Mitosis in Mougeotia sp.

1972 ◽  
Vol 50 (9) ◽  
pp. 1811-1816 ◽  
Author(s):  
Carla W. Bech-Hansen ◽  
Larry C. Fowke
Keyword(s):  
Cell Wall ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Short Distance ◽  
Late Anaphase ◽  
New Information ◽  
Early Anaphase

Combined light and electron microscope observations have provided new information concerning mitosis in Mougeotia. The distribution of microtubules during division suggests that intact wall microtubules moved at preprophase to form the spindle and returned to the cell wall at telophase. During metaphase and early anaphase, chromosomal microtubules were attached to distinct kinetochores; few interzonal microtubules were evident. The subsequent elongation of the spindle at late anaphase was accompanied by the appearance of numerous interzonal microtubules and the loss of the original nuclear envelope. The nucleoli dispersed during prophase and reformed at telophase. The wall septum appeared at prophase but extended only a short distance into the cell by telophase; microtubules were not associated with the developing septum.

scholarly journals The Endoplasmic Reticulum and the Golgi Structures in Maize Root Cells

1959 ◽  
Vol 5 (3) ◽  
pp. 501-506 ◽  
Author(s):  
W. Gordon Whaley ◽  
Hilton H. Mollenhauer ◽  
Joyce E. Kephart
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Wall ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Epoxy Resin ◽  
Maize Root ◽  
Root Tips ◽  
Animal Cells ◽  
Root Cells ◽  
Vesicular Structure

Maize root tips were fixed in potassium permanganate, embedded in epoxy resin, sectioned to show silver interference color, and studied with the electron microscope. All the cells were seen to contain an endoplasmic reticulum and apparently independent Golgi structures. The endoplasmic reticulum is demonstrated as a membrane-bounded, vesicular structure comparable in many aspects to that of several types of animal cells. With the treatment used here the membranes appear smooth surfaced. The endoplasmic reticulum is continuous with the nuclear envelope and, by contact at least, with structures passing through the cell wall. The nuclear envelope is characterized by discontinuities, as previously reported for animal cells. The reticula of adjacent cells seem to be in contact at or through the plasmodesmata. Because of these contacts the endoplasmic reticulum of a given cell appears to be part of an intercellular system. The Golgi structures appear as stacks of platelet-vesicles which apparently may, under certain conditions, produce small vesicles around their edges. Their form changes markedly with development of the cell.

scholarly journals THE RABBIT ZYGOTE

1972 ◽  
Vol 55 (3) ◽  
pp. 533-541 ◽  
Author(s):  
Bela J. Gulyas
Keyword(s):  
Endoplasmic Reticulum ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Smooth Endoplasmic Reticulum ◽  
Annulate Lamellae ◽  
Nuclear Pores ◽  
Late Anaphase ◽  
Dense Nucleus

The formation of the blastomere nucleus was examined in the rabbit zygote with the electron microscope. In late anaphase the chromosomes are bare and vesicles of the smooth endoplasmic reticulum are numerous in the vicinity of the chromosomes. In early telophase individual chromosomes attain their own nuclear envelope and they are called karyomeres. The envelope of the karyomeres contains small gaps within it at several places where the chromatin is exposed to the cytoplasm. Nuclear pores are also observed. In the cytoplasm short annulate lamellae appear adjacent to the karyomeres, and clusters of punctate substance are also present. From early telophase onward the karyomeres extend pseudopod-like structures, called karyopods, which extend toward other karyomeres or karyopods, and consequently fuse together and serve as chromosomal bridges. Eventually all of the karyomeres fuse into a dense nucleus and decondensation of the chromosomes occurs.

scholarly journals Mitosis in Barbulanympha. II. Dynamics of a two-stage anaphase, nuclear morphogenesis, and cytokinesis

1978 ◽  
Vol 77 (3) ◽  
pp. 655-684 ◽  
Author(s):  
S Inoué ◽  
H Ritter
Keyword(s):  
Nuclear Envelope ◽  
Morphological Change ◽  
Two Dimensional ◽  
Chromosome Movement ◽  
Central Spindle ◽  
Daughter Cells ◽  
Late Anaphase ◽  
Early Anaphase ◽  
Length Width ◽  
Anaphase B

