第七章信号的感受与传递 Chapter 7 signal perception and transduction 第一节 信号传递途径概述 信号传递途径的概念和过程 在发育过程中,植物细胞需要对各种内部信号和环境信号进行识别和作出反应 这些内部和外部信号通过序列的生物化学反应影响植物的生长发育,这些序列的 生物化学反应称为信号传递途径。已发现有几十种信号分子参与植物细胞的信号 传递。细胞信号传导途径,可分为四个阶段,即:受体感受信号,跨膜信号转换 胞内信号转导及蛋白质可逆磷酸化(图7.1)。细胞内,细胞间甚至整株植物间的 多种生理过程通过信号传递网络相互联系 Concept and process of signal transduction pathway Plant cells are required to recognize and respond to various internal and environmental signals during development. Such internal and external signaling agents typically bring about their effects by means of sequences of biochemical ions, called signal transduction pathy lved in the signal transduction of plant cells have been found. Signal transduction pathway can be distinguished into four phases;, which are(1) perception of a signal by a receptor. (2 trans-membrane signal transduction. (3)Further transduction and amplification inside cells,(4) reversible protein phosphorylation (figure7. 1). Many physiological processes within cells, among cells, and throughout the plant interact with each other hrough signal transduction network Genetic and epigenetic information systems 二遗传信息系统和表观遗传信息系统 虽然信号传递引起的生长或代谢的改变是多方面的,包括改变离子流,调 节代谢途径,调节基因表达和改变细胞骨架。但是大多数信号都是通过信 号传递途径引起基因转录的激活或抑制来实现对基因表达的调控。植物细 胞含有遗传和表观遗传两套信息系统(图7-2)。遗传信息系统的体现顺序是 DNA→RNA→蛋白质→表现型,这种因果顺序意味着结果的固定性和简 单性。在这种情况下,某个基因的表达和它所控制的表现型之间有一个直 接的关系。这些基因的表达受环境因素的影响很小,有些基因甚至完全不 受影响。如控制花的颜色和种子形态的基因,在植物生长发育过程中,随 环境条件的变化其表达不会发生变化。而受表观遗传信息系统调控的基因, 如许多控制生物量的合成,生长周期,分枝,光合产物在营养结构和生殖 结构间的分配,对胁迫的反应等表型性状的基因,其表达在很大程度上受 植物生长过程的环境条件而改变。这些表观遗传性状是相互作用的基因产 物复杂的网络联系与信号传递网络交织在一起产生的最终结果。由这些基 因决定的性状随环境的改变而变化。 The altered growth and metabolism that signal transduction result in include change ion flux, regulation of metabolism, regulation of gene expression and change in
第七章 信号的感受与传递 Chapter 7 signal perception and transduction 第一节 Section 1 信号传递途径概述 一 信号传递途径的概念和过程 在发育过程中，植物细胞需要对各种内部信号和环境信号进行识别和作出反应。 这些内部和外部信号通过序列的生物化学反应影响植物的生长发育，这些序列的 生物化学反应称为信号传递途径。已发现有几十种信号分子参与植物细胞的信号 传递。细胞信号传导途径，可分为四个阶段，即：受体感受信号，跨膜信号转换、 胞内信号转导及蛋白质可逆磷酸化(图 7.1)。细胞内，细胞间甚至整株植物间的 多种生理过程通过信号传递网络相互联系。 Concept and process of signal transduction pathway Plant cells are required to recognize and respond to various internal and environmental signals during development. Such internal and external signaling agents typically bring about their effects by means of sequences of biochemical reactions, called signal transduction pathways. Dozens of signals involved in the signal transduction of plant cells have been found. Signal transduction pathway can be distinguished into four phases; which are (1) perception of a signal by a receptor. (2) trans-membrane signal transduction. (3) Further transduction and amplification inside cells, (4) reversible protein phosphorylation (figure7.1). Many physiological processes within cells, among cells, and throughout the plant interact with each other through signal transduction network. Genetic and epigenetic information systems 二 遗传信息系统和表观遗传信息系统 虽然信号传递引起的生长或代谢的改变是多方面的，包括改变离子流，调 节代谢途径，调节基因表达和改变细胞骨架。但是大多数信号都是通过信 号传递途径引起基因转录的激活或抑制来实现对基因表达的调控。植物细 胞含有遗传和表观遗传两套信息系统(图 7-2)。遗传信息系统的体现顺序是 DNA→ RNA→ 蛋白质→ 表现型, 这种因果顺序意味着结果的固定性和简 单性。在这种情况下，某个基因的表达和它所控制的表现型之间有一个直 接的关系。这些基因的表达受环境因素的影响很小，有些基因甚至完全不 受影响。如控制花的颜色和种子形态的基因，在植物生长发育过程中，随 环境条件的变化其表达不会发生变化。而受表观遗传信息系统调控的基因， 如许多控制生物量的合成，生长周期，分枝，光合产物在营养结构和生殖 结构间的分配，对胁迫的反应等表型性状的基因，其表达在很大程度上受 植物生长过程的环境条件而改变。这些表观遗传性状是相互作用的基因产 物复杂的网络联系与信号传递网络交织在一起产生的最终结果。由这些基 因决定的性状随环境的改变而变化。 The altered growth and metabolism that signal transduction result in include change in ion flux, regulation of metabolism, regulation of gene expression and change in
