NaCl胁迫下黄瓜幼苗体内K+、Na+和Cl-分布及吸收特性的研究

采用营养液水培法,研究了不同浓度NaCl胁迫对黄瓜幼苗不同器官K 、Na 和Cl-含量的影响。结果表明,NaCl胁迫下黄瓜植株体内K 含量下降,Na 和Cl-含量升高,变化幅度随NaCl浓度的增加而增大;NaCl处理4 d后,各器官中K 含量下降幅度剧增,叶片中Na 和Cl-含量快速升高;3种离子在器官间呈区域化分布,Na 主要积累在根和茎部,K 和Cl-主要积累在茎部,而且K 的含量下降幅度由根向叶递减。在低浓度NaCl胁迫或高浓度NaCl短期胁迫下,黄瓜植株对K 的吸收选择性以及向地上部运输的选择性提高,离子区域化分布的能力增强,有利于避免离子代谢紊乱,减轻NaCl胁迫的伤害。可见,离子在器官水平的区域化分布是黄瓜植株耐盐性的重要机理之一。     

NaCl胁迫对黄瓜幼苗体内K+、Na+和Cl-分布的影响

采用营养液水培,以2个耐盐性不同的黄瓜品种为材料,研究了不同浓度NaCl处理下幼苗植株体内K 、Na 和Cl-在器官间的区域化分布及其吸收和运输特性的变化。结果表明:NaCl胁迫下,黄瓜植株体内K 含量下降,Na 和Cl-含量升高,变化幅度随NaCl浓度的升高而增大;不同器官间,茎中Na 和Cl-含量最高,上位叶中Na 和Cl-含量最低、K 含量下降幅度最小。与耐盐性较弱的“津春2号”相比,耐盐性较强的“长春密刺”根向茎运输的SK,Na值较高,根系对Na 的截留作用较强,茎向上位叶运输的SK,Na和SCl,Na值均较高,叶片中K 含量下降幅度较小,K/Na和Cl/Na比值均较高,功能叶中盐分离子尤其是Na 积累较少,植株生物量较高。说明根系对Na 的截留能力较强且向上位叶运输Na 的选择性较低,是“长春密刺”耐盐性较强的主要原因之一。     

外源硝酸钙对黄瓜幼苗盐胁迫伤害的缓解作用

采用营养液水培法,以较耐盐黄瓜品种'新泰密刺'为试材,研究了叶面喷施硝酸钙对盐胁迫(NaCl 65 mmol·L-1)下黄瓜幼苗生长、叶绿素含量、膜脂过氧化产物丙二醛(MDA)、脯氨酸及不同部位离子含量的影响.结果表明,叶面喷施硝酸钙能够显著提高盐胁迫下黄瓜幼苗的干鲜重、相对含水量和叶片叶绿素含量,显著减少MDA及渗透调节物质脯氨酸的积累;同时可显著降低盐胁迫下黄瓜幼苗体内Na+和Cl-含量,提高K+、Ca2+含量和 K+/Na+、Ca2+/Na+.可见,外源硝酸钙能缓解盐胁迫下黄瓜幼苗的失水程度和光合色素的下降幅度,保护膜的完整性,调节离子选择性吸收,从而减轻盐胁迫伤害,促进黄瓜植株生长.     

外源亚精胺对盐胁迫下黄瓜幼苗游离态多胺含量和多胺合成酶基因表达的影响

以黄瓜品种‘津春2号’（Cucumis sativusL.cv.Jinchun No.2）为材料,采用营养液栽培,研究了外源亚精胺（Spd）对NaCl胁迫下黄瓜幼苗叶片游离态多胺含量和多胺合成酶基因表达的影响。结果表明,75 mmol/LNaCl胁迫下,幼苗株高、茎粗和干鲜重显著降低,外源喷施1 mmol/L Spd处理可明显缓解盐胁迫对幼苗生长的抑制。盐胁迫下叶片游离态多胺含量显著增加,外源Spd进一步促进了游离态Spd和精胺（Spm）的积累,降低了游离态腐胺（Put）的积累。多胺合成酶基因表达分析表明,盐胁迫上调了adc、odc、samdc和spds基因的表达,施用外源Spd后进一步上调了samdc基因,下调了adc、odc、spds基因的表达。表明外源Spd参与了黄瓜幼苗体内多胺代谢的调节,通过下调盐胁迫下adc、odc基因的表达,抑制游离态Put的积累,上调samdc基因的表达促进游离态Spd和Spm的积累,进而缓解盐胁迫对植物生长的抑制。     

