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

研究了低氧条件下蚕豆根尖细胞核仁的结构组成，特别是含DNA的结构。低氧条件是将蒸馏水煮沸并立即降温至23ﾟC。随着暴露时间的延长，核仁的结构发生了以下变化：(1)核仁分离，(2)核仁分散，(3)出现嗜银支架，(4)完全消失。电子显微镜观察发现，随着大颗粒(35 nm颗粒)的出现，纤维中心逐渐发育，染色质和膜开始塌陷。当用抗DNA抗体进行免疫金标记时，致密纤维成分(DFC)在生长活跃的根细胞中呈中等程度的标记，而在低氧条件下，DFC上的标记随着时间的推移逐渐减少，FCS中的染色质样团被标记得最重。这表明，在低氧条件下，参与转录的rDNA从DFC退隐到FCS。在萝卜的核仁中可见细小的核仁。在分生组织细胞中，以粗核仁为主的核仁和以细核仁为主的核仁在分化的细胞中最常见。对包埋在Sspars树脂中的标本进行薄片银染。结果，核粒体节分为三种类型：(1)短片段堆叠，(2)双射线圆形片段和(3)环状片段。所有这些片段都以450 nm的宽度排列。这三种核粒线段的出现可以通过核粒线丝卷曲形成450 nm厚的核粒线束的观点得到很好的解释。核线团的这种卷曲可能反映了染色体螺线体。随着细胞的分化，这个线圈可能开始崩溃。

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.