The fine structure of fertilization in the fern Marsilea vestita

1978 ◽  
Vol 30 (1) ◽  
pp. 265-281
Author(s):  
D.G. Myles
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Plasma Membranes ◽  
Multilayered Structure ◽  
Thick Wall ◽  
Clear Space ◽  
Marsilea Vestita ◽  
Sperm Plasma Membrane ◽  
Sperm Penetration

The ultrastructural details of fertilization in the fern Marsilea vestita, including gamete approach and fusion, the fate of the spermatozoid organelles and the development of a possible block to polyspermy are described. The spermatozoid approaches the egg through layers of mucilage that surround the megaspores. It moves down the neck of the archegonium into the cavity above the egg. In order to reach the egg, it must move through a small hole in the thick wall that lies across the top of the egg. The fusion of the plasma membranes of the gametes results in an outflow of egg cytoplasm into the clear space under the sperm plasma membrane, creating a fertilization cone. All the organelles of the fertilizing spermatozoid, including nucleus, mitochondrion, microtubule ribbon, multilayered structure, and flagellar band, with approximately 150 flagella, enter the egg cytoplasm. The nucleus enters as a condensed rod of chromatin with no nuclear envelope. The chromatin begins to disperse immediately and a new nuclear envelope is formed around the chromatin by egg endoplasmic reticulum. The mitochondrion and the microtubules of the ribbon and flagella are broken down, but the fates of the flagellar band and the multilayered structure have not been determined. After spermatozoid penetration, a new extracellular layer appears above the surface of the egg, beginning in the region of sperm penetration and spreading across the top of the egg. This layer may be important in preventing other spermatozoids from fusing with the egg.

An ultrastructural study of the spermatozoid of the fern, Marsilea vestita

1975 ◽  
Vol 17 (3) ◽  
pp. 633-645
Author(s):  
D.G. Myles
Keyword(s):  
Nuclear Envelope ◽  
Ultrastructural Study ◽  
Spiral Structure ◽  
Multilayered Structure ◽  
Condensed Chromatin ◽  
Posterior Region ◽  
Cytoplasmic Vesicle ◽  
Marsilea Vestita ◽  
Shaped Cell ◽  
Dense Band

The ultrastructure of the mature spermatozoid of Marsilea vestita was studied after its release from the microspore and prior to its penetration of the egg. The psermatozoid is a pear-shaped cell with a complex spiral structure coiled around the edge in the narrow anterior end. This coil is composed of a large mitochondrion, elongated nucleus with highly condensed chromatin, a ribbon of microtubules, and a dense band of material (flagellated band) into which the flagella are inserted. There are over a hundred flagella protruding from each spermatozoid along the length of the coil. At the anterior tip of the coil is a short multilayered structure. It is not known what maintains the helical shape of the coil. The microtubular ribbon could be involved, but it is also possible that either the flagellated band, the condensed chromatin, or both, are sufficiently rigid to retain their shpaes unaided. When the spermatozoid is first released from the microspore it includes a cytoplasmic vesicle in the posterior region containing plastids, mitochondria, and other organelles. This vesicle is shed, taking the nuclear envelope with it, before the spermatozoid reaches the egg.

scholarly journals OBSERVATIONS ON THE DEVELOPMENT OF ERYTHROCYTES IN MAMMALIAN FETAL LIVER

1962 ◽  
Vol 14 (2) ◽  
pp. 235-254 ◽  
Author(s):  
Joseph A. Grasso ◽  
Hewson Swift ◽  
G. Adolph Ackerman
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Cell Size ◽  
Marked Decrease ◽  
Fetal Liver ◽  
Hepatic Parenchyma ◽  
Hemoglobin Synthesis ◽  
Hepatic Cells ◽  
Eventual Loss

