Ca++ fluxes in resealed synaptic plasma membrane vesicles

The effect of the monovalent cations Na⁺, Li⁺, and K⁺ on Ca⁺⁺ fluxes has been determined in resealed synaptic plasma membrane vesicle preparations from rat brain. Freshly isolated synaptic membranes, as well as synaptic membranes which were frozen (?80°C), rapidly thawed, and passively loaded with K₂/succinate and ⁴⁵CaCl₂, rapidly released approximately 60% of the intravesicular Ca⁺⁺ when exposed to NaCl or to the Ca⁺⁺ ionophore A 23187. Incubation of these vesicles with LiCl caused a lesser release of Ca⁺⁺. The EC₅₀ for Na⁺ activation of Ca⁺⁺ efflux from the vesicles was approximately 6.6mM. exposure of the Ca⁺⁺-loaded vesicles to 150 mM KCl produced a very rapid (?1 sec) loss of Ca⁺⁺ from the vesicles, but the Na⁺-induced efflux could still be detected above this K⁺ - sensitive effect. Vesicles pre-loaded with NaCl (150 mM) exhibited rapid ⁴⁵Ca uptake with an estimated EC₅₀ for Ca⁺⁺ of 7–10 μM. This Ca⁺⁺ uptake was blocked by dissipation of the Na⁺ gradient. These observations are suggestive of the preservation in these purified frozen synaptic membrane preparations of the basic properties of the Na⁺Ca⁺⁺ exchange process and of a K⁺ - sensitive Ca⁺⁺ flux across the membranes.     

Role of external calcium in sodium and chloride transport in the gills of seawater-adaptedMugil capito

Summary When the mulletMugil capito is transferred to medium lacking Ca⁺⁺ (either Ca⁺⁺-free seawater or distilled water) the passive permeability of the gill to Na⁺ and Cl^– is increased and the activating effect of external K⁺ on the Na⁺ and Cl^– effluxes in hyposaline media is inhibited. The permeability of the gill increases progressively in proportion to the time of Ca⁺⁺ deprivation; it declines when Ca⁺⁺ is added again to the external medium. The active mechanisms for ion excretion are not reversible. At external Ca⁺⁺ concentrations from 0.1 to 10 mM the Na⁺ permeability is constant but the activation of Na⁺ efflux by K⁺ shows a maximum at a Ca⁺⁺ concentration of about 1 mM. For activation of Cl^– efflux external bicarbonate must be present, in addition to Ca⁺⁺, suggesting the existence of a Cl^–/HCO ₃ ^– exchange. The mechanism by which Ca⁺⁺ controls the passive branchial permeability is thus probably different from that involved in K⁺ activation of ion excretion. The Ca⁺⁺ effect on the K⁺ sensitive ionic excretory mechanisms seems to be related to intracellular Ca⁺⁺ movements. Thus, on the one hand, substances such as Ruthenium Red and La⁺⁺⁺ which both inhibit Ca⁺⁺ exchange, in media containing Ca⁺⁺ and HCO ₃ ^– also inhibit K⁺ activation of Na⁺ and Cl^– effluxes; on the other hand, the ionophore A 23187, a stimulator of Ca⁺⁺ exchange, when added to these media, activates the Na⁺ and Cl^– effluxes; its maximal effect on the Na⁺ flux occurs at 2 mM Ca⁺⁺.Abbreviations ASW-Ca artificial seawater minus calcium - DW deionised water - DWCa deionised water with 1 mM Ca⁺⁺ added - DWCaHCO ₃ DW with calcium plus bicarbonate - DWHCO ₃ DW with 1 mM sodium bicarbonate added - FW freshwater (tap water) - FWK freshwater with K⁺ added - P. D. potential difference - SW seawater The experiments reported in this paper were done with Jean Maetz who tragically died in August 1977. It is the last report about several years of friendly collaboration     

