scholarly journals Ultrastructure and Differentiation in Chara (Fibrosa) IV. Spermatogenesis

1968 ◽  
Vol 21 (4) ◽  
pp. 655 ◽  
Author(s):  
JD Pickett-Heaps
Keyword(s):  
Structural Changes ◽  
Chromatin Condensation ◽  
Ultrastructural Level ◽  
Flat Band ◽  
Cell Organelles ◽  
Microtubule Organization ◽  
Golgi Bodies ◽  
Unknown Significance ◽  
Almost All ◽  
Spermatogenous Cells

Spermatogenesis in Ohara is described at the ultrastructural level. A large nwnber of mitoses form spermatogenous threads, derived from the capitula inside the antheridiwn. Centrioles appear in the spermatogenous cells early as indistinct organelles that quickly become conspicuous. There is some evidence for the existenc of a procentriole. Centrioles are subsequently associated in a normal fashion with the mitotic spindle. Intracellular differentiation commences after mitosis ceases. The nucleus moves to one side of the cell; a flat band of manchette microtubules is soon formed near it. The microtubules, which increase in nwnber and elongate considerably, are inserted at one end into (and possibly extruded from) a densely staining, homogeneous inclusion, termed the manchette adjunct, which appears close to the centrioles. The centrioles, connected together by a spindle-shaped ciliary rootlet structure, move to the edge of the cell and start extruding flagella, which are covered in scales; another organelle, termed the vesicular adjunct and of unknown significance, appears near these centrioles. The manchette grows in length, and so asswnes a spiral course in the cell; plastids then line up along the microtubules next to the nucleus. While still interconnecting cells, the cytoplasm shrinks steadily. With further elongation of the manchette, the flagella apparatus moves away from the nucleus, and mitochondria also line up along the manchette tubules between them. Lipid (?) bodies move near the plastids, which steadily accumulate starch. Golgi bodies show marked structural changes during differentiation; they are initially associated with a profusion of various vesicles, and later lose their identity, as does the endoplasmic reticulwn which earlier interconnected cells through plasmadesmata. The nucleolus disappears, and later chromatin condensation gives the elongating nucleus an increasingly lamellate structure; finally these lamellae fuse to form a dense homogeneous nucleus. The cytoplasm continues to shrink, eliminating almost all cell organelles. The mature spermatozoid, tightly coiled in the cell, finally contains plastids and (lipoid) inclusions at one end, next to the dense, elongate nucleus, with linearly arranged mitochondria at the other end, and flagella inserted above the mitochondria. Manchette microtubules run the length of the organism as a flat band opposed to the nucleus and plastids, and finally as a tubular sheath partly enclosing the mitochondria. Four other tubules, possibly derived from a ciliary root structure, are also close to the mitochondria. The flagella are quite long by this stage. The observations are discussed in terms of the functions of cell organelles. In particular, it is suggested that centriolar movement in mitosis may be only one example of everal morphogenic movements associated with microtubule organization; their unction is in flagella formation, and not in synthesis of spindle, manchette, or other ytoplasmic microtubules.

The Ultrastructure and Ontogeny of Pollen in Helleborus Foetidus L

1968 ◽  
Vol 3 (2) ◽  
pp. 161-174
Author(s):  
P. ECHLIN ◽  
H. GODWIN
Keyword(s):  
Cell Wall ◽  
Tapetal Cell ◽  
Pollen Grains ◽  
Ultrastructural Level ◽  
Low Molecular Weight ◽  
Cell Organelles ◽  
Helleborus Foetidus ◽  
Ubisch Bodies ◽  
Ubisch Body ◽  
Development Proceeds

