Salicylic Acid (SA) Induced Alterations in Growth,Biochemical Attributes and Antioxidant Enzyme Activity in Faba Bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.) Seedlings under NaCl Toxicity

In the present study we tried to evaluate the effect of salicylic acid (SA) in alleviating the negative effects of salinity stress. NaCl stress (50 and 100 mM) declines the shoot and root length and maximum decrease was observed at 100 mM concentration of NaCl. Similarly shoot dry weight decreased by 57.14% and root dry weight by 67.24% with 100 mM NaCl stress. The pigments and leaf relative water content (LRWC) were also observed to decline with increase in NaCl concentration. However, supplementation of SA to NaCl stressed seedlings showed enhanced length and dry weight of shoot and root. The pigment and LRWC also increased by the application of SA in the present study. NaCl stress also enhanced proline and glycine betaine (GB) by 3.01 and 2.04 folds, respectively; further enhancement was recorded by the application of SA. Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content also showed rise in accumulation, however, seedlings treated with SA and NaCl (100 mM + SA) declines the H₂O₂ accumulation to 1.90 from 2.45 folds and MDA to 1.69 from 2.34 folds over the control. Antioxidants were observed to increase with NaCl concentration and further increase was recorded by the application of SA. Indoleacetic acid (IAA) and indole butyric acid (IBA) decreased by 36.60 and 44.16%, respectively, and ABA increased by 750% with 100 mM NaCl. Addition of SA to NaCl stressed seedlings enhanced the IAA and IBA and decreased the ABA concentration to appreciable level. NaCl is also responsible for the higher accumulation of Na⁺ and Na⁺/K⁺ ratio and decreased uptake of Ca²⁺ and K⁺. Supplementation of SA decreased the Na⁺ accumulation and enhanced the uptake of Ca²⁺ and K⁺ in NaCl stressed seedlings. In conclusion, SA supplementation mitigates the negative effects of NaCl toxicity in faba bean seedlings through the modulation of different osmoprotectants, antioxidants and nutrients uptake.     

Two different effects of calcium on aquaporins in salinity-stressed pepper plants

Two different effects of calcium were studied, respectively, in plasma membrane vesicles and in protoplasts isolated from roots of control pepper plants (Capsicum annuum L cv. California) or of plants treated with 50 mM NaCl, 10 mM CaCl(2) or 10 mM CaCl(2) + 50 mM NaCl. Under saline conditions, osmotic water permeability (P ( f )) values decreased in protoplasts and plasma membrane vesicles, and the same reduction was observed in the PIP1 aquaporin abundance, indicating inhibitory effects of NaCl on aquaporin functionality and protein abundance. The cytosolic Ca(2+) concentration, [Ca(2+)](cyt), was reduced by salinity, as observed by confocal microscope analysis. Two different actions of Ca(2+) were observed. On the one hand, increase in free cytosolic calcium concentrations associated with stress perception may lead to aquaporin closure. On the other hand, when critical requirements of Ca(2+) were reduced (by salinity), and extra-calcium would lead to an upregulation of aquaporins, indicating that a positive role of calcium at whole plant level combined with an inhibitory mechanism at aquaporin level may work in the regulation of pepper root water transport under salt stress. However, a link between these observations and other cell signalling in relation to water channel gating remains to be established.     

Effect of CaSO4 and NaCl on mineral content ofLeucaena leucocephala

The effects of varying CaSO₄ and NaCl levels on the nutrient content ofLeucaena leucocephala were established by examining the concentrations of Na, Ca, Cl, K and Mg in leucaena roots, stems and leaves. Leucaena was grown in nutrient solution at four levels of CaSO₄ (0.5, 1.0, 2.5 and 5.0 mM) and NaCl (1, 25, 50 and 100 mM), in randomized blocks with five replications. Leucaena excluded sodium from stems and leaves when NaCl concentration was 50 mM or less. Sodium uptake decreased as CaSO₄ concentration increased. Calcium uptake was affected by NaCl concentration when substrate CaSO₄ concentration was 0.5 mM. At this level, 100 mM NaCl caused a marked decrease in leaf calcium and a marked increase in leaf Cl. In all other treatments, Cl uptake was not affected by CaSO₄ concentration. Potassium uptake was strongly depressed as NaCl concentration increased at low Ca concentration, but this effect was offset at high Ca. Magnesium uptake decreased as CaSO₄ levels increased.     