外源腐胺对根际低氧胁迫下黄瓜幼苗多胺和抗氧化系统的影响

采用营养液栽培,研究了外源腐胺(Put)对根际低氧胁迫下黄瓜幼苗体内多胺含量和抗氧化系统的影响.结果显示,低氧胁迫显著刺激了黄瓜幼苗体内活性氧(ROS)和内源多胺含量的增加,提高了抗氧化酶活性;外源Put进一步提高了低氧胁迫下黄瓜幼苗体内多胺的含量和抗氧化酶活性,降低了ROS含量,从而缓解了低氧胁迫的伤害作用;Put合成抑制剂D-精氨酸(D-Arg)不仅显著抑制黄瓜幼苗体内多胺的合成,而且抑制抗氧化酶活性,同时ROS大量积累,进一步抑制黄瓜幼苗的生长;而外源Put可缓解D-Arg的抑制作用;Put转化抑制剂甲基乙二醛-双(脒基腙)(MGBG)和Put降解抑制剂氨基胍(AG)的混合施用造成游离态Put的过量积累,以及亚精胺(Spd)、精胺(Spm)含量和抗氧化酶活性的显著降低,造成ROS大量积累,进一步加重了低氧胁迫对植株的伤害.结果表明,低氧胁迫下外源Put可提高黄瓜幼苗体内游离态Put含量,促进游离态Put向Spd和Spm转化,Spd、Spm含量的增加以及(free-Spd free-Spm)/free-Put比值的升高有利于提高植株抗氧化酶活性,增强清除ROS的能力,降低膜脂过氧化的伤害,从而增强植株的低氧胁迫耐性.     

外源亚精胺对盐胁迫下毕氏海蓬子体内多胺含量的影响

用含不同浓度(0、100、200、300、400和500 mmol·L 1)NaCl的Hoagland营养液及叶面喷施0.1 mmol·L-1外源亚精胺(Spd)处理毕氏海蓬子幼苗,研究外源Spd对NaCl胁迫下海蓬子体内游离态、结合态和束缚态3种形态多胺含量的影响,分析内源多胺含量的变化与植物耐盐性的关系.结果表明:(1)随盐胁迫浓度的升高,海蓬子幼苗叶片中3种形态腐胺(Put)含量均先降后升;同期的游离态Spd含量持续上升,结合态和束缚态Spd含量均先升后降;同期的游离和结合态精胺(Spm)含量均先升后降,而其束缚态Spm含量呈上升趋势;游离态和束缚态多胺(PAs)总量变化随盐浓度升高均呈上升趋势,而结合态PAs总量先升后降.(2)3种形态(Spd+ Spm) /Put比值均先升后降,而3种形态Put/PAs比值则均呈先降后升的相反趋势.(3)外源Spd处理提高了海蓬子幼苗叶片中结合态和束缚态PAs总量,也提高了游离态和束缚态(Spd+Spm)/Put比值.研究发现,外源Spd参与了NaCl胁迫下海蓬子内源PAs代谢的调节,可能通过促进盐胁迫植株中Put向Spd和Spm的转化,以及游离态多胺向结合态和束缚态多胺的转化来增强海蓬子耐盐性.     

