Precipitation of calcium carbonate byDeleya halophila in media containing NaCl as sole salt

The precipitation of calcium carbonate by 27 strains ofDeleya halophila using solid and liquid media containing different NaCl concentrations (2.5, 7.5, or 20%, wt/vol) as sole salt, and two incubation temperatures (22° and 32°C) have been studied. All the strains tested were able to precipitate calcium carbonate under the different environmental conditions assayed. Crystals formed were calcite and vaterite; the ratio of calcite to vaterite was dependent on total salts and on the type of medium.     

Isolation and characterization of phage F9-11 from a lysogenicDeleya halophila strain

Thirty-eight strains ofDeleya halophila species were examined for production of phage after mitomycin C induction. Thirty-two of them were able to inhibit growth of some other strains. Phage F9-11, isolated fromD. halophila strain F9-11, showed an isometric head and a noncontractile tail. The effects of salt concentrations variation on the stability and replication of this phage were established. Its replication was possible at a wide range of marine salt concentrations, from 2.5% to 15% (wt/vol). Stability seems to be influenced by osmolarity of medium rather than by NaCl level. The euryhaline character showed by F9-11 phage is evoked as an important factor for the survival of this phage in its environment.     

Stimulation of heterotrophic and autotrophic growth ofSphaerotilus discophorus by manganous ions

Growth ofS. discophorus in a casamino acids-mineral salts medium was stimulated 3-fold on addition of 0.05% MnSO₄·H₂O to the medium. Growth was measured by determinations of total nitrogen, protein and DNA on the washed cellular material.Autotrophic growth ofS. discophorus strain 43-R was obtained in an inorganic mineral salts medium supplemented with trace amounts of the essential vitamins, thiamin, biotin and cyanocobalamin and with Mn⁺⁺ as the sole available source of energy. A gas mixture of 5% CO₂-95% air was bubbled continuously through the cultures during incubation. Concomitant with growth, Mn⁺⁺ disappeared from the cultures and MnO₂ was formed.     

Comparative salt tolerance analysis between Arabidopsis thaliana and Thellungiella halophila, with special emphasis on K(+)/Na(+) selectivity and proline accumulation

The eco-physiology of salt tolerance, with an emphasis on K⁺ nutrition and proline accumulation, was investigated in the halophyte Thellungiella halophila and in both wild type and eskimo-1 mutant of the glycophyte Arabidopsis thaliana, which differ in their proline accumulation capacity. Plants cultivated in inert sand were challenged for 3 weeks with up to 500 mM NaCl. Low salinity significantly decreased A. thaliana growth, whereas growth restriction was significant only at salt concentrations equal to or exceeding 300 mM NaCl in T. halophila. Na⁺ content generally increased with the amount of salt added in the culture medium in both species, but T. halophila showed an ability to control Na⁺ accumulation in shoots. The analysis of the relationship between water and Na⁺ contents suggested an apoplastic sodium accumulation in both species; this trait was more pronounced in A. thaliana than in T. halophila. The better NaCl tolerance in the latter was associated with a better K⁺ supply, resulting in higher K⁺/Na⁺ ratios. It was also noteworthy that, despite highly accumulating proline, the A. thaliana eskimo-1 mutant was the most salt-sensitive species. Taken together, our findings indicate that salt tolerance may be partly linked to the plants’ ability to control Na⁺ influx and to ensure appropriate K⁺ nutrition, but is not linked to proline accumulation.     

Osmotic adaptation in halotolerant yeast, Debaryomyces nepalensis NCYC 3413: role of osmolytes and cation transport

