The Effect of Sodium Salts and pH on the Hydrogenase Activity of Haloalkaliphilic Sulfate-Reducing Bacteria

Hydrogenase is the main catabolic enzyme of hydrogen-utilizing sulfate-reducing bacteria. In haloalkaliphilic sulfate reducers, hydrogenase, particularly if it is periplasmic, functions at high concentrations of Na⁺ ions and low concentrations of H⁺ ions. The hydrogenases of the newly isolated sulfate-reducing bacteria Desulfonatronum thiodismutans, D. lacustre, and Desulfonatronovibrio hydrogenovorans exhibit different sensitivity to Na⁺ ions and remain active at NaCl concentrations between 0 and 4.3 M and NaHCO₃ concentrations between 0 and 1.2 M. The hydrogenases of D. lacustre and D. thiodismutans remain active at pH values between 6 and 12. The optimum pH for the hydrogenase of D. thiodismutans is 9.5. The optimum pH for the cytoplasmic and periplasmic hydrogenases of D. lacustre is 10. Thus, the hydrogenases of D. thiodismutans, D. lacustre, and Dv. hydrogenovorans are tolerant to high concentrations of sodium salts and extremely tolerant to high pH values, which makes them unique objects for biochemical studies and biotechnological applications.__________Translated from Mikrobiologiya, Vol. 74, No. 4, 2005, pp. 460–465.Original Russian Text Copyright © 2005 by Detkova, Soboleva, Pikuta, Pusheva.     

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     

Cell ultrastructure and fatty acid composition of lipids in vegetative organs of <Emphasis Type="Italic">Chenopodium album</Emphasis> L. under salt stress conditions

White goosefoot plants (Chenopodium album L. of the family Chenopodiaceae) grown at various NaCl concentrations (3–350 mM) in the nutrient solution were used to study the cell ultrastructure as well as the qualitative and quantitative composition of fatty acids in the lipids of vegetative organs. In addition, the biomass of Ch. album vegetative organs, the water content, and the concentrations of K⁺, Na⁺, and Cl^– were determined. The growth rates of plants raised at NaCl concentrations up to 200–250 mM were the same as for the control plants grown at 3 mM NaCl; the growth parameters remained rather high even at NaCl concentrations of 300–350 mM. The water content in Ch. album organs remained high at all NaCl concentrations tested. Analysis of the ionic status of Ch. album revealed a comparatively high K⁺ content in plant organs. At low NaCl concentrations in the nutrient solution, K⁺ ions were the dominant contributors to the osmolarity (the total concentration of osmotically active substances) and, consequently, to the lowered cell water potential in leaves and roots. As the concentration of NaCl was increased, the plant organs accumulated larger amounts of Na⁺ and Cl^–, and the contribution of these ion species to osmolarity became increasingly noticeable. At 300–350 mM NaCl the contribution of Na⁺ and Cl^– to osmolarity was comparable to that of K⁺. An electron microscopy study of Ch. album cells revealed that, apart from the usual response to salinity manifested in typical ultrastructural changes of chloroplasts, mitochondria, and the cytosol, the salinity response comprised the enhanced formation of endocytic structures and exosomes and stimulation of autophagy. It is supposed that activation of these processes is related to the removal from the cytoplasm of toxic substances and the cell structures impaired by salt stress conditions. The qualitative and quantitative composition of fatty acids in the lipids of Ch. album organs was hardly affected by NaCl level. These findings are consistent with the high salt tolerance of Ch. album, manifested specifically in retention of growth functions under wide-range variations of NaCl concentration in the nutrient solution and in maintenance of K⁺, Na⁺, and Cl^– content in organs at a constant level characteristic of untreated plants.     

