An Electron Microscopic Study on Spermatogenesis in Golfingia ikedai

The process of spermatogenesis in Golfingia ikedai was observed with electron microscope. Clusters of primary spermatocytes continued spermatogenesis while floating in the body fluid. No direct connections were found between the cells and no cytophore formation was observed. Preacrosomal vesicles were formed from small Golgi-bodies just after the meiosis. Subacrosomal substances were aggregated just under the acrosomal vesicle in the middle stage of spermiogenesis and changed into fibrous structures in the completed spermatozoon. A peculiar annulus structure developed around the base of the flagellum. The phylogenetic position of this worm was also discussed in relation to the polychaetes and other worms.     

An Electron Microscopic Study of the Bipolar Bodies in Crithidia oncopelti

SYNOPSIS. An electron microscopic study of the structure of the flagellate Crithidia oncopelti was carried out with particular reference to the nature of the bipolar body which occurs in the organism. Apart from the bipolar body, the fine structure of C. oncopelti is similar to that of the related flagellate, C. fasciculata. The bipolar body is typically a sausage-shaped organelle limited by 2 unit membranes. Outpouchings of these membranes into the cytoplasm of C. oncopelti were found, along with a constant absence of (a) ribosomes on the outer aspect of the external of the 2 membranes, (b) structures analogous to nuclear pores and (c) an internal structure analogous to a nucleolus. It is concluded that the balance of structural and biochemical evidence favors the idea that the bipolar body is a bacterial protoplast rather than a 2nd nucleus.     

Electron Microscopic Study of a Slime Layer

Slime layers are being studied in our laboratories in an attempt to understand their functions in the control of pollution in natural streams. A method for fixing, staining, and embedding microorganisms in the intact slime has been developed. In this method, epoxy resin discs are placed in a holder and are introduced into a simulated stream. After various periods of time the discs are punched out of the holder into the fixative. The disc with the attached slime is fixed, stained (4% osmium tetroxide plus ruthenium red), dehydrated, and embedded in epoxy resin so that thin sections can be cut through the vertical plane of the slime mass. Such thin sections permit detailed examination of the attached layer, the surface-slime interface, the spatial relationships between cells in the vertical slime structure, and the strands of extracellular material between and around cells. No special attachment structures were noted as the cells appeared to be attached to the surface by extracellular material alone. This material was observed in strands and netlike forms between cells which are positioned 1 to 4 mum apart in the slime.     

An Electron Microscopic Study of Antagonism between Cephalexin and Erythromycin in Staphylococcus aureus

This study concerns investigations at the cellular level of antagonism between cephalexin (CEX) and erythromycin (EM) with the aid of electron microscopes and a liquid scintillation counter. Exposure of Staphylococcus aureus 209-P to CEX and EM in combination was found to result in a marked antagonism between the two antibiotics in their effects on the growth of the organism. Observations under a scanning electron microscope revealed lysed cells in the presence of CEX alone but almost no lysis in the presence of a combination of CEX and EM. Observations under a transmission electron microscope, on the other hand, disclosed that nearly all of the cells exposed to 20 μg/ml of CEX were transformed into protoplasts with their morphological changes being most marked after 4 hr of exposure. When 1 μg/ml of EM was allowed to act alone, this exposure resulted in thickening of the cell walls. The combined use of CEX and EM, however, resulted in neither thickening of the cell walls as in the presence of EM alone nor in the formation of protoplasts as in the presence of CEX alone but merely produced the swelling of separating walls. Cellular uptake of ¹⁴C-L -lysine and N-acetylglucosamine-1-¹⁴C into the cell wall fraction and the protein fraction was affected by CEX and EM, respectively, when used alone or in combination.     

An Electron Microscopic Study of the Infection of Spikelets of Rice by Pyricularia oryzae

Penetration and colonization of spikelet tissue of a susceptible line of rice. ZTS, by Pyricularia aryzae was investigated by scanning and transmission electron microscopy. Application of a modified embodding procedure in which the period of resin infiltration was extended, gave excellent fixation of the hard spikelet tissue. Conidia germinated to produce appressoria and the epidermal cell walls were penetrated within 24 h. Hyphae had colonized sclerenchyma, parenchyma, vascular bundles, andlarge trichomes within 48 h after inoculation. Invasion of the sclerenchyma appeared to occur through pit-pairs, where the host cell wall is thin. Conidiophores erupted directly from the epidermis, from minute protuberances and from large trichomes on the spikelet 4 days after inoculation.     

