Intranuclear Inclusions in the Ameboid Cells of Protostelium zonatum*

SYNOPSIS. Two morphologically distinct types of intranuclear inclusions are found in ameboid cells of the protostelid mycetozoan Protostelium zonatum. One type of inclusion is a coiled tubular structure which in cross section appears as cisternae and oval to elliptical vesicles 40–60 nm in diameter. These tubular and vesicular structures are formed by a unit membrane that is connected directly with the inner nuclear membrane. The other type of inclusion is a membrane-bound structure that contains amorphous and/or fibrous material. These inclusions usually are present at several locations in a nucleus. No similar structures occur in the cytoplasm.     

Syncytial-type cell plates: a novel kind of cell plate involved in endosperm cellularization of Arabidopsis

Cell wall formation in the syncytial endosperm of Arabidopsis was studied by using high-pressure-frozen/freeze-substituted developing seeds and immunocytochemical techniques. The endosperm cellularization process begins at the late globular embryo stage with the synchronous organization of small clusters of oppositely oriented microtubules ( approximately 10 microtubules in each set) into phragmoplast-like structures termed mini-phragmoplasts between both sister and nonsister nuclei. These mini-phragmoplasts produce a novel kind of cell plate, the syncytial-type cell plate, from Golgi-derived vesicles approximately 63 nm in diameter, which fuse by way of hourglass-shaped intermediates into wide ( approximately 45 nm in diameter) tubules. These wide tubules quickly become coated and surrounded by a ribosome-excluding matrix; as they grow, they branch and fuse with each other to form wide tubular networks. The mini-phragmoplasts formed between a given pair of nuclei produce aligned tubular networks that grow centrifugally until they merge into a coherent wide tubular network with the mini-phragmoplasts positioned along the network margins. The individual wide tubular networks expand laterally until they meet and eventually fuse with each other at the sites of the future cell corners. Transformation of the wide tubular networks into noncoated, thin ( approximately 27 nm in diameter) tubular networks begins at multiple sites and coincides with the appearance of clathrin-coated budding structures. After fusion with the syncytial cell wall, the thin tubular networks are converted into fenestrated sheets and cell walls. Immunolabeling experiments show that the cell plates and cell walls of the endosperm differ from those of the embryo and maternal tissue in two features: their xyloglucans lack terminal fucose residues on the side chain, and callose persists in the cell walls after the cell plates fuse with the parental plasma membrane. The lack of terminal fucose residues on xyloglucans suggests that these cell wall matrix molecules serve both structural and storage functions.     

Three-dimensional ultrastructure of feeding tubes and interconnected endoplasmic reticulum in root-knot nematode-induced giant cells in rose balsam

We investigated the three-dimensional ultrastructure of feeding tubes and the surrounding region in giant cells induced in rose balsam (Impatiens balsamina L.) roots by the root-knot nematode Meloidogyne incognita, using osmium maceration coupled with field emission scanning electron microscopy (FE-SEM). In the roots of 35-day-old galled rose balsam plants, adult nematodes induced the formation of giant cells containing feeding tubes and numerous organelles, including tubular endoplasmic reticulum (ER), cisternal ER, and mitochondria. The feeding tubes were surrounded by fine tubular structures (20–50 nm in diameter), which were in turn surrounded by tubular ER (approximately 120 nm in diameter). The termini of the fine tubular structures appeared to be connected to the surface of the feeding tubes, suggesting that the fine tubular structures were continuous with narrow channels in the feeding tubes. The tubular ER arose from cisternal ER. Large bundles of tubular ER were present near the feeding tube, in the centers of the giant cells, and in the peripheral regions of the giant cells, such as cell wall ingrowths, while smaller bundles of tubular ER formed networks in the giant cells. These observations suggest that tubular ER functions as vascular bundles in giant cells, facilitating the transport of nutrients. We identified capsule-shaped structures (30 μm in diameter) in the giant cells that consisted of smooth, repeatedly branched ER tubules wrapped in several layers of cisternal ER. We propose that lipids and steroids are synthesized at the smooth branched ER and stored in these capsules until needed by the nematode.     