Calcium enhances the hemolytic action of bile salts

The lysis of human erythrocytes by bile salts in buffer containing isotonic saline was dramatically enhanced by the addition of 5-10 mM calcium chloride. All bile acids tested showed this effect, with a marked increase in lysis occurring at 0.75 mM for deoxycholate, 1 mM for chenodeoxycholate, 2.5 mM for ursodeoxycholate and 5.5 mM with cholate in the presence of 10 mM calcium chloride. The effect appeared to be specific for calcium; strontium chloride and magnesium chloride gave no stimulatory effect. The increased lysis of the erythrocytes in the presence of 1 mM deoxycholate and 1-10 mM calcium chloride was not associated with increased uptake of the bile salt by the cells (measured with [14C]deoxycholate). Using erythrocytes previously labelled with [3H]cholesterol, there was no evidence of an enhanced removal of that membrane component in the presence of calcium and deoxycholate, compared to deoxycholate alone. The sensitivity of the cells to the effect of calcium in the presence of 1 mM deoxycholate increased with the length of time of their storage at 4 degrees C. The sensitivity returned to that of fresh cells after incubation at 37 degrees C with 30 mM adenosine plus 25 mM glucose, but this treatment did not further diminish the lysis. Lysis in the presence of 10 mM calcium chloride and 1 mM deoxycholate was partially blocked by increasing the KCl concentration at the expense of NaCl. The maximum effect occurred with a buffer comprising 100 mM KCl/50 mM NaCl. A more dramatic reduction in the lysis followed the incorporation of the calcium chelator, quin2, into the cells. The lysis induced by 1 mM deoxycholate in the presence of calcium was reduced by 80% in quin-2-loaded cells compared to controls. The data suggest that bile acids can promote the influx of calcium into erythrocytes, leading to lysis as a result of the efflux of intracellular potassium and/or the uptake of sodium from the incubation medium. The data further suggest that cellular effects may occur at lower bile acid concentrations than that thought to be required for detergent damage.     

Utilization of osmoprotective compounds by hybridoma cells exposed to hyperosmotic stress