The fine structure of the erythrocyte during development in rabbit and human fetal liver has been studied. A morphologic description of representative erythropoietic cells and their relationship to the hepatic parenchyma is presented. Erythrocyte development was accompanied by a decrease in nuclear and cell size, fragmentation and eventual loss of nucleoli, and progressive clumping of chromatin at the nuclear margin. Mitochondria, endoplasmic reticulum, and Golgi elements decreased in size or abundance and eventually disappeared. Ribosome concentration initially increased, but subsequently diminished as the cytoplasm increased in electron opacity, probably through the accumulation of hemoglobin. Similar dense material, interpreted to be hemoglobin, infiltrated the nuclear annuli and, in some cases, appeared to extend into the interchromatin regions. There was a marked decrease in the number of annuli of the nuclear envelope. Possible relationships between nucleus and cytoplasm and of RNA to hemoglobin synthesis are discussed. In rabbits, erythroid and hepatic cells were separated by a 200 to 400 A space limited by the undulatory membranes of the respective cells. Membranes of adjacent erythropoietic cells were parallel and more closely apposed (100 to 200 A). In humans, relationship between various cells exhibited wide variation. Ferritin particles were observed within forming and formed "rhopheocytotic" vesicles.

scholarly journals The Fine Structure of the Rod-Bipolar Cell Synapse in the Retina of the Albino Rat

1958 ◽  
Vol 4 (4) ◽  
pp. 459-466 ◽  
Author(s):  
Aaron J. Ladman
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Fine Structure ◽  
Bipolar Cell ◽  
Plasma Membranes ◽  
Lower Pole ◽  
Albino Rat ◽  
Cytoplasmic Vesicles ◽  
Thin Lamella ◽  
Cell Synapse

The fine structure of the rod-bipolar synapse is described and illustrated. Each rod spherule possesses a large, single, oval or elongate mitochondrion approximately 0.5 x 2.0 microns. Surrounding the mitochondrion are elements of agranular endoplasmic reticulum. The bipolar dendrite projects into the lower pole of the spherule and usually terminates in two lobes separated by a cleft. The plasma membranes appear dense and thicker in the region of the synapse. In the rod spherule cytoplasm, contiguous with the plasma membrane is a dense, slightly concave arciform structure, the rod arciform density, extending from the base of the bipolar bifid process through the cleft to an equivalent point on the opposite side. Also within the spherule, and external (towards the sclera) to the rod arciform density, is a parallel, dense, thin lamella, the rod synaptic lamella. This is approximately 25 mµ in thickness and 400 mµ in width at its widest extent. This halfmoon-shaped plate straddles the cleft between the two lobes of the bipolar process. The lamella appears to consist of short regular rodlets or cylinders 5 to 7 mµ in diameter, oriented with their long axes perpendicular to the plane of the lamella. Minute cytoplasmic vesicles found in the cytoplasm of both the rod spherule and the bipolar terminal are most abundant near the rod synaptic lamella.

scholarly journals FINE STRUCTURE AND ORGANELLE ASSOCIATIONS IN BROWN ALGAE

1965 ◽  
Vol 26 (2) ◽  
pp. 523-537 ◽  
Author(s):  
G. Benjamin Bouck
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Golgi Apparatus ◽  
Nuclear Envelope ◽  
Brown Algae ◽  
Algal Cell ◽  
Plant Cells ◽  
Membrane Systems ◽  
Two Envelopes

The structural interrelationships among several membrane systems in the cells of brown algae have been examined by electron microscopy. In the brown algae the chloroplasts are surrounded by two envelopes, the outer of which in some cases is continuous with the nuclear envelope. The pyrenoid, when present, protrudes from the chloroplast, is also surrounded by the two chloroplast envelopes, and, in addition, is capped by a third dilated envelope or "pyrenoid sac." The regular apposition of the membranes around the pyrenoid contrasts with their looser appearance over the remainder of the chloroplast. The Golgi apparatus is closely associated with the nuclear envelope in all brown algae examined, but in the Fucales this association may extend to portions of the cytoplasmic endoplasmic reticulum as well. Evidence is presented for the derivation of vesicles, characteristic of those found in the formative region of the Golgi apparatus, from portions of the underlying nuclear envelope. The possibility that a structural channeling system for carbohydrate reserves and secretory precursors may be present in brown algae is considered. Other features of the brown algal cell, such as crystal-containing bodies, the variety of darkly staining vacuoles, centrioles, and mitochondria, are examined briefly, and compared with similar structures in other plant cells.

