拟南芥内膜Na+,K+/H+反向转运体研究进展

拟南芥内膜Na,K~+/H~+反向转运体(Endosomal NHX)的亚细胞定位、离子转运特性及生物学功能阐释取得了重要进展。拟南芥内膜Na~+,K~+/H~+反向转运体包含AtNHX5和AtNHX6两个成员,它们的氨基酸序列相似性为78.7%。研究表明,AtNHX5和AtNHX6具有功能冗余,它们都定位在高尔基体(Golgi)、反面高尔基体管网状结构(TGN)、内质网(ER)和液胞前体(PVC),参与调控耐盐胁迫、pH平衡和K~+平衡等。有报道显示内膜NHXs跨膜结构域存在能够调控自身离子活性的酸性保守氨基酸残基,对其自身功能具有决定性作用。最新研究结果表明,拟南芥内膜NHXs影响囊泡运输和蛋白存贮,并参与生长素介导的植物生长和发育。文中主要对拟南芥内膜NHXs的亚细胞定位、离子转运、功能及应用进展进行了概述。     

钙对盐胁迫下棉苗离子吸收分配的影响

研究了钙对NaCl胁迫下棉花幼苗体内离子分布的影响及其与根系质膜H^ -ATP酶、液泡膜H^ -dATP酶和H^ -PP酶活性的关系。不同器官离子含量和根系横切面X-射线微区分析结果表明,NaCl胁迫下外源钙明显减少棉花幼苗对Na^ 的吸收及其向茎杆、叶片的运输,增加对K^ 和Ca^2 的吸收及其向茎相杆、叶片的运输,增强棉苗体内的盐分区域化分配,提高根冠比和干物质积累,根系电解质渗漏率下降,钙明显提高盐胁迫下幼根细胞质膜H^ -ATP酶、液泡膜H^ -ATP酶和H^ -PP酶的活性,与钙调节棉花对离子的吸收、分配相一致,说明这些酶可以为根细胞中的Na^ 在液泡中积累以及K^ 、Ca^2 的选择性吸收和运输提供动力。     

质膜Na^＋／H^＋逆向转运蛋白与植物耐盐性

土壤盐碱化是造成农作物减产的主要原因之一。质膜Na^＋／H^＋逆向转运蛋白能够介导植物根部Na^＋的外排和体内Na^＋的长距离运输, 并能够调控细胞K＋的稳态平衡及细胞内pH值和Ca^2＋的转运, 因此其在植物耐盐性方面具有重要作用。该文概述了植物质膜Na^＋／H^＋逆向转运蛋白的分子结构、功能、表达调控及其与植物耐盐性关系等方面的研究进展, 并对今后有关该蛋白的主要研究方向作了分析和展望。     

硅改善盐胁迫下库拉索芦荟生长和离子吸收与分布

Si2．0mmol／L处理明显缓解NaCl 100、200mmol／L胁迫120d对库拉索芦荟（Aloevera）生长的抑制作用。Si可显著降低NaCl胁迫下芦荟植株中的Na^＋和Cl^-含量,提高K^＋含量,从而显著降低K^＋／Na^＋,促进根对K^＋的选择性吸收（ASK,Na）和K^＋向地上部的选择性运输（TSK,Na）,以维持植株体内的离子稳态。根系和叶片横切面的X-射线能谱微区分析结果进一步证实了这一结果。Si改善盐胁迫下芦荟对K^＋的选择性吸收和运输的机制之一是通过显著提高盐胁迫下芦荟根细胞质膜H^＋ATPase、液泡膜H^＋-ATPase和液泡膜H^＋-PPase的活性。     

拟南芥SNARE因子在膜泡运输中的功能

高等植物细胞含有复杂的内膜系统,通过其特有的膜泡运输机制来完成细胞内和细胞间的物质交流。膜泡运输主要包括运输囊泡的出芽、定向移动、拴留和膜融合4个过程。这4个过程受到许多因子的调控,如Coat、SM、Tether、SNARE和Rab蛋白等,其中SNARE因子在膜融合过程中发挥重要功能。SNARE因子是小分子跨膜蛋白,分为定位于运输囊泡上的v-SNARE和定位于靶位膜上的t-SNARE,两类SNARE结合形成SNARE复合体,促进膜融合的发生。SNARE蛋白在调控植物体生长发育以及对外界环境响应等生理过程中起重要作用。该文对模式植物拟南芥（Arabidopsis thaliana）SNARE因子的最新细胞内定位和功能分析等研究进展进行了概述。     