Debaryomyces nepalensis NCYC 3413, a food spoiling yeast isolated from rotten apple, has been previously demonstrated as halotolerant yeast. In the present study, we assessed its growth, change in cell size, and measured the intracellular polyol and cations (Na⁺ or K⁺) accumulated during growth in the absence and presence of different concentrations of salts (NaCl and KCl). Cells could tolerate 2 M NaCl and KCl in defined medium. Scanning electron microscopic results showed linear decrease in mean cell diameter with increase in medium salinity. Cells accumulated high amounts of K⁺ during growth at high concentrations of KCl. However, it accumulated low amounts of Na⁺ and high amounts of K⁺ when grown in the presence of NaCl. Cells grown in the absence of salt showed rapid influx of Na⁺/K⁺ on incubation with high salt. On incubation with 2 M KCl, cells grown at 2 M NaCl showed an immediate efflux of Na⁺ and rapid uptake of K⁺ and vice versa. To withstand the salt stress, osmotic adjustment of intracellular cation was accompanied by intracellular accumulation of polyol (glycerol, arabitol, and sorbitol). Based on our result, we hypothesize that there exists a balanced efflux and synthesis of osmolytes when D. nepalensis was exposed to hypoosmotic and hyperosmotic stress conditions, respectively. Our findings suggest that D. nepalensis is an Na⁺ excluder yeast and it has an efficient transport system for sodium extrusion.     

Modification of foliar solute concentrations by calcium in two species of wheat stressed with sodium chloride and/or potassium chloride

The effects of saline-stresses due to different salts on growth and on foliar solute concentrations in seedlings of two species of wheat that differed in salt tolerance. Triticum aestivum L. cv. Probred and Triticum turgidum L. (Durum group) cv. Aldura, were studied. Triticum aestivum is the more salt tolerant species. The salts used were NaCl, KCI, a 1:1 mixture of NaCI and KCI, and these same monovalent cation salts but mixed with CaCI₂ at a ratio of 2:1 on a molar basis of monovalent to divalent cation salts. Growth inhibition of both species was a function of media osmotic potentials. There was a small additional inhibition of growth if KCI replaced NaCI as the salinizing salt. CaCI₂ had little or no effect on growth inhibition beyond an osmotic effect except at the most severe stress level, i.e. when Ca²⁺ concentrations may be excessive. The amounts of water-soluble Ca²⁺ were about 10 times higher in leaves of plants grown in the presence of CaCI₂ than in its absence, but its concentrations even then were approximately 10% or less of those of the monovalent cations. Including CaCI₂ in growth media resulted in a reduction in the amount of Na⁺ in leaves compared to the amounts in plants grown at the same osmotic potential but in the absence of CaCI₂. Triticum aestivum was a better Na⁺-excluder than T. turgidum. With CaCI₂ in media, (Na⁺+ K⁺) remained relatively constant or increased by small amounts as media osmotic potentials décreased. In the absence of CaCI₂₊ (Na⁺+ K⁺) increased by large amounts when media osmotic potentials were at ?0.6 and ?0.8 MPa. It is concluded that the accumulation system in leaves for monovalent cations was under feed-back control, and that this control mechanism was inhibited by high media concentrations of Na⁺ and/or K⁺. Sucrose was present at a constant amount under all growth conditions. Proline started accumulating when (Na⁺+ K⁺) exceeded a threshold value of 200 μmol (g fresh weight)^?1. Its concentration was 5 to 13% of that portion of (Na⁺+ K⁺) that exceeded the threshold value.     

Cell walls from Actinopolyspora halophila,an extremely halophilic actinomycete

Cell wall components were prepared from Actinopolyspora halophila (strain wt), an extremely halophilic actinomycete requiring a minimum 12% NaCl concentration for growth, and from an erythromycin-resistant strain of A. halophila (strain ER) that required only 6% NaCl for growth. Both cell wall preparations contained glutamic acid, alanine, and diaminopimelic acid in a 1:2:1 molar ratio. On the basis of muramic acid content, peptidoglycans from the wt and ER strains contained 255 and 245 disaccharide units per mg dry weight respectively. In addition, both cell wall preparations contained from 10 to 20% more glucosamine than muramic acid, and equimolar amounts of d-galactose and d-arabinose. Analysis of cell walls before and after digestion with Myxobacter AL-1 protease indicated that nearly all glycan disaccharide units were peptide-substituted and that peptide cross-bridging was facilitated by direct peptide linkages between N-diaminopimelic acid and C-terminal alanine. While the peptidoglycan of A. halophila wt was 50% peptide cross-linked, that from A. halophila ER was approximately 67% peptide cross-linked. Chemical modifications involving substitution of non-N-acetylated hexosamines of the cell walls greatly enhanced their sensitivity to lysozyme. Although differences in peptidoglycan structure between the two strains of A. halophila were observed, these probably do not account for the reduced salt requirement for growth of the erythromycin-resistant strain.Issued as NRCC 25165     