Cytoplasmic streaming and ionic regulation inNitella flexilis having artificial cell saps of low ionic strength

The cell sap of the internode ofNitella flexilis was replaced with the isotonic artificial pond water of high Ca²⁺-concentration (0.1 mM KCl, 0.1 mM NaCl, 10 mM CaCl₂ and 275 mM mannitol) and changes in osmotic value and concentrations of K⁺, Na⁺ and Cl⁻ of the cells were followed. When the operated cells were incubated in the artificial pond water containing 0.1 mM each of KCl, NaCl, CaCl₂, they survived for only a short period of time (<10 hr). The cells did not absorb ions from the artificial pond water and showed a conspicuous decrease in the rate of cytoplasmic streaming. In such cell the concentration of K⁺ in the protoplasm decreased significantly. In order to reverse normal concentration gradients of K⁺ and Na⁺ across the protoplasmic layer, the cells of low vacuolar ionic concentrations were incubated in the artificial cell sap (90 mM KCl, 40 mM NaCl, 15 mM CaCl₂, 10 mM MgCl₂). It was found that the cells rapidly absorbed much K⁺, Na⁺ and Cl⁻ and survived for a longer period (1–2 days). During this period the rate of cytoplasmic streaming was nearly normal. Furthermore, the cell lost much mannitol, indicating an enormous increase in permeability to it. Since both absorption of ions and leakage of mannitol at 1 C occurred at nearly the same rates as at 22 C, the processes are assumed to be passive.     

Relation between Ion Accumulation of Salt-Sensitive and Isolated Stable Salt-Tolerant Cell Lines of Citrus aurantium

Four selected NaCl-tolerant cell lines of Sour orange (Citrus aurantium) were compared with the nonselected cell line in their growth and internal ion content of Na⁺, K⁺, and Cl⁻ when exposed to increasing NaCl concentrations. No difference was found among the various NaCl-tolerant cell lines in Na⁺ and Cl⁻ uptake, and all these cell lines took up similar or even larger amounts of Na⁺ and Cl⁻ than the NaCl-sensitive cell line. Exposure of cells of NaCl-sensitive and NaCl-tolerant lines to equal external concentrations of NaCl, resulted in a greater loss of K⁺ from the NaCl-sensitive cell line. This observation leads to the conclusion that growth and ability to retain high levels of internal K⁺ are correlated. Exposure of the NaCl-tolerant cell lines to salts other than NaCl resulted in even greater tolerance to Na₂SO₄, but rather poor tolerance to K⁺ introduced as either K₂SO₄ or KCl; the latter has a stronger inhibitory effect. The NaCl-sensitive cell line proved to be more sensitive to replacement of Na⁺ by K⁺. Analyses of internal Na⁺, K⁺, and Cl⁻ concentrations failed to identify any particular internal ion concentration which could serve as a reliable marker for salt tolerance.     

Sodium plays a more important role than potassium and chloride in growth of <Emphasis Type="Italic">Salicornia europaea</Emphasis>

Salicornia europaea is a succulent euhalophyte that belongs to the Chenopodiaceae family. It is found that moderate concentration of NaCl can dramatically stimulate the growth of S. europaea plants. To elucidate the mechanism underlying the phenomenon, morphological and physiological changes of S. europaea in response to different ions, including cations (Na⁺, K⁺, Li⁺, Cs⁺) and anions (Cl⁻, NO₃ ⁻, CH₃COO⁻) were investigated, and the effects of Na⁺, Cl⁻ and K⁺ on the growth of S. europaea were also studied. Na⁺ was more effective than K⁺ and Cl⁻ in stimulating shoot succulence, cell expansion, and stomatal opening. Plants treated with Na⁺ (including NaCl, Na⁺, NaNO₃) showed better plant growth, increased photosynthesis and less cell membrane damage than those untreated and treated with 200 mM of Cl⁻ and K⁺ (including KCl and KNO₃). Both SEM-X-Ray microanalysis and flame emission results revealed that well developed S. europaea plants had a higher content of sodium but lower potassium and chlorine. It is concluded that sodium plays a more important role in the growth and development of S. europaea than potassium and chloride.     