拟南芥SNARE因子在膜泡运输中的功能

高等植物细胞含有复杂的内膜系统, 通过其特有的膜泡运输机制来完成细胞内和细胞间的物质交流。膜泡运输主要包括运输囊泡的出芽、定向移动、拴留和膜融合4个过程。这4个过程受到许多因子的调控, 如Coat、SM、Tether、SNARE和Rab蛋白等, 其中SNARE因子在膜融合过程中发挥重要功能。SNARE因子是小分子跨膜蛋白, 分为定位于运输囊泡上的v-SNARE和定位于靶位膜上的t-SNARE, 两类SNARE结合形成SNARE复合体, 促进膜融合的发生。SNARE蛋白在调控植物体生长发育以及对外界环境响应等生理过程中起重要作用。该文对模式植物拟南芥(Arabidopsis thaliana)SNARE因子的最新细胞内定位和功能分析等研究进展进行了概述。     

Na+/H+逆向转运蛋白和植物耐盐性

Na^ /H^ 逆向转运蛋白对植物耐盐起着重要作用,它利用质膜H^ -ATPase或液泡膜H^ -ATPase及PPiase泵H^ 产生的驱动力把Na^ 排出细胞或在液泡中区隔化以消除Na^ 的毒害。主要讨论植物中Na^ /H^ 逆向转运蛋白研究在分子水平的最新进展。     

植物质膜H+-ATPase响应盐胁迫的分子机制

植物细胞质膜质子泵（PM H^＋-ATPase）有看家酶之称,是由多基因编码的,其主要功能是向细胞营养物质的吸收和离子跨膜运输提供驱动力。文章介绍PM H^＋-ATPase在植物抗盐中的作用及研究进展。     

水稻 Ca2+/H+ 反向转运体 OsCAX3 的功能分析和亚细胞定位研究

Ca2+/H+ 反向转运体作为一类 Ca2+外向转运器,在植物的营养和信号转导中起着非常重要的作用 . 克隆了水稻 Ca2+/H+ 反向转运体基因 OsCAX3 ,序列分析表明 OsCAX3 具有 11 个跨膜区,其中在第 6 和第 7 个跨膜区之间有一个 17 个氨基酸组成的酸性基序 (acid motif) ,功能互补实验证明 OsCAX3 具有转运 Ca2+ 的功能,并且其 N 端 26 个氨基酸序列对转运 Ca2+ 具有一定的抑制作用 . RT-PCR 分析表明 OsCAX3 的表达受到外源 Ca2+ 的诱导 . 利用 PSORT prediction 进行亚细胞定位分析,和利用 OsCAX3-GFP 融合蛋白瞬时表达分析证明, OsCAX3 定位于细胞质膜 . 以上结果表明, OsCAX3 是一种定位于细胞质膜上的 Ca2+/H+ 反向转运体 .     

植物Na+/H+反向转运蛋白的研究进展

盐胁迫是限制植物生长发育的主要因素之一,植物Na+/H+反向转运蛋白可通过将Na+逆向转运出细胞外或将Na+区隔化于液泡中来抵制环境中过高的Na+浓度.植物中Na+/H+反向转运蛋白存在于细胞质膜和液泡膜上,现在已得到多种编码这些Na+/H+反向转运蛋白的基因,对其结构功能特性进行了大量研究,并发现将这些基因转入非抗盐植物中过量表达可提高转基因植物的抗盐性.概述了Na+/H+反向转运蛋白及其编码基因的最新研究进展.     

