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  • 1
    Electronic Resource
    Electronic Resource
    Fine structure of mitosis and cytokinesis inUrospora (Acrosiphoniales, Chlorophyta) (1983)
    Springer
    Protoplasma 117 (1983), S. 142-153 
    Details
    ISSN: 1615-6102
    Keywords: Cytokinesis ; Green algae ; Mitosis ; Phycoplast ; Phylogeny ; Urospora
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The mitosis and subsequent cytokinesis in vegetative cells of the filamentous stage of the green algaUrospora have been examined in detail and are compared to the situation in other coenocytic (un-) branched filamentous green algae. Before the formation of transverse walls inUrospora numerous nuclei arrange themselves in a band at the equatorial plane. All nuclei, including those in the same cell but not in the band, divide synchronously. InUrospora wormskioldii (Mertens in Hornemann) Rosenvinge the nuclear envelope is often more or less broken down during mitosis, but inU. neglecta (Kornmann) Lokhorst and Trask it is seen almost intact. Cytokinesis is accomplished in the region of the band by means of a diaphragm-like furrow of the plasmalemma. Arrays of microtubules ensheath the developing septum, they are most distinct at its leading edge. It seems that this particular arrangement of microtubules represents a guiding mechanism for the development of the ingrowing septum. A second function attributed to these microtubules is that they act as a supporting skeleton, which protects the developing furrow during its cleavage through the less elastic, centrally-located vacuole. It is proposed to modify the definition of the term phycoplast so that it also comprises the orientation of microtubules allied with cytokinesis in coenocytic green algae. The implications of these findings for the taxonomic position ofUrospora and for recently proposed evolutionary lines and classifications in green algae will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288352
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  • 2
    Electronic Resource
    Electronic Resource
    Mitosis and cytokinesis inTribonema regulare (Tribophyceae, Chrysophyta) (1988)
    Springer
    Protoplasma 145 (1988), S. 7-15 
    Details
    ISSN: 1615-6102
    Keywords: Cytokinesis ; Tribophyceae ; H-shaped segment ; Phylogeny ; Mitosis ; Tribonema
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ultrastructure of mitosis and cytokinesis of the uninucleateTribonema regulare has been investigated by employing transmission electron microscopy. Prophase is characterized by settlement of a pair of centrioles at the presumptive poles of the spindle, metaphase by equatorial bulging of the nucleus, anaphase by non-synchronous separation of the chromosomes, and telophase by a persistent, strongly elongated, interzonal spindle. Throughout mitosis, at each pole dictyosomes are associated with the polar gaps of the nuclear envelope that otherwise remains intact. Cytokinesis does not immediately follow mitosis; from the static images it can be concluded that it is necessary for the daughter nuclei to approach each other before cytokinesis is initiated by complete division of the protoplast via plasma membrane cleavage. Afterwards, a ring of cell wall material is deposited close near the lateral wall in the plane of protoplast separation followed by a simultaneous or centripetal development of a single integral partitioning septum. Once the septum is completed, the cylindrical portion of the H-shaped segment is manufactured. The phylogenetic position ofTribonema amongst those algae, which may have evolved from unicells into filaments, is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323251
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