Divisions cellulaires au niveau de l'épiderme de l'hypocotyle du lin (Linum usitatissimum) cultivé in vitro

1985 ◽  
Vol 63 (10) ◽  
pp. 1691-1695 ◽  
Author(s):  
M. Sqalli ◽  
H. Chlyah
Keyword(s):  
Cell Division ◽  
Culture Cell ◽  
Epidermal Cells ◽  
Isolated Cells ◽  
Initiation And Propagation ◽  
A Cell ◽  
The Mean ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

A study of the initiation and propagation of cell divisions in the epidermis of flax hypocotyl segments cultured in vitro was made using surface observations (light and scanning electron microscopes) as well as transverse and longitudinal sections. Epidermal cells were of two types: long, narrow cells and short, wide cells. The latter, less numerous, rarely participated in cell division. Nuclear activation and the first mitoses appeared very early (after 4–8 h of culture). Cell division began in isolated cells and spread progressively to surrounding cells arranged transversely. At 24 h, approximately 50 cells in division or newly divided were observed on an epidermal strip of 10 × 2 mm composed of about 8000 original cells. At 48 h, about 110 cells had divided forming 22 division centers; 26 prophase, 10 metaphase, and 7 telophase figures were observed. The mean number of original cells which participated in the formation of a cell division center was three at 12 h, five at 72 h, with no increase thereafter. The percentage of cells in mitosis or already divided remained low (1.9%) in relation to the total number of epidermal cells. For 22 division centers, only 7 would participate in vegetative bud formation.

scholarly journals Seed morphology and histology of some Paronychia taxa (Caryophyllaceae) from Turkey

1970 ◽  
Vol 38 (2) ◽  
pp. 171-176 ◽  
Author(s):  
Ayse Kaplan ◽  
Hatice Çölgeçen ◽  
H Nurhan Büyükkartal
Keyword(s):  
Key Words ◽  
Seed Morphology ◽  
Epidermal Cells ◽  
Surface Structures ◽  
Dichotomous Key ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

Seed morphology and histology of 12 taxa (nine species, two subspecies, one variety) of Paronychia Miller (Caryophyllaceae) by light and scanning electron microscopes revealed that seeds are laterally compressed, reniform, and hilums are linear. Testa surface structures are alveolate-scalariform, colliculate, reticulate-alveolate, rugose and ruminate. Differences in cuticle and papillae properties of epidermal cells have been observed. A dichotomous key has been developed for Paronychia agryloba Stapf, P. angorensis Chaudri, P. arabica (L.) DC. subsp. euphratica Chaudri, P. carica Chaudri, P. cataonica Chaudri, P. condensata Chaudri, P. davisii Chaudri, P. dudleyi Chaudri, P. galatica Chaudri, P. kurdica Boiss subsp. kurdica var. kurdica, P. kurdica Boiss subsp. montis-munzur Chaudri and P. mughlaei Chaudri.   Key words: Paronychia; Caryophyllaceae; Seed morphology; Seed histology; Turkey DOI: 10.3329/bjb.v38i2.5142 Bangladesh J. Bot. 38(2): 171-176, 2009 (December)  

scholarly journals VARIABILITY OF THE SHAPE AND ARGENTAFFINITY OF THE GRANULES IN THE ENTEROENDOCRINE CELLS OF THE MOUSE DUODENUM

1974 ◽  
Vol 22 (10) ◽  
pp. 929-944 ◽  
Author(s):  
DAVID B. NICHOLS ◽  
HAZEL CHENG ◽  
C. P. LEBLOND
Keyword(s):  
Electron Microscope ◽  
Silver Nitrate ◽  
Wide Spectrum ◽  
Uranyl Acetate ◽  
Enteroendocrine Cells ◽  
Lead Citrate ◽  
A Cell ◽  
The Mean ◽  
Electron Microscopes ◽  
Ammoniacal Silver

