保卫细胞碳代谢与气孔运动

作为气孔运动渗透调节的代谢基础,气孔保卫细胞的碳代谢有特殊的调控机理。本文介绍了气孔保卫细胞中参与碳代谢的主要酶的特性及调控特点,特别是保卫细胞叶绿体中催化苹果酸形成的PEP羧化酶,其磷酸化和去磷酸化参与了保卫细胞信号传递。保卫细胞碳代谢调控在气孔运动调节中的作用,并讨论了保卫细胞碳代谢与能量代谢的关系。     

保卫细胞碳代谢与气孔运动

作为气孔运动渗透调节的代谢基础 ,气孔保卫细胞的碳代谢有特殊的调控机理。本文介绍了气孔保卫细胞中参与碳代谢的主要酶的特性及调控特点 ,特别是保卫细胞叶绿体中催化苹果酸形成的PEP羧化酶 ,其磷酸化和去磷酸化参与了保卫细胞信号传递。保卫细胞碳代谢调控在气孔运动调节中的作用 ,并讨论了保卫细胞碳代谢与能量代谢的关系     

植物保卫细胞离子通道在气孔运动中的作用

介绍保卫细胞质膜和液泡膜上的离子通道活性变化及其在气孔运动中的作用,同时对各种刺激引发气孔运动过程中的信使Ca2 、H2O2和pH等对离子通道的调节作用作了概述.     

气孔保卫细胞信号转导途径

从刺激与感受、信号转换、反应三方面简要介绍气孔保卫细胞的信号转导途径。     

细胞内离子在气孔运动中的作用

气孔运动与植物水分代谢密切相关。保卫细胞中的无机离子作为第二信使(Ca²⁺)或者渗透调节物质(K⁺、Cl^–)在响应 外界理化因子的刺激、调节保卫细胞膨压过程中发挥重要作用。保卫细胞质膜和液泡膜上的离子通道作为各种刺激因素作 用的靶位点, 是保卫细胞离子转运的关键组分, 在气孔运动调控过程中扮演关键角色。该文对近年来保卫细胞离子的作用 和离子通道研究的进展进行了综述。     

细胞内离子在气孔运动中的作用

气孔运动与植物水分代谢密切相关。保卫细胞中的无机离子作为第二信使（Ca2＋）或者渗透调节物质（K＋、Cl-）在响应外界理化因子的刺激、调节保卫细胞膨压过程中发挥重要作用。保卫细胞质膜和液泡膜上的离子通道作为各种刺激因素作用的靶位点,是保卫细胞离子转运的关键组分,在气孔运动调控过程中扮演关键角色。该文对近年来保卫细胞离子的作用和离子通道研究的进展进行了综述。     

气孔功能的结构基础

近年来,国际上十分关注气孔运动的调控机理,在保卫细胞内外的信息传递和转导途径的研究方面取得重要进展。保卫细胞的特殊结构和气孔功能密切相关,对保卫细胞壁特性、质膜上的各种结合蛋白、质膜和液泡膜上的离子通道的研究,以及对细胞骨架和气孔运动的关系的探索为阐明气孔运动的机理提供了更多的依据。     

蚕豆下表皮细胞外钙调素的存在及其对气孔运动的调节

细胞外钙调素可能作为多肽第一信使,调节细胞增殖,花粉萌发,特定基因表达等生理过程,气孔能灵敏地对外界刺激作出反应,快速开闭,本文用免疫电镜和免疫荧光显微镜技术证明保卫细胞及其它表皮细胞胞外都存在钙调素;外源纯化钙调素能促进气孔关闭,抑制气孔开放,最适浓度为10^-8mol/L;不能透过质膜的大分子钙调素拮抗剂W—-agarose和钙调素抗血清都能抑制气孔关闭,促进开放,说明保卫细胞的内源胞外钙调素确实能促进气孔关闭,抑制开放。而且只能在细胞外起作用,推测在自然情况下,保卫细胞内源胞外钙调素可能作为胞外第一信使和其它信号分子一起调节气孔的开关运动,而且可能在环境刺激与细胞响应之间起重要作用。     

植物气孔运动过程中的信号转导机制

气孔运动的信号转导机制一直是科研工作者研究的一个热点,文章就光、CO2、ABA、H2O2、NO、蛋白激酶、蛋白磷酸酶等对保卫细胞气孔运动的影响,介绍气孔运动机制的研究进展。     

