Gill microsomal (Na+,K+)-ATPase from the blue crab Callinectes danae: Interactions at cationic sites

Euryhaline crustaceans tolerate exposure to a wide range of dilute media, using compensatory, ion regulatory mechanisms. However, data on molecular interactions occurring at cationic sites on the crustacean gill (Na⁺,K⁺)-ATPase, a key enzyme in this hyperosmoregulatory process, are unavailable. We report that Na⁺ binding at the activating site leads to cooperative, heterotropic interactions that are insensitive to K⁺. The binding of K⁺ ions to their high affinity sites displaces Na⁺ ions from their sites. The increase in Na⁺ ion concentrations increases heterotropic interactions with the K⁺ ions, with no changes in K_0.5 for K⁺ ion activation at the extracellular sites. Differently from mammalian (Na⁺,K⁺)-ATPases, that from C. danae exhibits additional NH₄⁺ ion binding sites that synergistically activate the enzyme at saturating concentrations of Na⁺ and K⁺ ions. NH₄⁺ binding is cooperative, and heterotropic NH₄⁺ ion interactions are insensitive to Na⁺ ions, but Na⁺ ions displace NH₄⁺ ions from their sites. NH₄⁺ ions also displace Na⁺ ions from their sites. Mg²⁺ ions modulate enzyme stimulation by NH₄⁺ ions, displacing NH₄⁺ ion from its sites. These interactions may modulate NH₄⁺ ion excretion and Na⁺ ion uptake by the gill epithelium in euryhaline crustaceans that confront hyposmotic media.     

Biosorption of lead, cadmium and mercury by immobilized Microcystis aeruginosa in a column

Immobilized Microcystis aeruginosa in a flow-through sorption column was evaluated for the potential to remove Pb²⁺, Cd²⁺ and Hg²⁺ from aqueous solutions. M. aeruginosa showed high affinity for the three heavy metals with removal efficiency of 90% for Cd²⁺ and Hg²⁺, and 80% for Pb²⁺ at saturation conditions. Competitive sorption experiments conducted in paired and ternary systems indicated that Pb²⁺ was sequestered preferentially over Cd²⁺ and Hg²⁺. The presence of Cd²⁺ interfered only slightly with the uptake of Hg²⁺, as Pb²⁺ and Hg²⁺ did with Cd²⁺. In contrast, Hg²⁺ sorption was affected by Pb²⁺ to a great extent. Desorption with 1 M HCl was completed within 25 min with high efficiency and effectiveness for the three metals. The results of this study indicate that M. aeruginosa is to be a potential biosorbent material except when Hg²⁺ and Pb²⁺ are in the same contaminated solution.     

钙对盐胁迫下冰叶日中花不同器官离子含量和根部K~+、Na~+吸收的影响

以冰叶日中花(Mesembryanthemum crystallinum L.)实生苗为材料,经NaCl、NaCl+ CaCl_2、NaCl+LaCl_3处理后,利用电感耦合等离子发射光谱仪检测叶、茎、根中Na~+、K~+、Ca~(2+)、Mg~(2+)含量,计算K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+比值,利用非损伤微测技术测定根尖Na~+流和K~+流,研究盐胁迫下钙在维持离子平衡中的作用。结果显示,NaCl处理后,冰叶日中花各器官中Na~+含量增加,K~+、Ca~(2+)、Mg~(2+)含量降低,离子比值降低;CaCl_2处理降低了Na~+含量,提高了K~+、Ca~(2+)、Mg~(2+)含量,离子比值升高,而LaCl_3处理后的结果相反。经NaCl处理24 h后,冰叶日中花根尖Na~+和K~+明显外流,加入CaCl_2后,Na~+外流速度显著增加,K~+外流速度受到抑制,而加入LaCl_3后则降低了Na~+的外流速度,促进了K~+的外流。研究结果表明冰叶日中花受到盐胁迫后,钙参与了促进根部Na~+外排、抑制K~+外流的过程,进而保持各器官中较低的Na~+含量,表明钙在维持和调控离子平衡中起到重要作用。     

A Kinetic and ESR Investigation of Iron(II) Oxalate Oxidation by Hydrogen Peroxide and Dioxygen as a Source of Hydroxyl Radicals

