Electron microscopy of yeastlike cell development from the microconidium of Histoplasma capsulatum.

Fine details of the sequential morphological events occurring during transition of microconidia (spores less than 5 micrometer in diameter) to the yeastlike phase of Histoplasma capsulatum as seen in ultrathin section are described and illustrated by electron micrographs. Masses of microconidia were obtained when the fungas was grown on a garden soil extract medium. Spores were incubated under in vitro environmental conditions conducive for phase transition (an enriched medium at 37 degrees C). Within 48 h of incubation, the microconidia either germinated to give rise to a short mycelium or the germ tube process became a yeast mother cell without further extension. The wall of the yeast mother cell was thin and smooth, and its cytoplasmic content was ultrastructurally complex, consisting of numerous lipid bodies, vacuoles, glycogen-like deposits, and membrane systems. Within 96 h, the mother cell underwent multipolar budding to form simultaneously linear hyphal and/or ovate yeastlike daughter cells. During the transition, new cell wall materials of the germ tube, the mother cell, and yeastlike daughter cells arose by blastic action from the innermost layer(s) of the wall of the precursor form. Lomasome-like vesicles were often seen in association with areas of new cell wall formation. After organellar migration into and septation of the daughter cells, the yeast mother cell's cytoplasmic content underwent marked degenerative changes.     

Relationship of a Wall-Associated Enzyme with Specific Layers of the Cell Wall of a Gram-Negative Bacterium

In untreated cells of the marine pseudomonad studied here, alkaline phosphatase was found to be located in the periplasmic space, at the cell surface, and in the medium into which it had been shed during growth. Washing in 0.5 M NaCl, which removed the loosely bound outer layer, caused a shift of periplasmic enzyme to the outer aspect of the double-track layer and released some of the cell surface-associated enzyme. When the double-track layer of the cell wall was partially deranged, large amounts of this cell wall-associated enzyme were released, and, when the double-track was removed from the cells to produce mureinoplasts, alkaline phosphatase was released into the menstruum. There was no significant association of the enzyme with the peptidoglycan layer of the cell wall, which is the outermost structure of the mureinoplast, and no association of the enzyme with the cytoplasmic membrane of these modified cells. This study has shown that alkaline phosphatase is specifically associated with the outer layers of the cell walls of cells of this organism and is retained within the cell wall by virtue of this association.     

Electron microscopy of the medial cortex in the lizard Psammodromus algirus

The medial cortex of Psammodromus presents a three-layer organization. Most of the cell bodies are localized in a compact lamina, the cellular layer. Two plexiform layers, superficial and deep, enclose the cellular layer. The most external portion of the superficial plexiform layer is formed by a limiting glial sheet consisting of tanycytic processes that reach the surface of the cortex. Astrocytes are localized close to the glial sheet. There are two types of axon terminals within the superficial plexiform layer: type S with spheric vesicles and type F with pleomorphic vesicles. Large solitary neurons are present at middle levels of the layer. In the cellular layer there are three neuronal types: large neurons with dispersed chromatin, neurons of medium size with chromatin clumps, and electron-dense neurons. Protoplasmic astrocytes are found superficially in this layer. In the deep plexiform layer numerous neuronal cell bodies are visible, and three types can be distinguished: horizontal fusiform cells, globous neurons with indented nuclei, and electron-dense neurons. Protoplasmic astrocytes are present throughout this layer. Oligodendrocytes are more frequent in the inner third of the layer, often related to fibers of a thick fascicle running in contact with the ependyma, the alveus. The ependyma is formed by a single row of prismatic cells bordering the lateral ventricle.     

Ultrastructure of Fomes igniarius mycelium

The mycelium is composed of thin-walled hyphae, fiber hyphae and cuticular cells, the modified cells developing from the thin-walled hyphae with a dolipore septum at the differentiation point. The cell wall is usually triplelayered. occasionally, multilayered. Cell organelles such as endoplasmic reticulum, mitochondria and vesicles are found in abundance in thin-walled hyphae. Characteristic features of this fungus are the concentric membrane systems from which vesicles arise, the membrane-enclosed osmophilic bodies in vacuoles and the dense bodies in the cytoplasm. As the fiber hyphae and cuticular cells develop, the innermost layer of the wall thickens and the cell contents become disorganized so that, at the maturity of these cells, there is a reduced amount of diffuse cytoplasm, or none in the lumen.The study formed part of a doctoral dissertation submitted by the author to the University of Alberta, Edmonton, Alberta, Canada, 1971.     

