An electron-microscope study of the intranucleolar chromatin during nucleologenesis in root meristematic cells of Allium cepa

1975 ◽  
Vol 19 (1) ◽  
pp. 85-101
Author(s):  
L.A. Chouinard
Keyword(s):  
Electron Microscope ◽  
Allium Cepa ◽  
Current Knowledge ◽  
General Concept ◽  
Meandering Channel ◽  
Nucleolar Organizing Region ◽  
Morphological Findings ◽  
Nucleolar Chromosome ◽  
Late Telophase ◽  
Chromatin Material

The various states of condensation of the chromatin material contained inside the lacunar regions of the reforming nucleolus in Allium cepa, have been investigated by means of conventional electron-microscope techniques. The observations reveal that, in the emerging early to late telophase nucleoli, the intralacunar chromatin material in question appears both in an extended and a condensed condition; from late telophase th the mid G1 period of interphase, the intralacunar chromatin material of the rapidly growing and developing nucleoli is present in an extended state only. An attempt is made to interpret these morphological findings in the light of current knowledge concerning the structural relationship of the nucleolar organizing region of the nucleolar chromosome with the interphase nucleolus in plant cells. The relevant observational evidence would be consistent with the view that the chromatin-containing lacunar regions of the reforming nucleolus in Allium cepa correspond, in fact, to cross- or oblique sections of a meandering channel through which the nucleolar organizing segment of the nucleolar chromosome passes. Assuming the applicability to intranucleolar chromatin of the general concept of condensed-inactive versus extended-active chromatin, it is concluded that gradual uncoiling and subsequent decondensation of the chromatin of the nucleolar organizing region in the form of a convoluted loop structure are key morphological and functional events associated with the process of nucleologenesis in the species investigated.

An Electron-Microscope Study of the Intranucleolar Chromatin in Root Meristematic Cells of Allium Cepa

1974 ◽  
Vol 15 (3) ◽  
pp. 645-657
Author(s):  
L. A. CHOUINARD
Keyword(s):  
Electron Microscope ◽  
Allium Cepa ◽  
Current Knowledge ◽  
General Concept ◽  
Condensed Chromatin ◽  
Condensed State ◽  
Interphase Cell ◽  
Gradual Process ◽  
Nucleolar Chromosome ◽  
Chromatin Material

The various states of condensation and configuration of the chromatin material, contained inside the lacunar regions of the interphase nucleolus in Allium cepa, have been investigated by means of conventional electron-microscope techniques. The observations reveal that in a number of lacunar profiles, the chromatin material in question appears in an extended state only; in other lacunar profiles of the same or different nucleoli, the chromatin material is present both in an extended and a condensed condition. Moreover, in some lacunar profiles, a single mass of chromatin in a condensed state is observed; in others, several discrete and often seemingly interconnected masses of condensed chromatin are visualized. An attempt is made to interpret these morphological findings in the light of current knowledge concerning the structural relationship of the nucleolar organizing segment of the nucleolar chromosome with the interphase nucleolus in plant cells. The relevant observational evidence would be consistent with the view that the chromatin-containing lacunar regions of the interphase nucleolus in Allium cepa correspond, in fact, to cross or oblique sections of a meandering channel through which the nucleolar organizing segment of the nucleolar chromosome passes. Assuming the applicability to intranucleolar chromatin of the general concept of condensed-inactive versus extended-active chromatin, it is hypothesized that the various states of condensation of intralacunar chromatin merely reflect variations in the functional activity of the nucleolar organizing segment during the interphase cell cycle in the species investigated. With regard to variations in the configurational state of the intralacunar condensed chromatin, it is postulated that they are the cytological expression of the gradual process of coiling or folding upon itself of the nucleolar organizing segment during late interphase and in preparation for the next mitosis.

Localization of Intranucleolar Dna in Root Meristematic Cells of Allium Cepa

1970 ◽  
Vol 6 (1) ◽  
pp. 73-84
Author(s):  
L. A. CHOUINARD
Keyword(s):  
Electron Microscopy ◽  
Allium Cepa ◽  
Cross Sections ◽  
Light And Electron Microscopy ◽  
Meandering Channel ◽  
Meristematic Cells ◽  
Nucleolar Chromosome ◽  
Root Meristematic Cells

The problem of the localization of intranucleolar DNA in root meristematic cells of Allium cepa has been investigated under both light and electron microscopy following formaldehyde fixation coupled with deoxyribonuclease extraction. The observations reveal that most, if not all, of the intranucleolar DNA is located inside small lacunar spaces confined to the fibrillar regions of the nucleolar mass. These results would be consistent with the view that the DNA-containing lacunar spaces in question correspond, in fact, to cross-sections of a meandering channel containing the extended nucleolar organizing segment of the nucleolar chromosome.