The enteroendocrine cells of the mouse duodenum were examined in the light and electron microscopes by comparing Epon sections stained by Gomori's silver methenamine with adjacent sections stained by Masson's ammoniacal silver nitrate, iron hematoxylin or uranyl acetate and lead citrate. Furthermore, the granules present in the enteroendocrine cells stained with silver methenamine were investigated in the electron microscope: their shape was defined as either spherical or nonspherical and, in either case, their density was measured by cytophotometry. The comparison of adjacent sections of mouse duodenum by different techniques indicates that the granules of all enteroendocrine cells are stained by iron hematoxylin, whereas those of about 94% of the cells are stained by silver methenamine. Since silver methenamine stains exactly the same cells as ammoniacal silver nitrate, it may be used as a test of argentaffinity. It is concluded that about 94% of the enteroendocrine cells are argentaffin and about 6% are nonargentaffin. The argentaffin cells display a wide spectrum of granule shape. Nearly all of the granules of a cell may be spherical or nearly all nonspherical or, more commonly, there is a fair number of both kinds. In the few cells which are not argentaffin, over 70% of the granules are spherical. After silver methenamine staining, the mean density of spherical and nonspherical granules is statistically equal within any given cell. Yet, when cells are compared to one another, the mean density of the granules, and therefore the argentaffinity, increases with the proportion of nonspherical granules. It is concluded that, in the mouse duodenun, argentaffinity is most pronounced in the cells with irregular nonspherical granules, but it is by no means confined to such cells. Moreover, the argentaffinity as well as the shape of the granules varies within wide limits.

scholarly journals Probing the Catalytic Activity of a Cell Division-Specific Transpeptidase In Vivo with β-Lactams

2003 ◽  
Vol 185 (13) ◽  
pp. 3726-3734 ◽  
Author(s):  
Christian Eberhardt ◽  
Lars Kuerschner ◽  
David S. Weiss
Keyword(s):  
Catalytic Activity ◽  
Cell Division ◽  
Penicillin Binding Protein ◽  
In Vitro System ◽  
New Findings ◽  
Peptidoglycan Cell Wall ◽  
Dividing Cells ◽  
A Cell

ABSTRACT Penicillin-binding protein 3 (PBP3; also called FtsI) is a transpeptidase that catalyzes cross-linking of the peptidoglycan cell wall in the division septum of Escherichia coli. To determine whether the catalytic activity of PBP3 is activated during division, we assayed acylation of PBP3 with three β-lactams (cephalexin, aztreonam, and piperacillin) in growing cells. Acylation of PBP3 with cephalexin, but not aztreonam or piperacillin, appeared to be stimulated by cell division. Specifically, cephalexin acylated PBP3 about 50% faster in a population of dividing cells than in a population of filamentous cells in which division was inhibited by inactivation or depletion of FtsZ, FtsA, FtsQ, FtsW, or FtsN. However, in a simpler in vitro system using isolated membranes, acylation with cephalexin was not impaired by depletion of FtsW or FtsN. A conflicting previous report that the ftsA3(Ts) allele interferes with acylation of PBP3 was found to be due to the presence of a thermolabile PBP3 in the strain used in that study. The new findings presented here are discussed in light of the hypothesis that the catalytic activity of PBP3 is stimulated by interaction(s) with other division proteins. We suggest that there might be allosteric activation of substrate binding.

scholarly journals Efficacy of Hospital Cleaning Agents and Germicides Against EpidemicClostridium difficileStrains

2007 ◽  
Vol 28 (8) ◽  
pp. 920-925 ◽  
Author(s):  
Warren N. Fawley ◽  
Sarah Underwood ◽  
Jane Freeman ◽  
Simon D. Baines ◽  
Katie Saxton ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
Spore Form ◽  
Cleaning Agent ◽  
Cleaning Agents ◽  
A Cell ◽  
The Mean ◽  
Sporulation Rate ◽  
Hospital Cleaning

Objective.To compare the effects of hospital cleaning agents and germicides on the survival of epidemicClostridium difficilestrains.Methods.We compared the activity of and effects of exposure to 5 cleaning agents and/or germicides (3 containing chlorine, 1 containing only detergent, and 1 containing hydrogen peroxide) on vegetative and spore forms of epidemic and non-epidemicC. difficilestrains (3 of each). We carried out in vitro exposure experiments using a human fecal emulsion to mimic conditions found in situ.Results.Cleaning agent and germicide exposure experiments yielded very different results forC. difficilevegetative cells, compared with those for spores. Working-strength concentrations of all of the agents inhibited the growth ofC. difficilein culture. However, when used at recommended working concentrations, only chlorine-based germicides were able to inactivateC. difficilespores.C. difficileepidemic strains had a greater sporulation rate than nonepidemic strains. The mean sporulation rate, expressed as the proportion of a cell population that is in spore form, was 13% for all strains not exposed to any cleaning agent or germicide, and it was significantly increased by exposure to cleaning agents or germicides containing detergent alone (34%), a combination of detergent and hypochlorite (24%), or hydrogen peroxide (33%). By contrast, the mean sporulation rate did not change substantially after exposure to germicides containing either a combination of detergent and dichloroisocyanurate (9%) or dichloroisocyanurate alone (15%).Conclusions.These results highlight differences in the activity of cleaning agents and germicides againstC. difficilespores and the potential for some of these products to promote sporulation.

