Participation of vacuoles in regulation of levels of K+, Mg2+ and orthophosphate ions in cytoplasm of the yeast Saccharomyces carlsbergensis

Intracellular distributions of K⁺, Mg²⁺ and orthophosphate under various conditions of cultivation or incubation of the yeast Saccharomyces carlsbergensis were studied by differential extraction of ion pools. The decisive role of vacuolar compartmentation of ions in regulation of K⁺, Mg²⁺ and orthophosphate levels in the yeast cytoplasm was shown. The content of intracellular K⁺ and Mg²⁺ in yeast increased or decreased primarily depending on the increase or decrease in the vacuolar ion pool. The levels of K⁺ and Mg²⁺ in the cytoplasm were practically unchanged. Vacuoles were involved in regulation of Mn²⁺ concentration in the cytoplasm of the yeast S. carlsbergensis accumulating this ion in the presence of glucose. Alongside the vacuolar compartmentation, the chemical compartmentation, i. e. formation of bound Mg²⁺, Mn²⁺ and K⁺ was, evidently, also involved in the control of ion levels in the cytoplasm. The orthophosphate level in the yeast cytoplasm was regulated by its accumulation in vacuoles and biosynthesis of inorganic polyphosphates in these organelles. The biosynthesis of low-molecular weight polyphosphates occurred parallel to the accumulation of Mg²⁺ or Mn²⁺ in vacuoles, thus confirming the availability of the other mechanism for the transport of these ions through the tonoplast differing from the transport mechanism through the plasmalemma.     

The Effect of Copper and Lead Ions on Growth and Lipid Composition of the Fern Matteuccia sthruthiopteris

In the present study, the effect of copper (Cu²⁺) and lead (Pb²⁺) ions on the growth and lipid composition of various parts of the fern, Matteuccia sthruthiopteris, was examined. Plants were incubated in the presence or absence of 1, 10, 100 μM of Cu(NO₃)₂ or Pb(NO₃)₂. Cu²⁺ and Pb²⁺ ions at concentrations of 1 and 10 μM caused an increased growth of the roots and leaves. A higher concentration of Pb²⁺ did not show any effect on growth, whereas that of Cu²⁺ slowed down the growth of the whole plants. The roots accumulated more than 700 μg of Cu²⁺ and 400 μg of Pb²⁺ per 1 g dry weight when the plants were incubated with the higher concentrations of metals, whereas in the leaves the concentration of Cu²⁺ was much lower and did not exceed 12 μg/g dry weight. No accumulation of Pb²⁺ ions by leaves was detected. The lipid composition of photosynthetic leave tissues was shown to be affected by the presence of metal ions in the root medium at either concentration studied. Various changes in lipid classes were noted as responsive reactions of M. sthruthiopteris to the heavy metal ions in nutrient medium. Cu²⁺ ions decreased the content of total lipids, total phospholipids, and individual phosphatidylcholines and phosphatidylethanolamines, whereas Pb²⁺ ions caused a decrease in the content of total lipids and glycolipids. Changes in the lipid composition were more pronounced in the mature leaves than in the scrolls of the studied fern.     

The effect of inactivation of calcium channels by intracellular Ca2+ ions in the bursting pancreatic β-cells

Based on recently determined ionic channel properties, a simple theoretical model for the burst activity of the pancreatic β-cell is formulated in this paper. The model contains an inward voltage-activated Ca²⁺ current which is inactivated by intracellular calcium ions and an outward K⁺ current that is activated by the membrane potential. The probability of opening of the channel gates is represented by Boltzmann equations. Our model is applicable in a regime where an ATP-blockable K⁺ channel is inhibited. In this regime, glucose is treated as an activator for the rate of efflux of intracellular Ca²⁺ ions, and hence its effect is equated tok _Ca, the efflux rate constant. In addition, intracellular H⁺ ion, which is a byproduct of the glycolytic metabolic process, is treated as a competitive inhibitor for Ca²⁺ ion. Since H⁺ is a competitive inhibitor (according to our assumption), its effect is equated to the strength of the Ca_i dissociation constantK _h. In the model, a Ca²⁺ binding site is assumed to exist in the inner membrane of the voltage-gated Ca²⁺ channel. The model predicts that a spike and burst electrical pattern can be generated by varyingk _ca and that a given pattern may produce different levels of intracellular Ca²⁺ depending onK _h. In other words, it predicts that levels of [Ca²⁺]_i can be separated from the electrical activity by controlling the concentration of glucose and pH appropriately. This may account for the experimental observation of Lebrun et al. (1985) that insulin secretion is not correlated to the burst of electrical activity.     

