Monitoring detrital input and resuspension effects on sediment trap material using mineralogy and stable isotopes (δO and δC): the case of Lake Neuchâtel (Switzerland)

Isotopic analyses on bulk carbonates are considered a useful tool for palaeoclimatic reconstruction assuming calcite precipitation occurring at oxygen isotope equilibrium with local water and detrital carbonate input being absent or insignificant. We present results from Lake Neuchâtel (western Switzerland) that demonstrate equilibrium precipitation of calcite, except during high productivity periods, and the presence of detrital and resuspended calcite. Mineralogy, geochemistry and stable isotope values of Lake Neuchâtel trap sediments and adjacent rivers suspension were studied. Mineralogy of suspended matter in the major inflowing rivers documents an important contribution of detrital carbonates, predominantly calcite with minor amounts of dolomite and ankerite. Using mineralogical data, the quantity of allochthonous calcite can be estimated by comparing the ratio ankerite + dolomite/calcite + ankerite + dolomite in the inflowing rivers and in the traps. Material taken from sediment traps shows an evolution from practically pure endogenic calcite in summer (10–20% detrital material) to higher percentages of detrital material in winter (up to 20–40%). Reflecting these mineralogical variations, δ¹³C and δ¹⁸O values of calcite from sediment traps are more negative in summer than in winter times. Since no significant variations in isotopic composition of lake water were detected over one year, factors controlling oxygen isotopic composition of calcite in sediment traps are the precipitation temperature, and the percentage of resuspended and detrital calcite. Samples taken close to the river inflow generally have higher δ values than the others, confirming detrital influence. SEM and isotopic studies on different size fractions (<2, 2–6, 6–20, 20–60, >60 μm) of winter and summer samples allowed the recognition of resuspension and to separate new endogenic calcite from detrital calcite. Fractions>60 and <2 μm have the highest percentage of detritus. Fractions 2–6 and 6–20 μm are typical for the new endogenic calcite in summer, as given by calculations assuming isotopic equilibrium with local water. In winter such fractions show similar values than in summer, indicating resuspension. Using the isotopic composition of sediment traps material and of different size fractions, as well as the isotopic composition of lake water, the water temperature measurements and mineralogy, we re-evaluated the bulk carbonate potential for palaeoclimatic reconstruction in the presence of detrital and re-suspended calcite. This re-evaluation leads to the following conclusion: (1) the endogenic signal can be amplified by applying a particle-size separation, once the size of endogenic calcite is known from SEM study; (2) resuspended calcite does not alter the endogenic signal, but it lowers the time resolution; (3) detrital input decreases at increasing distances from the source, and it modifies the isotopic signal only when very abundant; (4) influence of detrital calcite on bulk sediment isotopic composition can be calculated.     

Atomistic models of carbonate minerals: Bulk and surface structures,defects, and diffusion

We review the use of interatomic potentials to describe the bulk and surface behavior of carbonate materials. Interatomic pair potentials, describing the Ca 2+ -O interactions and the C-O bonding of the CO 3 2 m anion group, are used to evaluate the lattice, elastic, dielectric, and vibrational data for calcite and aragonite. The resulting potential parameters for the carbonate group were then successfully transferred to models of the structures of rhombohedral carbonates of Mn, Fe, Mg, Ni, Zn, Co, and Cd. Simulations of the (10 1 4) cleavage surface of calcite, magnesite, and dolomite show that these surfaces undergo relaxation leading to the rotation and distortion of the carbonate group with associated movement of cations. The influence of water on the surface structure has been investigated for monolayer coverage. The extent of carbonate group distortion is greater for the dry surfaces compared to the hydrated surfaces, and for the dry calcite relative to that for dry dolomite or magnesite. Point defect calculations for the doping of calcite indicate an increase in defect formation energy with increasing size of the substituting divalent ion. Migration energies for Ca, Mg, and Mn in calcite suggest a strong preference for diffusion along pathways roughly parallel to the c -axis rather than along the ab -plane.     

