scholarly journals Mitotic Activity during the Early Differentiation of the Scleral Bones in the Chick

1956 ◽  
Vol s3-97 (39) ◽  
pp. 333-353
Author(s):  
L. J. HALE
Keyword(s):  
Cell Division ◽  
Population Density ◽  
Mitotic Activity ◽  
Mitotic Index ◽  
Cell Population ◽  
Early Differentiation ◽  
Cell Divisions ◽  
Do So

The dispositions of mitoses in the mesenchyme beneath the conjunctiva of parts of a 7-, 8-, 9-, and 10-day embryo have been ascertained. For the purpose of analysis, the number of mitoses, cell population density, and mitotic index have been found in small segments of annuli which include parts of the rings of bone primordia, and the mesenchyme between them. Twenty-three primordia were studied. It is found that the cell population density increases from about 4-14 x 105 per cubic mm within the primordia, but only from about 4-9 x 105 in the mesenchyme between them. Mitotic activity increases sharply within young primordia from about 12--27 mitoses per 1,000 cells, and thereafter decreases. It is found that this mitotic activity probably occurs in three waves of decreasing intensity. Between the primordia mitotic activity is at a markedly lower level and probably follows a simpler pattern. The cells involved in this mitotic activity in the primordia are particularly those just beneath the conjunctival papilla, and the number of mitoses decreases the greater the distance from the conjunctiva. In the 8- and 9-day embryos, the number of mitoses is inversely proportional to the distance. Calculation indicates that in each of the three waves of cell division, the cells that divide do so only once; and that this mitotic activity is adequate to account for the increase in cell population density which is found. The cause of the increase in the number of cell divisions in the primordia is not clear, but the result is probably the production of blastemas, the cells of which become the osteoblasts of the scleral bones.

Budding in hydra: the role of cell multiplication and cell movement in bud initiation

Development ◽  
1972 ◽  
Vol 27 (2) ◽  
pp. 301-316
Author(s):  
Gerald Webster ◽  
Susan Hamilton
Keyword(s):  
Cell Division ◽  
Mitotic Index ◽  
Cell Population ◽  
Cell Movement ◽  
Growth Zone ◽  
Cell Multiplication ◽  
Rapid Rise ◽  
The Mean ◽  
Bud Initiation

The work described in this paper is concerned with the role of cell multiplication and cell movement in relation to the initiation of buds in hydra. Hydra starved for 6 days do not initiate new buds; in such animals the mean mitotic index is only 10% of that in well-fed animals. When starved animals are re-fed, there is a rapid rise in mitotic index which reaches a maximum 12 h after feeding and thereafter declines. This cell division causes an increase in the cell population of about 30% in the 24 h following the meal. New buds are initiated at 24–72 h, i.e. at some time after the major part of the cell multiplication. Cell division occurs in all parts of the axis to more or less the same extent and there is no sign of a growth zone in the budding region. However, the cell population in the budding zone of re-fed animals shows a significantly greater increase than in other parts of the axis and this can only be accounted for if it is assumed that cells have moved into this region from other parts of the axis. Some cell multiplication is a necessary prerequisite for bud initiation, but grafting experiments with starved animals suggest that division per se is not necessary; the important factor seems to be the increase in size resulting from division. The mechanics and causes of the cell movement which results in bud initiation are briefly discussed. It is suggested that changes in intercellular adhesion may be important.

scholarly journals Effects of 5-fluorouracil on the mitotic activity of onion root tips apical meristem

2015 ◽  
Vol 45 (3) ◽  
pp. 225-237
Author(s):  
Waldemar Lechowicz
Keyword(s):  
Cell Division ◽  
Mitotic Activity ◽  
Mitotic Index ◽  
Apical Meristem ◽  
Root Tips ◽  
Onion Root ◽  
Control Value ◽  
Meristematic Cells ◽  
Cytological Changes ◽  
Chromatid Aberrations