Release of integrin macroaggregates as a mechanism of rear detachment during keratinocyte migration

Cell-substrate adhesion can be mediated by the relatively short-lived focal complexes and focal adhesions and by the more stable hemidesmosomes. During cell migration both types of cell-substrate adhesions must be disrupted allowing the cell rear to detach. Rear detachment has been described to be accompanied by membrane ripping and the loss of cellular material in a variety of cell types including fibroblasts and chondrocytes, but also in fast moving cells such as keratinocytes. Here we show that migrating keratinocytes leave behind "migration tracks" of cellular remnants that can be classified due to their size, distribution and molecular composition. Type I macroaggregates appeared as spherical and tubular structures with a diameter of about 50-100 nm that were arranged like "pearls on a string". These structures apparently derived from fragmentation of long tubular extensions, the retracting fibers, at the cell rear and contained high amounts of beta1 integrin and different alpha integrins that are components of fibronectin and laminin receptors in migrating keratinocytes usually found in focal adhesions. Type II macroaggregates were recognized as spherical structures with a diameter of about 30 - 50 nm that were arranged in clusters scattered over the gaps between type I, macroaggregates. In contrast to type I type II macroaggregates contained high amounts of beta4 integrin and seemed to derive from former hemidesmosomes. Both types of macroaggregates were completely membrane covered, impermeable compartments devoid of cytosolic proteins. Our observations strongly support the concept that the release of macroaggregates represents a distinct cellular mechanism of rear detachment based on the loss of adhesive receptors embedded in membrane-covered cellular remnants.     

Ultrastructural and cytochemical aspects of the basophilic cells in the hepatopancreas ofAplysia depilans(Mollusca, Opisthobranchia)

The basophilic cells ofAplysia depilanshave a pyramidal shape and a large nucleus usually located near the center or in the basal half of the cell. The nucleus possesses several clumps of condensed chromatin and a prominent nucleolus. The great profusion of rough endoplasmic reticulum cisterns in a major feature of these cells. Secretion granules are accumulated in the apical zone, and arylsulphatase was detected in some of them. In some basophilic cells a very substantial part of the cell volume was occupied by clear vacuoles, some of them reaching 9 mum. However, in other cells only a few vacuoles were observed. Probably the cells with just a few vacuoles are still young, and after a progressive accumulation, the vacuoles become abundant in old cells. The presence of a dark nucleus in the cells with a large number of vacuoles suggests that they are in a final stage of their life. Arylsulphatase was detected in the vacuoles and also in small secondary lysosomes containing substances in digestion. Bundles of tubules with 50 nm in diameter were found within some cisterns of rough endoplasmic reticulum. A cell fraction enriched in mannitol oxidase, extracted from the hepatopancreas of a terrestrial slug, consisted in very similar tubular structures. Using a histochemical method, mannitol oxidase was detected in the basophilic cells ofA. depilans, and it may be associated with the tubular structures of the endoplasmic reticulum. This is the first report of mannitol oxidase in opisthobranch molluscs. Almost spherical peroxisomes with a small nucleoid were abundant in these cells. The nucleoids presented a rectangular section, but a crystalline structure was not evident. The peroxisomes were stained after the cytochemical detection of catalase activity.     

金黄滴虫细胞核微丝系统的初步观察

金黄滴虫细胞核内经常存在着许多直径约为7nm的微丝。这些徽丝大多组合成走向不定的徽丝束,微丝束交织而成遍布核内的网架。核被下面微丝束较多,它们的存在常使核被外凸而成隆脊。核内微丝与核内结构如核仁、染色质等似乎都是相连的。有些微丝横跨核被,一端位于核内,另一端位于核周腔中,并靠近叶绿体。核周腔和内质网腔中也存在着微丝和另一种纤维,印管状纤维。用细胞松弛素B处理后,细胞核、核周腔和内质网腔中的微丝均消失,细胞核的形态也发生变化,似乎微丝网架有支持细胞核的作用。核内微丝可能是在内质网中组装,然后经核周腔进入核内的。     

Extramembraneous particles and structural variations of tubular myelin figures in rat lung surfactant

