Water and electrolyte balance in protoscoleces of Echinococcus granulosus incubated in vitro: general procedures for the determination of water,sodium, potassium and chloride in protoscoleces

Reisin I.L. and Rotunno C.A. 1981. Water and electrolyte balance in protoscoleces of Echimcoccus granulosus incubated in vitro: General procedures for the determination of water, sodium, potassium and chloride in protoscoleces. International Journal for Parasitology11: 399–404. Protoscoleces of E. granulosus (sheep strain) were incubated in vitro at 37°C in Ringer Krebs solution (RKS) for up to 3 h. When they were briefly washed in sucrose 0.3 M at 4°C, the water and electrolyte contents were: 1.768 ± 0.034 mlg^?1 d.w. for water content and 123 ± 2, 209 ± 2 and 78 ± 2 μmolg^?1 d.w. for Na⁺, K⁺ and Cl^? respectively. When protoscoleces were not washed in sucrose solution but were spun down from RKS, the K⁺ content suffered a very small change but larger values for Na⁺ and Cl⁺ contents were obtained. These higher Na⁺ and Cl^? contents are attributed to the RKS ions retained in the trapping space. The steady state distribution of Na⁺ and K⁺ in the protoscoleces incubated at 37°C indicates the activity of an active transport mechanism.     

The ionic relations of Porphyra purpurea(Roth) C.Ag. (Rhodophyta, Bangiales)

Abstract Radioisotope equilibration techniques have been used to determine the intracellular concentration of K⁺, Na⁺ and Cl_?, together with the unidirectional ion fluxes across the plasmalemma of Porphyra purpurea. Influx and efflux of ⁴²K⁺, ²⁴Na⁺ and ³⁶C1^? are biphasic, the rapid, initial uptake and loss of tracer from individual thalli being attributable to desorption from extracellular regions. Cellular fluxes are slower and monophasic, cells discriminating in favour of K⁺ and Cl^? and against Na⁺. A comparison between the equilibrium potential of individual ion species and the measured membrane potential demonstrates that there is an active component of K⁺ and Cl^? influx and Na⁺ efflux. ‘Active’ uptake and ‘passive’ loss of K⁺ and Cl^? are reduced when plants are kept in darkness, suggesting that a fraction of the transport of K⁺ and Cl^? may be due to ‘exchange diffusion’ (K⁺/K⁺ and Cl^?/Cl^?antiport).     

The role of potassium and chloride ions on the Na+/acidic amino acid cotransport system in rat intestinal brush-border membrane vesicles

The Na⁺/l-glutamate (l-aspartate) cotransport system present at the level of rat intestinal brush-border membrane vesicles is specifically activated by the ions K⁺ and Cl^?. The presence of 100 mM K⁺ inside the vesicles drastically enhances the uptake rate and the transient intravesicular accumulation (overshoot) of the two acidic amino acids. It has been demonstrated that the activation of the transport system depended only in the intravesicular K⁺ concentration and that in the absence of any sodium gradient, an outward K⁺ gradient was unable to influence the Na⁺/acidic amino acid transport system. It was also found that Cl^? could specifically activate the Na⁺-dependent l-glutamate (l-aspartate) uptake either in the presence or in the absence of K⁺. Also the effect of Cl^? was observed only in the presence of an inward Na⁺ gradient and it was noted to be higher when chloride ion was present on both sides of the membrane vesicles. No influence (activation or accumulation) was observed in the absence of the Na⁺ gradient and in the presence of chloride gradient. l-Glutamate uptake measured in the presence of an imposed diffusion potential and in the presence of K⁺ or Cl^? did not show any translocation of net charge.     

