Effect of Sodium on Phosphate Uptake in Unicellular and Filamentous Cyanobacteria

The effect of Na⁺ on phosphate uptake was studied in four strainsof cyanobacteria: Synechococcus PCC 7942, Gloeothece PCC 6501,Phormidium sp. and Chlorogloeopsis PCC 6912. Phosphate uptakewas stimulated by Na⁺ in all cases. Li⁺ and K⁺ acted as partialanalogues for Na⁺. Half-saturation [K_1/2(Na⁺)] of phosphateuptake was reached with Na⁺ concentrations ranging from 317µM in Chlorogloeopsis to 659 µM in Phormidium. Theconcentration of phosphate required to reach half-saturationof phosphate uptake [K_1/2(P_i)]was not changed by the presenceof Na⁺. (Received April 11, 1994; Accepted July 5, 1994)     

Na+ fluxes in Chara under salt stress

The influx and efflux of Na⁺ across the plasma membrane of Characorallina and Chara longifolia were examined under mild saltstress conditions. Na⁺ influx was found to be rapid in bothspecies with the freely exchangeable cytoplasmic Na⁺ cominginto isotopic equilibrium with external ²²Na⁺ within 1 h ofexposure to isotope. Cytoplasmlc Na⁺ concentration and Na⁺ influxwere greater in C. corallina than in C. longifolla under thesame conditions. Na⁺ influx across the tonoplast was much lowerthan the flux across the plasma membrane. Na⁺ efflux was stimulatedat pH 5 relative to pH 7 by 218% in C. coralllna and 320% inC. longifolia. In both species externally applied Li⁺ inhibitedNa⁺ efflux at pH 5 but not at pH 7. Na⁺ etflux was not significantlyinhibited by amiloride. Key words: Na⁺ influx, Na⁺ efflux, Na⁺/H⁺ antiport, Chara     

Effect of Divalent Cations on Na+ Permeability of Chara corallina and Freshwater Grown Chara buckellii

The effect of elevated Na⁺ concentration on Na⁺ permeability(P_Na) and Na⁺ influx in the presence of two levels of externaldivalent cations was determined in Chara corallina and freshwater-culturedChara buckellii. When Na⁺ in the medium was increased from 1.0to 70 mol m^–3, Na⁺ influx increased in both species ifCa²⁺ was low (0.1 mol m–3). If Ca²⁺ was increased to 7.0mol m^–3 when Na⁺ was increased, Na⁺ influx remained atthe low control level in C. corallina, and showed only a temporaryincrease in C. buckellii. Mg²⁺ was a better substitute for Ca²⁺in C. buckellii than in C. corallina. Na⁺ permeability data suggest that when the external Ca²⁺ concentrationis low, P_Na does not increase in the presence of elevated NaCl;the increase in Na⁺ influx appears to be due to the increasein external Na⁺ concentration alone. Ca^{2 +} supplementation appearsto decrease P_Na whereas supplemental Mg²⁺ has no effect. Na⁺ effluxes were computed from previously determined net fluxesand the influxes. It was found that for both species, fluxesin both directions were stimulated in response to all experimentaltreatments, but Na⁺ influx always exceeded efflux. This resultedin net Na⁺ accumulation in the vacuoles of both species. The results are discussed with reference to net flux and electrophysiologicaldata obtained previously under identical conditions, as wellas the comparative salinity tolerance of both species and theNa⁺/divalent cation ratio. Key words: Na⁺ influx, Na⁺ tolerance, membrane potential, permeability, Chara     

Regulation of K+ Influx in Barley: Evidence for a Direct Control of Influx by K+ Concentration of Root Cells

Siddiqi, M. Y. and Glass, A. D. M. 1987. Regulation of K⁺ influxin barley: Evidence for a direct control of influx by K⁺ concentrationof root cells.—J. exp. Bot. 38: 935–947. The kinetics of K⁺ (⁸⁶Rb⁺) influx into intact roots of barley(Hordeum vulgare L. cv. Fergus) seedlings having different combinationsof root and shoot [K⁺], different growth rates and differentroot:shoot weight ratios were studied. K⁺ influx was stronglycorrelated with root [K⁺]; shoot [K⁺], growth rates, and root:shoot ratios appeared to have little effect on K⁺ influx. Adetailed study showed that both V_max and K_m for K⁺ influx wereaffected by root [K⁺] but not by shoot [K⁺]. We have suggestedthat factors such as growth rates and root: shoot ratio mayaffect K⁺ influx indirectly primarily via their influence onroot factors such as root [K⁺]. We have reiterated that othertypes of kinetic control, e.g. increased or decreased synthesisof ‘carrier systems’, may operate in addition todirect (allosteric?) control of K⁺ influx by root [K⁺]. Thenegative feedback signal from root [K⁺] appeared to be the primeeffector in the regulation of K⁺ influx. Key words: Barley, K⁺ influx     

