Alterations of three-dimensional structure of nucleolar organizers during cell division and differentiation

用光学显微镜和电子显微镜对萝卜根尖细胞的核仁组成进行了研究，着重研究了其三维结构的组织。它的轮廓非常复杂，风干标本的厚度变化很大。它通常看起来是盘绕或蜿蜒的。核线体的纵向连续切片显示，首先是短核线体片段的堆叠，然后是一对突起的框架，中间有空间，再次是短核线体片段的堆叠。另一方面，横截面显示“C”形段，其开口的方向的变化。核线的形态测定表明，两类核线，每一个有510 nm和1.19 μ m的平均厚度，分别。细的核仁线体可以卷曲或折叠形成粗的核仁线体。纤维中心包括含DNA的结构与薄核紧密相关， 关于我们 lonem a，沿核仁线呈沿着间断排列。应用银浸渍技术的连续切片表明，核仁分离成两个区域，致密的纤维成分（DFC）的中心核心和颗粒成分（GC）的周边，并开发非彩色通道内DEC核心蜿蜒。电子显微镜观察表明，无色通道的出现是由纤维中心（FC）的发育和/或融合引起的，这些纤维中心被认为含有暂时静止的核糖体RNA基因（rDNA）。DFC的抗DNA抗体的标记显着强于胞质溶胶的标记，标记特异性是均匀的整个DEC。有趣的是，标记特异性的EC及其周围区域在暴露于缺氧条件下的标本中几乎是相同的，在正常条件下生长。与缺氧条件下FC的发展同时，在FC中形成直径约35 μ m的颗粒（35 nm颗粒）。它们完全没有被抗DNA抗体和RNase-gold复合物标记，表明它们既不含DNA也不含RNA。总的来说，含有可能参与RNA转录的核仁内DNA的DFC可能逐渐塌陷变成FC，同时释放失活的rDNA作为染色质样物质簇和Sonic核仁蛋白作为35 inn颗粒，当细胞暴露于缺氧条件时。少

The nucleoloneina of Raphanus sativus root-tip cells was studied with light and electron microscopy especially focusing on its three-dimensional structural organization. Its countour was very intricate and thc thickness showed a large variation in air-dried specimens. It usually appeared to coil or meander. Serial ultrathin sectioning of thc nucleolonema iii its longitudinal orientation first revealed the stack of short nucleolonema fragments, then a pair of knobbly frames with space in-between, and again the stack of the short nucleolonema segments. On the other hand, transversal sections revealed 'c'-shaped segments with the change of their openings' orientation. Morphometry of the nucleolonema indicated two categories of the nucleolonema ; each had an average thickness of 510 nm and 1.19mum, respectively. Taken together, the thin nucleolonema may coil or fold to form the thick one. The fibrillar centers including DNA-containing structures were closely associated with the thin nucleo … More lonem a and intermittently arranged along the nucleolonema.Localization of intranucleolar DNA under hypoxic conditions was examined in excised loot tips of Allium cepa. Application of a silver impregnation technique to serial ultrathin sections indicated that the nucleolus segregated into two regions, the central core of the dense fibrillar component (DFC) and the periphery of the granular component (GC), and developed achromatic channels meandering within the DEC core. Electron microscopy showed that the Qccurrence of the achromatic channel was caused by development and/or fusion of the fibrillar centers (FCs), which are believed to contain the temporarily resting ribosomal-RNA genes (rDNA). The label of the DFC with anti-DNA antibodies was significantly strong compared with that of the cytosol and the labeling specificity was uniform throughout the DEC.Interestingly, the labeling specificity of the ECs and their surrounding region in the specimens exposed to hypoxic condition was almost the same as those grown under a normal condition. Concurrently with the development of the FCs under hypoxic conditions, the granules about 35 um in diameter (35 nm granules) were formed in the FCs. They were not labeled at all with anti-DNA antibodies and RNase-gold complexes, indicating that they contain neither DNA nor RNA.Altogether, the DFC containing the intranucleolar DNA probably engaged in the RNA transcription may gradually collapses to turn into the FCs and simultaneously releases the inactivated rDNA as clusters of chromatin-likemasses and Sonic nucleolar proteins as the 35 inn granules, when the cells are exposed to hypoxic conditions. Less