A new and unusual eimerian (protozoa: Eimeriidae) from the liver of the Gulf killifish, Fundulus grandis

Oocysts and sporocysts of Eimeria funduli sp. n. are described from the Gulf killifish, Fundulus grandis, on the basis of light microscopy, transmission and scanning electron miscroscopy, and location in the liver of infected hosts. The spherical sporulated oocysts of E. funduli isolated from liver tissue measure 20-31 (25) micrometer across with ovoid sporocysts 9-11 X 5-7 (10 X 6) micrometer. A micropyle, polar granule, and oocyst residuum are absent, but sporocysts have Stieda and substieda bodies, a few residual granules, and 10-25 (15) unique projecting structures with expanded distal portions that we term "sporopodia". Sporopodia 1-3 (2) micrometer high support a transparent membrane that completely surrounds the sporocyst. Sporozoites have one large posterior refractile body. Ultrastructurally, the oocyst wall consists of two thin layers of granular material: an electron-dense outer layer with a rough external surface and an electron-lucent inner one of approximately equal thickness. One or two unit membranes line the inner surface of the inner layer. Each layer is 40-60 (55) nm thick. The sporocyst wall, 78-130 (110) nm thick, consists of an electron-lucent material with the outer surface being more electron dense and giving rise to osmiophilic sporopodia; closely associated with these and the outer surface are one or two unit membranes. A thin osmiophilic layer of fine granular material lines the inner surface.     

Studies of Ultrastructure and ATPase Localization of Mature Embryo Sac in Vicia faba L.

Studies of ultrastructure and ATPase localization of the mature embryo sac in Vicia faba L. show that the egg cell has no cell wall at thechalazal end, it has a chalazally located nucleus and a large micropylar vacuole. There are many nuclear pores in the nuclear membrane. The cytoplasm is restricted around the nucleus. Dictyosome and mitochondria are few. There are some starch grains and lipid grains in the egg cytoplasm. There are no obvious differences between two synergids. No cell wall is seen at the chalazal end either, but there are some vesicles which project to vacuole of the central cell and fuse with its vacuolar membrane. Plasmodesmata connections occur within the synergid wall where it is adjacent to the central cell. The synergid has a micropylarly located nucleus and a chalazal vacuole, the nucleus is irregularly shaped. The synergid cytoplasm is rich in organelles. The filiform aparatus is of relatively heterogeneous structure. The central cell is occupied by a large vacuole and its cytoplasm is confined to a thin layer along the empryo sac wall, but is rich in various organelles, starch grains and lipid bodies. Nucleolar vacuoles are often present two polar nuclei. The nuclear membranes of two polar nuclei have partly fused. ATPase reactive product was located obviously at the endoplasmic reticulum in cytoplasm of the egg cell and central cell. The embryo sac wall consists of different density of osmiophilic layer. There are some wall ingrowths in chalazal region of the embryo sac. The long-shaped and cuneate cells of chalazal region are peculiar. Special tracks of ATPase reactive products are visible at their intercellular space which may be related to transportation of nutrients.     

Ultrastructural and Chemical Alteration of the Cell Envelope of Pseudomonas aeruginosa, Associated with Resistance to Ethylenediaminetetraacetate Resulting from Growth in a Mg2+-Deficient Medium

