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     

Membrane potentials and ion permeabilities in flexor cells of the laminar pulvini of Phaseolus coccineus L.

The internal potential of flexor cells in slices of the laminar pulvini of Phaseolus coccineus has been recorded by standard microelectrode techniques in 100 eq m^-3 external salt solutions of various ionic compositions. The measured values are between-15 and-60 mV depending on the external medium. Treating the results with the Goldman equation yields the following relative permeabilities: K⁺, 1.00; Na⁺, 0.24; Cl^-, 0.19; NO ₃ ^- , 1.6. The membrane potential was only slightly sensitive to external pH and Ca²⁺. Metabolic inhibitors (azide, cyanide and salicylhydroxamic acid, carbonyl cyanid m-chlorphenyl hydrazone) caused only slight depolarizations (ca. 4 mV), which differed from the ion-induced changes by their slow time courses. The results are consistent with the hypothesis that the relatively impermeable Cl^- is actively transported and osmotically efficient, whereas the well-permeable K⁺ passively follows Cl^- to maintain electroneutrality and is osmotically of only minor significance.Abbreviations SHAM salicylhydroxamic acid - CCCP carbonyl cyanid m-chlorphenyl hydrazone     

The ionic components of the current pulses generated by developing fucoid eggs.

Using a newly developed, extracellular vibrating electrode, we studied the ionic composition of the current pulses which traverse the developing Pelvetia embryo. External Na⁺, Mg²⁺, or SO₄^2?, are not needed for the first 20 min of pulsing. In fact, lowering external Na⁺ or Mg²⁺ (or K⁺) actually stimulates pulsing. Since tracer studies show that Ca²⁺ entry is speeded by Na⁺, Mg²⁺, or K⁺ reduction, these findings suggest that Ca²⁺ entry triggers pulsing. A sevenfold reduction in external Cl^? raises pulse amplitudes by 60%. Moreover, Cl^? is the only major ion with an equilibrium potential near the pulse reversal potential. These facts suggest that Cl^? efflux carries much of the “inward” current. We propose a model for pulsing in which increased Ca²⁺ within the growing tip opens Cl^? channels. The resulting Cl^? efflux slightly depolarizes the membrane and thus drives a balancing amount of K⁺ out. Thus, the pulses release KCl and serve to relieve excess turgor pressure. By letting Ca²⁺ into the growing tip, they should also strengthen the transcytoplasmic electrical field which is postulated to pull growth components toward this tip.     

Sulfate transport in Desulfobulbus propionicus and Desulfococcus multivorans

Uptake of ³⁵S-labelled sulfate was studied with two sulfate-reducing bacteria, the freshwater species Desulfobulbus propionicus and the marine species Desulfococcus multivorans. Both bacteria were able to highly accumulate micromolar additions (2.5 M) of sulfate, if the reduction of sulfate to H₂S was prevented by low temperature (0° C) or oxygen. Sulfate accumulation was highest (accumulation factors 10³ to 10⁴) after growth under sulfate-limiting conditions, while cells grown with excess sulfate revealed accumulation factors below 300. With increasing sulfate concentrations added (up to 25 mM), the accumulation factors decreased down to 1.4. Sulfate accumulation in both strains was sensitive to carbonyl cyanide m-chlorophenylhydrazone (CCCP) and thiocyanate, but not directly correlated to the ATP content of the cells. Pasteurized cells did not accumulate sulfate. Sulfate transport was reversible. Accumulated ³⁵S-labelled sulfate was quickly released after addition of non-labelled sulfate or structural sulfate analogues (thiosulfate, selenate, chromate, less effect by molybdate, tungstate, sulfite, selenite). In D. propionicus, sulfate accumulation was independent of the presence or absence of Na⁺, K⁺, Li⁺, Mg²⁺, Cl^- and Br^-. Sulfate accumulation was reversibly enhanced at pH 5 and diminished at pH 9. In the marine bacterium D. multivorans, sulfate accumulation depended on the presence of Na⁺ ions. Na⁺ could partially be replaced by Li⁺. Sulfate accumulation in D. multivorans was sensitive to the Na⁺/H⁺ antiporter monensin and the Na⁺/H⁺ antiport inhibitor amiloride. It is concluded that in D. propionicus sulfate is accumulated electrogenically in symport with at least three protons, whereas for D. multivorans electrogenic symport with sodium ions is proposed. In both species, more than one sulfate transport system must be present. High affinity transport systems appear to be derepressed under sulfate limitation only. The high affinity transport system must be regulated to avoid energy-spoiling accumulation at high sulfate concentrations.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone - DCCD dicyclohexylcarbodiimide     

