Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236, Łódź, Poland.
Plant Cell Rep. 2018 Dec;37(12):1639-1651. doi: 10.1007/s00299-018-2335-0. Epub 2018 Aug 21.
DNA replication and continuous process of transcription during ongoing amitotic division accelerate the development of four-celled pea suspensor containing nuclei which create transient gradient of polyploidy necessary for correct embryo development. A suspensor, the link between embryo proper and surrounding tissues, differs significantly in size, morphology, and degree of polyploidy among the species. The suspensor of Pisum sativum consists of four polynuclear cells (two hemispherical and two elongated) formed in two layers. Their nuclei undergo endoreplication reaching, respectively, up to 256C and 128-256C DNA levels in its hemispherical and elongated parts. Our study shows that endoreplication first appears in the spherical part of the suspensor, and, subsequently, in the elongated one. At the next stages of suspensor development, the increase in DNA content takes place also in a similar order. Thus, despite simple construction of the suspensor, its development, supported by endoreplication, creates a certain gradient of polyploidy, which occurs in more extensive suspensors. Moreover, the rapid development of suspensor is supported both by the initiation of DNA replication prior to the completion of amitotic division of its polyploidal nuclei and by a continuous process of transcription, which is silenced by chromatin condensation throughout mitosis. Furthermore, the increase in DNA content correlates with the greater amount of transcripts; however, the multiplication of DNA copies does not entail an increase (but fluctuation) in the mean transcriptional activity of a particular nucleus during the next stages of suspensor development.
有丝分裂过程中的 DNA 复制和持续转录会加速豌豆悬浮培养物中含有核的四细胞形成，这些核会产生短暂的多倍体梯度，这是正确胚胎发育所必需的。悬浮培养物是胚胎本身和周围组织之间的联系，在大小、形态和多倍体程度方面在物种间有显著差异。豌豆的悬浮培养物由四个多核细胞（两个半球形和两个伸长形）组成，形成两层。它们的核经历内复制，分别达到其半球形和伸长形部分的 256C 和 128-256C 的 DNA 水平。我们的研究表明，内复制首先出现在悬浮培养物的球形部分，然后出现在伸长部分。在悬浮培养物发育的下一阶段，DNA 含量的增加也以类似的顺序发生。因此，尽管悬浮培养物的结构简单，但它的发育在多倍体核有丝分裂分裂完成之前启动 DNA 复制，并通过转录的持续过程来支持，而转录在整个有丝分裂过程中被染色质凝聚所抑制。此外，悬浮培养物的快速发育还得到了多倍体核有丝分裂分裂完成之前启动 DNA 复制和转录持续过程的支持，而转录在整个有丝分裂过程中被染色质凝聚所抑制。此外，DNA 含量的增加与转录物的数量成正比；然而，在悬浮培养物发育的下一阶段，DNA 拷贝的倍增并不意味着特定核的平均转录活性增加（而是波动）。