Mediation of beta-adrenergic stimulated amylase release from mouse parotid gland

Amylase released from mouse parotid fragments by the β-adrenergic agonist, isoproterenol, was associated with l) enhanced ⁴⁵Ca⁺⁺ efflux and 2) a dependence on the extracellular Na⁺ concentration. Monensin, a sodium ionophore, mimicked the effects of isoproterenol on ⁴⁵Ca⁺⁺ efflux. In the absence of extracellular sodium isoproterenol and monensin failed to significantly release ⁴⁵Ca⁺⁺. Complete inhibition of isoproterenol stimulated amylase release occurred when 75 per cent or greater of the extracellular Na⁺ was replaced by sucrose; carbachol stimulated amylase release was not affected. Tetracaine (0.2 mM to 1.0 mM) inhibited both isoproterenol and carbachol stimulated amylase release and inhibited the ⁴⁵Ca⁺⁺ uptake induced by carbachol. Monensin, a sodium ionophore, mimicked the effects of isoproterenol on amylase release; this effect was significantly reduced in the absence of extracellular Na⁺. It is proposed that a primary step in the release of amylase form mouse parotid gland in response to β-adrenergic stimulation is an increased influx of Na⁺ followed by release of intracellularly stored calcium.     

PTH release stimulated by high extracellular potassium is associated with a decrease in cytosolic calcium in bovine parathyroid cells

We employed the calcium (Ca⁺⁺)-sensitive, intracellular dye QUIN-2 to examine the role of cytosolic Ca⁺⁺ in the stimulation of PTH release by high extracellular potassium (K⁺) concentrations. Addition of 55 mM KCl to cells incubated with 115 mM NaCl and 5 mM KCl lowered cytosolic Ca⁺⁺ at either low (0.5 mM) extracellular Ca⁺⁺ (from 194±14 to 159±9 nM, p<.01, N=6) or high (1.5 mM) extracellular calcium (from 465±38 to 293±20 nM, p<.01, N=10). This reduction in cytosolic Ca⁺⁺ was due to high K⁺$\text{per}\text{se}$ and not to changes in tonicity since addition of 55 mM NaCl was without effect while a similar decrease in cytosolic Ca⁺⁺ occurred when cells were resuspended in 60 mM NaCl and 60 mM KCl. PTH release was significantly (p<.01) greater at 0.5 and 1.5 mM Ca⁺⁺ in QUIN-2-loaded cells incubated with 60 mM NaCl and 60 mM KCl than in those exposed to 115 mM NaCl and 5 mM KCl. In contrast to most secretory cells, therefore, stimulation of PTH release by high K⁺ is associated with a decrease rather than an increase in cytosolic Ca⁺⁺.     

Basal and potassium stimulated, calcium dependent, endorphins release from pituitary cells.

Mouse pituitary tumor cells grown in tissue culture release endorphins spontaneously to the culture medium. Depolarization of these cells by incubation with high K⁺ concentration (56 mM) increased 2–3 folds the release of endorphins. The K⁺ evoked release was Ca⁺⁺ dependent by that: $\text{a}$, removal of Ca⁺⁺ ions inhibited 90% of K⁺ stimulated release. $\text{b}$, ethyleneglycol-bis (β-aminoethyl ether) N,N′-tetraacetic acid (EGTA) inhibited release of endorphins in the presence of high K⁺ and Ca⁺⁺. It is suggested that dual regulatory system inhibit and/or stimulate $\text{in-vivo}$ release of endorphins from the pituitary glands.     

