Effect of monovalent ion adsorption on the electric charge of phosphatidylcholine - decylamine liposomal membranes

We examined the effect of adsorbed monovalent ions on the surface charge of phosphatidylcholine (PC) – decylamine (DA) liposomal membranes. Surface charge density values were determined from electrophoretic mobility measurements of lipid vesicles performed at various pH levels. The interaction between solution ions and the PC-DA liposomal surface was described by a six component equilibrium model. The previously determined association constants of the -PO^(-) and –N⁽⁺⁾(CH₃)₃ groups of PC with H⁺, OH^-, Na⁺ and Cl^- ions (K _A1H, K _B1OH, K _A1Na, K _B1C1) were used to calculate K _B2OH, and K _B2C1, the association constants of the –N⁽⁺⁾H₃ group of DA with OH^- and Cl^- ions, providing an experimental verification for the proposed model.     

Ionic effects on bumetanide binding to the activated Na/K/2Cl cotransporter: Selectivity and kinetic properties of ion binding sites

Summary The loop diuretic bumetanide binds specifically to the Na/K/2Cl cotransporter of many cell types including duck erythrocytes. Membranes isolated from these erythrocytes retain the ability to bind bumetanide when cells are exposed to cotransport activity stimuli prior to membrane isolation. An extensive study of the effects of ions on specific [³H]bumetanide binding to such membranes is presented here and compared to the activity of these ions in supporting transport function in intact cells. Both Na⁺ and K⁺ enhanced bumetanide binding in a saturable manner consistent with a single-site interaction. The K _m for each ion was dependent on the concentration of the other cation suggesting heterotropic cooperative interactions between the Na⁺ and K⁺ binding sites. Na⁺ and K⁺ were partially replaceable, with the selectivity of the Na⁺ site being Na⁺ > Li⁺ > NH ₄ ⁺ ; N-methyl-d-glucamine⁺, choline⁺ and tetramethylammonium⁺ also supported a small amount of specific binding when substituted for Na⁺. The selectivity of the K⁺ site was K⁺ Rb⁺ > NH ₄ ⁺ > Cs⁺; N-methyl-d-glucamine⁺, choline⁺ and tetramethylammonium⁺ were inactive at this site. The results of transport experiments revealed a slightly different pattern. Li⁺ could partially substitute for Na⁺ in supporting coteansport, but other monovalent cations were completely inactive. The order of potency at the K⁺ site was NH ₄ ⁺ > K⁺ Rb⁺ > Cs⁺ other monovalent cations. The effect of Cl^- on bumetanide binding was biphasic, being stimulatory at low [Cl^-] but inhibitory at high [Cl^-]. As this implies the existence of two Cl^- binding sites (termed Cl _H and Cl _L for the high- and low- affinity sites, respectively) each phase was examined individually. Cl^- binding to Cl _H could be described by a rectangular hyperbola with a K _m of 2.5 mm, while kinetic analysis of the inhibition of bumetanide binding at high [Cl^-] revealed that it was of a noncompetitive type (K _i = 112.9 mm). The selectivity of anion binding to the two sites was distinct. Cl _H was highly selective with Cl^- > SCN^- > Br^-; F^-, NO ₃ ^- , ClO ₄ ^- , MeSO ₄ ^- , gluconate^- and SO ₄ ^2- were inactive. The efficacy of anion inhibition of binding to Cl _L was ClO ₄ ^- > I^- > SCN^- > NO₃ > Cl^-; F^-, MeSO ₄ ^- , gluconate^-, and SO ₄ ^2- were inactive. Thus, Cl _H is much more selective than Cl _L and largely accounts for the specificity of the system with respect to anion transport. SO ₄ ^- , NO ₃ ^- , I^-, SCN^- and ClO ₄ ^- did not support cotransport when bound to Cl _L and the latter three anions were inhibitory. Mg²⁺ was found to stimulate binding at a narrowly defined peak around 1.5 mm, but was inhibitory at higher concentrations. Other divalent cations caused a similar inhibition of bumetanide binding but did not exert a stimulatory effect at 1.5 mm. Divalent cations have little effect on cotransport in intact cells at concentrations up to 20 mm, suggesting that their effects on diuretic binding reflect interactions at internally disposed sites. Bumetanide binding was optimal at a pH of 7.8–8.1 and declined sharply as the pH was lowered towards 6. The titration curve correlated well with the effect of pH on cotransport in intact cells; the inhibitory effect of low pH suggests that protonation of the cotransporter may inhibit its function.We thank Drs. Brad Pewitt, John Westley and Mrinalini Rao for discussion, Sara Leung and Artelia Watson for their excellent technical assistance, and Dr. R.J. Turner for his gift of [³H] bumetanide. This work was supported in part by Cystic Fibrosis Center grant #CF RO11 7-04.     