Biosynthesis of citric and isocitric acids from ethanol by mutant Yarrowia lipolytica N 1 under continuous cultivation

The effect of ethanol, zinc, and iron (Fe²⁺ and Fe³⁺) concentration and of oxygen supply on cell growth and the production of citric acid (CA) and isocitric acid (ICA) from ethanol by mutant Yarrowia lipolytica N 1 was studied under continuous cultivation. The following peculiarities of Y. lipolytica metabolism were found: (1) intensive CA production occurred under yeast growth limitation by nitrogen; (2) inhibition of yeast growth by ethanol was accompanied by significant alterations in fatty acid composition of lipids; (3) the production of CA and ICA from ethanol required high concentrations of zinc and iron ions; (4) the intracellular iron concentration determined whether CA or ICA was predominantly formed; (5) the cell's requirement for oxygen depended on the intracellular iron concentration. The events taking place in the production of CA and ICA were evaluated through the activities of enzyme systems involved in the metabolism of ethanol and CA in this strain. Electronic Publication     

Spatio-Temporal Distributions of Metal Ions and Taxol of Taxus cuspidata Cells Immobilized on Polyurethane Foam

Distinct spatio-temporal variations of metal ions and Taxol production were observed for Taxus cuspidata cells immobilized on polyurethane foam. The Taxol content in the inner foam layer reached 215 μg g⁻¹ at day 30, which was 40-fold higher than that in the outer foam layer, and the Ca²⁺ and Mg²⁺ contents were 5.3 and 3.7 times higher, while the K⁺ content was 5.5 times lower. Thus higher intracellular Ca²⁺ and Mg²⁺ contents and lower intracellular K⁺ content may favor the Taxol biosynthesis in immobilized Taxus cuspidata.     

Spontaneous inactivation of the Ca-sensitive K channels of human red cells at high intracellular Ca activity

Ionophore A23187-mediated Ca²⁺-induced oscillations in the conductance of the Ca²⁺-sensitive K⁺ channels of human red cells were monitored with ion specific electrodes. The membrane potential was continuously reflected in CCCP-mediated pH changes in the buffer-free medium, changes in extracellular K⁺ activity were followed with a K⁺-selective electrode, and changes in the intracellular concentration of ionized calcium were calculated on the basis of cellular ⁴⁵Ca content. An increased cellular ⁴⁵Ca content at the successive minima of the oscillations where the K⁺ channels are closed indicates that the activation of the channels might be a (dCa²⁺/dt)-sensitive process and that accommodation to enhanced levels of intracellular free calcium may occur. An incipient inactivation of the K⁺ channels at intracellular ionized calcium levels of about 10 μM and a concurrent membrane potential of about −65 mV was observed. At a membrane potential of about −70 mV and an intracellular concentration of about 2·10⁻⁴M no inactivation of K⁺ channels took place. Inactivation of the K⁺ channels is suggested to be a compound function of the intracellular level of free calcium and the membrane potential. The observed sharp peak values in cellular ⁴⁵Ca content support the notion that a necessary component of the oscillatory system is a Ca²⁺ pump operating with a significant delay in the activation/inactivation process in response to changes in cellular concentration of ionized calcium.     

Correlation between the activity of intracellular Ca<Superscript>2+</Superscript>-dependent proteinase and the content of membrane lipid components in mussel, <Emphasis Type="Italic">Mytilus edulis</Emphasis>, upon accumulation of heavy metals

The correlation between the activity of calpains and the content of membrane lipid components in the organs of mussels, Mytilus edulis L., is shown in the aquarium experiment on studying the response of mussels to the action of copper and cadmium ions. This correlation is most likely explained by the effector activity of membrane lipid components (arachidonic acid and phosphatidylinositol) with respect to Ca²⁺-channels. Thus, the correlation between the membrane lipid composition and the functional activity of proteins, which is defined by the level of intracellular Ca²⁺, is found in the experiment.     

