植物细胞质外体多肽与蛋白研究

细胞质膜以外的质外体是植物细胞的重要组成部分,质外体是植物细胞的重要信号源和细胞器。当植物遭受生物或非生物环境刺激时,可能首先引起质外体信号系统的变化;同时质外体作为植物细胞之间最方便的通道,在细胞间信号传递和信息交流上起重要作用,从而成为协调植物细胞分化、器官形成和整体生长发育的决定性因素之一。本文概括地介绍了我室在此领域的一些研究进展。     

植物细胞质外体pH感受机制的解析

质外体是植物感受和应答环境胁迫(包括生物和非生物胁迫)的前沿区域。质外体的pH值是被严格调控的重要生理参数。环境胁迫(如细菌病害)等会引起植物细胞质外体碱化现象。然而, 质外体pH如何协调根生长与免疫响应? 其分子调控机制尚不清楚。最近, 南方科技大学生命科学学院郭红卫团队与清华大学-德国马克斯普朗克研究所-科隆大学柴继杰团队以模式植物拟南芥(Arabidopsis thaliana)为研究材料, 通过遗传学、细胞生物学、生物化学和结构生物学等综合手段, 发现细胞表面小肽-受体复合物可作为质外体pH感受器, 感受和应答分子模式触发的免疫(PTI)引发的拟南芥根尖分生组织细胞质外体碱化。该研究揭示了植物根尖分生组织细胞质外体pH感受的蛋白质复合物及响应机制, 以及免疫与生长之间的协调机制, 加深了人们对植物如何平衡生长与免疫应答生物学反应过程的理解。     

细胞外钙调素——一种植物中的多肽信使?

钙调素历来被认为是细胞内钙信号的多功能受体蛋白,国内外10多年的研究已证实,它普遍存在于人、动物细胞外与植物质外体.我们的工作证明了钙调素不仅普遍存在于植物细胞外,而且在胞外位点具有促进悬浮培养细胞及其原生质体的增殖、调节花粉萌发与伸长和促进rbc小亚基基因的光不依赖性表达等多种重要生物学功能.在花粉体系中,还证明了胞外钙调素具有跨膜与胞外信号转导机制,其中包括异三聚体G蛋白、PLC/IP3/IP3R和胞内钙信号等组分的参与.因此,认为细胞外钙调素可能是植物中的一种多肽信使,这对传统上认为植物中不存在进行胞间通讯的多肽信使的观点,提出了新的质疑.     

植物质外体的研究方法

质外体是细胞之间的空间和细胞膜与细胞壁之间的微小空间通过细胞壁上的微孔连接而成的一个连续［１］。整株植物的质外体是连续的。它是养分运输的重要途径,并有贮存养分和活化养分的功能。因此,质外体在植物代谢中的作用倍受人们的重视。然而由于质外体在植物中所占的比例较小,它与膜内细胞质之间存在着水分与物质的平衡,从而给有关质外体的研究带来许多困难。近些年来,国际上在这方面的研究取得了一些进展。本文着重介绍目前在植物营养研究中几种常用的质外体研究方法。１植物地上部质外体的测定方法在质外体的研究中,根系质外体已…     

植物胞外钙调素与信号转导

植物体需要构建复杂的信号转导体系以调节自身的生长发育过程并适应外界环境的变化,这种功能的实现需要胞内和胞外诸多信号分子的参与,胞外钙调素的发现使人们开始相信植物细胞外多肽信使的存在。胞外钙调素的生物学功能极其广泛,几乎涉及到植物生长发育的各个阶段,其信号转导途径是目前研究得最多也是最为清楚的方面,异三聚体G蛋白、磷脂酶C(PLC)-肌醇三磷酸(IP3)-肌醇三磷酸受体(IP3R)信号通路、活性氧和Ca2 通道之间直接或间接的相互作用是胞外钙调素信号转导的核心。     