Cells of Pseudomonas aeruginosa became resistant to the lytic effect of ethylenediametetraacetate (EDTA) when grown in a Mg(2+)-deficient medium. To correlate ultrastructural changes in the cell wall associated with the shift to EDTA-resistance, a freeze-etch study was performed. Upon fracturing, the outer cell wall membrane split down the hydrophobic center to reveal the outer (concave) and inner (convex) layers. The concave cell wall layer of EDTA-sensitive cells grown in Mg(2+)-sufficient medium contained spherical units resting on an underlying smooth support layer. Upon EDTA treatment, approximately one-half of these spherical units were extracted. Cells grown in Mg(2+)-deficient medium were resistant to EDTA. The concave cell wall layer of EDTA-resistant cells had increased numbers of highly compacted spherical units, giving this layer a disorganized appearance. The highly compacted appearance of this layer was unaltered by EDTA treatment. Thus, growth in Mg(2+)-deficient medium resulted in cells which were resistant to EDTA and which possessed an ultrastructurally altered outer layer of the outer cell wall membrane. Cell envelopes from EDTA-resistant cells were found to possess 18% less phosphorus, 16.4% more total carbohydrate, and 13.3% more 2-keto-3-deoxyoctonate than cell envelopes from EDTA-sensitive cells. There were also qualitative, but not quantitative, differences in the protein content of cell envelopes from EDTA-resistant and EDTA-sensitive cells.     

Cutin plays a role in differentiation of endosperm-derived callus of kiwifruit

Cutin fluorescence, after auramine O treatment, was detected on the surface of organogenic areas (protuberances) of endosperm derived callus induced on Murashige and Skoog medium with thidiazuron (0.5 mg l⁻¹) in darkness. Electron micrographs of the protuberances revealed cuticle, visible as a dark-staining layer, and amorphous waxes on the cell wall. In some cases the cells of the epidermis-like layer and shoot buds at early stages of development showed thick and characteristically wavy cutin. This waviness corresponds with the wrinkled appearance of the cell wall as observed by scanning electron microscopy. The role of multivesicular bodies in cutin production and transfer to the plasma membrane is discussed.     

A Structural and Utrastructural Study of Nostoc commune

Nostoc commune which belongs to blue-green algae has been observed with microscope, scanning and transmission electron microscopes. The following special structures are found: 1. The structure in thallus is spongiform with an uneven surface. 2. The filaments made up of torulose cells are tortuous with different length, some are piled up, some are branchy, and the others arrange in a circle. 3. The cell wall of torulose cell is five-layered. The outermost layer is ripply and inlays with neighbour cells. 4. Torulose cells are typical prokaryote. The thylakoids disperse in the peripheral plasma. The nucleoplasm exists in the center of the cell. There are structured granules, polyhedral and polyphosphate bodies interspersing in cytoplasm. Ribosomes and phycobilins are found on the surface of thylakoid. 5. The heterocyst is surrounded by a thicking sheath. This is an additional envelope outside the cell wall and can be called “cell envelope”. In the cell envelope exist a transparent layer and a dense electron layer with hemispherical nodule in which there is an channel interlinking up with neighbour cell. 6. The reproductive manner of N. commune is of horizontal split, and the direction of split is different.     

Encystment ofBodo caudatus

Summary Before formation of the cyst wall, the food vacuoles are lost, the cell rounds up and the flagella lie close against the body in a flagellar groove. At this early stage, the contractile vacuole is very active, the Golgi apparatus is prominent and the basophilic cytoplasm is composed of closely packed ribosomes. As the cyst wall is secreted, layer by layer, the large Golgi apparatus is replaced by several smaller membrane stacks and mitochondrial changes occur involving local loss and modification of the cristae. Some parts of the mitochondrion undergo degenerative changes and may become surrounded by bacilliform bodies. These same bodies are also associated with small particles of sequestered cytoplasm which are present throughout the encystment process and are believed to be autophagic vacuoles. As the cyst wall thickens, cell shrinkage is manifest as a number of membrane invaginations. The final cyst wall is of uneven thickness and possesses a single operculum which is visible only by electron microscopy. Probable cyst wall precursor is found in small vesicles scattered throughout the cytoplasm.     

Cell Division in Yeasts: Movement of Organelles Associated with Cell Plate Growth of Schizosaccharomyces pombe

Electron microscopy of dividing fission yeast cells shows establishment of an annular rudiment (AR) of electron-transparent material under the old cell wall as the first sign of elaboration of the cell plate. The AR grows centripetally, finally closing at the mid-point of the cell. During the inward growth of the AR it is thickened by addition of denser material which becomes the scar plug after fission; the electron-transparent material is lost at fission. Lying always between the cytoplasmic membrane and the cell wall is a dark layer of variable thickness. This layer becomes markedly thickened into a fillet at the base of the centripetally growing cell plate. The fission process begins after the cell plate is completely elaborated. One striking feature of fission is the migration of dense material from the fillet at the base of the cell plate outwardly through the matrix of the cell wall to its final resting place as a dark ring, a "fuscannel," adjacent to the fission scar. The inclusion of Golgi bodies in many sections suggests their involvement in cell plate elaboration, presumably through production of the dense bodies which are seen to fuse with the dark layer proximal to the growing cell plate.     