A search was undertaken for osmoprotective compounds for mouse hybridoma cell line 6H11 grown in culture. When the osmolality of the growth medium was increased above the normal osmolality of 330 mOsmol/kg, growth rates were decreased in a dose-dependent fashion, reaching zero when the osmolality of the medium reached approx. 435 mOsmol/kg through the addition of KCl (60 mM), or 510 mOsmol/kg through the addition of NaCl (100 mM), or sucrose (175 mM). For NaCl or sucrose-stressed cultures, the inclusion of glycine betaine, sarcosine, proline, glycine, or asparagine in the growth medium gave a moderate to strong osmoprotective effect, measured as the ability of these compounds to enhance cell growth rates under hyperosmotic conditions. Inclusion of dimethylglycine may also give a strong osmoprotective effect under these stress conditions.In KCl-stressed cell cultures, addition of glycine betaine, sarcosine, or dimethylglycine gave strong osmoprotective effects. Of 38 compounds tested during NaCl stress, 7 gave weak osmoprotective effects and 25 gave no osmoprotective effect. The osmoprotective compounds accumulated inside the stressed cells. Accumulation was completed after 4 to 8 h, reaching intracellular concentrations of approx. 0.27 pmol/cell, or 0.15 M, in NaCl stressed cells (100 mM NaCl added).Glycine betaine, dimethylglycine, and sarcosine accumulation was observed only when these protectants were included in the medium. For all osmoprotectants, a growth medium concentration between 5 and 30 mM gave the maximal protective effect, with the exception of dimethylglycine, for which the optimum concentration was approx. 65 mM. Osmoprotective effects obtained with glycine, sarcosine, dimethylglycine, and glycine betaine, indicate that the more methylated compounds are the most effective protectants.The cellular content of glycine betaine and the glycine betaine uptake rate increased with medium osmolality in a linear fashion. Glycine betaine uptake was described by a model comprising a saturable component obeying Michaelis-Menten kinetics and a nonsaturable component. K(m) and V(max) for glycine betaine uptake were determined at 420 mOsmol/kg (50 mM NaCl added) and 510 mOsmol/kg (100 mM NaCl added). A K(m) value of approx. 2.5 mM was obtained at both medium osmolalities, while V(max) increased from 0.010 pmol/cell . h to 0.018 pmol/cell . h as the osmolality of the growth medium was increased, indicating an effect of medium osmolality on the maximal rate of transport rather than on the affinity of the transporters for glycine betaine. Hybridoma cells were not able to utilize the glycine betaine precursors choline or glycine betaine aldehyde for osmoprotection, suggesting that the cells lack part, or all, of the choline-glycine betaine pathway or the appropriate uptake mechanism.The uptake rate for glycine in NaCl-stressed hybridoma cells was approx. four times higher than the uptake rate for glycine betaine. Furthermore, if equimolar amounts of glycine betaine, glycine, sarcosine, and proline were simultaneously added to NaCl-stressed cell cultures, the intracellular concentrations of glycine, proline, and sarcosine were significantly higher than the concentration of glycine betaine.A 40% increase in hybridoma cell volume was observed when the growth medium osmolality was increased from 300 to 520 mOsmol/kg. (c) 1994 John Wiley & Sons, Inc.     

Furosemide and Ca2+ affect 86Rb+ efflux from pancreatic beta-cells by different mechanisms

The interaction between furosemide, calcium and D-glucose on the 86Rb+ efflux from beta-cell-rich mouse pancreatic islets was investigated in a perifusion system with high temporal resolution. Raising the glucose concentration from 4 to 20 mM induced an initial decrease in 86Rb+ efflux, which was followed by a steep increase and then a secondary decrease. Removal of extracellular calcium increased the 86Rb+ efflux at 4 mM D-glucose but reduced it at 20 mM. The initial biphasic changes in 86Rb+ efflux induced by 20 mM D-glucose were inhibited by calcium deficiency. Furosemide (100 microM) reduced the 86Rb+ efflux rate both at 4 and 20 mM D-glucose and the magnitudes appeared to be similar at either glucose concentration. Furosemide (100 microM) reduced the glucose-induced (10 mM) 45Ca+ uptake but did not affect the basal (3 mM D-glucose) 45Ca+ uptake. However, the ability of furosemide (100 microM) to reduce the 86Rb+ efflux at a high glucose concentration (20 mM) was independent of extracellular calcium. The inhibitory effects of furosemide and calcium deficiency on the 86Rb+ efflux rate appeared to be additive. It is concluded that the effect of furosemide on 86Rb+ efflux is not secondary to reduced calcium uptake and that the effects of furosemide and calcium deficiency are mediated by different mechanisms. The effect of furosemide is compatible with inhibition of loop diuretic-sensitive co-transport of Na+, K+ and Cl- and the effect of calcium deficiency with reduced activity of calcium-regulated potassium channels.     