The reaction of Fe^II oxalate with hydrogen peroxide and dioxygen was studed for oxalate concentrations up to 20 mM and pH 2-5, under which conditions mono- and bis-oxalate comlexes (Fe^II(ox) and Fe^II(ox)₂^2-) and uncomplexed Fe²⁺ must be considered. The reaction of Fe^II oxalate with hydrogen peroxide (Fe²⁺ + H₂O₂ → Fe³⁺ + *OH + OH^-) was monitored in continuous flow by ESR with t-butanol as a radical trap. The reaction is much faster than for uncomplexed Fe²⁺ and a rate constant, k = 1 × 10⁴ M-¹ s^-1 is deduced for Fe^II(ox). The reaction of Fe^II oxalate with dioxygen is strongly pH dependent in a manner which indicates that the reactive species is Fe^II(ox)₂^2-, for which an apparent second order rate constant, k = 3.6 M^-1 s^-1, is deduced. Taken together, these results provide a mechanism for hydroxyl radical production in aqueous systems containing Fe^II complexed by oxalate. Further ESR studies with DMPO as spin trap reveal that reaction of Fe^II oxalate with hydrogen peroxide can also lead to formation of the carboxylate radical anion (CO₂^*-), an assignment confirmed by photolysis of Fe^III oxalate in the presence of DMPO.     

Syntheses and characterization of mono- and di-N-hydroxyethylated tetraaza macrocycles containing eight C-methyl groups and their nickel(II) and copper(II) complexes

New partially N-hydroxyethylated 14-membered tetraaza macrocycles 1,8-bis(2-hydroxyethyl)-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L²) and 1-(2-hydroxyethyl))-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L³) have been synthesized selectively by the one-step reaction of 2,5,5,7,9,12,12,14-octamethyl-1,4,8,11-tetraazacyclotetradecane (L¹) with 2-hydroxyethyl bromide. The complexes [NiL³]²⁺, [CuL²]²⁺, and [CuL³]²⁺ have been prepared and characterized. The complex [CuL²](ClO₄)₂ has a square-pyramidal coordination geometry with one apical oxygen atom; only one of the two hydroxyethyl groups is coordinated to the metal ion. Electronic absorption spectra of [CuL³](ClO₄)₂ containing one hydroxyethyl pendant arm indicate that the geometry is similar to that of [CuL²](ClO₄)₂. Unexpectedly, the nickel(II) complex [NiL³](ClO₄)₂ has a severely distorted trigonal bipyramidal coordination geometry with the oxygen atom of the pendant arm at the equatorial position. The Ni---O bond distance of the nickel(II) complex is shorter, or not longer, than the Ni---N bond distances. The ligand in [CuL²]²⁺ is in the RRSS (trans-III) configuration, as usual, whereas that in [NiL³]²⁺ has the RRRR (trans-V) conformation. The coordination geometry and properties of [NiL³]²⁺ are quite different from those reported for other related nickel(II) complexes containing one functional pendant arm.     

氮形态对不同小麦基因型氮素吸收和光合作用的影响

利用水培试验,研究了3个小麦基因型对不同形态N素吸收和积累的差异.结果表明,在不同N浓度下,小麦对增铵营养和NH⁺的吸收速率显著高于NO₃^-营养,且在较高浓度下,增铵营养处理具有更强的吸收优势.与次敏感型莱州953和钝感型江东门相比,敏感型扬麦158不仅具有较强的NO₃^-和NH⁺吸收能力,而且具有最强的增铵营养吸收能力.增铵营养促进了扬麦158和莱州953对NO₃^-和NH⁺的吸收,但在一定程度上抑制了江东门对NO₃^-的吸收.与NO₃^-营养及NH⁺营养相比,增铵营养显著提高了扬麦158和莱州953的全株、地上部N积累量和叶片光合速率,而对江东门影响较小因此,增铵营养促进了植株的N吸收,提高了N积累和光合速率,从而促进了小麦生长     

Ins(1,4,5)P3 induces Ca2+ release from brain microsomes loaded either by the Ca2+ ATPase or by the Na+/Ca2+ exchanger.