气孔功能的结构基础

近年来,国际上十分关注气孔动动的调控机理,在保卫细胞内外的信息传递和转导途径的研究方面取得重要进展。保卫细胞的特殊结构和气孔功能密切相关,对保卫细胞壁特性、质膜上的各种结合蛋白、质膜和液泡膜上的离子通道的研究,以及对细胞骨架和气孔运动的关系的探索为阐明气孔运动的机理提供了更多的依据。     

Metabolite Transporter Regulation of ABA Function and Guard Cell Response

Pairs of guard cells form stomatal pores through which gas exchange occurs. Gas exchange includes transpirational water loss, and guard cell signaling in drought response has been studied for decades. Abscisic acid （ABA） is the major hormone that regulates drought responses. ABA and other metabolites can be synthesized in one cell type or subcellular compartment and transported across mem- branes by specific transporters to conduct biological func- tions. Two new papers, both taking advantage of reverse genetic methods, one focusing on a plasma membrane ABA efflux carrier （Zhang et al., 2014） and the other on a putative mitochondrial pyruvate carrier （Li et al., 2014）, have recently shown the importance of metabolite trans- porters in ABA function and guard cell response.     

Outward-Rectifying K+ Channels in Stomatal Guard Cell Protoplasts

Ion channels in stomatal guard cell protoplasts from Vicia fabawere examined using the patch-clamp technique. Most ion channelshaving unit conductance ranging between 10 and 30 pS showedclear outward-rectification in symmetrical 50mM KCl. The largeinside-out membranes contained these outward-rectifiers as themajor and relatively stable channels. The channels were K⁺ ion-selective.Kinetic analysis revealed that the channels have three conductancestates: open, closed and inactivated. The rates of transitionto and from the inactivated state were highly voltage-dependent. (Received April 6, 1988; Accepted May 25, 1988)     

Photosynthesis by Guard Cell Chloroplasts of Vicia faba L.: Effects of Factors Associated with Stomatal Movement

The properties of photosynthetic O₂ evolution by mesophyll cellchloroplasts (MCC) and guard cell chloroplasts (GCC) isolatedfrom protoplasts of Vicia faba L. have been studied and effectson O₂ evolution of factors known to regulate stomatal movementshave been compared. The O₂ evolution of GCC was CO₂-dependent.The saturating light intensity for O₂ evolution was between150 and 200 µmol m^–2s^–1 for MCC and was between400 and 1,000µmol m^–2s^–1 for GCC. Light quality(red vs. blue) had no significant effect on O₂ evolution byeither MCC or GCC. The O₂ evolution rate of MCC was stronglydependent on external K⁺ concentration, but GCC did not respondsignificantly to variations in external K⁺ concentration between0 and 250 mM. The optimal external pH for O₂ evolution by MCCwas approximately 7.5, and either higher or lower external pHsignificantly inhibited O₂ evolution. However, O₂ evolutionby GCC was only slightly enhanced when external pH was increasedfrom 6.0 to 8.0. Our observation of differential sensitivityof MCC and GCC to light intensity and to variations of cytoplasmicK⁺ and pH may indicate differential regulation of photosynthesisin MCC and GCC. ¹Current address: Biology Department, Pennsylvania State University,208 Mueller Laboratory, University Park, PA 16802, U.S.A.     

Guard Cell Pressures and Wall Properties during Stomatal Opening

Pressures required to produce stomatal apertures of differentwidths have been measured in guard cells of T. virginiana andC. communis. These pressures are lower than those that coulddevelop in guard cells at full turgor on account of their osmoticproperties. During the Spannungsphase the metabolism of guardcells seems to contribute towards a reduction of the elasticmodulus of their walls, whereas during the motorphase the volumetricmodulus of the cell as a whole, apparently increases gentlyat first and then more markedly as maximum apertures are approached.     

Photocontrol of the Functional Coupling between Photosynthesis and Stomatal Conductance in the Intact Leaf : Blue Light and Par-Dependent Photosystems in Guard Cells

The photocontrol of the functional coupling between photosynthesis and stomatal conductance in the leaf was investigated in gas exchange experiments using monochromatic light provided by lasers. Net photosynthesis and stomatal conductance were measured in attached leaves of Malva parviflora L. as a function of photon irradiance at 457.9 and 640.0 nanometers.

Photosynthetic rates and quantum yields of photosynthesis were higher under red light than under blue, on an absorbed or incident basis.

Stomatal conductance was higher under blue than under red light at all intensities. Based on a calculated apparent photon efficiency of conductance, blue and red light had similar effects on conductance at intensities higher than 0.02 millimoles per square meter per second, but blue light was several-fold more efficient at very low photon irradiances. Red light had no effect on conductance at photon irradiances below 0.02 millimoles per square meter per second. These observations support the hypothesis that stomatal conductance is modulated by two photosystems: a blue light-dependent one, driving stomatal opening at low light intensities and a photosynthetically active radiation (PAR)-dependent one operating at higher irradiances.

