Dissimilatory Reduction of NO(2) to NH(4) and N(2)O by a Soil Citrobacter sp

Dissimilatory reduction of NO(2) to N(2)O and NH(4) by a soil Citrobacter sp. was studied in an attempt to elucidate the physiological and ecological significance of N(2)O production by this mechanism. In batch cultures with defined media, NO(2) reduction to NH(4) was favored by high glucose and low NO(3) concentrations. Nitrous oxide production was greatest at high glucose and intermediate NO(3) concentrations. With succinate as the energy source, little or no NO(2) was reduced to NH(4) but N(2)O was produced. Resting cell suspensions reduced NO(2) simultaneously to N(2)O and free extracellular NH(4). Chloramphenicol prevented the induction of N(2)O-producing activity. The K(m) for NO(2) reduction to N(2)O was estimated to be 0.9 mM NO(2), yet the apparent K(m) for overall NO(2) reduction was considerably lower, no greater than 0.04 mM NO(2). Activities for N(2)O and NH(4) production increased markedly after depletion of NO(3) from the media. Amendment with NO(3) inhibited N(2)O and NH(4) production by molybdate-grown cells but not by tungstate-grown cells. Sulfite inhibited production of NH(4) but not of N(2)O. In a related experiment, three Escherichia coli mutants lacking NADH-dependent nitrite reductase produced N(2)O at rates equal to the wild type. These observations suggest that N(2)O is produced enzymatically but not by the same enzyme system responsible for dissimilatory reduction of NO(2) to NH(4).     

Cyclic variations in nitrogen uptake rate of soybean plants: effects of pH and mixed nitrogen sources.

To determine if the daily pattern of NO3- and NH4+ uptake is affected by acidity or NO3- : NH4+ ratio of the nutrient solution, non-nodulated soybean plants (Glycine max) were exposed for 21 days to replenished, complete nutrient solutions at pH 6.0, 5.5, 5.0, and 4.5 which contained either 1.0 mM NH4+, 1.0 mM NO3- [correction of NO3+], 0.67 mM NH4+ plus 0.33 mM NO3- (2:1 NH4+ : NO3-) [correction of (2:1 NH3+ : NO4-)], or 0.33 mM NH4+ plus 0.67 mM NO3- (1:2 NH4+ : NO3-). Net uptake rates of NH4+ and NO3- were measured daily by ion chromatography as depletion from the replenished solutions. When NH4+ and NO3- were supplied together, cumulative uptake of total nitrogen was not affected by pH or solution NH4+ : NO3- ratio. The cumulative proportion of nitrogen absorbed as NH4+ decreased with increasing acidity; however, the proportional uptake of NH4+ and NO3- was not constant, but varied day-to-day. This day-to-day variation in relative proportions of NH4+ and NO3- absorbed when NH4+ : NO3- ratio and pH of solution were constant indicates that the regulatory mechanism is not directly competitive. Regardless of the effect of pH on cumulative uptake of NH4+, the specific nitrogen uptake rates from mixed and from individual NH4+ and NO3- sources oscillated between maxima and minima at each pH with average periodicities similar to the expected interval of leaf emergence.     

The influence of pretreatment with different cations on anaerobic nitrite production by excisedPisum sativum roots