scholarly journals OBSERVATIONS ON SPERM PENETRATION IN THE RAT

1961 ◽  
Vol 10 (2) ◽  
pp. 275-283 ◽  
Author(s):  
Daniel G. Szollosi ◽  
Hans Ris
Keyword(s):  
Plasma Membrane ◽  
Cross Sections ◽  
Plasma Membranes ◽  
Previous Night ◽  
Egg Membrane ◽  
Sperm Plasma Membrane ◽  
Sperm Penetration ◽  
Sperm Midpiece ◽  
New Hypothesis ◽  
Structural Aspects

The structural aspects of sperm penetration in the rat egg were investigated by electron microscopy. Eggs were recovered at intervals between 8 and 10:30 A.M. from females which had mated during the previous night. The oviducts were flushed with hyaluronidase and the eggs transferred into a 2 per cent osmium tetroxide solution, buffered at pH 7.8. After fixation, the eggs were mounted individually in agar, dehydrated in ethyl alcohol, and embedded in butyl-methyl methacrylate (3:1). The sperm penetrating the egg is covered by a plasma membrane which is present only on the side facing toward the zona pellucida; no membrane is visible on the side facing toward the vitellus. The sperm plasma membrane becomes continuous with the egg plasma membrane and forms a deep fold around the entering sperm. Cross-sections through the sperm midpiece in the perivitelline space show an intact plasma membrane. At the place of entrance, the plasma membrane of the sperm appears to fuse with the egg plasma membrane. After the sperm has penetrated the vitellus, it has no plasma membrane at all. The nuclear membrane is also absent. These observations suggest a new hypothesis for sperm penetration. After the sperm has come to lie on the plasma membrane of the egg, the egg and sperm plasma membranes rupture and then fuse with one another to form a continuous cell membrane over the egg and the outer surface of the sperm. As a result the sperm comes to lie inside the vitellus, leaving its own plasma membrane incorporated into the egg membrane at the surface of the egg.

scholarly journals Submicroscopic Organization of Retinal Cones of the Rabbit

1958 ◽  
Vol 4 (6) ◽  
pp. 743-746 ◽  
Author(s):  
Eduardo De Robertis ◽  
Arnaldo Lasansky
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Chemical Composition ◽  
Outer Segment ◽  
Distal Portion ◽  
Cone Cell ◽  
Specific Chemical ◽  
General Plan ◽  
Clear Space ◽  
And Function

The fine structure of the cone cell of the rabbit is described and compared wtih that of the rod. The cone outer segment consists of a pile of flattened sacs with two membranes 30 A thick and a regular clear space in between of about 30 A. The membrane of the rod sacs is slightly thicker (∼40 A) and the clear space is less regular and frequently absent in the deeper regions. The distance between sacs is from 85 to 95 A in the cone and from 110 to 120 A in the rod, and the total repeating period is about 190 A and 210 A, respectively. These results are discussed in relation to the concentration of solids in both photoreceptors. A connecting cilium was observed in the cone cell and compared with that previously described in rods (4). This finding suggests that morphogenetically the cone may also result of the differentiation of a primitive cilium (5). The inner segment of the cone shows a distal portion with large concentration of elongated mitochondria and a proximal one with a large Golgi complex in the axis surrounded by components of the endoplasmic reticulum. It is concluded that both photoreceptors have a similar general plan of submicroscopic organization, with some minor difference in fine structure probably related to their specific chemical composition and function.

scholarly journals UNE FORME MICROTUBULAIRE ET PARACRISTALLINE DE RETICULUM ENDOPLASMIQUE DANS LES PHOTOCYTES DES ANNELIDES POLYNOINÆ