cytoskeleton, but most signals appear to induce altered gene expression through activation or repression of gene transcription. Plant cells contain two information systems(figure 7-2). The genetic information system flow in plant cells, DNA RNA protein phenotype, implies a certain rigidity and simplicity in result. In these cases, a direct relationship exists between the expression of a single gene and the phenotypic character it specifies, such that environmental variation has little impact on expression of the gene. Few genes, however, are unaffected by environmental factors. For example, the genes that specify flower color or seed morphology are invariant in expression under many different conditions of growth and development. In the epigenetic information system, the expression of many genes, forinstance, genes that control important phenotypic characteristics including production of biomass, duration of growth, branching, and responses to stress, are strongly modified by the environment in which the plant grows. a phenotypic character results from complex interactions involving one or more genes and environmental influences that impact signal transduction networks. These characters vary with the plants environment 二植物对信号刺激的反应 植物对刺激的反应根据植物发育阶段,之前所经历的环境条件,刺激发生的季节 和时间等的不同而变化。成熟细胞产生的反应可能是生理和生化的,而生长中的 细胞产生的反应可能是形态上和发育上的。植物对信号刺激的反应有的很快,有 的比较慢。有些反应,如触动含羞草引起叶片合拢,只需几秒钟,而有些通过 基因表达的改变引起形态和发育变化的反应需要几天时间才能发生。快反应和慢 反应都是通过基本的信号网络传递机制实现,都是信号的感受与传递的结果。有 些反应是通过多条信号传递途径相连形成最终的生理变化。例如:干旱引起植物 根部的水分胁迫,诱导编码植物激素脱落酸(ABA)合成途径所需酶的基因的激 活。ABA然后引发一连串的信号传递活动最终导致保卫细胞中的离子外流,导致 保卫细胞的关闭。降低蒸腾保存水分 The signals impact the cell at different sites and are perceived by different receptors Plant responses to stimulus are modulated by developmental age, previous environmental experience, and internal clocks that specify the time of year and the time of day. For mature plant cells, the response can be physiological and biochemical for growing cells, it can be morphological and developmental. The response to signal stimulus can be very quick or slow. Some responses, e.g., touch-induced leaflet drop of Mimosa, occur in seconds. Others, such as shifts in gene expression that changes morphology and development, may take days. Both fast and slow responses use the same basic transduction network machinery, and both are downstream results of a perceived stimulus. Several signal transduction pathways can be linked to bring about a final physiological change. For instance, drought imposes water stress on the roots of a plant, inducing the activation of genes encoding enzymes that synthesize the plant hormone abscisic acid(ABA). ABa then initiates a cascade of events that eventually results in the efflux of ions from the guard cells, thereby causing stomatal closure to minimize transpiration and conserve water
