Effects of quaternary ammonium salts on membrane potential and electric conductance in internodal cells of Nitettopsis obtusa

Effects of amphiphilic derivatives of glycine esters of the general formula (CH₃)₃N⁺CH₂COOC_nH_2n+1Cl- (n = 10, 12, 14, 16) on membrane potential and conductance in internodal cells of the alga Nitellopsis obtusa were studied. The compounds decreased the potential difference between vacuole and external medium and increased the electric conductance. The effects depended on the length of the alkyl chain (n) and the concentration of these quaternary ammonium salts. Light-induced hyperpolarization was suppressed by the salts. We suggest that the ammonium salts inhibit the electrogenic proton pump in the plasmalemma and enhance the passive efflux of Cl- from the algal cell.     

The tonoplast H+-pyrophosphatase of radish seedlings: biochemical characteristics

The activity of the H⁺-pyrophosphatase (H⁺-PPase) was characterized in microsomes from 24-h-old radish ( Raphanus sativus L., ev. Tondo Rosso Quarantino) seedlings, which are virtually devoid of the tonoplast H⁺-ATPase. The H⁺-PPase was localized to membranes which roughly comigrated with the plasma membrane in a sucrose density gradient, but clearly separated from plasma membrane when microsomes were partitioned in an aqueous dextran-polyethylene glycol two-phase system. The H⁺-PPase activity was strictly dependent on Mg²⁺ and on the presence of a monovalent cation (K⁺=Rb⁺=NH₃⁺Cs⁺≫Na⁺Li⁺) and was insensitive to anions such as Cl−, Br−, NO₃− and SO₄^2-. It was inhibited by F−, imidodiphosphate and Ca²⁺. It had a pH optimum between pH 7.5 and 8.5 and was saturated by low concentrations of pyrophosphate (half saturation at 30 μ M pyrophosphate). All of these characteristics are identical to those reported for the tonoplast H⁺-PPase from various plant materials. The functional molecular weight of the H⁺-PPase, measured with the radiation-inactivation technique was 96 kDa.     

Acute toxicology to an estuarine teleost of mixtures of cadmium, copper and zinc salts

Effects of mixtures of chloride salts of cadmium, copper and zinc on survival, whole body residues, and histopathology of mummichog, Fundulus heteroclitus (L.), were investigated in synthetic sea water at 20‰ salinity and 20°C. Mixtures of Cu²⁺ and Zn²⁺ as indicated by 96 h bioassay studies produced more deaths than expected on the basis of toxicities of individual components. Concentrations of Cd²⁺ not ordinarily lethal exerted a negative effect on survival of fish intoxicated by salts of copper, zinc, or both.
Atomic absorption determinations of Cd, Cu, and Zn residues in mummichog which survived 96 h exposures to each of these toxicants provided useful indices of total body burdens for these metals. Residues from survivors held in mixtures, especially Cd²⁺ and Zn²⁺ mixtures, did not conform to patterns observed for single elements. Whole body aggregates of Cd, Cu, and Zn from dead mummichogs were of limited worth owing to possible accumulation of these metals from the medium after death.
Renal and lateral line canal lesions were noted in all fish subjected to copper concentrations of 1 mg/1 and higher. Renal lesions observed in fish immersed in mixtures of Cu²⁺ and Cd²⁺ assumed a damage pattern characteristic of Cd²⁺; with mixtures of Cu²⁺ and Zn²⁺, lesion were typical of Cu²⁺-induced damage. Lesions induced in lateral line epithelium by Cu²⁺ were not affected by either Cd²⁺ or Zn²⁺. Epithelia lining the oral cavity were necrotized by the caustic action of high levels of Zn²⁺ (60 mg/1) and of Cu²⁺ (8 mg/1).     

