baculovims has been discovered and purified in lymphoid organs and such tissues as muscles of the shrimps which have been spontaneously attacked by diseases and artificially infected. With a diameter of 96–112 nm, this is the thickest baculovirus of shrimps ever known. In the center is the highrdensity nucleus. Between the capsid and the envelope is a broad space, which is not found in any of the baculoviruses of the prawns ever reported. On the surface of the purified nucleocapsid, there is a subunit of the spiral arrangement, which is also characteristic of this virus. It has not been observed and found in the epithelial cells of the livers, intestines and cheeks, which is quite different from the fact that prawn baculoviruses infect a certain epithepilial cell of the above-mentioned ones without exception. The viruses only multiplicate inside the core of target cells, which will not form occluded bodies or inclusion bodies. It is a new virus which has never been reported. It is called lymphoid cell nuclear baculovirus (LNBV).

Ultrastructure and anaerobic metabolism of mitochondria in the marine oligochaete Tubificoides benedii : effects of hypoxia and sulfide

Abstract: It has often been suggested that ultrastructural properties of mitochondria are correlated with oxygen and sulfide levels from the environment, although careful analyses of this question are rare. In this study the ultrastructure and distribution of mitochondria in Tubificoides benedii, a marine oligochaete from sulfide-rich sediments, were investigated after a series of oxic, hypoxic and hypoxic–sulfidic (200 μM H2S) incubations up to 24 h. Succinate, one of the key endproducts of an anaerobic metabolism, was used as an indicator of mitochondrial anaerobiosis. Consistent differences in mitochondrial ultrastructure were not observed in any of the incubations, even after 24 h. Stereological parameters of mitochondria (volume density, surface density of the outer mitochondrial membrane, and specific surface) in epidermal and intestinal tissues of T. benedii were not affected by hypoxia or sulfide either. On the other hand, succinate concentrations increased significantly within 24 h under hypoxic and hypoxic–sulfidic conditions. Thus, experimental hypoxia and sulfide clearly caused mitochondrial anaerobiosis without affecting ultrastructure or distribution of mitochondria in T. benedii. Distinct differences in ultrastructural and stereological parameters were common between different tissues and between individuals, showing that different forms of mitochondria can occur within one species. Our results imply that a mitochondrial ultrastructure specific to thiobiotic animals does not appear to exist.

Effects of Simulated Acid Rain on Chloroplast Ultrastructure of Primary Leaves of Phaseolus Vulgaris

Abstract: The ultrastructure of chloroplasts in the primary leaf of 10-d-old bean plants (Phaseolus vulgaris L., cv. Cheren Starozagorski) was studied 3, 5, 24, 48, 72 and 168 h after a single treatment with simulated acid rain (pH 2.4, 2.2, 2.0 and 1.8). Different changes in chloroplast structure till full destruction of organelles were traced. A determining factor for these changes was the histological localization of chloroplasts. In the chloroplasts of palisade parenchyma different degrees of expansion of thylakoids (3, 5, and 24 h after the single treatment), and conformational changes of the inner membrane system (48, 72 and 168 h) were observed. The chloroplasts of spongy parenchyma showed a significantly higher degree of structure resistance. The expansion of thylakoids was weak and did not depend on the duration of treatment. The ultrastructural changes of chloroplasts confirmed relative resistance of this species till pH 2.0.

The effects of freezing, storage, and thawing on cell compartment integrity and ultrastructure.

Abstract: The effects of slow freezing and thawing on enzyme compartmentalization and ultrastructure were studied in rat liver slices frozen in dry ice, isopentane/ethanol-dry ice, or liquid nitrogen, and stored at -80 degrees C for 1-14 days. Non-frozen slices served as controls. Frozen liver slices were thawed in a Karnovsky fixative and processed for transmission electron microscopy (TEM). After all freezing protocols, the outer zone of frozen-thawed tissue was ultrastructurally very similar to that of non-frozen liver. Towards the center of the tissue, the ultrastructure progressively deteriorated. Comparison with 50-microm cryostat sections prepared for TEM showed that thawing and not freezing is the detrimental step for fair preservation of ultrastructure. After thawing, homogenization, and differential centrifugation, distribution patterns of soluble marker enzymes were analyzed (cytosol, lactate dehydrogenase; mitochondrial matrix, glutamate dehydrogenase; lysosomes, acid phosphatase). The enzyme activities were not affected by storage for 2 weeks and the activity distributions showed that protein leakage from compartments was only minimally increased in frozen-thawed tissue compared with that from non-frozen tissue, irrespective of the method of freezing. In conclusion, fairly large tissue slices (20x5x3 mm) may be frozen and stored at -80 degrees C for biochemical, ultrahistochemical or ultrastructural studies. For ultrastructural analysis, only the periphery of the tissue slice should be used.