In this study we investigated the release of Ca²⁺ in brain microsomes after Ca²⁺ loading by the Ca²⁺-ATPase or by the Na⁺/Ca²⁺ exchanger. The results show that in microsomes loaded with Ca²⁺ by the Ca²⁺-ATPase, Ins(1,4,5)P₃ (5 μM) release 21±2% of the total Ca²⁺ accumulated, and that in the microsomes loaded with Ca²⁺ by the Na²⁺/Ca²⁺ exchanger, Ins(1,4,5)P₃ released 28±3% of the total Ca²⁺ accumulated. These results suggest that receptors of Ins(1,4,5)P₃ may be co-localized with the Na²⁺/Ca²⁺ exchanger in the endoplasmic reticulum membrane or that there are Ins(1,4,5)P₃ receptors in the plasma membrane where the Na²⁺/Ca²⁺ exchanger is normally present, or both. We also found that Ins(1,4,5)P₃ inhibited the Ca²⁺-ATPase by 33.7%, but that it had no significant effect on the Na²⁺/Ca²⁺ exchanger.     

Aluminum enhancement of plant growth in acid rooting media. A case of reciprocal alleviation of toxicity by two toxic cations

The generally rhizotoxic ion Al³⁺ often enhances root growth at low concentrations. The hypothesis that Al³⁺ enhances growth by relieving H⁺ toxicity was tested with wheat seedlings ( Triticum aestivum L.). Growth enhancement by Al³⁺ only occurred under acidic conditions that reduced root elongation. Al³⁺ increased cell membrane electrical polarity and stimulated H⁺ extrusion. Previous investigations have shown that Al³⁺ decreases solute leakage at low _pH and that the alleviation of H⁺ toxicity by cations appears to be a general phenomenon with effectiveness dependent upon charge (C³⁺>C²⁺>C^l+). Alleviation of one cation toxicity by another toxic cation appears to be reciprocal so that Al³⁺ toxicity is relieved by H⁺. It has been argued previously that this latter phenomenon accounts for the apparent toxicity of ALOH²⁺ and Al(OH)⁺₂. Reduction of cell-surface electrical potential by the ameliorative cation may reduce the cell-surface activity of the toxic cation.     

盐胁迫下外源褪黑素和Ca2+对甜瓜幼苗的缓解效应

以甜瓜品种‘羊角酥瓜’为试材,利用人工气候室控制环境条件(昼/夜25/18 ℃),研究盐胁迫条件下外源褪黑素(MT)和Ca²⁺对甜瓜幼苗根系和叶片中Cl^-、Na⁺、K⁺、Mg²⁺、Ca²⁺离子含量,Na⁺/K⁺、 Na⁺/Ca²⁺、Na⁺/Mg²⁺值,以及H⁺-ATP酶活性、渗透调节物质积累和细胞膜质过氧化的影响.结果表明: 与对照相比,盐胁迫处理显著抑制甜瓜幼苗生长,增加根系和叶片中Cl^-、Na⁺含量,降低K⁺、Mg²⁺、Ca²⁺含量.盐胁迫下,喷施外源MT或Ca²⁺处理均可以显著降低甜瓜根系和叶片中Cl^-、Na⁺含量,提高K⁺、Mg²⁺、Ca²⁺含量,植株体内Na⁺/K⁺、Na⁺/Ca²⁺和 Na⁺/Mg²⁺值下降;同时也提高了根系和叶片H⁺-ATP酶活性及叶片渗透调节物质的含量,降低盐胁迫对细胞膜的伤害,表现在甜瓜叶片相对电导率和丙二醛含量降低.总之,在盐胁迫条件下,外源MT、Ca²⁺单独和复配处理均可通过提高H⁺-ATP酶活性来降低盐害离子的含量,改善甜瓜幼苗中的离子平衡,同时增加渗透调节物质的含量,降低膜质过氧化水平,从而增强其对盐胁迫的适应性,其中MT和Ca²⁺复配处理时的效果更好.复配外施 MT 和Ca²⁺在诱导甜瓜幼苗提高耐盐方面具有协同增效作用.     

