The Ultrastructure and Ontogeny of Pollen in Helleborus Foetidus L

1968 ◽  
Vol 3 (2) ◽  
pp. 175-186
Author(s):  
P. ECHLIN ◽  
H. GODWIN
Keyword(s):  
Cell Membrane ◽  
Outer Part ◽  
Cell Plate ◽  
Thick Wall ◽  
Fibrous Layer ◽  
Helleborus Foetidus ◽  
Plate Area ◽  
The Individual ◽  
Mother Cells ◽  
Exine Patterning

During the early stages of microsporocyte ontogeny in Helleborus foetidus L. there is protoplasmic continuity between the cells of the tapetum and between the individual sporogenous cells, but not between the two tissues. The plasma canals and plasmodesmata are progressively sealed off by the deposition of thick callose walls, so that by the first meiotic division, each pollen mother cell is isolated from its neighbours and from the surrounding tapetum. Callose is formed by dictyosomes in the individual pollen mother cells. The four meiocytes are separated by the deposition and coalescence of masses of callose forming in the cell plate area. The exine pattern is initiated at the surface of the young microspores while they are still invested with a thick wall of callose. Periclinally arranged endoplasmic reticulum lying just below the microspore cell membrane corresponds with the position of the furrows. The cell membrane in the interfurrow region thickens and becomes highly convoluted. A fibrous layer appears between the outer part of the convolutions and the callose, and locally it becomes less electron-dense at places that become filled with material of moderate electron density corresponding to the probacula; these in turn will become the bacula of the mature exine. In spite of an extensive examination of material prepared by a variety of techniques, no organelle or cytoplasmic component may be consistently associated with the positioning of the first signs of exine patterning.

scholarly journals Studies on human red-cell membrane glycophorin A and glycophorin B genes in glycophorin-deficient individuals

1989 ◽  
Vol 263 (3) ◽  
pp. 993-996 ◽  
Author(s):  
C G Tate ◽  
M J A Tanner ◽  
P A Judson ◽  
D J Anstee
Keyword(s):  
Cell Membrane ◽  
Genomic Dna ◽  
Southern Blot Analysis ◽  
Glycophorin A ◽  
Red Cell ◽  
Red Cell Membrane ◽  
Single Deletion ◽  
The Individual ◽  
Glycophorin B ◽  
Human Red Cell Membrane

1. Genomic DNA derived from individuals who lack glycophorin A (GPA), glycophorin B (GPB) or both of these proteins was subjected to Southern-blot analysis using GPA and GPB cDNA probes. 2. Bands on the Southern blots were assigned to the GPA gene, GPB gene or to a putative pseudogene. 3. Genomic DNA derived from an individual of the Mk phenotype was shown to have deletions in the GPA and GPB genes. The simplest model for the results obtained is that a single deletion spans the GPA and GPB genes in the individual studied.

Comparative effects of phalloidin and cytochalasin B on motility and morphogenesis in Allium

1980 ◽  
Vol 58 (7) ◽  
pp. 773-785 ◽  
Author(s):  
Barry A. Palevitz
Keyword(s):  
Cytochalasin B ◽  
Cell Plate ◽  
Wall Thickening ◽  
Animal Cells ◽  
Host Fungus ◽  
Guard Mother Cells ◽  
Mother Cells ◽  
Chromosome Motion

Cytochalasin B (CB), thought to disaggregate F-actin in animal cells, and phalloidin (Phal), known to stabilize F-actin in vivo and in vitro, have nearly identical effects on cotyledon epidermal cells of Allium cepa. Both drugs rapidly induce cessation of streaming and both, by preventing normal telophase reorientation movement, lead to abnormal division planes in dividing guard mother cells. Neither, however, prevents normal microtubule deposition, wall thickening, and cellulose orientation during guard cell differentiation. Furthermore, both drugs have no effect on spindle formation and anaphase chromosome motion. Examination of Nitella and Chara cells, in which streaming had been stopped by either agent, shows that microfilament cables are still present. With both drugs, the minimum effective concentrations were routinely used (CB, 2 μM; Phal, 100–200 μM). Our results are discussed in terms of the mode of action of these drugs and their possible role in host-fungus interactions. Implications for the mechanisms underlying cell plate alignment, cellulose orientation, and cytoplasmic streaming are discussed.