Submicroscopic organization of M. pneumoniae studied by means of negative contrasting, ultrathin sections and scanning electron microscopy]

The ultrastructure of M. pneumoniae, grown on a solid culture medium and in a liquid one, was studied by a number of methods. Two types of cells were shown to prevail in the culture: spherical cells (0.5--1 micrometer) forming chains of different configurations and filamentous cells (5 micrometer long and greater) with spherical enlargements along their whole length. The absence of microcapsules made M. pneumoniae different from other species of mycoplasms, and the organism proliferated by division into 2 daughter cells, equal or unequal in size, by the segmentation of the cytoplasm and the formation of elementary bodies inside the cell and on its surface.     

Primary uroepithelial cultures. A model system to analyze umbrella cell barrier function.

Despite almost 25 years of effort, the development of a highly differentiated and functionally equivalent cell culture model of uroepithelial cells has eluded investigators. We have developed a primary cell culture model of rabbit uroepithelium that consists of an underlying cell layer that interacts with a collagen substratum, an intermediate cell layer, and an upper cell layer of large (25-100 micrometer) superficial cells. When examined at the ultrastructural level, the superficial cells formed junctional complexes and had an asymmetric unit membrane, a hallmark of terminal differentiation in bladder umbrella cells. These cultured "umbrella" cells expressed uroplakins and a 27-kDa uroepithelial specific antigen that assembled into detergent-resistant asymmetric unit membrane particles. The cultures had low diffusive permeabilities for water (2.8 x 10(-4) cm/s) and urea (3.0 x 10(-7) cm/s) and high transepithelial resistance (>8000 Omega cm2) was achieved when 1 mM CaCl2 was included in the culture medium. The cell cultures expressed an amiloride-sensitive sodium transport pathway and increases in apical membrane capacitance were observed when the cultures were osmotically stretched. The described primary rabbit cell culture model mimics many of the characteristics of uroepithelium found in vivo and should serve as a useful tool to explore normal uroepithelial function as well as dysfunction as a result of disease.     

Ultrastructural aspects of cell wall synthesis inSpirogyra

Summary Filaments ofSpirogyra were fixed in 2% osmium tetroxide dehydrated in alcohol and embedded in Araldite. The fine structure of cells with regard to wall synthesis was studied. The cell wall was shown to have four layers. The inner one contains microfibrils and is considered to be the cell wall proper. The outer three layers are components of the slime layer. The innermost of these, the second layer of the wall, was shown to be between 1m to 3m and the third 0.3m to 1m. The fourth layer appears as no more than a dark black line measuring 10 nm across. In the cytoplasm two types of vesicles were seen. The largest of these has contents similar in appearance to the slime layer of the wall. This same material was also seen in the large vesicles attached to the Golgi bodies. It is suggested that the smaller vesicles are derived from the larger vesicles and later fuse with the cell membrane. The Golgi bodies were found to be fairly large measuring up to 5m across. Small electron opaque blobs and flecks on the outside of the plasmalemma and in between the microfibrils of the cell wall proper are considered to be mucilage droplets travelling to the slime layer. It cannot be excluded that some of the material of the large vesicles is released directly into the cytoplasm and is transferred without vesicles through the plasma membrane. The negative contrast appearance of the microfibrils seen in the cell wall is thought to be due to the spaces between them being filled with this electron opaque mucilage.Intercisternal rodlets measuring 2.5 nm across were seen in the Golgi bodies.Transverse microtubules were found to occur near the plasmalemma having the same orientation as some of the microfibrils.Lomasome-like structures sometimes with many 5 nm fibrils in their vicinity were seen.     