The structure of a reduced mutant T4 glutaredoxin

The mutant T4 glutaredoxin where the active site residues Val¹⁵ and Tyr¹⁶ have been substituted by Gly and Pro, respectively, crystallizes in a form where the active site disulfide is accessible to reagents. Treatment of the crystals with dithiotreitol causes very subtle changes in the overall glutaredoxin structure. The main differences are seen around the active site where the sulfurs of Cys¹⁴ and Cys¹⁷ move apart slightly.     

Cu ions interact with cell membranes

The influence of Cu²⁺ ions on the physical properties of resealed human erythrocyte membranes was studied by fluorescence spectroscopy. A net ordering effect was observed at the hydrophobic–hydrophilic interface both in the bulk as well as in the lipid–protein boundary. The explanation for this result was found by X-ray diffraction performed in multilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. Cu²⁺ did not significatively affect the structure of DMPE; however, DMPC polar head and hydrocarbon chain arrangements were perturbed at low but reordered at high Cu²⁺ concentrations. These effects were respectively explained in terms of a limited and extended interaction between Cu²⁺ ions and DMPC PO₄⁻ groups. Thus, the ordering effect in the erythrocyte membrane could be based on the interaction of this cation with phosphatidylcholine phosphate groups located in its outer leaflet. This binding, besides producing a decrease of membrane fluidity, might also induce a change in its electric field. These two effects should affect the activity of membrane proteins, particularly of ion channels. In fact, it was found that increasing concentrations of Cu²⁺ ions applied to either the mucosal or serosal surface of the isolated toad skin elicited a dose-dependent decrease of the short-circuit current (SCC) and of the potential difference (PD). These results lead to the conclusion that Cu²⁺ ions inhibited Na⁺ transport across the epithelial cell membranes.     

Effects of soil frost on nitrogen net mineralization, soil solution chemistry and seepage losses in a temperate forest soil

Freezing and thawing may alter element turnover and solute fluxes in soils by changing physical and biological soil properties. We simulated soil frost in replicated snow removal plots in a mountainous Norway spruce stand in the Fichtelgebirge area, Germany, and investigated N net mineralization, solute concentrations and fluxes of dissolved organic carbon (DOC) and of mineral ions (NH₄⁺, NO₃⁻, Na⁺, K⁺, Ca²⁺, Mg²⁺). At the snow removal plots the minimum soil temperature was −5 °C at 5 cm depth, while the control plots were covered by snow and experienced no soil frost. The soil frost lasted for about 3 months and penetrated the soil to about 15 cm depth. In the 3 months after thawing, the in situ N net mineralization in the forest floor and upper mineral soil was not affected by soil frost. In late summer, NO₃⁻ concentrations increased in forest floor percolates and soil solutions at 20 cm soil depth in the snow removal plots relative to the control. The increase lasted for about 2–4 months at a time of low seepage water fluxes. Soil frost did not affect DOC concentrations and radiocarbon signatures of DOC. No specific frost effect was observed for K⁺, Ca²⁺ and Mg²⁺ in soil solutions, however, the Na⁺ concentrations in the upper mineral soil increased. In the 12 months following snowmelt, the solute fluxes of N, DOC, and mineral ions were not influenced by the previous soil frost at any depth. Our experiment did not support the hypothesis that moderate soil frost triggers solute losses of N, DOC, and mineral ions from temperate forest soils.     

