植物细胞中钙信号的时空多样性与信号转导

近年来,对钙信号的研究,包括对钙信号的产生,传导及最终靶蛋白的研究,越来越受到人们的重视,植物生长发育过程的信息传递,包括对各种内外刺激的反应都涉及到钙信号,钙信号的产生及传导是通过胞质自由钙离子的浓度变化来实现的,本文综述了胞质自由钙离子的测定,钙信号的时空多样性及钙信号的靶蛋白如CaM,Ca^2 依赖的蛋白激酶,钙调磷酸酶,磷脂酰肌醇－磷脂酶C等方面的一些最新进展,展望了今后钙信号研究的方向所用到的一些技术方法等。     

植物感受盐胁迫及相关钙信号的研究进展

盐胁迫对植物的生长和发育造成严重影响,其危害包括渗透胁迫、离子毒害等,严重损害了农业生产和粮食安全。在盐胁迫下,植物相关感受器接受刺激,使得Ca²⁺通过细胞膜以及细胞内钙库膜上打开的Ca²⁺通道进入细胞质基质,导致细胞质内Ca²⁺浓度升高,产生钙信号。钙离子作为重要的第二信使,在植物细胞内和细胞间传递信号,信号往下游传递,在不同生长和发育阶段引起植物一系列的生理响应来应对盐胁迫影响。钙信号主要通过钙调蛋白（CaM）、钙调素样蛋白（CML）、钙依赖性蛋白激酶（CDPK）、钙调磷酸酶B样蛋白（CBL）和CBL互作蛋白激酶（CIPK）感知并将特异的钙信号信息传递到下游;从而激活植物盐胁迫生理响应。本文主要综述植物如何感知盐胁迫刺激,以及钙信号产生与传导机制,并对该研究领域需解决的问题进行了展望。     

花粉管钙信号特性及其调控研究进展

花粉管在花柱中生长受多个信号分子的协同调控,钙离子在其中发挥着重要作用.钙是一种重要的第二信使,它将外界的多种生物或非生物信息转化为对细胞内基因表达以及细胞生理反应的调控.钙信号表达方式是胞内自由钙浓度的特异性变化.该文对国内外近年来有关花粉管生长中钙信号特性及其调控的研究进展,如花粉管尖端自由钙离子浓度梯度与胞内钙振荡、花粉管质膜钙转运体的鉴定及其调控特性、花粉管钙信号与微丝和ROP蛋白的关系以及花粉管钙信号与植物自交不亲和性反应的关系等进行综述,为深入开展相关研究提供参考.     

胞外Ca2+信号——动植物中的第一信使

钙离子作为重要的胞内第二信使, 控制着许多细胞的功能, 人们对此已经研究得比较深入。然而最近发现的一些细胞表面胞外Ca²⁺探测器使我们想到是否在胞外环境中, 钙离子也具有信号分子的功能。钙离子传感器包括已经研究得比较清楚的胞外Ca²⁺敏感受体—最初从甲状旁腺分离的G-耦联蛋白受体(CaR), 另外, 还有其他受体、通道和膜蛋白也都对胞外[Ca²⁺]的变化很敏感。最近从拟南芥保卫细胞中克隆到一个胞外钙离子受体蛋白(CAS), 通过胞外钙离子的变化引起胞内钙离子信号。这些受体蛋白的克隆, 使人们确信Ca²⁺在细胞中可以发挥第一信使的功能。     

植物钙吸收、转运及代谢的生理和分子机制

钙是植物必需的营养元素。酸性砂质土壤中含钙较少,导致在其土壤上生长的作物容易缺钙。另外由于果树果实、果菜类和包心叶菜类的蒸腾作用弱,导致果树和蔬菜普遍生理缺钙。根系维管束组织可能通过共质体和质外体两种途径进行钙素吸收,而果实则可通过非维管束组织直接吸收钙素。Ca2 通过Ca2 通道内流进入胞质,并通过Ca2 -ATPase和Ca2 /H 反向转运蛋白外流以保持胞质内低Ca2 浓度。为了应对植物发育和环境胁迫信号,Ca2 由质膜、液泡膜和内质网膜的Ca2 通道内流进入胞质,导致胞质Ca2 浓度迅速增加,产生钙瞬变和钙振荡,传递到钙信号靶蛋白,如钙调素、钙依赖型蛋白激酶及钙调磷酸酶B类蛋白,引起特异的生理生化反应。本文综述了植物钙素吸收、转运以及代谢研究的最新进展,包括植物对钙的需求和作物缺钙的原因,根系维管束组织及果实钙素吸收机理,Ca2 跨膜运输特性,钙的信使作用以及钙信号靶蛋白等方面内容。     