1966 ◽  
Vol 31 (1) ◽  
pp. 135-158 ◽  
Author(s):  
J. M. Bassot
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Contact Surface ◽  
Special Kind ◽  
The Other ◽  
Cytoplasmic Organelle ◽  
Specialized Form

Luminous cells of polynoid worm elytra have been examined by methods of electron microscopy, with special attention focused on the fine structure of photogenic grains. These cells send apical prolongations into the mid-part of the elytra. The plasma membrane is very sinuous, and a special kind of desmosome links two portions of the same membrane. In addition to all the organelles which can be found in nonluminescent epithelial cells of the elytra, numerous photogenic grains are contained in their cytoplasm. These grains are composed of undulating microtubules measuring 200 A in diameter; their disposition in the grain is highly regular, and the grains appear as paracrystals. At the borders of the grains, the walls of the microtubules are often in continuity with those of the endoplasmic reticulum and with the external membrane of the nuclear envelope. Because of this fact, the microtubules of the grains may be considered a cytoplasmic organelle, representing a specialized form of the endoplasmic reticulum. The microtubules permit the repartition, inside and outside their walls, of two different products, one being forty-three times more abundant than the other; thus, the contact surface, in comparison to the volume, is greatly increased. The induction of the luminous reaction by change in the permeability of the microtubule walls, allowing contact between the two substances, is suggested as a working hypothesis. There is an evolution of the grains along the axis of the photocytes. The grains are often surrounded by progressively increasing amounts of glycogen. Their paracrystalline disposition is altered at the apex of the luminous cells.

Fine Structure of the Cytoplasm in Salivary Glands of Simulium

1967 ◽  
Vol 2 (1) ◽  
pp. 137-144
Author(s):  
H. C. MACGREGOR ◽  
J. B. MACKIE
Keyword(s):  
Endoplasmic Reticulum ◽  
Fine Structure ◽  
Nuclear Envelope ◽  
Salivary Glands ◽  
Rough Endoplasmic Reticulum ◽  
Salivary Secretion ◽  
Septate Junction ◽  
Cell Junctions ◽  
Salivary Gland Cell ◽  
Apical Cytoplasm

The salivary glands of 3rd or 4th instar larvae of Simulium niditifrons are about 5 mm long and up to 400 µ wide. They have a capacious lumen which is normally filled with secretion. The apical (luminal) plasmalemma of the gland cells is thrown into numerous microvilli. The basal plasmalemma is usually straight but is infolded in places. The infoldings may be complex near to cell junctions. There is a thick, uniform basement membrane. Contact surfaces of adjacent cells often interdigitate. A septate junction extends inwards from the lumen for one-quarter the depth of the cells. Rough endoplasmic reticulum is distributed evenly throughout the cytoplasm. Many Golgi complexes with dark membrane-bounded granules are scattered throughout the cytoplasm. Solitary granules, often more than I µ in diameter, lie in the apical cytoplasm, especially near the apical border of the cell. These granules resemble the larger Golgi granules and the contents of the lumen. Solitary granules consisting of 2 components have been seen in various stages of passage through the cell membrane. The 2 components are present in roughly constant proportions and can be identified in the larger Golgi granules and in the secretion in the lumen. The nucleus is spherical. The nuclear envelope is smooth in the larger cells of a gland but may be folded in the smaller cells. There are 80-100 pores/µ2 of nuclear envelope. Each pore appears to have a small granule at its centre. Microtubules, about 180 Å thick, are numerous in the apical cytoplasm, particularly near the luminal border. Tubules which lie deep in the cytoplasm are flanked by a clear area 100-200 Å wide. The fine structure of a salivary gland cell of Simulium appears to indicate that the major components of the salivary secretion are synthesized in association with the ribosomes on the rough endoplasmic reticulum, concentrated in the Golgi regions, formed into secretion granules, and passed out of the cell into the lumen of the gland by reverse phagocytosis.

scholarly journals Intracellular labeling with ferritin conjugates. A specificity problem due to the affinity of unconjugated ferritin for selected intracellular sites.