The influence of pretreatment with some cations on anaerobic nitrite production (in an assay medium lacking nitrate) by excised primary roots of pea (Pisum sativum L., ov. Raman), detached from six-day-old seedlings germinated in distilled water, was investigated. When the excised roots were precultivated in one-salt-solutions of KNO3, then these roots produced at 9 mM and 15 mM NO3- concentrations under anaerobic conditions significantly more NO2-, than those precultivated in a nutrient solution containing besides K+ ions also Ca2+ and Mg2+ ions, and they produced nitrite for a longer time. The KNO3 dependent increase in anaerobic NO2- production was counteracted most by Ca2+ and to a lesser extent by Mg2+; Na+ was without effect. NH4+ at higher concentrations (12 and 15 mM) significantly depressed nitrite production both by roots precultivated in a solution containing besides NH4+ only K+, and by roots precultivated in a full nutrient solution containing K+, Ca2+ and Mg2+, however at lower NH4+ concentrations (0.6 and 2mMNH4+; 15mMNO3-) the decrease was more conspicuous in the KNO3 solution than in the full nutrient solution. Nitrate reductase level was not influenced by this pretreatment. When 6% and 7.5% n-propanol, which increases membrane permeability and causes mixing of storage and metabolic nitrate pools in the cells, was added to the assay medium lacking nitrate, anaerobic nitrite production increased and the differences caused by the precultivation disappeared. These results show that higher K+ concentrations in unbalanced one-salt-solutions of KNO3 can cause higher membrane permeability by accentuating Ca8+ deficiency, which results in a faster penetration of NO3- from the storage pool to the sites of its reduction and in an easier penetration of NO2- out of the roots, and that higher NH4+ concentrations can change nitrate compartmentation and diminish the metabolic NO3- pool which results in a slower nitrate reduction. Besides that, lower NH4+ concentrations in KNO3 solutions (15mMNO3-) probably partially counteract the K+ dependent increase in membrane permeability. The results obtained show that there is no simple, direct relationship between the so-called metabolic pool of nitrate (i.e. anaerobic nitrite production) and the level of nitrate reductase, but that the velocity of nitrate reduction can be influenced by nitrate compartmentation in the cell.     

Potential nitrification in alum-treated soil slurries amended with poultry manure

Alum is used to reduce environmental pollutants in poultry production. Alum decreases NH3 volatilization and increases total N and NH4+-N compared to untreated poultry manure. Nitrification in poultry wastes could therefore be stimulated due to higher NH4+ concentrations or could be inhibited because the soil environment is acidified. A 10-day laboratory study was conducted to study potential nitrification rates in soil slurries (20 g soil in 150 ml water) amended with 2.0 g alum-treated poultry manure. Fecal bacteria, NH4+, NO2-, NO3-, orthophosphate, pH, and NH3 were measured at 2-day intervals. Alum significantly reduced fecal bacteria concentrations through day 6. Water-soluble P was reduced 82% by day 10. Alum-treated manure had significantly increased NH4+ concentrations by day 8 and 10, and significantly decreased NO2- and NO3- concentrations by days 6-10. Alum's effect on potential nitrification was inhibitory in the soil environment. Slurries with alum-treated poultry manure had reduced nitrification rates, fecal bacteria, and soluble P. Therefore, in addition to reducing P loss, alum could temporarily reduce the risk for environmental pollution from land-applied manures in terms of both NO3- and fecal bacteria loss.     

Rapid effects of nitrogen form on leaf morphogenesis in tobacco

Ammonium (NH4+) instead of nitrate (NO3-) as the nitrogen (N) source for tobacco (Nicotiana tabacum L.) cultivated in a pH-buffered nutrient solution resulted in decreased shoot and root biomass. Reduction of shoot fresh weight was mainly related to inhibition of leaf growth, which was already detectable after short-term NH4+ treatments of 24 h, and even at a moderate concentration level of 2 mM. Microscopic analysis of the epidermis of fully expanded leaves revealed a decrease in cell number (50%) and in cell size (30%) indicating that both cell division and cell elongation were affected by NH4+ application. Changes in various physiological parameters known to be associated with NH4(+)-induced growth depression were examined both in long-term and short-term experiments: the concentrations of total N, soluble sugars and starch as well as the osmotic potential, the apparent hydraulic conductivity and the rate of water uptake were not reduced by NH4+ treatments (duration 1-12 d), suggesting that leaf growth was neither limited by the availability of N and carbohydrates, nor by a lack of osmotica or water supply. Although the concentration of K+ in leaf press sap declined in expanding leaves by approximately 15% in response to NH4+ nutrition, limitation of mineral nutrients seems to be unlikely in view of the fast response of leaf growth at 24 h after the start of the NH4+ treatment. No inhibitory effects were observed when NH4+ and NO3- were applied simultaneously (each 1 mM) resulting in a NO3-/NH4+ net uptake ratio of 6:4. These findings suggest that the rapid inhibition of leaf growth was not primarily related to NH4+ toxicity, but to the lack of NO3(-)-supply. Growth inhibition of plants fed solely with NH4+ was associated with a 60% reduction of the zeatine + zeatine riboside (Z + ZR) cytokinin fraction in the xylem sap after 24 h. Furthermore Z + ZR levels declined to almost zero within the next 4 d after start of the NH4+ treatment. In contrast, the concentrations of the putative Z + ZR precursors isopentenyl-adenine and isopentenyl-adenosine (i-Ade + i-Ado) were not affected by NH4+ application. Since cytokinins are involved in the regulation of both cell division and cell elongation, it seems likely that the presence of NO3- is required to maintain biosynthesis and/or root to shoot transfer of cytokinins at a level that is sufficient to mediate normal leaf morphogenesis.     

