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.

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.

Genetic load and biological changes to extant humans

2020 ◽  
pp. 1-4
Author(s):  
Arthur Saniotis ◽  
Maciej Henneberg ◽  
Kazhaleh Mohammadi
Keyword(s):  
Natural Selection ◽  
Current Knowledge ◽  
Genetic Load ◽  
Differential Fertility ◽  
Medical Interventions ◽  
Deleterious Alleles ◽  
Gradual Process ◽  
Genetic Complexity ◽  
Sexual Recombination ◽  
Improved Sanitation

Abstract Extant humans are currently increasing their genetic load, which is informing present and future human microevolution. This has been a gradual process that has been rising over the last centuries as a consequence of improved sanitation, nutritional improvements, advancements in microbiology and medical interventions, which have relaxed natural selection. Moreover, a reduction in infant and child mortality and changing societal attitudes towards fertility have led to a decrease in total fertility rates (TFRs) since the 19th century. Generally speaking, decreases in differential fertility and mortality have meant that there is less opportunity for natural selection to eliminate deleterious mutations from the human gene pool. It has been argued that the average human may carry ~250–300 mutations that are mostly deleterious, as well as several hundred less-deleterious variants. These deleterious alleles in extant humans mean that our fitness is being constrained. While such alleles are viewed as reducing human fitness, they may also have had an adaptive function in the past, such as assisting in genetic complexity, sexual recombination and diploidy. Saying this, our current knowledge on these fitness compromising alleles is still lacking.

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.

scholarly journals Modulation of Ca2+ efflux from heart mitochondria

1979 ◽  
Vol 178 (3) ◽  
pp. 673-680 ◽  
Author(s):  
E J Harris
Keyword(s):  
Electron Microscope ◽  
Rat Heart ◽  
Time Lag ◽  
Nucleotide Binding ◽  
Ruthenium Red ◽  
Heart Mitochondria ◽  
Condensed State ◽  
Active Uptake ◽  
Rat Heart Mitochondria ◽  
Bongkrekic Acid

The efflux of Ca2+ from rat heart mitochondria has been examined by using Ruthenium Red to inhibit active uptake after predetermined loadings with Ca2+. The efflux is proportional to the internal Ca2+ load; it is increased by Na+ applied when the mitochondria are respiring and this effect is inhibited by oligomycin. The efflux of Ca2+ is diminished by ATP and by ADP, with the latter the more effective. Both active uptake and efflux of Ca2+ are slowed by bongkrekic acid; this action has a time lag. The lower efflux found with the nucleotides and with bongkrekic acid seems to correspond to the more condensed state seen in the electron microscope when these agents are applied [Stoner & Sirak (1973) J. Cell Biol. 56, 51-64, 65-73]. The results are discussed in relation to the less-permeable state being contingent upon nucleotide binding to the membrane.

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.

scholarly journals Learning Stypes of Male and Female Students of Nepal

2018 ◽  
Vol 4 (1) ◽  
pp. 67-81
Author(s):  
Amrit Kumar Rai ◽  
Megha Raj Dhakal
Keyword(s):  
Learning Environment ◽  
Learning Styles ◽  
Learning Style ◽  
Private School ◽  
General Concept ◽  
Female Students ◽  
Primary Data ◽  
Public And Private ◽  
Male And Female ◽  
Gradual Process

Learning is natural phenomena starts with the birth; it is a gradual process of investigation of new knowledge. Every creature has their own learning styles as their biological and social nature. People have superior power to learn many things as they become interested. School is one platform to learn many things for the students. School creates the learning environment but learning style may be varied in student to student. The study aims to identify the learning styles of male and female students of public and private school of Nepal. Primary data were collected from Makwanpur, Chitwan, Gorkha and Dhading Districts among Chepang Community. The study is done among the 368 students of four districts. The three types of learning styles: Visual, Auditory, and Kinesthetic (VAK) model developed by Neil Fleming was used in field for data collection. The result shows that there is no significant different between male and female students regarding their learning styles. It indicates that achievement and performance of male and female is similar. In Nepalese society, there are some gender differences in social relationship. Still, in most of the society, daughters are given less priority for their growth and development because of the patriarchal concept of society but the study has given the different result than the general concept. It is shown that a daughter can give better result if she will get better learning environment. The result has challenged the discriminatory gender relation in society.

Electron Microscopy of Sprouting Seeds

1968 ◽  
Vol 26 ◽  
pp. 88-89
Author(s):  
R. F. W. Pease ◽  
T. L. Hayes
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Survival Rate ◽  
Scanning Electron Microscope ◽  
Allium Cepa ◽  
Water Loss ◽  
Raphanus Sativus ◽  
Control Sample ◽  
Scanning Electron

The examination of living insects in the scanning electron microscope (SEM) was reported in 1966. We now report the examination of living botanical specimens in the SEM. The specimens were the seeds of white sprouting onion (Allium cepa) and of the radish (Raphanus sativus) during the week following germination. The seeds were mounted initially using flour and water and later using a cement (“Elmer's Glue All”). In all cases the natural conductance of the seeds was sufficient to prevent undue charging. 12 onion seeds were examined within three days of placing in moist tissue and again on the three successive days (Figures 1 and 2). The survival rate (5 out of 12) was not significantly lower than in the control sample (about 50% of a large number), however the growth did appear to be retarded and this may have been due to the microscope environment. One notable exception was one seed which was accidentally immersed in the cement with only the sprout uncovered; it is possible that such immersion retarded water loss to the vacuum. The cement subsequently dissolved away as the sprouting seed developed in moist tissue.

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