Membrane permeability changes in amphibian eggs at ovulation

Electropotential differences between the cytoplasm and external medium have been compared in the mature R. pipiens occyte and the ovulated unfertilized egg as a function of [Na]_o, [K]_o, [Ca]_o and [Cl]_o. In solutions containing 1.0 mM Ca⁺⁺ the oocyte behaved as though it were predominantly permeable to K⁺ and Cl^?, i.e., like a KCl electrode. However, the steady potential decreased with decreasing [Ca]_o and in 5 × 10^?4 mM [Ca]_o the oocyte membrane behaved like a NaCl electrode. Studies on the steady potential as a function of [Na]_o, [K]_o and [Cl]_o in 1.0 mM Ca⁺⁺ or Ca-free solutions suggest that Ca⁺⁺ controls the passive permeability of the oocyte membrane to Na⁺ and Cl^?. In the ovulated unfertilized egg the K⁺ selectivity of the cell membrane disappeared and the system behaved like a NaCl electrode. No effect of external Ca⁺⁺ or K⁺ concentration changes on the steady potential was observed. These results indicate that the ion permeability properties of the ovulated egg are similar to that of the ovarian oocyte in Ca-deficient medium, and suggests that the mechanism of ovulation may involve the removal of Ca⁺⁺ regulation of ion permeability of the egg cell membrane.     

Role of calcium in the thyrotropin-releasing hormone-stimulated release of prolactin from pituitary cells in culture.

Thyrotropin-releasing hormone (TRH) or 50 mM K⁺ stimulated the acute release of prolactin from the GH₄C₁ strain of rat pituitary cells in culture. The enhanced release of prolactin was inhibited in a dose-related manner by the Ca⁺² antagonist Co⁺² (2.0 to 0.5 mM) as well as by the Ca⁺² chelator EGTA (1.0 mM). Co⁺² also reduced spontaneous basal prolactin release. There was partial reversal of the inhibitory effect of Co⁺² (2.0 mM) by Ca⁺² (2.0 mM) and complete reversal of the inhibitory effect of EGTA (1.0 mM) by Ca⁺² (2.0 mM). The enhanced release of prolactin stimulated by 50 mM K⁺ was maximal by 10–20 minutes in medium containing 0.67 to 0.74 mM Ca⁺². Na⁺ (50 mM) did not mimic the effect of high K⁺. We conclude that Ca⁺² is an essential cation in mediating the actions of high external K⁺ and TRH on the release of prolactin by GH₄C₁ cells.     

Low‐molecular weight carbohydrates modulate dormancy and are required for post‐germination growth in turions of Spirodela polyrhiza

The aquatic duckweed Spirodela polyrhiza propagates itself vegetatively by forming turions – bud‐like perennation organs – in the autumn, which spend the winter on the bottom of ponds and then germinate in the following spring and proliferate on the water surface. Newly formed turions usually require a period of cold after‐ripening and light to germinate effectively, but an ample supply of exogenous sugar can lead to germination even in the dark and independent of after‐ripening. The results of the present study indicate that the availability of readily metabolised carbohydrates is a determining factor for turion germination. Freshly harvested turions do not contain soluble, low‐molecular weight carbohydrates at a level sufficient to allow germination to take place, but after‐ripened turions do. Augmentation of the soluble carbohydrate content during after‐ripening derives from gradual breakdown of reserve starch of the turions. The long time required for any germination to be observed in turions incubated in darkness and the limited frequency of germination in the dark (about 50% of turion population), even with an ample external sugar, supply emphasise that both after‐ripening and light are essential for ensuring rapid germination and subsequent frond proliferation at an ecologically appropriate time. The carbohydrate supply required for rapid proliferation of the fronds produced at germination is provided by the rapid light‐induced breakdown of turion reserve starch.     

Triple helix formation and disulphide bonding during the biosynthesis of glomerular basement membrane collagen.

