Iso-osmotic Solutions Of NaCl Research Articles

Effect of pH and Hypo-Osmotic Stress on NaCl Electrolyte Permeation across Red Blood Cell Membrane

The study compares the effects produced by H+ concentrations in hypo-osmotically stressed NaCl solutions on permeation through RBC membrane. Iso-osmotic solutions of NaCl (160 mM) were prepared taking into account their molecular weight and osmotic concentration. Iso-osmotic solutions (25 mL) were diluted with 25 mL of distilled water to give half the initial concentrations (50 % hypotonic salt solutions). Hypotonic NaCl solutions of pH of 6.2, 6.8, 7.4 and 8.0 were prepared, mixed with 0.05 mL of RBC suspension and their absorbance/min for 16 min were measured using a UV/Visible spectrophotometer while the RBCs haemolyse. H+ concentration and hence pH was found to have a significant effect on ion permeability through RBC membrane. Permeation occurred faster in alkalinic solutions under hypo-osmotic stress. Permeation increased with every increase in pH and the increase is steeper at pH 7.4 – 8.0.Keywords: Ions, Electrolyte, Permeability, Red Blood Cell, Membrane

Influence of salinity and osmotic stress on germination process in an old sicilian landrace and a modern cultivar of Triticum Durum Desf.

In many world regions, osmotic and salt stresses are becoming the primary environmental conditions limiting successful establishment of crops. The old durum wheat landraces may provide a source of genes useful to enhance crop resilience to the abiotic stresses of dryland areas or foreseen as a result of climate change. With this in mind, in order to determine the effects of salt and osmotic stresses on durum wheat germination, an old Sicilian durum wheat landrace “Timilia” and a relatively recent cultivar “Mongibello” were investigated at various iso-osmotic solutions of NaCl and mannitol at osmotic potentials of: 0 − control, −0.125, −0.250, −0.500 and −0.750 MPa.Under stress conditions, different germination and early growth behavior was observed in the two durum wheat genotypes. Timilia presented almost stable germination even at the highest osmotic stresses (96.7% and 88.3% seed germination at 0 and −0.750 MPa, respectively) showing a higher capacity of seed imbibition than Mongibello. The latter thus showed a higher sensitivity than the old landrace to the studied stresses. The variability ascertained in the response to salinity stress indicate that Timilia could be a source of interesting genes for breeding programs.

Growth responses to sulfate and chloride are related to different phytohormone profiles in the halophyte Prosopis strombulifera

In this study, the profile of plant phytohormones traditionally considered as plant growth promoters (GA1, GA3, GA4, IAA and Z) was determined in roots and leaves of the halophyte Prosopis strombulifera grown hydroponically in iso-osmotic solutions of NaCl, Na2SO4 and their mixture. Hormonal levels were correlated with growth parameters and ABA levels. Different sodium salts in the medium differentially affected the synthesis of these compounds. NaCl treated plants showed the greatest accumulation of GA4 and GA1 and lower levels of their metabolites GA8 and GA34 both in root and leaves, in coincidence with the optimum growth observed at ?o -1.9 Mpa this response was also observed at ?o -2.6 MPa. IAA level was unaltered in these plants while Z content was higher in roots than in leaves. In contrast, both leaves and roots from Na2SO4 treated plants showed lower GA1 and GA4 and increased GA8 and GA34 levels at high salinity. High levels of IAA were found in roots of these plants, but the ABA/IAA ratio increased with increasing salt concentrations in the culture medium. This pattern was also observed in the high ABA/GAs ratios. Z levels were very low in all salt treatments. The results of this study show that the halophytic growth under NaCl treatment is mainly regulated by GA1 and GA4 and low relative levels of ABA and IAA. The toxicity of sulfate alters this pattern reversing the ratio ABA/GAs and increasing the synthesis of IAA in conjunction with increased lateral root formation. In bisaline-treated plants intermediate values were observed in the levels of these phytohormones as compared to monosaline treatment.