Influence of exogenously supplied potassium and sodium salts on the abscisic acid-induced proline accumulation in barley leaf segments

A stimulation of the abscisic acid (ABA)-induced increase in proline was observed in leaf segments of barley ( Hordeum vulgare L. cv. Georgie) if K⁺ or Na⁺ were supplied in the external medium as salts of monovalent anions such as NO₃, Br, Cr and I, but not when sulphate or phosphate were used. To a lesser extent, the effect was evident also with RbCl, but it did not occur when chlorides of Li⁺. Cs⁺, NH₄⁺, Mg:⁺ and Ca²⁺ were used. Both KC1 and NaCl in the concentration range 2–100 m M influence the ABA-dependent proline accumulation to the same extent; the increase induced was about 100% at 10 m M , and reached a maximum between 60 and 100 m M. The effect is not due to the osmotic activity of the salts and does not seem to depend on changes in K⁺ and Na⁺ levels within the leaf tissue, but it is somehow linked to their external concentration. The existence of a specific interaction between ABA and K⁺ or Na⁺, possibly at the cell membrane level, is proposed.     

Properties of NADP+-malic enzyme from pod walls of chickpea (Cicer arietinum)

NADP⁺-malic enzyme ( l -malate: NADP⁺ oxidoreductase, decarboxylating EC 1.1.1.40) from pod walls of chickpea was purified 51-fold by ammonium sulphate fractionation, DEAE- cellulose chromatography and gel filtration through Sepharose 4B. The purified enzyme required a divalent cation, either Mn²⁺ or Mg²⁺, for its activity. K_m values at pH 7.8 for malate, NADP⁺ and Mn²⁺ were 4.0, 0.031 and 0.71 m M , respectively. Mn²⁺-dependent activity was inhibited by heavy metal ions such as Cd²⁺, Zn²⁺, Hg²⁺, and to a lesser extent by Pb²⁺ and Al³⁺. Among the organic acids examined, sodium salts of oxalate and oxaloacetate were inhibitory. Kinetics of the reaction mechanism showed sequential binding of malate and NADP⁺ to the enzyme. Products of reaction, viz. pyruvate, bicarbonate and NADPH, inhibited the enzyme activity. At limiting concentrations of NADP⁺, pyruvate and bicarbonate induced a positive cooperative effect by malate. It is proposed that the activity of NADP⁺-malic enzyme is controlled by intracellular concentrations of substrates and products.     

Retardation and inhibition of the cation-induced superoxide generation in BY-2 tobacco cell suspension culture by Zn2+ and Mn2+

Salts at high concentrations may cause oxidative damage to plant cells since many studies indicated the involvement of reactive oxygen species in salt-stress response. Recently, we have demonstrated that treatment of tobacco ( Nicotiana tabacum ) cell suspension culture with various salts result in an immediate burst of superoxide production via activation of NADPH oxidase by ions of alkali metals (Li⁺, Na⁺, K⁺), alkali earth metals (Mg²⁺, Ca²⁺) or lanthanides (La³⁺, Gd³⁺). In this study, we tested the effect of extracellular supplementation of Zn²⁺ and Mn²⁺ on the cation-induced oxidative burst in tobacco cell suspension culture, measured with a superoxide-specific Cypridina luciferin-derived chemiluminescent reagent. Extracellular supplementation of Zn²⁺ and Mn²⁺ inhibited the generation of superoxide in response to addition of salts. Although both Zn²⁺ and Mn²⁺ inhibited the salt-induced generation of superoxide, the modes of inhibition by those ions seemed to be different since Mn²⁺ simply inhibited total production of superoxide while Zn²⁺ inhibited the early phase of superoxide production and induced the slow release of superoxide. Roles of Mn²⁺ and Zn²⁺ in protection of plant cells from salt stress, as an effective superoxide scavenger and an effective inhibitor of plasma membrane-bound NADPH oxidase, respectively, are discussed.     

