Genome. 1997 Feb;40(1):91-8. doi: 10.1139/g97-012.
Seeds of three inbred lines of maize, with contrasting numbers of heterochromatic knobs and stored under two different ageing treatments, were analyzed for the occurrence of abnormalities at mitotic anaphase in root meristems 3, 7, 21,42, and 56 days after germination, and in root meristems of their freshly harvested selfed progeny. The largest category of detectable aberrations involved breakage of knobbed chromosome arms. We have obtained evidence that knob heterochromatin plays a central role in the origin of primary chromosome bridges. The initial event responsible for the occurrence of breakages and lagging chromosomes was characterized by the nondisjunction of newly replicated sister chromatids, which was observed to occur preferentially at the knob level. Such configurations, and all the other types of abnormalities (as for example, lagging chromosomes, typical chromosome bridges, fragments, and micronuclei), were observed at decreasing frequencies throughout root growth. Nevertheless, we have detected the occurrence of breakage-fusion-bridge cycles that were initiated by broken chromosomes. The relationship between late-replicating DNA in maize knob heterochromatin and the vulnerability of such regions to breakage is discussed. Our observations suggest a similarity between the mechanisms involved or associated with the origin of the described abnormalities and those reported to occur in cultured maize cells.
三种玉米自交系的种子，具有不同数量的异染色体结节，并在两种不同的老化处理下储存，在萌发后 3、7、21、42 和 56 天的根尖分生组织和刚收获的自交后代的根尖分生组织中分析了有丝分裂后期的异常情况。可检测到的异常主要涉及结节染色体臂的断裂。我们已经获得了证据，证明结节异染色质在初级染色体桥的起源中起着核心作用。负责发生断裂和滞后染色体的初始事件的特征是新复制的姐妹染色单体的不分离，这种不分离优先发生在结节水平。这种构型以及所有其他类型的异常（例如滞后染色体、典型的染色体桥、片段和微核）在根生长过程中以降低的频率发生。然而，我们已经检测到了由断裂染色体引发的断裂-融合-桥循环的发生。讨论了玉米结节异染色质中晚期复制 DNA 与这些区域易发生断裂之间的关系。我们的观察结果表明，所描述的异常起源所涉及或相关的机制与在培养的玉米细胞中报告的机制相似。
