School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
Curr Biol. 2009 Dec 29;19(24):2102-7. doi: 10.1016/j.cub.2009.10.075.
Walled cells have the ability to remodel their shape while sustaining an internal turgor pressure that can reach values up to 10 atmospheres [1-7]. Although it is undisputed that this requires a tight and simultaneous regulation of cell wall assembly and mechanics, previous theoretical studies on tip growth focused either on the mechanical behavior of the cell wall or on its assembly [8-14]. To study the interplay between growth and mechanics in shaping a walled cell, we examine the particularly simple geometry of tip-growing cells [1, 3, 15, 16], which elongate via the assembly and expansion of cell wall in the apical region of the cell. We describe the observed irreversible expansion of the cell wall during growth as the extension of an inhomogeneous viscous fluid shell under the action of turgor pressure, fed by a material source in the neighborhood of the growing tip. This allows us to determine theoretically the radius of the cell and its growth velocity in terms of the turgor pressure and the secretion rate and rheology of the cell wall material. We derive simple scaling laws for the geometry of the cell and find that a single dimensionless parameter, which characterizes the relative roles of cell wall assembly and expansion, is sufficient to explain the observed variability in shapes of tip-growing cells. More generally, our description provides a framework to understand cell growth and remodeling in plants (pollen tubes [17], root hairs, etc. [18]), fungi (hyphal growth [19, 20] and fission and budding yeast [3]), and some bacteria [21], in the context of both tip growth and diffuse growth.
壁细胞具有在维持内部膨压的情况下重塑形状的能力,该膨压可达到 10 个大气压[1-7]。尽管无可争议的是,这需要细胞壁组装和力学的紧密和同时调节,但以前关于尖端生长的理论研究要么关注细胞壁的力学行为,要么关注其组装[8-14]。为了研究在塑造有壁细胞中生长和力学之间的相互作用,我们研究了尖端生长细胞的特别简单的几何形状[1,3,15,16],这些细胞通过在细胞的顶端区域组装和扩展细胞壁来伸长。我们将观察到的细胞壁在生长过程中的不可逆扩展描述为在膨压作用下,在由生长尖端附近的物质源供应的不均匀粘性流体壳的延伸,以此来研究生长过程中细胞壁的不可逆扩展。这使我们能够根据膨压、细胞壁物质的分泌速率和流变学理论上确定细胞半径及其生长速度。我们推导出细胞几何形状的简单比例定律,并发现一个单一的无量纲参数足以解释观察到的尖端生长细胞形状的可变性,该参数特征化了细胞壁组装和扩展的相对作用。更一般地,我们的描述为理解植物(花粉管[17]、根毛等[18])、真菌(菌丝生长[19,20]和酵母的分裂和出芽[3])和一些细菌[21]中的细胞生长和重塑提供了一个框架,这在尖端生长和弥散生长的背景下都适用。