植物钙吸收、转运及代谢的生理和分子机制

钙是植物必需的营养元素。酸性砂质土壤中含钙较少, 导致在其土壤上生长的作物容易缺钙。另外由于果树果实、果菜类和包心叶菜类的蒸腾作用弱, 导致果树和蔬菜普遍生理缺钙。根系维管束组织可能通过共质体和质外体两种途径进行钙素吸收, 而果实则可通过非维管束组织直接吸收钙素。Ca2+通过Ca2+通道内流进入胞质, 并通过Ca2+-ATPase 和Ca2+/H+反向转运蛋白外流以保持胞质内低Ca2+浓度。为了应对植物发育和环境胁迫信号, Ca2+由质膜、液泡膜和内质网膜的Ca2+通道内流进入胞质, 导致胞质Ca2+浓度迅速增加, 产生钙瞬变和钙振荡, 传递到钙信号靶蛋白, 如钙调素、钙依赖型蛋白激酶及钙调磷酸酶B类蛋白, 引起特异的生理生化反应。本文综述了植物钙素吸收、转运以及代谢研究的最新进展, 包括植物对钙的需求和作物缺钙的原因, 根系维管束组织及果实钙素吸收机理, Ca2+跨膜运输特性, 钙的信使作用以及钙信号靶蛋白等方面内容。     

质膜钙离子ATP酶

钙离子(Ca2+)是重要的第二信使,通过与效应蛋白的结合和解离,以及在不同细胞器之间的穿梭运动而精确调控细胞活动,参与多种重要生命过程。细胞内具有精确调节Ca2+时空分布的调控系统。在静息状态下,细胞内的游离Ca2+浓度约为100 nmol/L;而当细胞受到信号刺激后,胞内的Ca2+浓度可上升至1000 nmol/L甚至更高。细胞中存在多种跨膜运送Ca2+的膜蛋白,以精确调节Ca2+浓度的时空动态变化,其中,细胞质膜上的多种Ca2+通道(包括电压门控通道、受体门控通道、储存控制通道等),以及内质网/肌质网和线粒体等胞内"钙库"膜上的雷诺丁受体、三磷酸肌醇受体等膜蛋白复合物,均可提升胞内Ca2+浓度,而细胞质膜上的钠钙交换体、质膜Ca2+-ATP酶、"钙库"膜上的内质网Ca2+-ATP酶、线粒体Ca2+单向转运体等,可将Ca2+浓度降低至静息态水平。质膜钙ATP酶是向细胞外运送Ca2+的关键膜蛋白,本文将对其结构、功能及其酶活性的调控机制做一简要综述。     

应用重组表达钙离子敏感蛋白YC2.1研究粟酒裂殖酵母细胞内钙离子浓度的分布

把重组表达钙离子敏感蛋白的YC2．1基因（yellow cameleon 2．1）导入了粟酒裂殖酵母中,观察了粟酒裂殖酵母细胞内钙离子浓度的分布。结果发现,钙离子敏感蛋白所指示的钙离子呈细胞周缘胞质较高浓度分布,而在细胞胞质中部的钙离子浓度相对低一些。通过DAPI染色实验证实这是由于胞质中部细胞核的填充而形成。fluo-3染色的裂殖酵母细胞,由于fluo-3进入到细胞器（房室化现象）,所以出现胞质的内部区域高的荧光信号,而在周缘的胞质区相对弱,不能真实反应胞质钙离子的分布。因此重组表达钙离子敏感蛋白测定钙离子的方法优于fluo-3荧光探针的方法,对于裂殖酵母细胞胞内钙离子的研究具有良好的应用前景。     

植物机械响应中的钙通信北大核心CSCD

以胞质钙离子浓度变化(钙信号)为核心的钙通信系统在植物机械响应中发挥着不可替代的作用。本文综述了机械刺激诱导的植物细胞钙信号及其生理作用、植物机械敏感钙通道,以及TCH基因编码的钙调蛋白和钙调蛋白类似蛋白等的研究进展,总结了该领域尚待解决的问题,并对未来的研究方向进行了展望。     