磁化微咸水灌溉对欧美杨I-107离子稳态的影响

为探究微咸水磁化处理条件下植株的离子稳态特征,以欧美杨I-107一年生扦插苗为试材,于生长季节分别采用Hoagland营养液和4.0 g·L^-1 NaCl微咸水,经磁化处理后连续灌溉30 d.采用原子吸收分光光度法对叶片和根系中K⁺、Na⁺、Ca²⁺和Mg²⁺含量进行测定,分析离子平衡系数(K)和根-叶之间的离子选择性运输系数(S_Xi,Na).结果表明: 与非盐分胁迫处理相比,盐分胁迫处理根系和叶片中Na⁺和Ca²⁺含量及S_K,Na、S_Mg,Na升高,K⁺和Mg²⁺含量、K⁺/Na⁺及S_Ca,Na降低.与非磁化微咸水灌溉处理相比,磁化微咸水灌溉处理的根系和叶片中Na⁺含量降低、K⁺含量及K⁺/Na⁺提高;根系和叶片中Ca²⁺含量降低、Mg²⁺含量提高;磁化微咸水灌溉处理中K提高,且叶片中K值显著高于根系;S_K,Na和S_Mg,Na较非磁化微咸水灌溉提高,S_Ca,Na较其降低.磁化微咸水灌溉中根系和叶片Na⁺积累量减少,K⁺、Ca²⁺和Mg²⁺含量增加,且维持了较高水平的K⁺/Na⁺,这有利于植株整株水平生理代谢的调控.因此,盐分胁迫下磁化作用可通过调节离子的选择性吸收和运输来维持植株体内的离子平衡.     

Perchlorate and nitrate reductase activity in the perchlorate-respiring bacterium perclace

The perchlorate (ClO₄⁻)-respiring organism, strain perc1ace, can grow using nitrate (NO₃⁻) as a terminal electron acceptor. In resting cell suspensions, NO₃⁻ grown cells reduced ClO₄⁻, and ClO₄⁻ grown cells reduced NO₃⁻. Activity assays showed that nitrate reductase (NR) activity was 1.31 μmol min⁻¹ (mg protein)⁻¹ in ClO₄⁻ grown cells, and perchlorate reductase (PR) activity was 4.24 μmol min⁻¹ (mg protein)⁻¹ in NO₃⁻ grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 μmol min⁻¹ (mg protein)⁻¹. The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO₃⁻ and ClO₄⁻.     

Studies on the exchange of G-actin-bound calcium with bivalent cations

1. The possibility of the replacement of G-actin-bound calcium by various bivalent cations has been investigated. After the reaction with all cations studied, with the exception of Cu²⁺, action remains active, i.e., contains bound ATP and polymerizes in 0.1 M KCl.

2. The amount of G-actin-bound calcium, as well as the sum of bivalent cation after replacement, not removable by short-time Dowex-50 treatment, accounts to about 1 mole per 50000 g of G-actin.

3. The rate of exchange is of the same order for bivalent cations studied, including calcium.

4. G-actin-bound Ca²⁺ is fully replaced, besides free Ca²⁺, by free Mn²⁺ and Cd²⁺. The replacement with Mg²⁺, Co²⁺, Ni²⁺ and Zn²⁺ is not complete, and there is practically no reaction with Ba²⁺ and Sr²⁺.

5. Assuming the affinity constant of Ca²⁺ as 1, the following affinity constants for other bivalent cations were obtained: Mn²⁺, 0.90; Cd²⁺, 1.07; Mg²⁺, 0.27; Zn²⁺, 0.22; Co²⁺, 0.18; Ni²⁺, 0.08.

6. The results obtained show that there exists a close correlation between the ionic radius of a particular bivalent cation, and its ability to replace bound Ca²⁺.     