An Electron Microscopic Study of Double Fertilization in Allohexaploid Wheat Triticum aestivum L.

Double fertilization has been examined by electron microscopyin allohexaploid wheat, Triticum aestivum L. cv. Mardler. Serialsections through fertilized ovules revealed that following dischargeof the pollen tube contents into the degenerate synergid thelatter extended to form a continuum between the egg and centralcells. The two naked sperm nuclei were seen at the far end ofthis extended synergid. These observations suggest that thedegenerate synergid may play a role in transporting the spermnuclei to the site where they can be accepted by the egg andcentral cell. In comparison with double fertilization in Plumbagozeylanica L., we also suggest that the degenerate synergid preventsmale cytoplasms from being transmitted to the egg and centralcell. The present study also confirms that in the fertilizedcentral cell the maternal and paternal genomes remain physicallyseparate at least until the first nuclear division of the coenocyticphase of endosperm development. Double fertilization, degenerate synergid, Triticum aestivum     

An Electron Microscopic Study of the Intestinal Villus : I. The Fasting Animal

The structure of the intestinal villus of the rat was studied in thin sections of tissue fixed in buffered osmium tetroxide and embedded in methacrylate. The simple columnar epithelium investing the villus is surmounted by a striated border consisting of slender projections of the cell surface. These microvilli are arranged in almost crystalline, hexagonal array, and increase the apical surface area of the cell by a factor of 24. The core of each microvillus is filled with fine fibrils which arise from the filamentous substance of the terminal web underlying the striated border. Each microvillus is covered by a tubular extension of the plasma membrane of the epithelial cell. Pinocytotic vesicles originating from the plasma membrane occur at the bases of the intermicrovillous spaces. The nucleus, mitochondria, and the endoplasmic reticulum of the epithelial cell display no unusual features. Small bits of ergastoplasm occur in the apical cytoplasm. A thin basement membrane separates the epithelium from the lamina propria which consists of vessels, nerves, and numerous lymphocytes, eosinophiles, mast cells, plasma cells, smooth muscle fibers, and macrophages suspended in a delicate stroma of fibroblasts and collagen fibers. Intercellular fat droplets often occur in this stroma, even in animals fasted for 40 hours. The blood capillaries are distinguished by their extremely attenuated, fenestrated endothelial cells. The lacteal has a thicker endothelium which, although not fenestrated, appears to have significant interruptions, especially at the margins between neighboring lining cells. Strands of smooth muscle always accompany the lacteal but do not form an integral part of its wall. Unmyelinated nerves, many of which are too small to be distinguished with the light microscope, course through the lamina propria in association with the vessels. The nerve fibers evidently do not cross the basement membrane into the epithelium. Neuromuscular junctions or other terminal apparatus were not found.     

PASSAGE OF LIPID ACROSS VASCULAR ENDOTHELIUM IN NEWBORN RATS : An Electron Microscopic Study

An electron microscopic study of the fine blood vessels in the skin and muscle of 25 newborn rats (sucklings, and therefore subject to physiologic lipemia) has shown that blood-borne lipid particles may leave the lumen of these vessels by two pathways, intercellular and intracellular. (a) An intercellular pathway: Some capillaries, venous capillaries and venules contain intramural, extracellular deposits of lipid which is presumably hematogenous. In some animals these deposits are quite numerous; available evidence suggests that they are a consequence of intercellular gaps, too small or too transient to be observed except in rare instances. Plasma apparently escapes through these gaps and filters across the basement membrane, while lipid particles are retained, usually in sufficient number to fill the small defect; some lipid particles are then taken up by endothelial cells and pericytes, while a few escape and are incorporated into free phagocytes. These focal defects, though few in number, may explain the apparent incapacity of blood vessels of newborn rats to leak any further after a local injection of histamine. Discontinuities in the endothelium were found also in the renal glomerulus, sometimes accompanied by extensive interstitial accumulations of lipid particles. Similar intercellular gaps are known to exist in other types of immature endothelia. (b) An intracellular pathway: This is best demonstrated in the capillaries, venous capillaries and venules which supply the developing subcutaneous adipose tissue. Here the lipid particles adhere in large numbers to the endothelial surface; the morphologic evidence suggests that they are also taken up into the endothelium through phagocytosis by "flaps," or into pockets or crevices. The lipid is apparently metabolized in the vascular wall; some is found in the multivesicular bodies. There was no evidence of active transport by vesicles or vacuoles. Neither pathway was demonstrable in the adult.     

