Yi Hojae, Rui Yue, Kandemir Baris, Wang James Z, Anderson Charles T, Puri Virendra M
Department of Agricultural and Biological Engineering, The Pennsylvania State University, University Park, PA, United States.
Department of Biology, The Pennsylvania State University, University Park, PA, United States.
Front Plant Sci. 2018 Nov 5;9:1566. doi: 10.3389/fpls.2018.01566. eCollection 2018.
Stomata function as osmotically tunable pores that facilitate gas exchange at the surface of plants. Stomatal opening and closure are regulated by turgor changes in guard cells that result in mechanically regulated deformations of guard cell walls. However, how the molecular, architectural, and mechanical heterogeneities that exist in guard cell walls affect stomatal dynamics is unclear. In this work, stomata of wild type plants or of mutants lacking normal cellulose, hemicellulose, or pectins were experimentally induced to close or open. Three-dimensional images of these stomatal complexes were collected using confocal microscopy, images were landmarked, and three-dimensional finite element models (FEMs) were constructed for each complex. Stomatal opening was simulated with a 5 MPa turgor increase. By comparing experimentally measured and computationally modeled changes in stomatal geometry across genotypes, anisotropic mechanical properties of guard cell walls were determined and mapped to cell wall components. Deficiencies in cellulose or hemicellulose were both predicted to stiffen guard cell walls, but differentially affected stomatal pore area and the degree of stomatal opening. Additionally, reducing pectin molecular mass altered the anisotropy of calculated shear moduli in guard cell walls and enhanced stomatal opening. Based on the unique architecture of guard cell walls and our modeled changes in their mechanical properties in cell wall mutants, we discuss how each polysaccharide class contributes to wall architecture and mechanics in guard cells. This study provides new insights into how the walls of guard cells are constructed to meet the mechanical requirements of stomatal dynamics.
气孔起着渗透可调孔的作用，促进植物表面的气体交换。气孔的开闭由保卫细胞的膨压变化调节，这导致保卫细胞壁发生机械调节的变形。然而，保卫细胞壁中存在的分子、结构和机械异质性如何影响气孔动态尚不清楚。在这项工作中，对野生型植物或缺乏正常纤维素、半纤维素或果胶的突变体的气孔进行实验诱导使其关闭或开放。使用共聚焦显微镜收集这些气孔复合体的三维图像，对图像进行标记，并为每个复合体构建三维有限元模型（FEM）。模拟气孔在膨压增加5MPa时的开放。通过比较不同基因型气孔几何形状的实验测量和计算模拟变化，确定保卫细胞壁的各向异性力学性能并将其映射到细胞壁成分上。预测纤维素或半纤维素的缺乏都会使保卫细胞壁变硬，但对气孔孔面积和气孔开放程度有不同影响。此外，降低果胶分子量会改变保卫细胞壁中计算剪切模量的各向异性，并增强气孔开放。基于保卫细胞壁的独特结构以及我们在细胞壁突变体中模拟的其力学性能变化，我们讨论了每种多糖类如何对保卫细胞的壁结构和力学做出贡献。这项研究为保卫细胞壁如何构建以满足气孔动态的力学要求提供了新的见解。