Ionic Relations of Garden Orache, A triplex hortensis L.: Growth and Ion Distribution at Moderate Salinity and the Function of Bladder Hairs

The growth of garden orache, A triplex hortensis was studiedunder conditions of mild NaCl or Na₂SO₄ salinity. Growth, drymatter production and leaf size were substantially stimulatedat 10 mM and 50 mM Na⁺ salts. Increased growth, however, appearedto be due to a K⁺-sparing effect of Na⁺ rather than to salinityper se. The distribution of K⁺ and Na⁺ in the plant revealeda remarkable preference for K+ in the roots and the hypocotyl.In the shoot the K/Na ratio decreased strongly with leaf age.However, the inverse changes in K⁺ and Na⁺ content with leafage were dependent on the presence of bladder hairs, which removedalmost all of the Na⁺ from the young leaf lamina. Measurementsof net fluxes of K⁺ and Na⁺ into roots and shoots of growingAtriplex plants showed a higher K/Na selectivity of the netion flux to the root compared to the shoot. With increasingsalinity the selectivity ratio S_{K, Na}^* of net ion fluxes tothe roots and to the shoots was increased. The data suggestthat recirculation of K⁺ from leaves to roots is an importantlink in establishing the K/Na selectivity in A. hortensis plants.The importance of K⁺ recirculation and phloem transport forsalt tolerance is discussed. Key words: Atriplex hortensis, Salinity, Potassium, Sodium, K⁺ retranslocation, Bladder hairs, Growth stimulation     

Sodium-dependent inactivation of sodium/calcium exchange in transfected Chinese hamster ovary cells

High concentrations of cytosolic Na⁺ ions induce the time-dependent formation of an inactive state of the Na⁺/Ca²⁺ exchanger (NCX), a process known as Na⁺-dependent inactivation. NCX activity was measured as Ca²⁺ uptake in fura 2-loaded Chinese hamster ovary (CHO) cells expressing the wild-type (WT) NCX or mutants that are hypersensitive (F223E) or resistant (K229Q) to Na⁺-dependent inactivation. As expected, 1) Na⁺-dependent inactivation was promoted by high cytosolic Na⁺ concentration, 2) the F223E mutant was more susceptible than the WT exchanger to inactivation, whereas the K229Q mutant was resistant, and 3) inactivation was enhanced by cytosolic acidification. However, in contrast to expectations from excised patch studies, 1) the WT exchanger was resistant to Na⁺-dependent inactivation unless cytosolic pH was reduced, 2) reducing cellular phosphatidylinositol-4,5-bisphosphate levels did not induce Na⁺-dependent inactivation in the WT exchanger, 3) Na⁺-dependent inactivation did not increase the half-maximal cytosolic Ca²⁺ concentration for allosteric Ca²⁺ activation, 4) Na⁺-dependent inactivation was not reversed by high cytosolic Ca²⁺ concentrations, and 5) Na⁺-dependent inactivation was partially, but transiently, reversed by an increase in extracellular Ca²⁺ concentration. Thus Na⁺-dependent inactivation of NCX expressed in CHO cells differs in several respects from the inactivation process measured in excised patches. The refractoriness of the WT exchanger to Na⁺-dependent inactivation suggests that this type of inactivation is unlikely to be a strong regulator of exchange activity under physiological conditions but would probably act to inhibit NCX-mediated Ca²⁺ influx during ischemia. ischemia; cytosolic calcium concentration; cytosolic sodium concentration; cellular phosphatidylinositol-4,5-bisphosphate     

Na+ influx and Na+-K+ pump activation during short-term exposure of cardiac myocytes to aldosterone