Physiological behaviour of loquat and anger rootstocks in relation to salinity and calcium addition

The salinity tolerance of two commercial rootstocks used for loquat plants (Eribotrya japonica Lindl.), loquat and anger, was studied in a pot experiment. The plants were irrigated using solutions containing 5 and 50mM NaCl and 5 and 25mM calcium acetate for 4 months. The growth, tissue mineral content, water status, and leaf gas exchange responses to salt treatment with and without additional calcium were examined. Plant growth was not modified by salinity in anger (50mM), but was reduced in loquat; leaf biomass and stem diameter were particularly affected. However, Cl(-) levels leaf increased with salinity to a greater extent in anger, while the Na(+) content increased to the same extent in both species, indicating that ion transport from root to leaves was not inhibited in either species. Additional calcium (25mM) reduced Na(+) and Cl(-) concentrations in both species, but did not minimise the effects of salinity on the growth of salt-treated loquat plants. The decrease in K(+) concentrations had no effect on growth, as anger was the most tolerant rootstock and had lowest leaf K(+) content. Salinity reduced the Ca(2+) concentration in the roots of both species. However, when calcium was added, the concentration of Ca(2+) increased in the roots of salinised plants. Leaf water potential at pre-dawn decreased significantly in both species under saline conditions. Leaf gas exchange, stomatal conductance and, in particular, net CO(2) assimilation, decreased with salinity only in loquat, indicating that photosynthesis could be the growth-limiting factor in this species.     

Amylase release from rat parotid glands. II. Calcium kinetics.

The kinetics of 45Ca2+ uptake, efflux, and calcium potentiation of amylase release by slices of rat parotid glands were examined. Pretreatment of the tissue with 11.25 mM 45Ca2+ medium increased the total tissue 45calcium content. Lanthanum (1 mM) decreased tissue uptake, blocked the slow components of exchange and appeared to inhibit transcellular calcium movement. Neither dibutyryl cyclic AMP nor caffeine caused consistently significant effects on 45Ca2+ kinetics, or total 45calcium content. Carbamylcholine increased the initial rate of 45Ca2+ uptake, but had no effect on total uptake. Elevation of the extracellular Ca2+ concentration to 11.25 mM during stimulation of amylase release resulted in an initial decrease in the rate of amylase release followed by a potentiation of release which developed slowly, requiring 40--50 min to reach the maximal response. The inability to detect release-related changes in either calcium influx or mobilization, and the lengthy times and high Ca2+ concentrations required to achieve calcium potentiation suggests that calcium does not couple amylase release.     

Prevention of myocardial reperfusion injury by increasing artificial trans-membrane sodium gradient in "calcium paradox" and post-ischemic reperfusion

An effect of the high sodium gradient during "calcium paradox" and postischemic reperfusion has been studied. A decrease of Na/Ca exchange by high sodium gradient (200 mM NaCl in the perfusion solution) resulted in the reduction of myoglobin release from the heart during "calcium paradox". High sodium concentration solution (200 mM) increased protective effect of ATP during "calcium paradox". Exogenous phosphocreatine (100 mumol/mol) increased myoglobin release from the heart. During perfusion of the heart by high sodium concentration, phosphocreatine efficiently decreased myoglobin release from the heart during "calcium paradox". Exogenous ATP (as Na-pump activator) and high Na+ concentration solution (180 mM) prevented the LDH release from the myocardium, decreased ATP hydrolysis, inhibited Ca influx, maintained total adenine nucleotides, phosphate potential, energy charge of the cardiomyocytes.     

The role of calcium in the regulation of glucose uptake in isolated working rat heart

