Hetherington Alexander J, Dubrovsky Joseph G, Dolan Liam
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK.
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK; Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 510-3, Cuernavaca 62250, Mexico.
Curr Biol. 2016 Jun 20;26(12):1629-1633. doi: 10.1016/j.cub.2016.04.072. Epub 2016 Jun 2.
Roots and shoots of plant bodies develop from meristems-cell populations that self-renew and produce cells that undergo differentiation-located at the apices of axes [1].The oldest preserved root apices in which cellular anatomy can be imaged are found in nodules of permineralized fossil soils called coal balls [2], which formed in the Carboniferous coal swamp forests over 300 million years ago [3-9]. However, no fossil root apices described to date were actively growing at the time of preservation [3-10]. Because the cellular organization of meristems changes when root growth stops, it has been impossible to compare cellular dynamics as stem cells transition to differentiated cells in extinct and extant taxa [11]. We predicted that meristems of actively growing roots would be preserved in coal balls. Here we report the discovery of the first fossilized remains of an actively growing root meristem from permineralized Carboniferous soil with detail of the stem cells and differentiating cells preserved. The cellular organization of the meristem is unique. The position of the Körper-Kappe boundary, discrete root cap, and presence of many anticlinal cell divisions within a broad promeristem distinguish it from all other known root meristems. This discovery is important because it demonstrates that the same general cellular dynamics are conserved between the oldest extinct and extant root meristems. However, its unique cellular organization demonstrates that extant root meristem organization and development represents only a subset of the diversity that has existed since roots first evolved.
植物体的根和芽由分生组织发育而来，分生组织是位于轴顶端的细胞群体，能自我更新并产生经历分化的细胞[1]。能够对细胞解剖结构进行成像的最古老的保存下来的根顶端，发现于被称为煤球的矿化化石土壤结核中[2]，这些煤球形成于3亿多年前石炭纪的煤沼泽森林中[3 - 9]。然而，迄今为止所描述的化石根顶端在保存时并非处于活跃生长状态[3 - 10]。由于根生长停止时分生组织的细胞组织会发生变化，所以一直无法比较已灭绝和现存类群中干细胞向分化细胞转变时的细胞动态[11]。我们预测活跃生长的根的分生组织会保存在煤球中。在此我们报告首次发现了来自石炭纪矿化土壤的活跃生长的根分生组织的化石遗迹，其中保存了干细胞和分化细胞的详细信息。分生组织的细胞组织是独特的。Körper - Kappe边界的位置、离散的根冠以及在宽阔的原分生组织内许多垂周细胞分裂的存在，使其与所有其他已知的根分生组织区分开来。这一发现很重要，因为它表明最古老的已灭绝和现存的根分生组织之间存在相同的一般细胞动态。然而，其独特的细胞组织表明，现存根分生组织的组织和发育仅代表了自根首次进化以来所存在的多样性的一个子集。
