Roumeli Eleftheria, Ginsberg Leah, McDonald Robin, Spigolon Giada, Hendrickx Rodinde, Ohtani Misato, Demura Taku, Ravichandran Guruswami, Daraio Chiara
Department of Materials Science and Engineering, University of Washington, Seattle, WA 98195, USA.
Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA 91125, USA.
Plants (Basel). 2020 Dec 5;9(12):1715. doi: 10.3390/plants9121715.
Individual plant cells are the building blocks for all plantae and artificially constructed plant biomaterials, like biocomposites. Secondary cell walls (SCWs) are a key component for mediating mechanical strength and stiffness in both living vascular plants and biocomposite materials. In this paper, we study the structure and biomechanics of cultured plant cells during the cellular developmental stages associated with SCW formation. We use a model culture system that induces transdifferentiation of cells to xylem vessel elements, upon treatment with dexamethasone (DEX). We group the transdifferentiation process into three distinct stages, based on morphological observations of the cell walls. The first stage includes cells with only a primary cell wall (PCW), the second covers cells that have formed a SCW, and the third stage includes cells with a ruptured tonoplast and partially or fully degraded PCW. We adopt a multi-scale approach to study the mechanical properties of cells in these three stages. We perform large-scale indentations with a micro-compression system in three different osmotic conditions. Atomic force microscopy (AFM) nanoscale indentations in water allow us to isolate the cell wall response. We propose a spring-based model to deconvolve the competing stiffness contributions from turgor pressure, PCW, SCW and cytoplasm in the stiffness of differentiating cells. Prior to triggering differentiation, cells in hypotonic pressure conditions are significantly stiffer than cells in isotonic or hypertonic conditions, highlighting the dominant role of turgor pressure. Plasmolyzed cells with a SCW reach similar levels of stiffness as cells with maximum turgor pressure. The stiffness of the PCW in all of these conditions is lower than the stiffness of the fully-formed SCW. Our results provide the first experimental characterization of the mechanics of SCW formation at single cell level.
单个植物细胞是所有植物和人工构建的植物生物材料（如生物复合材料）的基本组成部分。次生细胞壁（SCW）是介导活的维管植物和生物复合材料机械强度和刚度的关键成分。在本文中，我们研究了与SCW形成相关的细胞发育阶段培养植物细胞的结构和生物力学。我们使用一种模型培养系统，在用地塞米松（DEX）处理后诱导细胞转分化为木质部导管分子。基于细胞壁的形态学观察，我们将转分化过程分为三个不同阶段。第一阶段包括仅具有初生细胞壁（PCW）的细胞，第二阶段涵盖已形成SCW的细胞，第三阶段包括液泡膜破裂且PCW部分或完全降解的细胞。我们采用多尺度方法研究这三个阶段细胞的力学性能。我们在三种不同的渗透条件下用微压缩系统进行大规模压痕试验。在水中进行原子力显微镜（AFM）纳米级压痕试验使我们能够分离细胞壁的响应。我们提出了一个基于弹簧的模型，以解卷积区分化细胞刚度中来自膨压、PCW、SCW和细胞质的竞争刚度贡献。在触发分化之前，低渗压力条件下的细胞比等渗或高渗条件下的细胞明显更硬，突出了膨压的主导作用。具有SCW的质壁分离细胞达到与具有最大膨压的细胞相似的刚度水平。在所有这些条件下，PCW的刚度低于完全形成的SCW的刚度。我们的结果提供了单细胞水平上SCW形成力学的首次实验表征。