Fine structure of the fungiform papilla in a ranid frog (Rana esculenta)

The freetop of the fungiform papilla shows a sensorial area about 100 micron in diameter, surrounded by a ring of ciliated cells. Externally to the ciliated cells, i.e., in the lateral wall, numerous large goblet cells can be seen devoid of their mucous content. The sensorial area is composed by three types of cells: mucous, supporting, and neuroepithelial cells. Mucous cells form the most superficial layer, while the cell bodies of the other two are deep, and from them basal and apical processes arise. The above mentioned cells are connected by desmosomes preferentially located between the mucous and the supporting cells, rather than between the supporting and the neuroepithelial cells. The lateral wall of the papilla is made up of a multilayered epithelium that comprises two types of cells: the first type contains electron-dense granules and an abundant rough endoplasmic reticulum, the others are ciliated cells. In the connective axis of the papilla, numerous fenestrated capillaries with endothelial vesiculated cells and nerve fibers are found.     

Histochemical and ultrastructural changes in the haustorium of date (Phoenix dactylifera L.)

Summary During imbibition ofPhoenix dactylifera embryos, all cotyledon cells show the same changes: protein and lipid bodies degrade, smooth endoplasmic reticulum (ER) increases in amount, and dictyosomes appear. At germination, the distal portion of the cotyledon expands to form the haustorium. At this time, epithelial cells have a dense cytoplasm with many extremely small vacuoles. Many ribosomes are present along with ER, dictyosomes, and mitochondria. The parenchyma cells have large vacuoles and a small amount of peripheral cytoplasm. Between 2 and 6 weeks after germination, epithelial cells still retain the dense cytoplasm and many organelles appear: glyoxysomes, large lipid bodies, amyloplasts, large osmiophilic bodies, and abundant rough and smooth ER which appear to merge into the plasmalemma. A thin electron-transparent inner wall layer with many small internal projections is added to the cell walls. Starch grains appear first in the subsurface and internal parenchyma and subsequently in the epithelium. Lipid bodies, glyoxysomes, protein, and osmiophilic bodies occur in the epithelial and subepithelial cell layers but not in the internal parenchyma. At 8 weeks after germination, the cytoplasm becomes electron transparent, vacuolation occurs, lipid bodies and osmiophilic bodies degrade, and the endomembranes disassemble. After 10 weeks, the cells are empty. These data support the hypothesis that the major functions of the haustorium are absorption and storage.     

Gelatin-induced Reversion of Protoplasts of Bacillus subtilis to the Bacillary Form: Electron-microscopic and Physical Study

Protoplasts of Bacillus subtilis plated on SD medium form L colonies in quantitative yield and propagate in the L form indefinitely. L bodies or protoplasts placed in 25% gelatin medium form bacillary colonies. Details of the reversion of naked bodies to the walled form are reported. In 25% gelatin medium, reversion begins earlier (about 50% reversion in 4 hr) than the multiplication of bacilli. Thus, virtually all the observed bacillary forms are themselves revertants and not the offspring of a few growing clones. The optimal temperature for reversion is 26 C in 25% gelatin. When cells reverting at 26 C are warmed to 40 C for 3 min, reversion is delayed markedly, whereas viability is unaffected. For electron microscopy, a dense protoplast inoculum was placed on a gelatin surface, incubated, and then fixed in situ. There was no multiplication, but crowding delayed reversion markedly. Successive events of reversion are as follows. The loose nucleoid of the protoplasts condenses in response to the gelatin medium and condenses further and further as reversion proceeds. A thin coat of wall develops around the bodies of various sizes and shapes and then increases uniformly in thickness until a wall of normal aspect is formed. Rod-shaped cells grow out from these bodies-sometimes in several directions at once. A few mesosomes begin to appear only after a thin coat of wall has been formed. These are dense, atypical structures compartmented by membranes. They are located at the cell periphery and do not seem to be in contact with the nucleoids. Quantitative estimates showed that only 20 to 25% of revertant cells or cells grown on gelatin contain even a single mesosome. The others have no mesosome at all. Mesosomes thus do not appear to play a significant role in reversion, and normal mesosome functions must presumably be performed elsewhere in the cell in gelatin-grown bacilli. The role of cell wall, its synthesis, and its chemical nature in successive steps in reversion are discussed.     