植物根中质外体屏障结构和生理功能研究进展

综述了近10年来植物根中质外体屏障结构和功能的研究进展。质外体屏障指根中内、外皮层初生壁的凯氏带,或次生壁栓质化和木质化,以及植物体表角质层组成的保护组织,能隔绝水、离子和氧气不能自由进出植物体的屏障结构,具有保护植物体的生理功能。根中凯氏带的分子发育机理研究表明根内皮层类似哺乳动物上皮组织的保护作用。植物根中质外体保证内部各种生理代谢在稳定的内部环境中进行,是植物适应各种逆境的重要屏障结构。根中质外体屏障在植物适应干旱、洪涝灾害、离子胁迫和病虫害的侵袭等方面具有重要作用,在探索适应并修复极端生态环境的植物资源中有广阔的应用前景。     

脂肪间充质干细胞来源外泌体的功能

外泌体是细胞外膜质纳米囊泡,将蛋白质、核酸(DNA和RNA)转运到靶细胞中,介导局部和系统的细胞间通信,从而改变受体细胞的行为.这些小泡在许多生物功能中发挥重要作用,如脂肪合成、免疫调节、神经再生和肿瘤调节等.脂肪间充质干细胞目前被认为是细胞治疗和再生医学领域中一种功能丰富的工具,可产生和分泌多种外泌体,继承细胞的多种...     

植物根系质外体屏障研究进展

根是植物吸收水分和矿质营养以维持生命活动的重要器官。根系的构型和超微结构具有物种特异性, 对水分和矿质营养的吸收有不同程度的影响。其中, 内、外皮层的木栓层和凯氏带是2种重要的质外体屏障, 可非定向地阻断水分和离子运输, 在植物生长发育及响应逆境胁迫中发挥重要作用。尽管如此, 植物根系质外体屏障的结构、化学组成、生理功能、生物合成及其调控仅在模式植物拟南芥(Arabidopsis thaliana)中被广泛研究。近年来, 关于作物大麦(Hordeum vulgare)、水稻(Oryza sativa)以及部分牧草的根系质外体屏障研究报道逐渐增多。该文系统比较了拟南芥、大麦、水稻以及部分牧草根系质外体屏障的异同, 提出今后的研究方向, 以期为深入探索禾本科作物和牧草根系质外体屏障在生长发育和逆境适应中的作用奠定理论基础, 并为作物和牧草育种工作提供新思路。     

钙调素及钙调素相关蛋白在植物细胞中的研究进展

植物对一系列生物和非生物刺激所产生的反应都与细胞内Ca2+信号转导有关,而钙调素、钙调素相关蛋白则是Ca2+信号转导的下游靶蛋白。该文介绍了钙调素的结构及其在植物细胞中的分布,钙调素及钙调素相关蛋白在植物细胞中的表达等方面的最近研究进展。     

微生物胞外多糖在修复重金属污染中的潜力及其生物化学机制

微生物常常通过分泌细胞外多糖类物质(胞外多糖)来保护细胞免受极端环境条件、不利因素(如干燥、高盐、辐射、高低温、强酸碱)以及有毒有害物质(如重金属等)的损伤。胞外多糖在微生物耐受和降低重金属污染中起重要作用,在环境科学研究中有重要意义。本文综述了微生物胞外多糖的生物化学性质,简述了重金属对微生物胞外多糖合成及其结构的影响,从生物吸附、生物转化两个方面总结了微生物胞外多糖降低环境重金属污染的生物化学机制,最后展望了未来的研究方向和有待解决的科学问题。     

Role of apoplastic ascorbate and hydrogen peroxide in the control of cell growth in pine hypocotyls

The growth cessation of plant axis has been related with the formation of diphenyl bridges among the pectic components of the cell wall caused by the action of apoplastic peroxidases using hydrogen peroxide as electron acceptor. The formation of diphenyl bridges is prevented by the presence of ascorbate in the apoplastic fluid which acts as a hydrogen peroxide scavenger. The current work focuses on the role of the apoplastic ascorbate and hydrogen peroxide in the cell growth. The addition of hydrogen peroxide caused an inhibition of the auxin-induced growth as well as a significant decrease in the cell wall creep induced by acid-pH solutions. The hydrogen peroxide content in apoplastic fluid increased with the hypocotyl age and along the hypocotyl axis of 10-day-old pine seedlings, as the growth capacity decreased. On the other hand, the ascorbate content in the apoplastic fluid decreased with the hypocotyl age and along the hypocotyl axis of 10-day-old seedlings. A very significant correlation between the hydrogen peroxide apoplastic level and the growth rate as well as between the ascorbate/hydrogen peroxide molar ratio and the growth rate of hypocotyls have been found suggesting that the redox state is the main factor controlling the cell wall stiffening mechanism and thus growth in pine hypocotyls.     