Late glacial and early Holocene palaeoenvironmental changes in Geneva Bay (Lake Geneva, Switzerland)

Detailed interdisciplinary investigations demonstrate that Geneva Bay (Lake Geneva) sediments clearly record important palaeoenvironmental and palaeoclimatic changes occurred during the Late glacial and early Holocene. Sediments are in fact differentiated by changes in texture, mineralogical and geochemical composition. Distal turbidite and glacial rhythmite deposition associated with wind-transported sediment supply dominate during the Oldest Dryas. These were replaced during the Allerød by detrital settling of sediment from turbid water and by endogenic calcite precipitation. The Younger Dryas climate reversal (for the first time in Lake Geneva well documented by a pollen record) was characterized by an increase in detrital supply owing to increased run-off from the bay slopes surrounding and within the catchment area, caused by thinning of vegetation cover. A brief pause in endogenic precipitation related to decreased productivity also occurs at this time. Endogenic carbonate sedimentation abruptly resumed at the start of the Preboreal biozone in response to the rapid global climatic warming. In the middle Preboreal, renewed detrital sedimentation is interpreted as the sedimentological response to increased erosion in high-altitude regions of the catchment area, caused by a minor early Holocene cooling phase (Preboreal oscillation), and interrupts the trend towards increasing endogenic calcite precipitation. Favourable limnic conditions are reached during the late Preboreal, when diatom–calcite rhythmites begin to form. Stable isotope analysis (δ¹⁸O, δ¹³C) in bulk carbonate highlight the transition from clastic-dominated to endogenic-dominated sedimentation. Endogenic calcite deposition continues during the Boreal biozone, occasionally interrupted by local high-energy sedimentary processes (wave-induced erosion and reworking of littoral deposits) enhanced by progressive lake-level lowering. During the Older Atlantic biozone, sedimentation was mainly dominated by low-energy deposition, creating enhanced conditions for the development of benthic fauna. We will discuss the factors that make Geneva Bay an important site for recording the Late glacial–Holocene climate and environmental changes. The comparison with other Swiss Plateau lacustrine systems allowed us to emphasize the role played by the particular geographical and morphological setting of the site investigated and links with climate-sensitive regions in the catchment area.     

不同炭化温度制备的蚕丝被废弃物生物炭对重金属Cd2+的吸附性能

以蚕丝被废弃物为原料,在300、500和700 ℃高温缺氧条件下热解炭化制备成3种生物炭(BC300、BC500和BC700).利用扫描电镜(SEM)、傅里叶红外光谱仪(FT-IR)、X-射线衍射仪(XRD)、比表面积分析仪等对其理化性质进行表征,并研究了不同温度下制备的生物炭对溶液中Cd²⁺的吸附特性.结果表明: 随着炭化温度上升,BET比表面积、pH、灰分均增大,生物炭表面形态结构越来越不规则.XRD结果显示:不同温度下获得的生物炭中均含有一定量的方解石,FT-IR光谱图上的峰主要为-OH和方解石典型的吸收峰;pH对生物炭吸附Cd²⁺的影响不大;Langmuir方程能更好地拟合3种生物炭对Cd²⁺的吸附等温过程,其最大吸附量分别为25.61、52.41和91.07 mg·g^-1.3种生物炭对Cd²⁺吸附过程均更符合准二级动力学方程,且BC700对Cd²⁺的吸附效果最佳.进一步研究离子浓度及阳离子共存对BC700吸附Cd²⁺的影响,结果显示: NaCl浓度越高,对Cd²⁺的吸附抑制越明显;共存阳离子中,Ca²⁺和Mg²⁺对Cd²⁺的吸附抑制更明显,而K⁺几乎无影响.因此,以蚕丝被废弃物制备的生物炭作为去除水体中Cd²⁺的吸附剂具有较强的应用潜力.     

Effects of divalent metal ions on chlorophyll a fluorescence in isolated spinach chloroplasts

The effects of divalent metal ions on the yields of chlorophyll a fluorescence were investigated in isolated spinach chloroplasts at room and liquid nitrogen temperatures. Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺ and Mn²⁺ increased the yields of fluorescence emission at 684 and 695 nm from pigment system II and decreased that at 735 nm from pigment system I. Al³⁺ showed similar but less significant effects on the fluorescence yields. Zn²⁺ and Cd²⁺ showed no significant effect on the fluorescence yields at concentrations lower than 5 mM.

