Boucheron-Dubuisson Elodie, Manzano Ana I, Le Disquet Isabel, Matía Isabel, Sáez-Vasquez Julio, van Loon Jack J W A, Herranz Raúl, Carnero-Diaz Eugénie, Medina F Javier
Université Pierre et Marie Curie - Paris 6, Sorbonne Universités, Institut de Systématique, Évolution, Biodiversité, ISYEB - UMR 7205 - CNRS, MNHN, UPMC, EPHE, 57 rue Cuvier, CP50, 75005 Paris, France.
Centro de Investigaciones Biológicas (CSIC), Ramiro de Maeztu 9, E-28040 Madrid, Spain.
J Plant Physiol. 2016 Dec 1;207:30-41. doi: 10.1016/j.jplph.2016.09.011. Epub 2016 Oct 19.
Environmental gravity modulates plant growth and development, and these processes are influenced by the balance between cell proliferation and differentiation in meristems. Meristematic cells are characterized by the coordination between cell proliferation and cell growth, that is, by the accurate regulation of cell cycle progression and the optimal production of biomass for the viability of daughter cells after division. Thus, cell growth is correlated with the rate of ribosome biogenesis and protein synthesis. We investigated the effects of simulated microgravity on cellular functions of the root meristem in a sequential study. Seedlings were grown in a clinostat, a device producing simulated microgravity, for periods between 3 and 10days. In a complementary study, seedlings were grown in a Random Positioning Machine (RPM) and sampled sequentially after similar periods of growth. Under these conditions, the cell proliferation rate and the regulation of cell cycle progression showed significant alterations, accompanied by a reduction of cell growth. However, the overall size of the root meristem did not change. Analysis of cell cycle phases by flow cytometry showed changes in their proportion and duration, and the expression of the cyclin B1 gene, a marker of entry in mitosis, was decreased, indicating altered cell cycle regulation. With respect to cell growth, the rate of ribosome biogenesis was reduced under simulated microgravity, as shown by morphological and morphometric nucleolar changes and variations in the levels of the nucleolar protein nucleolin. Furthermore, in a nucleolin mutant characterized by disorganized nucleolar structure, the microgravity treatment intensified disorganization. These results show that, regardless of the simulated microgravity device used, a great disruption of meristematic competence was the first response to the environmental alteration detected at early developmental stages. However, longer periods of exposure to simulated microgravity do not produce an intensification of the cellular damages or a detectable developmental alteration in seedlings analyzed at further stages of their growth. This suggests that the secondary response to the gravity alteration is a process of adaptation, whose mechanism is still unknown, which eventually results in viable adult plants.
环境重力调节植物的生长和发育，而这些过程受分生组织中细胞增殖与分化之间平衡的影响。分生细胞的特征在于细胞增殖与细胞生长之间的协调，即通过细胞周期进程的精确调控以及为分裂后子细胞的存活进行生物量的最佳生产。因此，细胞生长与核糖体生物合成和蛋白质合成的速率相关。在一项连续性研究中，我们研究了模拟微重力对根分生组织细胞功能的影响。幼苗在回转器（一种产生模拟微重力的装置）中生长3至10天。在一项补充研究中，幼苗在随机定位机（RPM）中生长，并在相似的生长时间段后依次取样。在这些条件下，细胞增殖速率和细胞周期进程的调控显示出显著变化，同时伴随着细胞生长的减少。然而，根分生组织的整体大小并未改变。通过流式细胞术分析细胞周期阶段，发现其比例和持续时间发生了变化，并且有丝分裂进入标记物细胞周期蛋白B1基因的表达降低，表明细胞周期调控发生了改变。关于细胞生长，模拟微重力下核糖体生物合成的速率降低，这通过核仁的形态和形态计量学变化以及核仁蛋白核仁素水平的变化得以体现。此外，在一个以核仁结构紊乱为特征的核仁素突变体中，微重力处理加剧了紊乱。这些结果表明，无论使用何种模拟微重力装置，分生组织能力的巨大破坏是在发育早期阶段检测到的对环境改变的首要反应。然而，在幼苗生长的进一步阶段进行分析时，较长时间暴露于模拟微重力并不会导致细胞损伤加剧或可检测到的发育改变。这表明对重力改变的次级反应是一个适应过程，其机制仍然未知，最终导致成年植物存活。