Fluxes and compartmentation of K+, Na+ and Cl−, and action of auxins in suspension-cultured Petroselinum cells

Transport of ⁸⁶Rb⁺/K⁺, ²²Na⁺, ³⁶Cl^?, and [³H]indole acetic acid (IAA) has been studied on suspension-cultured cells of the parsley, Petroselinum crispum (Mill) Nym. By compartmental analysis two intracellular compartments of K⁺, Na⁺, and Cl^? have been identified and ascribed to the cytoplasm and vacuole; half-times of exchange were around 200 s and 5 h, respectively. According to the Ussing-Teorell flux equation, active transport is required for the influx into the cytoplasm at the plasmalemma (K⁺, Cl^?) and the tonoplast (K⁺, Na⁺, Cl^?). The plasmalemma permeability pattern, P_K:P_Na:P_Cl=1.00:0.24:0.38, features an increased chloride permeability compared with cells from higher plant tissues. IAA uptake showed an exponential timecourse, was half-maximal after 10 min, and a linear function of the IAA concentration from 10^?9 to 10^?5 M. IAA and 2,4-dichlorophenoxy acetic acid reduce the apparent influx of K⁺, Na⁺, Cl^? during the initial 30 min after addition and subsequently accelerate both in- and efflux of these ions. We discuss that auxins could affect the ion fluxes in a complex way, e.g. by protonophorous activity and by control of the hypothetical proton pump.     

Kinetics of chloride transport in the cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. leopoliensis) PCC 7942

The kinetics of the light-driven Cl^? uptake pump of Synechococcus R-2 (PCC 7942) were investigated. The kinetics of Cl^? uptake were measured in BG-11 medium (pH_o, 7·5; [K⁺]_o, 0·35 mol m^?3; [Na⁺]_o, 18 mol m^?3; [Cl^?]_o, 0·508 mol m^?3) or modified media based on the above. Net³⁶Cl^? fluxes (?Cl^?_o,i) followed Michaelis-Menten kinetics and were stimulated by Na⁺ [18 mol m^?3 Na⁺ BG-11 ?Cl^?_max= 3·29±0·60 (49) nmol m^?2 s^?1 versus Na⁺-free BG-11 ?Cl^?_max= 1·02±0·13 (54) nmol m^?2 s^?1] but the Km was not significantly different in the presence or absence of Na⁺ at pH_o 10; the Km was lower, but not affected by the presence or absence of Na⁺ [Km = 22·3±3·54 (20) mmol m^?3]. Na⁺ is a non-competitive activator of net ?Cl^?_o,i. High [K⁺]_o (18 mol m^?3) did not stimulate net ?Cl^?_o,i or change the Km in Na⁺-free medium. High [K⁺]_o (18 mol m^?3) added to Na⁺ BG-11 medium decreased net ?Cl^?_o,i [18 mol m^?3K⁺ BG-11; ?Cl^?_max= 2·50±0·32 (20) nmol m^?2 s^?1 versus BG-11 medium; ?Cl^?_max= 3·35±0·56 (20) nmol m^?2 s^?1] but did not affect the Km 55·8±8·100 (40) mmol m^?3]. Na⁺-stimulation of net ?Cl^?_o,i followed Michaelis-Menten kinetics up to 2–5 mol m^?3 [Na⁺]_o but higher concentrations were inhibitory. The Km for Na⁺-stimulation of net ?Cl^?_o,i [K_1/2(Na⁺)] was different at 47 mmol m^?3 [Cl^?]_o (K_1/2[Na⁺] = 123±27 (37) mmol m^?3]. Li⁺ was only about one-third as effective as Na⁺ in stimulating Cl^? uptake but the activation constant was similar [K_1/2(Li⁺) = 88±46 (16) mmol m^?3]. Br^? was a competitive inhibitor of Cl^? uptake. The inhibition constant (Ki) was not significantly different in the presence and absence of Na⁺. The overall Ki was 297±23 (45) mmol m^?3. The discrimination ratio of Cl^? over Br^? (δCl^?/δBr^?) was 6·38±0·92 (df = 147). Synechococcus has a single Na⁺-stimulated Cl^? pump because the Km of the Cl^? transporter and its discrimination between Cl^? and Br^? are not significantly different in the presence and absence of Na⁺. The Cl^? pump is probably driven by ATP.     