The effects of various concentrations of 5-FU on the mitotic activity of onion root tips apical meristem were investigated during 24-hour incubation in 5-FU and postincubation in water. The incubation in 5-FU caused a reversible inhibition of mitotic activity, and waves of the partially synchronised mitoses were observed during the period of postincubation. The most pronounced synchronisation of mitoses was obtained after incubation in 100 mg/l. 5-FU but the mitotic index of the resumed mitotic activity amounted to only one half of the control value. 5-FU was found to cause some cytological changes in meristematic cells such as enlargement of the nucleoli, change in the interphasic nuclei structure, appearance of subchromatid and chromatid aberrations and micronuclei. The effects of 5-FU on nucleic acids and the cell division cycle ace discussed and compared with the effects of 5-FUdR.

STUDIES ON THE REVERSAL OF 5-FLUORODEOXYURIDINE-INDUCED MITOTIC INHIBITION BY THYMIDINE AND THYMIDINE ANALOGUES

1970 ◽  
Vol 12 (2) ◽  
pp. 230-240 ◽  
Author(s):  
George R. Hoffmann
Keyword(s):  
Cell Division ◽  
Mitotic Index ◽  
Vicia Faba ◽  
Rapid Recovery ◽  
Water Recovery ◽  
Root Tips ◽  
Simultaneous Exposure ◽  
Cell Divisions ◽  
Mitotic Inhibition ◽  
Synchronous Cell

At concentrations of 10−7 M and 10−8 M, 5-fluorodeoxyuridine (FUDR) completely inhibits cell division in root tips of Vicia faba. Suppression of cell division by 10−8 M FUDR is incomplete. In roots treated with 10−4 M thymidine (TDR), the level of mitosis is unchanged. In 10−3 M TDR, 10−4 M 5-bromodeoxyuridine (BUDR), or 10−4 M 5-iododeoxyuridine (IUDR), there is some decline in the mitotic index, particularly at later time periods.After a 2.5-hour treatment with 10−0 M FUDR, roots do not recover for more than 2 days in water. Recovery is faster in TDR. There is a slight enhancement of recovery in 10−6 M TDR and more rapid recovery at higher concentrations. The TDR analogues, BUDR and IUDR, are also somewhat effective in reversing FUDR-induced mitotic inhibition. TDR itself is most effective, followed by BUDR and IUDR, in that order. Renewed cell division, however, is often only temporary.When administered simultaneously with 10−3 M FUDR, TDR, at higher concentrations, provides some protection from mitotic inhibition. The protection from 10−6 M FUDR offered by simultaneous exposure to IUDR is slight. With simultaneous exposure to 10−6 M FUDR and 10−4 M BUDR, a decline in the level of mitosis is followed by partially synchronous cell divisions.

scholarly journals THE MECHANISM OF 5-AMINOURACIL-INDUCED SYNCHRONY OF CELL DIVISION IN VI CIA FABA ROOT MERISTEMS

1965 ◽  
Vol 24 (3) ◽  
pp. 401-414 ◽  
Author(s):  
Wolf Prensky ◽  
Harold H. Smith
Keyword(s):  
Cell Cycle ◽  
Cell Division ◽  
Dna Synthesis ◽  
Mitotic Activity ◽  
Vicia Faba ◽  
Mitotic Division ◽  
S Phase ◽  
Double Labeling ◽  
Cell Divisions ◽  
Exogenous Supply

Cessation of mitosis was brought about in Vicia faba roots incubated for 24 hours in the thymine analogue, 5-aminouracil. Recovery of mitotic activity began 8 hours after removal from 5-aminouracil and reached a peak at 15 hours. If colchicine was added 4 hours before the peak of mitoses, up to 80 per cent of all cells accumulated in mitotic division stages. By use of single and double labeling techniques, it was shown that synchrony of cell divisions resulted from depression in the rate of DNA synthesis by 5-aminouracil, which brought about an accumulation of cells in the S phase of the cell cycle. Treatment with 5-aminouracil may have also caused a delay in the rate of exit of cells from the G2 period. It appeared to have no effect on the duration of the G1 period. When roots were removed from 5-aminouracil, DNA synthesis resumed in all cells in the S phase. Although thymidine antagonized the effects of 5-aminouracil, an exogenous supply of it was not necessary for the resumption of DNA synthesis, as shown by incorporation studies with tritiated deoxycytidine.