Imaging the Probe Skirt in the Environmental SEM

2000 ◽  
Vol 6 (S2) ◽  
pp. 794-795
Author(s):  
B.L. Thiel ◽  
I.C. Bache ◽  
P. Smith
Keyword(s):  
Mean Free Path ◽  
High Energy ◽  
Large Area ◽  
Resolution Imaging ◽  
The Mean ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Primary Electrons ◽  
Environmental Sem ◽  
Better Than

In low vacuum scanning electron microscopes, the primary beam is partially scattered by the gas present in the specimen chamber. The development of these microscopes, in particular the so-called ‘Environmental’ SEM, was initiated when it was realized that this scattering does not necessarily compromise the imaging capabilities of the instrument. Indeed, some modern commercial instruments are capable of better than 2 nanometer resolution at gas pressures of several torr. The accepted explanation for this is as follows: The mean-free-path of the high energy primary electrons is several millimeters in one torr of water vapour (for example). Because the actual pathlength of electrons travelling through the gas is only a few millimeters, most of them do not scatter at all. Those that do scatter are supposedly distributed over a relatively large area. Thus, the probe features a high-intensity central region surrounded by a slowly decaying low-intensity skirt. High resolution imaging is possible because the signal-to-(skirt)background ratio is high.

The growth and behaviour in vitro of isolated plant cells

1955 ◽  
Vol 144 (914) ◽  
pp. 86-93 ◽  
Keyword(s):  
Plant Cells ◽  
Individual Plant ◽  
Isolated Cells ◽  
Mineral Salts ◽  
Cortical Cells ◽  
Differentiated Cells ◽  
A Cell ◽  
Cambial Cells ◽  
Vacuolated Cells

Individual plant cells from tissue cultures of carrot, sunflower crown and Parthenocissus were cultured in nutrient solutions containing sucrose and mineral salts supplemented with IAA and coconut milk. The vacuolated cells which could be isolated in this way were studied by phase-contrast microscopy. Both cyclosis and massive movements of the nucleus and cytoplasm were observed. Though these isolated cells frequently grew in size they were not observed to divide. The capacity for cell division was found to reside only in the cambial cells which, in the original tissue culture, formed spherical layers generating tracheids towards the interior and large cortical cells towards the exterior. Small numbers of such cambial cells would proliferate in the medium used. The smallest group of such cells which gave rise to a cell colony contained ten to fifteen cells. The cell colonies produced maintained the spherical cambial structure of the tissues from which they were derived. They continued to grow for as long as four months and gave rise to numerous secondary colonies all of which followed the same pattern of growth. It was not found possible to develop true cell cultures by any of the techniques employed. Even when very few cambial cells were transferred the structure obtained was always an organized tissue with formed elements generated by a spherical cambium. The differentiated cells were not observed to divide but showed active cyclosis for as long as 4 months.

scholarly journals Persistent Mycobacterium tuberculosis infection in mice requires PerM for successful cell division

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Ruojun Wang ◽  
Kaj Kreutzfeldt ◽  
Helene Botella ◽  
Julien Vaubourgeix ◽  
Dirk Schnappinger ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Cell Division ◽  
Acute Infection ◽  
Chronic Phase ◽  
Integral Membrane Protein ◽  
Cell Replication ◽  
Mycobacterium Tuberculosis Infection ◽  
A Cell ◽  
Underlying Mechanisms

The ability of Mycobacterium tuberculosis (Mtb) to persist in its host is central to the pathogenesis of tuberculosis, yet the underlying mechanisms remain incompletely defined. PerM, an integral membrane protein, is required for persistence of Mtb in mice. Here, we show that perM deletion caused a cell division defect specifically during the chronic phase of mouse infection, but did not affect Mtb’s cell replication during acute infection. We further demonstrate that PerM is required for cell division in chronically infected mice and in vitro under host-relevant stresses because it is part of the mycobacterial divisome and stabilizes the essential divisome protein FtsB. These data highlight the importance of sustained cell division for Mtb persistence, define condition-specific requirements for cell division and reveal that survival of Mtb during chronic infection depends on a persistence divisome.

scholarly journals Disassembly and degradation of MinD oscillator complexes by Escherichia coli ClpXP