Effects of chloride and sodium on gas exchange parameters and water relations of Citrus plants

Gas exchange parameters, water relations and Na⁺/Cl^- content were measured on leaves of one-year-old sweet orange ( Citrus sinensis [L.] Osbeck cv. Hamlin) seedlings grown at increasing levels of salinity. Different salts (NaCl, KCl and NaNO₃) were used to separate the effects of Cl⁻ and Na⁺ on the investigated parameters. The chloride salts reduced plant dry weight and increased defoliation. Accumulation of Cl⁻ in the leaf tissue caused a sharp reduction in photosynthesis and stomatal conductance. By contrast, these parameters were not affected by leaf Na⁺ concentrations of up to 478 m M in the tissue water. Leaf water potentials reached values near −1.8 MPa at high NaCl and KCl supplies. This reduction was offset by a decrease in the osmotic potential so that turgor was maintained at or above control values. The changes in osmotic potential were closely correlated with changes in leaf proline concentrations. Addition of Ca²⁺ (as calcium acetate) increased growth and halved defoliation of salt stressed plants. Furthermore, calcium acetate decreased the concentration of Cl⁻ and Na⁺ in the leaves, and increased photosynthesis and stomatal conductance. Calcium acetate also counteracted the reductions in leaf water and osmotic potentials induced by salinity. In addition, calcium acetate inhibited the accumulation of proline in the leaves which affected the reduction in osmotic potential. These results indicate that adverse effects of salinity in Citrus leaves are caused by accumulation of chloride.     

Effect of high external NaCl concentrations on ion transport within the shoot of Lupinus albus. I. Ions in xylem sap

Abstract. Xylem sap was collected from individual leaves of intact transpiring lupin plants exposed to increasing concentrations of NaCl by applying pneumatic pressure to the roots. Concentrations of Na⁺ and Cl⁻ in the xylem sap increased linearly with increases in the external NaCl concentration, averaging about 10% of the external concentration. Concentrations of K⁺ and NO₃⁻, the other major inorganic ions in the sap, were constant at about 2.5 and 1.5 mol m⁻³, respectively. There was no preferential direction of Na ⁺ or Cl⁻ to either young or old leaves: leaves of all ages received xylem sap having similar concentrations of Na⁺ and Cl⁻, and transpiration rates (per unit leaf area) were also similar for all leaves. Plants exposed to 120–160 mol m⁻³ NaCl rapidly developed injury of oldest leaves; when this occurred, the Na⁺ concentration in the leaflet midrib sap had increased to about 40 mol m⁻³ and the total solute concentration to 130 osmol m⁻³. This suggests that uptake of salts from the transpiration stream had fallen behind the rate of delivery to the leaf and that salts were building up in the apoplast.     

Different effects of supplied ammonium on glutamine synthetase activity in mustard (Sinapis alba) and pine (Pinus sylvestris) seedlings

The activity of glutamine synthetase (GS) in mustard ( Sinapis alba L.) and Scots pine ( Pinus sylvestris L.) seedlings was used as an index to evaluate the capacity to cope with excessive ammonium supply. In these 2 species GS activity was differently affected by the application of nitrogen compounds (NH₄⁺ or NO₃⁻). Mustard seedlings older than 5 days showed a considerable increase in GS activity after NH₄⁺ or NO₃⁻ application. This response was independent of the energy flux, but GS activity in general was positively affected by light. Endogenous NH₄⁺ did not accumulate greatly after nitrogen supply. In contrast, seedlings of Scots pine accumulated NH₄⁺ in cotyledons and roots and showed no stimulation of GS activity after the application of ammonium. In addition, root growth was drastically reduced. Thus, the pine seedlings seem to have insufficient capacity to assimilate exogenously supplied ammonium. NO₃⁻, however, did not lead to any harmful effects.     