White erythrocyte membranes, or ghosts, were monoconcave discocytes when incubated in 50mM N-tris (hydroxymethyl) methyl-2-aminoethane sulfonic acid titrated to pH 7.4 with triethanolamine. If 3mM MgCl₂ was included in the incubation medium, the ghosts were predominantly echinocytes. The echinocytic form could also be induced by Co⁺⁺, Ni⁺⁺, Li⁺, Na⁺, K⁺, $\text{NH}{}_4{}^{\mathrm{+}}$ and tetramethylammonium ion, all as chloride salts. The concentration of cation necessary for 50% of the ghosts to be echinocytes was correlated with the hydrated charge density of the cation with the most highly charged cations being the most effective. The cations Ca⁺⁺, Sr⁺⁺, Ba⁺⁺ and La⁺⁺⁺, (also as chloride salts) did not induce the normal echinocytic form, but at high levels induced a few misshapen forms with some resemblance to echinocytes. Instead Ca⁺⁺, Sr⁺⁺, Ba⁺⁺ and La⁺⁺⁺ suppressed the formation of echinocytes in the presence of Mg⁺⁺ and other ions. This suggests the presence of a specific Ca⁺⁺ binding site important to shape control in the erythrocyte membrane.     

菹草石芽大小和贮藏温度对萌发及幼苗生长的影响

通过萌发实验探讨了菹草石芽重量和贮藏温度对石芽萌发及幼苗生长的影响。结果表明：成熟的菹草石芽大小不一,按鲜重划分重量等级,各等级石芽数量占总数量的百分比差异很大,重量中等的石芽数量占到80%以上;重量对石芽最终萌发率没有影响,但重量小的石芽萌发时间较早,重量大的石芽虽然萌发较晚但是最终萌生的幼苗数目较多。石芽重量和萌发结束时幼苗数目之间呈显著的线性正相关(p＜0.05);连续去苗过程中,重量大的石芽萌发率和萌发幼苗数保持较高水平;经过贮藏的石芽与未经贮藏的石芽相比,萌发快且萌发整齐。经过15℃贮藏的石芽萌发最早,高温(25℃)和低温(4℃)贮藏均会使石芽最终萌发出的幼苗数目减少,3种温度下贮藏的石芽最终萌发率和幼苗长度无显著差异。     

An electrogenic Na+/Ca2+ antiporter in addition to the Ca2+ pump in cardiac sarcolemma

Vesicles isolated from rat heart, particularly enriched in sarcolemma markers, were examined for their sidedness by investigation of side-specific interactions of modulators with the asymmetric (Na⁺ + K⁺)-ATPase and adenylate cyclase complex. The membrane preparation with the properties expected for inside-out vesicles showed the highest rate of ATP-driven Ca²⁺ transport. The Ca²⁺ pump was stimulated 1.7- and 2.1-fold by external Na⁺ and K⁺, respectively, the half-maximal activation occurring at 35 mM monovalent cation concentration. In vesicles loaded with Ca²⁺ by pump action in a medium containing 160 mM KCl, a slow spontaneous release of Ca²⁺ started after 2 min. The rate of this release could be dramatically increased by the addition of 40 mM NaCl to the external medium. In contrast, 40 mM KCl exerted no appreciable effect on vesicles loaded with Ca²⁺ in a medium containing 160 mM NaCl. Ca²⁺ movements were also studied in the absence of ATP and Mg²⁺. Vesicles containing an outwardly directed Na⁺ gradient showed the highest Ca²⁺ uptake activity. These findings suggested the operation of a Ca²⁺/Na⁺ antiporter in addition to the active Ca²⁺ pump in these sarcolemmal vesicles. A valinomycin-induced inward K⁺-diffusion potential stimulated the Na⁺- Ca²⁺ exchange, suggesting its electrogenic nature. If in the absence of ATP and Mg²⁺ the transmembrane Na_i⁺/Na_o⁺ gradient exceeded 160/15 mM concentrations, Ca²⁺ uptake could be stimulated by the addition of 5 mM oxalate, indicating Na⁺ gradient-induced Ca²⁺ uptake to be a translocation of Ca²⁺ to the lumen of the vesicle. A sarcoplasmic reticulum contamination, removed by further sucrose gradient fractionation, contained rather low Na⁺-Ca²⁺ exchange activity. This result suggests that the activity can be entirely accounted for by the sarcolemmal content of the cardiac membrane preparation.     

Effects of morphine tolerance and dependence on Mg++ dependent ATPase activity of synaptic vesicles.