Early life stage salinity tolerance of wild and hatchery-reared juvenile pink salmon Oncorhynchus gorbuscha

Salinity tolerance in wild (Glendale) and hatchery (Quinsam) pink salmon Oncorhynchus gorbuscha (average mass 0·2 g) was assessed by measuring whole body [Na⁺] and [Cl^?] after 24 or 72 h exposures to fresh water (FW) and 33, 66 or 100% sea water (SW). Gill Na⁺, K⁺‐ATPase activity was measured following exposure to FW and 100% SW and increased significantly in both populations after a 24 h exposure to 100% SW. Whole body [Na⁺] and whole body [Cl^?] increased significantly in both populations after 24 h in 33, 66 and 100% SW, where whole body [Cl^?] differed significantly between Quinsam and Glendale populations. Extending the seawater exposure to 72 h resulted in no further increases in whole body [Na⁺] and whole body [Cl^?] at any salinity, but there was more variability among the responses of the two populations. Per cent whole body water (c. 81%) was maintained in all groups of fish regardless of salinity exposure or population, indicating that the increase in whole body ion levels may have been related to maintaining water balance as no mortality was observed in this study. Thus, both wild and hatchery juvenile O. gorbuscha tolerated abrupt salinity changes, which triggered an increase in gill Na⁺, K⁺‐ATPase within 24 h. These results are discussed in terms of the preparedness of emerging O. gorbuscha for the marine phase of their life cycle.     

Salt-Induced Hypodermal Transfer Cells in Roots of Prosopis farcta and Ion Distribution within Young Plants

Prosopis farcta was grown on hydroculture with additions of 0.5, 10, 50, and 100 mM NaCl and without salt treatment. In plants from a 0.5 mM NaCl treatment, Cl^? was taken up into stems and leaves, but Na⁺ was withheld from the shoot. At 10 mM NaCl, shoot K⁺ concentration was below that of the control; Na⁺ and Cl^? were taken up to stems and cotyledons in nearly equimolar amounts. However, in the leaves, Na⁺ concentrations were only half of those of Cl^?. With increasing salt stress, Na⁺ and Cl^? were transported to the shoot, but kept at relatively low levels in the roots. Na⁺/ K⁺ ratios in roots did not increase proportionally to those in the solution. At an external Na⁺/K⁺ of > 5 and a root Na⁺/K⁺ of >1 (10 mM NaCl treatment), K⁺ selectivity was induced which rose exponentially with increasing salt stress; and cell wall protuberances were discovered in the hypodermis at the zone of side root formation. These transfer cells were found neither in roots from the 0.5 mM NaCl treatment nor in the controls. Their possible role in the Na⁺/K⁺ selectivity of the roots of Prosopis farcta is discussed.     

Effect of temperature on ion content, ion fluxes and energy metabolism in Chara corallina

Abstract Effects of temperature on the ionic relations and energy metabolism of Chara corallina were investigated. Measurements were made of the ionic content, tracer ion fluxes, and photosynthetic and dark CO₂ fixation in isolated cells, and of O₂ exchange in photosynthesis and respiration in isolated shoot apices. The total intracellular concentration of K⁺, Na⁺ and Cl^? was the same in cells held for 5 days in non-growing medium at 15°C (the growth temperature) as in those held at 25°C or 5°C. The tracer influx in the light of all ions tested (Rb⁺, Na⁺, CH₃NH₃⁺, Cl^? and H₂PO₄^?) was lower at 5°C than at 15°C in experiments in which cells were subjected to 5°C for less than 24 h in toto. The influx at 25°C was greater than that at 15°C for H₂PO^?₄, there was no difference between the two temperatures for Na⁺, while the influx at 25°C was less than that at 15°C for Cl^?, Rb⁺ and CH₃NH₃⁺ For Cl^? and H₂PO^?₄ similar results were found in later experiments with cells grown at 20—23°C. Photosynthetic CO₂ fixation and O₂ evolution, and respiratory O₂ uptake, are greater at 25°C, and lower at 5°C, than they are at the growth temperature of 15°C. In longer-term pretreatments at the different temperatures, tracer Cl^? influx at 15°C and particularly at 25°C were lower than in short-term experiments, while the influx at 5°C was higher. It was concluded from these experiments, and from previous data on H⁺ free energy differences across the plasmalemma, that (1) the maintenance of internal ion concentrations involves a close balancing of influx and efflux of K⁺, Na⁺ and Cl^? at all experimental temperatures; (2) the regulation of the tracer fluxes of the ions is kinetic rather than thermodynamic and (3) that the tracer fluxes at low temperatures are not restricted by the rate at which respiration or photosynthesis can supply energy to them.     