Signal Integration by ABA in the Blue Light-Induced Acidification of Leaf Pavement Cells in Pea (Pisum sativum L. var. Argenteum)

Leaf pavement cell expansion in light depends on apoplastic acidification by a plasma membrane proton-pumping ATPase, modifying cell wall extensibility and providing the driving force for uptake of osmotically active solutes generating turgor. This paper shows that the plant hormone ABA inhibits light-induced leaf disk growth as well as the blue light-induced pavement cell growth in pea (Pisum sativum L.). In the phytochrome chromophore-deficient mutant pcd2, the effect of ABA on the blue light-induced apoplastic acidification response, which exhibits a high fluence phase via phytochrome and a low fluence phase via an unknown blue light receptor, is still present, indicating an interaction of ABA with the blue light receptor pathway. Furthermore, it is shown that ABA inhibits the blue light-induced apoplastic acidification reversibly. These results indicate that the effect of ABA on apoplastic acidification can provide a mechanism for short term, reversible adjustment of leaf growth rate to environmental change.Key Words: ABA, apoplastic acidification, blue light, epidermal pavement cell growth, leaf growth, pea (Pisum sativum L.), signal integration     

Review article. Apoplastic barriers in roots: chemical composition of endodermal and hypodermal cell walls

Based on the characterization of the chemical composition of endodermal and hypodermal cell walls isolated from seven monocotyledonous and three dicotyledonous plant species, a model of the composition of apoplastic barriers in roots is proposed. Depending on the species, endodermal and hypodermal cell walls of roots contained varying amounts of the biopolymers suberin, lignin, cell wall proteins, and carbohydrates. Although analysis of the chemical composition of these apoplastic barriers of roots is now possible, it is pointed out that conclusions from these data concerning the functional properties of these cell walls can not easily be drawn. However, in analogy to suberized periderms it is argued that the suberin should play a role in establishing an apoplastic transport barrier in roots, albeit not a perfect barrier. Furthermore, due to the combined occurrence of suberin, lignin and cell wall proteins it is argued that endodermal and hypodermal cell walls also have an important function as barriers towards pathogens. Finally, it is pointed out that additional experimental approaches combining the investigation of transport properties and of the chemical composition of apoplastic transport barriers in roots are necessary before the function of endodermal and hypodermal cell walls in roots can be fully understood.     

Apoplastic pH and Ammonium Concentration in Leaves of Brassica napus L

A vacuum infiltration technique was developed that enabled the extraction of apoplastic solution with very little cytoplasmic contamination as evident from a malate dehydrogenase activity of less than 1% in the apoplastic solution relative to that in bulk leaf extracts. The volume of apoplastic water, a prerequisite for determination of the concentration of apoplastic solutes, was determined by vacuum infiltration of indigo carmine with subsequent analysis of the dilution of the dye in apoplastic extracts. Indigo carmine was neither transported across the cell membrane nor significantly adsorbed to the cell walls, ensuring reproducible (SE < 2%) and precise determination of apoplastic water. Analysis of leaves from four different positions on senescing Brassica napus plants showed a similar apoplastic pH of 5.8, while apoplastic NH4+ increased from 1.1 mM in lower leaves to 1.3 mM in upper leaves. Inhibition of glutamine synthetase in young B. napus plants resulted in increasing apoplastic pH from 6.0 to 6.8 and increasing apoplastic NH4+ concentration from 1.0 to 25.6 mM, followed by a marked increase in NH3 emission. Calculating NH3 compensation points for B. napus plants on the basis of measured apoplastic H+ and NH4+ concentrations gave values ranging from 4.3 to 5.9 nmol NH3 mol-1 air, consistent with an estimate of 5.3 [plus or minus] 3.6 nmol NH3 mol-1 air obtained by NH3 exchange experiments in growth chambers. A strong linear relationship was found between calculated NH3 compensation points and measured NH3 emission rates in glutamine synthetase-inhibited plants.     