To examine the effect of aldosterone on sarcolemmalNa⁺ transport, we measuredouabain-sensitive electrogenicNa⁺-K⁺pump current(I_p) involtage-clamped ventricular myocytes and intracellularNa⁺ activity(aⁱ_Na) in right ventricularpapillary muscles. Aldosterone (10 nM) induced an increase in bothI_p and the rateof rise of aⁱ_Na duringNa⁺-K⁺pump blockade with the fast-acting cardiac steroid dihydroouabain. Thealdosterone-induced increase inI_p and rate ofrise of aⁱ_Na was eliminated bybumetanide, suggesting that aldosterone activates Na⁺ influx through theNa⁺-K⁺-2Clcotransporter. To obtain independent support for this, theNa⁺,K⁺, andCl concentrations in thesuperfusate and solution of pipettes used to voltage clamp myocyteswere set at levels designed to abolish the inward electrochemicaldriving force for theNa⁺-K⁺-2Clcotransporter. This eliminated the aldosterone-induced increase inI_p. We concludethat in vitro exposure of cardiac myocytes to aldosterone activates theNa⁺-K⁺-2Clcotransporter to enhance Na⁺influx and stimulate theNa⁺-K⁺pump.

     

Interaction of reactive oxygen species with ion transport mechanisms

The use ofelectrophysiological and molecular biology techniques has shed light onreactive oxygen species (ROS)-induced impairment of surface andinternal membranes that control cellular signaling. These deleteriouseffects of ROS are due to their interaction with various ion transportproteins underlying the transmembrane signal transduction, namely,1) ion channels, such asCa²⁺ channels (includingvoltage-sensitive L-type Ca²⁺currents, dihydropyridine receptor voltage sensors, ryanodine receptorCa²⁺-release channels, andD-myo-inositol1,4,5-trisphosphate receptor Ca²⁺-release channels),K⁺ channels (such asCa²⁺-activatedK⁺ channels, inward and outwardK⁺ currents, and ATP-sensitiveK⁺ channels),Na⁺ channels, andCl channels;2) ion pumps, such as sarcoplasmicreticulum and sarcolemmal Ca²⁺pumps,Na⁺-K⁺-ATPase(Na⁺ pump), andH⁺-ATPase(H⁺ pump);3) ion exchangers such as theNa⁺/Ca²⁺exchanger andNa⁺/H⁺exchanger; and 4) ion cotransporterssuch asK⁺-Cl,Na⁺-K⁺-Cl,andP_i-Na⁺cotransporters. The mechanism of ROS-induced modificationsin ion transport pathways involves1) oxidation of sulfhydryl groups located on the ion transport proteins,2) peroxidation of membrane phospholipids, and 3) inhibition ofmembrane-bound regulatory enzymes and modification of the oxidativephosphorylation and ATP levels. Alterations in the ion transportmechanisms lead to changes in a second messenger system, primarilyCa²⁺ homeostasis, which furtheraugment the abnormal electrical activity and distortion of signaltransduction, causing cell dysfunction, which underlies pathologicalconditions.

     

Permeability of Lipophilic Cations

The permeability (P) of a lipophilic cation, triphenylmethylphosphonium(TPMP⁺) which is frequently used as a membrane potential probe,has been measured in Chara australis (Charophyceae). P_TPMP+across biological membranes is usually thought to be very highbut this is not the case across the plasmalemma of Chara. Thepermeability of TPMP⁺ across the plasmalemma was found to betypical of inorganic cations, about 1.0 nm s^–1. Estimateswere made of the permeability of lipophilic cations across someother cell membranes, based on previously published work. Thepermeability of TPMP⁺ across the plasma membranes of the redalga, Griffithsia monilis and the blue-green alga, Anabaenavariabilis was about 2–5 nm s^–1. The permeabilityof TPMP⁺ across the plasma membranes of eukaryotes and prokaryotesappears to be similar. The permeability of lipophilic cationsacross the cristae of isolated mitochondria are exceptionallyhigh, about 170 nm s^–1. TPMP⁺ did not behave as a thiamineanalogue in Chara, unlike in the case of yeast. The means ofentry of TPMP⁺ into the Chara cell, driven by the electrochemicalgradient across the plasmalemma, has not been identified. Thepresence of a second lipophilic cation probe, DDA⁺ (dibenzyldimethylammonium),caused a decrease in the uptake flux of TPMP⁺; this suggeststhat the two lipophilic cations compete for the same site atthe surface of the plasmalemma. Key words: Chara australis, TPMP⁺, Permeability, Lipophilic cation     

Effects of Acriflavine on the Formation of the Plasma Membrane of Escherichia coli

