Comparative cytological investigation of unicellular green algae. X. Some peculiarities of mitosis in Chlamydomonas of Pseudagloe-group (Chlamydomonadales, Chlorophyta)

摘要

The karyology of Chlamydomonas agloeformis and the nuclear morphology of C.mutabilis are described. In both species the non-dividing nuclei are widely ovoid or roundish, about 4 #mu#m in diameter each, with a solitary compact nucleolus. The nuclei are located in the anterior part of the cell. The detail ultrastructural studies of C.agloeformis show that the condensed chromatin is scattered in the form of chromocenter-like bodies anywhere in the nuclear interior being especially concentrated adjacent to the nuclear envelope where they form a highly interrupted ring (the complex chromocenter type organization). In C.mutabilis in contrast to C.agloeformis the condensed chromatin appears only as a few minute chromocenter-like bodies distributed all over the nucleus (the simple chromocenter type organizaion). The mitosis follows the normal pattern although the details reveal some interesting features. Prior to the division the nucleus remains in its starting (interphase) position. The onset of mitosis is signaled by several nuclear changes which occur more or less simultaneously. The size of the nucleus increases and its shape changes. During prophase the nucleolus begins to lose its stainability. The chromatin condenses in chromosomes. At the late prophase the distinctive light unstainable (clear) zone is revealed and the forming chromosomes show a congregation in the form of a clew. This period is very short. In the metaphase the faintly-stained substance appears. The similar to each other small dot-like chromosomes (n=10) are arranged in equatorial plate and are embedded in this substance. The straight taper spindle is formed. The longitudinal axes of the spindle and cell are parallel to each other. At the onset of anaphase the interzonal spindle is developed between the groups of sister chromosomes. Later the spidle becomes bow-shaped. As a result, these groups slightly approach to each other. The septum originates in the cell. Telophase is a very prolonged stage of mitosis. Sometimes the telophase nuclei are noted even in the recently formed sister cells. Simultaneously binucleate cells appear. These cells probably arise by the inhibition of cytokinesis. The pyrenoid is presented throughout mitosis.