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  • 1
    Electronic Resource
    Electronic Resource
    The effect of supernumerary chromosomes on meiosis in Puschkinia libanotica (Liliaceae) (1970)
    Springer
    Chromosoma 30 (1970), S. 344-355 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The presence of the partly heterochromatic supernumerary chromosomes in pollen mother cells of Puschkinia libanotica raises the chiasma frequency in the A chromosome bivalents. The pattern of chiasma distribution along each of the five A bivalents was related to the DNA labelling pattern of mitotic chromosomes. Regions that showed heavy labelling at the end of the DNA synthetic phase had fewer chiasmata than lightly labelled regions. As this relation is the opposite to that found by Rees and Evans in another species we regard any correlation between labelling pattern and chiasma distribution as fortuitous.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00321066
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  • 2
    Electronic Resource
    Electronic Resource
    CYTOSKELETAL PERSPECTIVES ON ROOT GROWTH AND MORPHOGENESIS (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Plant Physiology and Plant Molecular Biology 51 (2000), S. 289-322 
    Details
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Growth and development of all plant cells and organs relies on a fully functional cytoskeleton comprised principally of microtubules and microfilaments. These two polymeric macromolecules, because of their location within the cell, confer structure upon, and convey information to, the peripheral regions of the cytoplasm where much of cellular growth is controlled and the formation of cellular identity takes place. Other ancillary molecules, such as motor proteins, are also important in assisting the cytoskeleton to participate in this front-line work of cellular development. Roots provide not only a ready source of cells for fundamental analyses of the cytoskeleton, but the formative zone at their apices also provides a locale whereby experimental studies can be made of how the cytoskeleton permits cells to communicate between themselves and to cooperate with growth-regulating information supplied from the apoplasm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.arplant.51.1.289
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  • 3
    Electronic Resource
    Electronic Resource
    An excision and squash technique for analysis of the cell cycle in the root quiescent centre of maize (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 87 (1993), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The quiescent centre of primary roots of Zea mays L. (cvs LG 11 and Golden Bantam) consists of a population of slowly cycling diploid cells. These metabolically inactive cells may be triggered to synthesise DNA under specific conditions and constitute a good model for studying the regulation of the cell cycle. An excision and squash technique is described for the quiescent centre which, when coupled with Feulgen and fluorochrome staining, allows nuclear DNA contents to be determined by microdensitometry in less than a day. This technique was coupled with experiments in which excised quiescent centres were placed on solid culture medium into which hormones and radioactive DNA precursors were incorporated. In complementary and control experiments [methyl-3H]thymidine was supplied to intact roots (with or without root caps) by means of fibre-glass cubes as donors.Progression of the cell cycle was followed by microdensitometry and autoradiography. Distribution of DNA content was similar in excised and squashed quiescent centres and in histological sections. Labelling experiments showed that the quiescent centre is made up of cells that differ in their cycle time. While some labelled cells had reached mitosis after 8 h, others were still in G2 after 16 h of continuous labelling. Excision and culture of the quiescent centre resulted in a dramatic activation of the cell cycle as shown by the labelling index that increased from 15% in intact roots fed during 16 h with [methyl-3H]thymidine to 31% in excised quiescent centres to which radioactive precursor was supplied during the same time. Supplying hormones (50 μM abscisic acid [ABA], 0. 1 μM zeatin, 1 μM zeatin riboside) to quiescent centres via the culture medium restored their inactivity (labelling indices dropped to 1% after ABA. and to 11% after zeatin and zeatin riboside treatments. respectively).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb01735.x
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  • 4
    Electronic Resource
    Electronic Resource
    Cell bodies in a cage (2004)
    [s.l.] : Nature Publishing Group
    Nature 428 (2004), S. 371-371 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ...The concept of the cell as the fundamental structural and functional unit of a multicellular organism stems from the observations of Robert Hooke in 1665 and Nehemiah Grew in 1682, both of whom reported on the ‘cells’ of plant tissues. It was 150 years before the universal ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/428371a
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  • 5
    Electronic Resource
    Electronic Resource
    Auxin and ethylene interactions control mitotic activity of the quiescent centre, root cap size, and pattern of cap cell differentiation in maize (2005)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 28 (2005), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Root caps (RCs) are the terminal tissues of higher plant roots. In the present study the factors controlling RC size, shape and structure were examined. It was found that this control involves interactions between the RC and an adjacent population of slowly dividing cells, the quiescent centre, QC. Using the polar auxin transport inhibitor 1-N-naphthylphthalamic acid (NPA), the effects of QC activation on RC gene expression and border cell release was characterized. Ethylene was found to regulate RC size and cell differentiation, since its addition, or the inhibition of its synthesis, affected RC development. The stimulation of cell division in the QC following NPA treatment was reversed by ethylene, and quiescence was re-established. Moreover, inhibition of both ethylene synthesis and auxin polar transport triggered a new pattern of cell division in the root epidermis and led to the appearance of supernumerary epidermal cell files with cap-like characteristics. The data suggest that the QC ensures an ordered internal distribution of auxin, and thereby regulates not only the planes of growth and division in both the root apex proper and the RC meristem, but also regulates cell fate in the RC. Ethylene appears to regulate the auxin redistribution system that resides in the RC. Experiments with Arabidopsis roots also reveal that ethylene plays an important role in regulating the auxin sink, and consequently cell fate in the RC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2005.01318.x