Buffered,phosphate-containing media suitable for aluminum toxicity studies

Studies of Al rhizotoxicity sometimes require the use of well-defined rooting media. For that reason, buffers and phosphate are often omitted from Al solutions for which species composition must be determined precisely. Homopipes and succinate appear to be suitable buffers for short-term studies with seedlings of an Al-sensitive wheat (Triticum aestivum L. cv. Scout 66) and white clover (Trifoliau repens L. cv. Huia). In the case of homopipes (homopiperazine-N,N-bis-2-[ethane-sulfonic acid]), a slight inhibition of root elongation must be taken into account, but no binding of Al³⁺ was observed. In the case of succinate, no inhibition of root elongation was observed, but Al³⁺ binding must be considered. Phosphate-containing media remain free of solid-phase or polynuclear species whenever {Al³⁺}²{HPO₄ ^2-}{OH^–}³ < 10^–47.0 (or {Al³⁺}{HPO₄ ^2-}{OH^–}< 10^–22.7) and when {Al³⁺}³ / {H⁺}³ < 10^8.8. These ion activity products, that define stable Al solutions in the laboratory, appear to apply in soils also, according to an analysis of published data. The published equilibrium values {AlH₂PO₄ ²⁺} / ({Al³⁺}{H₂PO₄ ^–}) = 10^3.0, {AlHPO₄ ⁺} / ({Al³⁺}{HPO₄ ^2-}) = 10^7.0, and {Alsuccinate⁺} / ({Al³⁺}{succinate ^2-}) = 10^4.62 appear to be suitable, because solution toxicity could be accounted for entirely on the basis of computed Al³⁺ even in solutions containing high levels of Alsuccinate⁺ and AlHPO₄ ⁺ (in every case {AlHPO₄ ⁺}>> {AlH₂PO₄ ²⁺}). Thus, AlHPO₄ ⁺ and Alsuccinate⁺ were not toxic at achieved concentrations.     

Atmospheric deposition, mass balances, and processes regulating streamwater solute concentrations in mixed-conifer catchments of the Sierra Nevada, California

Solute concentrations in atmospheric deposition and stream water were measuredfrom 1984 through 1993 to determine the fate and mobility of solutes in twogauged mixed-conifer catchments (Tharp's and Log creeks) located in theSierra Nevada, California. The two catchments contain mature forest standsdominated by Abies concolor (white fir), Sequoiadendron giganteum (giantsequoia), Abies magnifica (red fir) and Pinus lambertiana (sugar pine).Ammonium, Cl^-, Ca²⁺ and NO^- ₃were highest in concentration of the solutes measured in wet deposition;bulk deposition was highest in SO^{2- 4}, NH⁺ ₄,Cl^- and H⁺. Net retention ofH⁺, NO₃ ^-, NH₄ ⁺,SO₄ ^2- and Cl^- occurred in both catchments.Discharge was dominated by spring snowmelt with the largest export yieldsfor acid neutralizing capacity (ANC), SiO₂, andCa²⁺. Export yields of H⁺,NO₃ ^-, NH₄ ⁺ and PO₄ ^3-were relatively small (0.5 kg ha^-1 y^-1).Discharge-concentration relationships for ANC, SiO₂,Na⁺, K⁺, Ca²⁺ andMg²⁺ were inverse and their concentrations in stream waterwere primarily influenced by discharge and annual differences in the relativecontributions of snowmelt and groundwater. The mobility of these solutes iscontrolled by the rates of mineral weathering and ion exchange. The positiverelationship of SO₄ ^2- concentration with increasingdischarge suggests that atmospherically deposited SO₄ ^2-is temporarily stored and that its release is controlled by the extent of soilwater flushing.     