Effect of sulfur compounds on biological reduction of nitric oxide in aqueous Fe(II)EDTA2- solutions.

Biological reduction of nitric oxide (NO) in aqueous solutions of EDTA chelated Fe(II) is one of the main steps in the BioDeNOx process, a novel bioprocess for the removal of nitrogen oxides (NOx) from polluted gas streams. Since NOx contaminated gases usually also contain sulfurous pollutants, the possible interferences of these sulfur compounds with the BioDeNOx process need to be identified. Therefore, the effect of the sulfur compounds Na2SO4, Na2SO3, and H2S on the biological NO reduction in aqueous solutions of Fe(II)EDTA2- (25 mM, pH 7.2, 55 degrees C) was studied in batch experiments. Sulfate and sulfite were found to not affect the reduction rate of Fe(II)EDTA2- complexed NO under the conditions tested. Sulfide, either dosed externally or formed during the batch incubation out of endogenous sulfur sources or the supplied sulfate or sulfite, influences the production and consumption of the intermediate nitrous oxide (N2O) during Fe(II)EDTA2- bound NO reduction. At low concentrations (0.2 g VSS/l) of denitrifying sludge, 0.2 mM free sulfide completely inhibited the nitrosyl-complex reduction. At higher biomass concentrations (1.3-2.3 g VSS/l), sulfide (from 15 microM to 0.8 mM) induced an incomplete NO denitrification with N2O accumulation. The reduction rates of NO to N2O were enhanced by anaerobic sludge, presumably because it kept FeEDTA in the reduced state.     

Reduction of Fe(III) chelated with citrate in an NOx scrubber solution by Enterococcus sp. FR-3

Biological reduction of Fe(III) to Fe(II) is a key step in nitrogen oxide (NO(x)) removal by the integrated chemical absorption-biological reduction process. NO(x) removal efficiency strongly depends on the concentration of Fe(II) in the scrubbing liquid. In this study, a newly isolated strain, Enterococcus sp. FR-3, was used to reduce Fe(III) chelated with citrate to Fe(II). Strain FR-3 reduced citrate-chelated Fe(III) with an efficiency of up to 86.9% and an average reduction rate of 0.21 mM h(-1). SO(4)(2-) was not inhibitory whereas NO(2)(-) and SO(3)(2-) inhibited cell growth and thus affected Fe(III) reduction. Models based on the Logistic equation were used to describe the relationship between growth and Fe(III) reduction. These findings provide some useful data for Fe(III) reduction, scrubber solution regeneration and NO(x) removal process design.     

Ouabain-insensitive Na+ stimulation of an Mg-2+ -dependent ATPase in kidney tissue.

1. Freshly prepared microsomal fractions of the outermost cortex of guinea pig kidney show an Mg-2+-dependent ATPase activity which is partially inhibited by 100 mM NaCl, LiCl, KCl, RbCl, CsCl, NH4Cl or choline chloride. 2. If the microsomal preparation is aged by storage at 4 degrees C for 10-15 days, the Mg-2+-dependent activity shows stimulation by Na-+ and Li-+ but not by K-+, Rb-+, Cs-+, NH4-+ or choline. 3. Stimulation is similar with sodium salts of Cl-minus, HCO3-minus, CH3COO-minus, BR-minus, SO4-2-minus or methylsulphonate. 4. Stimulation is insensitive to 1 mM and 10 mM ouabain. 5. Stimulation is unaltered by the presence of 0.5 mM ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetracetic acid. 6. Stimulation is 100% inhibited by 2 mM ethacrynic acid, a concentration which inhibits only 30% of the Mg-2+-dependent ATPase and 50% of the (Na-++K-+)-stimulated ATPase. 7. Some of these characteristics coincide with those of an ouabain-resistant, K-+-independent, ethacrynic acid-sensitive mode of Na-+ extrusion out of guinea pig kidney cortex cells.     