Catecholamines or ischemia may increase myocardial glucose uptake by an increase in intracellular calcium. We tested the hypothesis that increasing or decreasing extracellular calcium supply would change glucose uptake. Hearts were perfused for 60 min at a physiological workload with Krebs-Henseleit buffer containing glucose (5 mM) and oleate (0.4 mM; bound to 1% BSA). Calcium concentration was 2.5 mM. In group A (control; n = 12), insulin (1 mU/ml) was added at 30 min. In Group B (n = 7), the calcium concentration was increased to 5.0 and 7.5 mM at 20 min and 40 min, respectively. In Group C (n = 7), verapamil was added at 20 min (0.25 M) and 40 min (1.0 M) to decrease calcium influx. In group D (n = 7), EDTA was added at 20 min (0.5 mM) and at 40 min (1.5 mM) to decrease the free extracellular calcium. Glucose uptake was measured by ³H₂O production from [2-³H]glucose and cardiac work was measured simultaneously. Cardiac power in group B was 8.24 ± 0.60 mW at 2.5 mM calcium, 9.45 ± 0.50 mW at 5 mM calcium and 7.99 ± 0.99 mW at 7.5 mM calcium (n.s.). The addition of verapamil decreased contractile function in a dose-dependent manner (8.50 ± 0.74 vs. 3.11 ± 0.84 vs. 1.48 ± 0.39 mW, p < 0.01) suggesting that verapamil decreased cytosolic calcium concentration. A similar dose-dependent reduction in contractile performance was observed in the EDTA group (8.44 ± 0.81 vs. 7.42 ± 0.96 vs. 4.03 ± 1.32 mW, p < 0.01). Glucose uptake was 1.35 ± 0.11 mol/min/g dry weight under control conditions. Glucose uptake increased threefold with the addition of insulin. Increasing extracellular [Ca²⁺] did not affect glucose uptake. Decreasing Ca²⁺ availability showed a trend towards a decrease in glucose uptake (n.s.), which was minor compared to the decrease in contractile function. We conclude that extracellular calcium does not regulate glucose uptake in the isolated working rat heart in the presence of glucose and fatty acids as substrates. The trend of decreased glucose uptake when calcium supply was limited may be due to dramatically reduced energy demand and not directly due to changes in calcium.     

The effects of NaCl and CaCl2 on photosynthesis and growth of alfalfa plants

The effects of 0, 30, 60, and 90 mM NaCl, and 0 and 5 mM CaCl2 on certain parameters of photosynthesis and growth in alfalfa (Medicago sativa L. cv. Ghara yonjeh) plants were studied. The increasing NaCl concentration in the Hoagland nutrient solution decreased the contents of chlorophylls and the net photosynthetic rate, and increased the rate of respiration (RD) and CO2 compensation concentration in the leaves of treated plants. The contents of carotenoids (Car) were not significantly affected. The addition of 5 mM CaCl2 enhanced the RD and increased the Car contents in treated leaves. With the NaCl concentration in the culture medium increasing, the dry matter production in both root and shoot decreased, as well as the relative growth rate (RGR), net assimilation rate (NAR), and leaf area ratio (LAR). The addition of CaCl2 caused a partial elimination of the NaCl effects on the root and shoot, RGR and NAR, and it decreased the LAR.     

Effects of environment on the uptake and distribution of calcium in tomato and on the incidence of blossom-end rot

Studies of Ca uptake and distribution in relation to environmental variables were used to relate Ca status of tomato fruit to blossom-end rot (BER) incidence. Ca uptake was highly correlated with solar radiation and root temperature. The rate of Ca uptake decreased linearly with increasing salinity. High humidity reduced Ca import by the leaves but increased that by the fruit. While total plant dry weight was reduced more than fruit dry weight by salinity, total Ca uptake and the Ca content of the fruit were decreased similarly. Thus, the concentration of calcium in the fruit was substantially reduced by salinity. The distal half of the fruit contained less Ca than the proximal half. The lowest % Ca was found in the distal placenta and locular tissues, where BER first develops. The incidence of BER was often stimulated more by high salinity achieved with the addition of major nutrients than with NaCl. The cause of BER is usually an interaction between the effects of irradiance and ambient temperature on fruit growth and the effects of environmental stress on calcium uptake and distribution within the whole plant.     

Effects of amiloride analogues on adult Notophthalmus viridescens limb stump currents

We have previously investigated the relevance to limb regeneration of epidermally driven, Na+-dependent limb stump currents by blocking epidermal Na+ channels with amiloride, 3,5-diamino-6-chloro-N-(diaminomethylene)pyrazinecarboxamide. In order to reduce Notophthalmus viridescens stump currents more effectively than with amiloride, we have examined six amiloride analogues. Of these, only benzamil, 3,5-diamino-6-chloro-N-[(benzylamino)aminomethylene]pyrazinecarboxamide, was more effective than amiloride. The concentration of benzamil that reduced stump currents to half their initial value was 0.034 microM, while this concentration for amiloride was 0.42 microM. We also found a contribution of calcium ions to these currents. When immersed in water whose Ca2+ concentration decreased stepwise from 1 to 0 mM, stump currents decreased significantly, although to a variable extent, depending on the batch of newts. With 30 microM benzamil and 0.5 mM calcium (in water that also contained 1.5 mM NaCl and 0.06 mM KCl) stump currents could be reduced to very low levels and, in many cases, changed to incurrents.     