Long-term effects of SO2 on plants,SO2 metabolism and regulation of intracellular pH

The impact of SO₂ on the ionic balance of plants and its implications for intracellular pH regulation was studied to find explanations for long-term effects of SO₂. When sulphur, taken up as SO₂ by the shoots of plants, is not assimilated in organic compounds, but stored as sulphate, an equivalent amount of H⁺ is produced. These H⁺ ions are not buffered chemically, but removed by metabolic processes.On the basis of knowledge on metabolic buffering mechanisms a conceptual model is proposed for the removal of shoot-generated H⁺ by (i) OH^- ions, produced in the leaves when sulphate and nitrate are assimilated in organic compounds and/or by (ii) OH^- ions produced by decarboxylation of organic anions (a biochemical pH stat mechanism). The form in which nitrogen is supplied largely determines the potential of the plant to neutralize H⁺ in the leaves during SO₂ uptake by the proposed mechanisms.In field experiments with N₂ fixing Vicia faba L. crops, the increase of sulphate in the shoots of SO₂-exposed plants was equivalent in charge to the decrease of organic anion content, calculated as the difference between inorganic cation content (C) and inorganic anion content (A), indicating that H⁺ ions produced in the leaves following SO₂ uptake were partly removed by OH^- from sulphate reduction and partly by decarboxylation of organic anions.The appearance of chronic SO₂ injury (leaf damage) in the field experiment at the end of the growing period is discussed in relation to the impact of SO₂ on the processes involved in regulation of intracellular pH. It is proposed that the metabolic buffering capacity of leaf cells is related to the rates of sulphate and nitrate reduction and the import rate of organic anions, rather than to the organic anion content in the vacuoles of the leaf cells.     

Non-phytotoxicity of the aluminum sulfate ion, AlSO+4

Aluminum is a phytotoxic element in many soils and occurs in a variety of chemical species. In order to determine whether AlSO⁺₄ is toxic, seedlings of wheat (Triticum aestivum L. cv. Tyler) and red clover (Trifolium pratense L. cv. Kenland) were transferred to solutions containing controlled activities of Al³⁺, AlSO⁺₄, Na⁺ and Ca²⁺. Root elongation was inhibited by Al³⁺ (or mononuclear hydroxy-Al species that are in equilibrium with Al³⁺), but not by AlSO⁺₄. We assumed a formation constant (K_AlSO⁺₄= {AlSO⁺₄}/[{Al³⁺} {SO^2-₄}]; braces indicate activities} of 10^3.2 for AlSO⁺₄ in the computation of ionic activities, but use of K_AlSO⁺₄ values ranging from 10^2.8 to 10^3.6 had very little effect on the computed toxicities of Al³⁺ and AlSO⁺₄. Sulfate did not promote the formation of polynuclear Al complexes in our experiments. A practice in studies of Al phytotoxicity has been to attribute toxicity to mononuclear Al, but now it would seem advisable to exclude AlSO⁺₄. That AlSO⁺₄ is non-toxic, or is at least 10-fold less toxic than Al³⁺, has implications for the physiology of Al toxicity and for the use of sulfate salts in experimental work and in agriculture.     

A hydroxide ion carrier in planar phospholipid bilayer membranes: (C6F5)2Hg (dipentafluorophenylmercury)

Although a number of molecules are known to function as current-carrying proton carriers across lipid bilayer membranes, no such hydroxide ion carriers have been found to date. We report that (C₆F₅)₂ Hg, which can function as a chloride ion carrier, can also carry a hydroxide ion. In 100 mM Na₂SO₄ solutions, membranes treated with (C₆F₅)₂Hg are almost ideally selective for H⁺/OH⁻ between pH 6.0 and 9.5. Membrane conductance varies linearly with [OH⁻] over this pH range and with the square of the (C₆F₅)₂Hg concentration. The presumed current-carrying species is the dimer [(C₆F₅)₂Hg]₂OH⁻, which, along with the neutral molecule (C₆F₅)₂Hg, shuttles back and forth within the bilayer. In 0.2 M NaCl at pH 9.5, the OH⁻ and Cl⁻ conductances are approximately equal. Thus, the carrier displays an approximately 10⁴-fold preference for OH⁻ over Cl⁻.     