Formation and role of glycine betaine in the moderate halophile Vibrio costicola

The moderate halophile Vibrio costicola, growing on a chemically-defined medium, transformed choline into glycine betaine (betaine) by the membrane-bound enzyme choline dehydrogenase and the cytoplasmic enzyme betainal (betaine aldehyde) dehydrogenase. Choline dehydrogenase was strongly induced and betainal dehydrogenase less strongly induced by choline. The formation of these enzymes was also regulated by the NaCl concentration of the growth medium, increasing with increasing NaCl concentrations. Intracellular betaine concentrations also increased with increasing choline and NaCl concentrations in the medium. This increase was almost completely blocked by chloramphenicol, which does not block the increase in salt-tolerant active transport on transfer from a low to a high salt concentration.Choline dehydrogenase was inhibited by chloride salts of Na⁺, K⁺, and NH _inf4 ^su+ , the inhibition being due to the Cl^- ions. Betainal dehydrogenase was stimulated by 0.5 M salts and could function in up to 2.0 M salts.Cells grew as well in the presence as in the absence of choline in 0.5 M and 1.0 M NaCl, but formed no intracellular betaine. Choline stimulated growth in 2.0 M NaCl and was essential for growth in 3.0 M NaCl. Thus, while betaine is important for some of the adaptations to high salt concentration by V. costicola, it by no means accounts for all of them.Abbreviations CDMM chemically-defined minimal medium - PPT proteose-peptone tryptone medium - SDS sodium dodecyl sulfate Deceased, 1987     

Differential effects of Na+, Mg2+, K+, Ca2+ and osmotic stress on the wild type and the NaCl-tolerant mutants stl1 and stl2 of Ceratopteris richardii

In order to identify physiological components that contribute to salinity tolerance, we compared the effects of Na⁺, Mg²⁺ and K⁺ salts (NaCl, Na₂SO₄, MgCl₂, MgSO₄, KCl and K₂SO₄), Ca₂₊ (CaSO₄), mannitol and melibiose on the wild type and the single-gene NaCl-tolerant mutants stl1 and stl2 of Ceratopteris richardii. Compared with gametophytic growth of the wild type, stl2 showed a low level of tolerance that was restricted to Na⁺ salts and osmotic stress. stl2 exhibited high tolerance to both Na⁺ and Mg²⁺ salts, as well as to osmotic stress. In response to short-term exposure (3 d) to NaCl, accumulation of K⁺ and Na⁺ was similar in the wild type and stl1. In contrast, stl2 accumulated higher levels of K⁺ and lower levels of Na⁺. Ca²⁺ supplementation (1.0 mol m^?3) ameliorated growth inhibition by Na⁺ and Mg²⁺ stress in wild type and stll, but not in stl2. In addition, under Na⁺ stress (175 mol m^?3) wild-type, stll and stl2 gametopbytes maintained higher tissue levels of K⁺ and lower levels of Na⁺ when supplemented with Ca²⁺ (1.0 mol m^?3). stl2 gametophytes were extremely sensitive to K⁺ supplementation. Growth of stl2 was greater than or equal to that of the wild type at trace concentrations of K⁺ but decreased substantially with increasing K⁺ concentration. Supplementation with K⁺ from 0 to 1.85 mol m^?3 alleviated some of the inhibition by 75 mol m^?3 NaCl in the wild type and in stl1. In stl2, growth at 75 mol m^?3 NaCl was similar at 0 and 1.85 mol m^?3 K⁺ supplementation. Although K⁺ supplementation above 1.85 mol m^?3 did not alleviate inhibition of growth by Na⁺ in any genotype, stl2 maintained greater relative tolerance to NaCl at all K⁺ concentrations tested.     