Tubular myelin figures of pulmonary surfactant were examined by electron microscopy after fixation in glutaraldehyde and postfixation in an osmium tetroxide-ferrocyanide mixture. Bilayered membranes were seen as parallel arrays or as lattices with spacings varying from about 36 to 50 nm. This method also produced good visualization of drumstick-like particles, 5 nm in diameter and about 15 nm in length. The particles were regularly spaced at intervals of 16 nm in rows along the rectangular angles of myelin membranes. Depending on the size of the tubules the particles contacted each other in the center of the tubules at low diameters (tubular diameter less than 40 nm) and formed a continuous filamentous central core, or they were separated from one another (tubular diameter greater than 40 nm). In the latter case the central core had a hollow appearance. Based on further findings employing tannic acid, lipid extraction with 2,2-dimethoxypropane, and a ruthenium red-osmium tetroxide technique for the demonstration of polyanionic proteins it is suggested that these particles are protein in nature and that they are involved in the formation and maintenance of the structure of tubular myelin. A new concept of the ultrastructure of tubular myelin figures is proposed.     

Fibrous and tubular inclusions in four xylariaceous fungi

Summary Intranuclear and cytoplasmic fibrous inclusions and cytoplasmic tubular inclusions have been studied using electron microscope techniques. The fibrous inclusions are composed of closely packed, rod-like structures. Each rod has an outside diameter of ± 24 nm, a hollow centre and lateral projections along its length. The tubular inclusions occur as densely packed bundles or loose arrays of 10–13 nm diameter tubules which are composed of subunits arranged in a double helical structure. The distribution, origin and possible function of these and similar inclusions is discussed.     

The nucleus preopticus and the nucleus lateralis tuberis in the roach,Leuciscus rutilus

Summary The hypothalamus of the teleost fish Leuciscus rutilus was investigated with the Falck-Hillarp technique. The nucleus preopticus (NPO) and the nucleus lateralis tuberis (NLT) contain no fluorescent, i.e. catecholaminergic cells. Green fluorescent fibers probably originating from the paraventricular organ and/or the preoptic recess organ, are intermingled with the cells.The electron microscopical study was based on the three fixatives glutaraldehyde-osmium tetroxide, osmium tetroxide and potassium permanganate. In the NPO two cell types are recognized, characterized mainly by dense core vesicles (dcv) with measured diameter of 130 nm and 170 nm across respectively. The endoplasmic reticulum in the former cell type generally has large dark inclusions measuring from 175 to 375 nm across, which are also found in the neurite. In the NLT, four different cell types are identified, some of which are subject to considerable variations. The rostral and the medial parts of the nucleus include a large cell type (I) with dcv of diameter 170 nm. The medial part also has a small cell type (II) with dcv of 80 nm. The lateral part is characterized by two cell types (III, IV). Cell type III occurs in three forms with dcv of about 140 nm. The fourth cell type (IV) is rare and contains irregularly formed granules, the most circular ones measuring about 130 nm and the most elongated ones 110 nm×210 nm. The ventrolateral part contains the same cell types (except for type II) as those found in the lateral and medial parts.The morphological differentiation of the NLT as well as its different cell types strongly indicates its functional diversity.After permanganate fixation the secretory granules of the different cell types in the NPO and the NLT appear as empty vesicles. This method also reveals that the cell types of the two nuclei have dcv of about 90 nm. The possible monoaminergic content and the role of these dcv are discussed.Supported by grants from the Swedish Natural Science Research Council (No 2502-1-7).I should like to express my gratitude to Doctor Gunnar Fridberg for initiating this work and for many stimulating discussions.     

Ultrastructural changes and small bacilliform particles associated with infection by rubus yellow net virus

A culture of rubus yellow net virus (RYNV) was obtained free from other detectable viruses by heat treatment of red raspberry (Rubus idaeus) cv. Mailing Jewel showing veinbanding mosaic symptoms. Graft inoculated black raspberry (JR. occidentalis) plants showed three kinds of ultrastructural abnormality: (1) cell wall outgrowths in many kinds of cells in the leaf blade and vascular bundles, (2) tubular structures c. 30 nm in diameter and up to 1100 nm long, in groups in the cytoplasm close to the nucleus and (3) small bacilliform virus-like particles c. 80–150 × 25 nm in size randomly distributed in the cytoplasm of many kinds of leaf cells, but especially in the phloem. The bacilliform particles, which in some cells were in large groups associated with lightly staining amorphous material, are considered to be those of RYNV.     

