Bicarbonate Uptake by Nitrifiers: Effects of Growth Rate, pH, Substrate Concentration, and Metabolic Inhibitors

The ratios of bicarbonate uptake to substrate oxidation were measured for three genera of nitrifying bacteria. The ratios for the two ammonium oxidizers tested were essentially the same; 0.0863 ± 0.0055 and 0.0868 ± 0.0091 μmol of bicarbonate were taken up per umol ammonium oxidized for Nitrosomonas europaea and a Nitrosospira strain, respectively. For Nitrobacter sp., a ratio of 0.0236 ± 0.0013 μmol of bicarbonate taken up per umol of nitrite oxidized was obtained. Cells were grown in substrate-limited continuous culture and in batch culture, with generation times ranging between 16 and 189 h for the ammonium oxidizers and 18 and 69 h for Nitrobacter sp. All ratios appeared to be independent of growth rates and pH. However, short-term changes in substrate concentration and certain metabolic inhibitors significantly changed the efficiency of bicarbonate uptake. The significance of these results to the application of the nitrapyrin-sensitive bicarbonate uptake method for measuring nitrification rates in natural samples is discussed.     

The Effect of ATP on Uptake of Monovalent Cations and Anions by Red Beet Slices

Externally added ATP inhibits sodium and potassium uptake byred beet tissue; this inhibition seems to be competitive. Theeffects of DNP and ATP additions on cation uptake were foundto be additive. ATP did not inhibit chloride and bromide uptake.The results and their implications are discussed.     

Inhibition of the Uptake and Long-Distance Transport of Calcium by Aluminium and Other Polyvalent Cations

Aluminium, scandium, and iron inhibit the uptake of calciumby week-old barley plants from acid culture solutions (pH 4.0–4.2).The inhibition by scandium can be detected when its ratio tocalcium is 1:1000. The onset of the inhibition may be quit rapidand will persist for at least. 24 h in the absence of the polyvalentcation. The inhibition caused by 25 and 50 µM aiuminiumsulphate may be overcome if the calicum chloride concentrationin the medium is raised to 15mM, but in this situation aluminiumstill inhibits root growth by more than 50 per cent. Elutionexperiments show that polyvalent cations reduce the amount ofcalcium held in the water free space (WFS) and the Donnan freespace (DFS) but increase both the exchangeable and absorbedchloide content of the root. Aluminium-treated roots transportedmuch less calcium to the shoot system than untreated plants.Autoradiographs showed that this difference was reflected ina greatly reduced labelled-calcium concentration over the tissuesof the stele. By contrast the non-exchangeable fraction of labelledcalicum in the cortex was similar in both treatments. Autoradiographsof ⁴⁶Sc showed that it was restricted to the epidermis and outerrank of cortical cells from whence it controls calicum movementthroughout the root. A theory to account for this control isoutlined.     

Multiphasic Uptake in Plants II. Mineral Cations, Chloride, and Boric Acid

Uptake of alkali cations, metal ions, chloride, and boric acid is shown by reanalysis of available data to be mediated by single, multiphasic mechanisms which may be fundamentally similar in a variety of plants and tissues.     

The Relationship Between Bicarbonate Ion, pH, and 59Fe Uptake by Plants

Iron absorption by barley, pea, and runner bean is stimulatedby bicarbonate but inhibited by increasing pH. Bicarbonate stimulatestranslocation of Fe in barley but inhibits it in pea and bean.Increasing pH stimulates translocation in barley and pea withno effect in bean. The presence of other ions in the externalsolution appears to inhibit absorption but enhances translocationof Fe in bean and pea. It is concluded that whether or not bicarbonatewill induce chlorosis in a plant depends on species and variety.     