Fast filtration for metabolome sampling of suspended animal cells

A new method for sampling suspended animal cells by fast filtration is presented that allows rapid quenching of cellular metabolism and efficient separation of the cells from culture medium. Compared to sampling with a microstructure heat exchanger or centrifugation without prior quenching, the adenylate energy charge and the measured concentrations especially of metabolites with a high turnover rate or of metabolites early in metabolic pathways were substantially higher. No leakage of ATP from the cells was observed when using iso-osmotic NaCl solution in the washing step. The combination of fast filtration and cold methanol extraction is therefore suitable for intracellular metabolomic studies of suspended animal cell cultures and superior to other methods currently applied.

Osmotic and ionic effects of NaCl and Na 2SO 4 salinity on Phragmites australis

Osmotic and ion-specific effects of NaCl and Na 2SO 4 on Phragmites australis (Cav.) Trin ex. Steud. were investigated in a laboratory experiment by examining effects of iso-osmotic solutions of NaCl and Na 2SO 4 on growth, osmolality of cell sap, proline content, elemental composition and gas exchange. Plants were supplied with a control standard nutrient solution ( Ψ = −0.09 MPa) or solutions of NaCl or Na 2SO 4 at water potentials of −0.50, −1.09 or −1.74 MPa. Salt treatments increased root concentrations of Na and S or Cl, whereas P. australis had efficient mechanisms for exclusion of Na and S and partly Cl ions from the leaves. Incomplete exclusion of Cl from the leaves may affect aboveground biomass production, which was significantly more reduced by NaCl than Na 2SO 4. Stomatal conductance was negatively influenced by decreasing water potentials caused by NaCl or Na 2SO 4, implying that a non-significant photosynthetic depression observed in plants grown at −1.74 MPa was mainly due to osmotically induced stomatal closure. This was supported by decreasing internal CO 2 concentrations. Saline conditions increased the intrinsic water use efficiency and did not alter photosynthetic parameters derived from light response curves, supporting the assumption of a well-functioning CO 2 utilization in salt stressed plants. The leaf proline concentration increased equally in NaCl and Na 2SO 4-treated plants, and may play an important role as a compatible organic solute. P. australis possesses a range of mechanisms conferring tolerance to both NaCl and Na 2SO 4 stress and except in terms of growth the phytotoxicity of NaCl and Na 2SO 4 are comparable.

Responses of germination and radicle growth of two Populus species to water potential and salinity

The effects of water potential, NaCl and Na2SO4 on germination and radicle growth of two riparian tree species, Populus euphratica Oliv. and P. pruinosa Schrenk (Salicaceae), were tested. Growth chamber studies revealed an optimum temperature range for seed germination of both species between 15–35°C. The final germination percentage of both species decreases with decreasing water potential in all types of solution applied in the experiments. P. pruinosa was less tolerant to low ψW stress than P. euphratica, especially in salt solutions. Germination percentages fell below 20% for P. pruinosa at −0.6 MPa (NaCl) or −0.4 MPa (Na2SO4) and for P. euphratica at −1.2 MPa (NaCl) or −0.6 MPa (Na2SO4). Radicle growth of both species was inhibited by high concentrations of PEG, NaCl and Na2SO4. However, growth was enhanced at −0.13 and −0.29 MPa in PEG or at −0.13 MPa in NaCl solutions compared to distilled water. Radicle growth of P. euphratica was higher than that of P. pruinosa. Germination and radicle growth of both species exhibited ion toxicity. Na2SO4 was more toxic than iso-osmotic solutions of NaCl. Radicle growth proved to be more sensitive than seed germination. Thus, flooding does not only yield the necessary soil moisture for germination but also favors seedling establishment of both species through leaching of salts from the soil surface. The different sensitivity of the species during their early growth stages might, moreover, contribute to the observed differences in their distribution in the Talim Basin (northwest China).