淋洗与植物作用耦合对盐渍化土壤的改良效应

以甘肃秦王川引大灌区盐渍化土壤为背景,以当地5种耐盐植物为材料,采用根袋法盆栽试验动态研究了淋洗结合植物种植对盐渍化土壤改良的效应。结果表明:与种前相比,单纯的淋洗作用对土壤pH值影响不大,而淋洗结合植物种植明显降低了土壤pH值,且根际土壤pH值小于非根际土壤的,5种耐盐植物中霸王根际土壤pH值降低幅度最大,达0.6个单位。K+、Ca2+、Na+、Mg2+、Cl-和SO2-4在5种植物根际土壤中均有不同程度的富集,富集程度因物种的不同而不同,随培养时间的延长而呈波动状态。5种供试植物和对照组土壤中的6种主要的可溶性盐分离子随淋洗次数和培养时间的延长呈下降趋势。在培养120d后,单纯淋洗的土壤中K+、Ca2+、Na+、Mg2+、Cl-和SO2-4的含量相比种前平均分别降低了33.3%、26.1%、35.6%、32.5%、35.5%和36.3%,植物吸收带走的上述各离子的含量平均分别占种前的46.2%、8.1%、30.2%、7.2%和21.6%,其中霸王吸收带走的盐分离子最多,而淋洗结合种植植物的土壤中上述各离子的含量与种前相比平均分别降低了67.25%、63.73%、83.8%、67.5%、81.55%和78.46%,由此可见,淋洗结合植物种植的脱盐效果优于单纯淋洗,且土壤中主要的盐分离子Na+、Cl-和SO2-4的含量降低幅度最大,通过计算得出,在Cl-、SO2-4和Na+减少的总量中还有37.73%的Na+、38.22%的Cl-和35.14%的SO2-4的减少量是由植物根系的物理化学作用机制引起的。     

Influence of anions on the potassium status and productivity of kiwifruit (Actinidia deliciosa) vines

The effects of K fertiliser (160 kg ha^-1) applied with Cl^- or SO₄ ^2- as the accompanying anion on the K nutrition of kiwifruit (Actinidia deliciosa var. deliciosa) were assessed in a field experiment, using vines with varying degrees of K deficiency. Leaf K concentrations in spring were significantly higher for vines receiving KCl, compared to those receiving K₂SO₄. This effect did not interact significantly with the degree of K deficiency, and persisted for about 6 weeks. Subsequently there was no significant difference between the leaf K concentrations for the vines receiving KCl or K₂SO₄. Applying K as KCl increased the leaf Cl concentration, especially in spring, while applying K as K₂SO₄ had no significant effect on the leaf S concentration at that time. These results implied a greater requirement for organic acid anions for K⁺ uptake from K₂SO₄ than from KCl, and the importance of organic acid anions for K⁺ uptake from different sources of K fertiliser is discussed. This transient effect of the accompanying anion on leaf K status was associated with large effects on flowering, and fruit yields were about 28% higher for plants receiving KCl rather than K₂SO₄.The effects on growth and tissue nutrient composition of varying the concentrations of Cl^-, NO₃ ^-, SO₄ ^2- and H₂PO₄ ^- around the roots of kiwifruit vines were examined in a solution culture experiment. For H₂PO₄ ^-, plant growth was very similar over a wide range of rates of addition. For the other anions, the range between deficiency and toxicity was clearly delineated. For Cl^- and NO₃ ^-, toxicity was associated with high tissue concentrations of Cl and N, respectively, and was consistent with competition for uptake between Cl^- and NO₃ ^-. However, for SO₄ ^2-, toxicity was associated with only a small increase in the tissue S concentration relative to that associated with maximum growth, and appeared to result more from effects on uptake of other anions and cations rather than from direct effects of high tissue S concentrations.It is concluded that the sensitivity of kiwifruit to the anion accompanying K⁺ in fertiliser may be related to the unusually high requirement for Cl previously reported for this species.     

An assessment of thermodynamic reaction constants for simulating aqueous environmental monomethylmercury speciation