The ontogeny of the tapetum and Ubisch bodies in Helleborus foetidus L. has been examined at the ultrastructural level, and their development has been closely linked with that of the sporogenous cell and pollen grains. During development the tapetum passes through successive phases of synthesis, maturity and senescence, ending in complete dissolution. During the anabolic phase of growth, precursors of the Ubisch bodies are formed as spheroidal vesicles of medium electron density within the tapetal cytoplasm; they are associated with a zone of radiating ribosomes, which, as development proceeds, can clearly be seen to be situated on strands of endoplasmic reticulum. The callose special wall round the microspores and the tapetal cell wall now disintegrate and the pro-Ubisch bodies are extruded through the cell membrance of the tapetal cells, where they remain on the surface of the anther cavity and soon become irregularly coated with sporopollenin. Deposition of sporopollenin continues on the Ubisch bodies at the same time as upon the exines of the developing pollen grains. In both cases, the later stages of sporopollenin deposition are associated with electron-transparent layers of unit-membrane dimensions appearing in section as white lines of uniform thickness. Continuing deposition of sporopollenin leads to the formation of compound or aggregate Ubisch bodies. It is conjectured that the sporopollenin is synthesized from the compounds of low molecular weight released into the anther loculus by the breakdown of the callose special wall and the tapetal cell wall. The final stages of tapetal autolysis involve the disappearance of all the cell organelles. An attempt is made to relate the findings to those described in other recent studies on Ubisch body formation and to combine them in a common ontogenetic pattern.

Ultrastructural changes of Basolateral Amygdaloid nuclei in the Sprague Dawley rats brain following exposure to naphthalene balls

2021 ◽  
Vol 12 (2) ◽  
pp. 1272-1275
Author(s):  
Angu Bala Ganesh K S V ◽  
Sujeet Shekhar Sinha ◽  
Kesavi Durairaj ◽  
Abdul Sahabudeen K
Keyword(s):  
Structural Changes ◽  
Corn Oil ◽  
Chromatin Condensation ◽  
Ultrastructural Changes ◽  
High Dose ◽  
Model Group ◽  
Sprague Dawley ◽  
Sprague Dawley Rats ◽  
The Brain ◽  
Amygdaloid Nuclei

Naphthalene is a bicyclic aromatic constituent commonly used in different domestic and marketable applications comprising soil fumigants, lavatory scent disks and mothballs. Accidentally, workers, children and animals are exposed to naphthalene mothballs, so there is a need to study the pathology behind this chemical toxicity. The current study was carried out to assess the ultra structural changes of basolateral amygdaloid nuclei in the Sprague Dawley rats brain in association to naphthalene toxicity. The toxicity model group was administered with naphthalene (200 and 400mg) using corn oil as a vehicle for 28 days. The post delayed toxicity of naphthalene high dose ingestion was also assessed in rats. After the experimental period, the brain tissue was processed to observe the ultra structural changes using a transmission electron microscope. The alterations in cell organelles, nuclei damage, mitochondrial swelling, chromatin condensation suggested naphthalene induced damage in the neurons of the basolateral amygdala of the brain in the toxicity model group. These experimental trials provide information about the alert of mothball usage in the home and identify risks linked with accidental exposure and misuse.

Changes in collagen ultrastructure, macroscopic properties and chemical composition of chick embryo cartilage induced by administration of a β-D-xyloside

Development ◽  
1979 ◽  
Vol 53 (1) ◽  
pp. 179-202
Author(s):  
J. T. Hjelle ◽  
K. D. Gibson
Keyword(s):  
Spatial Distribution ◽  
Chondroitin Sulfate ◽  
Drug Administration ◽  
Physiological Role ◽  
Ultrastructural Level ◽  
Interstitial Space ◽  
Collagen Fibrils ◽  
Embryonic Cartilage ◽  
Almost All