Mechanisms by which food intake elevates circulating levels of hyaluronan in humans

Plasma hyaluronan is a potentially useful clinical test, especially in liver disease. It rises after eating, but mechanisms by which this occurs are not known. The study aimed at defining the effect of different food and liquid intake on plasma hyaluronan and to address mechanisms. The effects on plasma hyaluronan of ingestion of high-fat and low-fat meals, glucose solution, and saline, and of intravenous metoclopramide and oral cisapride were defined in healthy fasted subjects by serial measurements over 5 h. Hyaluronan was measured by a radiometric assay. After test meals and glucose ingestion, plasma hyaluronan rose to 1.7-13 times the fasting levels in 11 healthy volunteers. Peak values were observed in most subjects 45-90 min after ingestion and reached levels in six subjects that might suggest the presence of hepatic fibrosis or cirrhosis. No change occurred after ingestion of 0.48 L iso-osmotic NaCl solution, equal in bulk to the glucose solution. Stimulation of gastrointestinal motility with metoclopramide had no effect but oral cisapride induced a pattern of elevated plasma hyaluronan which mimicked that induced by foodstuffs. Displacement of hyaluronan from gastrointestinal tissues prevails over the increased clearance expected from elevated portal blood flow. The heightened flux of tissue fluid necessary to displace tissue hyaluronan is best explained by vasodilatation in response to ingestion of nutrients, and subsequent increase in intestinal lymph flow, rather than by fluid absorption, together with gut contraction. The discriminating value of plasma hyaluronan in clinical practice may be greatly enhanced by sampling in fasted subjects at rest.

Controlled release of estradiol solubilized in carbopol/surfactant aggregates

The potential of carbopol/surfactant dispersions as solubilizing and controlled release systems of estradiol (a poorly water-soluble drug) was evaluated. The solubilization of estradiol in the dispersions of Carbopol® 934 (0.25%) and Pluronic F-127, Tween 80, sodium dodecylsulfate (SDS), or benzalkonium chloride (BkCl) was assessed, by differential scanning calorimetry (DSC) of films obtained by desiccation, as a decrease in estradiol melting temperature and enthalpy. The amounts of estradiol solubilized in carbopol/SDS and carbopol/Tween 80 aqueous dispersions were considerably greater (solubilization capacity: 1.3 and 9 times greater) than in the surfactant alone solutions and up to 100 times greater than in water. High aggregates/water equilibrium partition coefficients of estradiol in carbopol/SDS (1768 M −1) and carbopol/Tween 80 (14114 M −1) dispersions were found. Carbopol/(1%) SDS/(25 mg/dl) estradiol and carbopol/(0.1%) Tween 80/(5 mg/dl) estradiol dispersions had a pH of around 4, were easy flowing, and showed sustained release for at least 1 week. Estradiol diffusion coefficients were greater when the receptor medium was 0.3–1.0% SDS solution than when it was iso-osmotic NaCl solution or pH 7.5 phosphate buffer. At this pH, a viscoelastic gel is formed on the donor side of the membrane and the drug diffusion slowed down. When the receptor medium contains a surfactant, estradiol release seems to happen as a direct exchange between the carbopol/surfactant aggregates and the receptor surfactant micelles. If no surfactant is in the receptor fluid, estradiol/surfactant complexes migrate towards the receptor. Despite the low viscosity of these dispersions, estradiol diffusion coefficients were in the same order of magnitude as those obtained with a commercially available neutralized ethanol/water carbopol gel of estradiol (60 mg/dl). When the receptor medium had no surfactant, the low affinity of estradiol for water prevented drug diffusion from the commercial formulation. In summary, carbopol/surfactant aggregates act as efficient carriers of hydrophobic drugs; the affinity of estradiol for carbopol/surfactant aggregates, their dissociation, and the diffusivity of estradiol/surfactant complexes being key factors in the control of the drug release process.

Effect of salt and osmotic stresses on germination in durum wheat (Triticum durum Desf.)

In order to determine the relative importance of ionic toxicity versus the osmotic component of salt stress on germination in durum wheat (Triticum durum Desf.), seeds of three cultivars differing in their salt and drought resistance (Omrabi-5, drought-resistant; Belikh, salt-resistant and Cando, salt-sensitive) were incubated in various iso-osmotic solutions of NaCl, mannitol and polyethylene-glycol (PEG) (osmotic potential of −0.15 (control solution) −0.58, −1.05 or −1.57 MPa). Moderate stress intensities only delayed germination, whereas the highest concentration of NaCl and PEG reduced final germination percentages. PEG was the most detrimental solute, while mannitol had no effect on final germination percentages. All osmotica reduced endosperm starch and soluble sugars content as well as α-amylase activities recorded after 48 h of treatment while β-amylase activities were, in contrast, slightly stimulated in all cultivars. Deleterious effects of NaCl and PEG were higher on isolated embryos germinated onto an in vitro Linsmaier and Skoog (LS) medium comparatively to whole seeds. All PEG-treated embryos, however, recovered after the stress relief while NaCl-treated embryos exhibited a lower rate of recovery and some extent of abnormal germination after rinsing. It was concluded that stress inhibition of germination could not be attributed to an inhibition of mobilisation of reserves and that the main effect of PEG occurred via an inhibition of water uptake while detrimental effects of NaCl may be linked to long-term effects of accumulated toxic ions. The behaviour of the three cultivars during germination did not fully reflect their mean level of putative stress resistance in field conditions and germination is, therefore, not recommended as a reliable selection criterion for breeding purposes.