ABSTRACT

Monomethylmercury (CH₃Hg ⁺) is both the most ecologically significant and the least well characterized species of mercury in environmental settings. Our understanding of the environmental speciation behavior of this compound is limited both as the result of lesser available laboratory data (when compared to inorganic mercury) as well as the uncertainties associated with our understanding of the properties of environmental ligands. A careful examination and synthesis of data reported in the technical literature led to the following findings: (1) a 25°C, zero ionic strength bicarbonate ion complexation constant estimate is remarkably close to an earlier reported value at 0.4 M: CH₃Hg⁺ + HCo₃^-?CH₃HgHCO₃,log₁₀K = 2.6 (±0.22, 1 SD), (2) three 25°C zero ionic strength reaction constants reported by DeRobertis et al.(1998) were confirmed to within ~±0.1 log₁₀K units: CH₃Hg ⁺+ OH^-?CH₃HgOH, log₁₀K = 9.47; 2CH₃Hg ⁺ + H₂O?(CH₃Hg)₂OH ⁺ + H⁺, log₁₀K =?2.15; CH₃Hg ⁺+ Cl^-?CH₃HgCl, log₁₀K = 5.45, (3) “best estimate” literature complexation constants corrected to zero ionic strength include: CH₃Hg ⁺ + F^-?CH₃HgF, log₁₀K = 1.75 (20°C corr. Schwart-zenbach and Schellenberg, 1965); CH₃Hg ⁺ + Br^-?CH₃HgBr, log₁₀K = 6.87 (20°C corr. Schwartzenbach and Schellenberg, 1965); CH₃Hg ⁺ +1^-?CH₃HgI, log₁₀K = 8.85 (20°C corr. Schwartzenbach and Schellenberg, 1965); and CH₃Hg ⁺+ SO₄^2-?CH₃HgSO₄^-,log₁₀K = 2.64 (25°C, DeRobertis et al., 1998), (4) literature reported values for simulating monomethylmercury complexation with the carbonate ion may be too low: CH₃Hg ⁺+ CO₃^2-?CH₃HgCO₃^-, log₁₀K = 6.1 (Rabenstein et al., 1976; Erni, 1981), and (5) ‘‘best estimate’’ constants for simulating methyl mercury complexation with reduced environmental sulfur species include: CH₃Hg ⁺ + S^2-?CH₃HgS ^-, log₁₀K = 21.1; CH³Hg ⁺+ SH ^-? CH3HgSH, log₁₀K = 14.5 (H ⁺ + SH^-?CH₂S, log₁₀K = 6.88; Dyrssen and Wedborg, 1991); CH₃Hg ⁺ + RS^-?CH₃HgSR, log₁₀K = 16.5 (H + + RS^-?RSH, log₁₀K = 9.96; Qian et al., 2002); and CH₃Hg ⁺+ CH₃HgS^{1 -}?(CH₃Hg)₂S, log₁₀K = 16.32 (Schwartzenbach and Schellenberg, 1965; Rabenstein et al., 1978; and Erni, 1981).     

Glyphosate complexation to aluminium(III). An equilibrium and structural study in solution using potentiometry, multinuclear NMR, ATR-FTIR, ESI-MS and DFT calculations

The stoichiometries and stability constants of a series of Al³⁺-N-phosponomethyl glycine (PMG/H₃L) complexes have been determined in acidic aqueous solution using a combination of precise potentiometric titration data, quantitative ²⁷Al and ³¹P NMR spectra, ATR-FTIR spectrum and ESI-MS measurements (0.6 M NaCl, 25 °C). Besides the mononuclear AlH₂L²⁺, Al(H₂L)(HL), and Al(HL)L²⁻, dimeric Al₂(HL)L⁺ and trinuclear complexes have been postulated.¹H and ³¹P NMR data show that different isomers co-exist in solution and the isomerization reactions are slow on the ³¹P NMR time scale. The geometries of monomeric and dimeric complexes likely double hydroxo bridged and double phosphonate bridged isomers have been optimized using DFT ab initio calculations starting from rational structural proposals. Energy calculations using the PCM solvation method also support the co-existence of isomers in solutions.     

Forest vegetation affecting the deposition of atmospheric elements to soils

Atmospheric inputs of elements/ions into the soil through bulk precipitation and throughfall (precipitation below tree canopies) were monitored monthly at two forested catchments (Lesni Potok and Liz) in central and southwestern Bohemia, respectively. The annual deposition fluxes (expressed in μg/mg m^?2 yr^?1) of Al, As, Ba, Be, Ca, Cd, Cl^?, F^?, Fe, K, Mg, Mn, N_tot, Na, Ni, Pb, Rb, SO ₄ ^2? , Sr and Zn between 1997 and 2005 were calculated from their concentrations in monthly collected samples of both precipitation types. The flux of H⁺ was calculated from the monthly pH values as well. The more pristine character of the Liz catchment was manifested in lower inputs of anions of strong inorganic acids (mostly of anthropogenic origin) and of H⁺ in spite of higher precipitation amounts at the site. The comparison of fluxes in bulk precipitation (BP) and throughfall (TH) has shown significantly higher values for Rb, K, Mg, Mn, F^?, Ca, SO ₄ ^2? , Sr, Ba and Cl^? in the latter flux. It is declared that high fluxes of these elements/ions in TH significantly affect the forest soil water chemistry and that the forest vegetation significantly contributes to the mobilization of several elements in soil and to their redistribution throughout the soil profile.     