Plant and yeast NHX antiporters: roles in membrane trafficking

The plant NHX gene family encodes Na + /H + antiporters which are crucial for salt tolerance, potassium homeostasis and cellular pH regulation. Understanding the role of NHX antiporters in membrane trafficking is becoming an increasingly interesting subject of study. Membrane trafficking is a central cellular process during which proteins, lipids and polysaccharides are continuously exchanged among membrane compartments. Yeast ScNhx1p, a prevacuole/ vacuolar Na + /H + antiporter, plays an important role in regulating pH to control trafficking out of the endosome. Evidence begins to accumulate that plant NHX antiporters might function in regulating membrane trafficking in plants.     

Alkali cation exchangers: roles in cellular homeostasis and stress tolerance

Uptake and translocation of cations play essential roles in plant nutrition, signal transduction, growth, and development. Among them, potassium (K+) and sodium (Na+) have been the focus of numerous physiological studies because K+ is an essential macronutrient and the most abundant inorganic cation in plant cells, whereas Na+ toxicity is a principal component of the deleterious effects associated with salinity stress. Although the homeostasis of these two ions was long surmised to be fine tuned and under complex regulation, the myriad of candidate membrane transporters mediating their uptake, intracellular distribution, and long-distance transport is nevertheless perplexing. Recent advances have shown that, in addition to their function in vacuolar accumulation of Na+, proteins of the NHX family are endosomal transporters that also play critical roles in K+ homeostasis, luminal pH control, and vesicle trafficking. The plasma membrane SOS1 protein from Arabidopsis thaliana, a highly specific Na+/H+ exchanger that catalyses Na+ efflux and that regulates its root/shoot distribution, has also revealed surprising interactions with K+ uptake mechanisms by roots. Finally, the function of individual members of the large CHX family remains largely unknown but two CHX isoforms, AtCHX17 and AtCH23, have been shown to affect K+ homeostasis and the control of chloroplast pH, respectively. Recent advances on the understanding of the physiological processes that are governed by these three families of cation exchangers are reviewed and discussed.     

茄子砧木Na^＋、K^＋含量、Sk,Na运输与耐盐性关系研究

为考察不同茄子砧木在茄子耐盐性的作用,以茄子嫁接生产中常用的托鲁巴姆（Solanum torvum）、赤茄（Solanum integgrifolium）、刺茄（Solanum texanum）和刚果茄（Solanum sisymbriifl ium）为试材,研究了盐害指数、根系和地上部Na^＋、K^＋含量、Na^＋/K^＋比、SK,Na运输及其与耐盐性的关系。结果表明,各种砧木的盐害指数均随着盐浓度的增大呈上升趋势,同一盐浓度下,盐害指数由大到小依次为刚果茄〉赤茄〉刺茄〉托鲁巴姆。根系Na^＋含量、地上部K^＋含量、根系Na^＋/K^＋比及SK,Na运输在各盐浓度下均表现为托鲁巴姆〉刺茄〉赤茄〉刚果茄。地上部Na^＋含量、根中K^＋含量及地上部Na^＋/K^＋比在各盐浓度下均表现为托鲁巴姆〈刺茄〈赤茄〈刚果茄。茄子砧木耐盐性与根中Na^＋含量、根中Na^＋/K^＋比、SK,Na运输呈正相关,与地上部Na^＋含量、根中K^＋含量、地上部Na^＋/K^＋比呈负相关。这些结果表明,Na Cl处理下耐盐性强的砧木通过限制Na^＋向叶片中运输,增加了叶片中K^＋含量,从而降低Na^＋/K^＋比来提高植株耐盐性。     

pH Regulation by NHX-Type Antiporters Is Required for Receptor-Mediated Protein Trafficking to the Vacuole in Arabidopsis