NaCl-Dependent growth, ion content and regeneration of calluses initiated from the mangrove plant,Bruguiera sexangula

Calluses initiated from leaves and seedlings of the mangrove,Bruguiera sexangula, were isolated from the original tissues and subcultured. Effects of NaCl on growth and ion content of each callus were measured. The growth rate of calluses derived from leaves (leaf callus) gradually decreased as the NaCl concentration in the medium increased, while that of calluses derived from seedlings (seedling callus) was highest in the medium containing 100 mM NaCl. Concentrations of Na and Cl in both calluses increased with increasing the NaCl concentration in the culture medium. The concentration of K of leaf calluses greatly decreased at 300 mM NaCl, while the K concentration of seedling calluses decreased only slightly and remained relatively high even in the presence of 300 mM NaCl. Transient treatment of leaf calluses with media containing high concentrations of NaCl frequently induced regeneration of adventitious tissues.     

In vitro fertilization in inbred BALB/c mice II: effects of lactate, osmolarity and calcium on in vitro capacitation

To elucidate requirements for in vitro sperm capacitation in inbred BALB/c mice, osmolarity, calcium and lactate were optimized using modified simplex optimization medium (mKSOM). Modified human tubal fluid (mHTF), a capacitation-supporting medium, was used as a control. In the first series of experiments, the effects of calcium and osmolarity were studied in the presence of lactate. Although preincubation with >or=5 mM CaCl2 improved fertilization after insemination significantly, it was still significantly lower than incubation with mHTF. To obtain fertilization at the equivalent levels to that of mHTF, isotonic osmolarity (305 mOsmol) was required. Trehalose, an osmotic reagent, could substitute for NaCl partially. In the second series of experiments, the effects of lactate were examined using a concentration of 5 mM calcium and isotonic osmolarity. Preincubation with 75%), as well as the percentages of B (capacitated) pattern sperm (>or=40%) in chlortetracycline (CTC) staining, as compared with incubation in mHTF (46% and 28%, respectively; p<0.05). In the third series of experiments, the effects of osmolarity and calcium in the absence of lactate were examined. An increase in osmolarity during sperm preincubation increased both fertilization and B-pattern sperm significantly in a dose-dependent manner. Trehalose, sucrose and choline chloride could substitute for NaCl. An increase in CaCl2 concentration during preincubation had no effect on fertilization, but this increase reduced the percentages of B-pattern sperm. In vitro capacitation of inbred BALB/c mice is sensitive to lactate and osmolarity, but that sensitivity for calcium varies depending on the presence or absence of lactate.     