Viruses of Entamoeba histolytica. VII. Novel beaded virus.

A third amoebal virus type was isolated from four different strains of Entamoeba histolytica. The virus was most frequently seen as a linear structure about 235 nm long and consisting of 14 beadlike structures about 19 nm in diameter. A "dimer" of twice the length and consisting of 28 beads was occationally encountered. The virus replicated in the nucleus, forming ordered arrays. Acridine orange staining of viral aggregates in infected nuclei suggested the presence of double-stranded nucleic acid.     

Le spermatozoide de Ophidion sp. (Poisson,téléostéen): Particularités ultrastructurales du flagelle

The spermatozoon of Ophidion sp. possesses an elongated nucleus 8 μm long, a short midpiece (0,6 μm), and a long flagellum (100 μm). The flagellar membrane extends in the form of two diametrically opposed sidefins. Evolving spermatids and spermatozoa are found in the lumen of the seminiferous tubes. The sections of flagella show filamentary and tubular elements disposed parallel to the axoneme microtubules. We have divided the flagella into three types. In type 1 the tip of the sidefins contains 20 to 30 filaments 5 run in diameter and between these and the axoneme 20 to 30 tubular elements 15 to 20 nm in diameter. Type 2 possesses a dense cytoplasm and a few tubular elements 10 nm in diameter disposed at the tip of the sidefins. Type 3 contains a cytoplasm which is not dense and in which we found polysaccharides and 1 to 8 tubular elements forming a palisade which lines the plasma membrane at the tip of the sidefins. We interpret these three types as three successive stages in the organization of the flagellum during spermiogenesis. Type 3 corresponds to the spermatic flagellum. These 10-nm-diameter tubules do not have the same chemical composition as the microtubules. Elements of the cytoskeleton serve as a support for the sidefins.     

Formation of the cylindrical structure during the acrosome reaction of abalone spermatozoa

Spermatozoa of abalone Haliotis discus were examined before and during the acrosome reaction with special regard to one of the newly formed structures: a cylindrical structure surrounding a part of the elongated acrosomal process near the opening of the acrosomal vesicle. The structure, about 0.2 μm in diameter and about 1 μm in length, was revealed to be composed of a tightly coiled, fine tubular structure about 20 nm in diameter. In the course of the acrosome reaction, a triple-spiral structure appeared in the anterior part of the acrosomal vesicle. Since this spiral structure was also composed of a tightly coiled 20 nm tubule(s), it was concluded that this structure was transformed into the single-walled cylindrical structure by simple stretching in the direction of its longitudinal axis. In the clumps of spermatozoa that underwent acrosome reaction in suspension, the cylindrical structures were frequently found in contact with each other and/or other structures, indicating that they are very sticky.     

Helical structures in the cytoplasm of differentiating cells ofMicrasterias thomasiana

Summary Helical structures so far not known inMicrasterias are observed in the cytoplasm of differentiating cells ofMicrasterias thomasiana which were pretreated by a special fixation procedure. The structures measure about 45 nm in diameter and are situated in the area of the postmitotic nucleus and its surrounding microtubule system, sometimes close to different kinds of vesicle. Nature and function of the helical structures are still obscure; a relationship to microtubules is discussed.     