Stimulated Virus Production in Vinblastine and Cytochalasin-Induced Multinucleate Cells

1970 ◽  
Vol 28 ◽  
pp. 186-187
Author(s):  
Krishan Awtar
Keyword(s):  
Cell Division ◽  
Normal Cell ◽  
Virus Production ◽  
Multinucleate Cells ◽  
Daughter Cells ◽  
Cell Divisions ◽  
Nuclear Membranes ◽  
Division 2 ◽  
Vinblastine Sulfate

Exposure of cells to low sublethal but mitosis-arresting doses of vinblastine sulfate (Velban) results in the initial arrest of cells in mitosis followed by their subsequent return to an “interphase“-like stage. A large number of these cells reform their nuclear membranes and form large multimicronucleated cells, some containing as many as 25 or more micronuclei (1). Formation of large multinucleate cells is also caused by cytochalasin, by causing the fusion of daughter cells at the end of an otherwise .normal cell division (2). By the repetition of this process through subsequent cell divisions, large cells with 6 or more nuclei are formed.

Mitotic Activity Dynamics in Recalcitrant Seeds Acer sachharinum during Maturation and Germination

HortScience ◽  
1998 ◽  
Vol 33 (3) ◽  
pp. 479c-479
Author(s):  
L. Kozeko ◽  
V. Troyan ◽  
L. Musatenko
Keyword(s):  
Cell Division ◽  
Mitotic Activity ◽  
Quiescent State ◽  
Activity Levels ◽  
Recalcitrant Seeds ◽  
Mature Embryos ◽  
Before And After ◽  
Orthodox Seeds ◽  
Mature Seeds ◽  
Activity Dynamics

In orthodox seeds the cell division within the embryo meristems arrests during maturation at embryo moisture content (MC) 65% to 47%, and the maturation completion and transition of seeds to quiescent state occurs at MC about 10%. The arrest of cycling happens asynchronously in different meristematic tissues during desiccation: first in shoot and then in root. The aim of this work was to define a mitotic activity dynamics in recalcitrant seeds with the high MC at maturation end and the absence of quiescent state characteristic of it. The object was seeds of Acer saccharinum, using widely for planting of greenery in Kiev city. The mitotic activity was determined in 0.5 mm of the embryo root pole (RP) and 0.5 mm of the shoot pole with embryo leaves (SP). The A. sachharinum seeds completed them maturation at MC 53% (FW basis). During maturation the mitotic index (MI) in RP decreased from 3.2% in immature seeds (at embryos MC 80%) to 0 in mature seeds and in SP–from 5.4% to 3.3%, respectively. Cell division in SP arrested by dehydration of mature embryos to MC 46% by PEG 6000 (30%). The seeds lost viability by desiccation to MC 34%. The mature seeds were able to germinate immediately after abscission. During seed germination the cell division reactived in RP and increased in SP already before root protrusion. In plantlets 10–15 mm long the MI increased to 8% in RP and 12% in SP. Thus, the strategy of immediate germination of recalcitrant A. sachharinum seeds includes a preservation of cell division in SP of mature embryos, in contrast with orthodox seeds, and high mitotic activity levels in meristems of germinating embryos before and after root protrusion.