Cl− transport in apical plasma membrane vesicles isolated from bovine tracheal epithelium

The Cl^? transport properties of the luminal border of bovine tracheal epithelium have been investigated using a highly purified preparation of apical plasma membrane vesicles. Transport of Cl^? into an intravesicular space was demonstrated by (1) a linear inverse correlation between Cl^? uptake and medium osmolarity and (2) complete release of accumulated Cl^? by treatment with detergent. The rate of Cl^? uptake was highly temperature-sensitive and was enhanced by exchange diffusion, providing evidence for a carrier-mediated transport mechanism. Transport of Cl^? was not affected by the ‘loop’ diuretic bumetanide or by the stilbene-derivative anion-exchange inhibitors SITS (4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid) and DIDS (4,4′-diisothiocyanostilbene-2,2′-disulfonic acid). In the presence of the impermeant cation, tetramethylammonium (TMA⁺), uptake of Cl^? was minimal; transport was stimulated equally by the substitution of either K⁺ or Na⁺ for TMA⁺. Valinomycin in the presence of K⁺ enhanced further Cl^? uptake, while amiloride reduced Na⁺-stimulated Cl^? uptake towards the minimal level observed with TMA⁺. These results suggest the following conclusions: (1) the tracheal vesicle membrane has a finite permeability to both Na⁺ and K⁺; (2) the membrane permeability to the medium counterion determines the rate of Cl^? uptake; (3) Cl^? transport is not specifically coupled with either Na⁺ or K⁺; and, finally (4) Cl^? crosses the tracheal luminal membrane via an electrogenic transport mechanism.     

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.     

The Na+,K+,2Cl−-cotransport system in HeLa cells: Aspects of its physiological regulation

We have previously reported on the biochemical properties of a Na⁺,K⁺,2Cl^?-cotransport in HeLa cells and here we deal with aspects of its physiological regulation. Na⁺,K⁺,2Cl^?-cotransport in HeLa cells was studied by ⁸⁶Rb⁺ influx and ⁸⁶Rb⁺/²²Na⁺ efflux measurements. The effects of rat atrial natriuretic peptide (ANP), isoproterenol, and amino acids on ⁸⁶Rb⁺ flux, mediated by the bumet-anide-sensitive Na⁺, K⁺, 2Cl^?-cotransport system and the ouabain-sensitive Na⁺/K⁺-pump, were investigated. ANP reduced bumetanide-sensitive ⁸⁶Rb⁺ influx under isotonic as well as under hypertonic conditions. Similar decrease of bumetanide-sensitive ⁸⁶Rb⁺ influx was observed in the presence of 8-bromo-cGMP, while neither isoproterenol as a β-receptor agonist nor 8-bromo-cAMP-could alter bumetanide-sensitive ⁸⁶Rb⁺ influx. Furthermore, efflux of ⁸⁶Rb⁺ and ²²Na⁺ was greatly reduced in the presence of bumetanide and ANP. Together with our recent findings, showing functionally active, high affinity receptors for ANP on HeLa cells (Kort and Koch, Biochim. Biophys. Res. Commun. 168:148–154, 1990), this study indicates that ANP participates in the regulation of the Na⁺, K⁺, 2Cl^?-cotransport system in HeLa cells. Further measurements revealed that amino acids as present in the growth medium (Joklik's minimal essential medium) and the amino acid derivative α-methyl-aminoisobutyric acid (metAlB, 1 and 5 mM, respectively) also reduced Na⁺, K⁺, 2Cl^?-cotransport-mediated ⁸⁶Rb⁺ uptake and diminished the stimulatory effect of hypertonicity on the cotransporter. In addition, the Na⁺/K⁺-pump was markedly stimulated in the presence of amino acids, while neither ANP and 8-Br-cGMP nor isoproterenol and 8-Br-cAMP had a significant effect on the activity of the Na⁺/K⁺-pump.     