[14C]Carbon-dioxide fixation by isolated leaf epidermes with stomata closed or open

Following small hypo-osmotic shocks, ion concentrations (Na⁺, K⁺, Cl^-) in Platymonas subcordiformis decreased; this was due mainly to an increase of cell volume. With larger hypo-osmotic stresses, the decrease of ion concentration continued and, additionally, extrusion of mannitol was observed. The ion and mannitol concentrations were not regained after 240 min. In contrast, following hyperosmotic shocks, the ion concentrations increased transitorily during the first 20–40 min. The same was true for K⁺ following small hyperosmotic stresses and for Na⁺ and — partially — Cl^- with larger shocks. Large hyperosmotic stresses caused permanent accumulation of mannitol, which levelled off after 60–80 min. Thus the transient increase of ions bridged the concentration gap until mannitol was accumulated to a high enough concentration to account for the osmotic adaptation of Platymonas, together with a basal level of the ions K⁺, Na⁺, Cl^-.Abbreviations PS photosynthesis - Resp respiration     

Glucosylglycerol-phosphate synthase: target for ion-mediated regulation of osmolyte synthesis in the cyanobacterium Synechocystis sp. strain PCC 6803

The response of cyanobacteria to a changing osmotic environment includes the accumulation of organic osmolytes such as glucosylglycerol. The activation of the enzymes involved in glucosylglycerol synthesis [glucosylglycerol-phosphate synthase (GGPS) and glucosylglycerol-phosphate phosphatase (GGPP)] in Synechocystis sp. strain PCC 6803 by various salts and salt concentrations was investigated in vitro. GGPS seemed to be the target for salt-mediated regulation of glucosylglycerol synthesis in vitro. GGPS activation was dependent on the concentration of NaCl, and a sigmoidal plot was obtained. Sensitivity to NaCl was markedly enhanced by low Mg⁺² concentrations (optimal at 4 mM), but Mg²⁺ was not absolutely necessary for the Na⁺ stimulation. As in the case of NaCl, other salts (including MgCl₂) stimulated GGPS. The relative order of GGPS activation in the presence of chloride by the cations at constant ionic strength was Li⁺ > Na⁺ > K⁺, Mg²⁺ Mn²⁺. No absolute dependence on ionic strength was observed in Mg²⁺/Na⁺-exchange experiments. The degree of activation by ions at various concentrations was positively related to the increasing destabilizing properties of the cations according to the Hofmeister rule, where chaotropic cations are most efficient. Cations were responsible for activation since chaotropic anions counteracted the activating effect of cations. Received: 10 August 1998 / Accepted: 11 November 1998     

Sodium,potassium, chloride and proline concentrations of chloroplasts isolated from a halophyte,Mesembryanthemum crystallinum L.

Concentrations of four major solutes (Na⁺, K⁺, Cl^-, proline) were determined in isolated, intact chloroplasts from the halophyte Mesembryanthemum crystallinum L. following long-term exposure of plants to three levels of NaCl salinity in the rooting medium. Chloroplasts were obtained by gentle rupture of leaf protoplasts. There was either no or only small leakage of inorganic ions from the chloroplasts to the medium during three rapidly performed washing steps involving precipitation and re-suspension of chloroplast pellets. Increasing NaCl salinity of the rooting medium resulted in a rise of Na⁺ und Cl^- in the total leaf sap, up to approximately 500 and 400 mM, respectively, for plants grown at 400 mM NaCl. However, chloroplast levels of Na⁺ und Cl^- did not exceed 160–230 and 40–60 mM, respectively, based upon a chloroplast osmotic volume of 20–30 l per mg chlorophyll. At 20 mM NaCl in the rooting medium, the Na⁺/K⁺ ratio of the chloroplasts was about 1; at 400 mM NaCl the ratio was about 5. Growth at 400 mM NaCl led to markedly increased concentrations of proline in the leaf sap (8 mM) compared with the leaf sap of plants grown in culture solution without added NaCl (proline 0.25 mM). Although proline was fivefold more concentrated in the chloroplasts than in the total leaf sap of plants treated with 400 mM NaCl, the overall contribution of proline to the osmotic adjustment of chloroplasts was small. The capacity to limit chloroplast Cl^- concentrations under conditions of high external salinity was in contrast to an apparent affinity of chloroplasts for Cl^- under conditions of low Cl^- availability.Abbreviation Chl chlorophyll     