scholarly journals Revealing capture sites and movements by strontium isotope analyses in bones of Caiman yacare in the Beni river floodplain, Bolivia

2021 ◽  
Author(s):  
Marc Pouilly ◽  
Sergio Gomez ◽  
Christophe Pecheyrann ◽  
Sylvain Berail ◽  
Gustavo Alvarez ◽  
...  
Keyword(s):  
Isotopic Ratio ◽  
Outer Part ◽  
High Fidelity ◽  
River Floodplain ◽  
Individual Life ◽  
Isotopic Variation ◽  
Or Groups ◽  
The Individual ◽  
First Time ◽  
Isotope Analyses

Studying the distribution of organisms and their movements is fundamental to understand population dynamics. Most studies indicated that crocodilians do not move around much but several studies demonstrated that some species showed movement patterns. Detection of these movements along the individual life is still a challenge. In this study we analyzed the variation of strontium isotopic ratio (87Sr/86Sr) in the femur bones of 70 Caiman yacare individuals caught in 16 sites located in five hydrological sectors of the Beni river floodplain in Bolivia. Our results demonstrated for the first time that such a methodology could yield indications about the capture sites and reconstruct individual life history. Analyses of the outer part of the femur of 70 individuals showed that capture sites could be differentiated between sectors and even between sites or groups of sites in each sector. Studies of complete 87Sr/86Sr profiles along the femur, representing entire life of the individual, were performed on 33 yacares. We found that most of the individuals did not show any significant isotopic variation throughout their lives. This absence of variation could result from a high fidelity to the birth site, and/or from an insignificant isotopic variation between the water bodies through which the animal has potentially moved. However, 24% of the analyzed individuals presented significant variations that can be considered as movements between different habitats. Based on the observed low proportion of moving yacares, we advocated that each water body should be considered an individual management unit.

A Feasibility Study for Imaging Tissue Electroporation With Electrical Impedance Tomography

2002 ◽  
Author(s):  
Rafael V. Davalos ◽  
David M. Otten ◽  
Lluis M. Mir ◽  
Boris Rubinsky
Keyword(s):  
Cell Membrane ◽  
Electrical Impedance ◽  
Individual Cell ◽  
Pulse Number ◽  
Impedance Tomography ◽  
Tissue Electroporation ◽  
Electrical Pulses ◽  
Number Frequency ◽  
The Individual ◽  
Voltage Gradients

In tissue electroporation, electrodes are inserted around the targeted tissue and electrical pulses are applied to permeabilize the cell membrane to macromolecules such as gene constructs in genetic engineering or cancer treatment drugs [1, 2]. For a specific set of voltage parameters (e.g. pulse number, frequency, duration), the effect that the electric field has depends on the voltage gradients that develop across the individual cell [2].

scholarly journals “Three-Bullets” Loaded Mesoporous Silica Nanoparticles for Combined Photo/Chemotherapy

Nanomaterials ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 823 ◽  
Author(s):  
André Luiz Tessaro ◽  
Aurore Fraix ◽  
Ana Claudia Pedrozo da Silva ◽  
Elena Gazzano ◽  
Chiara Riganti ◽  
...  
Keyword(s):  
Mesoporous Silica ◽  
Silica Nanoparticles ◽  
Mesoporous Silica Nanoparticles ◽  
Outer Part ◽  
Green Light ◽  
Biological Evaluation ◽  
Light Sources ◽  
Good Tolerability ◽  
Physiological Conditions ◽  
The Individual