The effect of morphine on ATPase of synaptic plasma membranes (SPM) and synaptic vesicles isolated from the mouse brain was studied. The activity of synaptic vesicle Mg⁺⁺-dependent ATPase from mice rendered morphine tolerant and dependent by pellet implantation was 40% higher than that from placebo implanted mice. However, the activities of Mg⁺⁺-dependent ATPase and Na⁺, K⁺ activated ATPase of SPM of tolerant and nontolerant mice were not significantly different. The activity of synaptic vesicular Mg⁺⁺-dependet ATPase was dependent on the concentration of Mg⁺⁺ but not of Ca⁺⁺; maximum activity was obtained with 2 mM MgCl₂. On the other hand, Mg⁺⁺-dependent ATPase activity of SPM was dependent on both Mg⁺⁺ and Ca⁺⁺, activity being maximum using 2 mM MgCl₂ and 10^?5 M CaCl₂. It is suggested that this stimulation of ATPase activity may alter synaptic transmission and may thus be involved in some aspects of morphine tolerance and dependence.     

Increased cucumber salt tolerance by grafting on pumpkin rootstock and after application of calcium

Self-grafted and pumpkin rootstock-grafted cucumber plants were subjected to the following four treatments: 1) aerated nutrient solution alone (control), 2) nutrient solution with 10 mM Ca(NO₃)₂ (Ca), 3) nutrient solution with 90 mM NaCl (NaCl), and 4) nutrient solution with 90 mM NaCl + 10 mM Ca(NO₃)₂ (NaCl+Ca). The NaCl treatment decreased the plant dry mass and content of Ca²⁺ and K⁺ but increased the Na⁺ content in roots and shoots. Smaller changes were observed in pumpkin rootstock-grafted plants. Supplementary Ca(NO₃)₂ ameliorated the negative effects of NaCl on plant dry mass, relative growth rate (RGR), as well as Ca²⁺, K⁺, and Na⁺ content especially for pumpkin rootstock-grafted plants. Supplementary Ca(NO₃)₂ distinctly stimulated the plasma membrane (PM) H⁺-ATPase activity which supplies the energy to remove excess Na⁺ from the cells. The expressions of gene encoding PM H⁺-ATPases (PMA) and gene encoding a PM Na⁺/H⁺ antiporter (SOS1) were up-regulated when Ca(NO₃)₂ was applied. The pumpkin rootstock-grafted plants had higher PM H⁺-ATPase activity as well as higher PMA and SOS1 expressions than the self-grafted plants under NaCl + Ca treatment. Therefore, the addition of Ca²⁺ in combination with pumpkin rootstock grafting is a powerful way to increase cucumber salt tolerance.     

Properties of LHRH release from a hypothalamic synaptosomal fraction of estrogen-primed ovariectomized rats

The release of luteinizing hormone-releasing hormone (LHRH) from mitochondrial-synaptosomal fractions (P₂) of basomedial hypothalamus was examined under various conditions. Less than 3% of the LHRH in P₂ suspensions was released under control conditions while the addition of 60 mM KCl or NaCl effected an 8-fold increase in LHRH as measured by radioimmunoassay. Equiosmolar sucrose effected only a 1.8-fold increase in LHRH release. The stimulatory effects of both Na⁺ and K⁺ were significantly inhibited by Mn²⁺ or La³⁺. Two forms of released LHRH were observed, one soluble and the other particulate. Soluble LHRH release was effected by hypertonic sucrose or 60 mM KCl and was not inhibited by Ca²⁺ antagonists. The release of particulate LHRH was unaffected by hypertonic sucrose, was stimulated 10-fold by 60 mM KCl, and was abolished with Ca²⁺ antagonists. These results suggest that the released soluble LHRH results from nonspecific leakage while the release of particulate LHRH reflects a Ca²⁺-dependent secretory process.     

