Changes in the microtubular cytoskeleton of Dactylorhiza majalis (Rchb.) Hunt et Summerh. (Orchidaceae) during microsporogenesis were investigated by the immunofluorescence method. Dactylorhiza microsporocytes in microsporangia divide into tetrads after a regular meiosis, which is completed with simultaneous cytokinesis. Three typical configurations of the microtubular cytoskeleton appear during microsporogenesis: the microtubular system in the cytoplasm and at the nuclear envelope, meiotic spindles, and phragmoplasts. Microtubules of the early prophase I microsporocyte are dispersed throughout the cortical cytoplasm, and later the arrays of microtubules are visible at the nuclear envelope. During metaphase I, the microtubules form the spindle which also acts during anaphase I. At telophase I, interzonal microtubules of the first meiotic spindle disappear, and new microtubular arrays extend from the nuclei towards the equatorial plane of the microsporocyte. There, these microtubules form the phragmoplast, which disintegrates before the second meiotic division. During the second meiotic division, the microtubular cytoskeleton repeats the configurations from the first meiotic division. The microtubular arrays emanating from the telophase II nuclei form interconnections of all non-sister and sister nuclei. During the formation of the cell plates between the future microspores, these microtubular arrays disappear. The results support the view that cytoskeletal configurations participate in the formation of the nuclear-cytoplasmic domains of the dividing microsporocyte in its transition from mononucleate microsporocyte to undivided dyad, and to four microspore domains after the second meiotic division.
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