Physiological effects of Na2SO4 and NaCl on callus cultures of Brassica campestris (Chinese cabbage)

Hypocotyl-derived callus cultures of Brassica campestris L. ssp. pekinensis cv. Kim-jung (Chinese cabbage) were grown on Murashige and Skoog medium containing no additional salt, NaCl or Na₂SO₄. Na₂SO₄ was more than twice as inhibitory in comparison to the same concentration of NaCl when growth and fresh:dry weight ratios of established callus were measured. Levels of protein, starch, sucrose and α-amino nitrogen were not significantly altered in salt-grown callus. Concentrations of reducing sugars and chlorophyll were 2–3 times greater in callus grown on either salt. Proline concentration increased 15–20 fold on the highest levels of salt. Final concentrations (reached in 20–24 days) were closely correlated to the initial Na⁺ concentration of the medium, regardless of salt type. The osmotic potential in callus transferred to NaCl or Na₂SO₄ reached a maximum negative value after 16 days. For both salts, subsequent increases were correlated to increases in fresh:dry weight and growth. On both salts, turgor remained relatively constant (0. 6–0.75 MPa). Changes in Na⁺, K⁺, Mg²⁺ and Ca²⁺ content were correlated to initial Na⁺ concentration in the medium, not salt type. Accumulation of Na⁺ was accompanied by loss of K⁺ and Mg²⁺. Six to seven times less sulfate was measured in callus grown on Na₂SO₄ than chloride in callus grown on similar concentrations of NaCl.     

7Li Nuclear Magnetic Resonance Study for the Determination of Li+ Properties in Neuroblastoma SH-SY5Y Cells

Abstract: Lithium has been used clinically in the treatment of manic depression. However, its pharmacologic mode of action remains unclear. Characteristics of Li⁺ interactions in red blood cells (RBCs) have been identified. We investigated Li⁺ interactions on human neuroblastoma SH-SY5Y cells by developing a novel ⁷Li NMR method that provided a clear estimation of the intra- and extracellular amounts of Li⁺ in the presence of the shift reagent thulium-1,4,7,10-tetrazacyclododecane- N,N ', N ", N ‴-tetramethylene phosphonate (HTmDOTP⁴⁻). The first-order rate constants of Li⁺ influx and efflux for perfused, agarose-embedded SH-SY5Y cells in the presence of 3 m M HTmDOTP⁴⁻ were 0.055 ± 0.006 (n = 4) and −0.025 ± 0.006 min⁻¹ (n = 3), respectively. Significant increases in the rate constants of Li⁺ influx and efflux in the presence of 0.05 m M veratridine indicated the presence of Na⁺ channel-mediated Li⁺ transport in SH-SY5Y cells. ⁷Li NMR relaxation measurements showed that Li⁺ is immobilized more in human neuroblastoma SH-SY5Y cells than in human RBCs.     

Characterization of ammonium and methylamine transport systems in phototrophic sulfur bacteria

Abstract Transport of ammonium and methylamine into the cells of green sulfur bacterium Chlorobium limicola and purple sulfur bacterium Thiocapsa roseopersicina is carried out by a common transport system. This system has (for C. limicola and T. roseopersicina , respectively) pH optimum 7.0 and 7.5; V _max 0.6 and 4.2 nmol min⁻¹ (mg protein)⁻¹; K_m 5.9 × 10⁻⁵ M and 1.3 × 10⁻⁵ M, and is capable of forming 120- and 600-fold methylamine gradients. The methylamine transport can be energized by the artificially imposed transmembrane K⁺ diffusive potential and is inhibited by tetraphenylphosphonium or valinomycin and K⁺. The data presented indicate that methylamine transport in both studied species is exclusively driven by the membrane potential gradient (ΔΨ).     