植物体内钙信号及其在调节干旱胁迫中的作用

钙作为植物体内第二信使广泛参与了植物响应的各种非生物和生物胁迫的信号传导。胁迫信号通过激活位于细胞质膜上的钙离子通道,产生胞质内特异性的钙信号,传递至钙信号感受蛋白,如钙调素(calmodulin,CaM)、钙依赖蛋白激酶(Ca2+-dependent protein kinases,CDPK)和类钙调磷酸酶B蛋白(calcineurin B-like protein,CBL)等,进而引起胞内一系列生理生化变化,最终对胁迫做出响应。钙信号在植物响应干旱胁迫信号系统中起枢纽作用,主要通过调节气孔运动,水通道蛋白(aquaporin,AQP)和抗氧化酶活性来减少水分流失,提高水分利用率,最终降低干旱对植物细胞的伤害,并具有一定的生态学功能。该文对近年来国内外有关植物体内钙信号的研究进展以及在干旱逆境中的调节作用进行综述,并对今后的研究做了展望。     

Short-range intercellular calcium signaling in bone

The regulation of bone turnover is a complex and finely tuned process. Many factors regulate bone remodeling, including hormones, growth factors, cytokines etc. However, little is known about the signals coupling bone formation to bone resorption, and how mechanical forces are translated into biological effects in bone. Intercellular calcium waves are increases in intracellular calcium concentration in single cells, subsequently propagating to adjacent cells, and can be a possible mechanism for the coupling of bone formation to bone resorption. The aim of the present studies was to investigate whether bone cells are capable of communicating via intercellular calcium signals, and determine by which mechanisms the cells propagate the signals. First, we found that osteoblastic cells can propagate intercellular calcium transients upon mechanical stimulation, and that there are two principally different mechanisms for this propagation. One mechanism involves the secretion of a nucleotide, possibly ATP, acting in an autocrine action to purinergic P2Y2 receptors on the neighboring cells, leading to intracellular IP3 generation and subsequent release of calcium from intracellular stores. The other mechanism involves the passage of a small messenger through gap junctions to the cytoplasm of the neighboring cells, inducing depolarization of the plasma membrane with subsequent opening of membrane bound voltage-operated calcium channels. Next, we found that osteoblasts can propagate these signals to osteoclasts as well. We demonstrated that paracrine action of ATP was responsible for the wave propagation, but now the purinergic P2X7 receptor was involved. Thus, the studies demonstrate that calcium signals can be propagated not only among osteoblasts, but also between osteoblasts and osteoclasts in response to mechanical stimulation. Thus, intercellular calcium signaling can be a mechanism by which mechanical stimuli on bone are translated into biological signals in bone cells, and propagated through the network of cells in bone. Further, the observations offer new pharmacological targets for the modulation of bone turnover, and perhaps even for the treatment of bone metabolic disorders.     

Calcium signalling in early embryos

The onset of development in most species studied is triggered by one of the largest and longest calcium transients known to us. It is the most studied and best understood aspect of the calcium signals that accompany and control development. Its properties and mechanisms demonstrate what embryos are capable of and thus how the less-understood calcium signals later in development may be generated. The downstream targets of the fertilization calcium signal have also been identified, providing some pointers to the probable targets of calcium signals further on in the process of development.In one species or another, the fertilization calcium signal involves all the known calcium-releasing second messengers and many of the known calcium-signalling mechanisms. These calcium signals also usually take the form of a propagating calcium wave or waves. Fertilization causes the cell cycle to resume, and therefore fertilization signals are cell-cycle signals. In some early embryonic cell cycles, calcium signals also control the progress through each cell cycle, controlling mitosis.Studies of these early embryonic calcium-signalling mechanisms provide a background to the calcium-signalling events discussed in the articles in this issue.     