Evaluation of irrigation effects using diluted salted water based on electrophysiological properties of plants

Effect of salt stress and subsequent re-watering on growth and electrophysiological characteristics of Orychophragmus violaceus and Brassica napus was investigated, to construct a model for prediction of an appropriate regime for dilution of saline water. Different concentrations of NaCl, Na₂SO₄ and blend of both salts were applied with Hoagland solution. Growth and electrophysiology traits were highly restricted at high concentration levels. According to the results, the best dilution point was 5–2.5% for NaCl and Na₂SO₄ alternatively, whereas it was 10–0.0% for blend of salts. After re-watering, O. violaceus restore better leaf tensity under medium levels, because the effect of NaCl concentration on leaf tensity (X_NC–LT) was 1.66%, which was lower in O. violaceus than the effect of X_NC–LT (2.88%) in B. napus, followed by the same trend for all treatments. Therefore, the effect of salinity in O. violaceus and B. napus may also be reduced effectively by dilution of saline irrigation.     

Changes in growth and water-soluble solute concentrations in Sorghum bicolor stressed with sodium and potassium salts

Sorghum bicolor L. Moench, RS 610, was grown in liquid media salinized with NaCl, KCl, Na₂SO₄, K₂SO₄ or with variable mixtures of either NaCl/KCl or Na₂SO₄/K₂SO₄ at osmotic potentials ranging from 0 to -0.8 MPa. The purpose was to study the effects of different types and degrees of salinity in growth media on growth and solute accumulation. In 14-day-old plants the severity of leaf growth inhibition at any one level of osmotic potential in the medium increased according to the following order: NaCl < Na₂SO₄ < KCl = K₂SO₄. Inhibition of growth by mixtures of Na⁺ and K⁺ salts was the same as by K⁺ salts alone. Roots responded differently. Root growth was not affected by Na⁺ salts in the range of 0 to -0.2 MPa while it was stimulated by K⁺ salts. The major cation of leaves was K⁺ because S. bicolor is a Na⁺-excluder, while Na⁺ was the major cation in roots except at low Na⁺/K⁺ ratios in media. Anions increased in tissues linearly in relation to total monovalent cation, but not with a constant anion/cation ratio. This ratio increased as the cation concentrations in tissues increased. Sucrose in leaf tissue increased 75 fold in Chloride-plants (plants growing in media in which the only anion of the salinizing salts was Cl^?) and 50 fold in Sulphate-plants (the only anion of the salinizing salts was SO₄^2-). Proline increased 60 and 18 fold in Chloride- and Sulphate-plants, respectively, as growth media potentials decreased from 0 to -0.8 MPa. The concentrations of both sucrose and proline were directly proportional to the amount of total monovalent cation in the tissue. Sucrose concentrations began increasing when total monovalent cations exceeded 100 μmol (g fresh weight)^?1 (the monovalent cation level in non-stressed plants), but proline did not start accumulating until monovalent cation concentrations exceeded 200 μmol (g fresh weight)^?1. Therefore, sucrose seemed to be the solute used for osmotic adjustment under mild conditions of saline stress while proline was involved in osmotic adjustment under more severe conditions of stress. Concentrations of inorganic phosphate, glucose, fructose, total amino acids and malic acid fluctuated in both roots and leaves in patterns that could be somewhat correlated with saline stress and, sometimes, with particular salts in growth media. However, the changes measured were too small (at most a 2–3 fold increase) to be of importance in osmotic adjustment.     