Aquaporin functionality in relation to H+-ATPase activity in root cells of Capsicum annuum grown under salinity

As water and nutrient uptake should be related in the response of plants to salinity, the aim of this paper is to establish whether or not aquaporin functionality is related to H⁺-ATPase activity in root cells of pepper ( Capsicum annuum L.) plants. Thus, H⁺-ATPase activity was measured in plasma membrane vesicles isolated from roots and aquaporin functionality was measured using a cell pressure probe in intact roots. Salinity was applied as 60 m M NaCl or 60 m M KCl, to determine which ion (Na⁺, K⁺ or Cl⁻) is producing the effects. We also investigated whether the effects of both salts were ameliorated by Ca²⁺. Similar results were obtained for cell hydraulic conductivity, Lp_c, and H⁺-ATPase activity, large reductions in the presence at NaCl or KCl and an ameliorative effect of Ca²⁺. However, fusicoccin (an activator of H⁺-ATPase) did not alter osmotic water permeability of protoplasts isolated from roots. Addition of Hg²⁺ inhibited both ATPase and aquaporins, but ATPase also contains Hg-binding sites. Therefore, the results indicate that H⁺-ATPase and aquaporin activities may not be related in pepper plants.     

Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor

Abstract Until now, oxidation of ammonium has only been known to proceed under aerobic conditions. Recently, we observed that NH₄⁺ was disappearing from a denitrifying fluidized bed reactor treating effluent from a methanogenic reactor. Both nitrate and ammonium consumption increased with concomitant gas production. A maximum ammonium removal rate of 0.4 kg N · m⁻³ · d⁻¹ (1.2 mM/h) was observed. The evidence for this anaerobic ammonium oxidation was based on nitrogen and redox balances in continuous-flow experiments. It was shown that for the oxidation of 5 mol ammonium, 3 mol nitrate were required, resulting in the formation of 4 mol dinitrogen gas. Subsequent batch experiments confirmed that the NH₄⁺ conversion was nitrate dependent. It was concluded that anaerobic ammonium oxidation is a new process in which ammonium is oxidized with nitrate serving as the electron acceptor under anaerobic conditions, producing dinitrogen gas. This biological process has been given the name ‘Anammox” (anaerobic ammonium oxidation), and has been patented.     

Ca2+ acts synergistically with brassinosteroid and indole-3-acetic acid in stimulating ethylene production in etiolated mung bean hypocotyl segments

Brassinosteroid (BR) and indole-3-acetic acid (IAA) were used in combination with Ca²⁺ in order to determine if there was a synergistic effect in the stimulation of ethylene production in etiolated mung bean ( Vigna radiata L. Rwilez ev. Berken) hypocotyl segments. Ca²⁺ was found to act synergistically with BR. IAA or a combination of the two in promoting a stimulation in ethylene production. EDTA, which chelates Ca²⁺, greatly reduced the effectiveness of calcium salts in promoting ethylene production in the presene of either BR, IAA or a combination of the two. Neither K⁺, Mg²⁺ nor Mn²⁴ (chloride salts) acted synergistically with BR and IAA.     

Photosynthate costs associated with the utilization of different nitrogen–forms: influence on the carbon balance of plants and shoot–root biomass partitioning

The photosynthate costs of processes (amino acid and protein synthesis and turnover, and pH regulation) associated with the utilization of nitrate (NO₃⁻), ammonium (NH₄⁺) or glutamine (Gln) for plant growth were estimated. Based on these estimates, the effects of these forms of nitrogen (N) on the carbon balance of plants and on shoot–root biomass allocation were evaluated. The results indicated that NO₃⁻ as an N source for plant growth is not substantially more expensive to utilize than either NH₄⁺ or Gln, particularly in the long term when costs due to protein turnover dominate the total costs of N utilization. It is also suggested that the photosynthate use in processes associated with N assimilation has little impact on the carbon balance of plants, and hence on shoot–root biomass allocation.     

Calcium and plant action potentials

Abstract. Under normal conditions the action potential in Characeae is dependent on the presence of both Cl⁻ and Ca²⁺. Cl⁻ seems to play a straightforward part as a transient depolarizing flow. The role of Ca²⁺, however, is emerging as an increasingly complex one: there are Ca²⁺ concentration changes in the cytoplasm, as well as transient Ca²⁺ currents across the plasmalemma and possibly the tonoplast. In most Characeae Ca²⁺ is necessary for the Cl⁻ channel to function, and it is also involved in the cessation of the cytoplasmic streaming observed at the time of excitation.
The function of Ca²⁺ at the time of the action potential is being revealed by experimental techniques of increasing sophistication. The development of these methods and possible associated artefacts are considered.     

