Three-dimensional structures of interphasic nucleous organizing regions in higher plants

对缺氧条件下蚕豆根尖细胞核仁的结构组织，特别是含dna结构进行了研究。通过煮沸蒸馏水并立即冷却至23ºC来达到缺氧条件。随着暴露时间的延长，核仁的结构发生了如下变化：(1)核仁偏析，(2)核仁分散，(3)亲银支架的出现，(4)完全消失。电镜观察显示，纤维中心逐渐发育，内部出现大颗粒（35 nm），染色质和膜开始塌陷。当使用抗dna抗体免疫金标记时，活跃根细胞中的致密纤维成分（DFC）被适度标记，而在缺氧条件下，DFC上的标记随着时间的推移逐渐减少，Fcs中的染色质样团块被标记得最重。这表明在缺氧条件下，参与转录的rDNA从DFC退入FCs。萝卜核仁可见厚核仁瘤和薄核仁瘤。分生细胞的核仁主要有厚核仁和薄核仁两种类型，而分化细胞的核仁以薄核仁为多见。用Spurrs树脂包埋的薄片进行银染色。结果鉴定出三种类型的核仁线段；(1)短碎片堆，(2)两束圆形碎片，(3)环状碎片。所有这些片段都以450nm的宽度排列。这三种类型的核仁线段的外观很好地阐明了核仁线段丝缠绕形成450 nm厚的核仁线段的想法。核小线束的卷曲可以反映染色体螺线管。当细胞分化时，这个线圈可能开始塌陷。

The structural organization of the nucleolus, especially the DNA-containing structure, was examined in Vicia faba root-tip cells exposed to hypoxia. Hypoxic conditions were attained by boiling distillled water and immediately cooling down to 23ﾟC.The nucleoli suffered stepwise structural alterations with exposure time as follows ; (1) nucleolar segregation, (2) nucleolar dispersion, (3) appearance of argyrophilic stands and (4) complete disappearance. Electron microscopy showed that the fibrillar centers (FCs) gradually develop with appearance of large particles (35 nm granules) inside and concomitantly with these phenomenon, chromatin and endomenbrane began to collapse. When immunogold labeling with an anti-DNA antibody was applied, the dense fibrillar component (DFC) was moderately labeled in cells of an actively growing root, whereas under hypoxia the label on the DFC gradually decreased with time and chromatin-like masses in the Fcs were most heavily labeled. This suggest that rDNA engaged in transcription retired from the DFC into the FCs under hypoxia.Thick and thin nucleolonema were seen in the nucleolus of Raphanus sativus. In meristematic cells, the two types of nucleoli, those with mainly thick nucleolonema and with mostly thin nucleolonema, were seen while the nucleoli with thin nucleolonema wes most frequently found in the differentiated cells. Silver staining was applied to thin sections of the specimen embedded in Spurrs resin. As the result, three types of nucleolonema segments were appreciated ; (1) stack of short fragments, (2) two rays of round-shape segments and (3) ring-shape segments. All these segments were arranged in 450 nm width. The appearance of these three types of nucleolonema segments is well elucidated by an idea that the nucleolonema filament coils up to form 450 nm thick nucleolonema. This coiling of the nucleolonema may reflect chromosome solenoid. This coil probably begin to collapse as cells differentiate.