Polyamine Uptake, Kinetics, and Competition among Polyamines and between Polyamines and Inorganic Cations

Polyamine uptake, the kinetics of this uptake, and the competition among polyamines and between polyamines and inorganic cations were studied in petals of Saintpaulia ionantha Wendl. Uptake experiments using ¹⁴C-labeled polyamines were carried out on single petals, at room temperaure (20°C) and in the light. The results show that putrescine, spermidine, and spermine uptake was dependent on the external pH and occurred up to high external polyamine concentrations with K_m values of 8.6, 1.2, and 2.1 millimolar, respectively, with spermidine being the most absorbed at low concentration (17 micromolar). Putrescine and spermidine did not seem to compete for the same site of absorption. Furthermore, putrescine and spermidine uptake was not inhibited by Ca²⁺, Mg²⁺, and K⁺ at the same concentrations (17 micromolar), whereas 1.7 millimolar Ca²⁺ inhibited and K⁺ enhanced spermidine uptake. The intracellular localization of the absorbed putrescine was determined using two different methods. Very little label was found in the apoplast, while most of it was localized in the 98,500g supernatant. According to our data the vacuole, which represents a substantial part of Saintpaulia parenchyma cells, could be a site of putrescine accumulation. 2,4-Dinitrophenol and diethylstilbestrol did not inhibit uptake; however, at 0°C there was a 35% inhibition of spermidine uptake, compared with the controls kept at 20°C as well as a 68% inhibition with 20 millimolar NaSCN.     

Vanadium Requirements and Uptake Kinetics in the Dinitrogen-Fixing Bacterium Azotobacter vinelandii

Vanadium is a cofactor in the alternative V-nitrogenase that is expressed by some N₂-fixing bacteria when Mo is not available. We investigated the V requirements, the kinetics of V uptake, and the production of catechol compounds across a range of concentrations of vanadium in diazotrophic cultures of the soil bacterium Azotobacter vinelandii. In strain CA11.70, a mutant that expresses only the V-nitrogenase, V concentrations in the medium between 10⁻⁸ and 10⁻⁶ M sustain maximum growth rates; they are limiting below this range and toxic above. A. vinelandii excretes in its growth medium micromolar concentrations of the catechol siderophores azotochelin and protochelin, which bind the vanadate oxoanion. The production of catechols increases when V concentrations become toxic. Short-term uptake experiments with the radioactive isotope ⁴⁹V show that bacteria take up the V-catechol complexes through a regulated transport system(s), which shuts down at high V concentrations. The modulation of the excretion of catechols and of the uptake of the V-catechol complexes allows A. vinelandii to precisely manage its V homeostasis over a range of V concentrations, from limiting to toxic.     

pH Dependence and Kinetics of Glycolate Uptake by Intact Pea Chloroplasts

Experiments in which [1-¹⁴C]glycolate uptake is carried out in conjunction with measurements of stromal pH indicate that only glycolic acid and not the glycolate anion is crossing the pea (Pisum sativum var. Progress No. 9, Agway) chloroplast envelope. This mechanism of glycolate transport appears to be too slow to account for observed photorespiratory carbon fluxes in C₃ plants.     

Selectivity and Kinetics of Ion Uptake by Barley Plants Following Nutrient Deficiency

Barley plants grown without an external supply of phosphorus,sulphur, chlorine or nitrogen subsequently absorbed these nutrients,as phosphate, sulphate, chloride and nitrate, more rapidly thandid nutrient, sufficient control plants under similar conditions.With phosphorus, sulphur and chlorine, increased absorptionwas restricted to the nutrient which had been deficient, orto close chemical analogues of it, the uptake of other anionsbeing unaffected or decreased. The selectivity of enhanced nitrateuptake by nitrogen-deficient plants was not examined. The differencesin the rates of phosphate, sulphate and chloride absorptionby plants of differing nutrient status were due principallyto changes in the maximum transport capacity for these anionsper unit weight of root, although in plants grown without externalchloride there was some evidence that the roots also developedan increased affinity for that ion. Hordeum vulgare, barley, mineral nutrient deficiency, ion absorption, kinetics of ion uptake, phosphate, sulphate, chloride, arsenate, bromide, selenate     

