Dynamics of cytoskeleton myosin during the differentiation of xylem cells in trees

树木形成层细胞经过细胞膨胀、细胞壁增厚、木质化和细胞死亡的过程，向次生木质部细胞分化。在分化过程中，木质部细胞通过细胞壁材料的局部沉积产生细胞壁的变化，如凹坑和螺旋增厚。我们之前的研究结果表明，细胞壁形成的局部化与细胞骨架成分，即皮质微管和肌动蛋白丝的局部出现和消失有关，表明细胞骨架成分控制着细胞壁物质的局部沉积。然而，我们只有几篇论文显示如何控制细胞骨架成分的定位。我们在这里分析了肌凝蛋白，即所谓的运动蛋白，在树木木质部细胞分化中的作用，因为肌凝蛋白利用ATP沿着肌动蛋白丝产生机械力。首先，我们建立了木质部细胞肌球蛋白可视化的方法。用抗肌球蛋白单克隆抗体对肌球蛋白进行免疫染色，然后用fitc偶联二抗对肌球蛋白进行免疫染色。用激光共聚焦扫描显微镜观察。在分化的木质部细胞中观察到肌球蛋白产生的荧光。肌凝蛋白聚集在气管间边界凹陷的孔洞处。随着木质部细胞的分化，肌球蛋白聚集物的直径减小。肌凝蛋白直径的减小与边缘凹的形成有关。这种肌凝蛋白的定位与分化木质部细胞中肌动蛋白丝的定位相似。我们的结果表明，肌动蛋白收缩系统，与哺乳动物肌肉的收缩方式相似，可能存在于凹坑形成的部位。我们认为肌球蛋白在木质部次生细胞的形态发生中起着重要的调控作用。

Cambial cells in tress differentiate into secondary xylem cells through a process of cell expansion, cell wall thickenings, lignification and cell death. During the differentiation, xylem, cells develop modifications of the cell wall such as pits and helical thickenings by the localized deposition of cell wall materials. Our previous results indicated that the localization of cell wall formation was related to the localized appearance and disappearance of components of the cytoskeleton, namely cortical microtubules and actin filaments, indicating that components of the cytoskeleton control the localized deposition of cell wall materials. However, we have only a few papers showing how the localization of components of the cytoskeleton is controlled. We analyzed here the role of myosins, so called motor-proteins, in the differentiation of xylem cells in tress because myosins utilize ATP to generate mechanical force along actin filaments. Firstly, we established the method of visualization of myosin in xylem cells. Myosins were immuno-stained with a monoclonal antibody against myosins and then FITC-conjugated secondary antibody. They were observed by confocal laser scanning microscopy. Fluorescence derived from myosins was observed in differentiating xylem cells. Myosins were aggregated at the sites of apertures of intertracheal bordered pits. As xylem cells differentiated, the aggregation of myosins decreased in diameter. The reduction in diameter of myosins was associated with the development of bordered pits. Such a localization of myosins was a similar to that of actin filaments in differentiating xylem cells. Our results indicate that an acto-myosin contractile system, being a similar manner to the contraction of mammalian muscle, might be present at the site of pit formation. We conclude that myosins play an important role in the formation of modified structure, therefore controlling the morphogenesis of secondary xylem cells.