Improved ultrastructural preservation of Petunia and Brassica ovules and embryo sacs by high pressure freezing and freeze substitution.

Abstract: In order to improve the ultrastructural preservation of the female gametophyte ofPetunia x hybrida andBrassica napus we tested several cryofixation techniques and compared the results with those of conventional chemical fixation methods. Ovules fixed with glutaraldehyde and osmium tetroxide in the presence or absence of potassium ferrocyanide showed poor cell morphological and ultrastructural preservation. In ovules cryo-fixed by plunging into liquid propane, the cell morphology was well preserved. However, at the ultrastructural level structure-distorting ice crystals were detected in all tissues. Due to the large size of the ovules, cryofixation by plunging in liquid propane is not adequate for ultrastructural studies. In contrast,P. x hybrida andB. napus ovules cryo-fixed by high pressure freezing showed improved cell morphological as well as ultrastructural preservation of the embryo sac and the surrounding integumentary tissues. The contrast of the cellular membranes after freeze substitution with 2% osmium tetroxide and 0.1% uranyl acetate in dry acetone was high. At the ultrastructural level, the most prominent improvements were: straight plasma membranes which were appressed to the cell walls; turgid appearing organelles with smooth surface contours; minimal extraction of cytoplasmic and extracellular substances. In contrast to the chemically fixed ovules, in high pressure frozen ovules numerous microtubules and multivesicular bodies could be distinguished.

An ultrastructural histochemistry and light microscopy study of the early development of renal proximal tubular vacuolation after a single administration of the contrast enhancement medium "Iotrolan"

Abstract: The time course of contrast media (CM)-induced renal proximal tubular vacuolation was investigated in rats by light microscopy, transmission electron microscopy (TEM), and ultrastructural histochemistry for acid phosphate activity. Young adult male rats were treated with a single dose of 3.0 g I/kg Iotrolan (Isovist 300 mg I/ml) and sacrificed at 0 min, 5-min, 15-min, 15-min, 2-hr, and 24-hr intervals. Light microscopy of vibratome sections of freshly excised tissue of cryostat and paraffin sections was also performed to allow comparison of the appearance of the vacuoles in the fresh state with light and electron microscopy. The sequence of events seen to occur can be summarized as follows. CM-induced vacuolation occurred at a low level a soon as 5 min after compound administration. The vacuolation was observed by TEM but could not be detected by light microscopy. This was followed by an increase in size and numbers of vacuoles up to the 24-hr timepoint with a sequential increase in the staining for acid phosphatase activity of the vacuoles, most marked at the 24-hr timepoint. At timepoints less than 24 hr there appeared to be no marked increased in the normal complement by lysosomes or in the components of the Golgi-endoplasmic reticulum-lysosome pathway. At 24 hr, the vast majority, but not all, of the CM-induced vacuoles were positive for acid phosphatase activity. The intensity of staining varied, and there was evidence of infusion of small lysosomes with CM-induced vacuoles. These results suggest that formation of CM-induced vacuoles is a 2-stage process, following a normal pathway for the handling of endogenous and exogenous substances.

Transmission X-ray microscopy of intact hydrated PtK2 cells during the cell cycle.

Abstract: Transmission X-ray microscopy makes it possible to investigate biological specimens, i.e. cells and organelles, in their natural wet environment. The main processes determining the contrast in X-ray microscopy are photoelectric absorption and phase shift. X-ray microscopic experiments can therefore be carried out in both amplitude and phase contrast. The Gottingen X-ray microscope at the BESSY storage ring in Berlin is described. PtK2 cells were examined during different stages of the cell cycle. All major constituents of the mitotic apparatus, e.g. chromosomes, centromeres, microtubules and centrosomes, could be visualized, as well as the main structural compartments and organelles of the interphase cell, e.g. nuclear membrane, interphase chromatin, nucleolus and cytoplasmic mitochondria, as well as parts of the cytoskeletal apparatus. In this way new information can be obtained with regard to the ultrastructure of the constituents of intact and unstained cells at a resolution which bridges the gap between light microscopy and electron microscopy. The prospects for the future application of transmission X-ray microscopy in biomedical research are discussed.

