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  • 1
    Digitale Medien
    Digitale Medien
    Nuclear cytoplasmic domains, microtubules and organelles in microsporocytes of the slipper orchid Cypripedium californicum A. Gray dividing by simultaneous cytokinesis (1996)
    Springer
    Sexual plant reproduction 9 (1996), S. 145-152 
    Details
    ISSN: 1432-2145
    Schlagwort(e): Cytokinesis ; Microtubules ; Microsporogenesis ; Orchids ; Phragmoplast ; Pollen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Microsporocytes of the slipper orchidCypripedium californicum A. Gray divide simultaneously after second meiosis. The organization and apportionment of the cytoplasm throughout meiosis are functions of nuclear-based radial microtubule systems (RMSs) that define domains of cytoplasm - a single sporocyte domain before meiosis, dyad domains within the undivided cytoplasm after first meiosis, and four spore domains after second meiosis. Organelles migrate to the interface of dyad domains in the undivided cytoplasm after first meiotic division, and second meiotic division takes place simultaneously on both sides of the equatorial organelle band. Microtubules emanating from the telophase II nuclei interact to form columnar arrrays that interconnect all four nuclei, non-sister as well as sister. Cell plates are initiated in these columns of microtubules and expand centrifugally along the interface of opposing RMSs, coalescing in the center of the sporocyte and joining with the original sporocyte wall at the periphery to form the tetrad of microspores. Organelles are distributed into the spore domains in conjunction with RMSs. These data, demonstrating that cytokinesis in microsporogenesis can occur in the absence of both components of the typical cytokinetic apparatus (the preprophase band of microtubules which predicts the division site and the phragmoplast which controls cell-plate deposition), suggest that plant nuclei have an inherent ability to establish a domain of cytoplasm via radial microtubule systems and to regulate wall deposition independently of the more complex cytokinetic apparatus of vegetative cells.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02221394
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  • 2
    Digitale Medien
    Digitale Medien
    Division polarity and plasticity of the meiosis I spindle inCypripedium californicum (Orchidaceae) (1998)
    Springer
    Protoplasma 203 (1998), S. 168-174 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Confocal laser scanning microscopy ; Cytoplasmic domains ; Meiosis ; Microtubules ; Organelle band ; Polarity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Establishment of division polarity and meiotic spindle organization in the lady's slipper orchidCypripedium californicum A. Gray was studied by immunocytochemistry, confocal and transmission electron microscopy. Prior to organization of the spindle for meiosis I, the cytoplasmic domains of the future dyad and spindle polarity are marked by: (1) constriction of the prophase nucleus into an hourglass shape; (2) reorganization of nuclear-based radial microtubules into two arrays that intersect at the constriction; and (3) redistribution of organelles into a ring at the boundary of the newly defined dyad domains. It is not certain whether the opposing microtubule arrays contribute directly to the anastral spindle which is organized in the perinuclear areas of the two hemispheres. By late prophase each half-spindle consists of a spline-like structure from which depart the kinetochore fibers. This peculiar spindle closely resembles the spline-like spindle of generative-cell mitosis in certain plants where the spindle is distorted by physical constraints of the slender pollen tube. In the microsporocyte, the elongate spindle of late prophase/metaphase is curved within the cell so that the poles are not actually opposite each other and chromosomes do not form a plate at the equator. By late telophase the poles of the shortened halfspindles lie opposite each other. Plasticity of the physically constrained plant spindle appears to be due to its construction from multiple units terminating in minipoles. Cytokinesis does not follow the first meiosis. However, the dyad domains are clearly defined by radial microtubules emanating from the two daughter nuclei and the domains themselves are separated by a disc-like band of organelles.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01279473
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  • 3
    Digitale Medien
    Digitale Medien
    Polarization predicts the pattern of cellularization in cereal endosperm (1996)
    Springer
    Protoplasma 192 (1996), S. 168-177 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Cereals ; Endosperm ; Development ; Polarity ; Microtubules