cytoskeleton, but most signals appear to induce altered gene expression through activation or repression of gene transcription. Plant cells contain two information systems (figure 7-2). The genetic information system flow in plant cells, DNA→ RNA→ protein → phenotype, implies a certain rigidity and simplicity in result. In these cases, a direct relationship exists between the expression of a single gene and the phenotypic character it specifies, such that environmental variation has little impact on expression of the gene. Few genes, however, are unaffected by environmental factors. For example, the genes that specify flower color or seed morphology are invariant in expression under many different conditions of growth and development. In the epigenetic information system, the expression of many genes, forinstance, genes that control important phenotypic characteristics including production of biomass, duration of growth, branching, and responses to stress, are strongly modified by the environment in which the plant grows. A phenotypic character results from complex interactions involving one or more genes and environmental influences that impact signal transduction networks. These characters vary with the plant’s environment. 二植物对信号刺激的反应 植物对刺激的反应根据植物发育阶段，之前所经历的环境条件，刺激发生的季节 和时间等的不同而变化。成熟细胞产生的反应可能是生理和生化的，而生长中的 细胞产生的反应可能是形态上和发育上的。植物对信号刺激的反应有的很快，有 的比较慢。有些反应，如触动含羞草引起叶片合拢，只需几秒钟， 而有些通过 基因表达的改变引起形态和发育变化的反应需要几天时间才能发生。快反应和慢 反应都是通过基本的信号网络传递机制实现，都是信号的感受与传递的结果。有 些反应是通过多条信号传递途径相连形成最终的生理变化。例如：干旱引起植物 根部的水分胁迫，诱导编码植物激素脱落酸（ABA）合成途径所需酶的基因的激 活。ABA 然后引发一连串的信号传递活动最终导致保卫细胞中的离子外流，导致 保卫细胞的关闭。降低蒸腾保存水分。 The signals impact the cell at different sites and are perceived by different receptors. Plant responses to stimulus are modulated by developmental age, previous environmental experience, and internal clocks that specify the time of year and the time of day. For mature plant cells, the response can be physiological and biochemical; for growing cells, it can be morphological and developmental. The response to signal stimulus can be very quick or slow. Some responses, e.g., touch-induced leaflet drop of Mimosa, occur in seconds. Others, such as shifts in gene expression that changes in morphology and development, may take days. Both fast and slow responses use the same basic transduction network machinery, and both are downstream results of a perceived stimulus. Several signal transduction pathways can be linked to bring about a final physiological change. For instance, drought imposes water stress on the roots of a plant, inducing the activation of genes encoding enzymes that synthesize the plant hormone abscisic acid (ABA). ABA then initiates a cascade of events that eventually results in the efflux of ions from the guard cells, thereby causing stomatal closure to minimize transpiration and conserve water
第二节受体感受信号 Section 2 perception of signals by receptors 1.受体 启动信号传递,信号首先要被受体识别。受体是指在位于细胞质膜上或细胞质内 能识别胞内或胞外信号物质,并引发胞内变化的特殊分子。大多数已知的受体镶 嵌于质膜上,有些存在于细胞质和其他细胞器上(图7-3)。大多数已知的受体是 蛋白质。在动物细胞中至少已发现三种类型的受体,分别是:G蛋白结合受体, 类受体蛋白激酶和离子通道受体。这三类受体是否都存在于植物细胞中还不清 楚。大多数受体是蛋白质,受体一般应符合以下几个特点:1.配体与受体的结合 是特异的,配体只与其自身受体的特异位点结合。2.受体与配体有较高的亲和 力。这种结合必须有足够的强度并维持一定的时间保证下游反应的激活。3.受体 与配体的结合是可逆的,使得系统能根据配体浓度的变化做出反应 Receptors To initiate transduction, a signal must first be sensed by a receptor. A receptor is a molecule found on the cell surface or inside of a cell, which receives sp ecific signals from neighboring cells or the environment, and trigger intracellula r changes. Most known receptorsare embedded in the plasma membrane, some are located in the cytosol or other cellular compartments (figure 7-3). At lea st three different classes of cell surface receptors have been detected in animal