In accordance with the results of our previous study concerning the effects of Mg²⁺ on the excitation transfer in the chloroplasts, it was concluded that ions of alkaline earths and manganese suppress the excitation transfer from bulk chlorophylla of pigment system II to that of pigment system I.     

The chemical microenvironment of the symbiotic planktonic foraminifer Orbulina universa

Microsensor measurements of CO₂, O₂, pH and Ca²⁺ in the vicinity of the symbiont-bearing planktonic foraminifer Orbulina universa showed major light-modulated changes in the chemical microenvironment due to symbiont photosynthesis, respiration of the holobiont, and precipitation of the calcite shell. Under saturating light conditions, microprofiles measured towards the shell surface showed an O₂ increase of up to 220% air saturation, a decrease in CO₂ concentration to 4.9 μM, and a pH increase to 8.8 due to symbiont photosynthesis. The Ca²⁺ concentration decreased to ∼9.6 mM in two specimens, while it increased to 10.2-10.8 mM in three other specimens kept in light. In darkness, the respiration of the community decreased the O₂ concentration to 82% of air saturation, CO₂ increased up to 15 μM, the pH decreased to 8.0, and the Ca²⁺ concentration increased up to 10.4 mM. These data, and derived calculations of the distribution of HCO₃^- and CO₃^2- near the shell, showed that the carbonate system in the vicinity of O. universa was significantly different from conditions in the surrounding seawater, both in light and darkness, due to the metabolism of the foraminifer and its associated algae. Experimental light-dark cycles indicated a sufficient CO₂ supply sustaining high carbon fixation rates of the symbiotic algae via conversion of HCO₃^- or via CO₂ release from calcification and host respiration. Our findings on irradiance-dependent CO₂ and pH changes in the vicinity of symbiont-bearing planktonic foraminifera give direct experimental evidence for the predictions of isotope fractionation models used in palaeoclimatology stating that metabolic processes affect the isotopic carbon signal (δ¹³C) in foraminifera.     

Perlwapin, an abalone nacre protein with three four-disulfide core (whey acidic protein) domains, inhibits the growth of calcium carbonate crystals

We have isolated a new protein from the nacreous layer of the shell of the sea snail Haliotis laevigata (abalone). Amino acid sequence analysis showed the protein to consist of 134 amino acids and to contain three sequence repeats of approximately 40 amino acids which were very similar to the well-known whey acidic protein domains of other proteins. The new protein was therefore named perlwapin. In addition to the major sequence, we identified several minor variants. Atomic force microscopy was used to explore the interaction of perlwapin with calcite crystals. Monomolecular layers of calcite crystals dissolve very slowly in deionized water and recrystallize in supersaturated calcium carbonate solution. When perlwapin was dissolved in the supersaturated calcium carbonate solution, growth of the crystal was inhibited immediately. Perlwapin molecules bound tightly to distinct step edges, preventing the crystal layers from growing. Using lower concentrations of perlwapin in a saturated calcium carbonate solution, we could distinguish native, active perlwapin molecules from denaturated ones. These observations showed that perlwapin can act as a growth inhibitor for calcium carbonate crystals in saturated calcium carbonate solution. The function of perlwapin in nacre growth may be to inhibit the growth of certain crystallographic planes in the mineral phase of the polymer/mineral composite nacre.     

Mechanism of iron uptake by plants

Abstract. Green plants require a continuous supply of Fe as they grow, because Fe does not not move from the older to the newer leaves. Soils do not lack Fe per se , but it may not be available to plants grown in alkaline soils. Plants are classed 'Fe-efficient' if they respond to Fe-deficiency stress by inducing biochemical reactions that make Fe available in a useful form, and 'Fe-inefficienT' if they do not. Iron uptake induced in response to Fe stress involves release of hydrogen ions and reductants by the root. The lowered pH and presence of reductant at the root zone, along with reduction of Fe³⁺ to Fe²⁺ at the root surface, enables Fe²⁺ to be taken up primarily through the young lateral roots. Ferrous iron is present throughout the protozylem and may or may not have entered the root by a carrier. The root-absorbed Fe²⁺ is oxidized to Fe³⁺ at the junction of the protoxylem and the metaxylem, chelated by citrate, and then transported in the metaxylem to the plant top. In the plant, the chemical reactions injuced by Fe-deficiency stress may affect nitrate reductase activity, use of Fe from Fe³⁺ phosphate and chelating agents, and tolerance to heavy metals. An efficient mechanism for Fe uptake in roots appears to be important for the efficient use of Fe in plant tops.     