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The endosperm of cereal grains develops as a multinucleate mass of wall-less cytoplasm (syncytium) that lines the periphery of the central cell before becoming cellular. The pattern of initial wall formation is precisely oriented and is followed by a round of precisely oriented formative cell division that gives rise to initials for the two tissues of endosperm. The initial anticlinal walls form at boundaries of nuclear-cytoplasmic domains (NCDs) defined by radial microtubules emanating from nuclei in the syncytium. Polarized growth of the NCDs in axes perpendicular to the embryo sac wall and centripetal elongation of the anticlinal walls results in a single layer of open ended alveoli overtopped by the remaining syncytial cytoplasm. This arboreal stage, so named because the elongate nucleate columns of cytoplasm resemble an orchard of trees, predicts the division polarity of the imminent formative division. Mitosis occurs as a wave which, like polarization, moves in both directions from ventral to dorsal. Spindles are oriented parallel to the long axis of the alveoli and cell plates give rise to periclinal walls. The outer daughter nuclei (aleurone initials) are thus completely enclosed by walls and the inner nuclei (starchy endosperm initials) are in alveoli adjacent to the central vacuole.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01273889
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  • 4
    Digitale Medien
    Digitale Medien
    Transition from mitotic apparatus to cytokinetic apparatus in pollen mitosis of the slipper orchid (1997)
    Springer
    Protoplasma 198 (1997), S. 43-52 
    Details
    ISSN: 1615-6102
    Schlagwort(e): Confocal microscopy ; Microtubules ; Mitosis ; Orchid ; Phragmoplast ; Pollen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Cytokinesis following asymmetrical pollen mitosis was studied in the slipper orchidCypripedium fasciculatum using techniques of immunofluorescence, confocal laser scanning, and transmission electron microscopy. Data from stereo reconstructions of double labelled preparations (microtubules/nuclei) show that the contribution of residual spindle fibers to development of the interzonal array is minor; rather, new populations of microtubules are nucleated in association with the two groups of anaphase chromosomes. As kinetochores reach the poles, trailing arms of the chromosomes and nonkinetochore microtubules are displaced outward in the equatorial zone and by early telophase the interzone is left virtually free of microtubules. The interzonal apparatus has its origin in a massive proliferation of microtubules from the polar regions and surfaces of contracting chromosomes. Each polar region appears as a hub from which microtubules radiate in a spoke-like configuration and numerous tufts of microtubules appear to emanate from margins of the chromosomes themselves. These newly organized arrays of microtubules extend to the equatorial region where they interact to form the interzonal apparatus. Increasing organization of microtubules in the interzone results in development of a typical phragmoplast configuration consisting of opposing cone-like bundles of microtubules bisected by an unstained equatorial line.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01282130
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  • 5
    Digitale Medien
    Digitale Medien
    Pattern and process of wall formation in developing endosperm (1995)
    New York, NY : Wiley-Blackwell
    BioEssays 17 (1995), S. 803-812 
    Details
    ISSN: 0265-9247
    Schlagwort(e): Life and Medical Sciences ; Cell & Developmental Biology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Medizin
    Notizen: Endosperm is emerging as a system for investigating the genetic control of wall placement and deposition in plant development. Development of endosperm progresses in distinct stages from a wall-less syncytial stage to a cellular stage that is entirely typical of plant meristems where the division plane is predicted by a preprophase band of microtubules (PPB) and cytokinesis is completed by formation of a cell plate in association with a phragmoplast. Four developmentally different types of walls, each associated with a different microtubule system, are sequentially produced: (1) free growing walls deposited in the absence of mitosis and phragmoplasts; (2) walls guided by cytoplasmic phragmoplasts formed adventitiously in the absence of mitosis; (3) walls formed by interzonal phragmoplasts in a cell cycle that lacks PPBs; and (4) wall deposition driven by interzonal phragmoplasts in a cycle that includes PPBs. We are using methods of differential screening to isolate cDNA clones corresponding in temporal and spatial pattern to the types of wall development, and are studying mutants for clues to the genetic controls of wall development.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bies.950170910
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