Induction of poplar leaf nitrate reductase: a test of extrachloroplastic control of isoprene emission rate

Several recent studies have suggested that control of isoprene emission rate is in part exerted by supply of extrachloroplastic phosphoenolpyruvate to the chloroplast. To test this hypothesis, we altered PEP supply by differential induction of cytosolic nitrate reductase (NR) and PEP carboxylase (PEPC) in plants of Populus deltoides grown with NO3- or NH4+ as the sole nitrogen source. Growth with 8 mM NH4+ produced a high leaf nitrogen concentration, compared with 8 mM NO3-, as well as slightly elevated rates of photosynthesis and significantly enhanced rates of isoprene emission and content of dimethylallyl diphosphate (DMAPP, a precursor to isoprene biosynthesis), chlorophyll (a+b) and carotenoids. Growth with 8 mM NO3- resulted in parallel reductions in both leaf isoprene emission rate and DMAPP. The differential effects of growth with NH4+ or NO3- were not observed when plants were grown with 4 mM nitrogen. The effects of reduced DMAPP availability were specific to isoprene emission and were not propagated to higher isoprenoids, as the correlations between nitrogen content and either leaf chlorophyll (a+b) or total carotenoids were unaffected by nitrogen source. Biochemical analysis revealed significantly higher levels of NR and PEPC activity in leaves of 8 mM NO3- -grown plants, consistent with their fundamental roles in nitrate assimilation. Taken together, these results support the hypothesis that foliar assimilation of NO3- reduces isoprene emission rate by competing for carbon skeletons (mediated by PEPC) within the cytosol and possibly reductant within the chloroplast. Cytosolic competition for PEP is a major regulator of chloroplast DMAPP supply, and we offer a new "safety valve" hypothesis to explain why plants emit isoprene.     

The effects of ruthenium tetraammine compounds on vascular smooth muscle.

The time course of the relaxation effect induced by a single dose (3 x 10(-6) mol/L) of trans-[Ru(NH3)4L(NO)]3+ (L=nic, 4-pic, py, imN, P(OEt)3, SO(3)(2-), NH3, and pz) species and sodium nitroprusside (4 x 10(-9) mol/L) was studied in aortic rings without endothelium and pre-contracted with noradrenaline (1 x 10(-6) mol/L). All the compounds induced a relaxing effect in the aortic rings, but the intensity and time of relaxation were different. Only the species where L=py, 4-pic, and P(OEt)3 were able to induce 100% (99-100%) of the relaxing effect during the assay. trans-[Ru(NH3)4(L)(NO)]3+ (L=SO(3)(2-) and NH3) showed the lowest relaxing effect (36 and 37%, respectively) when compared with the other compounds. Relationship was observed between the time corresponding to half of the maximum relaxation intensity observed and, respectively, k-NO, E0'[Ru(NO)]3+/[Ru(NO)]2+ in trans-[Ru(NH3)4(L)(NO)]3+ species and E0'Ru(III)/Ru(II) in trans-[Ru(NH3)4(L)(H2O)]3+ ions. These relationships strongly suggested that the NO liberation from the reduced nitrosyl complexes was responsible for the observed relaxation.     

Escherichia coli sulfite reductase hemoprotein subunit. Prosthetic groups, catalytic parameters, and ligand complexes