Distinct External Signals Trigger Sequential Release of Apical Organelles during Erythrocyte Invasion by Malaria Parasites

The invasion of erythrocytes by Plasmodium merozoites requires specific interactions between host receptors and parasite ligands. Parasite proteins that bind erythrocyte receptors during invasion are localized in apical organelles called micronemes and rhoptries. The regulated secretion of microneme and rhoptry proteins to the merozoite surface to enable receptor binding is a critical step in the invasion process. The sequence of these secretion events and the external signals that trigger release are not known. We have used time-lapse video microscopy to study changes in intracellular calcium levels in Plasmodium falciparum merozoites during erythrocyte invasion. In addition, we have developed flow cytometry based methods to measure relative levels of cytosolic calcium and study surface expression of apical organelle proteins in P. falciparum merozoites in response to different external signals. We demonstrate that exposure of P. falciparum merozoites to low potassium ion concentrations as found in blood plasma leads to a rise in cytosolic calcium levels through a phospholipase C mediated pathway. Rise in cytosolic calcium triggers secretion of microneme proteins such as the 175 kD erythrocyte binding antigen (EBA175) and apical membrane antigen-1 (AMA-1) to the merozoite surface. Subsequently, interaction of EBA175 with glycophorin A (glyA), its receptor on erythrocytes, restores basal cytosolic calcium levels and triggers release of rhoptry proteins. Our results identify for the first time the external signals responsible for the sequential release of microneme and rhoptry proteins during erythrocyte invasion and provide a starting point for the dissection of signal transduction pathways involved in regulated exocytosis of these key apical organelles. Signaling pathway components involved in apical organelle discharge may serve as novel targets for drug development since inhibition of microneme and rhoptry secretion can block invasion and limit blood-stage parasite growth.     

Bioengineering plant resistance to abiotic stresses by the global calcium signal system

Considerable progresses have taken place both in the methodology available to study changes in intracellular cytosolic calcium and in our understanding of calcium signaling cascades. It is generally accepted that the global calcium signal system functions importantly in coping with plant abiotic stresses, especially drought stress, which has been proved further by the recent transgenic and molecular breeding reports under soil water deficits. In plant cells, calcium plays roles as a universal transducer coupling a wide range of extracellular stimuli with intracellular responses. Different extracellular stimuli trigger specific calcium signatures: dynamics, amplitude and duration of calcium transients specify the nature, implication and intensity of stimuli. Calcium-binding proteins (sensors) play a critical role in decoding calcium signatures and transducing signals by activating specific targets and corresponding metabolic pathways. Calmodulin (CAM) is a calcium sensor known to regulate the activity of many mammalian proteins, whose targets in plants are now being identified. Higher plants possess a rapidly growing list of CAM targets with a variety of cellular functions. Nevertheless, many targets appear to be unique to higher plant cells and remain characterized, calling for a concerted effort from plant and animal scientists to elucidate their functions. To date, three major classes of plant calcium signals encoding elements in the calcium signal system, including calcium-permeable ion channels,Ca(2)+/ H(+) antiporters and Ca(2)+-ATPases, are responsible for drought stress signal transduction directly or indirectly. This review summarizes the current knowledge of calcium signals involved in plant abiotic stresses and presents suggestions for future focus areas of study.     

Advances of calcium signals involved in plant anti-drought

Considerable progresses have taken place, both in the methodology available to study changes in intracellular cytosolic calcium and in our understanding of calcium signaling cascades, but how calcium signals function in plant drought resistance is questionable. In plant cells, calcium plays roles as a second messenger coupling a wide range of extracellular stimuli with intracellular responses. Different extracellular stimuli trigger specific calcium signatures: dynamics, amplitude and duration of calcium transients specify the nature, implication and intensity of stimuli. Calcium-binding proteins (sensors) play a critical role in decoding calcium signatures and transducing signals by activating specific targets and corresponding metabolic pathways. Calmodulin is a calcium sensor known to regulate the activity of many mammalian proteins, whose targets in plants are now being identified. Higher plants possess a rapidly growing list of calmodulin targets with a variety of cellular functions. Nevertheless, many targets appear to be unique to higher plants and remain characterized, calling for a concerted effort to elucidate their functions. To date, three major classes of plant calcium signals, including calcium permeable ion channels, Ca(2+)/H(+) antiporters and Ca(2+)-ATPases, have been responsible for drought-stress signal transduction. This review summarizes the current knowledge of calcium signals involved in plant anti-drought and plant water use efficiency (WUE) and presents suggestions for future focus of study.