This contribution reports the design, preparation, photophysical and photochemical characterization, as well as a preliminary biological evaluation of mesoporous silica nanoparticles (MSNs) covalently integrating a nitric oxide (NO) photodonor (NOPD) and a singlet oxygen (1O2) photosensitizer (PS) and encapsulating the anticancer doxorubicin (DOX) in a noncovalent fashion. These MSNs bind the NOPD mainly in their inner part and the PS in their outer part in order to judiciously exploit the different diffusion radius of the cytotoxic NO and 1O2. Furthermore this silica nanoconstruct has been devised in such a way to permit the selective excitation of the NOPD and the PS with light sources of different energy in the visible window. We demonstrate that the individual photochemical performances of the photoactive components of the MSNs are not mutually affected, and remain unaltered even in the presence of DOX. As a result, the complete nanoconstruct is able to deliver NO and 1O2 under blue and green light, respectively, and to release DOX under physiological conditions. Preliminary biological results performed using A375 cancer cells show a good tolerability of the functionalized MSNs in the dark and a potentiated activity of DOX upon irradiation, due to the effect of the NO photoreleased.

Anther and Ovule Development in Tasmannia (Winteraceae)

1992 ◽  
Vol 40 (6) ◽  
pp. 877 ◽  
Author(s):  
N Prakash ◽  
AL Lim ◽  
FB Sampson
Keyword(s):  
Mother Cell ◽  
Female Gametophyte ◽  
Cell Plate ◽  
Basic Type ◽  
Ovule Development ◽  
Linear Tetrad ◽  
Polygonum Type ◽  
Secretory Type ◽  
Mother Cells ◽  
Female Gametophyte Development

Three species of Tasmannia R.Br. ex DC., T. glaucifolia, T. insipida and T. stipitata are studied. The anther is tetrasporangiate and its waU development conforms to the Basic type. The tapetum follows the secretory type of development. Cytokinesis in the microspore mother cells is simultaneous but an evanescent cell plate is present at telophase I and anaphase I1 during meiosis. Pollen tetrads are permanent and tetrahedral. The mature pollen is anaulcerate, reticulate and 2-celled. The ovule. is anatropous, bitegmic and crassinucellate. The micropyle in T. stipitata and T. Glaucifolia is formed by the inner integument only whereas in T. insipida it is formed by both the integuments and is zigzag in outline. Meiosis in the single megaspore mother cell produces a linear or T-shaped megaspore tetrad in T. stipitata and T. glaucifolia but only a linear tetrad in T. insipida. Female gametophyte development is of the monosporic Polygonum type. Fertilisation is porogamous; triple fusion and syngamy occur simultaneously.

Studies on the formation of ‘floating’ guard cell mother cells in Anemia

1986 ◽  
Vol 80 (1) ◽  
pp. 29-55
Author(s):  
B. Galatis ◽  
P. Apostolakos ◽  
D. Palafoutas
Keyword(s):  
Guard Cell ◽  
Intercellular Space ◽  
Cortical Microtubule ◽  
Cell Plate ◽  
Cell Polarization ◽  
Periclinal Wall ◽  
Wall Area ◽  
Cortical Zone ◽  
Neighbouring Region ◽  
Mother Cells

