Reza Mehedi, Ruokolainen Janne, Vuorinen Tapani
Department of Applied Physics, Aalto University, P.O. Box 11100, 00076, Aalto, Finland.
Planta. 2014 Sep;240(3):565-73. doi: 10.1007/s00425-014-2107-1. Epub 2014 Jun 26.
A 3D model of the tracheid wall has been proposed based on high-resolution cryo-TEM where, in contrast to the current understanding, the cellulose elementary fibrils protrude from the cell wall plane. The ultrastructure of the tracheid walls of Picea abies was examined through imaging of ultrathin radial, tangential and transverse sections of wood by transmission electron microscopy and with digital image processing. It was found that the elementary fibrils (EFs) of cellulose were rarely deposited in the plane of the concentric cell wall layers, in contrast to the current understanding. In addition to the adopted concept of longitudinal fibril angle, EFs protruded from the cell wall plane in varying angles depending on the layer. Moreover, the out-of-plane fibril angle varied between radial and tangential walls. In the tangential S2 layers, EFs were always out-of-plane whereas planar orientation was typical for the S2 layer in radial walls. The pattern of protruding EFs was evident in almost all axial and transverse images of the S1 layer. Similar out-of-plane orientation was found in the transverse sections of the S3 layer. A new model of the tracheid wall with EF orientation is presented as a summary of this study. The outcome of this study will enhance our understanding of the elementary fibril orientation in the tracheid wall.
基于高分辨率冷冻透射电子显微镜，已经提出了一种管胞壁的三维模型，与目前的认识相反，纤维素原纤维从细胞壁平面突出。通过透射电子显微镜对木材的超薄径向、切向和横向切片进行成像，并结合数字图像处理，研究了欧洲云杉管胞壁的超微结构。结果发现，与目前的认识相反，纤维素原纤维（EFs）很少沉积在同心细胞壁层的平面内。除了采用的纵向纤维角度概念外，EFs根据层的不同以不同角度从细胞壁平面突出。此外，径向壁和切向壁的平面外纤维角度不同。在切向S2层中，EFs总是在平面外，而径向壁S2层的典型取向是平面内。在S1层几乎所有的轴向和横向图像中，突出的EFs模式都很明显。在S3层的横向切片中也发现了类似的平面外取向。作为本研究的总结，提出了一种具有EF取向的管胞壁新模型。本研究结果将增进我们对管胞壁中原纤维取向的理解。