Ecophysiological Characterization of Dormancy States in Turions of the Aquatic Carnivorous Plant Aldrovanda vesiculosa

Two main dormancy states, innate and imposed dormancy, were characterized in turions (winter buds) of the aquatic carnivorous plant Aldrovanda vesiculosa L. (Droseraceae) kept at 3 ± 1 °C in a refrigerator over the winter. As a result of the breaking of imposed dormancy by a temperature increase (at 15 – 20 °C), some of the turions rose to the water surface within 1 – 3 d and germinated. Turion leaves contained large lacunae with a slimy reticulum and were filled by water over winter. As a result of breaking imposed dormancy, the proportion of gas volume in inner turion leaves rose from 10 – 20 % to 100 % of leaf lacunae volume. The aerobic dark respiration rate of the turions [0.74 – 1.5 μmol O₂) kg⁻¹(FM) s⁻¹] slightly increased during innate dormancy after 1 – 2 d at 20 °C, while it was almost constant during the breaking of imposed dormancy. The anaerobic fermentation rate of the turions was only 1.5 – 7 % of the oxygen respiration rate and also was constant during the breaking of imposed dormancy. In turions, the content of glucose, fructose, and sucrose was the same for the two states of dormancy, but starch content was greatly reduced for the imposed dormancy (10 – 11 vs. 32 % DM). It may be suggested that a temperature increase causes an increase of fermentation or respiration which is responsible for the evolution of gas in turion lacunae and, thus, for turion rising.     

INTERFERENCE POTENTIAL OF PLUCHEA LANCEOLATA (ASTERACEAE): GROWTH AND PHYSIOLOGICAL RESPONSES OF ASPARAGUS BEAN,VIGNA UNGUICULATA VAR. SESQUIPEDALIS

The water-soluble compounds synthesized by the weed, Pluchea lanceolata, and released by it into the soil significantly reduced seed germination, number of nodes, internode length, shoot and root lengths, nodule number and weight, and Chl a and b and Chl a/b ratio of asparagus bean plants. The pattern of accumulation of nutrients in shoot and root of asparagus bean was also affected. In contrast, the net photosynthetic rate and stomatal conductance of fully expanded leaves were higher in plants grown with treated soil. The concentrations of Mg⁺⁺, Zn⁺⁺, and PO₄^3- were higher and K⁺ was lower in shoots of plants grown with treated soil as compared to those grown with the control soil. Also, roots of plants grown with treated soil showed greater accumulation of Mg⁺⁺ and NO₃^-. Shoot/root ratio of nutrients in plants grown with control soil were higher for Zn⁺⁺, Na⁺, Ca⁺⁺, and NO₃^-, whereas plants grown with treated soil had higher ratios for PO₄^3-. These results provide evidence for allelopathic interference by P. lanceolata to the growth of asparagus bean.     

Response of sugarcane to different types of salt stress

Summary Due to climatic conditions and prevailing water regime the yield and sucrose recovery in sugarcane are high in South Western India. However, excessive irrigation, poor drainage and luxuriant use of fertilizers have resulted in conversion of large fertile areas into saline lands. The salinity is due to the excess of Na⁺, Ca⁺⁺, Mg⁺⁺, SO₄ ^– and Cl^– ions. Individual salts of NaCl, Na₂SO₄, MgCl₂ and MgSO₄ were employed in culture experiments to study salt stress effect on sugarcane variety Co 740. It was observed that sulphate salinity was more toxic to sugarcane than the chloride one. Sulphate salts caused more inhibition of growth, chlorophyll synthesis, PEPCase activity, decreased the uptake of K⁺ and Ca⁺⁺ ions but stimulated nitrate reductase. The stress did not result in proline accumulation in the sugarcane cultivar Co 740. The degree of toxicity of different ions in decreasing order in sugarcane cultivar Co 740 is SO₄ ^–>Na⁺>Cl^–>Mg⁺⁺.     