黄河口湿地柽柳灌丛土壤盐渍化特征

为探究黄河三角洲湿地柽柳灌丛下土壤的盐渍化特征，在黄河三角洲国家级自然保护区(37°35''-12''N，118°33''-119°20''E)黄河入海口附近，根据长势基本一致的原则分别在碱蓬群落、柽柳群落和芦苇群落各选3株柽柳，采集柽柳灌丛下土壤样品，分析土壤盐分和盐碱化参数的空间分布以及距基茎不同距离处研究对象(土壤总盐(TS)、电导率(EC)、pH、交换性钠百分率(ESP))和环境因子(Na⁺、K⁺、Ca²⁺、Mg²⁺、Cl^-、HCO₃^-、SO^2-₄)之间的关系。结果表明：(1)研究区土壤为弱碱化盐土，离子含量由高到低依次为Cl^->Na⁺>SO^2-₄ >Ca²⁺>Mg²⁺>HCO^-₃>K⁺。除pH在土壤表层数值最低外，表层土壤TS、EC、ESP和盐分离子大于深层土壤，显示表聚性。(2)土壤盐分和盐碱化参数空间分布总体为：在柽柳基茎周围形成"盐谷"、"碱谷"效应， Na⁺、Mg²⁺、Cl^-表现为"盐谷"，K⁺ 、SO^2-₄ 、Ca²⁺ 表现为"盐岛"。(3)在整个土壤剖面中，与TS、EC相关性最强的阴阳离子为Mg²⁺、Cl^-，从灌丛中心到灌丛间裸地Ca²⁺、SO^2-₄与TS、EC的相关性逐渐减弱，Mg²⁺、Cl^-与TS、EC的相关性逐渐增强。Ca²⁺和SO^2-₄与pH表现为较强的负相关性；与ESP相关性最强的阴离子为HCO^-₃，与之相关性最强的阳离子为Na⁺和K⁺，并且Na⁺和K⁺与ESP的相关性表现出从灌丛中心向外逐渐增强。(4)土壤盐渍化主要受控于Na⁺，从灌丛下到灌丛间裸地Cl^-对盐渍化程度的影响逐渐增加，SO^2-₄的影响逐渐降低。     

基于典范对应分析的滨海湿地土壤季节性盐渍化特征

为了更好地开发利用黄河三角洲湿地土壤资源和生态环境建设,运用单因素方差分析(One-way ANOVA)和典范对应分析方法(CCA),对黄河口湿地0—10 cm土壤全盐量(TS)、盐分离子组成、pH、钠吸附比(SAR)、电导率(EC)的季节性变化特征及数量关系进行了分析。结果表明:该区土壤属于盐土类型,春季(5月)、夏季(8月)、秋季(10月)全盐含量均高于17.9 g/kg,且春季、秋季的含盐量高于夏季,造成春、秋季积盐,夏季脱盐。盐分阳离子以Na~+为主,阴离子以Cl~-为主,除Mg~(2+)在夏季、秋季和Cl~-在秋季表现出强烈的变异性外,其余离子在不同季节均表现出中等强度的变异性。春季,Cl~-与Na~+、Mg~(2+),SO■与K~+;夏季,Cl~-与HCO~-_3,SO■与Mg~(2+)、Ca~(2+),Ca~(2+)与Mg~(2+);秋季,Cl~-与SO■,SO■与Mg~(2+),Ca~(2+)与Mg~(2+),均有很好的关联性。pH值均介于7.7—8.1之间,各个季节受盐分离子的影响较小,分布较为均匀。SAR介于3.08—5.29之间,春季受控于HCO~-_3;夏季受控于K~+;秋季受各离子的影响均较小,分布较为均匀。EC介于7.16—13.04 mS/cm,春季受各离子的影响均较小,其空间分布较为均匀;夏季受控于SO■、Ca~(2+)、Mg~(2+);秋季受控于Na~+。TS与Cl~-、Na~+、Mg~(2+)在季节变化上的差异性一致,且各个季节均受控于Cl~-。故通过合理的措施控制或减少Cl~-来源是一条减轻黄河口湿地土壤盐渍化的合适途径。     

渗透胁迫和离子毒害对转Bt基因棉幼苗生长及离子分布的影响

研究了渗透和盐胁迫处理对转Bt基因抗虫棉(Gossypium hirsutum) 99B种子的萌发和幼苗生长的影响,以及幼苗不同器官离子吸收和分配的差异。结果表明:渗透和盐胁迫均对转Bt基因抗虫棉幼苗的生长有抑制作用,其中PEG的抑制作用最强,而3种盐的抑制程度以CaCl₂>NaCl>Na₂SO₄,且在Na⁺含量相同时,Cl^-的毒害大于SO₄^2-。渗透胁迫下使根、茎和叶中的Na⁺和Cl^-含量提高,K⁺、Ca²⁺、SO₄^2-含量和K⁺/Na⁺、Ca²⁺/Na⁺和SO₄^2-/Cl^-比值降低,且地上部的变化幅度大于地下部的,其中以PEG的影响最为显著,其次是CaCl₂,Na₂SO₄处理最弱。这些说明,转Bt基因抗虫棉99B的耐盐性较弱。     