Tracing root permeability: comparison of tracer methods

Root epidermis and apoplastic barriers (endodermis and exodermis) are the critical root structures involved in setting up plant-soil interface by regulating free apoplastic movement of solutes within root tissues. Probing root apoplast permeability with “apoplastic tracers” presents one of scarce tools available for detection of “apoplastic leakage” sites and evaluation of their role in overall root uptake of water, nutrients, or pollutants. Although the tracers are used for many decades, there is still not an ideal apoplastic tracer and flawless procedure with straightforward interpretation. In this article, we present our experience with the most frequently used tracers representing various types of chemicals with different characteristics. We examine their behaviour, characteristics, and limitations. Here, we show that results gained with an apoplastic tracer assay technique are reliable but depend on many parameters–chemical properties of a selected tracer, plant species, cell wall properties, exposure time, or sample processing.     

Peroxidase Activity in the Leaf Elongation Zone of Tall Fescue : II. Spatial Distribution of Apoplastic Peroxidase Activity in Genotypes Differing in Length of the Elongation Zone

Previous work suggested that cell wall peroxidase activity increased as cells were displaced through the elongation zone in leaf blades of tall fescue (Festuca arundinacea Schreb.). In this study, two genotypes that differ in length of the elongation zone were used to examine the relationship between peroxidase activity in apoplastic fluid of intact leaf blade segments and the spatial distribution of leaf growth. Apoplastic fluid was extracted by vacuum infiltration and centrifugation, and peroxidase activity was assayed spectrophotometrically. Isoelectric focusing was used to characterize the isoforms of apoplastic peroxidase within the region of elongation and in the region of secondary cell wall deposition, which is distal to the elongation zone. A striking correlation was found in each genotype between both the location and timing of increase in apoplastic peroxidase activity and the onset of growth deceleration. Only cationic isoforms of apoplastic peroxidase could be identified in the elongation zone, whereas additional anionic isoforms appeared in the region of secondary cell wall deposition. We conclude that cessation of elongation growth in tall fescue leaf blades is likely to be related to the secretion of cationic isoforms of peroxidase into the cell wall.     

Use of the pressure vessel to measure concentrations of solutes in apoplastic and membrane-filtered symplastic sap in sunflower leaves

A simple, repeatable, and accurate method is described for the collection of apoplastic and membrane-filtered symplastic sap fractions, and for the determination of the origin of these fractions within the leaf. The apoplastic distribution patterns of the naturally occurring apoplastic leaf solutes, and the apoplastic dye PTS (trisodium 3-hydroxy-5, 8, 10-pyrenetrisulfonate) were compared. Aliquots of sap were expressed from detached sunflower leaves in a pressure chamber over intervals of 0.02 to 0.04 megapascal. Three distinct fractions were detected in the expressed sap volume. These were successively released and identified as a petiole-midrib fraction, a minor vein-cell wall fraction, and a mixed fraction consisting of a contribution from the minor vein-cell wall with an increasing proportion of membrane-filtered cell sap.     

Relationship between changes in the guard cell abscisic-acid content and other stress-related physiological parameters in intact plants

The relationships of guard cell ABA content to eight stress-related physiological parameters were determined on intact Vicia faba L. plants that were grown hydroponically with split-root systems. Continuous stress was imposed by the addition of PEG to part of the root system. The water potentials of roots sampled after the addition of PEG were 0.25 MPa lower than the water potentials of other roots of the same plant, which were similar to the roots of untreated plants. The leaflet water potentials of plants sampled within 2 h of stress imposition were similar to those of control plants. However, leaf conductance was lower in plants sampled after only 20 min of stress imposition, and the root- and leaflet apoplastic ABA concentrations of these plants were higher than those of untreated plants. As the essence of this report, there was a linear relationship between guard cell ABA content and leaf conductance. Leaflet apoplastic ABA concentrations <150 nM were also linearly related to leaf conductance, but higher leaflet apoplastic ABA concentration did not cause equally large further declines in leaf conductance. It is suggested that evaporation from guard cell walls caused ABA to accumulate in the guard cell apoplast and this pool was saturated at high leaflet apoplastic ABA concentrations.