When low intensity blue light was used to illuminate a leaf already irradiated with high intensity, 640 nanometers light, the leaf exhibited substantial increases in stomatal conductance. Net photosynthesis changed only slightly. Additional far-red light increased net photosynthesis without affecting stomatal conductance. These observations indicate that under conditions where the PAR-dependent system is driven by high intensity red light, the blue light-dependent system has an additive effect on stomatal conductance.

The wavelength dependence of photosynthesis and stomatal conductance demonstrates that these processes are not obligatorily coupled and can be controlled by light, independent of prevailing levels of intercellular CO₂. The blue light-dependent system in the guard cells may function as a specific light sensor while the PAR-dependent system supplies a CO₂-modulated energy source providing functional coupling between the guard cells and the photosynthesizing mesophyll.

     

Guard Cell Chloroplasts Are Essential for Blue Light-Dependent Stomatal Opening in Arabidopsis

Blue light (BL) induces stomatal opening through the activation of H⁺-ATPases with subsequent ion accumulation in guard cells. In most plant species, red light (RL) enhances BL-dependent stomatal opening. This RL effect is attributable to the chloroplasts of guard cell, the only cells in the epidermis possessing this organelle. To clarify the role of chloroplasts in stomatal regulation, we investigated the effects of RL on BL-dependent stomatal opening in isolated epidermis, guard cell protoplasts, and intact leaves of Arabidopsis thaliana. In isolated epidermal tissues and intact leaves, weak BL superimposed on RL enhanced stomatal opening while BL alone was less effective. In guard cell protoplasts, RL enhanced BL-dependent H⁺-pumping and DCMU, a photosynthetic electron transport inhibitor, eliminated this effect. RL enhanced phosphorylation levels of the H⁺-ATPase in response to BL, but this RL effect was not suppressed by DCMU. Furthermore, DCMU inhibited both RL-induced and BL-dependent stomatal opening in intact leaves. The photosynthetic rate in leaves correlated positively with BL-dependent stomatal opening in the presence of DCMU. We conclude that guard cell chloroplasts provide ATP and/or reducing equivalents that fuel BL-dependent stomatal opening, and that they indirectly monitor photosynthetic CO₂ fixation in mesophyll chloroplasts by absorbing PAR in the epidermis.     

Induction of CAM in Mesembryanthemum crystallinum Abolishes the Stomatal Response to Blue Light and Light-Dependent Zeaxanthin Formation in Guard Cell Chloroplasts

Facultative CAM plants such as Mesembryanthemum crystallinum(ice plant) possess C3 metabolism when unstressed but developCAM under water or salt stress. When ice plants shift from C3metabolism to CAM, their stomata remain closed during the dayand open at night. Recent studies have shown that the stomatalresponse of ice plants in the C3 mode depends solely on theguard cell response to blue light. Recent evidence for a possiblerole of the xanthophyll, zeaxanthin in blue light photoreceptionof guard cells led to the question of whether changes in theregulation of the xanthophyll cycle in guard cells parallelthe shift from diurnal to nocturnal stomatal opening associatedwith CAM induction. In the present study, light-dependent stomatalopening and the operation of the xanthophyll cycle were characterizedin guard cells isolated from ice plants shifting from C3 metabolismto CAM. Stomata in epidermis detached from leaves with C3 metabolismopened in response to white light and blue light, but they didnot open in response to red light. Guard cells from these leavesshowed light-dependent conversion of violaxan-thin to zeaxanthin.Induction of CAM by NaCI abolished both white light- and bluelight-stimulated stomatal opening and light-dependent zeaxanthinformation. When guard cells isolated from leaves with CAM weretreated with 100 mM ascorbate, pH 5.0 for 1 h in darkness, guardcell zeaxanthin content increased at rates equal to or higherthan those stimulated by light in guard cells from leaves inthe C3 mode. The ascorbate effect indicates that chloroplastsin guard cells from leaves with CAM retain their competenceto operate the xanthophyll cycle, but that zeaxanthin formationdoes not take place in the light. The data suggest that inhibitionof light-dependent zeaxanthin formation in guard cells mightbe one of the regulatory steps mediating the shift from diurnalto nocturnal stomatal opening typical of plants with CAM. (Received July 5, 1996; Accepted December 12, 1996)