Escherichia coli NADPH-sulfite reductase can be dissociated into an oligomeric flavoprotein and a monomeric hemoprotein (HP) subunit in 4 M urea. HP catalyzes stoichiometric 6-electron reductions of SO32- (to S2-) and of NO2-, as well as 2-electron reduction of NH2OH, with reduced methyl viologen (MV+) as reductant. While Vmax values are highest with the nitrogenous substrates, Km for SO32- is 2 to 3 orders of magnitude less than the Km for NO2- or NH2OH. EPR spectroscopic and chemical analyses show that HP contains one siroheme and one Fe4S4 center per polypeptide. The heme is in the high spin Fe3+ state in HP as isolated. Near-quantitative reduction of the Fe4S4 center to a state yielding a g = 1.94 type of EPR spectrum by S2O42- and/or MV+ could be achieved if HP was converted to either the CN- or CO complex or treated with 80% dimethyl sulfoxide. HP binds one SO32- or CN- per peptide. Binding of these ligands, as well as CO, appears to be mutually exclusive and to involve the heme. The heme Fe3+/Fe2+ potential is shifted from -340 mV in the free HP to -155 mV in the HP-CN- complex. The potential of the Fe4S4 center is approximately 70 mV more negative in the CN- as opposed to the CO-ligated HP (-420 mV), a result which indicates the presence of heme-Fe4S4-ligand interaction in the HP complexes.     

The effect of ionic strength on the lipid peroxidation of porcine intestinal brush-border membrane vesicles

The effects of salt concentration gradient (inside to outside) on the lipid peroxidation of porcine intestinal brush-border membrane vesicles have been studied and several interesting features of the peroxidation have been elucidated. The addition of dithiothreitol and Fe2+ is far more effective in induction of the lipid peroxidation than any of the other metal ion species tested (Fe3+, Cu2+, Ni2+, Zn2+ and Cr3+). The peroxidation rate of the membrane vesicles induced by dithiothreitol plus Fe2+ was sensitive for the incubation temperature and was increased with increase of the temperature. Imposition of an inward salt concentration gradient on the membrane vesicles preloaded with 300 mM mannitol by addition of 100 mM chloride of K+, Na+, Li+, Rb+, NH4+ or choline to medium produces a very large reduction of the lipid peroxidation induced by dithiothreitol plus Fe2+. The membrane peroxidation is depressed more with the mannitol (300 mM)-preloaded vesicles than with the K2SO4 (100 mM)-preloaded vesicles when they are incubated in medium containing 20-100 mM of K2SO4. Addition of membrane-permeant anions such as SCN- and I-, but not addition of NO3-, to incubation medium has been found to decrease markedly the lipid peroxidation of the mannitol-preloaded vesicles. From these results it is suggested that the lipid peroxidation of the brush-border membranes by addition of dithiothreitol plus Fe2+ is sensitively changed with change in ionic strength.     

Role of intracellular pH in secretion from adrenal medulla chromaffin cells

The role of intracellular pH in stimulus-secretion coupling was investigated in cultured bovine adrenal medullary chromaffin cells. NH4Cl (1-25 mM) did not affect basal catecholamine or ATP release but markedly inhibited nicotine- or high K+-induced release by up to 60%. The inhibition had a rapid onset (less than 1 min) and was maximal at about 5 mM NH4Cl. The effect of NH4Cl was largely sustained over 20 min and was reversed upon NH4Cl removal. Sodium propionate did not affect secretion but partially reversed the inhibition by NH4Cl in a concentration-dependent manner. Methylamine (10 mM) produced a similar, but slower, inhibition than NH4Cl. Monensin (1-10 microM) inhibited catecholamine secretion by 30-60%, and its effect was reduced in the presence of NH4Cl. Using the fluorescent Ca2+ probe Fura-2, we found that the increase of [Ca2+]i following stimulation was not altered by concentrations of NH4Cl which inhibited secretion maximally. Measurement of cytosolic pH (pHi) with the fluorescent probe 2',7'-bis-carboxyethyl-5(6)-carboxyfluorescein (BCECF) revealed an alkalinization by NH4Cl (2.5-25 mM) of 0.1-0.23 pH units and acidification by sodium propionate (10-20 mM) of 0.2-0.25 pH units, with intermediate combined effects. Monensin (1 microM) caused a cytosolic acidification of 0.26 pH units. All pHi changes were partly recovered in 15 min. Fluorescence quenching measurements using the weakly basic fluorescent probe acridine orange indicated the accumulation of the probe into acidic compartments, presumably the chromaffin granules, which was strongly reduced by both NH4Cl and monensin. From these findings we conclude that the pH of the chromaffin granule modulates secretion by affecting some step in the secretory process unrelated to the rise in [Ca2+]i.     