ENHANCEMENT OF INTRACELLULAR PROLINE LEVEL IN CELLS OF ANACYSTIS NIDULANS (CYANOBACTERIA) EXPOSED TO DELETERIOUS CONCENTRATIONS OF COPPER1

The intracellular proline level in Anacystis nidulans cells was enhanced when the cells were exposed to sublethal concentrations of Cu²⁺; the degree of enhancement was positively related to the concentration of Cu²⁺. Analysis by high-performance liquid chromatography confirmed that the enhancement of proline levels was the most pronounced change in the composition of the free amino acid pool during copper treatment. A direct supply of exogenous proline to the cultures lowered the inhibitory influence of Cu²⁺on the growth of cells. Further experiments showed that the supply of exogenous proline lowered the leakage of potassium ions from cells exposed to deleterious concentrations of Cu²⁺. The inhibition of potassium leakage was particularly pronounced when proline was supplied prior to Cu²⁺treatment. The present study suggests that enhanced proline protects cell membranes from being affected by deleterious concentrations of Cu²⁺.     

Local ion currents controlling the localized cytoplasmic movement associated with feeding initiation ofNoctiluca

Summary We used an extracellular vibrating probe to investigate local transmembrane ion currents that occur just before and during localized cytoplasmic movement associated with feeding initiation in the marine dinoflagellateNoctiluca, Our results indicates that the currents flow only through a specialized cellular region, the sulcus, suggesting a heterogeneous distribution of an ion channel in the cell membrane. A current enters into the middle of the sulcus where the cytostome exists and leaves from both ends of the sulcus. The mean inward and outward current densities were approx. + 11 and — 1 A·cm^–2, respectively. The cytoplasm began to stream toward the cytostome in association with the currents and then aggregated around it. Removal of Ca²⁺, Na⁺, or Mg²⁺ ions from the external medium diminished the inward current. Ca²⁺ ions were proved to carry only 5% of the inward current. The Ca²⁺ current appears to be enough to raise Ca²⁺ concentration in a localized region of the cytoplasm, causing the cytostome-directed cytoplasmic movement. Rest of the current seems to be carried by Na⁺ ions. Most of the outward current was inhibited by an ion pump inhibitor, but the current-carrying ion species could not be identified.     

Effects of calcium and manganese ions on the helix–coil transition of DNA

The thermal denaturation method was employed to study the effect of Ca²⁺ and Mn²⁺ ions on the DNA helix–coil transition parameters at Na⁺ concentrations of 10^?3–10^?1M. At low ion concentrations, thermal stability increases, the melting range passes through a maximum, and the denaturation curves become asymmetric. These changes are quantitatively similar for Mn²⁺ and Ca²⁺ ions. With a further increase in the concentration of bivalent ions, the conformational transition temperatures pass through a maximum, and the melting range first tends to saturation and then rapidly decreases to 1–2°C. The Mn²⁺ concentrations, at which the above effects occur, are an order of magnitude lower than the Ca²⁺ concentrations. Comparison of experimental results and calculation in terms of the ligand theory permitted estimation of binding constants characterizing association between Mn²⁺ and Ca²⁺ ions and bases of native and denatured DNA. We show that, unlike the interaction with phosphates, bivalent ion–DNA base binding is weakly dependent on monovalent ion concentration in the solution.     

Dual role of ryanodine-sensitive calcium stores in central neurons

The ryanodine-sensitive intracellular Ca²⁺ stores are known to play a major role in excitation-contraction coupling in muscles. Although these stores are also abundantly present in central neurons, their functional role in these cells remains unclear. Using fluorometric digital imaging of the intracellular Ca²⁺ concentration ([Ca²⁺] _i ) in rat hippocampal slices, we investigated the dynamic properties of the ryanodine-sensitive Ca²⁺ stores inCA1 hippocampal pyramidal cells. We found that at rest the ryanodine-sensitive Ca²⁺ stores are functioning predominantly as a “sink” for Ca ions responding to an increase in [Ca²⁺] _i with an increase in the amount of Ca ions accumulated inside the stores. If, however, [Ca²⁺] _i increases significantly, as happens during strong neuronal discharges, the ryanodine-sensitive Ca²⁺ stores respond with Ca²⁺ release, thus acting as an amplifier of the intracellular Ca²⁺ signal.     