Nine-day chick embryos were injected with a β-xyloside and their sternal cartilage was examined 3 days and a week later. Sterna from 16-day embryos showed a reduction in size as compared to controls, with little or no change in the fraction of extracellular space, and a significant decrease in tensile strength. At the ultrastructural level, collagen fibrils in control sterna were dispersed evenly in the interstitial space, with few contacts between adjacent fibrils. In sterna from treated embryos, almost all collagen fibrils were aggregated into clumps and arrays throughout the interstitial space, with fibril-free areas in between. No abnormalities could be detected in the morphology of individual fibrils or in the ultrastructure of the chondrocytes. The changes in spatial distribution of collagen were fully evident 3 days after drug administration. The hydroxyproline/DNA ratio was the same in control and treated sterna, and no changewas observed in the type of collagen. The uronic acid/DNA ratio was reduced by 14% 3 days after drug administration and by 40% after a week. The degree of sulfation of chondroitin sulfate was reduced from 80% in control sterna to 40% in treated sterna; almost allof this chondroitin sulfate was attached to peptide and the sedimentation pattern of the proteoglycan resembled that of normal cartilage proteoglycan. The function of chondroitin sulfate in embryonic cartilage is discussed in terms of our results and others. It is suggested that a major physiological role of the proteoglycan is to control the spatial distribution of collagen fibrils as they assemble to form a cross-linked gel.

scholarly journals Morphological and ultrastructural analysis of normal, injured and osteoarthritic human knee menisci

2019 ◽  
Vol 63 (1) ◽  
Author(s):  
Michela Battistelli ◽  
Marta Favero ◽  
Debora Burini ◽  
Giovanni Trisolino ◽  
Dante Dallari ◽  
...  
Keyword(s):  
Structural Changes ◽  
Complex Geometry ◽  
Chromatin Condensation ◽  
Meniscal Tear ◽  
Joint Stability ◽  
Future Design ◽  
Meniscal Tissue ◽  
Treatment Indications ◽  
Healthy Control ◽  
End Stage

The human meniscus plays a crucial role for transmission and distribution of load across the knee, as well as shock absorption, joint stability, lubrication, and congruity. The aim of this study was to compare the complex geometry, and unique ultrastructure and tissue composition of the meniscus in healthy (control) and pathological conditions to provide understanding of structural changes that could be helpful in the future design of targetted therapies and improvement of treatment indications. We analyzed meniscus samples collected from 3 healthy multi-organ donors (median age, 66 years), 5 patients with traumatic meniscal tear (median age, 41 years) and 3 patients undergoing total knee replacement (TKR) for end-stage osteoarthritis (OA) (median age, 72 years). We evaluated the extracellular matrix (ECM) organization, the appearance and distribution of areas of calcification, and modifications of cellular organization and structure by electron microscopy and histology. The ECM structure was similar in specimens from traumatic meniscus tears compared to those from patients with late-stage OA, showing disorganization of collagen fibers and increased proteoglycan content. Cells of healthy menisci showed mainly diffuse chromatin and well preserved organelles. Both in traumatic and in OA menisci, we observed increased chromatin condensation, organelle degeneration, and cytoplasmic vacuolization, a portion of which contained markers of autophagic vacuoles. Areas of calcification were also observed in both traumatic and OA menisci, as well as apoptotic-like features that were particularly prominent in traumatic meniscal tear samples. We conclude that meniscal tissue from patients with traumatic meniscal injury demonstrate pathological alterations characteristic of tissue from older patients undergoing TKR, suggesting that they have high susceptibility to develop OA.

A study of the molecular–cellular interface in visual photoreceptors by light scattering photometry

1985 ◽  
Vol 63 (7) ◽  
pp. 1933-1939 ◽  
Author(s):  
T. Borys ◽  
S. Deshpande ◽  
R. Jones ◽  
E. W. Abrahamson
Keyword(s):  
Light Scattering ◽  
Structural Changes ◽  
Time Range ◽  
Relaxation Techniques ◽  
Cell Organelles ◽  
Whole Cells ◽  
Cellular Events ◽  
Molecular Events ◽  
Cytological Changes ◽  
Non Destructive

The correlation of molecular events with structural changes within the cell requires a non-destructive relaxation technique that can be adapted to measure such cellular changes in a time range of milliseconds to minutes. Light scattering relaxation techniques have proved useful for such studies as they can often be measured simultaneously or in parallel with absorption or fluorescence spectral changes characterizing molecular or macromolecular processes. Such techniques are proving useful in the study of photobiological processes such as visual photoreception where specific cytological changes produced photochemically can be effected by alternate controlled perturbations such as osmotic shrinking or swelling of cell organelles and (or) whole cells. This paper illustrates how light scattering relaxation spectrophotometry can be applied to the correlation of molecular and cellular events in visual photoreceptors.

scholarly journals Formation of the chorion (zona pellucida) in the teleost, Oryzias latipes. II. Polysaccharide cytochemistry of early oogenesis.

