Plastids, an essential group of plant cellular organelles, proliferate by division to maintain continuity through cell lineages in plants. In recent years, it was revealed that the bacterial cell division protein FtsZ is encoded in the nuclear genome of plant cells, and plays a major role in the plastid division process forming a ring along the center of plastids. Although the best-characterized type of plastid division so far is the division with a single FtsZ ring at the plastid midpoint, it was recently reported that in some plant organs and tissues, plastids are pleomorphic and form multiple FtsZ rings. However, the pleomorphic plastid division mechanism, such as the formation of multiple FtsZ rings, the constriction of plastids and the behavior of plastid (pt) nucleoids, remains totally unclear. To elucidate these points, we used the cultured cell line, tobacco (Nicotiana tabacum L.) Bright Yellow-2, in which plastids are pleomorphic and show dynamic morphological changes during culture. As a result, it was revealed that as the plastid elongates from an ellipsoid shape to a string shape after medium renewal, FtsZ rings are multiplied almost orderly and perpendicularly to the long axis of plastids. Active DNA synthesis of pt nucleoids is induced by medium transfer, and the division and the distribution of pt nucleoids occur along with plastid elongation. Although it was thought that the plastid divides with simultaneous multiple constrictions at all the FtsZ ring sites, giving rise to many small plastids, we found that the plastids generally divide constricting at only one FtsZ ring site. Moreover, using electron microscopy, we revealed that plastid-dividing (PD) rings are observed only at the constriction site, and not at swollen regions. These results indicate that in the pleomorphic plastid division with multiple FtsZ rings, the formation of PD rings occurs at a limited FtsZ ring site for one division. Multiplied FtsZ rings seem to localize in advance at the expected sites of division, and the formation of a PD ring at each FtsZ ring site occurs in a certain order, not simultaneously. Based on these results, a novel model for the pleomorphic plastid division with multiple FtsZ rings is proposed.

中文翻译：

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烟草 BY-2 细胞中具有多个 FtsZ 环的多形质体的分裂。


质体是植物细胞器的重要组成部分，通过分裂增殖以维持植物细胞谱系的连续性。近年来，人们发现细菌细胞分裂蛋白FtsZ编码于植物细胞的核基因组中，在质体分裂过程中沿着质体中心形成环发挥着重要作用。虽然迄今为止最具特征的质体分裂类型是质体中点具有单个 FtsZ 环的分裂，但最近报道在一些植物器官和组织中，质体是多形性的并形成多个 FtsZ 环。然而，多形性质体分裂机制，例如多个 FtsZ 环的形成、质体的收缩和质体 (pt) 核的行为，仍然完全不清楚。为了阐明这些观点，我们使用了培养的细胞系烟草（Nicotiana tabacum L.）Bright Yellow-2，其中质体是多形性的，并且在培养过程中表现出动态形态变化。结果表明，当质体在介质更新后从椭圆体形状伸长为绳状时，FtsZ环几乎有序地且垂直于质体长轴地倍增。 pt核仁的活性DNA合成是由培养基转移诱导的，并且pt核仁的分裂和分布随着质体的伸长而发生。尽管人们认为质体在所有 FtsZ 环位点同时分裂，产生许多小质体，但我们发现质体通常仅在一个 FtsZ 环位点分裂收缩。此外，使用电子显微镜，我们发现质体分裂（PD）环仅在收缩部位观察到，而不是在肿胀区域。 这些结果表明，在具有多个FtsZ环的多形性质体分裂中，PD环的形成发生在一次分裂的有限FtsZ环位点处。倍增的 FtsZ 环似乎提前定位在预期的分裂位点，并且每个 FtsZ 环位点处 PD 环的形成以一定的顺序发生，而不是同时发生。基于这些结果，提出了一种具有多个 FtsZ 环的多形质体分裂的新模型。