Monovalent Cations Induce Microsporidian Spore Germination In Vitro

ABSTRACT The relative capacity of Na⁺, K⁺ and Cl^- to stimulate germination of spores of the microsporidian Nosema algerae, a pathogen of mosquitoes, was examined by ion substitution experiments. Sodium at 0.1 M was ineffective to produce the high percentage of germination that typically occurs with 0.1 M NaCl (the normal stimulation solution) if Cl^- was substituted with the usually impermeant anions SO₄^2-, HPO₄^2-, or the organic acids oxalate, cacodylate, EGTA, MES and HEPES. However, substantial concentration- and pH-dependent germination was seen with Na₂SO₄ in the 0.2-0.8 M Na⁺ range. Similar results were obtained with solutions of K⁺ accompanied by impermeant anions. In contrast, the chloride salts of usually impermeant cations, like choline and triethanolamine, failed to germinate spores even at 0.8 M unless Na⁺ or K⁺ was independently added. The presence of 0.5 M choline chloride in the medium reduced the levels of Na₂SO₄ required to produce germination down to equivalence with those of Na⁺ in the normal stimulation solution. Monensin, a Na⁺ ionophore, facilitated the germination induced by a medium-level stimulus (0.04 M NaCl) in sonicated samples. These findings indicate that N. algerae spores germinate in response to the alkali metal cations, while CI^- plays a passive role by diffusing to maintain internal electroneutrality during cation influx. A possible mechanism of cation action in spore germination is suggested on the basis of these results and observations on other systems of intracellular motility.     

Anion binding studies of tris(2-aminoethyl)amine based amide receptors with nitro functionalized aryl substitutions: A positional isomeric effect

Syntheses and crystal structures of tren-based amide, L¹, N,N′,N″-tris[(2-amino-ethyl)-4-nitro-benzamide] and L², N,N′,N″-tris[(2-amino-ethyl)-2-nitro-benzamide] are reported and compared with previously published tripodal amide receptor L³, N,N′,N″-tris[(2-amino-ethyl)-3-nitro-benzamide]. The crystallographic results show intramolecular and intermolecular hydrogen-bonding interactions between two arms of the tripodal receptor and two other adjacent molecules in cases of L¹ and L² whereas in addition to the above interactions an aromatic π···π stacking among tripodal arms is also observed in L³. Receptors L¹, L² and L³ having electron withdrawing -NO₂ substituted (para, ortho and meta, respectively) phenyl moieties are explored toward their solution state anion binding properties and selectivity studies. The substantial changes in chemical shifts are observed for the amide protons (-NH) and aromatic protons (-CH) with F⁻ and Cl⁻ in cases of L¹ and L³, and only with F⁻ for L², indicating the participation of -NH and -CH protons in the solution state binding events. Binding constants for the above cases are calculated by ¹H NMR titration upon monitoring the -NH signal. Receptor L² shows exclusive selectivity toward F⁻ in dimethyl sulfoxide (DMSO). The structural aspects of binding I⁻, ClO₄⁻ and SiF₆²⁻ with the monoprotonated L¹, L¹H⁺·I⁻·DMF (1), L¹H⁺·ClO₄⁻·DMF (2) and L¹H⁺·0.5SiF₆²⁻·H₂O (3), respectively are examined crystallographically. Anion binding with multiple receptor units is observed via amide N-H···anion as well as aryl C-H···anion hydrogen-bonding interactions in all the complexes as observed in cases of previously reported crystal structures of anionic complexes of protonated L³. The aryl group having nitro functionality that contributes to solution state anion binding with the neutral receptor and solid state coordination in complexes 1-3 through CH···anion interactions is noteworthy.     