Early cleavage to formation of the unilaminar blastocyst in the marsupial Antechinus stuartii: ultrastructure.

Abstract: The development of Antechinus stuartiifrom the 2-cell stage to the blastocyst stage in vivo was examined by routine transmission electron microscopy. The 2–8-cell stages had a similar organization of organelles, whereas the 16- to 32-cell stages had pluriblast cells and trophoblast cells forming an epithelium closely apposed to the zona pellucida. Specialized cell–zona plugs were formed at the 8-cell stage, and primitive cell junctions appeared in later conceptuses. The cytoplasmic organelles included mitochondria, lysosomes, aggregates of smooth endoplasmic reticulum, lipid and protein yolk bodies and fibrillar arrays, possibly contractile in function. Nuclei had uniformly-dispersed dense chromatin. Nucleoli of 2–4-cell conceptuses were dense, compact and fibrillar, and those of 8-cell conceptuses and later conceptuses were finely granular and became progressively reticulated. The embryonic genome is probably not switched on before the 8-cell stage. Sperm tails were detected in cells in several early conceptuses. The yolk mass had the same organelles as cells. Centrioles were discovered for the first time in marsupial conceptuses. These were prominently situated at a spindle pole in a 32-cell blastomere and were associated with a nucleus and sperm tail at the 4-cell stage. It is very likely that the paternal centrosome is inherited at fertilization and perpetuated in Antechinus embryos during cleavage.

Ultrastructure of conidia and conidium germination in the plant pathogenic fungus Alternaria cassiae

Abstract: Transmission electron microscopy of plunge-frozen and freeze-substituted samples was used to examine germinating conidia of Alternaria cassiae, a plant pathogenic fungus used as a biological control agent for sicklepod (Cassia obtusifolia). Hydrated conidia on small pieces of dialysis membrane were incubated for 1, 2, or 3 h on the surface of corn meal agar prior to fixation. Conidia were large, darkly pigmented, and surrounded by a thick, two-layered wall. Each conidium was divided by transverse and longitudinal septa into multiple cells, a few of which sometimes appeared necrotic. Each septum tapered to a small central pore region with which Woronin bodies were associated. Each healthy cell of a conidium contained a typical complement of cellular organelles including multiple nuclei. With the exception of lipid bodies, all the various organelles were well preserved by plunge freezing and freeze substitution. Evidence of germ tube development was visible by 2 h post-incubation and well-developed germ tub...

Ultrastructure and ion permeability of the two types of epithelial cell arranged alternately in the gill of the fresh water branchiopod Caenestheriella gifuensis (Crustacea)

Abstract: The adult freshwater branchiopod, Caenestheriella gifuensis, has, as respiratory organs, fifteen pairs of slender cone-shaped gills composed of a thick epithelium. The silver nitrate/nitric acid technique revealed that the gill epithelium consisted of two kinds of cell, types I and II, which were alternately arranged with irregular interdigitations to form a unique, daisy pattern. Only type I cells were darkly stained by this technique, indicating high permeability of these cells to chloride ions and appearing to be responsible for the ion transport and osmoregulation. Further, electron microscopy disclosed fine structural characteristics of the two distinct types of epithelial cell covered by an extremely thin and soft cuticle layer, suggesting high permeability to gases and ions. The type I epithelial cell was characterized by an abundance of mitochondria, well-developed infoldings of the basal cell membrane exceeding two-thirds of the epithelial thickness, (which produce a magnification of the basolateral surface area of the cell), sparse microvillous projections of the apical border, and complicated interdigitations with the other type of epithelial cell. In the type II epithelial cell, on the other hand, these characteristics were less developed. These results suggest that in addition to their respiratory function, type I epithelial cells are of the ion-transporting type and play an important role in the active absorption of electrolytes to maintain a constant osmotic pressure of the hemolymph in extremely salt-deficient, freshwater environments. The type II epithelial cells may function mostly as respiratory epithelial cells.