当膨压超过细胞壁的抗张程度时细胞才能生长;另一种是让细胞壁松弛,减弱壁 的强度。 Cell growth Definition of cell growth An irreversible increase in volumn is the main factor of cell growth. Since most of the volumn of any cell is water, it follows that for a cell to increase its volumn it must take up water. The driving force for cell enlargement is water uptake. Water potential of a cell is regulated primarily by changes in turgor, the pressure generated by the expanding protoplast against the cell wall. Turgor pressures developed in cell can be quite large. In order to resist such pressures, cel walls must be very strong and rigid. The critical restriction on the capacity of plant cells to grow is imposed by the strength and rigidity of the cell wall. Thus, in order for a cell to increase in size, turger pressure has to increase until it exceeds the resistance of cell wall; another way for a cell to increase in size is to weaken the strength and rigidity of the cell wall 细胞生长方向的调控 细胞生长过程,使得松弛的细胞壁得以延伸的原动力是膨压。膨压产生的向 外的张力是均等地向各个方向的。如果没有壁的束缚,在膨压的作用下,细胞应 向各个方向均衡地生长,呈射线状扩展成球状。然而,植物细胞都有各自的形态, 因为细胞壁的结构,尤其是微纤丝在细胞壁中的取向决定细胞的生长方向(图) 微纤丝在细胞壁中的取向又是由微管在质膜内侧面的排列方向控制。有些激素 (例如:赤霉素,乙烯等)和一些外界因素因能影响微管在质膜内侧的排列方向, 从而影响微纤丝在细胞壁中的沉积方向,进而影响到细胞的伸长和植株的形态。 Regulation of cell growth directionality During growth, the loosened cell wall is extended by physical forces generated from cell turgor pressure. Turgor pressure creates an outward-directed force, equal in all directions. If there is no restriction of the cell wall, the cell would grow equally in all directions, expanding radially to generate a sphere. However, plant cells have all different shapes, because the structure of the cell wall--in particular, the orientatio of cellulose microfibril orientation determines growth directionality of cells. The orientation of newly deposited cellulose microfibrils is determined by the orientation of microtubules in the cortical cytoplasm. Certain hormones, (i.e, GA and ethylene and some environmental factors can influence the orientation of microtubules in cortical cytoplasm; therefore influence the direction of orientation of newly de cellulose microfibrils, and eventually affect cell expansion and plant shape 生长素的酸生长学说 生长中的细胞壁的一个重要特性是在酸性环境下延伸速度比中性环境下要 快很多,这种形象被称为酸生长。根据酸生长学说,生长素的功能之一是能通过 激活质膜上的ATP酶诱导细胞可将细胞质中的H分泌到细胞壁中。生长素诱导 的质子排出有两种可能的机制:激活已经存在的质子泵,或促进质膜上的ATP 酶的合成。而低pH值一方面通过激活膨胀素降低壁中多糖间氢键的结合程度 另一方面通过提髙壁中适于酸化条件的水解酶的活性,使壁发生松驰。壁一旦松 驰,在膨压的作用下,细胞就得以伸展。在质子排出的同时,长时间的酸生长效 应还包括溶质的吸收和一些新合成的成壁物质会填充于壁中。 he acid growth hypothesis for auxin action An important characteristic of growing cell walls is that they extend much faster at acidic pH than at neutral pH. This phenomenon is called acid growth. According to当膨压超过细胞壁的抗张程度时细胞才能生长；另一种是让细胞壁松弛，减弱壁 的强度。 Cell growth Definition of cell growth An irreversible increase in volumn is the main factor of cell growth. Since most of the volumn of any cell is water, it follows that for a cell to increase its volumn it must take up water. The driving force for cell enlargement is water uptake. Water potential of a cell is regulated primarily by changes in turgor, the pressure generated by the expanding protoplast against the cell wall. Turgor pressures developed in cells can be quite large. In order to resist such pressures, cel walls must be very strong and rigid. The critical restriction on the capacity of plant cells to grow is imposed by the strength and rigidity of the cell wall. Thus, in order for a cell to increase in size, turger pressure has to increase until it exceeds the resistance of cell wall; another way for a cell to increase in size is to weaken the strength and rigidity of the cell wall. 细胞生长方向的调控 细胞生长过程，使得松弛的细胞壁得以延伸的原动力是膨压。膨压产生的向 外的张力是均等地向各个方向的。如果没有壁的束缚，在膨压的作用下，细胞应 向各个方向均衡地生长，呈射线状扩展成球状。然而，植物细胞都有各自的形态， 因为细胞壁的结构，尤其是微纤丝在细胞壁中的取向决定细胞的生长方向(图)。 微纤丝在细胞壁中的取向又是由微管在质膜内侧面的排列方向控制。有些激素 （例如：赤霉素，乙烯等）和一些外界因素因能影响微管在质膜内侧的排列方向， 从而影响微纤丝在细胞壁中的沉积方向，进而影响到细胞的伸长和植株的形态。 Regulation of cell growth directionality During growth, the loosened cell wall is extended by physical forces generated from cell turgor pressure. Turgor pressure creates an outward-directed force, equal in all directions. If there is no restriction of the cell wall, the cell would grow equally in all directions, expanding radially to generate a sphere. However, plant cells have all different shapes, because the structure of the cell wall—in particular, the orientation of cellulose microfibril orientation determines growth directionality of cells. The orientation of newly deposited cellulose microfibrils is determined by the orientation of microtubules in the cortical cytoplasm. Certain hormones, (i.e., GA and ethylene) and some environmental factors can influence the orientation of microtubules in the cortical cytoplasm; therefore influence the direction of orientation of newly deposited cellulose microfibrils; and eventually affect cell expansion and plant shape. 生长素的酸生长学说 生长中的细胞壁的一个重要特性是在酸性环境下延伸速度比中性环境下要 快很多，这种形象被称为酸生长。根据酸生长学说，生长素的功能之一是能通过 激活质膜上的 ATP 酶诱导细胞可将细胞质中的 H +分泌到细胞壁中。生长素诱导 的质子排出有两种可能的机制：激活已经存在的质子泵，或促进质膜上的 ATP 酶的合成。而低 pH 值一方面通过激活膨胀素降低壁中多糖间氢键的结合程度， 另一方面通过提高壁中适于酸化条件的水解酶的活性，使壁发生松驰。壁一旦松 驰，在膨压的作用下，细胞就得以伸展。在质子排出的同时，长时间的酸生长效 应还包括溶质的吸收和一些新合成的成壁物质会填充于壁中。 The acid growth hypothesis for auxin action An important characteristic of growing cell walls is that they extend much faster at acidic pH than at neutral pH. This phenomenon is called acid growth. According to