S, which are G-protein-linked receptor; receptor-like protein kinases and ion cha nnels; but whether all three exist in plants is still uncertain. Generally, the foll owing set of criteria need to be fulfilled to identify a molecule as a receptor (1)The binding of ligands to their receptor should be specific, ligands only bi ceptor should be of relatively high affinity, and of sufficient strength so that th e associated downstream processes can be activated. (3) The binding of ligands to their receptor should be reversible, allowing the system to respond to chan Categories of signals 2.信号的种类 在整个生命周期中,植物和植物细胞必须不断地对各种信号作出反应并通过信号 传递来改变其生理,形态和发育。这些将信息传递给植物的信号根据其来源可分 为胞内和胞外信号;根据其性质可分为物理信号和化学信号。物理信号包括光 重力,膨压,机械张力,风,热,冷,冻。化学信号包括矿质营养,有机代谢产 物,生长调节物和激素。植物细胞感受到的信号种类和数量每时每刻都不同,有 些信号分子通过木质部或韧皮部传递,这些信号能以较快的速度传递以较大量 地积累。细胞感受到物理或化学信号后,将信息从胞外传向胞内。 Throughout their life cycle, plants and plant cells continually respond to signals that they use to alter their physiology, morphology, and development. Signals that convey information to plants can be classified into external signals and internal signals based on their origins. Signals can also be grouped into physical signals and chemical signals based on their properties. Physical signals are in the form of light, gravity turgor, mechanical tensions, wind, heat, cold and freezing. Chemical signals include
第二节 受体感受信号 Section 2 perception of signals by receptors 1.受体 启动信号传递，信号首先要被受体识别。受体是指在位于细胞质膜上或细胞质内 能识别胞内或胞外信号物质，并引发胞内变化的特殊分子。大多数已知的受体镶 嵌于质膜上，有些存在于细胞质和其他细胞器上(图7-3)。大多数已知的受体是 蛋白质。在动物细胞中至少已发现三种类型的受体，分别是: G蛋白结合受体， 类受体蛋白激酶和离子通道受体。这三类受体是否都存在于植物细胞中还不清 楚。大多数受体是蛋白质, 受体一般应符合以下几个特点：1.配体与受体的结合 是特异的, 配体只与其自身受体的特异位点结合。2.受体与配体有较高的亲和 力。这种结合必须有足够的强度并维持一定的时间保证下游反应的激活。3.受体 与配体的结合是可逆的,使得系统能根据配体浓度的变化做出反应。 Receptors To initiate transduction, a signal must first be sensed by a receptor. A receptor is a molecule found on the cell surface or inside of a cell, which receives sp ecific signals from neighboring cells or the environment, and trigger intracellula r changes. Most known receptorsare embedded in the plasma membrane, some are located in the cytosol or other cellular compartments (figure 7-3). At lea st three different classes of cell surface receptors have been detected in animal s, which are G-protein-linked receptor; receptor-like protein kinases and ion cha nnels; but whether all three exist in plants is still uncertain. Generally, the foll owing set of criteria need to be fulfilled to identify a molecule as a receptor. (1) The binding of ligands to their receptor should be specific, ligands only bi nd to the specific site of their receptors. (2) The binding of ligands to their re ceptor should be of relatively high affinity, and of sufficient strength so that th e associated downstream processes can be activated. (3) The binding of ligands to their receptor should be reversible, allowing the system to respond to chan ges in ligand concentration, Categories of signals 2. 信号的种类 在整个生命周期中，植物和植物细胞必须不断地对各种信号作出反应并通过信号 传递来改变其生理，形态和发育。这些将信息传递给植物的信号根据其来源可分 为胞内和胞外信号； 根据其性质可分为物理信号和化学信号。物理信号包括光， 重力，膨压，机械张力，风，热，冷，冻。化学信号包括矿质营养，有机代谢产 物，生长调节物和激素。植物细胞感受到的信号种类和数量每时每刻都不同，有 些信号分子通过木质部或韧皮部传递， 这些信号能以较快的速度传递以较大量 地积累。细胞感受到物理或化学信号后，将信息从胞外传向胞内。 Throughout their life cycle, plants and plant cells continually respond to signals that they use to alter their physiology, morphology, and development. Signals that convey information to plants can be classified into external signals and internal signals based on their origins. Signals can also be grouped into physical signals and chemical signals based on their properties. Physical signals are in the form of light, gravity, turgor, mechanical tensions, wind, heat, cold and freezing. Chemical signals include