Glycine Betaine, Carnitine, and Choline Enhance Salinity Tolerance and Prevent the Accumulation of Sodium to a Level Inhibiting Growth of Tetragenococcus halophila

Natural-abundance ¹³C-nuclear magnetic resonance was used to probe the intracellular organic solute content of the moderately halophilic bacterium Tetragenococcus halophila. When grown in complex growth media supplemented or not with NaCl, T. halophila accumulates glycine betaine and carnitine. Unlike other moderate halophiles, T. halophila was not able to produce potent osmoprotectants (such as ectoines and glycine betaine) through de novo synthesis when cultured in defined medium under hyperosmotic constraint. Addition of 2 mM carnitine, glycine betaine, or choline to defined medium improved growth parameters, not only at high salinity (up to 2.5 M NaCl) but also in media lacking NaCl. These compounds were taken up when available in the surrounding medium. The transport activity occurred at low and high salinities and seems to be constitutive. Glycine betaine and carnitine were accumulated by T. halophila in an unmodified form, while exogenously provided choline led to an intracellular accumulation of glycine betaine. This is the first evidence of the existence of a choline-glycine betaine pathway in a lactic acid bacterium. An assay showed that the compatible solutes strikingly repressed the accumulation of glutamate and slightly increased the intracellular potassium level only at high salinity. Interestingly, osmoprotectant-treated cells were able to maintain the intracellular sodium concentration at a relatively constant level (200 to 300 nmol/mg [dry weight]), independent of the NaCl concentration of the medium. In contrast, in the absence of osmoprotectant, the intracellular sodium content increased sharply from 200 to 2,060 nmol/mg (dry weight) when the salinity of the medium was raised from 1 to 2 M. Indeed, the imported compatible solutes play an actual role in regulating the intracellular Na⁺ content and confer a much higher salt tolerance to T. halophila.     

Salt tolerance of two differently drought-tolerant wheat genotypes during germination and early seedling growth

Summary Osmotic and specific ion effect are the most frequently mentioned mechanisms by which saline substrates reduce plant growth. However, the relative importance of osmotic and specific ion effect on plant growth seems to vary depending on the drought and/or salt tolerance of the plant under study. We studied the effects of several single salts of Na⁺ and Ca²⁺−NaCl, NaNO₃, Na₂SO₄, NaHCO₃, Na₂CO₃, and Ca(NO₃)₂—on the germination and root and coleoptile growth of two wheat (Triticum aestivum L.) cultivars, TAM W-101 and Sturdy, the former being more drought tolerant than the latter. The concentrations used were: 0, 0.02, 0.04, 0.08, 0.16, and 0.32 mol L⁻¹. Significant two- and three-way interactions were observed between cultivar, kind of salt, and salt concentration for germination, growth of coleoptile and root, and root/coleoptile ratio. Salts differed significantly (P<0.001) in their effect on seed germination, coleoptile and root growth of both cultivars. Germination of TAM W-101 seeds was consistently more tolerant than that of Sturdy to NaCl, CaCl₂, Ca(NO₃)₂, and NaHCO₃ salts at concentrations of 0.02, 0.04, 0.08, 0.16 mol L⁻¹. The osmotic potential, at which the germination of wheat seeds was reduced to 50% of that of the control, was different depending on the kind of salt used in the germination medium. NaCl at low concentrations (0.02 and 0.04 mol L⁻¹) stimulated the germination of both wheat cultivars. At concentrations of 0.02 to 0.16 mol L⁻¹, Ca²⁺ salts (CaCl₂ and Ca(NO₃)₂) were consistently more inhibitory than the respective Na⁺ salts (NaCl and NaNO₃) for germination of Sturdy. This did not consistently hold true for TAM W-101. Among the Na⁺ salts, NaCl was the least toxic and NaHCO₃ and Na₂CO₃ were the most toxic for seed germination. Root and coleoptile (in both wheat cultivars) differed in their response to salts. This differential response of coleoptile and root to each salt resulted in seedlings with a wide range of root/coleoptile ratios. For example, the root/coleoptile ratio of cultivar TAM W-101 changed from 2.09 (in the control) to 3.77, 3.19, 2.8, 2.44, 1.31, 0.32, and 0.0 when subjected to 0.08 mol L⁻¹ of Na₂SO₄, NaCl, CaCl₂, NaNO₃, Ca(NO₃)₂, NaHCO₃, and Na₂CO₃, respectively. Na₂CO₃ at 0.08 mol L⁻¹ inhibited root growth to such an extent that germinated wheat seeds contained coleoptile but no roots. The data indicate that, apart from the clear and more toxic effects of NaHCO₃ and Na₂CO₃ and lesser toxic effect of NaCl on germination and seedling growth, any toxicity-ranking of other salts done at a given concentration and for a given tissue growth may not hold true for other salt concentrations, other tissues and/or other cultivars. The more drought-tolerant TAM W-101, when compared to the less drought tolerant Sturdy, showed higher tolerance (at most concentrations) to NaCl, CaCl₂, Ca(NO₃)₂ and NaHCO₃ during its seed germination and to Na₂SO₄ and CaCl₂ for its root growth. This supports other reports that some drought-tolerant wheat cultivars are more tolerant to NaCl. In contrast, the coleoptile growth of drought-sensitive Sturdy was noticeably more tolerant to NaNO₃, Ca(NO₃)₂ and NaHCO₃ than that of drought-tolerant TAM W-101. Based on the above and the different root/coleoptile ratios observed in the presence of various salts, it is concluded that in these wheat cultivars: a) coleoptile and root tissues are differently sensitive to various salts, and b) at the germination stage, tolerance to certain salts is higher in the more drought-tolerant cultivar.     

