Panzera F, Giménez-Abián M I, López-Sáez J F, Giménez-Martín G, Cuadrado A, Shaw P J, Beven A F, Cánovas J L, De la Torre C
Centro de Investigaciones Biológicas, CSIC, Velázquez 144, E-28006 Madrid, Spain.
Chromosoma. 1996 Jul;105(1):12-9. doi: 10.1007/BF02510034.
Roots from Allium cepa L. (cv. Francesa) bulbs in which a maximum of two nucleoli per nucleus developed were selected for this study. Five rDNA clusters were detected by fluorescent in situ hybridization on chromosomal squashes (2n = 16) with a rhodamine-labelled wheat rDNA repeat. The rDNA clusters were located on four chromosomes: the largest cluster occurred on the small arm of a single homologue of the smallest pair 8. Its homologue showed two different small rDNA clusters, one near each telomere. The two homologues of the satellited chromosomes 6 also showed different rDNA contents, which were intermediate to those found in pair 8. The same five well-differentiated hybridization signals were observed in interphase cells that were inactive in transcription because they were in dormant roots, or in proliferating ones in which the synthesis of the large rRNA precursor was prevented. After multipolarizing agent was applied in anaphase followed by inhibition of cytokinesis, multinucleate autotetraploid cells were formed, which often contained more than four nucleoli. Thus, at least two of the three nucleolar organizer regions that consistently failed to develop a nucleolus in normal mononucleate cells were capable of developing nucleoli when segregated into different nuclei in multinucleate cells.
本研究选用了来自洋葱（品种：弗朗西斯卡）鳞茎的根，这些根中每个细胞核最多发育出两个核仁。通过用罗丹明标记的小麦rDNA重复序列对染色体压片（2n = 16）进行荧光原位杂交，检测到五个rDNA簇。rDNA簇位于四条染色体上：最大的簇出现在最小的第8对同源染色体中一条的短臂上。其同源染色体显示出两个不同的小rDNA簇，分别靠近每个端粒。具随体的第6对同源染色体也显示出不同的rDNA含量，介于第8对染色体中的含量之间。在间期细胞中观察到相同的五个分化良好的杂交信号，这些细胞由于处于休眠根中而转录不活跃，或者处于阻止大rRNA前体合成的增殖根中。在后期施加多极剂并随后抑制胞质分裂后，形成了多核同源四倍体细胞，这些细胞通常含有超过四个核仁。因此，在正常单核细胞中始终未能发育出核仁的三个核仁组织区中，至少有两个在多核细胞中被分隔到不同细胞核时能够发育出核仁。