Protein trafficking requires proper ion and pH homeostasis of the endomembrane system. The NHX-type Na⁺/H⁺ antiporters NHX5 and NHX6 localize to the Golgi, trans-Golgi network, and prevacuolar compartments and are required for growth and trafficking to the vacuole. In the nhx5 nhx6 T-DNA insertional knockouts, the precursors of the 2S albumin and 12S globulin storage proteins accumulated and were missorted to the apoplast. Immunoelectron microscopy revealed the presence of vesicle clusters containing storage protein precursors and vacuolar sorting receptors (VSRs). Isolation and identification of complexes of VSRs with unprocessed 12S globulin by 2D blue-native PAGE/SDS-PAGE indicated that the nhx5 nhx6 knockouts showed compromised receptor-cargo association. In vivo interaction studies using bimolecular fluorescence complementation between VSR2;1, aleurain, and 12S globulin suggested that nhx5 nhx6 knockouts showed a significant reduction of VSR binding to both cargoes. In vivo pH measurements indicated that the lumens of VSR compartments containing aleurain, as well as the trans-Golgi network and prevacuolar compartments, were significantly more acidic in nhx5 nhx6 knockouts. This work demonstrates the importance of NHX5 and NHX6 in maintaining endomembrane luminal pH and supports the notion that proper vacuolar trafficking and proteolytic processing of storage proteins require endomembrane pH homeostasis.     

罗布麻对不同浓度盐胁迫的生理响应

利用网室盆栽实验,研究不同浓度的NaCl（100-400mmol·L^-1）胁迫对罗布麻（Apocynum venetum）生长及生理特性的影响。结果表明,100mmol·L^-1NaCl处理显著降低了罗布麻植株的鲜重,但对其干重影响不大;随着盐浓度继续增加,罗布麻鲜重和干重显著下降。在盐胁迫下,罗布麻叶片内的丙二醛含量、电解质渗漏率、根部和地上部Na^＋的含量明显增加,K^＋的含量随着盐离子浓度的增加而降低。盐胁迫显著降低了地上部Ca^2＋的含量,而对根部Ca^2＋的含量没有影响。植株K^＋/Na^＋和Ca^2＋/Na^＋比值随着盐胁迫强度的增加而降低。盐胁迫显著促进了罗布麻根部对K^＋和Ca^2＋的选择性吸收及对K^＋的选择性运输。当NaCl浓度小于或等于200mmol·L^-1时,随着盐离子浓度的增加,罗布麻叶片内的脯氨酸和可溶性糖积累显著增加,而当NaCl浓度大于200mmol·L^-1时,这2种有机溶质含量显著下降。总体上,罗布麻通过积累无机离子、合成有机溶质及维持较高的K^＋、Ca^2＋选择性吸收和运输来适应一定浓度（≤200mmol·L^-1NaCl）的盐胁迫。     

双酚A暴露对东亚三角涡虫急性毒性及神经酶的影响

旨在探讨双酚A (BPA)对东亚三角涡虫的急性毒性及神经系统相关酶活性的影响。采用不同浓度的BPA处理涡虫24 h、48 h、72 h,求出半致死浓度,以此为基础,采用不同浓度的BPA处理涡虫24 h、72 h、144 h,测定AchE、ChAT及Na+~K+^-ATP酶活性。BPA对三角涡虫的24 h、48 h、72 h,LC50分别为12.18 mg/L、8.49 mg/L、6.43 mg/L。ChE、ChAT、Na+~K+^-ATP酶活性对BPA反应敏感,具有较好的规律性。24 h处理组,AChE酶活力随BPA浓度的升高而升高,72 h和144 h处理组则呈现先上升后下降的趋势,除0.643 mgBPA/L以外,其它处理组均表现出了时间-效应关系;在BPA胁迫下,ChAT酶活力均呈现降低趋势,在BPA浓度为0.643 mg/L、1.286 mg/L时,表现出了时间-效应关系;24 h、72 h处理组Na+~K+^-ATP酶活力随BPA浓度升高呈现先上升后下降的趋势,144 h处理组则呈现下降趋势,Na+~K+^-ATP酶活力随BPA胁迫时间的延长呈现先升高后下降的趋势。BPA对涡虫具有较强的生态毒性,AchE、ChAT、Na+~K+^-ATP酶活性可与其他敏感指标一起作为水体BPA污染的早期监测指标。     