Growth characteristic and ion contents of rice callus under the influence of NaCl and hydroxyproline

Calli of salt tolerant (Bhoora rata) and salt susceptible (GR₁₁) rice varieties were cultured on Linsmaeir and Skoog’s medium containing LD₅₀ concentration of NaCl (200 mM) and hydroxyproline (10 mM). Growth rate of callus and Na⁺, K⁺, Cl⁻, Mg⁺², and Ca⁺² contents of the cultured rice tissues were determined at the end of 0, 2, 4 and 6 weeks of incubation. Hydroxyproline resistant calli of both rice varieties when cultured on Linsmaeir and Skoog’s medium containing both NaCl and hydroxyproline showed increased dry weight and enhanced intracellular levels of K⁺, Mg⁺² and Ca⁺². The accumulation of Na⁺ and Cl⁻ ions was less in the hydroxyproline resistant calli.     

Callus culture from hypocotyls of Kosteletzkya virginica (L.) seedlings

It was shown that callus established from Kosteletzkya virginica (L.) Presl. (Malvaceae) can grow in salinities higher than 200 mM NaCl if previously accomodated stepwise. Callus lines developed from seedlings of different harvests or of the same harvest at different times, all showed the same pattern of growth and sensitiviy to salinity. The absorption of Na⁺ into the callus increased with increasing external NaCl concentration. In the callus, Na⁺ was apparently distributed outside and inside a cellular membrane (possibly the plasmalemma). This membrane was, apparently, capable of regulating the Na⁺ concentration in the protoplast. Outside this membrane Na⁺ accumulated to concentrations higher than in the external growth medium. Exogenously supplied proline or glycine-betaine did not affect the growth of the callus. Externally applied ABA stimulated growth under saline conditions and increased the accumulation of proline. Growth and proline content were positively correlated in callus exposed to salinity, but in the presence of ABA they were negatively correlated. ABA was involved in both growth and proline accumulation, but there was no clear relationship between these two effects. Both ABA and proline, if added to the growth medium, improved the appearence of the callus.Abbreviations ABA abscisic acid - B₅ Gamborg's medium - BA benzylalanine - 2,4-d 2,4-dichlorophenoxy acetic acid - FW fresh weight - G B₅ medium without growth regulators - GH B₅ medium supplemented with growth regulators - NAA naphthalene acetic acid - PGR plant growth regulators - Q _T total amount of a certain ion in the tissue - Q _s amount of the ion that has leaked out - QAC Quaternarty Ammonium Compounds - RGR mean relative growth rate - W₁ and W₂ fresh weight at times t₁ and t₂     

Intrasynaptosomal Free Mg2+ Concentration Measured with the Fluorescent Indicator Mag-Fura-2: Modulation by Na+ Gradient and by Extrasynaptosomal ATP

