Three-dimentional images of deposition of microfibrils and matrix substances in the cell wall

应用激光共聚焦显微镜对针叶树皮层微管在管胞分化过程中的排列进行了研究。初生壁形成过程中，管胞内微管排列不规则，主要取向由纵向变为横向。在次生壁的形成过程中，MT的排列是有序的，随着管胞分化的进行，它们的取向逐渐从平坦的S-螺旋变为陡峭的Z-螺旋，然后变为平坦的S-螺旋。FE-SEM观察到的细胞壁最内表面上的纤维素微纤丝（MF）的取向以类似的方式改变的MT。在次级壁的形成过程中，MF改变了它们的方向，顺时针旋转（从管腔侧观察），从平坦的S-螺旋到陡峭的Z-螺旋，然后从陡峭的Z-螺旋到平坦的S-螺旋。这些结果为针叶树管胞细胞壁半螺旋结构形成过程中微管和微管的共排列提供了有力的证据。在分化的连续步骤中，在任何径向系列中都没有观察到MT被分解的管胞。MTs的取向可能会逐渐改变而不解聚的MT，支持动态螺旋模型。在此基础上，我们提出了一个管胞分化过程中微管和微纤维取向的模型。

The arrangement of cortical microtubules (MTs) in differentiating tracheids of conifers was examined by confocal laser scanning microscopy after immunofluorescent staining. The arrays of MTs in the tracheids during formation of the primary wall were not well ordered and the predominant orientation changed from longitudinal to transverse. During formation of the secondary wall, the arrays of MTs were well ordered and their orientation changed progressively from a flat S-helix to a steep Z-helix and then to a flat S-helix as the differentiation of tracheids proceeded. The orientation of cellulose microfibrils (MFs) on the innermost surface of cell walls observed by FE-SEM changed in a similar manner to that of the MTs. The MFs changed their orientation, with clockwise rotation (viewed from the lumen side), from a flat S-helix to a steep Z-helix and then from a steep Z-helix to a flat S-helix during the formation of secondary wall. These results provide strong evidence for the co-alignment of MTs and MFs during the formation of the semi-helicoidal texture of the cell wall in conifer tracheids. No tracheids in which the MTs had been disassembled were observed in any radial series during the successive steps of differentiation. The orientation of MTs might change progressively without depolymerization of MTs, supporting the dynamic helical model. On the basis of our results, we propose a model for the orientation of MTs and MFs during the differentiation of tracheids.