the acid growth hypothesis, one of the important actions of auxin is to induce cells to transport protons into the cell wall by stimulating the plasma membrane H+-ATPase Two mechanisms have been proposed for auxin-induced proton extrusion: direct activation of the proton pump and enhanced synthesis of the plasma membrane H+-ATPase. The ability of protons to cause cell wall loosening is mediated by a class of proteins called expansins. Expansins loosen the cell wall by breaking hydrogen bonds between the polysaccharide components of the wall. With loosened cell wall cell is able to extend under turger pressure. In addition to proton extrusion, long-term auxin-induced growth involves the uptake of solutes and the synthesis and deposition of polysaccharides 赤霉素促进细胞壁的伸展 赤霉素和生长素都能影响细胞壁的特性。生长素的作用主要是通过诱导细胞 壁的酸化引起细胞壁松弛。然而赤霉素的作用机制和生长素的不同。关于赤霉素 促进细胞伸长的机制有多种假说,例如:有实验证据显示赤霉素通过提高木葡聚 糖内转糖基酶的活性促进细胞伸长。木葡聚糖内转糖基酶的功能可能是促进膨胀 素进入细胞壁,该酶还能引起细胞壁成分的重新排列。赤霉素诱导的细胞伸长过 程可能需要膨胀素和木葡聚糖内转糖基酶的共同参与。 Gibberellins Enhance Cell Wall Extensibility Both gibberellin and auxin seem to exert their effects by modifying cell wall properties. In the case of auxin, cell wall loosening appears to be mediated in part by cell wall acidification. However, this does not appear to be the mechanism of ibberellin action. Various suggestions have been made regarding the mechanism of gibberellin-stimulated cell elongation. For example, there is evidence that Ga stimulate the enzyme activity of xyloglucan endotransglycosylase (XET). The function of XET may be to facilitate the penetration of expansins into the cell wall XET is also involved in the reorganization of cell wall. Both expansins and XET may be required for gibberellin-stimulated cell elongation 3细胞分化 细胞分化的概念 从一种同质的细胞类型转变成形态结构和功能与原来不相同的异质细胞类 型的过程称为分化。例如:从受精卵细胞分裂转变成胚的过程就是分化。植物细 胞的分化常常是可逆的特别是当已经完成分化过程的细胞处于离体状态,在组 织培养的条件下,细胞就会发生脱分化(失去其分化后的特性,重新开始细胞分 裂。如果给脱分化的细胞提供合适的养分和激素,这些细胞能发育成一株完整的 植株 Cell differentiation Definition of cell differentiation Cell Differentiation is the process by which a cell acquires metabolic, structural, and functional properties that are distinct from those of its progenitor cell. fe example: Embryogenesis that transforms a single-celled zygote into a multicellular, microscopic, embryonic plant; the development of meristematic cells to tracheary elements; are processes of cell differentiation. Differentiated plant cells retain all the genetic information required for the development of a complete plant, a property termed totipotency. This totipotency property can be demonstrated by cell dedifferentiation. Plants cell differentiation is frequently reversible, particularly when differentiated cells are removed from the plant and placed in tissue culture. Under these conditions, cells dedifferentiate (i.e, lose their differentiated characteristics)the acid growth hypothesis, one of the important actions of auxin is to induce cells to transport protons into the cell wall by stimulating the plasma membrane H+-ATPase. Two mechanisms have been proposed for auxin-induced proton extrusion: direct activation of the proton pump and enhanced synthesis of the plasma membrane H+-ATPase. The ability of protons to cause cell wall loosening is mediated by a class of proteins called expansins. Expansins loosen the cell wall by breaking hydrogen bonds between the polysaccharide components of the wall. With loosened cell wall, cell is able to extend under turger pressure. In addition to proton extrusion, long-term auxin-induced growth involves the uptake of solutes and the synthesis and deposition of polysaccharides. 赤霉素促进细胞壁的伸展 赤霉素和生长素都能影响细胞壁的特性。生长素的作用主要是通过诱导细胞 壁的酸化引起细胞壁松弛。然而赤霉素的作用机制和生长素的不同。关于赤霉素 促进细胞伸长的机制有多种假说，例如：有实验证据显示赤霉素通过提高木葡聚 糖内转糖基酶的活性促进细胞伸长。木葡聚糖内转糖基酶的功能可能是促进膨胀 素进入细胞壁，该酶还能引起细胞壁成分的重新排列。赤霉素诱导的细胞伸长过 程可能需要膨胀素和木葡聚糖内转糖基酶的共同参与。 Gibberellins Enhance Cell Wall Extensibility Both gibberellin and auxin seem to exert their effects by modifying cell wall properties. In the case of auxin, cell wall loosening appears to be mediated in part by cell wall acidification. However, this does not appear to be the mechanism of gibberellin action. Various suggestions have been made regarding the mechanism of gibberellin-stimulated cell elongation. For example, there is evidence that GA stimiulate the enzyme activity of xyloglucan endotransglycosylase (XET). The function of XET may be to facilitate the penetration of expansins into the cell wall； XET is also involved in the reorganization of cell wall. Both expansins and XET may be required for gibberellin-stimulated cell elongation 3 细胞分化 细胞分化的概念 从一种同质的细胞类型转变成形态结构和功能与原来不相同的异质细胞类 型的过程称为分化。例如：从受精卵细胞分裂转变成胚的过程就是分化。植物细 胞的分化常常是可逆的,特别是当已经完成分化过程的细胞处于离体状态, 在组 织培养的条件下, 细胞就会发生脱分化(失去其分化后的特性), 重新开始细胞分 裂。如果给脱分化的细胞提供合适的养分和激素, 这些细胞能发育成一株完整的 植株。 Cell Differentiation Definition of cell differentiation Cell Differentiation is the process by which a cell acquires metabolic, structural, and functional properties that are distinct from those of its progenitor cell. For example: Embryogenesis that transforms a single-celled zygote into a multicellular, microscopic, embryonic plant; the development of meristematic cells to tracheary elements; are processes of cell differentiation. Differentiated plant cells retain all the genetic information required for the development of a complete plant, a property termed totipotency. This totipotency property can be demonstrated by cell dedifferentiation. Plants cell differentiation is frequently reversible, particularly when differentiated cells are removed from the plant and placed in tissue culture. Under these conditions, cells dedifferentiate (i.e., lose their differentiated characteristics)