Abstract: Synaptosomes can be loaded with mag-fura-2 without significant perturbation of their ATP content by incubation for 10 min at 37°C with 10 µM mag-fura-2 acetoxymethyl ester in Hanks'-HEPES buffer (pH 7.45). The intrasynaptosomal free Mg²⁺ concentration ([Mg²⁺]_i) was found to be dependent on external Mg²⁺ concentration, increasing from 0.8 to 1.25 mM when the concentration of Mg²⁺ in the incubation medium increased from 1 to 8 mM. Dissipation of the Na⁺ gradient across the plasma membrane of synaptosomes by treatment with the Na⁺ ionophore monensin (0.2 mM) or with veratridine (0.2 mM) and ouabain (0.6 mM) produced a moderate increase of [Mg²⁺]_i, from 1.0 to 1.2–1.3 mM in an incubation medium containing 5 mM Mg²⁺. Plasma membrane depolarization by incubation of synaptosomes in a medium containing 68 mM KCl and 68 mM NaCl had no effect on [Mg²⁺]_i. Reversal of the Na⁺ gradient by incubation of synaptosomes in a medium in which external Na⁺ was replaced by choline increased [Mg²⁺]_i up to 1.6 and 2.2 mM for extrasynaptosomal Mg²⁺ concentrations of 1 and 8 mM, respectively. We conclude that a Na⁺/Mg²⁺ exchange operates in the plasma membrane of synaptosomes. In the presence of Mg²⁺ in the incubation medium, extrasynaptosomal ATP, but not ADP or adenosine, increased [Mg²⁺]_i from 1.1 ± 0.1 up to 1.6 ± 0.1 mM. The nonhydrolyzable ATP analogue adenosine 5′-(βγ-imido)triphosphate antagonized the effect of ATP, but had no effect by itself on [Mg²⁺]_i. It is concluded that Mg²⁺ transport across the plasma membrane of synaptosomes is modulated by the activity of an ecto-ATPase or an ecto-protein kinase.     

Growth and solute accumulation in 3-week-old seedlings of Agropyron elongatiun stressed with sodium and potassium salts

Agropyron elongatum [Host. (Beauv.)] [^cv. Arizona Glendale, was grown in liquid medium salinized with either NaCl, KCI, or a 50:50 mixture of these two salts at osmotic potentials ranging from 0 to –1.6 MPa. The amount of growth in 21 days was measured, and extracts were made of the shoots at this time. The extracts were assayed for low-molecular-weight organic compounds (glucose, fructose, sucrose, be-taine, proline) and inorganic solutes (Na⁺, K⁺, Cl^?, P.). The purpose was to determine if there was any correlation between the harmful effect of salinity on growth and the concentrations of solutes in tissues. Growth inhibition of A. elongatum was roughly proportional to the osmotic potential of the growth medium and was independent of the ionic composition of the salinizing salts. Total monovalent cation (the sum of Na⁺ and K⁺) concentrations and the ratio of these two cations in leaves were mainly a function of the ionic compostion of the salt in growth media, and, to a lesser degree, of osmotic potentials. F At an osmotic potential of –0.2 MPa, total monovalent cation in leaves was the same as in non-stressed plants. However, if the salinizing salt contained NaCl, there was an increase in foliar Na⁺ with a balancing decrease in K⁺. At stress levels between –0.4 and –1,6 MPa, and, if the media were salinized with either 100% NaCl or a 50:50 mixture of NaCl and KCI, total monovalent cation concentrations remained constant at a value that was twice that in non-stressed plants. Although total monovalent cation concentrations were equal in plants grown under these two salinity conditions, the K⁺/Na⁺ ratios shifted from a value of 1:2 in plants grown in 100% NaCl to 3:1 in plants subjected to the 50:50 mixture. If 100% KCI was used to salinize media, total monovalent cation was 80% of its concentration in NaCl-treated plants in the range of –0.4 to -1.2 MPa. At –1.6 MPa due to 100% KCI, total monovalent cation was double that in plants subjected to -0.4 MPa. In the range of osmotic potentials from–0.2 to –1.2 MPa, the chloride:cation ratio was 1:2. At –1.6 MPa the ratio changed to 3:4. Proline started accumulating in leaves of A. elongatum when the tissue concentration of total monovalent cation exceeded 200 μ (g fresh weight)^?1. Above this threshold value of total monovalent cation, the proline concentration of leaves was 6% of the amount of total monovalent cation that exceeded 200 umol (g fresh weight)¹.     