1977 ◽  
Vol 25 (12) ◽  
pp. 1376-1380 ◽  
Author(s):  
J V Tesoriero
Keyword(s):  
Positive Reaction ◽  
Zona Pellucida ◽  
Oryzias Latipes ◽  
Ultrastructural Level ◽  
Mechanism Of Formation ◽  
Reactive Material ◽  
Golgi Bodies ◽  
Precursor Material ◽  
Bismuth Subnitrate

It has been proposed that the mechanism of formation of the chorion of Oryzias latipes involves the transfer of precursor material from the Golgi bodies of the oocyte to the chorion by means of a population of dense cored vesicles. Thin sectioned ovarian material was investigated by means of several techniques available for the resolution of periodate reactive material at the ultrastructural level. The techniques employed were modifications of the thiocarbohydrazide, thiosemicarbazide, alkaline bismuth subnitrate and silver methenamine reactions. These all demonstrated a positive reaction in the material of the chorion and that of the dense cored vesicles. This finding is in accord with the hypothesis that the dense cored vesicles are transporting material from the Golgi to the growing chorion.

CHANGES IN CELL FINE STRUCTURE OF LIMA BEAN AXES DURING EARLY GERMINATION

1966 ◽  
Vol 44 (3) ◽  
pp. 331-340 ◽  
Author(s):  
Shimon Klein ◽  
Yehuda Ben-Shaul
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Cell Walls ◽  
Lipid Droplets ◽  
Lima Bean ◽  
Amorphous Substance ◽  
Golgi Bodies ◽  
Early Germination ◽  
Almost All ◽  
Vacuolar Content

Changes in cell fine structure were studied in axes of green lima bean seeds soaked in water for 1–48 hours. At the beginning of the imbibition period the cortical and pith cells and to a smaller degree the cells of the future conductive tissues contain several vacuoles filled with an amorphous substance. Almost all of the cells contain lipid droplets arranged exclusively along cell walls. The endoplasmic reticulum appears in the form of long tubules, predominantly occupying the peripheral parts of the cell, surrounding the nucleus. A large concentration of ribosomes, mostly unattached, can be found in the cytoplasm. Similar particles make up the bulk of the nucleolus, but could not be found in plastids, which frequently contained starch, but were devoid of internal membranes. Only very few Golgi bodies occur. No changes in fine structure seem to occur during the first 4 hours of imbibition, but after 24 hours the lipid droplets and the vacuolar content have disappeared, the endoplasmic reticulum is more evenly distributed throughout the cells, and a large number of Golgi bodies can be seen.

scholarly journals Pleistocene megafaunal interaction networks became more vulnerable after human arrival

2015 ◽  
Vol 282 (1814) ◽  
pp. 20151367 ◽  
Author(s):  
Mathias M. Pires ◽  
Paul L. Koch ◽  
Richard A. Fariña ◽  
Marcus A. M. de Aguiar ◽  
Sérgio F. dos Reis ◽  
...  
Keyword(s):  
Structural Changes ◽  
Ecological Communities ◽  
Ecological Interactions ◽  
Ecological Data ◽  
The Past ◽  
As Species ◽  
Extinction Events ◽  
Almost All ◽  
The Impact ◽  
Unstable Dynamics

The end of the Pleistocene was marked by the extinction of almost all large land mammals worldwide except in Africa. Although the debate on Pleistocene extinctions has focused on the roles of climate change and humans, the impact of perturbations depends on properties of ecological communities, such as species composition and the organization of ecological interactions. Here, we combined palaeoecological and ecological data, food-web models and community stability analysis to investigate if differences between Pleistocene and modern mammalian assemblages help us understand why the megafauna died out in the Americas while persisting in Africa. We show Pleistocene and modern assemblages share similar network topology, but differences in richness and body size distributions made Pleistocene communities significantly more vulnerable to the effects of human arrival. The structural changes promoted by humans in Pleistocene networks would have increased the likelihood of unstable dynamics, which may favour extinction cascades in communities facing extrinsic perturbations. Our findings suggest that the basic aspects of the organization of ecological communities may have played an important role in major extinction events in the past. Knowledge of community-level properties and their consequences to dynamics may be critical to understand past and future extinctions.