When cells of acriflavine-sensitive (acrA) and acriflavine-resistant(acrA⁺) Escherichia coli K-12 strains were treated with a ratherhigh concentration (100 µg ml^-1) of acriflavine in mediumthat had been adjusted to pH 8.1, distinct whirlpool-like structuresderived from the plasma membrane appeared not only in the acrAcells but also in the acrA⁺ cells. Chemical analysis was performedto determine the lipid composition of the cells by thin-layerchromatography on silica gel and gas-liquid chromatography.The amount of total fatty acids was significantly higher inthe acrA cells than in the acrA⁺ cells, when cells were culturedin the presence of acriflavine. This difference seems to becaused by the greater accumulation of unsaturated fatty acids(palmitoleic and cis-vaccenic acid) in the acrA mutant cellsthan in the acrA⁺ cells and by the acceleration of this accumulationas a result of the presence of the dye. A comparison of phospholipidcontents between the acrA and acrA⁺ cells cultured under acriflavine-freeconditions showed that the former cells contained more phosphatidylethanolamine(PE) and, in particular, more cardiolipin (CL) than the lattercells. However, the situation was reversed in the case of phosphatidylglycerol(PG). Addition of acriflavine to the medium led to a markedincrease in levels of PE and CL in both acrA and acrA⁺ cellsbut an increase in levels of PG was found only in the acrA⁺cells. (Received October 13, 1992; Accepted May 31, 1993)     

Efficiency of K+ Utilization by Barley Varieties: Activation of Pyruvate Kinase

Barley (Hordeum vulgare L.) varieties differed in their raponseto [K⁺]₀, in terms of their utilization efficiencies (UE = freshweight. concentration of [K⁺]₁^–1). At low [K⁺]₀, Compana,an efficient-non-responder demonstrated superior utilizationof absorbed K⁺. On the other hand, at high [K⁺]₀, Fergus (anefficient responder) and BT 334 (an inefficient responder) hadhigher UE values for K⁺ than Compana which performed poorlyat this [K⁺]₀. Kinetic parameters for K⁺ activation of the enzyme pyruvatekinase from 12 barley varieties, representing a range of UEvalues, were determined. Varieties showed substantial differencesin their V_max values (P<0·01). Compana, an efficientvariety, had the highest V_max (31 µmol g^–1 freshwt. h^–1) which was about 50% higher than that of Mingo,an inefficient variety. By contrast, K_m values for the enzymeswere not significantly different among varieties The mean valuesfor all varieties (3·9±0·15 mol m^–3K⁺) is far below the estimated cytoplasmic [K⁺] (100-200 molm^–3). It is, therefore, unlikely that differences in theutilization of K⁺ by these varieties can be explained on thebasis of differential requirements for (K⁺) activation of theseenzymes. Alternative possibilities for differences in the utilizationof K⁺ are discussed. Key words: K⁺ utilization efficiency, Pyruvate kinase, Barley varieties     

Na+/H+ Antiporter in Tonoplast Vesicles from Rice Roots

The Na⁺/H ⁺ antiporter in vacuolar membranes transports Na⁺from the cytoplasm to vacuoles using a pH gradient generatedby proton pumps; it is considered to be related to salinitytolerance. Rice (Oryza sativa L.) is a salt-sensitive crop whosevacuolar antiporter is unknown. The vacuolar pH of rice roots,determined by ³¹P-nuclear magnetic resonance (NMR), increasedfrom 5.34 to 5.58 in response to 0.1 M NaCl treatment. Transportof protons into the tonoplast vesicles from rice roots was fluorometricallymeasured. Efflux of protons was accelerated by the additionof Na⁺. Furthermore, the influx of ²²Na⁺ into the tonoplastvesicles was accelerated by a pH gradient generated by proton-translocatingadenosine 5'-triphosphatase (H⁺-ATPase) and proton-translocatinginorganic pyro-phosphatase (H⁺-PPase). We concluded that thisNa⁺/H⁺antiporter functioned as a Na⁺ transporter in the vacuolarmembranes. The antiporter had a K_m of 10 mM for Na⁺ and wascompetitively inhibited by amiloride and its analogues. TheKⁱ values for 5-(N-methyl-N-isobutyl)-amiloride (MIA), 5-(N-ethyl-N-isopropyI)-amiloride(EIPA), and 5-(N, N-hexamethylene)-amiloride (HMA) were 2.2,5.9, and 2.9 µ M, respectively. Unlike barley, a salt-tolerantcrop, NaCl treatment did not activate the antiporter in riceroots. The amount of antiporter in the vacuolar membranes maybe one of the most important factors determining salt tolerance. ¹This work was supported by a grant from Bio-Media Project ofthe Japanese Ministry of Agriculture, Forestry and Fisheries(BMP96-III-1).     