Actin and cortical fiber reticulation in the siphonaceous alga Vaucheria sessilis

Since light-induced organellae aggregation in the siphonaceous alga Vaucheria sessilis (Vauch.) D.C. is accompanied by the formation of a cortical fiber reticulum in the light, we proposed that this process of reticulation might be causally related to aggregation (Blatt and Briggs, 1980). In this paper we report the tentative identification of actin filaments and filament bundles in the cortical cytoplasm of V. sessilis, and present additional evidence, obtained using the inhibitors cytochalasin B and phalloidin and indicating that aggregation in response to low-intensity point irradiation with blue light is dependent upon the formation of a cortical fiber reticulum. Phalloidin stabilized the cortical fibers, preventing both reticulum formation and organelle aggregation in blue light. Cytochalasin B partially destabilized the cortical fibers to the extent of permitting light-induced reticulum formation and organelle aggregation in the light in the presence of phalloidin.C.I.W.-D.P.B. Publication No. 643     

[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     

Prolactin controls branchial clcn2c but not atp1a1a.2 in zebrafish Danio rerio

This study examined the branchial epithelium of stenohaline zebrafish Danio rerio, and in particular Na⁺–Cl⁻ cotransporter-like 2 (Slc12a10.2)-expressing ionocytes (Na⁺–Cl⁻ cotransporter [Ncc]-cells), which mediate the active uptake of ions from freshwater environments. The study assessed whether the pituitary hormone prolactin (Prl) stimulates the expression of messenger (m)RNAs encoding a Clc Cl⁻ channel family member (clcn2c) and a Na⁺–K⁺-ATPase α1 subunit (atp1a1a.2) expressed in Ncc-cells. Branchial clcn2c, but not atp1a1a.2 levels, were sensitive to Prl both in vitro and in vivo. These observations suggest that Prl contributes to maintaining systemic Cl⁻ balance via the regulation of clcn2c.     

Growth characteristics and ion contents of non-selected and salt-selected callus lines of highbush blueberry (Vacdnium corymbosum) cultivars Blue Crop and Denise Blue

Non-selected and sodium chloride selected callus lines of Vacdnium corymbosum L.cv Blue Crop and cv. Denise Blue were grown on media supplemented with 0–100 mM NaCl. For both cultivars, fresh weight and dry weight yields were greater in selected lines on all levels of NaCl. Selected lines of Blue Crop displayed better growth than selected lines of Denise Blue at most concentrations of NaCl. Internal Na⁺ and Cl^– concentrations in selected and non-selected lines of both cultivars increased as external concentration was raised. However, selected lines of Blue Crop and Denise Blue accumulated more Na⁺ and Cl^– than non-selected lines. Selected lines of both cultivars maintained higher levels of K⁺ than non-selected lines on all external NaCl levels. Selected lines of Blue Crop had higher levels of Na⁺ and Cl^– than that of Denise Blue. The results suggest Na⁺ and Cl^– accumulation could be a mechanism allowing better growth in selected lines at moderate salinity levels (50–75 mM NaCl).     

Effects of abscisic acid on sequestration and exchange of Na+ by barley roots

Excised Na⁺-starved barley roots were suspended in solutions of Na⁺ in combination with NO ₃ ^- , Cl^-, and SO ₄ ^2- , and effects of the added phytohormone, abscisic acid (ABA), to the medium were determined. Abscisic acid increased the rate of Na⁺ (²²Na⁺) accumulation and the amount of Na⁺ deposited in the vacuoles. These stimulating effects of ABA were modified by anions following the sequence NO ₃ ^- >Cl^->SO ₄ ^2- . Testing whether the magnitude of the pH gradient across the plasmalemma of the cells of the root cortex affects rates of Na⁺ accumulation and their dependence upon ABA, we observed that, in the pH range from 4 to 8, the ABA-induced stimulation was strongest at pH 5.8, and least at pH 4. Changes in pH during the experiment caused changes in the rates of Na⁺ accumulation in agreement with experiments performed at constant pH values. Simultaneously with ABA-enhanced accumulation, loss of Na⁺ occurred. Loss of Na⁺ was strongest at pH 4 and was affected by anions, being greatest with SO ₄ ^2- and following the sequence SO ₄ ^2- >Cl^->NO ₃ ^- . On the basis of the finding that initial acceleration of uptake as well as loss of Na⁺ depended on the pH of the medium we suggest that, in barley roots, ABA stimulates an exchange of Na⁺ for H⁺ at the plasmalemma of the cortical cells. The results indicate that ABA-stimulated expulsion of Na⁺, in combination with ABA-stimulated sequestration in the vacuoles, constitutes one of the mechanisms which enable barley plants to tolerate higher than normal levels of Na⁺.Abbreviations ABA abscisic acid - FW fresh weight     