Response of Suaeda aegyptiaca to KCl, NaCl and Na2SO4 treatments

The response of Suaeda aegyptiaca (Hasselq.) Zoh. to various salinity treatments was tested in sand culture. Growth was promoted by NaCl and by Na₂SO₄ at all tested concentrations, but not by KCl. The effect of NaCl on growth was stronger than that of Na₂SO₄ and it increased gradually up to a 125 eq. m⁻³ optimum. Ion uptake was also affected by the different salts. Cl⁻ was taken up in similar quantities from KCl and from NaCl solutions and the content of the respective cations was also similar to one another. The presence of Na⁺ in the medium lowered the content of K⁺ in the plants and at the same time increased growth by as much as 900%. Transpiration was reduced and water use efficiency increased by Na⁺-salts. Highest water use efficiency was exhibited by plants which were treated with 125 eq. m⁻³ NaCl. It is concluded that Na⁺ at the macronutrient level has a specific promotive effect on the physiological processes of S. aegyptiaca. This effect is not due to replacement of K⁺ by Na⁺; neither can it be achieved by increasing the K⁺ concentration. Cl⁻ has an additional positive effect on growth of S. aegyptiaca. This effect is only expressed in the presence of Na⁺.     

l-Methionine-dl-sulfoximine resistant Het+ Nif+ and Het− Nif− strains of Nostoc muscorum assimilating methylamine as ammonium nitrogen source

Abstract The Het⁺ Nif⁺ and Het⁻ Nif⁻ strains of Nostoc muscorum sensitive to growth inhibition by methylamine (MA), overcame the MA inhibition as a result of their mutation to l -methionine- dl -sulfoximide (MSX)-resistant phenotype, which enabled them to assimilate MA like an ammonium nitrogen source. The MSX-resistant Het⁺ Nif⁺ strain synthesized the inhibitor-resistant transferase-defective glutamine synthetase (GS), which unlike parental GS underwent MA-dependent in vivo activation. These results suggest the involvement of GS enzyme in control of MA assimilation in cyanobacteria.     

Serotoninergic modulation of GABAergic synaptic transmission in developing rat CA3 pyramidal neurons

Serotoninergic modulation of GABAergic mIPSCs was investigated in immature (postnatal 12–16-days old) rat CA3 pyramidal neurons using a conventional whole-cell patch clamp technique. Serotonin or 5-hydroxytryptamine (5-HT) (10 μmol/L) transiently and explosively increased mIPSC frequency with a small increase in the current amplitude. However, 5-HT did not affect the GABA-induced postsynaptic currents, indicating that 5-HT acts presynaptically to facilitate the probability of spontaneous GABA release. The 5-HT action on GABAergic mIPSC frequency was completely blocked by 100 nmol/L MDL72222, a selective 5-HT₃ receptor antagonist, and mimicked by mCPBG, a selective 5-HT₃ receptor agonist. The 5-HT action on GABAergic mIPSC frequency was completely occluded either in the presence of 200 μmol/L Cd²⁺ or in the Na⁺-free external solution, suggesting that the 5-HT₃ receptor-mediated facilitation of mIPSC frequency requires a Ca²⁺influx passing through voltage-dependent Ca²⁺channels from the extracellular space, and that presynaptic 5-HT₃ receptors are less permeable to Ca²⁺. The 5-HT action on mIPSC frequency in the absence or presence of extracellular Na⁺ gradually increased with postnatal development. Such a developmental change in the 5-HT₃ receptor-mediated facilitation of GABAergic transmission would play important roles in the regulation of excitability as well as development in CA3 pyramidal neurons.