The Effect of Salinity Changes Upon the Physiology of Eulittoral Green Macroalgae from Antarctica and Southern Chile: II INTRACELLULAR INORGANIC IONS AND ORGANIC COMPOUNDS

The effects of hypo- and hypersaline treatments ranging from7–68% on the intracellular inorganic ion and organic soluteconcentrations were determined in the eulittoral green macroalgaeUlothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa,Acrosiphonia arcta, and Ulva rigida from Antarctica and SouthernChile. The main inorganic cations were K⁺, Na⁺, and Mg²⁺ inall species. The major osmolyte in E. bulbosa, A. arcta, andU. rigida was K⁺ at increasing salinities. In both Ulothrixspecies, however, K⁺ levels declined during hypersaline stressand Na⁺ concentrations rose significantly. The main inorganicanions were Cl^-, SO²_4-, and PO³_4- in all algae, while E. bulbosaand U. rigida also contained NO⁺₃. A. arcta showed an extremelyhigh SO^2-₄ content. The organic solutes proline, sucrose, andß-dimethylsulphoniopropionate (DMSP) played an importantrole in osmotic acclimation. The occurrence of three organicosmolytes suggests an additional function of these solutes ascryoprotectants in the cold-water macroalgae investigated.     

Proton/Pyruvate Cotransport into Mesophyll Chloroplasts of C4 Plants

Light-enhanced active pyruvate uptake into mesophyll chloroplastsof C₄ plants was reported to be mimicked by either of the twotypes of cation jump: H⁺-jump in maize and phylogenically relatedspecies (H⁺-type) and Na⁺-jump in all the other C₄ species tested(Na⁺-type) [Aoki, N., Ohnishi, J. and Kanai, R. (1992) PlantCell Physiol. 33: 805]. In this study, medium and stromal pH was monitored in the suspensionof C₄ mesophyll chloroplasts. Medium alkalization lasting for5 to 10 seconds after pyruvate addition was detected by a pHelectrode and observed only in the light and only in mesophyllchloroplasts from H⁺-type species, Zea mays L. and Coix lacryma-jobiL., but not in those from Na⁺-type species Panicum miliaceumL., Setaria italica (L.) Beauv. and Panicum maximum Jacq. Theinitial rate of H⁺ consumption showed good correlation with[¹⁴C]pyruvate uptake measured by silicone oil filtering centrifugation,both being inhibited by N-ethylmaleimide and 7-chloro-4-nitrobenzo-2-oxa-l,3-diazole to the same degree. The ratio of the rate of H⁺ uptaketo that of pyruvate uptake was always about 1. Pyruvate-inducedacidification of the stroma was observed in maize mesophyllchloroplasts. These results show one to one cotransport of H⁺and pyruvate anion into mesophyll chloroplasts of H⁺-type C₄species in the light. (Received January 5, 1994; Accepted May 6, 1994)     

Changes of action potentials and force at lowered [Na+]o in mouse skeletal muscle: implications for fatigue

We examined 1) whether the effects of lowered trans-sarcolemmal Na⁺ gradient on force differed between nonfatigued fast- and slow-twitch muscles of mice and 2) whether effects on action potentials could explain the decrease of force. The Na⁺ gradient was reduced by lowering the extracellular [Na⁺] ([Na⁺]_o). The peak force-[Na⁺]_o relationships for the twitch and tetanus were the same in nonfatigued extensor digitorum longus and soleus muscles: force was maintained over a large range of [Na⁺]_o and then decreased abruptly over a much smaller range. However, fatigue was significantly exacerbated at a lowered [Na⁺]_o that had little effect in nonfatigued soleus muscle. This finding suggests that substantial differences exist in the Na⁺ effect on force between nonfatigued and fatigued muscle. The reduced contractility in nonfatigued muscles at lowered [Na⁺]_o was largely due to 1) an increased number of inexcitable fibers and threshold for action potentials, 2) a reduction of action potential amplitude, and 3) a reduced capacity to generate action potentials throughout trains. sodium gradient; muscle contraction; action potential train; extensor digitorum longus; soleus     