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of abscisic acid on cell growth, cell division and DNA synthesis in the maize root meristem (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 62 (1984), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Cis-abscisic acid (ABA), when applied to maize (Zea mays L. cv. LG 11) roots, decreases the rates of cell growth and cell division in the meristem. It also decreases the rate at which nuclei become labelled with [3H]-thymidine and enter mitosis. Removing the root cap accelerates the entry of nuclei into the DNA synthetic phase of the mitotic cycle and enhances the rate of cell proliferation in the quescent centre. ABA diminishes these effects, but does not suppress them. Thus, ABA cannot wholely substitute for the presence of a cap. One of the primary effects of applied ABA is to retard cell enlargement which may in turn affect the rate of cell division; natural endogenous ABA may act similarly. ABA might in this way assist in maintaining the quiescent centre in intact roots, but cannot be the sole agent involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb00359.x
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  • 7
    Electronic Resource
    Electronic Resource
    Mitotic activity and cell elongation in geostimulated roots of Zea mays (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 54 (1982), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Mitotic activity was investigated in the primary meristem of horizontally oriented excised root tips of Zea mays during the first six hours of their georeaction. The only statistically significant change that could be detected in the meristem was a decrease of the length of its upper half. No significant difference in mitotic activity was found between the upper and lower halves of roots kept continuously horizontal for 6 h. Cell proliferation thus seems relatively insensitive to changes in the redistribution of endogenous growth regulators that are believed to occur within the meristem during the onset of geotropism. In the zone of bending proximal to the meristem cell length was significantly greater in the upper half than in either the lower half or in the equivalent position in vertical control roots. Thus, cell elongation seems to be promoted in the upper half of the horizontal root. Thus, The differences in cell length were not accompanied by any change in the proportion of nuclei synthesising DNA in these elongating, non-meristematic cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1982.tb06316.x
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  • 8
    Electronic Resource
    Electronic Resource
    The relationship of the dispersion phase of chromocentric nuclei in the mitotic cycle to DNA synthesis (1976)
    Springer
    Protoplasma 90 (1976), S. 381-392 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A small proportion of nuclei in root meristems ofAllium flavum, Bryonia dioica andLupinus angustifolius exhibit a dispersion of their chromocentres; the structure of such nuclei corresponds to the “Zerstäubungsstadium” (Z-phase) described byHeitz. Microdensitometry and autoradiography were employed to determine the location of the Z-phase in the mitotic cycle. In bothAllium andBryonia Z-phase is located at the end of the DNA-synthetic (S) phase and not at early prophase as has been assumed hitherto; inLupinus Z-phase is also associated with the S-phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01275688
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  • 9
    Electronic Resource
    Electronic Resource
    Cytological studies on the organization of DNA in giant trophoblast nuclei of the mouse and the rat (1974)
    Springer
    Chromosoma 47 (1974), S. 119-131 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Giant trophoblast nuclei of the mouse and the rat, known to contain hundreds, or even thousands, of times the haploid amount of DNA, have been studied by a number of cytological techniques. These nuclei appear in two morphological states:“reticulate,” in which large numbers of chromatin threads of uniform size intermingle throughout the nucleus, often radiating from clumps of heterochromatin adjacent to the nucleoli, and “homogeneous,” in which the chromatin is more evenly dispersed and individual threads are more difficult to distinguish. Intermediate morphologies are also observed. In neither case were structures resembling polytene chromosomes discernible. — Centromeric heterohromatin as revealed by the Giemsa BSG technique has been quantitatively analyzed in giant versus diploid trophoblast nuclei. Although the median number of chromocenters is slightly greater in giant than in diploid nuclei, the range is similar. In both cases, the chromocenter number is usually less than the diploid number of chromosome pairs, indicating the attraction between centromeres not only of homologous, but also of heterologous, chromosomes. By scanning microdensitometry, we have observed a constant ratio of chromocenter area: total nuclear area in giant cells. This ratio, which likely reflects the ratio of chromocenter volume: total nuclear volume, is in good agreement with that of satellite DNA: total DNA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331800
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  • 10
    Electronic Resource
    Electronic Resource
    Differential cell division in human X chromosome mosaics (1972)
    Springer
    Human genetics 〈Berlin〉 14 (1972), S. 122-127 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Kulturen von Fibroblasten der Haut dreier weiblicher Individuen mit Sexchromatin-Mosaiks zeigten folgende chromosomale Zusammensetzung: 45,X/46,XX; 45,X/46XXqi und 45,X/47,XXX. Mit Hilfe von Thymidinmarkierung und Akkumulation von Metaphasen durch Colcemid konnte gezeigt werden, daß in allen 3 Mosaikkulturen die 45,X-Zellen einen schnelleren Zellcyclus haben als die zweite Zellpopulation. Der Unterschied in der Dauer des Zellcyclus beruht auf der längeren G1-Phase der Zellen mit 2 oder 3 X-Chromosomen. Die 2 Zellpopulationen im Mosaik differieren nur in der Zahl der heterochromatischen X-Chromosomen, so daß angenommen werden könnte, daß Heterochromatin einen retardierenden Effekt ausübt.
    Notes: Summary Fibroblasts were grown from skin explants of 3 human females who are sex chromosome mosaics. The 3 cultures had the following chromosome complements: 45,X/46,XX, 45,X/46,XXqi and 45,X/47,XXX. Using thymidine labelling and Colcemid accumulation of metaphases it was found that in all 3 mosaic cultures the 45,X cells had a faster cell cycle than the second cell population. The difference in cell cycle duration was attributed to the longer G1 phase in the cells with 2 or 3 X chromosomes. The 2 populations of cells in the mosaic only differ in the number of heterochromatic X chromosomes and it is argued that heterochromatin has a retardative effect on cell division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00273295
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