盐胁迫下外源褪黑素和Ca2+对甜瓜幼苗的缓解效应

以甜瓜品种‘羊角酥瓜’为试材,利用人工气候室控制环境条件(昼/夜25/18 ℃),研究盐胁迫条件下外源褪黑素(MT)和Ca²⁺对甜瓜幼苗根系和叶片中Cl^-、Na⁺、K⁺、Mg²⁺、Ca²⁺离子含量,Na⁺/K⁺、 Na⁺/Ca²⁺、Na⁺/Mg²⁺值,以及H⁺-ATP酶活性、渗透调节物质积累和细胞膜质过氧化的影响.结果表明: 与对照相比,盐胁迫处理显著抑制甜瓜幼苗生长,增加根系和叶片中Cl^-、Na⁺含量,降低K⁺、Mg²⁺、Ca²⁺含量.盐胁迫下,喷施外源MT或Ca²⁺处理均可以显著降低甜瓜根系和叶片中Cl^-、Na⁺含量,提高K⁺、Mg²⁺、Ca²⁺含量,植株体内Na⁺/K⁺、Na⁺/Ca²⁺和 Na⁺/Mg²⁺值下降;同时也提高了根系和叶片H⁺-ATP酶活性及叶片渗透调节物质的含量,降低盐胁迫对细胞膜的伤害,表现在甜瓜叶片相对电导率和丙二醛含量降低.总之,在盐胁迫条件下,外源MT、Ca²⁺单独和复配处理均可通过提高H⁺-ATP酶活性来降低盐害离子的含量,改善甜瓜幼苗中的离子平衡,同时增加渗透调节物质的含量,降低膜质过氧化水平,从而增强其对盐胁迫的适应性,其中MT和Ca²⁺复配处理时的效果更好.复配外施 MT 和Ca²⁺在诱导甜瓜幼苗提高耐盐方面具有协同增效作用.     

库布齐沙漠东部不同生物结皮发育阶段土壤温室气体通量

以流动沙地为对照,采用时空替代法分析库布齐沙漠东部固定沙地上不同发育阶段生物结皮藻类结皮和地衣结皮土壤温室气体通量特征及其与环境因子之间的关系,研究生物结皮发育对荒漠土壤温室气体通量的影响.结果表明: 荒漠土壤CO₂排放通量大小为地衣结皮(128.5 mg·m^-2·h^-1)>藻结皮(70.2 mg·m^-2·h^-1)>流动沙地(48.2 mg·m^-2·h^-1),CH₄吸收通量大小为地衣结皮(30.4 μg·m^-2·h^-1)>藻结皮(21.2 μg·m^-2·h^-1)>流动沙地(18.2 μg·m^-2·h^-1),N₂O排放通量大小为地衣结皮(6.6 μg·m^-2·h^-1)>藻结皮(5.4 μg·m^-2·h^-1)>流动沙地(2.5 μg·m^-2·h^-1).CO₂排放具有明显的季节变化,生长季显著大于非生长季;CH₄和N₂O季节变化差异不显著,前者生长季吸收大于非生长季,后者非生长季排放大于生长季.土壤有机碳和全氮含量、土壤微生物数量均是影响温室气体通量的重要因素,环境水热因子是影响土壤CO₂排放的关键因子,但CH₄和N₂O通量对水热因子的变化不敏感.随着植被恢复和生物结皮发育,荒漠土壤温室气体累积通量的不断增大导致其百年尺度的全球增温潜势亦显著提高,依次为地衣结皮(1135.7 g CO₂-e·m^-2·a^-1)>藻结皮(626.5 g CO₂-e·m^-2·a^-1) >流动沙地(422.7 g CO₂-e·m^-2·a^-1).     

Uptake of Cd2+ and Fe2+ by excised roots of Tamarix aphylla

The uptake of Cd²⁺ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd²⁺ uptake approached saturation with a single phase hyperbola. The time course of Cd²⁺ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q₁₀ of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q₁₀ values were only 1–1.3. It is concluded that Cd²⁺ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd²⁺ and for Fe²⁺ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe²⁺, with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd²⁺ was inhibited. Adsorption and absorption of Cd²⁺ were strongly inhibited by Ca²⁺ and by Mg²⁺, but were unaffected by Fe²⁺. Monovalent ions (Na⁺, K⁺, Li⁺) also reduced Cd²⁺ absorption, but to a lesser extent than Ca²⁺ and Mg²⁺. Uptake of Cd⁺ was reduced at lower pH of the medium. The importance of interfering cations for Cd²⁺ tolerance of T. aphylla is emphasized.     