Control of membrane potential and excitability ofChara cells with ATP and Mg2+

Summmary Electric characteristics of internodalChara australis cells, from which the tonoplast had been removed by vacuolar perfusion with media containing EGTA, were studied in relation to intracellular concentrations of ATP and Mg²⁺ using the ordinary microelectrode method and the open-vacuole method developed by Tazawa, Kikuyama and Nakagawa (1975.Plant Cell Physiol. 16:611). The concentration of ATP was decreased by introducing hexokinase and glucose into the cell and that of Mg²⁺ by introducing EDTA or CyDTA. The membrane potential decrease and the membrane resistance increase were both significant when the ATP or Mg²⁺ concentration was decreased. An ATP-dependent membrane potential was also found in other species of Characeae,Nitella axillaris andN. pulchella. Excitability of the membrane was also completely lost by reducing the ATP or Mg²⁺ concentration. Both membrane potential and excitability were recovered by introducing ATP or Mg²⁺ into ATP- or Mg²⁺-depleted cells.The time course of membrane potential recovery was followed by the open-vacuole method. Recovery began as soon as intracellular perfusion with medium containing ATP and Mg²⁺ was started. Reversible transition of the membrane potential between polarized and pepolarized levels by controlling the intracellular concentration of ATP or Mg²⁺ could be repeated many times by the open-vacuole method, when the excitability was suppressed by addition of Pb²⁺ to the external medium.The ineffectiveness of an ATP analog, AMP-PNP, and the synergism of ATP and Mg²⁺ in maintaining the membrane potential and excitability strongly suggest that ATP act via its hydrolysis by Mg²⁺-activated ATPase. The passive nature of the membrane, as judged from responses of the membrane potential to changes of the external K⁺ concentration, was not altered by lowering the ATP concentration in the cell. The mechanism of membrane potential generation dependent on ATP is discussed on the basic of an electrogenic ion pump. Involvement of the membrane potential generated by the ion pump in the action potential is also discussed.     

一株耐酸微藻的分离鉴定及其对锰离子胁迫的生理响应

[目的]探讨在酸性含锰极端水环境中油球藻的生长特性及其对环境pH和Mn2+的影响.[方法]从某硫铁矿山的酸性废水库中分离获得纯化藻株,通过形态观察及18S rRNA基因测序对其进行鉴定,并着重考察了不同pH和典型金属离子Mn2+浓度对其生长特性的影响,并通过测定藻生物量、光合色素、丙二醛(malondialdehyde...     

Role of glutamine synthetase in citric acid fermentation byAspergillus niger

The activity of glutamine synthetase fromAspergillus niger was significantly lowered under conditions of citric acid fermentation. The intracellular pH of the organism as determined by bromophenol blue dye distribution and fluorescein diacetate uptake methods was relatively constant between 6·0–6·5, when the pH of the external medium was varied between 2·3–7·0.Aspergillus niger glutamine synthetase was rapidly inactivated under acidic pH conditions and Mn²⁺ ions partially protected the enzyme against this inactivation. Mn²⁺-dependent glutamine synthetase activity was higher at acidic pH (6·0) compared to Mg²⁺-supported activity. While the concentration of Mg²⁺ required to optimally activate glutamine synthetase at pH 6·0 was very high (≥ 50 mM), Mn²⁺ was effective at 4 mM. Higher concentrations of Mn²⁺ were inhibitory. The inhibition of both Mn²⁺ and Mg²⁺-dependent reactions by citrate, 2-oxoglutarate and ATP were probably due to their ability to chelate divalent ions rather than as regulatory molecules. This suggestion was supported by the observation that a metal ion chelator, EDTA also produced similar effects. Of the end-products of the pathway, only histidine, carbamyl phosphate, AMP and ADP inhibitedAspergillus niger glutamine synthetase. The inhibitions were more pronounced when Mn²⁺ was the metal ion activator and greater inhibition was observed at lower pH values. These results permit us to postulate that glutamine synthesis may be markedly inhibited when the fungus is grown under conditions suitable for citric acid production and this block may result in delinking carbon and nitrogen metabolism leading to acidogenesis     