Anaphase in Barbulanympha proceeds in two discrete steps. In anaphase-A, chromosomal spindle fibers shorten and chromosomes move to the stationary centrosomes. In anaphase-B, the central spindle elongates and ("telophasic") bouquets of chromosomes, with kinetochores still connected by the shortened chromosomal fibers to the centrosomes, are moved far apart. The length, width, and birefringence of the central spindle remain unchanged throughout anaphase-A. In anaphase-B, the central spindle elongates up to fivefold. During elongation, the peripheral fibers of the central spindle splay, first anteriorly and then laterally. The remaining central spindle progressively becomes thinner and the retardation decreases; however, the coefficient of birefringence stays approximately constant. The nuclear envelope persists throughout mitosis in Barbulanympha and the nucleus undergoes an intricate morphological change. In prophase, the nucleus engulfs the spindle; in early anaphase-A, the nuclear envelope forms a seam anterior to the spindle, the nucleus thus transforms into a complete sleeve surrounding the central spindle. In late anaphase-A, the middle of the seam opens up in a cleft as the lips part; in anaphase-B, the cleft expands posteriorly, progressively exposing the central spindle. Finally, the cleft partitions the nucleus into two. The nuclear envelope shows an apparent elasticity and two-dimensional fluidity. Localized, transient deformations of the nuclear envelope indicate poleward and counter-poleward forces acting on the kinetochores embedded in the envelope. These forces appear responsible for nuclear morphogenesis as well as anaphase chromosome movement. At the end of anaphase-B, the two rostrate Barbulanympha may swim apart of be poked apart into two daughter cells by another organism cohabiting the host's hindgut.

Freeze-Fracture Replication in the Ultrastructure of Blue-Green Algae

1967 ◽  
Vol 25 ◽  
pp. 74-75
Author(s):  
L. V. Leak
Keyword(s):  
Cell Wall ◽  
Electron Microscope ◽  
Green Algae ◽  
Three Dimensional ◽  
Freeze Fracture ◽  
Electron Microscopic ◽  
Photosynthetic Membranes ◽  
Blue Green Algae ◽  
Cell Biol ◽  
Cellular Components

Electron microscopic observations of freeze-fracture replicas of Anabaena cells obtained by the procedures described by Bullivant and Ames (J. Cell Biol., 1966) indicate that the frozen cells are fractured in many different planes. This fracturing or cleaving along various planes allows one to gain a three dimensional relation of the cellular components as a result of such a manipulation. When replicas that are obtained by the freeze-fracture method are observed in the electron microscope, cross fractures of the cell wall and membranes that comprise the photosynthetic lamellae are apparent as demonstrated in Figures 1 & 2.A large portion of the Anabaena cell is composed of undulating layers of cytoplasm that are bounded by unit membranes that comprise the photosynthetic membranes. The adjoining layers of cytoplasm are closely apposed to each other to form the photosynthetic lamellae. Occassionally the adjacent layers of cytoplasm are separated by an interspace that may vary in widths of up to several 100 mu to form intralamellar vesicles.

Sites of Adsorption of the Bacteriophages T3 and T5 on the Wall of Escherichia Coli B.

1967 ◽  
Vol 25 ◽  
pp. 96-97
Author(s):  
Manfred E. Bayer
Keyword(s):  
Escherichia Coli ◽  
Cell Wall ◽  
Electron Microscope ◽  
Uranyl Acetate ◽  
E Coli ◽  
Receptor Sites ◽  
Rigid Cell Wall ◽  
Host Cell Surface ◽  
Bacterial Viruses ◽  
Escherichia Coli B

Bacterial viruses adsorb specifically to receptors on the host cell surface. Although the chemical composition of some of the cell wall receptors for bacteriophages of the T-series has been described and the number of receptor sites has been estimated to be 150 to 300 per E. coli cell, the localization of the sites on the bacterial wall has been unknown.When logarithmically growing cells of E. coli are transferred into a medium containing 20% sucrose, the cells plasmolize: the protoplast shrinks and becomes separated from the somewhat rigid cell wall. When these cells are fixed in 8% Formaldehyde, post-fixed in OsO4/uranyl acetate, embedded in Vestopal W, then cut in an ultramicrotome and observed with the electron microscope, the separation of protoplast and wall becomes clearly visible, (Fig. 1, 2). At a number of locations however, the protoplasmic membrane adheres to the wall even under the considerable pull of the shrinking protoplast. Thus numerous connecting bridges are maintained between protoplast and cell wall. Estimations of the total number of such wall/membrane associations yield a number of about 300 per cell.