RNase and DNase activities in the alfalfa and lentil grown in iso-osmotic solutions of NaCl and mannitol

Summary Nucleolytic activities from two plants of Leguminosae family were determined in order to consider if the nucleases of plants which belong to the same family or to the same species responded in similar ways to stress conditions during growth. Growth parameters of both plants were examined in parallel. In detail, seedlings from two plants, alfalfa ( Medicago sativa L. cv. Luzerne Euver) and lentil ( Lens culinaris cv. Thessalia), showed significant differences in response to iso-osmotic solutions of NaCl (100 mmol · L −1 solution equivalent to conductivity 8.0 dS m −1 ) and mannitol (190 mmol · kg −1 ). Plant height and dry weight of mannitol/NaCl-treated seeds in both plants were lower in comparison to controls (water). Mannitol stress reduced height and dry weight in alfalfa seedlings more than did NaCl. By contrast, lentil seedling growth was inhibited more by NaCl stress than mannitol. In addition, DNase and RNase response to mannitol stress differed in each plant compared to the controls. Mannitol stress induced a sharp increase in DNase- and RNase-specific activity during the initial stages of alfalfa seedlings' growth, followed by a decrease during subsequent days; in lentil seedlings, these activities were inhibited throughout the entire growth period. NaCl stress inhibited the above activities in both plants. After native electrophoresis on gels polymerized in the presence of DNA/RNA, the overall band intensities confirmed the above quantitative results of alfalfa RNase and DNase activity. In addition, the active gel analysis revealed that the decrease of nucleolytic activities in mannitol-treated alfalfa seedlings was mainly due to the strong reduction of acid nucleases. This is the first report of different non-ionic osmotic response of type I plant nucleases during seedlings' growth. In vitro, the addition of up to 300 mmol/L mannitol did not affect acid and neutral nuclease activity in enzyme preparations extracted, purified, and separated from control and mannitol-treated alfalfa seedlings. Our results suggest that plant nucleases responded in a different way to osmotic stress and ionic stress conditions during seedlings' growth.

Effect of Salinity on Germination and Seedling Growth of twoAtriplexspecies (Chenopodiaceae)

Salinity is one of the environmental factors that has a critical influence on the germination of halophyte seeds and plant establishment. Salinity affects imbibition, germination and root elongation. However, the way in which NaCl exerts its influence on these vital processes, whether it is through an osmotic effect or a specific ion toxicity, is still not resolved. Dimorphic seeds of the halophytesAtriplex prostrataandA. patulawere treated with various iso-osmotic solutions of NaCl and polyethylene glycol (PEG). For each treatment, imbibition, germination rate, percent germination, germination recovery and nuclear area of root tip cells were compared. Higher concentrations of NaCl (-1.0 MPa) were more inhibitory to imbibition, germination and seedling root elongation than iso-osmotic PEG solutions. All seeds recovered from a pre-treatment with -2.0 MPa NaCl and PEG solutions, except large seeds ofA. prostratawhich failed to germinate following transfer from -2.0 MPa NaCl. NaCl caused a greater increase in nuclear volume than iso-osmotic PEG solutions. These data suggest that the influence of NaCl is a combination of an osmotic effect and a specific ion effect.

