1. Freeze-cracked meiotic chromosomes and kinetochores in pollen mother cells : Three-dimensional ultrastructure of in situ chromosomes and kinetochores of Tradescantia reflexa anther cells by scanning electron microscopy

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Dynamic morphological changes of meiotic chromosomes and the ultrastructure of the kinetochore of Tradescantia reflexa pollen mother cells were investigated entirely throughout the dividing stages stereoscopically by SEM using the freeze-cracking method. Chromosomes showed an entangled thread-like structure with a rough surface appearance in prophase II (0.7-0.8μm in diameter), a double coiling configuration with a smooth surface appearance (2.4- 3.5μm) in metaphase II and anaphase I, the network-like structure composed of threads (0.3-0.6μm) and extremely thin fibers in telophase I. In prophase I and metaphase I, chromosornes showed thread-like structures with a fuzzy surface appearance and cylindrical shape respectively. In the quartet (tetrad) stage, decondensed chromosomes were reformed into a network-like structure similar to telophase I. Furthermore, some holes were recognized frequently in the center of cracked bivalent and univalent chromosomes along the coil axis. Consequently, it is suggested that meiotic chromosomes increase their own thickness gradually toward metaphase by chromatin compacting and coiling during the first condensation process and reform their entire architecture into a network-like structure during the decondensation process. Kinetochores were demonstrated as protrusions from which spindle fibers emanated in a bundle and as low contrasted granular images on the cracked inside view.
財団法人染色体学会の論文