The protodermal cells producing the ‘floating’ guard cell mother cells (GMCs) in three Anemia species undergo an extraordinary polarization and an unexpected shaping. During interphase an intercellular space is initiated at the internal proximal end of the cell, while the polar region bulges outwards. At this stage a microtubule girdle traverses the cortical cytoplasm underneath the rims of the external periclinal wall curvature. In addition, another system of microtubules converges on a cortical site adjoining the wall delimiting the intercellular space and, or, the neighbouring region of the internal periclinal wall (internal polar cortical site, IPCS). Vacuoles are found in all regions of the cell except for that between the centrally located nucleus and the intercellular space. As the cell approaches mitosis, the growing vacuolar system retreats from the cytoplasmic region below the external periclinal wall curvature. In most cells the polarized cytoplasm forms an inclined truncated cone, the bases of which abut on the external periclinal wall curvature and the wall lining the IPCS. The organization of the cortical microtubule cytoskeleton does not change significantly during preprophase-prophase. A preprophase microtubule band (PMB) is localized in the cortex lining the rims of the external periclinal wall curvature, while some microtubules traverse the IPCS and the cytoplasm adjacent to the neighbouring wall regions. The mitotic spindle axis is diagonal, while the cell plate separating the GMCs exhibits an unusual mode of growth. It gradually encircles the proximal daughter nucleus, becoming funnel-shaped. One of its periclinal edges fuses with the external periclinal wall area lined by the PMB cortical zone and the other with the internal periclinal wall area adjoining the IPCS. The latter region seems to behave like the PMB cortical zone. The results show that the morphogenetic mechanism underlying the formation of the conical GMCs includes a series of highly integrated processes, initiated or carried out during cell polarization.

On the differential divisions and preprophase microtubule bands involved in the development of stomata of Vigna sinensis L

1979 ◽  
Vol 37 (1) ◽  
pp. 11-37
Author(s):  
B. Galatis ◽  
K. Mitrakos
Keyword(s):  
Cell Polarity ◽  
Cell Plate ◽  
Equatorial Position ◽  
Anticlinal Wall ◽  
Vigna Sinensis ◽  
Daughter Cells ◽  
Preprophase Microtubule Band ◽  
Dicotyledonous Plants ◽  
Mother Cells ◽  
Dictyosome Vesicles

The manifestation of premitotic cell polarity and the resultant structural asymmetry of the differential divisions participating in the development of stomata of Vigna sinensis vary considerably. However, two morphologically distinct types of differential division were distinguished: (a) ‘asymmetrical differential divisions’, in which the premitotic polarization of the cell, the eccentric position of the nucleus during division and the differences in size and organization of the daughter cells are obvious; and (b) differential divisions in which the above features are inconspicuous or almost absent. The former occur in the ordinary protodermal cells, the latter in some meristemoids. The organization of a sharply demarcated preprophase microtubule band (PMB) precedes, all differential and non-differential divisions. In the first type of differential division the PMB is formed eccentrically, while in the second it may display either an approximately symmetrical or a clearly asymmetrical disposition, always indicating with surprising accuracy the sites where the succeeding cell plate will join the parent walls. The PMB foreshadowing the highly curved cell plates in meristemoids I of the mesoperigenous process, as well as in meristemoids I and II of the mesogenous one, are apposed only on one anticlinal wall and therefore do not encircle the nucleus or traverse the cell. In the symmetrical divisions of guard cell mother cells (GMC), as well as in those of protodermal cells, the PMB runs right round the internal plasmalemma surface in an equatorial position, coinciding with that of the future cell plate. In the former cells the wall abutting the cortical cytoplasm traversed by the band becomes locally thickened. The variability in the pattern of the microtubules of the band along the walls of the GMC is directly mirrored in the pattern of the thickening. It seems that in GMC the PMB mediates a directed exocytosis of dictyosome vesicles. In contrast to what is now generally accepted in dicotyledonous plants, each meristemoid I of both the mesogenous and mesoperigenous stomata in Vigna sinensis leaves does not inhibit but induces the formation of other meristemoids close to it.