scholarly journals Correlative scanning and transmission electron microscopic study on the ependymal surface of Cebus apella

1986 ◽  
Vol 44 (4) ◽  
pp. 334-340 ◽  
Author(s):  
Cáudio A. Ferraz de Carvalho ◽  
II-Sei Watanabe ◽  
Romeu Rodrigues de Souza
Keyword(s):  
Electron Microscope ◽  
Cebus Apella ◽  
Gold Coating ◽  
Electron Microscopic ◽  
Transmission Electron Microscopic Study ◽  
Morphological Findings ◽  
Transmission Electron ◽  
Critical Point Drying ◽  
Transmission Electron Microscopic ◽  
Brain Ventricular System

Topographical variations of the ependymal surface of the whole brain ventricular system of Cebus apella, a wild Brazilian species, were studied at the scanning electron microscope after C02 critical point drying and carbon-gold coating. Certain selected areas were also studied at the transmission electron microscope, following standard technical procedures. We observed distinct patterns in the distribution of cilia, microvilli, other cell projections, and the so called supraependymal structures. Based on the morphological findings, functional considerations are made.

Oxidation of Manganese-Containing Aluminum Alloys Studied by SEM

2014 ◽  
Vol 794-796 ◽  
pp. 1095-1100
Author(s):  
Shawn C. Wilson ◽  
Anne Kvithyld ◽  
Thorvald Abel Engh ◽  
Gabriella Tranell
Keyword(s):  
Electron Microscope ◽  
Chemical Composition ◽  
Scanning Electron Microscope ◽  
Oxide Film ◽  
Current Knowledge ◽  
Sem Analysis ◽  
Muffle Furnace ◽  
Mn Content ◽  
Small Clusters ◽  
Scanning Electron

During remelting of aluminum manganese-containing alloys, some industrial experience has indicateda tendency toward increased oxidation losses when compared to unalloyed Al. A goal of thiswork is to increase current knowledge of oxidation of Mn-containing aluminum. An oxidation studywas performed on 99.99% Al, Al-1%Mn and Al-5%Mn materials in a muffle furnace in air. Theseoxidized materials were analyzed in the Scanning Electron Microscope using Energy Dispersive xraySpectroscopy (EDS) both for chemical composition and to analyze the structure of the oxide thatwas formed. The main findings from the SEM analysis of the oxidized 99.99% Al, Al1%Mn andAl5%Mn materials are: 1) The oxides formed on the Al1Mn and Al5Mn materials contained onlyminute amounts of Mn. However, small clusters of Mn metal were found among the Al2O3 particleson the surface of the Al1Mn and Al5Mn samples. 2) Dissolved Mn increased from the surface to theinterior, and Mn-rich particles were present in the interior of the Al1Mn and Al5Mn samples. 3) Theoxide layer thickness increases with Mn content, and the oxide film is more fragmented.

Ultrastructural association of the chromatin-containing lacunar spaces with the vacuolar component of the interphase nucleolus in Allium cepa

1982 ◽  
Vol 60 (12) ◽  
pp. 2624-2628 ◽  
Author(s):  
L. A. Chouinard
Keyword(s):  
Granular Material ◽  
Allium Cepa ◽  
Ultrastructural Level ◽  
Observational Evidence ◽  
The Other ◽  
Active Chromatin ◽  
Meristematic Cells ◽  
Fibrillar Material ◽  
Nucleolar Organizing Region ◽  
Root Meristematic Cells

At the ultrastructural level, some of the chromatin-containing lacunar spaces of the interphase nucleolus in root meristematic cells of Allium cepa are seen to be walled off, on one side, by dense-fibrillar material and to be contiguous, on the other side, to electron-transparent areas, of variable sizes and shapes, bordered by dense-granular material continuous with and indistinguishable from the dense-granular component of the nucleolar mass. These electron-transparent areas associated with the lacunar spaces are equated with nucleolar vacuoles since they contain scattered preribosomal-like granules and fibrils and are rimmed by dense-granular material. The relevant observational evidence would be consistent with the view that loops of transcriptionnally active chromatin emanating from the nucleolar organizing region project radially into either only the dense-fibrillar or both the dense-fibrillar and the interior of the electron-transparent vacuolar areas seen to be contiguous to the lacunar spaces in question. In relation to this problem, it is of interest to note that the vacuolar spaces of the interphase nucleolus in Allium cepa occasionally display within their confines discrete masses of fibrillar material, possibly chromatinic in character, and in various states of condensation and configuration.