外源亚精胺对盐胁迫下黄瓜(Cucumis sativus L.)叶绿体活性氧清除系统和结合态多胺含量的影响

采用营养液水培,研究了外源亚精胺(Spd)对NaCl胁迫下抗盐能力不同的两个黄瓜品种幼苗生长、叶绿体中活性氧清除系统、转谷酰胺酶(TGase)活性、结合态多胺含量及植株光合速率的影响.结果表明,外源Spd能提高NaCl胁迫下叶绿体中TGase活性、叶绿体结合态腐胺(Put)、Spd、精胺(Spm)及总多胺含量;提高超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性,提高抗坏血酸(AsA)、类胡萝卜素(Car)、还原型谷胱甘肽(GSH)含量及还原型谷胱甘肽/氧化型谷胱甘肽(GSH/ GSSG)比值,降低脱氢抗坏血酸/抗坏血酸(DAsA/AsA)比值;同时显著降低叶绿体过氧化氢(H2O2)和丙二醛(MDA)含量,提高植株净光合速率,缓解NaCl胁迫对幼苗生长的抑制.表明Spd对黄瓜盐害的缓解作用之一可能是通过提高叶绿体结合态多胺含量和叶绿体活性氧清除能力,从而缓解盐胁迫对叶绿体膜的伤害.     

多胺浸种改善盐胁迫大麦根系液泡膜功能的机理

研究了0.1 mmol/L 腐胺 (Put) 和0.5 mmol/L 亚精胺 (Spd) 浸种对200 mmol/L NaCl胁迫下大麦(Hordeum vulgare L.)幼苗生长速率、干物质积累、离子分布、液泡膜蛋白结合多胺含量以及液泡膜膜脂组分与功能的影响.结果表明,Put和Spd浸种均可缓解盐胁迫对大麦幼苗的盐害,促进生长和干物质积累,降低大麦幼苗体内[Na+]/[K+].与盐处理的对照植株相比,Put和Spd浸种均可提高大麦幼苗根系液泡膜磷脂含量,降低糖脂结合半乳糖含量,而膜上非共价结合多胺含量Spd+PAx (一种未知多胺) 与 Put+Dap (二氨基丙烷)之比((Spd+PAx)/(Put+Dap))、共价和非共价结合多胺总量均上升.统计分析结果表明,液泡膜非共价结合多胺(Spd+PAx)/(Put+Dap)与H+-ATPase和H+-PPase活性呈显著正相关关系.     

外源亚精胺对盐胁迫下黄瓜植株氮化合物含量和硝酸还原酶活性的影响

研究了外源亚精胺(Spd)在营养液栽培中,对盐胁迫下耐盐性不同的两品种黄瓜幼苗体内硝态氮、铵态氮、脯氨酸(Pro)含量和硝酸还原酶(NR)活性的影响。结果表明,外源Spd显著减小了盐胁迫引起的铵态氮、Pro含量的升高幅度和NR活性、硝态氮含量的降低幅度,且对盐敏感型黄瓜品种影响幅度较大。表明Spd可明显减缓盐胁迫对黄瓜幼苗氮素营养代谢的影响。     

盐胁迫对四种基因型冬小麦幼苗Na+、K+吸收和累积的影响

以4种不同基因型冬小麦品种为试验材料，研究了盐胁迫下小麦幼苗的生长及Na^＋、K^＋和Cl^-的吸收、累积规律。结果表明，盐胁迫下小麦吸水困难，幼苗生长受抑；幼苗含水量、生物量及干物质量明显下降；Na^＋、Cl^-含量和单株累积量显著增加。K^＋含量和单株累积量则明显降低。Na^＋／K^＋比值随介质中的盐浓度的增加而升高。盐胁迫下各基因型冬小麦幼苗Na^＋、K^＋和Cl^-的单株累积量及其在地上部分和根系中的含量变化较大，说明小麦根系对Na^＋、K^＋和Cl^-的吸收存在基因型差异。盐处理下，暖型小麦NR9405对K^＋的选择吸收能力强，对Na^＋的吸收和累积少，植株体内的K^＋浓度较高，Na^＋／K^＋比值小；幼苗的生物量较大，耐盐性强。冷型小麦RB6对K^＋的选择能力差，对Na^＋的吸收和累积量大，幼苗的Na^＋／K^＋比值大，生物量小，耐盐性较差。低盐浓度下，Na^＋可作为渗透调节物质维持植物体内渗透平衡。高盐浓度下，Na^＋的过度吸收和累积可能是盐害的主要原因。维持体内较低的Na^＋水平和Na^＋／K^＋比值是小麦耐盐性的一个重要特征。     

Kinetic studies on the (Na+ + K+)-dependent ATPase. Evidence for coexisting sites for Na+, K+ and Mg2+