Effects of external NaCl on the growth of Atriplex amnicola and the ion relations and carbohydrate status of the leaves

Abstract Atriplex amnicola, was grown in nutrient solution cultures with concentrations of NaCl up to 750 mol m^?3. The growth optimum was at 25–50 mol m^?3 NaCl and growth was 10–15% of that value at 750 mol m^?3 NaCl. Sodium chloride at 200 mol m^?3 and higher reduced the rate of leaf extension and increased the time taken for a leaf to reach its maximal length. Concentrations of Na⁺, K⁺ and Mg²⁺ in leaves of different ages were investigated for plants grown at 25, 200 and 400 mol m^?3 NaCl. Although leaves of plants grown at 200 and 400 mol m^?3 NaCl had high Na⁺ concentrations at young developmental stages, much of this Na⁺ was located in the salt bladders. Leaves excluding bladders had low Na⁺ concentrations when young, but very high in Na⁺ when old. In contrast to Na⁺, K⁺ concentrations were similar in bladders and leaves excluding bladders. Concentrations of K⁺ were higher in the rapidly expanding than in the old leaves. At 400 mol m^?3 NaCl, the K⁺:Na⁺ ratios of the leaves excluding bladders were 0.4–0.6 and 0.1 for rapidly expanding and oldest leaves, respectively. The Na⁺ content in moles per leaf, excluding bladders, increased linearly with the age of the leaves; concurrent increases in succulence were closely correlated with the Na ⁺ concentration in the leaves excluding the bladders. Soluble sugars and starch in leaves, stems and buds were determined at dusk and dawn. There was a pronounced diurnal fluctation in concentrations of carbohydrates. During the night, most plant parts showed large decreases in starch and sugar. Concentrations of carbohydrates in most plant organs were similar for plants grown at 25 and 400 mol m^?3 NaCl. One notable exception was buds at dusk, where sugar and starch concentrations were 30–35% less in plants grown at 400 mol m^?3 NaCl than in plants grown at 25 mol m^?3 NaCl. The data indicate that the growth of A. amnicola at 400 mol m^?3 NaCl is not limited by the availability of photosynthate in the plant as a whole. However, there could have been a growth limitation due to inadequate organic solutes for osmotic regulation.     

Salicylic Acid Induced Salinity Tolerance Through Manipulation of Ion Distribution Rather than Ion Accumulation

In this research, the effect of different SA concentrations (0, 0.5, 1.0, 1.5, and 2.0 mM) on biological and grain yield as well as Na⁺, K⁺, Cl^?, Ca²⁺, and Mg²⁺ distribution and accumulation in barley plants was examined under nonsaline (2 dS m^?1) and saline (12 dS m^?1) conditions in a three-year field study (2012–2015 growing seasons). Storage factor (SF) was defined as the concentration of an ion in the root, as a proportion of total uptake of that ion, to quantify ion partitioning between root and shoot. Salt stress decreased SF for K⁺, Ca²⁺, and Mg²⁺ and enhanced it for Na⁺ and Cl^?, which led to reduce grain and biological yield. Nonetheless, foliar-applied SA in varying concentrations could lower some of these adverse effects on ion transport and accumulation. At the 2nd and 3rd years, unfavorable climatic conditions such as less precipitation and higher temperature intensified salt stress and decreased the alleviating impact of SA. Foliar application of SA at higher levels increased SF for Na⁺ and Cl^? ions and decreased that for K⁺ indicating that SA helped barley plants keep more Na⁺ and Cl^? and less K⁺ ions in the root system, which suggested the probable role of SA in altering ion transport within the plant in favor of salt stress tolerance. SF was found to be more correlated with grain yield under both nonsaline and saline conditions. Overall, SF might be considered as a potential criterion for salt tolerance in barley plants.     

Na+ transport processes in isolated guinea pig nasal gland acinar cells

In the dispersed acinar cells of the submucosal nasal gland in the guinea pig, intracellular Na⁺ concentration ([Na⁺]i) was measured with a microfluorimetric imaging method and the cytosolic indicator dye, sodium-binding benzofuran isophthalate, under HCO₃^?-free conditions. In the unstimulated condition, the [Na⁺]i was averaged to 12.8 ± 5.2 mM. Addition of 100 μM ouabain or removal of external K⁺ caused an increase in [Na⁺]i. Replacement of external Cl^? with NO₃^? or addition of 0.5 mM furosemide reversibly decreased the [Na⁺]i. The recovery process from the reduced [Na⁺]i was inhibited by removal of either K⁺ or Cl^? in the bath solution. These findings indicate the presence of a continuous influx of Na⁺ coupled with K⁺ and Cl^? movement. Application of acetylcholine (ACh, 1 μM) caused an increase in [Na⁺]i by about 15–20 mM, which was completely inhibited by addition of 10 μM atropine. Increased cytosolic Na⁺ induced by ACh was extruded by the Na⁺-K⁺ pump. Removal of external Cl^? and addition of 50 μM dimethylamiloride inhibited ACh-induced increase in [Na⁺]i by about 66% and 19%, respectively. In both unstimulated and stimulated state, Na⁺-K⁺ pump, Na-K-Cl cotransport, and Na⁺-H⁺ exchange play a critical role in maintaining intracellular electrolyte environment and in controlling a continuous secretion of nasal fluids. © 1995 Wiley-Liss, Inc.     

