【摘要】 <正> 关于本株四膜虫的接合生殖,包括接合前的行为、减数分裂、核的分化以及接合后体的发育等,我们曾进行过光学显微镜的观察(陈阅增等1982)。我们发现本株四膜虫在接合前有聚集成团的现象,克隆内接合形成的接合后体能正常分裂,并产生正常的大核系更多还原

【Abstract】 The selfer strain of Tetrahymena pyriformis S1 (Chen et al., 1982) was used for this study. Selfing was easily induced by starvation. For electron microscopy, cells collected at various intervals were washed with de-ionized water, centrifuged and fixed in 2,5% gluta-raldehyde in phosphate buffer solution (pH 7.4). Post-fixation was cassied aur at room temperature in 1%OsO4 in the same buffer solution and embedded in epoxy resin "618" (native product). Sections were cut with a LKB Ⅲ ultramicrotome, stained with uranyl acetate and lead dtrate, and examined with a JEM 100 cx electron microscope.It was found that with the elongation of the micronucleus, the formerly condensed chromatin became granular and evenly distributed throughout the whole nucleus. At the much elongated crescent stage, chromatin appeared as scattered electron dense granules and no discrete chromosomes could be discerned. Only when the crescest micronucleus became shortened to about half the length of the cell body did the 10 chromosomes make their appearance. Coilings and kinetochores of some of the chromosomes, as well as some of the developing stages of meioses, i.e., pairing of chromosomes and chiasmata formations could be clearly seen. Not infrequently sharp constrictions were noted at the surface of the elongated ribbon-like micronucleus (Fig. 17). The misleading condusion (Elliott, 1953; Ray, 1956; Chen et al., 1982) that paired chromosomes could be discerned microscopically at the stage of elongation of the micronucleus is believed to be caused by these surface constrictions. Small bundles of no more than 20 microtubules were found in the interphase micro-nucleus. It seemed that the elongation of the micronucleus is initiated by the simultaneous ex-tention of the microtubules and the covering nudear envelopes. When the ribbon-like mi-cronudeus became shortened and discrete chromosomes appeared, a fully developed mic-rotubular system could be seen which consisted of a peripheral layer of microtubules lying beneath the nudear envelope acting as a skeletal support of the micronucleus, and microtubules constituting the meiotic spindle.更多还原