1979 ◽  
Vol 27 (7) ◽  
pp. 1095-1102 ◽  
Author(s):  
E L Parr
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Nuclear Envelope ◽  
Phosphate Buffer ◽  
Plasma Membranes ◽  
Cell Types ◽  
Purification Procedure ◽  
Nonspecific Binding ◽  
Wide Range ◽  
Antibody Conjugates

Nonspecific binding of ferritin to chromatin and the cytoplasmic aspect of the nuclear envelope was observed when nonantigenic, serum-washed hepatocyte nuclei were incubated in ferritin-antibody conjugates. This labeling was duplicated when nuclei from a wide range of species and cell types were exposed to unconjugated ferritin. Unconjugated ferritin binding to nuclei did not depend on a subpopulation of denatured molecules or on the ferritin purification procedure. Binding occurred equally on unfixed and formaldehyde-fixed nuclei, but no ferritin bound to glutaraldehyde-fixed nuclei. Inconjugated ferritin also bound to the cytoplasmic aspects of the rough endoplasmic reticulum and the plasma membrane. The tracer did not bind to lysosomes, mitochondria, Golgi vesicles, the extracellular surface of plasma membranes, or the intracisternal surfaces of ruptured nuclear envelopes. The addition of 0.4 M KCl or 0.7 M NaCl to ferritin solutions and washing media at neutral pH reduced the binding of conjugated and unconjugated ferritin to nuclei to about 3% of that seen in 0.10 M phosphate buffer alone. The added salts caused little extraction of nuclear contents from formaldehyde-fixed nuclei. The use of one of these salts in ferritin conjugates should considerably improve the specificity of intracellular labeling.

A possible structural basis for the extracellular release of acetylcholinesterase

1975 ◽  
Vol 191 (1103) ◽  
pp. 271-283 ◽  
Keyword(s):  
Endoplasmic Reticulum ◽  
Nuclear Envelope ◽  
Chromaffin Cells ◽  
Plasma Membranes ◽  
Cholinesterase Activity ◽  
Smooth Endoplasmic Reticulum ◽  
Splanchnic Nerve ◽  
Ultrastructural Localization ◽  
Acetylcholinesterase Activity ◽  
Structural Basis

The ultrastructural localization of acetylcholinesterase and non-specific cholinesterase activity has been studied in sections of ox adrenal medulla by cytochemical methods. Non-specific cholinesterase activity, identified by using butyrylthiocholine as substrate and ethopropazine as inhibitor, occurs intracellularly in some adrenaline-containing chromaffin cells: the reaction end-product is deposited within the cisternae of the endoplasmic reticulum and in the nuclear envelope. Reaction end-product of non-specific cholinesterase also occurs in the endoplasmic reticulum of pericytes, around sinusoids and capillaries and within smooth muscle cells. Acetylcholinesterase activity, identified by using acetylthiocholine as substrate and BW 284C51 as inhibitor, occurs in both the splanchnic nerve and in chromaffin cells. Reaction end-product is found at the following sites (i) around myelinated and unmyelinated non-terminal axons of splanchnic nerve, between the axolemma and the Schwann cell membrane; (ii) within the cisternae of axonal smooth endoplasmic reticulum; sometimes these cisternae appear to be connected to the axolemma; (iii) between the axolemmas of preterminal axons and the plasma membranes of chromaffin cells; (iv) between the axolemmas of nerve terminals and the plasma membranes of chromaffin cells, including the synaptic cleft; (v) within cisternae of rough and smooth endoplasmic reticulum, and also within the nuclear envelope, of both adrenaline- and noradrenaline-containing chromaffin cells; (vi) between the plasma membranes of adjacent chromaffin cells, but only when one or both of these cells contain reaction product within the cisternae of its endoplasmic reticulum; these cisternae sometimes appear to be connected to the plasma membrane. These observations raise the question whether the acetylcholinesterase activity released from the perfused adrenal gland might originate from the cisternae of the endoplasmic reticula of splanchnic nerve and/or chromaffin cell.

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