An investigation of the fatigue life of typical aircraft gas turbine compressor discs

1966 ◽  
Vol 1 (2) ◽  
pp. 121-132 ◽  
Author(s):  
M. J. Owen ◽  
B. R. Dudley
Keyword(s):  
Gas Turbine ◽  
Testing Machine ◽  
Outer Part ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Maximum Speed ◽  
Sufficient Magnitude ◽  
Run Up ◽  
The Individual ◽  
High Level

The numerous discs which are incorporated in gas turbine rotors are subjected to high level stresses at full engine speed. Each time the engine is operated and run up to maximum speed one cycle of stress is applied to each disc. In the course of time there exists the possibility of a fatigue failure. The life of a component cannot be predicted accurately from the properties of laboratory specimens of the material because of the more complicated stress pattern and the number of manufacturing variables which affect the fatigue properties. A special testing machine was built to subject compressor discs to cyclic loading at the blade fastenings whilst the disc remained stationary. Stress distributions for a typical disc were calculated for rotating and non-rotating conditions. Strain gauges were used to measure the stresses under the non-rotating conditions of the testing machine. Comparisons of theoretical and experimental results were made. It was concluded that by applying loads of sufficient magnitude at the rim it was possible to produce stresses at the bore of the same magnitude as those produced under rotating conditions and that the method of loading produced a reasonable simulation of the stress distribution in the central part of the disc. Under non-rotating conditions with these high loads the tangential stresses in the outer part of the disc were about 30 per cent higher and the radial stresses about 60 per cent higher than under rotating conditions. It was found necessary to make modifications to the discs for the fatigue tests. When loaded through the standard pinhole blade fastening, the discs failed from the pinholes because of the increased nominal stress in the rim and the high local load. By cutting off most of the rim and using grips instead of the standard pin fastening it was possible to obtain failures in the diaphragm of the discs. Although the individual discs failed in different modes with fractures arising from several sources the lives of all the discs tested lay between 34 000 and 130 000 cycles. These lives were satisfactory compared with service requirements. Typical aircraft engines accumulate from 1000 to 4000 flight cycles per year according to service conditions.

Distribution of Membranes and the Cytoskeleton During Cell Plate Formation in Pollen Mother Cells of Tradescantia

1991 ◽  
Vol 100 (4) ◽  
pp. 717-728 ◽  
Author(s):  
CHRISTEL R. SCHOPFER ◽  
PETER K. HEPLER
Keyword(s):  
Laser Scanning ◽  
Polarized Light ◽  
Cell Plate ◽  
Confocal Laser Scanning Microscope ◽  
Temporal Organization ◽  
Ion Concentration ◽  
Confocal Laser ◽  
Surface Binding ◽  
Pollen Mother Cells ◽  
Mother Cells

The cellular pattern and distribution of membranes have been analyzed during cytokinesis in pollen mother cells of Tradescantia and compared with those of actin microfilaments (MFs) and microtubules (MTs). Membranes have been stained with DiOC6(3) and MFs with rhodamine-labeled phalloidin (RP); analysis has been carried out on the confocal laser scanning microscope. MTs have been visualized as birefringent elements in the polarized light microscope. The results show that when the interzone first appears in mid anaphase it contains an even distribution of membranes. However, by late anaphase these elements have been cleared away, leaving the interzone largely devoid of DiOC6(3)-positive material. MTs are found throughout this zone, while MFs appear in two non-overlapping sets on both sides of the cell equator. Thereafter membrane elements reappear in the interzone, but only along the equatorial line of the forming cell plate. Presumably these equatorial elements are composed of endoplasmic reticulum and Golgi vesicles, since the larger organelles, including amyloplasts and mitochondria, are excluded from the phragmoplast. MFs, like MTs, arrange preferentially normal to the cell plate, forming a dense array on both sides, but being absent from the zone occupied by the membranes. By contrast, the parallel set of MTs, while excluding larger organelles from the phragmoplast, intermingle with the membrane elements in the cell equator. As cytokinesis proceeds membranes continue to concentrate on the cell plate as indicated by its marked increase in staining with DiOC6(3). From a consideration of spatial and temporal organization of the phragmoplast components it is reasonable to suggest that both cytoskeletal components participate in the aggregation of vesicles that give rise to the cell plate. Membranes, on the other hand, through the provision of surface binding sites and/or through the regulation of the cytoplasmic calcium ion concentration, might be involved in the assembly and stabilization of the cytoskeleton.

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