Modern TEM systems architecture

1986 ◽  
Vol 44 ◽  
pp. 602-605
Author(s):  
U. Gross ◽  
P. Hagemann
Keyword(s):  
Electron Microscope ◽  
Information Gathering ◽  
Systems Architecture ◽  
Control Functions ◽  
Transmission Electron ◽  
New Information ◽  
Comprehensive Information ◽  
Scanning Transmission ◽  
Diffraction Patterns ◽  
Analytical Equipment

By addition of analytical equipment, scanning transmission accessories and data processing equipment the basic transmission electron microscope (TEM) has evolved into a comprehensive information gathering system. This extension has led to increased complexity of the instrument as compared with the straightforward imaging microscope, since in general new information capacity has required the addition of new control hardware. The increased operational complexity is reflected in a proliferation of knobs and buttons.In the conventional electron microscope design the operating panel of the instrument has distinct control elements to alter optical conditions of the microscope column in different modes. As a consequence a multiplicity of control functions has been inevitable. Examples of this are the three pairs of focus and magnification controls needed for TEM imaging, diffraction patterns, and STEM images.

Prefertilization ovule development in Capsella: the dyad, tetrad, developing megaspore, and two-nucleate gametophyte

1986 ◽  
Vol 64 (4) ◽  
pp. 875-884 ◽  
Author(s):  
Patricia Schulz ◽  
William A. Jensen
Keyword(s):  
Cell Wall ◽  
Electron Microscope ◽  
Acid Phosphatase ◽  
De Novo ◽  
Periodic Acid ◽  
Aniline Blue ◽  
Ovule Development ◽  
Periodic Acid Schiff ◽  
Fluorescent Material ◽  
Autophagic Vacuoles

Ovules of Capsella bursa-pastoris at the dyad and tetrad stages of meiosis and at the megaspore and two-nucleate stages of the gametophyte were studied with the electron microscope. The cells of the dyad and tetrad are separated by aniline blue fluorescent cross walls and receive all types of organelles and autophagic vacuoles that were present in the meiocyte. Autophagic vacuoles enclose ribosomes and organelles and show reaction product for acid phosphatase. Autophagic vacuoles and some plastids are absorbed into the enlarging vacuoles of the growing megaspore. Other plastids appear to survive meiosis and there is no evidence for their de novo origin. Some mitochondria appear to degenerate in the enlarging megaspore but others look healthy and there is no evidence for the de novo origin of mitochondria. The nucleolus of the developing megaspore becomes very large and the cytoplasm is extremely dense with ribosomes. The cell wall is thickened by an electron-translucent, periodic acid – Schiff negative, aniline blue fluorescent material and contains plasmodesmata that link the megaspore with the nucellus. The plasmalemma of the growing megaspore produces microvilluslike extensions into this wall that disappear with the formation of the two-nucleate gametophyte. Plasmodesmata disappear from the cell wall at the four-nucleate stage.

Electron microscopy of the replicative events of A25 bacteriophages in group A streptococci

1972 ◽  
Vol 18 (1) ◽  
pp. 93-96 ◽  
Author(s):  
S. E. Read ◽  
R. W. Reed
Keyword(s):  
Electron Microscopy ◽  
Cell Wall ◽  
Electron Microscope ◽  
Nucleic Acid ◽  
Group A Streptococcus ◽  
Group A Streptococci ◽  
Virulent Phage ◽  
Acid Pool ◽  
Group A ◽  
A Cell

The replicative events of a virulent phage (A25) infection of a group A Streptococcus (T253) were studied using the electron microscope. The first intracellular evidence of phage replication in a cell occurred 30 min after infection with arrest of cell division and increase in the nucleic acid pool. Phage heads were evident in the nucleic acid pool of the cells 45 min after infection. Release of phages occurred by splitting of the cell wall along discrete lines. This appeared to be at sites of active wall synthesis, i.e., near the region of septum formation. Many phage components were released but relatively few complete phages indicating a relatively inefficient replicative system.