Cd2+和Pb2+对花翅摇蚊(Chironomus kiiensis)幼虫生长发育的影响及富集效应

河流、湖泊等水生环境中普遍存在的重金属污染破坏水生生态系统并间接威胁人类健康。为探究重金属胁迫下水生昆虫花翅摇蚊（Chironomus kiiensis）生态毒理,测定了重金属Cd²⁺和Pb²⁺胁迫对花翅摇蚊化蛹率和羽化率的影响,检测了摇蚊的口器致畸与富集效应。研究结果表明,Cd²⁺和Pb²⁺影响摇蚊幼虫化蛹和羽化过程,单一重金属离子处理14 d Pb²⁺处理组的化蛹率和羽化率分别为22.22%和8.89%,低于Cd²⁺的化蛹率（25.56%）和羽化率（11.11%）,表现出更强的抑制效应。混合离子1：2和2：1配比处理组化蛹率和羽化率均为11.11%和4.44%,显著低于单一重金属离子胁迫下的化蛹率和羽化率。单一重金属离子及混合离子处理均能导致花翅摇蚊幼虫口器致畸,表现为上颚前齿断裂,中齿和基齿磨损、缺失,下唇板齿部不规则,下唇板边缘齿与中央齿磨损、断裂、增生、缺失。不同重金属离子处理下幼虫口器致畸率不同,并与暴露时间呈正相关,其中1：2配比处理14 d致畸率达到40.61%。重金属离子在摇蚊幼虫体内产生生物富集效应,单一重金属离子处理下的Pb²⁺富集含量7 d至14 d由11.46 mg/kg上升至31.32 mg/kg,不同配比混合离子处理下Pb²⁺富集含量均呈增加趋势,其中1：2配比处理组由15.48 mg/kg上升至42.50 mg/kg,而Cd²⁺在单一重金属与1：1混合离子处理组7 d至14 d的富集含量无显著性变化,2：1配比处理组由14.20 mg/kg下降至9.52 mg/kg,1：2配比由5.85 mg/kg上升至20.99 mg/kg。这些研究结果表明Cd²⁺和Pb²⁺胁迫影响花翅摇蚊幼虫生长发育且口器出现畸型,与重金属在幼虫体内的富集密切相关,为研究重金属对水生生态系统多重效应提供了理论依据。     

Copper dissociation as a mechanism of fungal laccase denaturation by humic acid

Effects of humic acid on removal of hydroxy polychlorobiphenyls (PCBs) with laccase from Trametes versicolor were studied. In the absence of humic acid, hydroxy PCBs were rapidly degraded by laccase. However, the rate constants decreased with increasing humic acid concentration, the reactions being completely inhibited at 150 mg l^-1 of humic acid. Peroxidase from Arthromyces ramosus was not inhibited by the same treatment. The activity of humic acid-deactivated laccase was completely restored by copper ions (500 M of Cu²⁺ in 150 mg l^-1 of humic acid), but not by other metal ions (Zn²⁺, Fe²⁺ and Hg²⁺). Humic acid-deactivated laccase purified by gel permeation chromatography (GPC) showed no activity against 2,2-azino-bis(3-ethylbenzthiazoline sulfonic acid) diammonium salt and 3,5-dichloro-4-hydroxybiphenyl, but its activity was restored by copper ion treatment. Humic acid-deactivated laccase showed similar properties, such as GPC retention time and copper ion requirements for activity, to those of laccase deactivated by nitrilotriacetic acid. The extent of humic acid inhibition, expressed as activity non-recoverable by copper ion treatment, increased over time more rapidly than that of the humic acid-free control. These results suggest that short-term inactivation of laccase, i.e., less than 1 day, is attributable to a depletion of copper ion.     

Effects of growth conditions on the ion composition of Bifidobacterium bifidum subsp. pennsylvanicum

The cation content of Bifidobacterium bifidum subsp. pennsylvanicum was markedly influenced by the washing procedure of the cells, by the growth phase and the temperature, and by the composition of the culture medium. Optimal retention of cations was achieved by washing with 0.25 M MgCl₂ at 20 C. The intracellular Na⁺ concentration rose during growth in normal medium to a constant value in the stationary phase, the K⁺ concentration rose in the exponential phase, but fell in the stationary phase. Cells from 29-C cultures contained more Na⁺ and less K⁺ in the stationary phase than did cells from 37-C cultures, but the total cation content was the same at 29 and 37 C.Intracellular Na⁺ and K⁺ concentrations were dependent on the concentrations in the medium and on its osmolarity. The intracellular Na⁺/K⁺ ratio varied from 0.04 to 2.3. The concentrations of Na⁺, K⁺ and phosphate in the medium hardly affected growth. Mg²⁺-deficiency of the medium markedly decreased the concentration of Mg²⁺ within the cell; its concentration in the cell sap was greatly affected, but the amount of sedimentable, bound Mg²⁺ only slightly. The content of K⁺ within the cell decreased in Mg²⁺-deficient medium, but the concentration of Na⁺ did not. Omission of Tween 80 as well as its substitution by Tween 20 caused a decrease of intracellular K⁺. Cells from Tween 40 and Tween 60 cultures additionally contained markedly less Na⁺.The present investigations have been carried out with financial support from the Netherlands Organization for the Advancement of Pure Research (ZWO) through the Netherlands Foundation for Chemical Research (SON).     