Amphotericin B Kills Unicellular Leishmanias by Forming Aqueous Pores Permeable to Small Cations and Anions

The polyene antibiotic amphotericin B (AmB) is known to form two types of ionic channels across sterol-containing liposomes, depending on its concentration and time after mixing (Cohen, 1992). In the present study, it is shown that AmB only kills unicellular Leishmania promastigotes (LPs) when aqueous pores permeable to small cations and anions are formed. Changes of membrane potential across ergosterol-containing liposomes and LPs were followed by fluorescence changes of 3,3' dipropylthiadicarbocyanine (DiSC3(5)). In KCl-loaded liposomes suspended in an iso-osmotic sucrose solution, low AmB concentrations (</=0.1 microM) induced a polarization potential, indicating K+ leakage, but no movement of cations and anions was allowed until AmB concentrations greater than 0.1 microM were added. In agreement with these data, it was found that AmB altered the negative membrane potential held across LPs in a manner consistent with the differential cation/anion selectivity exhibited by the channels formed in liposomes. Thus, LPs suspended in an iso-osmotic sucrose solution did not exhibit any AmB-induced membrane depolarization effect brought about by efflux of anions until 0.1 microM or higher AmB concentrations were added. By contrast, LPs suspended in an iso-osmotic NaCl solution and exposed to 0.05 microM AmB exhibited a nearly total collapse of the negative membrane potential, indicating Na+ entry into the cells. The concentration dependence of the AmB-induced permeability to different salts was also measured across vesicles derived from the plasma membrane of leishmanias (LMVs), by using a rapid mixing technique. At concentrations above 0.1 microM, AmB induced the formation of aqueous pores across LMVs with a positive cooperativity, yielding Hill coefficients between 2 to 3. Measured anion selectivity across such aqueous pores followed the sequence: SCN > NO3 > Cl > I > Br > acetate (SO2-4 being impermeable). Cell killing by AmB was followed by fluorescence changes of the DNA-binding compound ethidium bromide (EB). At low concentrations (</=0.1 microM), AmB was found to be nonlethal against LPs but, above this concentration, leishmanias were rapidly killed. The rate and extent of such an effect were found to be dependent on the type of cation and anion present in the external aqueous solution. For both NH+4 and Na+ salts, the measured rank order of AmB cell killing followed the same sequence that was determined for AmB-induced salt permeation across LMVs. Further, replacement of either extracellular Na+ by choline or Cl- by SO2-4, or its partial substitution by sucrose, in iso-osmotic conditions, led to a complete inhibition of the killing effect exerted by otherwise lethal AmB concentrations. Finally, it was shown that tetraethylammonium (TEA+), an organic cation that is known to block AmB-induced salt permeation across LMVs was able to retard the time lag observed for EB incorporation across LPs, indicating that this parameter can be taken to represent the time taken for salt accumulation inside the parasites. The present results thus indicate clearly that low AmB concentrations (</=0.1 microM) were able to form across LPs, cation channels that collapsed the parasite membrane potential but are not lytic. At high concentrations (>/=0.1 microM), a salt influx via the aqueous pores formed by the antibiotic was followed by osmotic changes leading to cell lysis. This last stage is supported by electron microscopy observations of the changes of parasite morphology immediately upon addition of AmB, which indicated that the typical elongated promastigote cell forms became rounded and the flagella swells and round up. The present work is the first demonstration of the in vitro sensitivity of Leishmania promastigotes to osmotic lysis by AmB.

Ammonia and urea metabolism in relation to gill function and acid-base balance in a marine elasmobranch, the spiny dogfish (Squalus acanthias)

