External Salt Concentration Research Articles

Effect of Light Intensity on Adaptation ofDunaliellato Very High Salt Concentrations

Light intensity was found to have a strong effect on the adaptation to high salt concentrations of a green microalga, Dunaliella parva, normally grown at low and medium salt concentrations. At high light intensities (∼200 μmol m -2 s -1 ) the content increased in parallel with an increase in external salt concentration; protein synthesis and cell division continued with no period of arrest. At low light intensities no glycerol synthesis occurred as the external salt concentration was raised; protein synthesis and cell division were equally arrested. The importance of high light intensity during the initial phase of increase of salt concentration was demonstrated and was found to be a requirement for protein synthesis and cell division

Ectoine accumulation and osmotic regulation in Brevibacterium linens

Brevibacterium linens can grow in media of relatively high osmotic strength (up to 3 M-NaCl). Optimal growth in minimal medium occurred with either added NaCl (0.5-1 M) or other osmolytes developing an equivalent osmotic pressure. Above 1 M-NaCl the growth rate slowed, but was enhanced by adding the osmoprotectant glycine betaine or its precursor choline (1 mM) to the media. Neither soluble carbohydrates nor ninhydrin-reacting compounds accumulated during osmotic treatment. However, a Dragendorff-positive compound, together with K+ ions, accumulated (7-fold) as a consequence of elevating the medium osmolality. Spectral characteristics of the purified compound were similar to those of synthesized 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (ectoine). In the absence of exogenously supplied osmoprotectants, a strict dependence between the intracellular ectoine content and the external salt concentration (up to 1 M-NaCl) was observed. From 1 to 2 M-NaCl, the ectoine content decreased, and this signalled decreased self-osmoprotection by this bacterium. Interestingly, at these salt concentrations, exogenous glycine betaine led to the greatest beneficial effect. Glycine betaine or choline added to the medium was actively taken up by the cells in an osmolality-dependent manner, and the resulting betaine accumulation caused a sharp decrease in intracellular ectoine content. Radiolabelling of ectoine occurred only when L-[U-14C]glutamate was used as a precursor; de novo synthesis was dependent on the external osmolality and was strongly inhibited by exogenously supplied glycine betaine. These results imply that ectoine may play a major role in counteracting the effects of osmotic stress in media of osmotic pressure equivalent to ⋜ 1 M-NaCl.

Effect of salinity on growth of four strains of Rhizobium and their infectivity and effectiveness on two species of Acacia

Two Rhizobium strains (WU1001 and WU1008) were isolated from nodules of Acacia redolens growing in saline areas of south-west Australia, and two strains selected from the University of Western Australia's culture collection (WU429 isolated from A. saligna and WU433 from A. cyclops). The growth of each in buffered, yeast extract mannitol broth culture was largely unaffected by salt up to 300 mM NaCl. A slight increase in lag time occurred at concentrations of 120 mM NaCl and above, but cell number at the static phase was not affected. Each of the four Rhizobium strains tested accumulated Na+ but showed decreasing levels of sugar with increasing salt in the external medium. Amino acid levels also increased, in some cases by more than tenfold. However, the relative proportion of each remained fairly constant in the bacteria, irrespective of salt treatment. Only trace quantities of proline were detected and there was no increase in this amino acid with salt. Acidic amino acids (glutamate and aspartate) remained as a constant proportion. Rhizobium strains WU429, WU1001 and WU1008 produced effective nodules on both A. cyclops and A. redolens grown in sand with up to 80 mM NaCl (added in nutrient solutions free of nitrogen). Strain WU433 was highly infective on both Acacia species tested at low salt concentrations (2–40 mM NaCl), but infection was sensitive to salt levels at 120 mM NaCl and above. Nodules formed with strain WU433 were, however, ineffective on both A. redolens and on A. cyclops and showed nil or negligible rates of acetylene reduction at all salt concentrations. Strains WU429, WU1001 and WU1008 in combination with a highly salt-tolerant provenance of A. redolens formed symbioses which did not vary significantly in nodule number and mass, specific nodule activity or total N content irrespective of salt level up to 160 mM NaCl. On a more salt sensitive provenance of A. redolens and on A. cyclops the infectivity and effectivity of the Rhizobium strains tested usually decreased as the external salt concentration increased. These data are interpreted to indicate that tolerance of the legume host was the most important factor determining the success of compatible Rhizobium strains in forming effective symbioses under conditions of high soil salinity.