Soy isoflavones and cellular mechanics

Soy isoflavones are diphenolic compounds that are frequently used for alternative treatment of ageing symptoms in both genders. They operate at principally two hierarchical levels of functional organization – cellular and molecular, while these ‘types’ of action appear to have indefinite borders. Soy isoflavone action at the cellular level involves inter alia the effects on cell mechanics. This epigenetic and modular determinant of cell function and fate is defined by: the anchorage to extracellular matrix (ECM) and neighboring cells, cytoskeleton organization, membrane tension and vesicle trafficking. Soy isoflavones have been reported to: (i) generally fashion an inert cell phenotype in some cancers and enhance the cell anchorage in connective tissues, via the effects on ECM proteins, focal adhesion kinases-mediated events and matrix metalloproteinases inhibition; (ii) affect cytoskeleton integrity, the effects being related to Ca²⁺ ions fluxes and involving cell retraction or differentiation/proliferation-related variations in mechanical status; (iii) increase, remain “silent” or decrease membrane tension/fluidity, which depends on polarity and a number and arrangement of functional groups in applied isoflavone; (iv) provoke inhibitory effects on vesicle trafficking and exo-/endocytosis, which are usually followed by changed cell morphology. Here we present and discuss the abundance of effects arising from cells’ “encounter” with soy isoflavones, focusing on different morphofunctional definers of cell mechanics.     

Mutational analysis of the intramembranous H10 loop of yeast Nhx1 reveals a critical role in ion homoeostasis and vesicle trafficking

Yeast Nhx1 [Na+(K+)/H+ exchanger 1] is an intracellular Na+(K+)/H+ exchanger, localizing to the late endosome where it is important for ion homoeostasis and vesicle trafficking. Phylogenetic analysis of NHE (Na+/H+ exchanger) sequences has identified orthologous proteins, including HsNHE6 (human NHE6), HsNHE7 and HsNHE9 of unknown physiological role. These appear distinct from well-studied mammalian plasma membrane isoforms (NHE1-NHE5). To explore the differences between plasma membrane and intracellular NHEs and understand the link between ion homoeostasis and vesicle trafficking, we examined the consequence of replacing residues in the intramembranous H10 loop of Nhx1 between transmembrane segments 9 and 10. The critical role for the carboxy group of Glu355 in ion transport is consistent with the invariance of this residue in all NHEs. Surprisingly, residues specifically conserved in the intracellular isoforms (such as Phe357 and Tyr361) could not be replaced with closely similar residues (leucine and phenylalanine) found in the plasma membrane isoforms without loss of function, revealing unexpected side chain specificity. The trafficking phenotypes of all Nhx1 mutants, including hygromycin-sensitivity and missorting of carboxypeptidase Y, were found to directly correlate with pH homoeostasis defects and could be proportionately corrected by titration with weak base. The present study demonstrates the importance of the H10 loop of the NHE family, highlights the differences between plasma membrane and intracellular isoforms and shows that trafficking defects are tightly coupled with pH homoeostasis.     

外源ATP对盐胁迫下油菜幼苗生长的影响

研究了外源ATP处理对盐胁迫下油菜幼苗生长的影响,探讨了过氧化氢(H₂O₂)和钙离子(Ca²⁺)作为信号分子在ATP对油菜幼苗耐盐性调控过程中的作用。结果表明:与单独Na Cl处理相比,ATP+Na Cl处理降低了油菜幼苗死细胞数量、ROS(■和H₂O₂)含量、离子(Ca²⁺、Na⁺、Cl^-)含量、MDA含量及Na⁺/K⁺比和相对电导率,增加了叶片中叶绿素、脯氨酸、可溶性糖含量和抗氧化酶(SOD、POD、CAT、APX)活性,提高了抗氧化酶基因(CAT、SOD、APX、GR)、NADPH氧化酶基因(RBOHD、RBOHF)、P5CS1基因、MAPK激酶基因(MAPK3、MAPK6)、耐盐基因(NHX1、SOS1)转录;与ATP+Na Cl处理相比,ATP+Na Cl+抑制剂(DPI、DMTU和EGTA)处理下油菜幼苗中相对电导率、MDA、叶绿素、脯氨酸、可溶性糖含量和抗...