Pb and Cd uptake in rice roots

Pb and Cd are heavy metal pollutants that inhibit plant growth. Using a cultivated rice variety (Dongjin, Oryza sativa L.), we studied how the transport and toxicity of Pb²⁺ and Cd²⁺ are affected by the presence of K⁺, Ca²⁺ or Mg²⁺. K⁺ had a little effect on uptake or toxicity of Pb²⁺ and Cd²⁺. Ca²⁺ or Mg²⁺ blocked both Cd²⁺ transport into rice roots and Cd²⁺ toxicity on root growth, which suggested that their detoxification effect is directly related to their blocking of entry of the heavy metals. Similarly, Ca²⁺ blocked both Pb²⁺ transport into the root and Pb²⁺ toxicity on root growth. The protective effect of Ca²⁺ on Pb²⁺ toxicity may be related to its inhibition of the heavy metal accumulation in the root tip, a potential target site of Pb²⁺ toxicity. Mg²⁺ did not ameliorate the Pb²⁺ toxicity on root growth as much as Ca²⁺ did, although it decreased Pb²⁺ uptake into roots similarly as Ca²⁺ did. These results suggest that the protective effect of Ca²⁺ on Pb²⁺ toxicity may involve multiple mechanisms including competition at the entry level, and that Pb²⁺ and Cd²⁺ may compete with divalent cations for transport into roots of rice plants.     

Kinetics and mechanism of the oxidation of ammineruthenium(II) complexes by bromine

The reactions of Ru(NH₃)₅py²⁺, Ru(NH₃)₄bpy²⁺, Ru₂(NH₃)₁₀pz⁵⁺, RuRh(NH₃)₁₀pz⁵⁺ and Ru(NH₃)₅pz²⁺ with bromine are first-order in ruthenium and first-order in bromine. The rates decrease with increasing bromide ion concentration and, except for Ru(NH₃)₅pz²⁺, are independent of hydrogen ion concentration. The reactions are postulated to proceed via outer-sphere, one-electron transfer from Ru(II) to Br₂ with the formation of Br₂⁻ as a reactive intermediate. The bromide inhibition is ascribed to the formation of Br₃⁻ which is unreactive in outer-sphere reactions because of the barrier imposed by the need to undergo reductive cleavage. The reaction of Ru(NH₃)₅pz²⁺ is inhibited by hydrogen ions. The hydrogen ion dependence shows that Ru(NH₃)₅pzH³⁺ has a pK_a of 2.49 and is at least 500 times less reactive than Ru(NH₃)₅pz²⁺. The reaction of Ru₂(NH₃)₁₀pz⁴⁺ with bromine is biphasic. The second phase has a rate identical to that of the Ru₂(NH₃)₁₀pz⁵⁺-Br₂ reaction. A detailed analysis shows that the reaction of Ru₂(NH₃)₁₀pz⁴⁺ with bromine proceeds by a sequence of one-electron steps, Br₂⁻ being produced as an intermediate. A linear free energy relationship between rate constants and equilibrium constants, obeyed for all the reactions studied, provides an estimate of 1.5 × 10² M⁻¹ s⁻¹ for the self-exchange rate constant of the Br₂/Br₂⁻ couple.     

Responses of apical ion fluxes to NaCl stress in Elaeagnus angustifolia seedlings