Morphological and physiological responses to increased salinity in marsh and dune ecotypes ofSporobolus virginicus (L.) Kunth

Sporobolus virginicus (L.) Kunth is a halophytic grass native to tropical and warm temperate coasts throughout the world. A rhizomatous perennial with erect culms,S. virginicus occurs as two genetically distinct growth forms, which are designated by their characteristic habitats as "marsh" and "dune". What accounts for the specific distribution and maintenance of two separate ecotypes ofS. virginicus is not known. The present study examined the effects of seawater salinity on several morphological and physiological responses of hydroponically cultivated marsh and dune plants to determine whether differential tolerance to substrate salinity might contribute to the observed pattern of habitation. Both marsh and dune form plants survived prolonged exposure to full-strength seawater and reproduced vegetatively via culms and rhizomes. Salinity-induced reductions in culm height, internode length, and leaf size led to a miniaturization of marsh and dune plants. Sodium ion levels were low (<1.0 mmol/g dry weight) in various organs of salinized plants irrespective of ecotype, and potassium ion content increased in all salt-challenged plants, as did quarternary ammonium compounds and proline. Significant differences, however, between marsh and dune plants with respect to the effects of salinity on resource allocation, flowering phenology, and protein composition suggested that external salt concentration has a role in determining ecotype distribution.

Effect of external salinity changes on cellular composition of some ions and amino acids inDeleya halophila

Changes in total cellular composition of some ions and amino acids of the moderate halophile Deleya halophila were studied in response to external salinity changes. Among the 14 amino acids investigated, the cellular glycine and aspartic acid content increased with increasing salinity. D. halophila also accumulated Na+ at the highest external salt concentrations.

Development of callus and suspension cultures of potato resistant to NaCl and mannitol and their response to stress

Callus and suspension cultures adapted to various concentrations of NaCl or mannitol were developed from the cultivated potato Solanum tuberosum cv. Desire. Growth of the calli was less inhibited by mannitol than by iso-osmotic concentrations of NaCl. Reduction of growth by both NaCl and mannitol was considerably lower in osmotically adapted calli than in non-adapted ones. Salt-adapted suspension cultures that grew in the medium to which they had been originally adapted had a shorter lag in growth as well as a shorter time required to achieve the maximum growth, as compared with non-adapted cells. Suspension cultures adapted to NaCl concentrations higher than 150 mM were obtained only after preadaptation to osmotic stress. Adaptation of these cells was found to be stable. Accumulation of Na+ was lower and level of K+ was more stable in osmotically adapted than in non-adapted calli, when both were exposed to salt. Potassium level in NaCl-adapted calli exposed to saline medium was lower than that in non-adapted calli in standard medium. The maximum of Cl− and Na+ accumulation was reached at higher external salt concentration in salt-adapted than in non-adapted suspension cultures. In both callus and suspension cultures, Cl− accumulated more than Na+. Potassium level decreased more in non-adapted than in NaCl-adapted suspension cultures. The decrease of osmotic potential in osmotically adapted calli exposed to mannitol and in salt-adapted calli and suspension cultures exposed to salt was correlated to the increase of the external concentration. Such a correlation was not found in osmotically adapted calli exposed to salt. Non-electrolytes were found to be the main contributors to the decrease is osmotic potential in both callus and suspension cultures.

13C NMR study of the interrelation between synthesis and uptake of compatible solutes in two moderately halophilic eubacteria : Bacterium Ba 1 and Vibro costicola

The synthesis and uptake of intracellular organic osmolytes (compatible solutes) were studied with the aid of natural abundance 13C NMR spectroscopy in two unrelated, moderately halophilic eubacteria: Ba 1 and Vibrio costicola. In minimal media containing 1 m NaCl, both microorganisms synthesized the cyclic amino acid, 1,4,5,6-tetrahydro-2-methyl-4-pyrimidinecarboxylic acid (trivial name, ectoine) as the predominant compatible solute, provided that no glycine betaine was present in the growth medium. When, however, the minimal medium was supplemented with glycine betaine or the latter was a component of a complex medium, it was transported into the cells and the accumulating glycine betaine replaced the ectoine. In Ba 1, grown in a defined medium containing glucose as the single carbon source, ectoine could only be detected if the NaCl concentration in the medium was higher than 0.6 m; the ectoine content increased with the external salt concentration. At NaCl concentrations below 0.6 m, α,α-trehalose was the major organic osmolyte. The concentration of ectoine reached its peak during the exponential phase and declined subsequently. In contrast, the accumulation of glycine betaine continued during the stationary phase. The results presented here indicate that, at least in the two microorganisms studied, ectoine plays an important role in haloadaptation.