Low-affinity Na+ uptake in the halophyte Suaeda maritima

Na(+) uptake by plant roots has largely been explored using species that accumulate little Na(+) into their shoots. By way of contrast, the halophyte Suaeda maritima accumulates, without injury, concentrations of the order of 400 mM NaCl in its leaves. Here we report that cAMP and Ca(2+) (blockers of nonselective cation channels) and Li(+) (a competitive inhibitor of Na(+) uptake) did not have any significant effect on the uptake of Na(+) by the halophyte S. maritima when plants were in 25 or 150 mM NaCl (150 mM NaCl is near optimal for growth). However, the inhibitors of K(+) channels, TEA(+) (10 mM), Cs(+) (3 mM), and Ba(2+) (5 mM), significantly reduced the net uptake of Na(+) from 150 mM NaCl over 48 h, by 54%, 24%, and 29%, respectively. TEA(+) (10 mM), Cs(+) (3 mM), and Ba(2+) (1 mm) also significantly reduced (22)Na(+) influx (measured over 2 min in 150 mM external NaCl) by 47%, 30%, and 31%, respectively. In contrast to the situation in 150 mm NaCl, neither TEA(+) (1-10 mM) nor Cs(+) (0.5-10 mM) significantly reduced net Na(+) uptake or (22)Na(+) influx in 25 mM NaCl. Ba(2+) (at 5 mm) did significantly decrease net Na(+) uptake (by 47%) and (22)Na(+) influx (by 36% with 1 mM Ba(2+)) in 25 mM NaCl. K(+) (10 or 50 mM) had no effect on (22)Na(+) influx at concentrations below 75 mM NaCl, but the influx of (22)Na(+) was inhibited by 50 mM K(+) when the external concentration of NaCl was above 75 mM. The data suggest that neither nonselective cation channels nor a low-affinity cation transporter are major pathways for Na(+) entry into root cells. We propose that two distinct low-affinity Na(+) uptake pathways exist in S. maritima: Pathway 1 is insensitive to TEA(+) or Cs(+), but sensitive to Ba(2+) and mediates Na(+) uptake under low salinities (25 mM NaCl); pathway 2 is sensitive to TEA(+), Cs(+), and Ba(2+) and mediates Na(+) uptake under higher external salt concentrations (150 mM NaCl). Pathway 1 might be mediated by a high-affinity K transporter-type transporter and pathway 2 by an AKT1-type channel.     

Caclium uptake and associated adenosine triphosphatase activity in fragmented sarcoplasmic reticulum. Requirement for potassium ions.

The effects of monovalent cations on calcium uptake by fragmented sarcoplasmic reticulum have been clarified. Homogenization of muscle tissue in salt-containing solutions leads to contamination of this subcellular fraction with actomyosin and mitochondrial membranes. When, in addition, inorganic cations are contributed by the microsomal suspension and in association with nucleotide triphosphate substrates there is an apparent inhibition of the calcium transport system by potassium and other cations. However, when purified preparations were obtained after homogenization in sucrose medium followed by centrifugation on a sucrose density gradient in a zonal rotor, calcium uptake and the associated adenosine triphosphatase activity were considerably activated by potassium and other univalent cations. When plotted against the log of the free calcium concentration there was only a slight increase in calcium uptake and ATPase activity in the absence of potassium ions but sigmoid-shaped curves were obtained in 100 mM K+ with half-maximal stimulation occurring at 2 muM Ca2+ for both calcium uptake and ATPase activity. The augmentation in calcium uptake was not due to an ionic strength effect as Tris cation at pH 6.6 was shown to be inactive in this respect. Other monovalent cations were effective in the order K+ greater than Na+ greater than NH4+=Rb+=Cs+ greater than Li+ with half-maximal stimulation in 11 mM K+, 16 mM Na+, 25 mM NH4+, Rb+, and Cs+ and in 50 mM Li+. There was nos synergistic action between K+ AND Na+ ions and both calcium uptak and associated ATPase were insensitive to ouabain. Thallous ions stimulate many K+-requiring enzymes and at one-tenth the concentration were nearly as effective as K+ ions in promoting calcium uptake. The ratio of Ca2+ ions transported to P1 released remained unchanged at 2 after addition of K+ ions indicating an effect on the rate of calcium uptake rather than an increased efficiency of uptake. In support of this it was found that during the stimulation of calcium uptake by Na+ ions there was a reduction in the steady state concentration of phosphorylated intermediate formed from [gamma-32P]ATP. It is considered that there is a physiological requirement for potassium ions in the relaxation process.     