Aims Elaeagnus angustifolia is one of the most salt-tolerant species. The objective of this study was to understand the mechanisms of ion transporation in E. angustifolia exposed to different salt concentrations through manipulations of K⁺/Na⁺ homeostasis.
Methods Seedlings of two variants of the species, Yinchuan provenance (YC, salt-sensitive type) and the Alaer provenance (ALE, salt-tolerant type), were treated with three different NaCl application modes, and the ion fluxes in the apical regions were measured using non-invasive micro-test technology (NMT). In mode 1, Na⁺ and K⁺ fluxes were measured after 150 mmol·L^-1 NaCl stress lasted for 24 h. In mode 2, K⁺ and H⁺ fluxes were quantified with a transient stimulation of NaCl solution. In mode 3, Amiloride (Na⁺/H⁺ antiporters inhibitor) and tetraethylammonium (TEA, K⁺ channel inhibitor) was used to treat apical regions of E. angustifolia seedlings after NaCl stress for 24 h, respectively.
Important findings Under NaCl stress for 24 h, net effluxes of Na⁺ and K⁺ were increased significantly. The net Na⁺ effluxes of YC provenance seedlings (720 pmol·cm^-2•s^-1) were lower than that of ALE provenance (912 pmol·cm^-2·s^-1), but the net K⁺ efflux was higher in YC provenance. Under the instantaneous NaCl stimulation, net K⁺ efflux was remarkably increased, with the net K⁺ efflux of YC provenance always higher than that of ALE provenance. Interestingly, H⁺ at the apical regions was found from influx to efflux, with the net H⁺ efflux of ALE provenance greater than that of the YC provenance. Under the NaCl and NaCl + Amiloride treatment, the net Na⁺ efflux of ALE provenance seedlings was higher than that of YC provenance, while the net K⁺ efflux was less in ALE provenance seedlings. On the other hand, the differences in net Na⁺ and K⁺ effluxes were insignificant between the two provenances under the control group and NaCl + TEA treatment. In conclusion, NaCl stress caused Na⁺ accumulation and K⁺ outflows of E. angustifolia seedlings; The E. angustifolia seedlings utilize Na⁺/H⁺ antiporters to reduce Na⁺ accumulation by excretion; and the maintenance of K⁺/Na⁺ homeostasis in salt-tolerant E. angustifolia provenance seedlings roots accounted for a greater Na⁺ extrusion and a lower K⁺ efflux under NaCl stress. Results from this study provide a theoretical basis for further exploring salt-tolerant E. angustifolia germplasm resource.     

ENERGETICS OF AMINO ACID TRANSPORT INTO BRAIN SLICES: EFFECTS OF K+ DEPLETION AND Rb+ OR Cs+ SUBSTITUTION ON AMINO ACID UPTAKE

Abstract— Mouse brain slices were depleted of K⁺ by three 10-min incubations-in oxygenated HEPES-buffered medium lacking glucose and K⁺. Addition of K⁺ or Rb⁺ (or Cs⁺, to a smaller degree) with glucose, or with succinate, malate, and pyruvate (SMP) before incubation at 37°C with ¹⁴C-amino acids restored active low-affinity transport of d -Glu, α-aminoisobutyrate (AIB), GABA, Gly, His, Val, Leu, Lys, and Orn. Ouabain at 1–2μ m with Rb⁺ was more inhibitory with SMP than with glucose, suggesting that the glycoside may affect specific energy coupling to transport. Valinomycin, in contrast, showed no specificity of inhibition of amino acid uptake with glucose or SMP and K⁺ or Rb⁺. Cs⁺ partially restored amino acid uptake, but Li⁺ was less effective than Cs ⁺. NaF at 10 m m with SMP + Rb⁺, or SMP + K⁺ did not inhibit amino acid uptake. Therefore, it was possible to dissociate glycolysis and Na⁺, K ⁺ -ATPase activity from amino acid transport. The ion replacements for K ⁺ that supported active amino acid transport indicate that the specificity of ions in possible ionic gradients for transport energetics should be reexamined.     

Copper-Ligand Interactions and Physiological free Radical Processes. Part 2. Influence of Cu2+ Ions on Cu+-Driven Oh Generation and Comparison with Their Effects on Fe2+-Driven Oh Production

In our search to establish a reference ·OH production system with respect to which the reactivity of copper(II) complexes could then be tested, the influence of free Cu²⁺ ions on the Cu⁺/H₂O₂ reaction has been investigated.

This influence depends on the C_Cu²⁺/C_Cu⁺ ratio. At low Cu²⁺ concentrations, ·OH damage to various detector molecules decreases with increasing Cu²⁺ concentrations until C_Cu²⁺/C_Cu⁺ reaches unity. Above this value, ·OH damage increases sharply until C_Cu²⁺/C_Cu⁺ becomes equal to 5 with salicylate and 2 with deoxyribose, ratios for which the protective effect of Cu²⁺ cancels. Finally, at higher concentrations, Cu²⁺ ions logically add their own ·OH production to that normally expected from Cu⁺ ions. The possible origin of this unprecedented alternate effect has been discussed. The possible influence of Cu⁺ ions on the generation of ·OH radicals by water gamma radiolysis has also been tested and, as already established for Cu²⁺ in a previous work, shown to be nonexistent. This definitely confirms that either form of ionised copper cannot scavenge ·OH radicals in the absence of a Iigand.