Copper-Ligand Interactions and Physiological Free Radical Processes. pH-Dependent Influence of Cu2+ Ions on Fe2+-Driven OH- Generation

Prior to comparative studies on the reactivity of various copper complexes with respect to OH radicals, the influence of free Cu²⁺ ions on the superoxide-independent generation of OH radicals through Fenton assays and water gamma radiolysis has been tested in the present work.

Cu²⁺ ions have been shown to behave in a distinct manner towards each of these two production systems. As was logically expected from the noninvolvement of copper in OH^- radical production through gamma radioiysis, no influence of Cu²⁺ ions has been observed on the amount of radicals detected in that case. In contrast, Cu²⁺ ions do influence OH^- radical generation through iron-driven Fenton reactions, but differently depending on copper concentration.

When present in high concentrations, Cu²⁺ ions significantly contribute to OH^- radical production, which confirms previous observations on the reactivity of these in the presence of hydrogen peroxide. At lower levels corresponding to copper/iron ratios below unity on the contrary, Cu²⁺ ions behave as inhibitors of the OH^- production in a pH-dependent manner over the 1-6 range investigated: the lower the pH, the greater the inhibition.

The possible origin of this previously unreported inhibitory effect is discussed.     

丛枝菌根真菌调控根系构型与矿质元素平衡提高西瓜植株耐盐性的研究

丛枝菌根（arbuscular mycorrhiza,AM）真菌可通过多种途径或机制来增强植物的耐盐性,进而促进植株的生长发育。本研究在盆栽条件下设西瓜Citrullus lanatus品种‘京欣四号’幼苗接种变形球囊霉Glomus versiforme和不接种以及施加和不施加100mmol/L NaCl共4个处理,测定植株根系菌根侵染状况、根系构型及其根茎叶中钾（K）、钙（Ca）、磷（P）、钠（Na）含量、K⁺/Na⁺、Ca²⁺/Na和植株生长状况等。AM真菌显著增加了盐胁迫下西瓜植株总根长度、根表面积、根体积和根尖数量,改善了根系构型;促进了西瓜根系对K、Ca和P的吸收,提高了茎Ca和P含量、根系K和P含量、K⁺/Na⁺和Ca²⁺/Na⁺,而降低了根Na⁺含量;茎P和Na⁺、叶K和Ca的含量显著高于其他器官相应含量。典范对应分析表明,根系K含量、K⁺/Na⁺和Ca²⁺/Na⁺与总根长度、主根长度、根表面积、根体积、根尖数量、根平均直径呈正相关;叶K⁺/Na⁺与主根长度呈正相关;根系Na⁺含量与根系总根长、根平均直径和根尖数量呈负相关。接种AM真菌改善了矿质元素平衡及其分配状况。盐胁迫后西瓜植株对菌根的依赖性增强。结果表明,K、Ca、P是AM真菌介导植物耐盐性的关键养分;K⁺/Na⁺和Ca²⁺/Na⁺是重要的矿质元素平衡指标,接种AM真菌能调控植物根系构型和矿质元素平衡状况,从而缓解盐胁迫对西瓜生长的抑制作用,提高植株的耐盐性。     

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.     