Salt tolerance inNitellopsis obtusa

Summary The mechanism of salt tolerance was studied using isolated internodal cells of the charophyteNitellopsis obtusa grown in fresh water. When 100 mM NaCl was added to artificial pond water (0.1 mM each of NaCl, KC1, CaCl₂), no cell survived for more than one day. Within the first 30 minutes, membrane potential (E_m) depolarized and membrane resistance (R_m) decreased markedly. Simultaneously, cytoplasmic Na⁺ increased and K⁺ decreased greatly. At steady state the increase in Na⁺ content was roughly equal to the decrease in K⁺ content. The Cl^– content of the cytoplasm did not change. These results suggest that Na⁺ enters the cytoplasm by exchange with cytoplasmic K⁺. Both the entry of Na⁺ and the exit of K⁺ are assumed to be passive and the latter being caused by membrane depolarization. Vacuolar K⁺, Na⁺, and Cl^– remained virtually constant, suggesting that rapid influx of Na⁺ from the cytoplasm did not occur.In 100 mM NaCl containing 10 mM CaCl₂, membrane depolarization, membrane resistance decrease and changes in cytoplasmic [Na⁺] and [K⁺] did not occur, and cells survived for many days. When cells treated with 100 mM NaCl were transferred within 1 hour to 100 mM NaCl containing 10 mM CaCl₂, Em decreased, Rm increased, cytoplasmic Na⁺ and K⁺ returned to their initial levels, and cells survived. Two possible mechanisms for the role of Ca²⁺ in salt tolerance inNitellopsis are discussed; one a reduction in plasmalemma permeability to Na⁺ and the other a stimulation of active Na⁺-extrusion.     

Involvement of protons in the ion transport cycle of Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase

The effect of pH on electrogenic sodium transport by the Na⁺,K⁺-ATPase has been studied. Experiments were carried out by admittance recording in a model system consisting of a bilayer lipid membrane with adsorbed membrane fragments containing purified Na⁺,K⁺-ATPase. Changes in the membrane admittance (capacitance and conductance increments in response to photo-induced release of ATP from caged ATP) were measured as function of AC voltage frequency, sodium ion concentration, and pH. In solutions containing 150 mM Na⁺, the frequency dependence of capacitance increments was not significantly dependent on pH in the range between 6 and 8. At a low NaCl concentration (3 mM), the capacitance increments at low frequencies decreased with the increasing pH. In the absence of NaCl, the frequency-dependent capacitance increment at low frequencies was similar to that measured in the presence of 3 mM NaCl. These results may be explained by involvement of protons in the Na⁺,K⁺-ATPase pump cycle, i.e., electroneutral exchange of sodium ions for protons under physiological conditions, electrogenic transport of sodium ions at high pH, and electrogenic transport of protons at low concentrations (and in the absence) of sodium ions.     

Effects of NaCl and mannitol induced stress on sugarcane (<Emphasis Type="Italic">Saccharum</Emphasis> sp.) callus cultures

The effects of NaCl and mannitol iso-osmotic stresses on calli issued from sugarcane cultivars (cvs.) R570, CP59-73 and NCo310 were investigated in relation to callus growth, water content, ion and proline concentrations. Callus growth and water content decreased under both stresses with the highest reduction under mannitol-induced osmotic stress. The ion concentration was drastically affected after exposure to NaCl and mannitol. Salt stress induced an increase in Na⁺ and Cl⁻ accumulation and a decrease in K⁺ and Ca²⁺ concentrations. Under mannitol-induced osmotic stress, K⁺ and Ca²⁺ concentrations decreased significantly while Na⁺ and Cl⁻ concentrations remained unchanged. Free proline accumulation occurred under both stresses and was more marked in stress-sensitive cv. than in stress-resistant one. Our results indicated that the physiological mechanisms operating at the plant cell level in response to salt- and osmotic-induced stress in sugarcane cvs. are different. Among the cvs., we concluded that the stress resistance is closely related to the maintain of an adequate water status and a high level of K⁺ and Ca²⁺ under both stresses and a low level of Na⁺ concentration in the presence of NaCl. Thus, sugarcane (Saccharum sp.) can be regarded as a Na⁺ excluder. We also provided evidence that proline accumulation is a stress-sensitive trait rather than a stress resistance marker.     