Characterization of monovalent ion transport systems in an insect cell line (Manduca sexta embryonic cell line che)

The monovalent ion transport systems of an immortalized insect cell line (CHE) have been investigated. These cells are unusual in that unlike most vertebrate cells, their normal extracellular environment consists of high potassium and low sodium concentrations. CHE cells maintained high intracellular [K⁺] through both a furosemide-inhibitable and a vanadate-inhibitable transport system. Intracellular exchangeable [Na⁺] was slightly lower than the extracellular [Na⁺] and was maintained at this level through a vanadate-sensitive transport system. Na⁺ uptake was also inhibited by furosemide: however, the stoichiometry of furosemide-sensitive Na⁺ uptake when compared with furosemide-sensitive K⁺ uptake indicated that these cations are not cotransported. 4,4′-Diisothiocyano-2,2′-disulfonic acid stilbene (DIDS) inhibited Na⁺, K⁺, and Cl^? uptake. Vanadate and furosemide decreased cytoplasmimic pH, while cytoplasmic pH increased in the presence of DIDS. A model is presented explaining how Na⁺, K⁺, Cl^?, H⁺ and HCO₃ ^? fluxes are regulated in these cells.     

Evidence that arbuscular mycorrhizal and phosphate-solubilizing fungi alleviate NaCl stress in the halophyte Kosteletzkya virginica: nutrient uptake and ion distribution within root tissues

The effects of an arbuscular mycorrhizal (AM) fungus, Glomus mosseae, and a phosphate-solubilizing microorganism (PSM), Mortierella sp., and their interactions, on nutrient (N, P and K) uptake and the ionic composition of different root tissues of the halophyte Kosteletzkya virginica (L.), cultured with or without NaCl, were evaluated. Plant biomass, AM colonization and PSM populations were also assessed. Salt stress adversely affected plant nutrient acquisition, especially root P and K, resulting in an important reduction in shoot dry biomass. Inoculation of the AM fungus or/and PSM strongly promoted AM colonization, PSM populations, plant dry biomass, root/shoot dry weight ratio and nutrient uptake by K. virginica, regardless of salinity level. Ion accumulation in root tissues was inhibited by salt stress. However, dual inoculation of the AM fungus and PSM significantly enhanced ion (e.g., Na⁺, Cl^?, K⁺, Ca²⁺, Mg²⁺) accumulation in different root tissues, and maintained lower Na⁺/K⁺ and Ca²⁺/Mg²⁺ ratios and a higher Na⁺/Ca²⁺ ratio, compared to non-inoculated plants under 100 mM NaCl conditions. Correlation coefficient analysis demonstrated that plant (shoot or root) dry biomass correlated positively with plant nutrient uptake and ion (e.g., Na⁺, K⁺, Mg²⁺ and Cl^?) concentrations of different root tissues, and correlated negatively with Na⁺/K⁺ ratios in the epidermis and cortex. Simultaneously, root/shoot dry weight ratio correlated positively with Na⁺/Ca²⁺ ratios in most root tissues. These findings suggest that combined AM fungus and PSM inoculation alleviates the deleterious effects of salt on plant growth by enabling greater nutrient (e.g., P, N and K) absorption, higher accumulation of Na⁺, K⁺, Mg²⁺ and Cl^? in different root tissues, and maintenance of lower root Na⁺/K⁺ and higher Na⁺/Ca²⁺ ratios when salinity is within acceptable limits.     

Identification of quantitative trait loci for ion homeostasis and salt tolerance in barley (Hordeum vulgare L.)