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     

Passive sodium movements across the opercular epithelium: The paracellular shunt pathway and ionic conductance

Summary The unidirectional Na⁺, Cl^–, and urea fluxes across isolated opercular epithelia from seawater-adaptedFundulus heteroclitus were measured under different experimental conditions. The mean Na⁺, Cl^–, and urea permeabilities were 9.30×10^–6 cm·sec^–1, 1.24×10^–6 cm·sec^–1, and 5.05×10^–7 cm·sec^–1, respectively. The responses of the unidirectional Na⁺ fluxes and the Cl^– influx (mucosa to serosa) to voltage clamping were characteristic of passively moving ions traversing only one rate-limiting barrier. The Na⁺ conductance varied linearly with, and comprised a mean 54% of, the total tissue ionic conductance. The Cl^– influx and the urea fluxes were independent of the tissue conductance. Triaminopyrimidine (TAP) reduced the Na⁺ fluxes and tissue conductance over 70%, while having no effect on the Cl^– influx or urea fluxes. Mucosal Na⁺ substitution reduced the Na⁺ permeability 60% and the tissue conductance 76%, but had no effect on the Cl^– influx or the urea fluxes. Both the Na⁺ and Cl^– influxes were unaffected by respective serosal substitutions, indicating the lack of any Na⁺/Na⁺ and Cl^–/Cl^– exchange diffusion.The results suggest that the unidirectional Na⁺ fluxes are simple passive fluxes proceeding extracellularly (i.e., movement through a cation-selective paracellular shunt). This pathway is dependent on mucosal (external) Na⁺, independent of serosal (internal) Na⁺, and may be distinct from the transepithelial Cl^– and urea pathways.     

Growth and ion relations in response to combined salinity and waterlogging in the perennial forage legumes Lotus corniculatus and Lotus tenuis

Lotus tenuis (Wadst. & Kit.) is a perennial legume widely grown for pasture in the flood-prone and salt affected Pampa region of Argentina. The physiology of salt and waterlogging tolerance in L. tenuis (four cultivars) was evaluated, and compared with Lotus corniculatus (three cultivars); the most widely cultivated Lotus species. Overall, L. tenuis cultivars accumulated less Na⁺ and Cl⁻, and more K⁺ in shoots than L. corniculatus cultivars, when exposed to 200 mM NaCl for 28 days in aerated or in stagnant solutions. Root porosity was higher in L. tenuis cultivars due to greater aerenchyma formation. In a NaCl dose–response experiment (0–400 mM NaCl in aerated solution), L. tenuis (cv. Chaja) accumulated half as much Cl⁻ in its shoots than L. corniculatus (cv. San Gabriel) at all external NaCl concentrations, and about 30% less shoot Na⁺ in treatments above 250 mM NaCl. Ion distributions in shoots were determined for plants at 200 mM NaCl. L. tenuis (cv. Chaja) again accumulated about half as much Cl⁻ in old leaves, young leaves and stems, compared with concentrations in L. corniculatus (cv. San Gabriel). There were not, however, significant differences between the two species for Na⁺ concentrations in the various shoot tissues. The higher root porosity, and maintenance of lower shoot Cl⁻ and Na⁺ concentrations in L. tenuis, compared with L. corniculatus, contributes to the greater tolerance to combined salt and waterlogging stress in L. tenuis. Moreover, significant variation for tolerance to combined salinity and waterlogging stress was identified within both L. tenuis and L. corniculatus.     

Osmotic acclimation of the brackish water xanthophyceae,Vaucheria dichotoma (L.) MARTIUS: Inorganic ion composition and amino acids

The salinity tolerance ofVaucheria dichotoma, a siphonous Xanthophycean alga was investigated. The alga survived an external osmotic potential range between 74 and 1, 176 mOsmol (ca. 2.5 and 40.0 ppt. (parts per thousand]). Turgor pressure was regulated in salinities ranging from 74 to 441 mOsmol. With further increase of the salinity, turgor pressure decreased from 153 to 9 mOsmol (0.44 to 0.08 MPa). At 441 mOsmol salinity the major intracellular ions were present in the following concentrations (mM/l cell water): K⁺, 145; Na⁺; 90; sulphate, 91; Cl⁻, 91. Under the most severe salinity stress (1,176 mOsmol) the ionic concentration increased to (mM/l cell water): K⁺, 250; Na⁺, 75; sulphate, 35; Cl⁻, 351. The content of amino acids: alanine (Ala), threonine (Thr and glutamic acid (Glu) was lower, nerver exceeding 5–11 mM, however; the concentrations were positively correlated with salinity.     