Effects of root-zone solutes on Eucalyptus camaldulensis and Eucalyptus bicostata seedlings: Responses to Na+, Mg2+ and Cl-

Specific-ion effects in salt-treated eucalypts were examined with two species known to differ in salt tolerance viz. E. camaldulensis (more tolerant) and E. bicostata (less tolerant). Sand-cultured plants were irrigated with different nutrient solutions designed to impose either osmotic stress (concentrated macronutrients with balanced cations and anions) or specific ion stress from either NaCl or MgCl₂, or from nutrient solutions rich in particular ions viz. Na⁺, Mg²⁺ and Cl^- (balancing counter ions were provided in all cases). Half-strength Hoagland nutrient solution served as control. All treatments were applied at osmotic pressures of approximately 0.52 MPa by appropriate concentrations of each solution. In general, salt-induced growth reductions were greater for E. camaldulensis than for E. bicostata, although E. camaldulensis showed strongest exclusion of Na⁺, Mg²⁺ and Cl^- from shoots. Application of NaCl and concentrated macronutrients resulted in similar growth reductions. E. bicostata seedlings exposed to high Cl^- concentrations in the presence of Mg²⁺ and concentrated cations suffered significantly more shoot and root reduction than those exposed to other salts. Treatment with solution rich in Cl^- resulted in extensive leaf damage, which suggested that Cl^- may have exerted a specific effect. No specific Na⁺ effect was observed for either species, even though shoot Na⁺ concentrations were considerably higher for E. bicostata than for E. camaldulensis. Root growth was considerably less for plants treated with Mg²⁺ salts and this effect was associated with low root Ca²⁺ concentrations.     

Intracellular and luminal ion concentrations in sea turtle salt glands determined by x-ray microanalysis

Summary The lachrymal salt glands of hatchlings of the green sea turtle (Chelonia mydas) secrete a hyperosmotic (up to 2000 mosmol·kg^–1) NaCl solution. X-ray microanalysis of frozen-hydrated glands showed that during secretion intracellular Na⁺ concentration in the principal cells increased from 13 to 34 mmol·l^–1 of cell water, whilst Cl^– and K⁺ concentrations remained unchanged at 81 mmol·l^–1 and 160–174 mmol·l^–1, respectively. The high Cl^– concentration and the change in Na⁺ concentration are consistent with the prevailing paradigm for secretion by the structurally and functionally similar elasmobranch rectal gland. Concentrations of Na⁺, Cl^– and K⁺ in the lumina of secretory tubules of secreting (Na⁺ 122, Cl^– 167, K⁺ 38 mmol·l^–1) and non-secreting (Na⁺ 114, Cl^–1 174, K⁺ 44 mmol·l^–1) glands were similar and the fluid was calculated to be approximately isosmotic with blood. In the central canals Na⁺ and Cl^– concentrations were similar but K⁺ concentration was lower (11–15 mmol·l^–1). It is concluded that either a high transepithelial NaCl gradient in secretory tubules and central canals is very rapidly dissipated during the short time between gland excision and freezing, or that ductal modification of an initial isosmotic secretion occurs.     

Significance of Na<Superscript>+</Superscript> and K<Superscript>+</Superscript> for Sustained Hydration of Organ Tissues in Ecologically Distinct Halophytes of the Family Chenopodiaceae

The contents of Na⁺, K⁺, water, and dry matter were measured in leaves and roots of euhalophytes Salicornia europaea L. and Climacoptera lanata (Pall.) Botsch featuring succulent and xeromorphic cell structures, respectively, as well as in saltbush Atriplex micrantha C.A. Mey, a halophyte having bladder-like salt glands on their leaves. All three species were able to accumulate Na⁺ in their tissues. The Na⁺ content in organs increased with elevation of NaCl concentration in the substrate, the concentrations of Na⁺ being higher in leaves than in roots. When these halophytes were grown on a NaCl-free substrate, a trend toward K⁺ accumulation was observed and was better pronounced in leaves than in roots. Particularly high K⁺ concentrations were accumulated in Salicornia leaves. There were no principal differences in the partitioning of Na⁺ and K⁺ between organs of three halophyte species representing different ecological groups. At all substrate concentrations of NaCl, the total content of Na⁺ and K⁺ in leaves was higher than in roots. This distribution pattern persisted in Atriplex possessing salt glands, as well as in euhalophytes Salicornia and Climacoptera. The physiological significance of such universal pattern of ion accumulation and distribution among organs in halophytes is related to the necessity of water absorption by roots, its transport to shoots, and maintenance of sufficient cell water content in all organs under high soil salinity.     