The Structure of Sycamore Callus Cells During Division in a Partially Synchronized Suspension Culture

1970 ◽  
Vol 6 (2) ◽  
pp. 299-321
Author(s):  
K. ROBERTS ◽  
D. H. NORTHCOTE
Keyword(s):  
Cell Wall ◽  
Electron Microscope ◽  
Cell Plate ◽  
Optical Microscope ◽  
The Other ◽  
Active Movement ◽  
Developmental Sequence ◽  
Golgi Bodies ◽  
Dividing Cells ◽  
Peripheral Cytoplasm

Sycamore suspension callus cells have been partially synchronized to give a culture with a mitotic index of 15%. Living dividing cells of the culture have been examined with Nomarski differential interference optics and a comparable study made on fixed cells with the electron microscope. An organized band of reticulate cytoplasm partially encircles the nucleus at mitosis. The cell divides by the formation of a phragmosome which grows across the large vacuole; this allows the organization of the cytoplasm which forms the cell plate to be examined separately from the more general cytoplasm of the cell. The cell plate grows from one side of the cell to the other and down its length a complete developmental sequence can be seen. The Golgi bodies and the endoplasmic reticulum are probably involved in the formation of material for the construction of the cell plate and young cell wall. Microfibrils are formed within the plate in the more mature regions, while material contained within vesicles is incorporated at the young growing edge. At the edge of the plate microtubules are found and these correspond to the fibrillar appearance of the phragmoplast seen with the optical microscope. In the living cell an active movement of organelles along the peripheral cytoplasm can be seen and with fixed cells viewed with the electron microscope microtubules are often found adjacent to the plasmalemma and lying close to mitochondria, crystal-containing bodies and plastids. The appearance of crystal-containing bodies and plastids containing phytoferritin is described.

When rDNA transcription is arrested during mitosis, UBF is still associated with non-condensed rDNA

1997 ◽  
Vol 110 (19) ◽  
pp. 2429-2440 ◽  
Author(s):  
J. Gebrane-Younes ◽  
N. Fomproix ◽  
D. Hernandez-Verdun
Keyword(s):  
Secondary Constriction ◽  
Three Dimensional ◽  
Ribosomal Gene ◽  
Rdna Transcription ◽  
Transcription Machinery ◽  
Late Anaphase ◽  
Early Anaphase ◽  
Dimensional Distribution ◽  
Open Question ◽  
Kinetics Of

The mechanisms that control inactivation of ribosomal gene (rDNA) transcription during mitosis is still an open question. To investigate this fundamental question, the precise timing of mitotic arrest was established. In PtK1 cells, rDNA transcription was still active in prophase, stopped in prometaphase until early anaphase, and activated in late anaphase. Because rDNA transcription can still occur in prophase and late anaphase chromosomes, the kinetics of rDNA condensation during mitosis was questioned. The conformation of the rDNA was analyzed by electron microscopy from the G2/M transition to late anaphase in the secondary constriction, the chromosome regions where the rDNAs are clustered. Whether at transcribing or non-transcribing stages, non-condensed rDNA was observed in addition to axial condensed rDNA. Thus, the persistence of this non-condensed rDNA during inactive transcription argues in favor of the fact that mitotic inactivation is not the consequence of rDNA condensation. Analysis of the three-dimensional distribution of the rDNA transcription factor, UBF, revealed that it was similar at each stage of mitosis in the secondary constriction. In addition, the colocalization of UBF with non-condensed rDNA was demonstrated. This is the first visual evidence of the association of UBF with non-condensed rDNA. As we previously reported that the rDNA transcription machinery remained assembled during mitosis, the colocalization of rDNA fibers with UBF argues in favor of the association of the transcription machinery with certain rDNA copies even in the absence of transcription. If this hypothesis is correct, it can be assumed that condensation of rDNA as well as dissociation of the transcription machinery from rDNA cannot explain the arrest of rDNA transcription during mitosis. It is proposed that modifications of the transcription machinery occurring in prometaphase could explain the arrest of transcription, while reverse modifications in late anaphase could explain activation.

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