Nitrogenous waste excretion in resting dogfish occurred largely (>90 %) as urea-nitrogen (urea-N) efflux across the gills, with a very small urea efflux via the kidney. Ammonia excretion, almost entirely at the gills, accounted for less than 3 % of total nitrogen excretion. Given the extremely high blood urea levels (approximately 640 mmol-N l-1) 'retained' for osmoregulation, and blood ammonia levels (approximately 80 &micro;mol-N l-1) comparable to those of teleosts, the gills of resting dogfish were exceptionally impermeable to both urea and ammonia. Experiments investigated the origins of these low permeabilities and the responses of urea-N and ammonia-N excretion and acid&shy;base status to 6 h infusions with iso-osmotic solutions of NaCl (control), NH4Cl, NaHCO3, urea and its analogues thiourea and acetamide. NaCl had no effects, whereas NH4Cl loading caused intense acidosis and marked elevation of acidic equivalent, ammonia-N and urea-N excretion rates, the latter despite unchanged blood levels of urea-N. Apparent branchial ammonia permeability increased greatly. Acidosis resulted from both stimulated urea production and branchial NH3 loss, the former making the larger contribution. NaHCO3 loading caused intense alkalosis, a marked elevation of basic equivalent excretion and a moderate stimulation of urea-N excretion. Blood urea-N levels were again unchanged. Infusion of urea itself raised blood urea-N levels, but initially reduced branchial urea-N excretion. Acetamide and thiourea infusions both moderately elevated branchial urea-N excretion. We suggest that the low ammonia permeability may arise metabolically from an ammonia scavenging system in the gills, that a 'back-transport' mechanism in the gills may contribute to the low urea permeability, and that the dissociation between blood urea-N levels and excretion rates may reflect urea production at extrahepatic sites. These studies demonstrate that urea synthesis in the dogfish is linked more to nitrogen availability than to acid&shy;base status.

Volume regulation in Spiroplasma floricola: Evidence that Na+ is extruded by a Na+/H+ antiporter

Marked cell swelling followed by lysis was observed when Spiroplasma floricola cells were incubated in iso-osmotic solutions of NaCl, KCI, choline chloride or sorbitol in the absence of an energy source. In the presence of an energy source the cells did not swell suggesting that S. floricola relies on an energy-dependent mechanism(s) for cell volume regulation. An ammonium chloride dilution procedure was utilized to generate a pH gradient (inside acid) across the cell membrane of S. floricola cells. The addition of NaCl resulted in an intracellular alkalization suggesting the presence of a Na+/H+ exchange activity. In 22Na+-loaded cells, glucose-dependent 22Na+ extrusion was observed at acidic pH in both the presence and absence of Na+ ions. The extrusion was completely inhibited by carbonyl cyanide m-chlorophenylhydrazone (CCCP, 10 μM) and partially inhibited by dicyclohexylcarbodiimide (DCCD, 100 μM) indicating that in S. floricola, Na+ movement is driven by the electrochemical gradient of H+ via a Na+/H+ antiporter. The specific ATPase activity of S. floricola membranes was at least twofold higher than that described in other mollicutes. Activity was Mg2+-dependent over the pH range (6.5-8.5) tested, but was very little affected by Na+ (up to 100 mM). DCCD (25 μM) markedly inhibited both membrane-bound and solubilized ATPase activity, whereas orthovanadate (50 μM) had only a small inhibitory effect. The properties of the enzyme are consistent with a F0F1-ATPase. It is suggested that the enzyme operates in the direction of hydrolysing ATP formed by glycolysis leading to the generation of a δpH, which is the major driving force for the Na+/H+ antiport activity.

Protein Phosphorylation-Dephosphorylation in Alfalfa Seeds Germinating under Salt Stress

Summary When seeds of alfalfa (Medicago sativa L. cv. Luzerne Euver) were germinated under iso-osmotic solutions of NaCl (0.10M solution equivalent to conductivity 8.0 dSm-1) and mannitol (0.19m) or an increased level of NaCl (0.15M solution equivalent to conductivity 11.6dSm-1) seedling growth indicated a continuous decrease in plant height and dry weight in subsequent days of germination. In contrast, the extractable proteins of NaCl and mannitol stressed seedlings were more comparable to controls. Protein kinase (EC 2.7.1.37) and protein phosphatase (EC 3.1.3.16) specific activities were determined in crude extracts of alfalfa seedlings. At both concentrations of NaCl protein kinase specific activities towards endogenous substrates were higher than the control or mannitol except at day 7 under 11.6 dSm-1 NaCl. Unlike protein kinase specific activities, the protein phosphatase specific activities against 32P-labeled bovine casein were inhibited in the presence of NaCl at all days of germination, except at day 5, when 8.0 dSm-1 NaCl enhanced them. The presence of mannitol (0.19 m) also inhibited protein phosphatase specific activites. These observations suggest that some specific ionic effect of salt was responsible for the behaviour of the enzymes. SDS-electrophoresis followed by autoradiography revealed three major groups of in vitro phosphorylated proteins (in the presence of Ca2+ or Mn2+) in ungerminated seeds: a low molecular group (Mrs ca. 10–20,000), a medium molecular group (Mrs ca. 35–50,000) and a high molecular group (Mrs ca. 50-86,000). The latter was absent from the seedlings in all treatments. An increase in salinity (11.6dS m-1 NaCl) retarded the disappearance of medium molecular group protein bands in contrast to control or mannitol where these almost disappeared from the first day of germination. A condition of normal alfalfa seedling growth may be regulated by dephosphorylation of medium molecular group protein bands.