High salt‐treatment‐induced Na+ extrusion and low salt‐treatment‐induced Na+ accumulation in suspension‐cultured cells of the mangrove plant,Bruguiera sexangula

A suspension‐cultured cell strain of the mangrove plant (Bruguiera sexangula) was established from a callus culture and maintained in an amino acid medium in the absence of NaCl. NaCl non‐adapted cells were transferred to media containing 0–200 mm NaCl. The initial growth rate decreased gradually with increasing salt concentrations. However, at up to 150 mm NaCl, cell number growth at the highest point was almost the same as that at lower salt concentrations. Cells even continued to grow in the presence of 200 mm NaCl. Cells incubated in a medium containing 50 mm NaCl for 3 weeks accumulated Na⁺, while those incubated in 150 mm NaCl for 2 d showed only a transient increase in Na⁺ and Cl^– concentrations. In the latter treatment, the intracellular concentration of Na⁺ returned to the original low level within 2 weeks. It took a longer time for Cl^– to return to its original level. As a result, the Na⁺ and Cl^– concentrations in cells cultured with 50 mm NaCl were much larger than those in cells cultured with 150 mm NaCl. The intracellular distribution of ions after transfer to the medium containing 150 mm NaCl was analysed by isolating the vacuoles. Treatment with amiloride, an inhibitor of the Na⁺/H⁺ antiporter, suppressed the recovery of Na⁺ to the original level in the cells. Treatment with 150 mm NaCl for 3 d stimulated the activities of both the vanadate‐dependent H⁺‐ATPase and the Na⁺/H⁺ antiporter in the plasma membrane fraction.     

Influence of salts and pH on the growth as well as NADH oxidase of the halotolerant bacterium A505

Growth yield of the halotolerant bacterium A505 was increased by the supplement of Na⁺, K⁺, or Rb⁺ into the culture media with pH 7.5, and inhibited by Li⁺ or Cs⁺. In the presence of less than 0.1 M NaCl or KCl alkaline growth media, pH 9.2 to 9.7, afforded optimal growth of this strain. Intracellular ion content of this microbe changed reflecting on the Na⁺ or K⁺ concentration in the media, although it tended to accumulate K⁺ and extrude Na⁺ in the media without NaCl supplemented. A 1.2 to 1.4-fold stimulation of in vitro NADH oxidase activity was obtained by supplement of salts, except for LiCl. The rate of NADH oxidation in the absence of salts correlated with the pH and showed clear maxima at pH about 8, irrespective of growth conditions. In the presence of 0.5 M NaCl or KCl, on the other hand, pH dependence was less significant and showed only a flat maximum at pH around 7. Effects of anions on NADH oxidase were realized following the lyotropic series: SO ₄ ^2- >F^->CH₃COO^->Cl^->I^->SCN^-, aside from NO ₃ ^- , which exhibited the largest stimulation on enzyme activity in all the anions examined.Abbreviations HEPES 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid - HQNO 2-heptyl-4-hydroxyquinoline-N-oxide - MES 4-morpholineethanesulfonic acid - Tris tris(hydroxy-methyl)methylamine     

The effects of salinity on ion concentrations within the root cells of Zea mays L.

Zea mays is a salt-sensitive crop species which in saline (100 mol m^-3 NaCl) conditions suffers considerable growth reduction correlated with elevated Na⁺ and Cl^- concentration within the leaves. To increase understanding of the regulation of ion uptake and transport by the roots in saline conditions, ion concentrations within individual root cortical cells were determined by X-ray microanalysis. There was variation in Na⁺, K⁺ and Cl^- distributions among individual cells, which could not be correlated with their spatial position in the roots. Generally, however, in response to saline growth conditions (100 mol m³ NaCl) Na⁺ and Cl^- were mostly localized in the vacuoles, although their concentrations were also sometimes increased in the cytoplasm and cell walls. The concentration of K⁺ in the cytoplasm was usually maintained at a level (mean 79 mol m^-3) compatible with the biochemical functions ascribed to this ion.Abbreviation (T)AEM (Transmission) analytical electron microscopy     