Ionic Currents across the Plasmalemma ofChara inflataCells

Osmotic and ionic effects on the properties of K + and Cl − conductances in the plasmalemma of Chara inflata. Separation of the effects of increased external salt concentrations on membrane ionic conductance from the osmotic effects

Dependence of the stiffness of the xanthan chain on the external salt concentration

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDependence of the stiffness of the xanthan chain on the external salt concentrationB. Tinland and M. RinaudoCite this: Macromolecules 1989, 22, 4, 1863–1865Publication Date (Print):April 1, 1989Publication History Published online1 May 2002Published inissue 1 April 1989https://doi.org/10.1021/ma00194a058RIGHTS & PERMISSIONSArticle Views384Altmetric-Citations80LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (314 KB) Get e-Alerts Get e-Alerts

Salinity-stress-induced proteins in two nitrogen-fixing Anabaena strains differentially tolerant to salt

Salinity altered the protein synthesis patterns in two cyanobacterial strains: Anabaena torulosa, a salt-tolerant brackish water strain, and Anabaena sp. strain L-31, a salt-sensitive freshwater strain. The cyanobacterial response to salinity was very rapid, varied with time, and was found to be correlated with the external salt (NaCl) concentration during stress. Salinity induced three prominent types of modification. First, the synthesis of several proteins was inhibited, especially in the salt-sensitive strain; second, the synthesis of certain proteins was significantly enhanced; and third, synthesis of a specific set of proteins was induced de novo by salinity stress. Proteins which were selectively synthesized or induced de novo during salt stress, tentatively called the salt-stress proteins, were confined to an isoelectric pI range of 5.8 to 7.5 and were distributed in a molecular mass range of 12 to 155 kilodaltons. These salt-stress proteins were unique to each Anabaena strain, and their expression was apparently regulated coordinately during exposure to salt stress. In Anabaena sp. strain L-31, most of the salt-stress-induced proteins were transient in nature and were located mainly in the cytoplasm. In A. torulosa, salt-stress-induced proteins were evenly distributed in the membrane and cytoplasmic fractions and were persistent, being synthesized at high rates throughout the period of salinity stress. These initial studies reveal that salinity-induced modification of protein synthesis, as has been demonstrated in higher plant species, also occurs in cyanobacteria and that at least some of the proteins preferentially synthesized during salt stress may be important to cyanobacterial osmotic adaptation.

Physiological Responses to Salt Stress of Two Ecologically Different Cladophora Species

The effects of changes in external salt concentration upon Cladophora rupestris (L.) Kutz and C. glomerata (L.) Kutz have been studied. Net photosynthesis and dark respiration during salinity treatment (0 —102%0) were used as indirect measures of salinity tolerance. C. rupestris showed a broad salt tolerance compared with a very restricted tolerance in C. glomerata. The effect of salinity change on thallus ion contents was also investigated. Levels of Na+, K+, Cl~, Ca2+ and Mg2+ were measured following salinity treatment. Cladophora rupestris was found to maintain intracellular ionic balance over a much wider range of salinities than C. glomerata.

Growth rate and some physiological features of Deleya halophila CCM 3662 at different salt concentrations

The growth rate of the type strain of the new, moderately halophilic species Deleya halophila ( Deleya halophila CCM 3662) at different salt concentrations was determined and its optimal marine salt concentration for growth was established. Oxygen uptake and some cellular chemical composition characteristics of cells grown at their optimal salt concentration (7.5 % w/v) and at a higher concentration (15 % w/v) were compared, showing that both protein and carbohydrate intracellular contents decreased when the external medium salt concentration was increased, with the carbohydrate content reaching 50 % of the value presented by cells cultured at optimal salinity conditions. Oxygen uptake and poly-β-hydroxybutyric acid content were not significantly affected by changes in external salinity.

Cation exchange membranes as solid solutions

The ion exchange equilibrium between KCl and SrCl 2 solutions and the cation selective membrane CR61 AZL386 has been examined. Equilibrium isotherms are measured for membrane—electrolyte equilibria for two total concentrations of Cl −in the electrolyte solution and at three different temperatures. The results show that Sr 2+ is strongly preferred to K + in the membrane. Selectivity increases with temperature in the range 10°C to 40°C. It decreases with increasing total concentration from 0.01 N to 0.03 N. Electrolyte absorption in the membrane was not detected for the experimental conditions used. Contents of water in the membrane is constant for external salt concentrations between 3 x 10 −8 N and 3 x 10 −2 N. The difference in water content between the pure K form and the pure Sr form is approximately 5%. A thermodynamic treatment of ion exchange is presented. The thermodynamic equilibrium constant for the exchange reaction 2 KR + SrCl 2 = SrR 2+ 2 KCl has been determined by two different integration procedures, R being an ion exchange site in the membrane. The variations of the thermodynamic functions Δ G mix, Δ H mix and Δ S mix are calculated from experimental data for an assumed mixing process of membranes in the pure forms. Activity coefficients for the membrane components are calculated from experimental data. Results are compared to two lattice models. A model with a random distribution of K +, Sr 2+ and a vacant site seems preferred at low concentration of Sr 2+. At high concentrations, Sr 2+ and the vacant site associate.