The effect of nitrogen nutrition on cluster root formation and proton extrusion by Lupinus albus

Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.     

主要营养成分对悬浮培养玫瑰茄细胞生长和花青素合成的影响

本文研究了培养基中碳源和氮源变化对悬浮培养玫瑰茄细胞生长和花青素合成的影响。在８种不同的碳源中,麦芽糖有利于花青素的积累,而蔗糖和葡萄糖适合细胞生长,并有较高的花青素产率。在１％～１０％蔗糖浓度范围内,４％浓度下细胞生长和花青素产率最高,而６％浓度下细胞花青素含量最高,高渗环境较有利于细胞花青素的积累。１３５ｍＭ的氮源总量已足够维持玫瑰茄细胞生长和花青素合成,氮源总量增加对细胞代谢有抑制作用。ＮＨ＋４对细胞有显著抑制作用。总量１３５ｍＭ,ＮＯ－３与ＮＨ＋４比例２５∶２和２３∶４时细胞生长和花青素合成最佳。     

Ammonium effects on colonic Cl- secretion: anomalous mole fraction behavior

A significant amount of ammonium (NH4+) is absorbed by the colon. The nature of NH4+ effects on transport and NH4+ transport itself in colonic epithelium is poorly understood. The goal of this study was to elucidate the effects of NH4+ on cAMP-stimulated Cl- secretion in the colonic cell line T84. In HEPES-buffered solutions, application of basolateral NH4+ resulted in a reduced level of Cl- secretory current. The effect of NH4+ appears to occur by at least three mechanisms: 1) basolateral membrane depolarization, 2) a competitive effect with K+, and 3) a long-term (>20 min) increase in transepithelial resistance (TER). The competitive effect with K+ exhibits anomalous mole fraction behavior. Transepithelial current relative to that in 10 mM basolateral K+ was inhibited 15% by 10 mM NH4+ alone and by 30% with a mixture of 2 mM K+ and 8 mM NH4+. A mole fraction mix of 2 mM K+:8 mM NH4+ produced a greater inhibition of basolateral membrane K+ current than pure K+ or NH4+ alone. Similar anomalous behavior was also observed for inhibition of bumetanide-sensitive 36Cl- uptake, e.g., Na+-K+-2Cl- -cotransporter (NKCC-1). No anomalous effect was observed on Na+-K+-ATPase current. Both NKCC-1 and Na+-K+-ATPase activity were elevated in 10 mM NH4+ with respect to 10 mM K+. The effect on TER did not exhibit anomalous mole fraction behavior. The overall effect of basolateral NH4+ on cAMP-stimulated transport is dependent on the [K+]o /[NH4+]o ratio at the basolateral membrane, where o is outside of the cell.     

Effect of nitrate on methane production and fermentation by slurries of human faecal bacteria

Most probable number counts showed that denitrifying species were the numerically predominant NO3- reducing bacteria in the faeces of five methanogenic individuals [about 10(10) bacteria (g dry wt faeces)-1]. In faecal slurries, however, denitrification was a relatively minor route of NO3- dissimilation, since only about 3% of the NO3- was converted to gaseous products, with NO3- being mainly reduced to NO2- and NH4+. When KNO2 was added to the slurries, denitrification became quantitatively more significant with approximately 23% of the NO2- being lost as gaseous products. The addition of KNO3 (10 mM) to slurries containing either starch or casein significantly decreased H2 and CH4 production. The effect of NO3- on methanogenesis was twofold: firstly, H2 accumulation decreased due to diversion of electrons towards NO3-/NO2- reduction, and as a result of H2 being used as an electron donor for NO3- reduction, resulting in the removal of the methanogenic substrate; secondly, there was direct inhibition of methane-producing bacteria by NO3- and NO2-. In starch-containing slurries, acetate: butyrate molar ratios were increased when NO3- was added but this effect was not observed when casein replaced starch. These results show that the ability of NO3-/NO2- to act as an electron sink can significantly influence the major products of the human colonic fermentation.     