Hydrogel modified uptake of salt ions and calcium in<Emphasis Type="Italic"> Populus euphratica</Emphasis> under saline conditions

The effects of hydrogel on growth and ion relationships of a salt resistant woody species, Populus euphratica , were investigated under saline conditions. The hydrogel used was Stockosorb K410, a highly cross-linked polyacrylamide with about 40% of the amide group hydrolysed to carboxylic groups. Amendment of saline soil (potassium mine refuse) with 0.6% hydrogel improved seedling growth (2.7-fold higher biomass) over a period of 2 years, even though plant growth was reduced by salinity. Hydrogel-treated plants had approximately 3.5-fold higher root length and root surface area than those grown in unamended saline soil. In addition, over 6% of total roots were aggregated in gel fragments. Tissue and cellular ion analysis showed that growth improvement appeared to be the result of increased capacity for salt exclusion and enhancement of Ca²⁺ uptake. X-ray microanalysis of root compartments indicated that the presence of polymer restricted apoplastic Na⁺ in both young and old roots, and limited apoplastic and cytoplastic Cl^– in old roots while increasing Cl^– compartmentation in cortical vacuoles of both young and old roots. Collectively, radical transport of salt ions (Na⁺ and Cl^–) through the cortex into the xylem was lowered and subsequent axial transport was limited. Hydrogel treatment enhanced uptake of Ca²⁺ and microanalysis showed that enrichment of Ca²⁺ in root tissue mainly occurred in the apoplast. In conclusion, enhanced Ca²⁺ uptake and the increased capacity of P. euphratica to exclude salt were the result of improved Ca²⁺/Na⁺ concentration of soil solution available to the plant. Hydrogel amendment improves the quality of soil solutions by lowering salt level as a result of its salt-buffering capacity and enriching Ca²⁺ uptake, because of the polymers cation-exchange character. Accordingly, root aggregation allows good contact of roots with a Ca²⁺ source and reduces contact with Na⁺ and Cl^–, which presumably plays a major role in enhancing salt tolerance of P. euphratica.     

Simulation analysis of intracellular Na and Cl homeostasis during β1-adrenergic stimulation of cardiac myocyte

To quantitatively understand intracellular Na⁺ and Cl⁻ homeostasis as well as roles of Na⁺/K⁺ pump and cystic fibrosis transmembrane conductance regulator Cl⁻ channel (I_CFTR) during the β1-adrenergic stimulation in cardiac myocyte, we constructed a computer model of β1-adrenergic signaling and implemented it into an excitation-contraction coupling model of the guinea-pig ventricular cell, which can reproduce membrane excitation, intracellular ion changes (Na⁺, K⁺, Ca²⁺ and Cl⁻), contraction, cell volume, and oxidative phosphorylation. An application of isoproterenol to the model cell resulted in the shortening of action potential duration (APD) after a transient prolongation, the increases in both Ca²⁺ transient and cell shortening, and the decreases in both Cl⁻ concentration and cell volume. These results are consistent with experimental data. Increasing the density of I_CFTR shortened APD and augmented the peak amplitudes of the L-type Ca²⁺ current (I_CaL) and the Ca²⁺ transient during the β1-adrenergic stimulation. This indirect inotropic effect was elucidated by the increase in the driving force of I_CaL via a decrease in plateau potential. Our model reproduced the experimental data demonstrating the decrease in intracellular Na⁺ during the β-adrenergic stimulation at 0 or 0.5 Hz electrical stimulation. The decrease is attributable to the increase in Na⁺ affinity of Na⁺/K⁺ pump by protein kinase A. However it was predicted that Na⁺ increases at higher beating rate because of larger Na⁺ influx through forward Na⁺/Ca²⁺ exchange. It was demonstrated that dynamic changes in Na⁺ and Cl⁻ fluxes remarkably affect the inotropic action of isoproterenol in the ventricular myocytes.     

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.     