Dependence of Na+-K+ pump current-voltage relationship on intracellular Na+, K+, and Cs+ in rabbit cardiac myocytes

To examine effects of cytosolicNa⁺, K⁺, and Cs⁺ on the voltagedependence of the Na⁺-K⁺ pump, we measuredNa⁺-K⁺ pump current (I_p)of ventricular myocytes voltage-clamped at potentials(V_m) from 100 to +60 mV. Superfusates weredesigned to eliminate voltage dependence at extracellular pump sites.The cytosolic compartment of myocytes was perfused with patch pipette solutions with a Na⁺ concentration ([Na]_pip)of 80 mM and a K⁺ concentration from 0 to 80 mM or withsolutions containing Na⁺ in concentrations from 0.1 to 100 mM and K⁺ in a concentration of either 0 or 80 mM. When[Na]_pip was 80 mM, K⁺ in pipette solutionshad a voltage-dependent inhibitory effect on I_pand induced a negative slope of theI_p-V_m relationship. Cs⁺ in pipette solutions had an effect onI_p qualitatively similar to that ofK⁺. Increases in I_p with increasesin [Na]_pip were voltage dependent. The dielectriccoefficient derived from[Na]_pip-I_p relationships at thedifferent test potentials was 0.15 when pipette solutions included 80 mM K⁺ and 0.06 when pipette solutions were K⁺ free.

     

Characterization and Translation of Poly(A)+RNA from Wounded and Crown Gall Tissues of Potato Tubers

Poly(A)⁺ and poly(A)^–RNA from wounded potato tuber tissuesand crown gall tumors were separated from total RNA by oligodeoxythymidylicacid-cellulose affinity chromatography. The poly(A)⁺RNA wascharacterized by sucrose density gradient centrifugation, hybridizationwith ³(H)polyuridylic acid [Poly(U)] and in vitro translationin a rabbit reticulocyte lysate system. The tumor poly(A)⁺RNAwas a heterodisperse mixture from 3.5S to 35S. Upon poly(U)hybridization of the gradient fractions two major hybridizationpeaks at 7S and 21S and two peaks at 11S and 16S appeared. Inan in vitro translation system the poly(A)⁺RNA programmed thesynthesis of 23 different polypeptides of 9,000 to 79,800 daltonsmolecular weight as determined by SDS-polyacrylamide gel electrophoresis.The 21S poly(A)+RNA was about 5 times more active in in vitroprotein synthesis than the 7S poly(A)⁺RNA. The poly(A)⁺RNA from wounded tissues was also heterodisperse(from 4.5S to 31S) with a modal peak at 18S. This RNA codedfor at least 28 polypeptides, which were different from thoseof crown gall tumor tissues. On a per unit poly(A)⁺RNA basis the tumor RNA was slightly moreactive in translation than that from wounded tissues. The translationof tumor poly(A)⁺RNA was completely blocked by 0.5 mM 7-methylguanosine5'-phosphate, but not by 7-methylguanosine, suggesting the presenceof a 5'-cap structure. (Received May 15, 1982; Accepted June 30, 1982)     

Effects of Fusicoccin and Abscisic Acid on Sugar and lon Transport from Plant Glands

Fusicoccin (FC) inhibited net excretion of Cl^– by theglands of the pitchers of the carnivorous plant Nepenthes hookeriana;of Na⁺ and Cl^– by the salt glands of the halophytes Limoniumvulgare and L. pectinatum and of K⁺ in the nectar of Acer platanoidesflowers. It had no effect on K⁺ elimination with nectar of Impatienswalleriana (extrafloral nectaries) and Abutilon striatum. Abscisicacid (ABA) stimulated net excretion of K⁺ and Cl^– in Nepenthesand of Na⁺ and Cl^– in Limonium but had no effects on K⁺in nectar. Thus, FC and ABA had opposing effects on ion excretionby the salt eliminating glands of Limonium and Nepenthes. Bothcompounds, however, had similar effects on sugar secretion ofnectary glands which was either inhibited or unaffected by FCand ABA. It is suggested that the effects of FC and ABA on ion excretionby gland cells could be reconciled with literature showing FC-stimulationand possible ABA-inhibition of proton pumps at the plasmalemmaof plant cells. Nepenthes hookeriana, Limonium vulgare, Limonium pectinatum, Acer platanoides, salt-glands, nectaries, excretion, fusicoccin, abscisic acid, proton pump