Polyamines Stimulate Mitochondrial Calcium Transport in Rat Brain

The effects of the polyamines spermine and spermidine on rat brain mitochondrial calcium transport were examined using a variety of techniques for measuring the kinetics of calcium uptake and the buffering capabilities of isolated mitochondria. Spermine both increased the rate of calcium accumulation and decreased the set-point to which isolated mitochondria buffer free calcium concentration. In the presence of physiological concentrations of sodium and magnesium, spermine lowered the extramitochondrial calcium level to approximately 0.3 microM, a value close to the resting intracellular calcium concentration. The effect of polyamines was concentration dependent, with a half-maximal effect of spermine observed at approximately 0.1-0.4 mM (respiratory substrate dependent), whereas spermidine was approximately 10 times less potent. Calcium transport by hippocampal mitochondria was stimulated markedly more by spermine than was calcium transport by mitochondria isolated from brainstem. The stimulatory effect of spermine was not due to an increase in the transport of respiratory substrates inside the mitochondria nor to an effect on the enzymes using these respiratory substrates. An examination of the effect of spermine on the kinetics of calcium uptake indicated that spermine increased calcium uptake maximally at low calcium concentrations. Beyond that level, the stimulatory effect of spermine decreases, and spermine can even inhibit calcium uptake. These results are in good agreement with previous reports on the effects of polyamines on calcium transport in mitochondria from peripheral tissue. They support the hypothesis that spermine increases the rate of calcium uptake by mitochondria by increasing the affinity of the uniporter for calcium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alleviation of detrimental effects of NaCl by silicon nutrition in salt-sensitive and salt-tolerant genotypes of sugarcane (Saccharum officinarum L.)

Salt stress is a major environmental factor which adversely affects the crop yield and quality. However, adequate regulation of mineral nutrients may ameliorate the deleterious effects of salts and help to sustain crop productivity under salt stress. Salt-sensitive (SPF 213) and salt-tolerant (HSF 240) sugarcane genotypes were grown in gravel at 0 and 100 mM NaCl by supplying 0, 1.4 mM, 2.1 mM and 2.8 mM of Si as calcium silicate. Results revealed that plants treated with NaCl alone showed a significant (P?≤?0.05) reduction in dry matter production, K⁺ concentration, cane yield and juice quality in both genotypes but the magnitude of reduction was relatively more in salt-sensitive genotype than salt-tolerant. Addition of Si significantly (P?≤?0.05) reduced the uptake and translocation of Na⁺ but increased K⁺ concentrations particularly in shoots of both sugarcane genotypes. Cane yield and yield attributes were significantly (P?≤?0.05) higher where Si was added. Juice quality characteristics were significantly (P?≤?0.05) improved in salt-sensitive and salt-tolerant sugarcane genotypes with the application of Si. The results suggested that added Si interacted with Na⁺, reduced its uptake and transport to shoots and consequently improved cane yield and juice quality in salt-sensitive and salt-tolerant sugarcane genotypes under salt stress.     

Response to increasing rates of boron and NaCl on shoot proliferation and chemical composition of in vitro kiwifruit shoot cultures

The in vitro response of kiwifruit (Actinidia deliciosa) to increasing concentrations of boron (B) and NaCl in the culture medium was studied. Kiwifruit shoot cultures were grown in vitro for 12 weeks on an MS medium containing two B concentrations (0.1 and 2 mM) combined with five NaCl concentrations (0, 10, 20, 40 and 80 mM). Kiwifruit produced the longest shoots with 2 mM B when NaCl concentration was 0--20 mM. More shoots were produced with 2 mM B for all NaCl treatments. More shoots were produced with 2 mM B and 10 and 20 mM NaCl. High B concentrations in the culture medium significantly increased shoot proliferation. Explants exhibited a moderate chlorotic appearance with 40 mM NaCl and shoots died with 80 mM NaCl. With 2 mM B, the B concentration of explants was 5--9X greater for the various NaCl treatments compared to the control. Increasing the NaCl concentration from 10 to 80 mM, resulted in higher Na and Cl concentrations in explants for all B treatments, while K and Ca concentrations decreased. Phosphorus concentration in the explants was significantly increased by increasing the NaCl concentration reaching a maximum value at 80 mM NaCl for the two B concentrations.