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  • DNA content  (1)
  • Microtubule  (1)
  • 1990-1994  (2)
  • 1
    ISSN: 1615-6102
    Keywords: Cell cycle ; Microtubule ; Microtubule organizing center ; Synchronization ; Tobacco BY-2 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A 49 kDa protein in tobacco BY-2 cells has been found to be cross-reactive with antibodies raised against a 51 kDa protein that was isolated from sea urchin centrosomes and identified as a microtubule-organizing center (MTOC) in animal cells. Tracing the fate of the 49 kDa protein during progression of the cell cycle in highly synchronized tobacco BY-2 cells revealed that this protein was colocalized with plant microtubules (MTs): the location of the 49 kDa protein coincided with preprophase bands (PPBs), mitotic spindles and phragmoplasts. Furthermore, between the M and G1 phases, the 49 kDa protein was observed in the perinuclear regions, in which the initials of MTs are organizing to form cortical MTs. At the G1 phase the location of the 49 kDa protein in the cell cortex coincided with that of the cortical MTs. It appeared that the 49 kDa protein in the cell cortex was transported as granules from the perinuclear regions. Thus, it is highly probable that the 49 kDa protein, which reacts with antibodies against the 51 kDa protein in sea urchin centrosomes, plays the role of an MTOC in plant cells. Thus, the mechanisms for organizing MTs in higher organisms appear to share a common protein, even though the organization of MTs is superficially very different in plant and animal cells.
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  • 2
    ISSN: 1615-6102
    Keywords: Cell culture ; DNA content ; Mitochondrial DNA ; Mitochondrial genome ; Nicotiana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The molecular size of mitochondrial DNA (mtDNA) molecules and the number of copies of mtDNA per mitochondrion were evaluated from cultured cells of the tobacco BY-2 line derived fromNicotiana tabacum L. cv. Bright Yellow-2. To determine the DNA content per mitochondrion, protoplasts of cultured cells were stained with 4′,6-diamidino-2-phenylindole (DAPI), and the intensity of the fluorescence emitted from the mitochondrial nuclei (mt-nuclei) was measured with a video-intensified photon counting microscope system (VIM system). Each mitochondrion except for those undergoing a division contained one mt-nucleus. The most frequently measured size of the DNA in the mitochondria was between 120 and 200 kilobase pairs (kbp) throughout the course of culture of the tobacco cells. Mitochondria containing more than 200 kbp of DNA increased significantly in number 24 h after transfer of the cells into fresh medium but their number fell as the culture continued. Because division of mitochondria began soon after transfer of the cells into fresh medium and continued for 3 days, the change of the DNA content per mitochondrion during the culture must correspond to DNA synthesis of mitochondria in the course of mitochondrial division. By contrast, the analyses of products of digestion by restriction endonucleases indicated that the genome size of the mtDNA was at least 270 kbp. Electron microscopy revealed that mtDNAs were circular molecules and their length ranged from 1 to 35 μm, and 60% of them ranged from 7 to 11 μrn. These results indicate that the mitochondrial genome in tobacco cells consists of multiple species of mtDNA molecules, and mitochondria do not contain all the mtDNA species. Therefore, mitochondria are heterogeneous in mtDNA composition.
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