Osmoacclimation inBangia atropurpurea(Rhodophyta, Bangiales): the osmotic role of floridoside

Aspects of the osmotic physiology of freshwater-grown plants of the euryhaline alga Bangia atropurpurea (Roth) C. Ag. have been studied over the salinity range from freshwater to full-strength sea-water (35‰). Synthesis of floridoside [O-α-d-galactopyranosyl-(1 → 2)-glycerol], the major low molecular weight organic solute in B. atropurpurea, occurred upon transfer of plants from a freshwater-based medium to saline media, with a maximum level of 134 mmol kg (cell water)-1 being recorded for thalli incubated in 100% sea-water for 24 h. In contrast, photosynthetic activity was depressed in high-salt media. Differences in the kinetics of floridoside production and photosynthetic rate were also observed during transfer to 100% sea-water; floridoside showed a rapid increase, doubling in concentration within 30 min and reaching a new elevated steady state within 24 h while photosynthetic activity showed a transient decrease of approximately 75% upon transfer, followed by a recovery to 60% of the initial (freshwater) rate. Studies using 14C showed an increasing allocation of radiocarbon to floridoside with increasing external salt concentration, with a six-fold increase in the percentage of 14C incorporated into this heteroside between freshwater and sea-water. Overall, the data are consistent with the hypothesis that changes in floridoside concentration serve to compensate, in part at least, for changes in external osmolality.

Salinity responses of the marine microalga Brachiomonassubmarina Bohlin

Brachiomonas submarina Bohlin, a green flagellate isolated from a coastal marine environment grows over the salinity range of 0.5 to 400% artificial sea water (ASW: 100% ASW = 3.4% salinity), remains motile at salinities up to 750% ASW, and survives the saturation of sea water. However, the capacity of the alga to tolerate salinity is diminished markedly when the temperature of the growth medium is lowered to 5°C. The alga exhibits greater sensitivity to non-ionic than to ionic osmotic stress. The alga can photoassimilate bicarbonate at salinities as high as 750% ASW when the external salinity is increased gradually. However, photosynthesis is completely abolished when cells are transferred from 5 to 200% ASW. Conversely, cells transferred from 200 to 5% ASW show an increase in the photoassimilation rate. Glycerol is the major osmoregulatory organic solute in this alga. The glycerol content of the cells increases almost linearly with increases in the external salt concentration from 10 to 300% ASW. The cell content of free amino acids, including proline, also increases in B. submarina in response to salinity increases, but this increase is quantitatively much less important than that of glycerol.

The osmotic role of mannitol in the Phaeophyta: an appraisal

Natural abundance 13C nuclear magnetic resonance spectroscopy (NMR) has shown mannitol to be the only major low molecular weight organic compound present in osmotically significant amounts within cells of the following marine brown algae: Alaria esculenta, Ascophyllum nodosum, Ectocarpus siliculosus, Fucus serratus, F. spiralis, F. vesiculosus, Halidrys siliquosa, Laminaria digitata, L. hyperborea, L. saccharina and Pilayella littoralis. Samples of the top-shore alga Pelvetia canaliculata were found to contain volemitol in addition to mannitol. Quantitative gas-liquid chromatographic analyses have confirmed the presence of mannitol, at concentrations ranging from 83.3 to 314.0 mmol kg−1 (expressed in terms of intracellular water content) for plants maintained in a full-strength (100%) sea water medium. A study of the changes in intracellular mannitol concentration of six marine brown macroalgae immersed in hyposaline and hypersaline media (20–150% EA 1 sea water medium) showed that mannitol concentration varied as a direct function of salinity in all cases, providing support for the hypothesis that mannitol is intimately involved in osmotic adjustment in response to changes in external water status. Plants of the filamentous form P. littoralis maintained in darkness also showed a marked sensitivity of intracellular mannitol concentration to alterations in the external salt concentration. Overall, the data support an osmotic, rather than a respiratory role for the large internal pools of mannitol in such algal cells.