An Electron Microscopic Study of the Ductuli Efferentes and Rete Testis of the Guinea Pig

The ductuli efferentes and rete testis of the guinea pig were isolated by micro dissection, fixed in cold buffered osmium tetroxide, and sectioned for examination with the light and electron microscopes. Proximal and distal segments of the ductuli efferentes were identified and their respective cytological organizations characterized. The cytological components of the rete testis are briefly described and figured. Non-ciliated and ciliated cells are found in both segments of the ductuli efferentes. The non-ciliated cells have a microvillous border, mitochondria, a Golgi complex, an ubiquitous endoplasmic reticulum, and numerous cytoplasmic vacuoles. The ciliated cells contain more mitochondria, an endoplasmic reticulum with a relatively sparse distribution, and few, if any, cytoplasmic vacuoles. A regional difference exists in proximal and distal segments based on the distribution, size, number, and electron opacity of the cytoplasmic vacuoles. Attention was paid to the disposition of the endoplasmic reticulum and its relation to the system of cytoplasmic vacuoles. These findings are interpreted as suggesting that the continuity of the vacuolar system with elements of the endoplasmic reticulum represents a pathway for transfer of large quantities of fluid, an activity which has long been ascribed to the epithelium of the ductuli efferentes. Periductular capillaries possess pore-like apertures in their endothelia similar to those in other tissues known to engage in fluid transfer.     

Electron Microscopic Study of the Phagocytosis Process in Lung

Diluted India ink was instilled into the nasal cavity of mice and the lungs of some animals were fixed with osmium tetroxide at various intervals after one instillation. The lungs of other animals were fixed after 4, 7, 9, 16, or 18 daily instillations. The India ink was found to be phagocytized almost exclusively by the free alveolar macrophages. A few particles are occasionally seen within thin portions of alveolar epithelium, within the "small" alveolar epithelial cells, or within occasional leukocytes in the lumina of alveoli. The particles are ingested by an invagination process of the plasma membrane resulting in the formation of intracellular vesicles and vacuoles. Ultimately large amounts of India ink accumulate in the cell, occupying substantial portions of the cytoplasm. The surfaces of phagocytizing macrophages show signs of intense motility. Their cytoplasm contains numerous particles, resembling Palade particles, and a large amount of rough surfaced endoplasmic reticulum. These structures are interpreted as indicative of protein synthesis. At the level of resolution achieved in this study the membranes of this reticulum appear as single dense "lines." On the other hand, the plasma membrane and the limiting membranes of vesicles and of vacuoles often exhibit the double-line structure typical of unit membranes (Robertson, 37). The inclusion bodies appear to be the product of phagocytosis. It is believed that some of them derive from the vacuoles mentioned above, and that they correspond to similar structures seen in phase contrast cinemicrographs of culture cells. Their matrix represents phagocytized material. Certain structures within this matrix are considered as secondary and some of these structures possess an ordered form probably indicative of the presence of lipid. The possible origin and the fate of alveolar macrophages are briefly discussed.     

Effect and Localization of Trifluralin in Plasmodium falciparum Gametocytes: An Electron Microscopic Study1

Trifluralin, a herbicide which is known to bind to plant and algal tubulin, induced ultrastructural changes in the microtubules of the mature Plasmodium falciparum gametocytes in vitro. Trifluralin treatment led to disassembly of the well ordered subpellicular microtubules, whereas it had no effect on microtubules of human platelets or of rat neuronal cells in vitro. The disassembled microtubules showed fragmented large tubular structures, which frequently were associated with the pellicular membranes. Electron microscopic autoradiography showed radioactive trifluralin associated with the microtubule fragments. These results provide evidence that trifluralin selectively binds to microtubules in malaria parasites and causes disruption of their structure.     