ELECTRON MICROSCOPE STUDIES OF THE EPIDERMIS OF ALLIUM CEPA

1958 ◽  
Vol 45 (6) ◽  
pp. 449-461 ◽  
Author(s):  
Flora Murray Scott ◽  
Karl C. Hamner ◽  
Elizabeth Baker ◽  
Edwin Bowler
Keyword(s):  
Electron Microscope ◽  
Allium Cepa

scholarly journals Toxicity of meta-Tyrosine

Plants ◽  
2021 ◽  
Vol 10 (12) ◽  
pp. 2800
Author(s):  
Marcin Tyminski ◽  
Katarzyna Ciacka ◽  
Pawel Staszek ◽  
Agnieszka Gniazdowska ◽  
Urszula Krasuska
Keyword(s):  
Oxidative Stress ◽  
Current Knowledge ◽  
Plant Competition ◽  
Harmful Effect ◽  
General Concept ◽  
Elevated Concentration ◽  
Chemical Weapon ◽  
Animal Cells ◽  
Cellular Redox ◽  
Living Organisms

L-Tyrosine (Tyr) is one of the twenty proteinogenic amino acids and also acts as a precursor for secondary metabolites. Tyr is prone to modifications, especially under conditions of cellular redox imbalance. The oxidation of Tyr precursor phenylalanine leads to the formation of Tyr non-proteinogenic isomers, including meta-Tyr (m-Tyr), a marker of oxidative stress. The aim of this review is to summarize the current knowledge on m-Tyr toxicity. The direct m-Tyr mode of action is linked to its incorporation into proteins, resulting in their improper conformation. Furthermore, m-Tyr produced by some plants as an allelochemical impacts the growth and development of neighboring organisms. In plants, the direct harmful effect of m-Tyr is due to its modification of the proteins structure, whereas its indirect action is linked to the disruption of reactive oxygen and nitrogen species metabolism. In humans, the elevated concentration of m-Tyr is characteristic of various diseases and ageing. Indeed, m-Tyr is believed to play an important role in cancer physiology. Thus, since, in animal cells, m-Tyr is formed directly in response to oxidative stress, whereas, in plants, m-Tyr is also synthesized enzymatically and serves as a chemical weapon in plant–plant competition, the general concept of m-Tyr role in living organisms should be specified.

Electron Microscope Observations on DNA and Chromatin Fibres of Hydra Vulgaris and Ephydatia Meyeni

1972 ◽  
Vol 30 ◽  
pp. 198-199
Author(s):  
Anjali Mookerjee
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Fresh Water ◽  
Cell Lysis ◽  
Laboratory Culture ◽  
Hydra Vulgaris ◽  
Chromatin Material ◽  
Protein Monolayer

The present paper reports the observations made on DNA and chromatin material obtained from Hydra vulgaris (raised in laboratory culture) and a fresh water sponge Ephydatia meyeni. Both samples were prepared following Marmur's method, with slight modifications. For the chromatin fibres, samples were used just after the cell lysis stage without any shaking or further purification procedures. The specimens for electron microscopy were prepared by the protein monolayer technique.The diameter of rotary shadowed purified DNA samples from H. vulgaris and E. meyeni was 60-80 A and the length of the Fibres varied between 5-18 /u (Fig. 1), and 5-10/u respectively.

The nucleolus in telophase, interphase and prophase

1980 ◽  
Vol 41 (1) ◽  
pp. 321-329
Author(s):  
M. Ashraf ◽  
M.B. Godward
Keyword(s):  
Electron Microscope ◽  
Green Alga ◽  
Relevant Literature ◽  
Nucleolar Organizer ◽  
Early Prophase ◽  
Condensed Chromosome ◽  
Fibrillar Material ◽  
Nucleolar Organizing Region ◽  
Early Stages ◽  
Late Anaphase

The ultrastructure of telophase to interphase has been followed in a green alga, Spirogyra submargaritata. A series of changes transitional between the late anaphase chromatid, the decondensing chromatid of telophase, and the ‘pale fibrillar material’ occupying channels in the nucleolus at interphase have been demonstrated. Early stages in the regeneration of the nucleolus are described. It has been shown that the pale fibrillar material in the nucleolus is attached to, and continuous with, the fully condensed (chromocentric) part of the nucleolar-organizing chromosome at interphase. It is also shown that in early prophase, the channels in the nucleolonema of the nucleolus are no longer occupied by pale fibrillar material, but instead a long section of condensed chromosome is present, traversing the nucleolonema. It is contended that these observations taken together constitute evidence that the pale fibrillar material of the nucleolus is the chromatin of the nucleolar-organizing region of the chromosome, expanded for transcription. A model of the nucleolus as it is seen in most electron-microscope sections, and as it can be interpreted in the light of present-day knowledge about it, is presented. A brief review of the relevant literature considers the views supporting the mode, and the contrary views, implicating the use of the term ‘nucleolar organizer’, that are still current at the present time.

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