Ion fluxes inAcetabularia: Vesicular shuttle

Summary Ion flux relations in the unicellular marine algaAcetabularia have been investigated by uptake and washout kinetics of radioactive tracers (²²Na⁺,⁴²K⁺,³⁶Cl^– and⁸⁶Rb⁺) in normal cells and in cell segments with altered compartmentation (depleted of vacuole or of cytoplasm). Some flux experiments were supplemented by simultaneous electrophysiological recordings. The main results and conclusions about the steady-state relations are: the plasmalemma is the dominating barrier for translocation of K⁺ with influx and efflux of about 100 nmol·m^–2·sec^–1×K⁺ passes three- to sevenfold more easily than Rb⁺ does. Under normal conditions, Cl^– (the substrate of the electrogenic pump, which dominates the electrical properties of the plasmalemma in the resting state) shows two efflux components of about 17 and 2 mol·m^–2·sec^–1, and a cytoplasmic as well as vacuolar [Cl^–] of about 420mm ([Cl^–] _o =529mm). At 4°C, when the pump is inhibited, both influx and efflux, as well as the cellular [Cl^–], are significantly reduced. Na⁺ ([Na⁺] _i : about 70mm, [Na⁺] _o : 461mm), which is of minor electrophysiological relevance compared to K⁺, exhibits rapid and virtually temperature-insensitive (electroneutral) exchange (two components with about 2 and 0.2 mol·m^–2·sec^–1 for influx and efflux). Some results with Na⁺ and Cl^– are inconsistent with conventional (noncyclic) compartmentation models: (i) equilibration of the vacuole (with the external medium) can be faster than equilibration of the cytoplasm, (ii) absurd concentration values result when calculated by conventional compartmental analysis, and (iii) large amounts of ions can be released from the cell without changes in the electrical potential of the cytoplasm. These observations can be explained by the particular compartmentation of normalAcetabularia cells (as known by electron micrographs) with about 1 part cytoplasm, 5 parts central vacuole, and 5 parts vacuolar vesicles. These vesicles communicate directly with the central vacuole, with the cytoplasm and with the external medium.     

Quantitative ion localization within Suaeda maritima leaf mesophyll cells

Grown under saline conditions, Suaeda maritima accumulates Na⁺ and Cl^- into its leaves, where individual mesophyll cells behave differently in their compartmentation of these ions. Measurements of ion concentrations within selected subcellular compartments show that freeze-substitution with dry sectioning is a valuable preparative technique for analytical electron microscopy of highly vacuolate plant material. Using this approach, absolute estimates were made of Na⁺, K⁺ and Cl^- concentrations in the cytoplasm, cell walls, chloroplasts and vacuoles of leaf mesophyll cells.Abbreviation TAEM transmission analytical electron microscopy     

Na+, K+, Cl− cotransport and its regulation in Ehrlich ascites Tumor cells. Ca2+/Calmodulin and protein kinase C dependent pathways

Summary Net Cl^– uptake as well as unidirectional³⁶Cl influx during regulatory volume increase (RVI) require external K⁺. Half-maximal rate of bumetanide-sensitive³⁶Cl uptake is attained at about 3.3mm external K⁺. The bumetanide-sensitive K⁺ influx found during RVI is strongly dependent on both Na⁺ and Cl^–. The bumetanide-sensitive unidirectional Na⁺ influx during RVI is dependent on K⁺ as well as on Cl^–. The cotransporter activated during RVI in Ehrlich cells, therefore, seems to transport Na⁺, K⁺ and Cl^–. In the presence of ouabain and Ba⁺ the stoichiometry of the bumetanide-sensitive net fluxes can be measured at 1.0 Na⁺, 0.8 K⁺, 2.0 Cl^– or approximately 1 : Na, 1 : K, 2 : Cl. Under these circumstances the K⁺ and Cl^– flux ratios (influx/efflux) for the bumetanide-sensitive component were estimated at 1.34 ±0.08 and 1.82 ± 0.15 which should be compared to the gradient for the Na⁺, K⁺, 2Cl^– cotransport system at 1.75 ± 0.24.Addition of sucrose to hypertonicity causes the Ehrlich cells to shrink with no signs of RVI, whereas shrinkage with hypertonic standard medium (all extracellular ion concentrations increased) results in a RVI response towards the original cell volume. Under both conditions a bumetanide-sensitive unidirectional K⁺ influx is activated. During hypotonic conditions a small bumetanide-sensitive K⁺ influx is observed, indicating that the cotransport system is already activated.The cotransport is activated 10–15 fold by bradykinin, an agonist which stimulates phospholipase C resulting in release of internal Ca²⁺ and activation of protein kinase C.The anti-calmodulin drug pimozide inhibits most of the bumetanide-sensitive K⁺ influx during RVI. The cotransporter can be activated by the phorbol ester TPA. These results indicate that the stimulation of the Na⁺, K⁺, Cl^– cotransport involves both Ca²⁺/calmodulin and protein kinase C.     

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.