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

树的形成层细胞通过细胞扩张、细胞壁加厚、木质化和细胞死亡等过程分化为次生木质部细胞。在木质部的分化过程中，由于细胞壁物质的局部沉积，细胞壁发生变化，如凹坑和螺旋状加厚。我们以前的研究结果表明，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细丝的局部出现和消失有关，这表明细胞骨架的成分控制着细胞壁物质的局部沉积。然而，我们只有几篇论文展示了细胞骨架成分的局部化是如何控制的。我们在这里分析了肌球蛋白，即所谓的马达蛋白，在STRESS木质部细胞分化中的作用，因为肌球蛋白利用ATP产生沿肌动蛋白细丝的机械力。首先，我们建立了木质部细胞肌球蛋白的可视化方法。肌球蛋白用抗肌球蛋白的单抗进行免疫染色，然后用FITC标记的第二抗体进行免疫染色。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来自肌球蛋白的荧光。肌球蛋白聚集在气管内交界处。随着木质部细胞的分化，肌球蛋白的聚集直径减小。肌球蛋白直径的减小与交界性凹陷的发展有关。肌球蛋白的这种定位类似于肌动蛋白细丝在分化木质部细胞中的定位。我们的结果表明，在凹陷形成处可能存在一种类似于哺乳动物肌肉收缩方式的肌球蛋白收缩系统。我们认为，肌球蛋白在修饰结构的形成中起重要作用，从而控制次生木质部细胞的形态发生。

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.