金鱼早期仔鱼体表的电镜观察

应用扫描和透射电镜技术对金鱼(Carassius auratus)孵出1 d3、d9、d龄仔鱼的体表进行了观察。仔鱼的上皮细胞呈扁平、多边形,彼此之间由增厚的边缘嵴状突紧密连接,细胞向内凹陷的表面有指纹状嵴突。孵出3 d的仔鱼体表两侧各有一列间隔有序呈丘状突起的味蕾,外被单层上皮细胞,味孔处有一根粗圆的感觉毛。粘液细胞出现在仔鱼头部、腹部、体侧的表皮上,并开口于多个相邻上皮细胞间的连接处。粘液细胞胞质比例大,内含丰富、平行排列的粗面内质网,旁边有大量大小不一、内含物液化状、近圆形的粘原颗粒。9 d后仔鱼体表完全被粘液覆盖,初步建立了以粘液细胞为基础的防病和抗病机制,以机械和化学感觉为主的Ⅰ型味蕾觅食方式。     

Budding and Metamorphosis in Acineta tuberosa. An Electron Microscopic Study on Morphogenesis in Suctoria

SYNOPSIS. All stages (except conjugation) of the life cycle in Acineta tuberosa (Suctoria) were studied in the electron microscope. Budding starts with the invagination of a small pellicular area near the opening of the vacuole and bearing rows of barren basal bodies. Some of these basal bodies are incorporated into the swarmer-anlage and give rise to 8 rows of cilia, while the other basal bodies remain barren on the mother cell's side of the brood pouch. They will provide their own genetic continuity and later give rise to the swarmer of the next generation. Kineties are not spaced on the growing swarmer-anlage until their cilia are fully grown. Further details on the stalk-forming crganelle and general features of the development of the larvae are given.
Metamorphosis starts with the formation of basal disc and stalk. The stalk-forming material is released thru scopular pores into a tube-like mold formed by the scopula after having been pulled inward. Later, scopula pores spread from the scopular area proper and move upward. On their way to the apical part of the animal the cuticle is secreted. The differentiation of tentacles is described and new observations regarding a possible mode of haptocyst formation are given.
The results are discussed with respect to the morphogenetic potentialities of cortical structures in general.     

小鼠精母细胞联会复合体RNA组分的电镜研究

本文运用常规染色和Bernhard染色方法对切片标本中小鼠粗线期精母细胞联会复合体(SC)的超微结构和电镜细胞化学特点进行了研究。经常规染色后,可见SC由侧生组分(LE)、中央组分(CE)和L-C纤维组成;SC宽约210nm,LE宽约60nm,中央间隔区宽约90nm。在Bernhard染色标本中,SC的LE、CE和L-C纤维着色较深,说明其中含有RNA;SC各结构组分的宽度和形态特点与常规染色标本中的基本一致。本文讨论了SC中存在有RNA等问题。     

An Electron Microscopic Study of the Intestinal Villus : II. The Pathway of Fat Absorption

