Deltour R, de Barsy T
J Cell Sci. 1985 Jun;76:67-83. doi: 10.1242/jcs.76.1.67.
The activation of the nucleolus of primary root cells of Sinapis alba embryos during the first 72 h of germination was monitored by autoradiographic, ultrastructural and microstereological methods. Autoradiographs showed that within 48 h, the nucleolus progressively resumed the capacity to synthesize pre-rRNA molecules at a high rate. In quiescent embryos the nucleolus was small, compact and composed of mixed granular and fibrillar components. Within the first 6 h of germination a strong nucleolar vacuolation occurred, accompanied by a decrease in the volume of the nucleolus and a concomitant high loss of its ribonucleoproteins (RNPs). From 6 to 24 h, nucleolar vacuolation decreased to reach a stable level. During this last period the volume of the nucleolus increased by the accumulation of the fibrillar component resulting from a slow pre-rRNA processing. At 24 h the nucleolus presented a predominantly fibrillar texture. After 24 h, nucleolus growth continued but was due to the accumulation of the granular component, indicating that pre-rRNA processing occurred at a higher rate than during the first day of germination. From 48 h the nucleolus was composed of well-delineated granular and fibrillar areas. Dense nucleolus-associated chromatin as well as fibrillar centres were always observed during the whole period of observation. In addition, previous studies on the nucleolus of radicle cells of Zea mays embryo during early germination were completed by studying changes in the nucleolar volume and in the density of pre-ribosomal subunits of the granular component. On the basis of the data obtained with both species we suggest that a possible function for the nucleolar vacuoles is the increase in the nucleolus-nucleoplasm exchange interface in response to a rapid increase in the output of nucleolar RNPs. The nucleolar growth pattern during early germination is also discussed.
通过放射自显影、超微结构和显微立体学方法监测了白芥胚胎萌发最初72小时内初生根细胞中核仁的激活情况。放射自显影片显示，在48小时内，核仁逐渐恢复以高速率合成前体核糖体RNA（pre-rRNA）分子的能力。在静止胚胎中，核仁小而致密，由颗粒和纤维成分混合组成。在萌发的最初6小时内，核仁出现强烈的空泡化，同时核仁体积减小，其核糖核蛋白（RNP）大量损失。从6小时到24小时，核仁空泡化减少至稳定水平。在这最后一个时期，由于前体rRNA加工缓慢，纤维成分积累导致核仁体积增加。24小时时，核仁呈现出主要为纤维状的结构。24小时后，核仁继续生长，但这是由于颗粒成分的积累，表明前体rRNA加工的速率高于萌发第一天。从48小时起，核仁由界限分明的颗粒区和纤维区组成。在整个观察期间，始终观察到致密的核仁相关染色质以及纤维中心。此外，通过研究玉米胚胎胚根细胞在早期萌发过程中核仁体积和颗粒成分中核糖体前体亚基密度的变化，完成了之前关于玉米胚胎胚根细胞核仁的研究。基于这两个物种获得的数据，我们认为核仁空泡的一个可能功能是响应核仁RNP输出的快速增加，增加核仁与核质的交换界面。还讨论了早期萌发期间核仁的生长模式。