Postpollination placental development of a diploid Solatium tuberosum

1988 ◽  
Vol 66 (9) ◽  
pp. 1813-1817 ◽  
Author(s):  
A. Randall Olson
Keyword(s):  
Solanum Tuberosum ◽  
Cell Division ◽  
Mitotic Activity ◽  
Solanum Tuberosum L ◽  
Cell Enlargement ◽  
Placental Development ◽  
Developing Seeds ◽  
Solatium Tuberosum

Gynoecial placentation of Solanum tuberosum L. is axile with each parenchymatous placenta covered with numerous ovules. Three days after pollination, mitotic activity in the placental surface and subjacent layers initiates tissue proliferations, which develop between the ovules. Continued cell division and subsequent cell enlargement result in expanded placental projections, which separate the developing seeds from one another and form an interface with the inner pericarp within 10 – 12 days after pollination. Eventually, the placenta fills the remaining ovarian locular space and embeds the seeds.

discordia mutations specifically misorient asymmetric cell divisions during development of the maize leaf epidermis

Development ◽  
1999 ◽  
Vol 126 (20) ◽  
pp. 4623-4633 ◽  
Author(s):  
K. Gallagher ◽  
L.G. Smith
Keyword(s):  
Cell Division ◽  
Preprophase Band ◽  
Cytochalasin D ◽  
Leaf Epidermis ◽  
Asymmetric Cell Divisions ◽  
Maize Leaf ◽  
Cell Divisions ◽  
Cytoskeletal Structure ◽  
Dividing Cells ◽  
Preprophase Bands

In plant cells, cytokinesis depends on a cytoskeletal structure called a phragmoplast, which directs the formation of a new cell wall between daughter nuclei after mitosis. The orientation of cell division depends on guidance of the phragmoplast during cytokinesis to a cortical site marked throughout prophase by another cytoskeletal structure called a preprophase band. Asymmetrically dividing cells become polarized and form asymmetric preprophase bands prior to mitosis; phragmoplasts are subsequently guided to these asymmetric cortical sites to form daughter cells of different shapes and/or sizes. Here we describe two new recessive mutations, discordia1 (dcd1) and discordia2 (dcd2), which disrupt the spatial regulation of cytokinesis during asymmetric cell divisions. Both mutations disrupt four classes of asymmetric cell divisions during the development of the maize leaf epidermis, without affecting the symmetric divisions through which most epidermal cells arise. The effects of dcd mutations on asymmetric cell division can be mimicked by cytochalasin D treatment, and divisions affected by dcd1 are hypersensitive to the effects of cytochalasin D. Analysis of actin and microtubule organization in these mutants showed no effect of either mutation on cell polarity, or on formation and localization of preprophase bands and spindles. In mutant cells, phragmoplasts in asymmetrically dividing cells are structurally normal and are initiated in the correct location, but often fail to move to the position formerly occupied by the preprophase band. We propose that dcd mutations disrupt an actin-dependent process necessary for the guidance of phragmoplasts during cytokinesis in asymmetrically dividing cells.

The growth of supernumerary legs in the cockroach

Development ◽  
1986 ◽  
Vol 92 (1) ◽  
pp. 115-131
Author(s):  
Paul R. Truby
Keyword(s):  
Wound Healing ◽  
Cell Division ◽  
Rapid Rate ◽  
Large Area ◽  
Anteroposterior Axis ◽  
Cell Divisions ◽  
Leucophaea Maderae ◽  
Different Types ◽  
Local Cell

When the anteroposterior axis of a cockroach leg is reversed at a graft by exchanging a left leg for a right leg at the mid-tibia level, regeneration occurs in the region of the graft/host junction. This results in the formation of a pair of lateral supernumerary legs. In these experiments the patterns of cell division which take place during supernumerary leg formation were observed in sections of regenerating legs of the cockroach Leucophaea maderae. Early patterns of cell division resemble those seen in control grafts in which no axial reversal had been carried out during grafting. These cell divisions are associated with the process of wound healing. Later, a large area of the epidermis proximal to the graft/host junction becomes activated and shows a rapid rate of cell division. This area forms two outgrowths which grow by cell division throughout their epidermis to form the epidermis of the supernumerary legs. The results are more consistent with the view that the formation of supernumerary legs involves dedifferentiation of the epidermis in the region of the graft/host junction to form a blastema, rather than being due to local cell division at the point of maximum pattern discontinuity. This conclusion is used to offer an explanation for the range of different types of outcome of left-right grafts that has been observed.

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