Osmotic adjustment and organic solute accumulation in unicellular cyanobacteria from freshwater and marine habitats

The intracellular concentrations of low-molecular weight carbohydrates and quaternary ammonium compounds present in 26 axenic isolates of unicellular cyanobacteria have been studied over a range of external salinity from freshwater up to 300% seawater (100%=35‰ S). In all cases, a single carbohydrate, either sucrose or glucosylglycerol, was identified as the principal organic osmoticum, showing major variation in response to the external salt concentration; quaternary ammonium compounds were present in osmotically insignificant amounts. Glucosylglycerol was accumulated as primary osmoticum by nine of the isolates from saline habitats and by five of the freshwater isolates; trace amounts of sucrose were also prsent. The remaining twelve freshwater strains accumulated sucrose as sole osmoticum. Glucosylglycerol-accumulating strains grew over the widest salinity range (up to 200 to 250% seawater), whether isolated from saline or non-saline habitats. Sucrose-accumulating strains were more stenohaline, growing only in up to 50 to 100% seawater and showing no sustained growth in hypersaline media (>100% seawater). The data suggest that (1) glycosylglycerol accumulation is not unique to marine cyanobacteria, and (2) the upper salinity limit for growth may be linked to organic solute accumulation, rather than habitat, with glucosylglycerol-accumulating isolates having a greater potential for growth in salt-stressed conditions than sucrose accumulators.

Osmotic adjustment in cyanobacteria from hypersaline environments

The intracellular concentrations of the monovalent inorganic cations K+ and Na+, low molecular weight carbohydrates and quaternary ammonium compounds have been determined for 4 strains of cyanobacteria (Aphanothece halophytica, Coccochloris elabens, Dactylococcopsis salina and Synechocystis DUN52) originally isolated from hypersaline habitats (i.e. habitats with a salinity greater than that of seawater) over a range of external salt concentration (from 50% to 400% seawater). Intracellular cation levels (Na+ and K+) were determined to be within the range 80–320 mmol · dm-3 (cell volume), showing only minor changes in response to salinity. Intracellular carbohydrates were found to comprise a negligible component of the intracellular osmotic potential [at 2–19 mmol · dm-3 (cell volume)], throughout the salinity range. Quaternary ammonium compounds, however, were recorded in osmotically significant quantities [up to 1,640 mmol · dm-3 (cell volume)] in these strains, showing major variation in response to salinity. Thus Synechocystis DUN 52 showed an increase in quaternary ammonium compounds in the oder of 1,200 mmol · dm-3 between 50% and 400% seawater medium, accounting for a significant proportion of the change in external osmotic potential. Examination of intact cells and cell extracts using 13C and 1H nuclear magnetic resonance (NMR) spectroscopy confirmed the presence of the quaternary ammonium compound glycine betaine as the major osmoticum in the 4 strains; no other compounds were detected during NMR assays. These results suggest a common mechanism of osmotic adjustment, involving quaternary ammonium compounds, in cyanobacteria from hypersaline environments.

Use and abuse of osmo‐terminology

Abstract The terminology currently employed in studies concerned with the osmotic responses of plant cells is reviewed with specific reference to (1) the suitability of expressions in general use and (2) the application of such terms to experimental studies. The widely used term osmoregulation is shown to be an inappropriate and misleading expression when used to describe the adjustments in cellular solute concentration which frequently accompany changes in external salt concentration. Such usage of osmoregulation should be discouraged; more suitable expressions (e.g. osmoacclimation, osmotic adjustment, turgor/volume regulation or turgor maintenance, osmoadaptation) should be employed, depending upon the context.

Uptake of electrolytes by cellulose acetate membranes

The distribution in cellulose acetate (CA) membranes of a solution of two electrolytes with a common anion has been studied. The system composed of a generic acid H xAn and a generic symmetric salt MeAn has been studied and a theoretical model based on Donnan and dielectric exclusion Phenomena has been developed. This model can be used to obtain the patterns of Me +x counterion and An −x coion distribution coefficients as a function of external salt concentration. Satisfactory agreement has been found between theoretical and experimental patterns for both HCl + NaCl and H 2SO 4 + + NISO 4 systems. The most significant fact is the strong effect of external solution pH on the distribution coefficients. The system composed of the two salts AB x + DB x has also been studied. Also in this case a quantitative model has been developed to predict the patterns of the distribution coefficients of the two cations A +x and D +x as a function of the ratio between the concentrations of the two salts. Particular attention has been focussed on the effects of salt distribution coefficients and cations valency on cation distribution coefficients in the case of ZnCl 2 + CuCl 2 and CrCl 3 + FeCl 3 systems. Metal separation efficiency in the distribution process increases as the metalls valency increases.