2020 ◽  
Author(s):  
Christopher J. LaBreck ◽  
Catherine E. Trebino ◽  
Colby N. Ferreira ◽  
Josiah J. Morrison ◽  
Eric C. DiBiasio ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Division ◽  
Linear Polymers ◽  
Atp Binding Site ◽  
Ftsz Ring ◽  
Degradation Reactions ◽  
A Cell ◽  
The Mind

AbstractMinD is a cell division ATPase in Escherichia coli that oscillates from pole to pole and regulates the spatial position of the cell division machinery. Together with MinC and MinE, the Min system restricts assembly of the FtsZ-ring to midcell, oscillating between the opposite ends of the cell and preventing FtsZ-ring misassembly at the poles. Here, we show that the ATP-dependent bacterial proteasome complex ClpXP degrades MinD in reconstituted degradation reactions in vitro, through direct recognition of the MinD N-terminal region, and in vivo. MinD degradation is enhanced during stationary phase, suggesting that ClpXP regulates levels of MinD in cells that are not actively dividing. MinC and MinD are known to co-assemble into linear polymers, therefore we monitored copolymers assembled in vitro after incubation with ClpXP and observed that ClpXP promotes rapid MinCD copolymer disassembly as a result of direct MinD degradation by ClpXP. The N-terminus of MinD, including residue Arg 3, which is near the ATP-binding site, is critical for degradation by ClpXP. Together, these results demonstrate that ClpXP degradation modifies conformational assemblies of MinD in vitro and depresses Min function in vivo during periods of reduced proliferation.

scholarly journals Role of the Murein Precursor UDP-N-Acetylmuramyl-l-Ala-γ-d-Glu- meso-Diaminopimelic Acid-d-Ala-d-Ala in Repression of β-Lactamase Induction in Cell Division Mutants

2002 ◽  
Vol 184 (15) ◽  
pp. 4233-4239 ◽  
Author(s):  
Tsuyoshi Uehara ◽  
James T. Park
Keyword(s):  
Cell Wall ◽  
Cell Division ◽  
High Ratio ◽  
Diaminopimelic Acid ◽  
Breakdown Product ◽  
A Cell ◽  
Cell Wall Breakdown ◽  
Ts Mutant

ABSTRACT Certain β-lactam antibiotics induce the chromosomal ampC β-lactamase of many gram-negative bacteria. The natural inducer, though not yet unequivocally identified, is a cell wall breakdown product which enters the cell via the AmpG permease component of the murein recycling pathway. Surprisingly, it has been reported that β-lactamase is not induced by cefoxitin in the absence of FtsZ, which is required for cell division, or in the absence of penicillin-binding protein 2 (PBP2), which is required for cell elongation. Since these results remain unexplained, we examined an ftsZ mutant and other cell division mutants (ftsA, ftsQ, and ftsI) and a PBP2 mutant for induction of β-lactamase. In all mutants, β-lactamase was not induced by cefoxitin, which confirms the initial reports. The murein precursor, UDP-N-acetylmuramyl-l-Ala-γ-d-Glu-meso-diaminopimelic acid-d-Ala-d-Ala (UDP-MurNAc-pentapeptide), has been shown to serve as a corepressor with AmpR to repress β-lactamase expression in vitro. Our results suggest that β-lactamase is not induced because the fts mutants contain a greatly increased amount of corepressor which the inducer cannot displace. In the PBP2(Ts) mutant, in addition to accumulation of corepressor, cell wall turnover and recycling were greatly reduced so that little or no inducer was available. Hence, in both cases, a high ratio of repressor to inducer presumably prevents induction.

Development of cell arrangement in ostracod carapaces

Paleobiology ◽  
1981 ◽  
Vol 7 (2) ◽  
pp. 276-280 ◽  
Author(s):  
Yutaka Okada
Keyword(s):  
Epidermal Cell ◽  
Epidermal Cells ◽  
Ontogenetic Development ◽  
Gene Control ◽  
Ontogenetic Changes ◽  
Cell Arrangement ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

The correlation between epidermal cells and cuticular reticulation was clearly shown by transmission and scanning electron microscopes with larval ostracods just before ecdysis. Comparison of the reticulation patterns of Recent and Pleistocene specimens revealed that the epidermal cell arrangement of the adult ostracods is both consistent in the Recent population and conservative in phylogeny. Ontogenetic changes of the reticulation pattern were studied with specimens cultivated separately. Some gene control over the mitosis of epidermal cells was assumed, based on the ontogenetic development of the reticulation pattern. The pattern of fossil specimens suggests that the control has been well maintained in ostracod phylogeny.

Sign in / Sign up

Export Citation Format

Share Document