Specific Effects of Kinetin on the Uptake of Monovalent Cations by Sunflower Cotyledons

Kinetin promoted the uptake of K⁺ and Rb⁺ into detached sunflower cotyledons. This action was concomitant with an acceleration of growth. A slighter promotion of Li⁺ uptake was also noted, but there was no consistent influence on that of Na⁺. A small inhibitory effect on NH₄⁺₄ uptake was apparent when the latter was computed per average weight of sample during the course of incubation. Light also promoted the growth of the cotyledons, but depressed their capacity to absorb potassium. The action of kinetin on cotyledons removed from 5–7 day old seedlings was weaker than on those removed from 2–4 day old seedlings with regard to growth but stronger with regards to K⁺ uptake. When K⁺ uptake by cotyledons taken from 7-day old seedlings was followed with time the kinetin effect was already detectable within a few hours, but it became more pronounced after 10 hours' incubation. Kinetin did not accelerate growth or K⁺ uptake in hypo-cotyl segments. IAA, which was previously shown to promote these processes in hypocotyl segments, inhibited them in cotyledons. A working hypothesis is suggested according to which endogenous auxins and cytokinins regulate the absorption of K⁺ in shoot cells of the intact plant in a manner similar to that in which they act in excised tissues and in this way affect the distribution and redistribution of K⁺ in the shoot; and that they are among the factors which determine the selectivity of ion uptake in the intact plant.     

The Uptake and Metabolism of Sulphate in Scenedesmus as Influenced by Citrate, Carbon Dioxide, and Metabolic Inhibitors

The incorporation of sulphur from external sulphate into different fractions was studied in cells with a P content of 0.6 to 1 mg/g fresh weight as against 3 to 5 mg/g fresh weight in normal cells. — There is a flat and broad optimum for the action of pH in the region between 5.7 and 7. — In most cases, citrate inhibits the uptake of sulphur. — Five per cent CO₂ in the air enhances the incorporation of S. It is suggested that the effects of CO₂ may well be exerted by way of the carboxylation and decarboxylation mechanisms in the cells. — Selenate inhibits the formation of DNA-S and protein S more than that of lipid S, but the main effect in both cases seems to be in an early step of the assimilation of sulphate. In the absence of external phosphate, the inhibition is counteracted by CO₂, especially in darkness. Phosphate enhances the action of selenate on the organic S fractions, and in its presence CO₂ and darkness make the inhibition more pronounced. — Without P in the medium, the effects of selenate on uptake into the inorganic sulphate fraction are smaller than when the organic fractions are concerned. In the presence of CO₂ even stimulations due to selenate have been observed. External phosphate brings the inhibition of uptake into cellular SO₄^2- to the same level as found in the case of organic S. More than one pathway for the uptake as SO₄^2-seem possible. — Anaerobiosis and menadione affect the organic S fractions more than the sulphate; 2,4-dinitrophenol has a more uniform action all over the field.     

The Effects of Alkali Metal Cations and Common Anions on the Frog Skin Potential

The effects on the potential difference across isolated frog skin (R. catesbeiana, R. pipiens) of changing the ionic composition of the bathing solutions have been examined. Estimates of mean values and precision are presented for the potential changes produced by substituting other alkali metal cations for Na at the outside border and for K at the inside border. In terms of ability to mimic Na at the outside border of bullfrog skin, the selectivity order is Li > Rb, K, Cs; at the outside border of leopard frog skin, Li > Cs, K, Rb. In terms of ability to mimic K at the inside border of bullfrog and leopard frog skin: Rb > Cs > Li > Na. Orders of anion selectivity in terms of sensitivity of the potential for the outside border of bullfrog skin are Br > Cl > NO₃ > I > SO₄, isethionate and of leopard frog skin are Br, Cl > I, NO₃, SO₄. An effect of the solution composition (ionic strength?) on the apparent Na-K selectivity of the outside border is described. The results of the investigation have been interpreted and discussed in terms of the application of the constant field equation to the Koefoed-Johnsen-Ussing frog skin model. These observations may be useful in constructing and testing models of biological ionic selectivity.     