SALINITY ADAPTATION BY DUNALIELLA TERTIOLECTA. I. INCREASES IN CARBONIC ANHYDRASE ACTIVITY AND EVIDENCE FOR A LIGHT-DEPENDENT Na+/H+ EXCHANGE1,2

When Dunaliella tertiolecta, previously adapted to medium containing 0.5 M NaCl, is transferred to higher salinities, there is a lag in growth, suggesting an adaptation period. Since there is no significant difference in the Na⁺ content of cells grown between 0.5 and 3.5 M NaCl, a mechanism for Na⁺ extrusion or exclusion is indicated. Increasing the salinity of cell suspensions stimulates an incorporation of H⁺ by the cells, suggesting an H⁺/Na⁺ exchange. Cells adapted to higher salinities have, increased carbonic anhydrase activity, suggesting that increased CO₂ or HCO₃^? transport may be required at higher salinities. Growth, of D. tertiolecta at salinities above 2.5 M requires continuous illumination; therefore a light-driven H⁺/Na⁺ exchange accompanied by a HCO₃^? influx is proposed.     

Effects of NaCl and Na2SO4 on red-osier dogwood (Cornus stolonifera Michx) seedlings

Sodium chloride and sodium sulfate are commonly present in extraction tailings waters produced as a result of surface mining and affect plants on reclaimed areas. Red-osier dogwood (Cornus stolonifera Michx) seedlings were demonstrated to be relatively resistant to these high salinity oil sands tailings waters. The objectives of this study were to compare the effects of Na₂SO₄ and NaCl, on growth, tissue ion content, water relations and gas exchange in red-osier dogwood (Cornus stolonifera Michx) seedlings. In the present study, red-osier dogwood seedlings were grown in aerated half-strength modified Hoagland's mineral solution containing 0, 25, 50 or 100 mM of NaCl or Na₂SO₄. After four weeks of treatment, plant dry weights decreased and the amount of Na⁺ in plant tissues increased with increasing salt concentration. Na⁺ tissue content was higher in plants treated with NaCl than Na₂SO₄ and it was greater in roots than shoots. However, Cl^– concentration in the NaCl treated plants was higher in shoots than in roots. The decrease in stomatal conductance and photosynthetic rates observed in presence of salts is likely to contribute to the growth reduction. Our results suggest that red-osier dogwood is able to control the transport of Na⁺ from roots to shoots when external concentrations are 50 mM or less.     

Turgor regulation in a novel Halomonas species

The mechanisms by which a novel eubacterium, identified as belonging to the genus Halomonas, adapted to increases in the extracellular osmotic potential were investigated. It was shown that the ability of the bacterium to grow after hyperosmotic shock was dependent on the presence of potassium ions. Growth of the bacterium in 2 M NaCl medium could be limited by low concentrations of K⁺ and this enabled the affinity for K⁺ to be determined (K _s=21.5 M). Rubidium salts could be substituted for those of potassium, but the lowest concentration of Rb⁺ that allowed growth in 2 M NaCl medium was 50-fold greater than the minimum concentration of K⁺. ¹³C-NMR spectroscopy and HPLC analysis were used to demonstrate the accumulation of organic solutes in the cytoplasm after exposure to high salinities. The major osmolyte was ectoine, but glutamate and ectoine hydroxide were also present. Addition of exogenous glycine betaine to 3.25 M NaCl medium resulted in the accumulation of high intracellular concentrations of glycine betaine in the bacterium. This reduced the level of ectoine accumulation but did not fully inhibit the synthesis of this compound in the cytoplasm.Abbreviation Specific growth rate (generations/h)