Fine structure of ocelli of the larval black fly Simulium vittatum (Diptera: Simuliidae)

1987 ◽  
Vol 65 (1) ◽  
pp. 142-150 ◽  
Author(s):  
Joyce M. Nyhof ◽  
Susan B. McIver
Keyword(s):  
Fine Structure ◽  
Polarized Light ◽  
Cell Organelles ◽  
Golgi Bodies ◽  
Simulium Vittatum ◽  
Pigment Granules ◽  
Transmission Electron ◽  
Structural Differences ◽  
Numerous Cell ◽  
Retinular Cells

The fine structure of light- and dark-adapted ocelli of last instar larval Simulium vittatum Zetterstedt was described using scanning and transmission electron microscopy. Larvae have six ocelli arranged in groups of three on each side of the head. The larger two ocelli of each group are externally visible as two darkly pigmented eyespots. The third, smaller ocellus lacks pigmentation and, therefore, is not externally visible. Each ocellus has its long axis oriented dorso-ventrally, has 13 retinular cells, and lacks an expanded cuticular lens. Conspicuous rhabdoms occur in the three ocelli. The rhabdoms of the pigmented ocelli are centrally located and enveloped by pigment granules. The microvilli of the rhabdoms are oriented primarily in one plane, an indication of a possible sensitivity to polarized light. The rhabdom of the unpigmented ocellus is eccentrically located and its microvilli are not uniplanar. Each ocellus has numerous cell organelles, including mitochondria, ribosomes, endoplasmic reticulum, and Golgi bodies. Especially conspicuous are membranous figures, which are associated with the nuclei and vary in size and complexity from simple stacks to lamellar whorls. These latter organelles are probably involved in the turnover processes of the rhabdomeric membranes. In light- and dark-adapted ocelli the only structural differences were associated with the microvilli and multivesicular bodies. Differences in location of pigment granules and in size of rhabdomeres and membranous figures were not observed.

scholarly journals Numerical simulation of turbulent flow through Schiller’s wavy pipe

2014 ◽  
Vol 761 ◽  
pp. 241-260 ◽  
Author(s):  
G. Daschiel ◽  
V. Krieger ◽  
J. Jovanović ◽  
A. Delgado
Keyword(s):  
Turbulent Flow ◽  
Structural Changes ◽  
Stokes Equations ◽  
Resistance Coefficient ◽  
Navier Stokes ◽  
Cross Sectional ◽  
Navier Stokes Equations ◽  
Flow Through ◽  
Pressure Resistance ◽  
Almost All

AbstractThe development of incompressible turbulent flow through a pipe of wavy cross-section was studied numerically by direct integration of the Navier–Stokes equations. Simulations were performed at Reynolds numbers of $4.5\times 10^{3}$ and $10^{4}$ based on the hydraulic diameter and the bulk velocity. Results for the pressure resistance coefficient ${\it\lambda}$ were found to be in excellent agreement with experimental data of Schiller (Z. Angew. Math. Mech., vol. 3, 1922, pp. 2–13). Of particular interest is the decrease in ${\it\lambda}$ below the level predicted from the Blasius correlation, which fits almost all experimental results for pipes and ducts of complex cross-sectional geometries. Simulation databases were used to evaluate turbulence anisotropy and provide insights into structural changes of turbulence leading to flow relaminarization. Anisotropy-invariant mapping of turbulence confirmed that suppression of turbulence is due to statistical axisymmetry in the turbulent stresses.

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