Na⁺-ATPase activity of a dog kidney (Na⁺ + K⁺)-ATPase enzyme preparation was inhibited by a high concentration of NaCl (100 mM) in the presence of 30 μM ATP and 50 μM MgCl₂, but stimulated by 100 mM NaCl in the presence of 30 μM ATP and 3 mM MgCl₂. The $\text{K}{}_{0.5}$ for the effect of MgCl₂ was near 0.5 mM. Treatment of the enzyme with the organic mercurial thimerosal had little effect on Na⁺-ATPase activity with 10 mM NaCl but lessened inhibition by 100 mM NaCl in the presence of 50 μM MgCl₂. Similar thimerosal treatment reduced (Na⁺ + K⁺)-ATPase activity by half but did not appreciably affect the $\text{K}{}_{0.5}$ for activation by either Na⁺ or K⁺, although it reduced inhibition by high Na⁺ concentrations. These data are interpreted in terms of two classes of extracellularly-available low-affinity sites for Na⁺: Na⁺-discharge sites at which Na⁺-binding can drive E₂-P back to E₁-P, thereby inhibiting Na⁺-ATPase activity, and sites activating E₂-P hydrolysis and thereby stimulating Na⁺-ATPase activity, corresponding to the K⁺-acceptance sites. Since these two classes of sites cannot be identical, the data favor co-existing Na⁺-discharge and K⁺-acceptance sites. Mg²⁺ may stimulate Na⁺-ATPase activity by favoring E₂-P over E₁-P, through occupying intracellular sites distinct from the phosphorylation site or Na⁺-acceptance sites, perhaps at a coexisting low-affinity substrate site. Among other effects, thimerosal treatment appears to stimulate the Na⁺-ATPase reaction and lessen Na⁺-inhibition of the (Na⁺ + K⁺)-ATPase reaction by increasing the efficacy of Na⁺ in activating E₂-P hydrolysis.     

Relative roles of Ca2+, Sr2+, Ba2+ and Mg2+ in controlling lens permeability characteristics

The effects of barium, strontium and magnesium upon lens permeability characteristics were studied in the presence and absence of 2 mM calcium in the bathing medium. Permeability characteristics were determined by measuring lens potential, resistance and ⁴²K efflux rates. Barium and strontium at equimolar concentrations to calcium were able to substitute for calcium in controlling lens sodium permeability. Magnesium was ineffective in this respect.Small changes in resistance and ⁴²K efflux rates occurred when calcium was eliminated from bathing solution containing either 2 mM barium or strontium. These changes were interpreted to be the result of an increase in lens permeability to potassium. When 2 mM strontium was added to calcium-containing solution, there was no significant change in the electrical or flux parameters of the lens. However, the addition of 2 mM barium to calcium-containing solution resulted in a 54% increase in lens resistance and a 13 mV depolarization. These observations indicated a barium-induced decrease in lens permeability to potassium, and this was confirmed by an observed decrease in ⁴²K efflux rate constant under similar experimental conditions.The rapid time course of all the observed changes implies that they are the result of changes in the permeability characteristics of membranes lying close to the surface of the lens.     

Effects of interrupted K+ supply on growth and uptake of K+, Ca2+, Mg2+ and Na+ in spring wheat