mineral nutrients, organic metabolites, growth regulators and hormones. Signals can vary in quality and quantity from minute to minute. Some of the signals are carried by xylem and phloemthe circulatory system, which can accommodate very large and rapid fluxes. Once a cell picks up a chemical or physical signal, it must transmit this information from the surface to the interior parts of the cell 第三节跨膜信号传递 Transmembrane signal transduction G-蛋白介导跨膜信号传递的过程 信号分子与它相应的受体结合只是信号传递的第一步。信息必须通过跨膜传递到 达细胞内部。我们以G-蛋白参与信号传递为例来说明信号是如何实现跨膜传递 的。G-蛋白是GTP水解酶大家族的一个亚家族,异源三聚体G蛋白含有三种亚基 (α、β、γ)。在信号的跨膜传递过程中,G-蛋白和它所结合GTP进行着周期性 的变化。G-蛋白处于非活化状态时,与GDP结合;处于活化状态时,与GTP结合。 异源三体G蛋白以非活化状态位于膜内侧靠近受体处,三个亚基结合在一起。当 某种刺激信号与其膜上的特异受体结合后,激活的受体将信号传递给G蛋白,G 蛋白的α亚基结合GTP替换原来的GDP。活化的a亚基与β和γ亚基复合体分离 继而触发效应器,把胞外信号转换成胞内信号。α亚基与效应器相互作用后即水 解它所结合的GTP从而转变为非活性状态,重新与与β和γ亚基结合。信号在G 蛋白的循环过程得以放大,因为一个活化的G-蛋白能激活无数个效应器。 Process of G-protein mediated transmembrane signal transduction The binding of a signal to its cognate receptor is only the beginning of the signaling process. The information has to be conveyed across the plasma membrane to get inside the cell. We will take the involvement of G-protein in signal transduction pathway as an example to explain the transmembrane transduction processes G-proteins are a special subset of a GTPase superfamily. Hetertrimeric G-proteins are composed of three subunits(a, B and y). During the process of transmembrane signal transduction, heterotrimeric G-proteins undergo a modified cycle with GTP G-protein binds GDP when it is inactive, when active, it binds GTP. The G protein normally lies near the receptor in an inactive state with 3 subunits bound together When the receptor gets activated by ligand binding, it will rapidly bind to the g protein, causes the release of GDP from the a-subunit and its replacement by GTP Once this happens, the G-protein loses affinity for the receptor, dissociates from it, the activated a-subunit also dissociate from B-and y-subunits of the G-protein, and moves over and interact with its target protein, the information from outside a cell is thus conveyed into the cell. After encounter with its target protein, the alpha subunit of the G protein will hydrolyze its bound GTP, thereby reverting to an inactive state. It will then rejoin the beta and gamma subunits. Signal amplification is inherent in the G-protein cycle because one activated G-protein can interact with and activate numerous target proteins G-蛋白在植物细胞信号传递中的作用 植物G蛋白的研究始于20世纪80年代。实验数据显示G蛋白参与蓝光,红光,生
