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  • 1
    Electronic Resource
    Electronic Resource
    Preprophasic microtubule systems and development of the mitotic spindle in hornworts (Bryophyta) (1988)
    Springer
    Protoplasma 143 (1988), S. 11-21 
    Details
    ISSN: 1615-6102
    Keywords: Bryophytes ; Immunofluorescence ; Microtubules ; Mitotic apparatus ; Monoplastidy ; Preprophase band
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Studies of monoplastidic mitosis in hornworts (Bryophyta) using transmission electron microscopy and indirect immunofluorescence staining of microtubules have revealed that two mutually perpendicular microtubule systems predict division polarity in preprophase. Events of cytoplasmic reorganization in preparation for division occur in the following order: migration of the single plastid to a position perpendicular to the division site, constriction of the plastid where its midpoint intersects the division site, development of an axial system of microtubules parallel to the elongating plastid isthmus, and appearance of an atypical preprophase band of microtubules (PPB). The PPB is asymmetrical with a tight band of microtubules on the side over the plastid isthmus and a broad band of widely spaced microtubules over the nucleus. The axial system contributes directly to development of the spindle. In prometaphase, the axial system separates at the equator and additional microtubule bundles project from polar regions, creating two opposing halfspindles. The PPB is still present during asymmetrical organization of the spindle and microtubules extending from the broad portion of the PPB to poles appear to be incorporated into the developing spindle. Dynamic changes in the microtubular cytoskeleton demonstrate (1) intimate relationship of plastid and nuclear division, (2) contribution of preprophase/prophase microtubule systems to spindle development in monoplastidic cells, and (3) dynamic reorientation of microtubules from one system to another.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01282954
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  • 2
    Electronic Resource
    Electronic Resource
    Division polarity, development and configuration of microtubule arrays in Bryophyte meiosis (1987)
    Springer
    Protoplasma 137 (1987), S. 84-99 
    Details
    ISSN: 1615-6102
    Keywords: Meiosis ; Microtubules ; Mitotic apparatus ; Immunofluorescence ; Spindle ; Bryophytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Immunofluorescence and TEM studies of meiosis in two mosses (Bryophyta) provide evidence that the prophasic tetrahedral system of microtubules contributes directly to the metaphase I spindle. Intense staining of tubulin, conspicuously absent around the nuclear envelope, is first seen associated with plastids. By mid-prophase, microtubules radiate from the plastids to the nuclear envelope and become organized into six bands that interconnect the four plastids, forming a tetrahedral cytoskeleton surrounding the nucleus. During transition of prophase to metaphase, the four poles of the tetrahedral microtubule system converge in pairs toward opposite cleavage furrows. Opposite furrows occupy mutually perpendicular planes and the pair of microtubule focal points straddling one furrow lies at right angles to the pair straddling the opposite furrow. Additional microtubules terminate in numerous small clusters in the concave polar regions arching over the cleavage furrows. By early anaphase, the microtubule focal points lie very close to the division axis. We conclude that microtubules recruited from the prophasic quadripolar system are incorporated into the mature metaphase I spindle and the two principal focal points at each pole are those derived from poles of the prophasic quadripolar system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01281144
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  • 3
    Electronic Resource
    Electronic Resource
    Division polarity, development and configuration of microtubule arrays in bryophyte meiosis (1987)
    Springer
    Protoplasma 138 (1987), S. 1-10 
    Details
    ISSN: 1615-6102
    Keywords: Meiosis ; Microtubules ; Cytokinesis ; Immunofluorescence ; Bryophytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary First and second division spindles and the three cell plates of moss meiosis are oriented in accordance with polarity established during meiotic prophase. Plastids are located at the second division poles and cytoplasmic infurrowing marks the planes along which the cytoplasm will cleave into four spores. Anaphase I spindles that terminate in two focal points of microtubules straddling opposite cleavage furrows reflect the unusual tetrahedral origin of the functionally bipolar spindle. The organelles (except for the plastids which remain in the four cytoplasmic lobes) are polarized in the first division equatorial region at the time of phragmoplast microtubule assembly and remain in a distinct band after microtubule disassembly. Prophasic spindles appear to be directly transformed into metaphase II spindles in the predetermined axes between mutually perpendicular pairs of plastids. Cell plates form by vesicle coalescence in the equatorial regions of the two sets of second division phragmoplasts at approximately the same time as a cell plate belatedly forms in the organelle band. The cytoplasmic markers (plastid migration, cytoplasmic lobing and infurrowing) that predict poles and cleavage planes in free cells lacking a preprophase band strongly strengthens the concept that division sites are capable of preserving preprogrammed signals that can be triggered later in the process of cell division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01281179
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