Abscisic-acid-induced turion formation in Spirodela polyrrhiza L. IV. Comparative ion flux characteristics of the turion and the vegetative frond and the effect of ABA during early turion development

Abstract Using the method of compartmental analysis, the ion fluxes and compartment concentrations of Ca²⁺, K⁺ and Cl^- have been compared in the untreated vegetative frond and the abscisic acid (ABA) induced turion of Spirodela polyrrhiza. The ABA-induced turion is characterized by reduced Ca²⁺ exchange across the tonoplast and low vacuolar Ca²⁺ concentration relative to the vegetative frond. In addition the turion exhibits a higher plasmalemma flux with a correspondingly high Ca²⁺ concentration in the cytoplasm. The concentration of K⁺ and Cl^- is much lower in the cytoplasm of the ABA-induced turion than in the vegetative frond with the influx/efflux ratio at both the plasmalemma and the tonoplast being less than 1, a finding exhibited also in dormant storage tissue. Treatment of vegetative fronds with ABA for 18 h resulted in a reduced K⁺ plasmalemma efflux relative to untreated vegetative fronds and a concomitant increase in the cytoplasmic concentration. There was no rapid effect of ABA on Ca²⁺, K⁺ or Cl^- fluxes through either membrane. These results are consistent with the notion that drastic changes in ion fluxes and concentrations in the turion are a secondary consequence of ABA-induced development, possibly due to prior regulation by ABA of enzymes inherent to processes involved in membrane transport.     

Ion metabolism in a halophilic blue-green alga,Aphanothece halophytica

The intracellular ion content of the halophilic blue-green alga, Aphanothece halophytica was studied as a function of age, external sodium and external potassium concentration. Intracellular Na⁺ was found to be about 0.38 millimoles/g dry mass. Intracellular K⁺ concentrations were as high as 1 M and varied directly with external salinity. Intracellular Ca⁺⁺ and Mg⁺⁺ were in the range previously reported for fresh water blue-green algae despite their extremely high extracellular concentrations. Average cell size is consistent at room temperature with two exceptions. When the outside K⁺ is lower than 6.5 mM the cells tend to be smaller with less intracellular K⁺ and high Ca⁺⁺. In stationary phase cultures the cells are larger with high intracellular Mg⁺⁺ and low K⁺.     

A strategy of Ca2+ alleviating Na+ toxicity in salt-treated Cyclocarya paliurus seedlings: photosynthetic and nutritional responses

Cyclocarya paliurus seedlings were subjected to 85?mM NaCl and 0, 6, 12 or 18?mM Ca(NO₃)₂ treatments to study changes in plant growth, photosynthetic parameters and distribution and/or accumulation of organic and inorganic solutes. Na⁺ toxicity symptoms were observed in plants non-treated with Ca(NO₃)₂, while 12?mM Ca(NO₃)₂ supplementation produced a significant promotion of shoot growth; meanwhile chlorophyll content, photosynthetic rate and optimum quantum yield of photosystem II (PSII), represented by the F_v/F_m ratio and pigments content as well as proline and soluble sugars, significantly increased. Ca(NO₃)₂ supply increased K⁺ and Ca²⁺ concentration, whereas the Na⁺ transport to the shoot was inhibited. There was a strong increase in the K⁺/Na⁺ ratio in shoot of Ca(NO₃)₂-treated plants. X-Ray microanalysis of roots showed that K⁺, Ca²⁺ and Na⁺ accumulated mainly in the epidermal cells and cortical cells of roots with 12?mM Ca(NO₃)₂ supply, and low accumulation was observed in stelar parenchyma, indicating exogenous Ca²⁺ possibly induced or strengthened effects of Casparian bands on ion transport. These results suggest that Ca(NO₃)₂ supplement increased inorganic and organic solutes accumulation in shoot and leaf, and restricted Na⁺ transport to the shoot by reinforcing barrier effects for attenuating salt injuries in plants, which could be a strategy of Ca²⁺ alleviating Na⁺ toxicity in C. paliurus seedlings subjected to salt stress.