Effects of Cations on the Cytoplasmic pH of Chara corallina

Smith, F. A. and Gibson, J.–L. 1985. Effects of cationson the cytoplasmic pH of Chara corallina.—J.exp. Bot.36: 1331–1340 Removal of external Ca²⁺ from cells of Chara corallina lowersthe cytoplasmic pH, as determined by the intracellular distributionof the weak acid 5,5–dimethyloxazolidine2–,4–dione(DM0), when the external pH is below about 60. This effect isreversed, at least partially, by addition of the following cationsto Ca²⁺-free solutions: tetraethylammonium (TEA⁺) and Na⁺ at5 or 10 mol m^-3, Li⁺ and Cs⁺ (10 mol m^-3), or Mg²⁺, Mn²⁺ andLa³⁺ (02 or 05 mol m^-3). Under the same conditions, increasesin pH sometimes, but not always, occur in the presence of 10mol m^-3 K⁺ or Rb⁺ The results are discussed in relation to the major transportprocesses that determine pH and the electric potential differenceacross the plasma membrane, namely fluxes of H⁺ and of K⁺. Thesimplest explanation of the effects of the various cations testedin this study is that they primarily affect pHi_c via changesin influx of H⁺ but direct effects on the H⁺ pump or on K⁺ fluxesmay also be involved Key words: Chara corallina, cytoplasmic pH, cations, H⁺transport     

Effect of Metal Cations and pH on the Antibacterial Activity and Uptake of Long Chain Fatty Acids

S ummary . The bactericidal activity of long chain saturated fatty acids was antagonized by alkaline earth metals. The activity of linoleic acid was less effectively antagonized but was more sensitive to reversal by ferric and stannous ions. With increasing pH value the bactericidal activity of lauric acid decreased but that of the longer chain saturated acids increased. Both Gram positive and Gram negative bacteria reversibly adsorbed fatty acids. Uptake increased with decreasing pH value and increasing chain length. Although adsorbed to a lesser extent, the intrinsic activity of linoleic acid was greater than lauric acid. The uptake appeared to be non-specific and governed by the physicochemical properties of both the acids and the bacterial cell surfaces. Sensitivity to the fatty acids increased with decreasing pH value. Protoplasts of Bacillus megaterium adsorbed fatty acids to a greater extent than whole cells. Resistance of the Gram negative Pseudomonas phaseolicola was not due to non-adsorption of the fatty acids.     

Estimation of Nitrifying Bacterial Activities by Measuring Oxygen Uptake in the Presence of the Metabolic Inhibitors Allylthiourea and Azide

The effects of two metabolic inhibitors on an enriched nitrifying biomass during incubation for short periods of time were investigated by determining respirometric measurements. Allylthiourea (86 μM) and azide (24 μM) were shown to be strong, selective inhibitors of ammonia and nitrite oxidation, respectively. Consequently, a differential respirometry method for estimating nitrifying and heterotrophic bacterial activities within a mixed biomass is proposed.     

Uptake,Metabolic Effects and Toxicity of Arsenate and Arsenite in Astrocytes

The inorganic arsenic species arsenate and arsenite are common environmental toxins which contaminate the drinking water in many countries. Chronic intoxication with arsenicals has been connected with various diseases, but causes also neurological complications and impairs cognitive development, learning and memory. In brain, astrocytes have a pivotal role as partners of neurons in homeostatic and metabolic processes. In addition, astrocytes are the first parenchymal brain cell type which encounters substances which cross the blood–brain barrier and are considered as first line of defence against the toxic potential of xenobiotics. Therefore, astrocytes are likely to play a prominent role in the metabolism and potential detoxification of arsenicals in brain. This article summarizes the current knowledge on the uptake and toxicity of arsenate and arsenite in astrocytes and discusses the modulation of the astrocytic glucose and glutathione metabolism by arsenicals.