Effects of Anions on the Capacity and Affinity of Copper Adsorption in Two Variable Charge Soils

Effects of nitrate,(NO₃⁻) chloride (Cl⁻), sulfate (SO₄^2-, and acetate (Ac⁻) on Cu²⁺ adsorption and affinity of the adsorbed Cu²⁺ were evaluated in two Fe and Al enriched variable charge soils from Southern China. The maximum adsorption of Cu²⁺ (M, a parameter from the Langmuir isotherm model) in the presence of different anions decreased in the order Cl⁻ > Ac⁻ > NO₃⁻ > SO₄^2- for both soils. The clayey loamy soil (mixed siliceous thermic Typic Dystrochrept, TTD), developed on the Arenaceous rock, adsorbed less Cu²⁺ than the clayey soil (kaolinitic thermic Plinthudults, KTP), derived from the Quaternary red earths, regardless of anion type present in the medium. The affinity of adsorbed Cu²⁺ to both soils could be characterized by the Kd (distribution coefficient) values and successive extraction of the adsorbed Cu²⁺ with 1-mol NH₄Ac L⁻¹. The log₁₀Kd value was smaller for the TTD soil than for the KTP soil and decreased in the order of Cl⁻ > NO₃⁻ > SO₄^2- > Ac⁻ at low initial Cu²⁺ concentrations (≤40 mg Cu²⁺L⁻¹), whereas at 80 mg Cu²⁺L⁻¹, the log₁₀Kd value was similar for NO₃⁻, SO₄^2-, and Ac⁻, but was slightly higher for Cl⁻. Complete extraction of Cu²⁺ adsorbed in the presence of Ac⁻ was achieved. Influence of NO₃⁻ and SO₄^2- on the affinity of adsorbed Cu²⁺ was similar, but the effects of Cl⁻ depended on the initial Cu²⁺ concentrations. The extracted percentage of the adsorbed Cu²⁺ in the presence of NO₃⁻ or SO₄^2- increased with increasing Cu²⁺ adsorption saturation. The presence of Cl⁻, NO₃⁻, or SO₄^2- markedly decreased the equilibrium solution pH for both soils with increasing initial Cu²⁺ concentrations, and the delta pH values at the highest Cu²⁺ level were 0.5, 0.63, and 0.55 U for the TTD soil and 0.79, 0.84, and 0.93 U for the KTP soil, respectively for the three anions. The presence of Ac⁻ had a minimal influence on the equilibrium solution pH because of the buffering nature of the NaAc/HAc medium which buffered the released protons. The effects of anions on Cu²⁺ adsorption and affinity of the adsorbed Cu²⁺ were dependent on anion types and were apparently related to the altered surface properties caused by anion adsorption and/or the formation of anion– Cu²⁺ complexes.     

Geochemical aspects of aluminium in forest soils in Galicia (N.W. Spain)

The aqueous speciation of Al was studied in acid forest soils in N.W. Spain. Aluminum concentrations were 10–70 mol L^–1, with variable proportions oflabile, nonlabile, andacid-soluble Al. Almost all thelabile Al was found complexed with F^–, Al³⁺ concentrations being low. The importance of organic matter was seen in the formation of Al-organic complexes in the solid soil fraction and the presence of aqueous alumino-organic complexes in superficial horizons (umbric epipedons) rich in organic matter.     

Assessing the phytotoxicity of mononuclear hydroxy-aluminum

Abstract Al³⁺ is an important rhizotoxic ion in acid soils around the world. Al³⁺ is in equilibrium with mononuclear hydroxy-Al species, such as AlOH²⁺ and AL(OH)₂⁺, but the toxicity of these species has not been determined. Polynuclear Al may also coexist with Al³⁺, and one of these species, AlO₄Al₁₂(OH)₂₄(H₂O)₁₂⁷⁴, is very toxic. In order to determine the toxicity of mononuclear hydroxy-Al we have reanalysed the results of previously published, solution-culture experiments and have performed new experiments. Several problems are inherent in these studies. At pH values less than 5.0, the activities of the mononuclear hydroxy-Al species are low relative to Al³⁺, but attempts to change the ratio by raising the pH generally initiate the formation of polynuclear Al. (We discovered that mononuclear solutions are stable for many days when {Al³⁺}/{H⁺}³≤ 10^8.8, where braces denote activities.) We avoided, or accounted for, polynuclear Al in our studies. In addition, we used up-to-date equilibrium constants to compute Al species, very simple culture media (generally containing CaCl₂, AlCl₃ and HCl as the only inputs), short-term (2d) growth, and an Al-sensitive wheat variety (Triticum aestivum L. cv. Tyler) that permitted low Al levels and, consequently, higher pH values without Al polymerization. Experiments were designed in which the solutions were constant in {Al³⁺} and variable in mononuclear hydroxy-Al or were orthonal (factorial) in {Al³⁺} and {AlOH²⁺}. Linear and nonlinear, simple and multiple, regression analyses of these and previous experiments failed to reveal any toxicity for mononuclear hydroxy-Al to Tyler wheat.