SDS-capped 1-pyrenecarboxaldehyde nanoprobe for selective detection of Cu2+ ion from water samples: Spectroscopic approach

Sodium dodecyl sulfate (SDS)-capped 1-pyrenecarboxaldehyde nanoparticles (PyalNPs) were prepared using a reprecipitation method in an aqueous medium and exhibited red-shifted aggregation-induced enhanced emission (AIEE). The dynamic light scattering (DLS) examination showed narrower particle size distribution with an average particle size of 41 nm, whereas −34.5 mV zeta potential value indicate the negative surface charge and good stability of nanoparticles (NPs) in an aqueous medium. The AIEE was seen at λ_max = 473 nm in a fluorescence spectrum of a PyalNP suspension. In the presence of Cu²⁺ ions, the fluorescence of PyalNPs quenches very significantly, even in the presence of other metal ions like Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Al³⁺, Fe²⁺, Hg²⁺, Ni²⁺ and Mg²⁺. The changes in the fluorescence lifetime of PyalNPs in the presence of Cu²⁺ ions suggested that the type of quenching was dynamic. The fluorescence quenching data for the NPs suspension fitted well into a typical Stern–Volmer relationship in the concentration range 1.0–25 μg/ml of Cu²⁺ ions. The estimated value of the correlation coefficient R² = 0.9877 was close to 1 and showed the linear relationship between quenching data and Cu²⁺ ion concentration. The limit of detection (LOD) was found to be 0.94 ng/ml and is far below the tolerable intake limit value of 1.3 μg/ml accepted by the World Health Organization for Cu²⁺ ions in drinking water. The fluorescence quenching approach for a SDS-capped Pyal nanosuspension for copper ion quantification is of high specificity and coexisting ions were found to interfere very negligibly. The developed method was successfully applied for the estimation of copper ions in river water samples.     

Calcium transport affinity,ion competition and cholera toxin effects on cytosolic Ca concentration

Summary The physiological relevance of an apparent ionophore activity of cholera toxin towards Ca²⁺ has been examined in several different systems designed to measure affinity, specificity, rates of ion transfer, and effects on intracellular ion concentrations. Half-maximal transfer rates across porcine jejunal brush-border vesicles were obtained at a concentration of 0.20 M Ca²⁺. When examined in the presence of competing ions the transfer process was blocked by very low concentrations of La³⁺ or Cd²⁺. Sr²⁺, Ba²⁺ and Mg²⁺ were relatively inefficient competitors for Ca²⁺ transport mediated by cholera toxin. The relative affinities observed would be compatible with a selectivity for Ca²⁺ transfer at physiological ion concentrations, as well as an inhibition of this ionophore activity by recognized antagonists of cholera toxin such as lanthanum ions. Entry rates of Ca²⁺ into brush-border vesicles exposed to cholera toxin were large enough to accelerate the collapse of a Ca²⁺ gradient generated by endogenous Ca, Mg-ATPase activity. The treatment of isolated jejunal enterocytes with cholera toxin caused a significant elevation in cytosolic Ca²⁺ concentrations as measured by Quin-2 fluorescence. This effect was specifically prevented by prior exposure of the cholera toxin to excess ganglioside G_M1. We conclude that cholera toxin has many of the properties required for promoting transmembranes Ca²⁺ movement in membrane vesicles and appears to be an effective Ca²⁺ ionophore in isolated mammalian cells.     

The effects of La(III) on the peroxidation of membrane lipids in wheat seedling leaves under osmotic stress

The physiological effects of the rare earth ion La³⁺ on the peroxidation of membrane lipids in wheat (Triticum aestivum L.) seedling leaves under osmotic stress were determined. With the passage of time under osmotic stress, the inhibition ability of lanthanum ions to the relative membrane permeability and concentration of malondialdehyde, Superoxide radicals, and hydrogen peroxide caused by osmotic stress increased substantially, but no changes were noted in ferrous and relative water content. It indicated that lanthanum ions could not retain the water content because of osmotic stress. However, La³⁺ appears to decrease the production of OH by reducing the content of O₂ and H₂O₂ of Haber-Weiss and Fenton reactions, which efficiently alleviated peroxidation of membrane lipids under osmotic stress and, to some degree, protected the membrane from injury of free radicals. Thus, La³⁺ increased the tolerance ability of plant to osmotic stress, which could assure the function of membrane normal temporally after stressed.