Ion homeostasis is considered to be one of the most important mechanisms underlying salt stress tolerance. We used the Steptoe × Morex barley doubled haploid population to screen for genetic variation in response to salinity stress at an early development stage in a hydroponics system, focusing on ion homeostasis. Salinity induced a strong adverse effect on growth of the parents and their derived population, with Steptoe as the more tolerant parent. Steptoe maintained higher concentrations of K⁺, Na⁺ and Cl^? in the roots and a similar shoot/root ion ratio (<1) under stress conditions compared to control conditions. In contrast, Morex had higher concentrations of these ions in the shoots under stress and a doubled shoot/root ion ratio relative to control conditions, indicating that salt exclusion might contribute to the higher tolerance of Steptoe. Correlation and path analysis demonstrated that shoot Cl^? contents most strongly affected salt tolerance and suggest that both Na⁺ and Cl^? contents are important for salinity stress tolerance in barley. We identified 11 chromosomal regions involved in the control of the variation observed for salt tolerance and various salt stress response traits, including Na⁺, Cl^? and K⁺ contents in shoots. Two specific regions on chromosomes 2H and 3H were found controlling ion contents and salt tolerance, pointing to genes involved in ion homeostasis that contribute to salt tolerance.     

Stimulated fluid secretion is sodium dependent in the Malpighian tubules of Locusta migratoria

The ionic dependencies of stimulated and unstimulated Locusta tubules have been studied. K⁺, Na⁺, Cl^? are essential to both basal and stimulated secretion. K⁺ is secreted against a concentration gradient in unstimulated tubules. In response to diuretic hormone or cAMP application, there is a dramatic influx of K⁺ into the lumen. A high level of Na⁺ and Cl^? in the bathing medium is required to allow maximal fluid secretion. The tubules show an apparent impermeability to Na⁺; its concentration in the secreted fluid is always much less than in the bathing medium. If Na⁺ is omitted from the medium and excess K⁺ added (80 mM K), then although basal secretion occurs (2.5 nl/min), the tubules fail to respond to stimulation. Clearly Na⁺ has an important indirect role to play in stimulated fluid secretion.     

Physiological adjustment to salt stress in Jatropha curcas is associated with accumulation of salt ions,transport and selectivity of K+, osmotic adjustment and K+/Na+ homeostasis

This study assessed the capacity of Jatropha curcas to physiologically adjust to salinity. Seedlings were exposed to increasing NaCl concentrations (25, 50, 75 and 100 mm ) for 15 days. Treatment without NaCl was adopted as control. Shoot dry weight was strongly reduced by NaCl, reaching values of 35% to 65% with 25 to 100 mm NaCl. The shoot/root ratio was only affected with 100 mm NaCl. Relative water content (RWC) increased only with 100 mm NaCl, while electrolyte leakage (EL) was much enhanced with 50 mm NaCl. The Na⁺ transport rate to the shoot was more affected with 50 and 100 mm NaCl. In parallel, Cl^? transport rate increased with 75 and 100 mm NaCl, while K⁺ transport rate fell from 50 mm to 100 mm NaCl. In roots, Na⁺ and Cl^? transport rates fell slightly only in 50 mm (to Na⁺) and 50 and 100 mm (to Cl^?) NaCl, while K⁺ transport rate fell significantly with increasing NaCl. In general, our data demonstrate that J. curcas seedlings present changes in key physiological processes that allow this species to adjust to salinity. These responses are related to accumulation of Na⁺ and Cl^? in leaves and roots, K⁺/Na⁺ homeostasis, transport of K⁺ and selectivity (K–Na) in roots, and accumulation of organic solutes contributing to osmotic adjustment of the species.     

Sodium balance in the catfish Clarias mossambicus exposed to acid water

African catfish, Clarias mossambicus showed no ill effects when kept in acid water pH 4–5 for 3–4 days. Their ionic regulatory response was examined and during 24 h exposure to water of pH 4, Na⁺ efflux increased significantly but was not matched by an increase in Na⁺ influx resulting in a substantial net loss of body Na⁺, which was reduced from 65.4 mmol · kg^?1 to 35.6 mmol · kg^?1, with smaller losses of Cl^? and K⁺.