Effects of interrupted K⁺ supply on different parameters of growth and mineral cation nutrition were evaluated for spring wheat (Triticum aestivum L. cv. Svenno). K⁺ (2.0 mM) was supplied to the plants during different periods in an otherwise complete nutrient solution. Shoot growth was reduced before root growth after interruption in K⁺ supply. Root structure was greatly affected by the length of the period in K⁺ -free nutrient solution. Root length was minimal, and root branching was maximal within a narrow range of K⁺ status of the roots. This range corresponded to cultivation for the last 1 to 3 days, of 11 in total, in K⁺ -free nutrient solution, or to continuous cultivation in solution containing 0.5 to 2 mM K⁺. In comparison, both higher and lower internal/external K⁺ concentrations had inhibitory effects on root branching. However, the differing root morphology probably had no significant influence on the magnitude of Ca²⁺, Mg²⁺ and Na⁺ uptake. Uptake of Ca²⁺ and especially Mg²⁺ significantly increased after K⁺ interruption, while Na⁺ uptake was constant in the roots and slowly increased in the shoots. The two divalent cations could replace K⁺ in the cells and maintain electroneutrality down to a certain minimal range of K⁺ concentrations. This range was significantly higher in the shoot [110 to 140 μmol (g fresh weight)^?1] than in the root [20 to 30 μmol (g fresh weight)^?1]. It is suggested that the critical K⁺ values are a measure of the minimal amount of K⁺ that must be present for physiological activity in the cells. At the critical levels, K⁺ (⁸⁶Rb) influx and Ca²⁺ and Mg²⁺ concentrations were maximal. Below the critical K⁺ values, growth was reduced, and Ca²⁺ and Mg²⁺ could no longer substitute for K⁺ for electrostatic balance. In a short-term experiment, the ability of Ca²⁺ to compete with K⁺ in maintaining electroneutrality in the cells was studied in wheat seedlings with different K⁺ status. The results indicate that K⁺, which was taken up actively and fastest at the external K⁺ concentration used (2.0 mM), partly determines the size of Ca²⁺ influx.     

Mechanisms by which Li+ stimulates the (Na++K+)-dependent ATPase

The addition of LiCl stimulated the (Na⁺+K⁺)-dependent ATPase activity of a rat brain enzyme preparation. Stimulation was greatest in high Na⁺/low K⁺ media and at low Mg. ATP concentrations. Apparent affinities for Li⁺ were estimated at the α-sites (moderate-affinity sites for K⁺ demonstrable in terms of activation of the associated K⁺-dependent phosphatase reaction), at the β-sites (high-affinity sites for K⁺ demonstrable in terms of activation of the overall ATPase reaction), and at the Na⁺ sites for activation. The relative efficacy of Li⁺ was estimated in terms of the apparent maximal velocity of the phosphatase and ATPase reactions when Li⁺ was substituted for K⁺, and also in terms of the relative effect of Li⁺ on the apparent K_M for Mg· ATP. With these data, and previously determined values for the apparent affinities of K⁺ and Na⁺ at these same sites, quantitative kinetic models for the stimulation were examined. A composite model is required in which Li⁺ stimulates by relieving inhibition due to K⁺ and Na⁺ (i) by competing with K⁺ for the α-sites on the enzyme through which K⁺ decreases the apparent affinity for Mg·ATP and (ii) by competing with Na⁺ at low-affinity inhibitory sites, which may represent the external sites at which Na⁺ is discharged by the membrane NA⁺/K⁺ pump that this enzyme represents. Both these sites of action for Li⁺ would thus lie, in vivo, on the cell exterior.     

Effect of calmodulin,Ca2+ and Mg2+ on the (Ca2+ + Mg2+)-ATPase of erythrocyte membranes

Calmodulin-depleted isotonic erythrocyte ghosts contain 200 ng residual calmodulin/mg protein which is not removed by extensive washings at pCa²⁺ > 7. Specific activity and Ca²⁺-affinity of the (Ca²⁺ + Mg²⁺)ATPase increase at increasing calmodulin, with K_{0.5 Ca} of 0.38 μM at calmodulin concentrations corresponding to that in erythrocytes. High Ca²⁺ concentrations inhibit the enzyme. Specific activity and Ca²⁺-affinity of the enzyme decrease at increasing Mg²⁺ concentrations. The Ca²⁺ ? Mg²⁺ antagonism is likewise observed at inhibitory Ca²⁺ concentrations.     

Gel electrophoretic identity of the (Na+ + Mg2+)- and (Na+ + Ca2+)-stimulated phosphorylations of rat brain ATPase