Diffusion and Electric Mobility of Ions within Isolated Cuticles of Citrus aurantium: Steady-State and Equilibrium Values

We report a new method for measuring cation and anion permeability across cuticles of sour orange, Citrus aurantium, leaves. The method requires the measurement of two electrical parameters: the diffusion potential arising when the two sides of the cuticle are bathed in unequal concentrations of a Cl⁻ salt; and the electrical conductance of the cuticle measured at a salt concentration equal to the average of that used in the diffusion-potential measurement. The permeabilities of H⁺, Li⁺, Na⁺, K⁺, and Cs⁺ ranged from 2 × 10⁻⁸ to 0.6 × 10⁻⁸ meters per second when cuticles were bathed in 2 moles per cubic meter Cl⁻ salts. The permeability of Cl⁻ was 3 × 10⁻⁹ meters per second. The permeability of Li⁺, Na⁺, and K⁺ was about five times less when measured in 500 moles per cubic meter Cl⁻ salts. We also report an asymmetry in cuticle-conductance values depending on the magnitude and the direction of current flow. The asymmetry disappears at low current-pulse magnitude and increases linearly with the magnitude of the current pulse. This phenomenon is explained in terms of transport-number effects in a bilayer model of the cuticle. Conductance is not augmented by current carried by exchangeable cations in cuticles; conductance is rate limited by the outer waxy layer of the cuticle.     

Effects of NaCl on ion relations and carbohydrate status of roots and on osmotic regulation of roots and shoots of Atriplex amnicola

Abstract Atriplex amnicola was grown at 25, 200 or 400 mol m³ NaCl. Root tissues at different stages of development were investigated for concentrations of K⁺, Na⁺ and Mg²⁺, and in some cases for Cl^?. Sugar and starch concentrations were measured for plants grown at 25 or 400 mol m³ NaCl. In the ‘slightly vaeuolated’ root tips, Na⁺ was only 40 mol m^?3 at an external concentration of 400 mol m^?3 NaCl. The concentrations of K⁺ were not affected substantially by external NaCl between 25 mol m^?3 and 400 mol m^?3. The ‘highly vacuolated’ root tissues had substantially higher concentrations of K⁺, Na⁺ and Cl^? in plants grown at 200 and 400 mol m ³ NaCl than in plants grown at 25 mol m^?3 NaCl. Concentrations of Cr and of the sum of the cations in recently expanded tissue were similar to those in the bulk of the roots, consisting mainly of old cells. However, the K⁺: Na⁺ decreased with age; at 400 mol m^?3 external NaCl with a K⁺: Na⁺ of 0.012, the K⁺: Na⁺ in recently expanded 12 mm root tips was as high as 1.6, compared with 0.7 for the bulk of the roots. These ion data were used to estimate cytoplasmic and vacuolar concentrations of K⁺ and Na ⁺. Such calculations indicated that between 25 mol m³ and 400 mol m^?3 external NaCl the concentration of the sum of (Na⁺+K⁺) in the cytoplasm was maintained at about 180–200 mol m^?3 (cell water basis). In contrast, the (Na⁺+ K⁺) concentration in the vacuole was 170 mol m^?3 for plants grown at 25 mol m^?3 NaCl and 420 mol 400 mol m^?3 NaCl. The expanding root (issues exhibited greatly decreased soluble sugars and starch between dusk and dawn. Ai both times, sugar and starch concentrations in these tissues were 2.5–4.0 times greater in plants grown at 400 mol m^?3 NaCl compared with plants grown at 25 mol m^?3 NaCl. In contrast, carbohydrate concentrations in expanded root tissues were very similar at 25 and 400 mol m^?3 and showed little diurnal fluctuation. This paper considers the causes for the slower growth of A. amnicola at 400 than at 25 mol m”³ NaCl, using the data for the roots described here, and those for the shoots presented in the preceding paper (Aslam et al., 1986). There is no support for possible adverse effects by high internal ion concentrations. Instead, there may be deficiencies in supply of organic solutes for osmotic regulation; during part of the night a limited supply of such solutes may well restrict the rate of expansion of cells in plants growing at 400 mol m^?3 NaCl. There is insufficient evidence to decide whether this limitation in the expanding tissues is particularly prominent for the roots or for the shoots.