Microtubule organization during successive microsporogenesis in Allium cepa and simultaneous cytokinesis in Nicotiana tabacum |
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Authors: | Y N Zhang D M Wei Y Y Song L Chen X Y Zhu and H Q Tian |
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Institution: | (1) Key Laboratory for Genetics and Breeding of Forest Trees and Ornamental Plants, Ministry of Education, Beijing Forestry University, 100083 Beijing, People’s Republic of China;(2) Present address: Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, 100081 Beijing, People’s Republic of China |
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Abstract: | Microtubule cytoskeleton organization during microspore mother cell (MMC) meiosis in Allium cepa L. and microsporogenesis in Nicotiana tabacum L. was examined. The MMC microtubules (MTs) were short and well dispersed in the cytoplasm of both taxa. As the MMCs of both
species entered metaphase of meiosis I, the MTs constructed a spindle that facilitated the chromosomes to orient in the meridian
plane. At anaphase of meiosis I, the spindle MTs differentiated into two types: one MT type became short, pulled the chromosomes
toward the two poles, and was designated as centromere MTs; the second type of MT connected the two poles, and was designated
as pole MTs. In A. cepa, where successive cytokinesis was observed, pole MTs assumed a tubbish shape. Some new short MTs aggregated in the meridian
plane and constricted to form a phragmoplast, which developed into a cell plate, divided the cytoplasm into two parts and
produced a dyad. However, in tobacco, a phragmoplast was not generated in anaphase of meiosis I and II and cytokinesis did
not occur. The spindle MTs depolymerized and reorganized the radial arrangement of MTs from the nucleate surface to the periplasm
during anaphase. Following telophase of meiosis II, the cytoplasm produced centripetal furrows, which met in the center of
the cell and divided it into four parts, serving as a form of cytokinesis. In this process, MTs appeared to bear no relationship
to cytokinesis. |
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