The classical E₂-P intermediate of (Na⁺ + K⁺)-ATPase dephosphorylates readily in the presence of K⁺ and is not affected by the addition of ADP. To determine the significane in the reaction cycle of (Na⁺ + K⁺)-ATPase of kinetically atypical phosphorylations of rat brain (Na⁺ + K⁺)-ATPase we compared these phosphorylated components with the classical E₂-P intermediate of this enzyme by gel electrophoresis. When rat brain (Na⁺ + K⁺)-ATPase was phosphorylated in the presence of high concentrations of Na⁺ a proportion of the phosphorylated material formed was sensitive to ADP but resistant to K⁺. Similarly, if phosphorylation was carried out in the presence of Na⁺ and Ca²⁺ up to 300 pmol/mg protein of a K⁺-resistant, ADP-sensitive material were formed. If phosphorylation was from [γ-³²P]CTP up to 800 pmol ³²P/mg protein of an ADP-resistant, K⁺-sensitive phosphorylated matterial were formed. On gel electrophoresis these phosphorylated materials co-migrated with authentic Na⁺-stimulated, K⁺-sensitive, E₂-P-phosphorylated intermediate of (Na⁺ + K⁺)-ATPase, supporting suggestions that they represent phosphorylated intermediates in the reaction sequence of this enzyme.     

A reconstituted Na++K+ pump in liposomes containing purified (Na++K+-ATPase from kidney medulla

Liposomes containing either purified or microsomal (Na⁺,K⁺)-ATPase preparations from lamb kidney medulla catalyzed ATP-dependent transport of Na⁺ and K⁺ with a ratio of approximately 3Na⁺ to 2K⁺, which was inhibited by ouabain. Similar results were obtained with liposomes containing a partially purified (Na⁺,K⁺-ATPase from cardiac muscle. This contrasts with an earlier report by Goldin and Tong (J. Biol. Chem. 249, 5907–5915, 1974), in which liposomes containing purified dog kidney (Na⁺,K⁺)-ATPase did not transport K⁺ but catalyzed ATP-dependent symport of Na⁺ and Cl^?. When purified by our procedure, dog kidney (Na⁺,K⁺)-ATPase showed some ability to transport K⁺ but the ratio of Na⁺ : K⁺ was 5 : 1.     

Binding of Cd2+, Ni2+, Cu2+ and Zn2+ by isolated envelopes of Pseudomonas fluorescens

Abstract Cell envelopes of Pseudomonas fluorescens , cytoplasmic membrane, peptidoglycan and outer membrane were obtained from a fractionation procedure and tested for their metal binding capacity. Isolated envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) were chemically modified and functional carboxyl groups transformed to electropositive amine groups, using carbodiimide ethylenediamine. Transformation of carboxyl groups was evaluated by measuring total amine groups in all fractions (modified or not). Using equilibrium dialysis and Scatchard plots for the data, we have established that isolated unmodified cell envelopes (cytoplasmic membrane, peptidoglycan and outer membrane) possess at least two types of metal binding sites with different association constants ( K _a and K '_a). Introduction of positive charges into the bacterial envelopes resulted in the disappearance of one type of metal binding site which had the highest association constant value for Ni²⁺, Cu²⁺ and Zn²⁺. All fractions, modified or not, always presented at least two types of binding sites with different association constants for Cd²⁺.     

Interaction of Ca2+ with (Na+ + K+)-ATPase: Properties of the Ca2+-stimulated phosphatase activity

Ca²⁺ inhibited the Mg²⁺-dependent and K⁺-stimulated p-nitrophenylphosphatase activity of a highly purified preparation of dog kidney (Na⁺ + K⁺)-ATPase. In the absence of K⁺, however, a Mg²⁺-dependent and Ca²⁺-stimulated phosphatase was observed, the maximal velocity of which, at pH 7.2, was about 20% of that of the K⁺-stimulated phosphatase. The Ca²⁺-stimulated phosphatase, like the K⁺-stimulated activity, was inhibited by either ouabain or Na⁺ or ATP. Ouabain sensitivity was decreased with increase in Ca²⁺, but the K_0.5 values of the inhibitory effects of Na⁺ and ATP were independent of Ca²⁺ concentration. Optimal pH was 7.0 for Ca²⁺-stimulated activity, and 7.8–8.2 for the K⁺-stimulated activity. The ratio of the two activities was the same in several enzyme preparations in different states of purity. The data indicate that (a) Ca²⁺-stimulated phosphatase is catalyzed by (Na⁺ + K⁺)-ATPase; (b) there is a site of Ca²⁺ action different from the site at which Ca²⁺ inhibits in competition with Mg²⁺; and (c) Ca²⁺ stimulation can not be explained easily by the action of Ca²⁺ at either the Na⁺ site or the K⁺ site.