岩溶洞穴微生物沉积碳酸钙——以贵州石将军洞为例

为探讨洞穴微生物沉积碳酸钙作用对洞穴沉积物的影响,利用传统生物学方法,采集贵州中西部地区石将军洞洞穴沉积物表面的微生物样品,结合洞穴监测数据和理化背景资料,利用B-4培养基和B-4C培养基对洞穴细菌进行筛选和纯化,分离出能沉积碳酸钙的菌种,观察和了解洞穴细菌形成的CaCO3晶体,应用X射线衍射分析仪(XRD)分析细菌形成的CaCO3晶体成分,并利用扫描电子显微镜(SEM)观察晶体结构特征。结果表明:1)在B-4培养基下微生物产生的碳酸钙晶体主要为方解石、球霰石和方解石混合物、球霰石,这种变化与培养基pH值的增幅相关;同时,在添加Mg离子的B-4C培养基下形成的碳酸钙晶体主要为方解石,此外,研究中并未检测到文石晶体。2)通过SEM扫描,发现微生物作用形成的碳酸钙晶体存在不规则六方体、柱状体、四方体层状、半球状等,这些晶体形态在化学作用系统下少见,多见于微生物作用形成的方解石。此外,晶体中微生物作用痕迹明显,微生物作用贯穿于整个沉积过程。     

The role of calcium in buffering soils

Abstract. Calcium is the soluble cation that occurs in largest amount in most soils. It does not take part directly in the proton transfer reactions involved in pH-buffering, but it provides the cation charge balance for these reactions. It is also the complementary cation in formulations of chemical potential for many other ions in soils. The presence of free calcium carbonate in calcareous soils. The presence of free calcium carbonate in calcareous soils ensures a very high soil buffer capacity; d AB/ d pH ≃ 1000 Eq. m⁻³.
In acid mineral soils, dissolution and precipitation of aluminium ions contribute to the buffering processes, but most of the buffering in non-calcareous soils is caused by specific ion adsorption at variable-charge sites, in particular those associated with the dissociation of humus acids. Typical buffer capacity values of non-calcareous soils vary from 10 Eq. m⁻³ for sandy soils to 100 Eq. m⁻³ for peats. The pH changes associated with buffering are produced by leaching of calcium from soil, or by adding calcium to soil in liming materials.     

Allosteric Properties of Ox Brain Nicotinamide–Adenine Dinucleotide Dependent Isocitrate Dehydrogenase

Abstract: The kinetic and regulatory properties of a partly purified preparation of ox brain NAD⁺-dependent isocitrate dehydrogenase have been studied at pH 7.5. The enzyme exhibits rate cooperativity with respect to isocitrate but shows normal hyperbolic kinetics with respect to NAD⁺. ADP activates the enzyme by decreasing the substrate concentrations that are necessary to give half-maximal velocity, but it has no effect on the Hill constant for isocitrate unless Mg²⁺ ions are replaced by Mn²⁺ ions in the reaction mixture. Citrate and tricarballylate activate the enzyme in a similar fashion to ADP. Higher concentrations of citrate cause inhibition but this could be overcome by raising the concentration of Mg²⁺ ions, suggesting that the inhibition by this compound might be due to its acting as a chelating agent. NADH and NADPH were competitive inhibitors with respect to NAD⁺ but the product, 2-oxoglutarate, was not inhibitory. γ-Aminobutyrate and a number of other compounds involved in the γ-aminobutyrate pathway had no significant effect on the activity of the enzyme.     

Ion supply capacity of roots in relation to rejuvenation of primary leaves in vivo