mineral nutrients, organic metabolites, growth regulators and hormones. Signals can vary in quality and quantity from minute to minute. Some of the signals are carried by xylem and phloemthe circulatory system, which can accommodate very large and rapid fluxes. Once a cell picks up a chemical or physical signal, it must transmit this information from the surface to the interior parts of the cell 第三节 跨膜信号传递 Transmembrane signal transduction G-蛋白介导跨膜信号传递的过程 信号分子与它相应的受体结合只是信号传递的第一步。信息必须通过跨膜传递到 达细胞内部。我们以G-蛋白参与信号传递为例来说明信号是如何实现跨膜传递 的。G-蛋白是GTP水解酶大家族的一个亚家族，异源三聚体G蛋白含有三种亚基 (α 、β 、γ )。在信号的跨膜传递过程中，G-蛋白和它所结合GTP进行着周期性 的变化。G-蛋白处于非活化状态时，与GDP结合；处于活化状态时，与GTP结合。 异源三体G蛋白以非活化状态位于膜内侧靠近受体处，三个亚基结合在一起。当 某种刺激信号与其膜上的特异受体结合后，激活的受体将信号传递给G蛋白，G 蛋白的α亚基结合GTP替换原来的GDP。活化的α 亚基与β 和γ 亚基复合体分离， 继而触发效应器，把胞外信号转换成胞内信号。α 亚基与效应器相互作用后即水 解它所结合的GTP从而转变为非活性状态，重新与与β 和γ 亚基结合。信号在G- 蛋白的循环过程得以放大，因为一个活化的G-蛋白能激活无数个效应器。 Process of G-protein mediated transmembrane signal transduction The binding of a signal to its cognate receptor is only the beginning of the signaling process. The information has to be conveyed across the plasma membrane to get inside the cell. We will take the involvement of G-protein in signal transduction pathway as an example to explain the transmembrane transduction processes. G-proteins are a special subset of a GTPase superfamily. Hetertrimeric G-proteins are composed of three subunits ( and ). During the process of transmembrane signal transduction, heterotrimeric G-proteins undergo a modified cycle with GTP. G-protein binds GDP when it is inactive; when active, it binds GTP. The G protein normally lies near the receptor in an inactive state with 3 subunits bound together. When the receptor gets activated by ligand binding, it will rapidly bind to the G protein, causes the release of GDP from the α-subunit and its replacement by GTP. Once this happens, the G-protein loses affinity for the receptor, dissociates from it, the activated α-subunit also dissociate from β- and γ-subunits of the G-protein, and moves over and interact with its target protein, the information from outside a cell is thus conveyed into the cell. After encounter with its target protein, the alpha subunit of the G protein will hydrolyze its bound GTP, thereby reverting to an inactive state. It will then rejoin the beta and gamma subunits. Signal amplification is inherent in the G-protein cycle because one activated G-protein can interact with and activate numerous target proteins. G-蛋白在植物细胞信号传递中的作用 植物G蛋白的研究始于20世纪80年代。实验数据显示G-蛋白参与蓝光，红光，生
长素,赤霉素等的信号转导。例如,已发现G蛋白激动剂 GT PYS在保卫细胞 中有降低钾离子流入细胞的功能。唯一已知在植物中存在的α亚基基因在处于分 裂时期的细胞中表达最强,该基因的蛋白质产物似乎跟质膜和内质网相连。目前 已从多种植物中分离得到G蛋白α、β、Y亚基的cDNA或基因。很多研究结果表 明G蛋白作为功能分子参与植物细胞跨膜离子运输、气孔运动、植物形态建成等 生理活动的信号转导 The studies on plant G-protein started in the late 1980s. There are evidences suggesting the involvement of G-proteins in the transduction of blue light, red light auxin, and gibberellin signals. For example, GTPyS was found to reduce inward K+ current in guard cells. The only G-protein a-subunit known in plants is expressed most strongly in dividing cells. The encoded protein appears to be attached to the plasma membrane and the er. The cDNAs or genes for all a, B, and y subunits of G-protein have been isolated from many plant species. Research results have revealed that the g proteins are functional molecules participating in the signal transduction of many plant physiological events, e. g. transmembrane ion transportation, stomatal aperture regulation, and morphogenesis 第四节胞内信号的转导 Section 4 transduction of signals inside cells 第二信使系统 1.第二信使的概念。如果将胞外各种刺激信号作为细胞信号传导过程中的初级信 号或第一信使,那么则可以把由胞外刺激信号激活或抑制的、具有生理调节活性 的细胞内因子称细胞信号传导过程中的第二信使( second messenger)。大部分的第 二信使都是小分子,因而可以在细胞质内迅速扩散。第二信使有多个下游靶物, 所以可以将信号放大。