The intestinal pathway for absorbed fat was traced in thin sections of intestinal villi from rats fed corn oil by stomach tube after a fast of 24 to 40 hours. For electron microscopy the tissues were fixed in chilled buffered osmium tetroxide and embedded in methacrylate. For light microscopy, other specimens from the same animals were fixed in formal-calcium, mordanted in K₂Cr₂O₇, and embedded in gelatin. Frozen sections were stained with Sudan black B or Sudan IV. About 20 minutes after feeding, small fat droplets (65 mµ maximal diameter) appear in the striated border between microvilli. At the same time fat particles are seen within pinocytotic vesicles in the immediately subjacent terminal web. In later specimens the fat droplets are generally larger (50 to 240 mµ) and lie deeper in the apical cytoplasm. All intracellular fat droplets are loosely enveloped in a thin membrane, the outer surface of which is sometimes studded with the fine particulate component of the cytoplasm. This envelope, apparently derived from the cell surface by pinocytosis, has at this stage evidently become a part of the endoplasmic reticulum. Just above the nucleus numerous fat droplets lie clustered within the dilated cisternae of the Golgi complex. As absorption progresses fat droplets appear in the intercellular spaces of the epithelium, in the interstitial connective tissue spaces of the lamina propria, and in the lumen of the lacteals. All of these extracellular fat droplets are devoid of a membranous envelope. The picture of fat absorption as reconstructed from these studies involves a stream of fat droplets filtering through the striated border, entering the epithelial cell by pinocytosis at the bases of the intermicrovillous spaces, and coursing through the endoplasmic reticulum to be discharged at the sides of the epithelial cell into extracellular spaces. From the epithelial spaces, the droplets move into the lamina propria and thence into the lymph. If the lumen of the endoplasmic reticulum is considered as continuous with the extracellular phase, then the entire pathway of fat absorption may be regarded as extracellular. However, it is impossible to evaluate from the electron microscopic evidence thus far available the quantitative importance of particulate fat absorption by the mechanism described.     

INTERCELLULAR MIGRATION OF CENTRIOLES IN THE GERMARIUM OF DROSOPHILA MELANOGASTER : An Electron Microscopic Study

A cluster of centrioles has been found in the early Drosophila oocyte. Since the oocyte is connected to 15 nurse cells by a system of intercellular bridges or ring canals, the possibility that the cluster of centrioles arose in the germarium from an intercellular migration of centrioles from the nurse cells to the oocyte was analyzed in serial sections for the electron microscope. Initially, all of the 16 cells of the future egg chambers possess centrioles, which are located in a juxtanuclear position. At the time the 16 cell cluster becomes arranged in a lens-shaped layer laterally across the germarium, the centrioles lose their juxtanuclear position and move towards the oocyte. By the time the 16 cell cluster of cells is surrounded by follicle cells (Stage 1), between 14 and 17 centrioles are found in the oocyte. Later, these centrioles become located between the oocyte nucleus and the follicle cell border and become aggregated into a cluster less than 1.5 µ in its largest dimension. The fate of these centrioles in the oocyte is not known. The fine structure of the germarium and the early oocyte is also described.     

Migration Behavior of Granule Cell Neurons in Cerebellar Cultures. II. An Electron Microscopic Study

We examined the fine structure of migrating granule cell neurons in cerebellar microexplant cultures. Radially migrating bipolar cells extended microspikes or small filopodia from their soma and processes and frequently made contact with neighboring cells. These microspikes contained microfilaments but no microtubules. At the later phase of the migration, in which they had symmetrical bipolar long processes, filopodia extending from perikarial region of cells contained microtubules, suggesting that they are precursors of the future thick perpendicular processes. When cell bodies changed orientation from radial to perpendicular, microtubules that were nucleated from perinuclear centrioles frequently extended into both thick radial and perpendicular processes from the perikarial region. Bundles of 10nm intermediate filaments also appeared in these processes. During migration by the perpendicular contact guidance, many filopodia extending from both the thick leading processes and thin trailing processes made close contacts with the radial parallel neurite. These findings suggest that; 1) The direct contact of the filopodia from both the growth cones and their processes of the granule cells to the neurite bundle plays roles in both the parallel and perpendicular contact guidances. 2) The spacial and temporal changes of cytoskeletons and the association of microtubules with perinuclear centrioles are important for the formation of perpendicular processes and initiation of the perpendicular contact guidance.     

Electron Microscopic Study of the Morphogenesis of Vesicular Stomatitis Virus

Except for the rate, vesicular stomatitis virus (VSV) grows as well at 25 C as at 37 C in primary chick embryo fibroblast cells and in a pig kidney cell line [PK(H13)]. Maximal yields were reached at about 28 hr at 25 C and 10 hr at 37 C in these cells. Morphogenesis, as observed by electron microscopy, was similar at the two temperatures. The main feature was accumulation of virus in intracytoplasmic vacuoles. Mode of release of VSV has been controversial; both budding (as displayed by myxoviruses) and maturation at membranes of cytoplasmic vacuoles (as with arboviruses) have been claimed. Our observations support the latter view, and the apparent dichotomy in interpretation is discussed.