Removal of the shoot above the primary node (detopping) of 3-week-old bean plants ( Phaseolus vulgaris L. cv. Contender) altered the metabolism and development of the remaining leaves. An increase in levels of chlorophyll, protein, stomatal opening, photosynthesis and growth, i.e. rejuvenation of primary leaves, was established within 7 days of detopping. These levels were maintained while the primary leaves of equivalent intact plants senesced.
The flux of xylem solution (mineral ions, cytokinins and water) into leaves is related to the leaf area to be supplied and root supply capacity; it has been suggested that detopping leads to an increased availability of root-supplied solutes and hence rejuvenation of the remaining leaves. This assumes however that root output of solutes is not decreased by the defoliation treatment.
We found that root output of ions (electrical conductivity of passive xylem exudate) in detopped plants was 30% lower than in intact plants after 24 h and 60% lower after 7 days. The output of Ca²⁺, Mg²⁺ and K⁺ were similarly reduced 7 and 14 days after detopping as were fresh and dry weights of roots. Furthermore, neither the calculated xylem flux of ions nor directly measured levels of Ca²⁺, Mg²⁺ and K⁺ were significantly increased in leaves of detopped plants during their rejuvenation. We therefore conclude that root output is tightly coupled to shoot demand and that the apparent rejuvenation of primary leaves caused by detopping bean plants is not a consequence of increased xylem flux of mineral ions into the leaves.     

Interfacial tension of phosphatidylcholine-phosphatidylserine system in bilayer lipid membrane

The effect of pH of electrolyte solution on the interfacial tension of lipid membrane formed of phosphatidylcholine (PC, lecithin)–phosphatidylserine (PS) system was studied. In this article, three models describing the H⁺ and OH⁻ ions adsorption in the bilayer lipid surface are presented. In Model I and Model II, the surface is continuous with uniformly distributed functional groups constituting the centres of H⁺ and OH⁻ ions adsorption while in the other the surface is built of lipid molecules, free or with attached H⁺ and OH⁻ ions. In these models contribution of the individual lipid molecule forms to interfacial tension of the bilayer were assumed to be additive. In Model III the adsorption of the H⁺ and OH⁻ ions at the PC–PS bilayer surface was described in terms of the Gibbs isotherm. Theoretical equations are derived to describe this dependence in the whole pH range.     

Formation and mosaicity of coccolith segment calcite of the marine algae Emiliania huxleyi

Coccolithophores belong to the most abundant calcium carbonate mineralizing organisms. Coccolithophore biomineralization is a complex and highly regulated process, resulting in a product that strongly differs in its intricate morphology from the abiogenically produced mineral equivalent. Moreover, unlike extracellularly formed biological carbonate hard tissues, coccolith calcite is neither a hybrid composite, nor is it distinguished by a hierarchical microstructure. This is remarkable as the key to optimizing crystalline biomaterials for mechanical strength and toughness lies in the composite nature of the biological hard tissue and the utilization of specific microstructures. To obtain insight into the pathway of biomineralization of Emiliania huxleyi coccoliths, we examine intracrystalline nanostructural features of the coccolith calcite in combination with cell ultrastructural observations related to the formation of the calcite in the coccolith vesicle within the cell. With TEM diffraction and annular dark‐field imaging, we prove the presence of planar imperfections in the calcite crystals such as planar mosaic block boundaries. As only minor misorientations occur, we attribute them to dislocation networks creating small‐angle boundaries. Intracrystalline occluded biopolymers are not observed. Hence, in E. huxleyi calcite mosaicity is not caused by occluded biopolymers, as it is the case in extracellularly formed hard tissues of marine invertebrates, but by planar defects and dislocations which are typical for crystals formed by classical ion‐by‐ion growth mechanisms. Using cryo‐preparation techniques for SEM and TEM, we found that the membrane of the coccolith vesicle and the outer membrane of the nuclear envelope are in tight proximity, with a well‐controlled constant gap of ~4 nm between them. We describe this conspicuous connection as a not yet described interorganelle junction, the “nuclear envelope junction”. The narrow gap of this junction likely facilitates transport of Ca²⁺ ions from the nuclear envelope to the coccolith vesicle. On the basis of our observations, we propose that formation of the coccolith utilizes the nuclear envelope–endoplasmic reticulum Ca²⁺‐store of the cell for the transport of Ca²⁺ ions from the external medium to the coccolith vesicle and that E. huxleyi calcite forms by ion‐by‐ion growth rather than by a nanoparticle accretion mechanism.