Role of Na+ cycle in cell volume regulation of Mycoplasma gallisepticum.

The mechanism for the extrusion of Na+ from Mycoplasma gallisepticum cells was examined. Na+ efflux from cells was studied by diluting 22Na+-loaded cells into an isoosmotic NaCl solution and measuring the residual 22Na+ in the cells. Uphill 22Na+ efflux was found to be glucose dependent and linear with time over a 60-s period and showed almost the same rate in the pH range of 6.5 to 8.0. 22Na+ efflux was markedly inhibited by dicyclohexylcarbodiimide (DCCD, 10 microM), but not by the proton-conducting ionophores SF6847 (0.5 microM) or carbonyl cyanide m-chlorophenylhydrazone (CCCP, 10 microM) over the entire pH range tested. An ammonium diffusion potential and a pH gradient were created by diluting intact cells or sealed membrane vesicles of M. gallisepticum loaded with NH4Cl into a choline chloride solution. The imposed H+ gradient (inside acid) was not affected by the addition of either NaCl or KCl to the medium. Dissipation of the proton motive force by CCCP had no effect on the growth of M. gallisepticum in the pH range of 7.2 to 7.8 in an Na+-rich medium. Additionally, energized M. gallisepticum cells were stable in an isoosmotic NaCl solution, even in the presence of proton conductors, whereas nonenergized cells tended to swell and lyse. These results show that in M. gallisepticum Na+ movement was neither driven nor inhibited by the collapse of the electrochemical gradient of H+, suggesting that in this organism Na+ is extruded by an electrogenic primary Na+ pump rather than by an Na+-H+ exchange system energized by the proton motive force.

Germination of the Salt-Tolerant Grass Diplachne fusca. II. Salinity Responses

The responses -of germination of the salt-tolerant grass Diplachne fusca (L.) Beauv. to salinity and various temperature regimes are described. At temperatures of 30/20°C (12 h light and dark periods), final germination was 70% in distilled water, decreased to 50% in 175 mol m-3 NaCl (π = - 0.8 MPa) and 7% in 380 mol m-3 NaCl (π = -1.8 MPa). Increasing salinity from 0-130mol m-3 NaCl decreased the final germination percentage, but did not modify the threshold temperatures (day or night temperature &gt; 27°C) at which germination occurred. Presoaking in distilled water or 1% CaCl2· 2H20 solution did not significantly affect the final germination percentage of seeds which were subsequently placed in solutions with a range of salinities from 0-210 mol m-3 NaCl (*#960 = 0 to - 1.0 MPa). How- ever, addition of CaCl2 to NaCl solution increased the final germination percentage compared with that in pure NaCl solution. Presoaking in concentrated (400 mol m-3) NaCl solution caused a decrease in subsequent germinability of 20 or 40% in 0 and 40 mol m-3 NaCl, respectively. Under field conditions (in soil with mean daily maximum temperature of 33°C and mean daily minimum temperature of 15°C), rates of seedling establishment were similar (16% of seed sown) in soils irrigated with 0 or 50 mol m-3 NaCl, and were 1% in those irrigated with 100 mol m-3 NaCl. The inhibition of germination in NaCl solution was largely an osmotic effect since there was a similar reduction in the final germination percentage in iso-osmotic solutions of NaCl and mannitol. However, the proportion of seeds germinating in NaCl solution was enhanced by adding calcium. The inhibition of germination was greater in sulfate solutions compared with that in chloride solutions and, to a lesser degree, in potassium compared with sodium solutions. The practical implications of our results are discussed. The incorporation of gypsum into the soil and measures to leach salts from the topsoil are recommended before D. fusca is sown on saline land.