Atmospheric deposition of nitrogen and sulphur compounds in the Czech Republic

Estimates of dry and wet deposition of nitrogen and sulphur compounds in the Czech Republic for the years 1994 and 1998 are presented. Deposition has been estimated from monitored and modeled concentrations in the atmosphere and in precipitation, where the most important acidifying compounds are sulphur dioxide, nitrogen oxides, ammonia, and their reaction products. Measured atmospheric concentrations of SO2, NOx, NH3, and aerosol particles (SO4(2-), NO3-, and NH4+), along with measured concentrations of SO4(2-), NO3-, and NH4+ in precipitation, weighted by precipitation amounts, were interpolated with Kriging technique on a 10- x 10-km grid covering the whole Czech Republic. Wet deposition was derived from concentration values for SO4(2-), NO3-, and NH4+ in precipitation and from precipitation amounts. Dry deposition was derived from concentrations of gaseous components and aerosol in the air, and from their deposition velocities. A multiple resistance model was used for calculation of SO2, NOx, and NH3 deposition velocities. Deposition velocities of particles were parameterized. It was estimated that the annual average deposition of SOx in the Czech Republic decreased from 1384 to 1027 mol H + ha(-1) a(-1) between 1994 and 1998. The annual average NOy deposition was estimated to be 972 and 919 mol H + ha(-1) a(-1) in 1994 and 1998, respectively. The annual average NHx deposition was estimated to be 887 mol H+ ha(-1) a(-1) and 779 mol H + ha(-1) a(-1) in 1994 and 1998, respectively. It was estimated that the annual average of the total potential acid deposition decreased from 3243 to 2725 mol H + ha(-1) a(-1) between 1994 and 1998. Sulphur compounds (SOx) contributed about 38%, oxidized nitrogen species (NOy) 34%, and reduced nitrogen species (NHx) 28% to the total potential acid deposition in 1998. The wet deposition contributed 42% to the total potential acid deposition in 1998.     

Effect of sulphate on glutamate synthesis by intact spinach (Spinacia oleracea) chloroplasts.

During the course of NH4+ (or NO2-)-plus-alpha-oxoglutarate-dependent O2 evolution in spinach (Spinacia oleracea) chloroplasts, glutamate was continuously excreted out of the chloroplasts. Under these conditions, for each molecule of NO2- or NH4+ which disappeared, one molecule of glutamate accumulated in the medium and the concentration of glutamate in the stroma space was maintained constant. SO4(2-) (or SO3(2-) behave as inhibitors of NH4+ incorporation into glutamate by intact chloroplasts. This considerable inhibition of glutamate synthesis by SO4(2-) was correlated with a rapid decline in the stromal Pi concentration. The reloading of stromal Pi with either external Pi or PPi4- relieved SO4(2-)-induced inhibition of glutamate synthesis by intact chloroplasts. It was concluded that SO4(2-) induced a rapid efflux of stromal Pi out of the chloroplast, leading to a limitation of ATP synthesis and therefore to an arrest of ATP-dependent glutamine synthetase functioning.     

Response of Anabaena species to different nitrogen sources

Nitrogenase activity, ammonia excretion and glutamine synthetase (GS) activity were examined in five strains of Anabaena (A. anomala ARM 314, A. fertilissima ARM 742, A. variabilis ARM 310, A. oryzae ARM 313 and A. oryzae ARM 570) in the presence of 2.5 mM NO3-N (KNO3), 2.5 mM NH-4-N [(NH4)2SO4] and diatomic nitrogen (N2). Ammonium-N was more inhibitory to nitrogenase activity as compared to NO3-N in all the strains. Maximum GS activity was exhibited in NO3-N medium, irrespective of the cyanobacterial strains studied. Uninduced release of ammonia was observed in all the species, with A. oryzae ARM 313 and Anabaena variabilis ARM 310 exhibiting maximum excretion of 0.25-0.31 and 0.27-1.23 mu moles NH4 mg Chl(-1) respectively on the 15th day of incubation. The glutamine synthetase activity of A. oryzae ARM 313 was relatively very high as compared to Anabaena variabilis ARM 310. There was no nitrate reductase activity in any of the Anabaena sp. grown on NH3-N or N2-N on the 15th day of incubation.