The fine structure of the gill epithelium of a fresh-water flea,Daphnia magna (Crustacea: Phyllopoda) and changes associated with acclimation to various salinities

Two kinds of epithelial cells, dark and light types, are alternately arranged in the gill of Daphnia magna. The dark cell has numerous mitochondria and an elaborate tubular system containing two kinds of cytoplasmic tubules, small about 70 nm in diameter, and large about 130 nm in diameter. The former occur in bundles and seem to be smooth-surfaced endoplasmic reticulum. The latter, lined with a ridged surface coat and frequently open at the lateral and basal cell membrane, are regarded as extensions of the cell membrane. The atypical cell membrane of the dark cell is modified by repeated subunits of a cytoplasmic coat on the inner leaflet of the unit membrane. The light cell exhibits a high degree of basal infoldings of the cell membrane, which represent a magnification of the surface area of the cell. Large mitochondria between the infoldings often come into intimate association with the infolded cell membrane to form a regular array of parallel mitochondria interposed with the double cell membranes. The results suggest that at least the dark epithelial cells play an important role in the osmoregulation of this animal.     

Electron microscopic observations of prokaryotic surface appendages

Prokaryotic microbes possess a variety of appendages on their cell surfaces. The most commonly known surface appendages of bacteria include flagella, pili, curli, and spinae. Although archaea have archaella (archaeal flagella) and various types of pili that resemble those in bacteria, cannulae, and hami are unique to archaea. Typically involved in cell motility, flagella, the thickest appendages, are 20–26 nm and 10–14 nm wide in bacteria and archaea, respectively. Bacterial and archaeal pili are distinguished by their thin, short, hair-like structures. Curli appear as coiled and aggregative thin fibers, whereas spinae are tubular structures 50–70 nm in diameter in bacteria. Cannulae are characterized by ～25 nm-wide tubules that enter periplasmic spaces and connect neighboring archaeal cells. Hami are 1–3 μm in length and similar to barbed grappling hooks for attachment to bacteria. Recent advances in specimen preparation methods and image processing techniques have made cryo-transmission electron microscopy an essential tool for in situ structural analysis of microbes and their extracellular structures.     

Formation of macromolecular lignin in ginkgo xylem cell walls as observed by field emission scanning electron microscopy

Formation of macromolecular lignin in ginkgo cell walls. In the lignifying process of xylem cell walls, macromolecular lignin is formed by polymerization of monolignols on the pectic substances, hemicellulose and cellulose microfibrils that have deposited prior to the start of lignification. Observation of lignifying secondary cell walls of ginkgo tracheids by field emission scanning electron microscopy suggested that lignin-hemicellulose complexes are formed as tubular bead-like modules surrounding the cellulose microfibrils (CMFs), and that the complexes finally fill up the space between CMFs. The size of one tubular bead-like module in the middle layer of the secondary wall (S2) was tentatively estimated to be about 16+/-2 nm in length, about 25+/-1 nm in outer diameter, with a wall thickness of 4+/-2 nm; the size of the modules in the outer layer of the secondary wall (S1) was larger and they were thicker-walled than that in the middle layer (S2). Aggregates of large globular modules were observed in the cell corner and compound middle lamella. It was suggested that the structure of non-cellulosic polysaccharides and mode of their association with CMFs may be important factors controlling the module formation and lignin concentration in the different morphological regions of the cell wall.     

Presence of macrotubules and their induction by colchicine in grasshopper spermatids

Ultrastructural studies show that groups of tubular structures of about 45 nm. in diameter appear in the cytoplasm of grasshopper spermatids. These tubules, or macrotubules, appear to have a fuzzy coat or to be twisted, and in some cases their bundles attain a length of 10 um. When grasshoppers were treated with colchicine, spermatid microtubules which composed the manchette are depolymerized and a large number of macrotubules appears. The relationship between these two types of tubules is discussed.     

贮藏洋葱抽苔时鳞片叶表皮细胞的细胞学变化

利用透射电镜观察了洋葱抽苔时其鳞片叶表皮细胞的亚显微结构变化。幼嫩鳞片叶表皮细胞结构正常：液泡在细胞中央,细胞质在靠近细胞壁的边缘;细胞质中富含质体、线粒体和核糖体等细胞器;胞间连丝直径约为５０ｎｍ。伴随着细胞的衰退,细胞质变得松散,在液泡中出现大量絮状物,细胞器逐渐解体。少数胞间连丝直径扩大,达到８０ｎｍ左右,它可能在大分子胞间转移中起重要作用。在衰老细胞中,核和质体已解体但多数胞间连丝仍维持正常状态。