在已经发现的众多第二信使中,对Ca2+,DAG,IP3, cAMP等的研究较为深入 Second messenger If the extracellular signaling molecular (environmental and intercellular signals) in the transmission of biological information are termed as"primary messengers"or"first messengers', molecule inside cells, that are activated or repressed by external signals and have physiological regulation activities, can be called second messengers of signal transduction pathway. Many second messenger molecules are small and therefore diffuse rapidly through the cytoplasm, enabling information to move quickl throughout the cell. In addition, second messengers can have multiple downstream targets, thereby expanding the scope of signal transmission. A large number of second messenger molecules have been characterized, the well studied second messengers include calcium ions, Inositol 1, 4, 5-trisphosphate(IP3), diacylglycerol(DAG), and cyclic AMP 2钙信号系统。植物细胞内的游离钙离子是细胞信号转导过程中重要的第二信 使。通过Ca2+进行传导的能引起胞内游离钙离子浓度的变化的胞外刺激信号包 括红光,蓝光、温度、触摸、风、重力、各种植物激素、真菌诱导因子等化学物 质。植物细胞质中Ca2+含量一般在10-7~10-6molL-1,而细胞壁,液泡和内质 网中Ca2+浓度比胞质中的高4-5个数量级。在质膜、液泡膜、内质网膜上都有钙 离子泵和钙离子通道的存在。通过钙离子打开使得胞内钙离子浓度瞬间迅速升
长素，赤霉素等的信号转导。例如，已发现Ｇ蛋白激动剂ＧＴＰγＳ在保卫细胞 中有降低钾离子流入细胞的功能。唯一已知在植物中存在的α 亚基基因在处于分 裂时期的细胞中表达最强，该基因的蛋白质产物似乎跟质膜和内质网相连。目前 已从多种植物中分离得到G-蛋白α 、β 、γ 亚基的cDNA或基因。很多研究结果表 明G-蛋白作为功能分子参与植物细胞跨膜离子运输、气孔运动、植物形态建成等 生理活动的信号转导。 The studies on plant G-protein started in the late 1980s. There are evidences suggesting the involvement of G-proteins in the transduction of blue light, red light, auxin, and gibberellin signals. For example, GTPγS was found to reduce inward K+ current in guard cells. The only G-protein α-subunit known in plants is expressed most strongly in dividing cells. The encoded protein appears to be attached to the plasma membrane and the ER. The cDNAs or genes for all α, β, and γ subunits of G-protein have been isolated from many plant species. Research results have revealed that the G proteins are functional molecules participating in the signal transduction of many plant physiological events, e. g. transmembrane ion transportation, stomatal aperture regulation, and morphogenesis. 第四节 胞内信号的转导 Section 4 transduction of signals inside cells 一．第二信使系统 1.第二信使的概念。如果将胞外各种刺激信号作为细胞信号传导过程中的初级信 号或第一信使，那么则可以把由胞外刺激信号激活或抑制的、具有生理调节活性 的细胞内因子称细胞信号传导过程中的第二信使(second messenger)。大部分的第 二信使都是小分子，因而可以在细胞质内迅速扩散。 第二信使有多个下游靶物， 所以可以将信号放大。在已经发现的众多第二信使中，对 Ca2+， DAG， IP3， cAMP 等的研究较为深入。 Second messenger If the extracellular signaling molecular (environmental and intercellular signals) in the transmission of biological information are termed as “primary messengers” or “first messengers”, molecule inside cells, that are activated or repressed by external signals, and have physiological regulation activities, can be called second messengers of signal transduction pathway. Many second messenger molecules are small and therefore diffuse rapidly through the cytoplasm, enabling information to move quickly throughout the cell. In addition, second messengers can have multiple downstream targets, thereby expanding the scope of signal transmission. A large number of second messenger molecules have been characterized, the well studied second messengers include calcium ions, Inositol 1,4,5-trisphosphate (IP3), diacylglycerol (DAG), and cyclic AMP. 2.钙信号系统。 植物细胞内的游离钙离子是细胞信号转导过程中重要的第二信 使。通过Ca2+进行传导的能引起胞内游离钙离子浓度的变化的胞外刺激信号包 括红光，蓝光、温度、触摸、风、重力、各种植物激素、真菌诱导因子等化学物 质。植物细胞质中Ca2+含量一般在10-7～10-6mol·L-1 ，而细胞壁, 液泡和内质 网中Ca2+浓度比胞质中的高4-5个数量级。在质膜、液泡膜、内质网膜上都有钙 离子泵和钙离子通道的存在。通过钙离子打开使得胞内钙离子浓度瞬间迅速升