Characteristics of the cytodifferentiation of omega-particle symbiotic bacteria from the micronucleus of Paramecium caudata clone M1-48]

The structure of the omega-particle-bacteria, growing in the micronucleus of Paramecium caudatum (Ciliata, Protozoa), was studied by electrom microscopy in the course of their life cycle. The cytoplasm of the spindle-shaped vegetative cells contains a large number of dense particles and transparent regions comprising the fibrillar material. Such cells, via several intermediate stages, are transformed into elongated twisted cells that are regarded as spores. The spore consists of two parts: homogeneous, and that containing the membrane system and rounded light bodies. The membranes are often double and connected with the fibrils. The cell wall is constructed, during all stages, of the outer membrane layer and the inner electron-dense layer.     

Variation in the Fine Structure of a Marine Achromobacter and a Marine Pseudomonad Grown Under Selected Nutritional and Temperature Regimes

Certain features of the fine structure of a marine achromobacter and a marine pseudomonad were dependent upon the conditions of growth. Cells of achromobacter grown at 10 C in a low peptone-seawater (SW) medium displayed the characteristic morphology of the achromobacter: a regularly undulant outer element of the cell wall and a planar inner element, tightly packed ribonucleoprotein (RNP) particles in the cytoplasm, deoxyribonucleic acid (DNA) disposed in a lobate manner, and dense inclusion bodies. Few mesosomes, however, were seen. Cells of achromobacter grown at 10 C in a high peptone-SW medium had larger and more highly organized mesosomes. At 22 C, in a low peptone-SW medium, no mesosomes were seen, but the inclusions were more frequently seen and were larger in the achromobacter cells. At 22 C, in a high peptone-SW medium, these cells revealed the greatest variation in cellular morphology. They contained both small and large mesosomes, or no mesosomes, and both small and large inclusions, or no inclusions. Pseudomonad cells at 10 C in a low peptone-SW medium revealed a typical gram-negative morphology: double-layered, irregularly undulant cell wall; more nearly planar cytoplasmic membrane; densely stained, lightly packed RNP particles; finely fibrillar, axially disposed DNA; simple mesosomes. At 10 C, in a high peptone-SW medium, pseudomonad cells revealed associated strands of material and intracytoplasmic ringlike structures. At 22 C, in a low peptone-SW medium, pseudomonad cells had a more undulant cell-wall and a more nearly planar cytoplasmic membrane. At 22 C, in a high peptone-SW medium, these cells revealed prominent blebs of the cell wall.     

Ultrastructurally different muscle cell types in Eisenia foetida (Annelida,Oligochaeta)

Muscles in the body wall, intestinal wall, and contractile hemolymphatic vessels (pseudohearts) of an oligochaete anelid (Eisenia foetida) were studied by electron microscopy. The muscle cells in all locations, except for the outer layer of the pseudohearts, are variants of obliquely striated muscle cells. Cells comprising the circular layer of the body wall possess single, peripherally located myofibrils that occupy most of the cytoplasm and surround other cytoplasmic organelles. The nuclei of the cells lie peripherally to the myofibrils. The sarcomeres consist of thin and thick myofilaments that are arranged in parallel arrays. In one plane of view, the filaments appear to be oriented obliquely to Z bands. Thin myofilaments measure 5–6 nm in diameter. Thick myofilaments are fusiform in shape and their width decreases from their centers (40–45 nm) to their tips (23–25 nm). The thin/thick filament ratio in the A bands is 10. The Z bands consist of Z bars alternating with tubules of the sarcoplasmic reticulum. Subsarcolemmal electron-dense plaques are found frequently. The cells forming the longitudinal layer of the body wall musculature are smaller than the cells in the circular layer and their thick filaments are smaller (31–33 nm centrally and 21–23 nm at the tips). Subsarcolemmal plaques are less numerous. The cells forming the heart wall inner layer, the large hemolymphatic vessels, and the intestinal wall are characterized by their large thick myofilaments (50–52 nm centrally and 27–28 nm at the tips) and abundance of mitochondria. The cells forming the outer muscular layer of the pseudohearts are smooth muscle cells. These cells are richer in thick filaments than vertebrate smooth muscle cells. They differ from obliquely striated muscle cells by possessing irregularly distributed electron-dense bodies for filament anchorage rather than sarcomeres and Z bands and by displaying tubules of smooth endoplasmic reticulum among the bundles of myofilaments. © 1995 Wiley-Liss, Inc.