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1.
Interstitial water profiles of SeO 42−, SeO 32−, SO 42−, and Cl − in anoxic sediments indicated removal of the seleno-oxyanions by a near-surface process unrelated to sulfate reduction. In sediment slurry experiments, a complete reductive removal of SeO 42− occurred under anaerobic conditions, was more rapid with H 2 or acetate, and was inhibited by O 2, NO 3−, MnO 2, or autoclaving but not by SO 42− or FeOOH. Oxidation of acetate in sediments could be coupled to selenate but not to molybdate. Reduction of selenate to elemental selenium was determined to be the mechanism for loss from solution. Selenate reduction was inhibited by tungstate and chromate but not by molybdate. A small quantity of the elemental selenium precipitated into sediments from solution could be resolublized by oxidation with either nitrate or FeOOH, but not with MnO 2. A bacterium isolated from estuarine sediments demonstrated selenate-dependent growth on acetate, forming elemental selenium and carbon dioxide as respiratory end products. These results indicate that dissimilatory selenate reduction to elemental selenium is the major sink for selenium oxyanions in anoxic sediments. In addition, they suggest application as a treatment process for removing selenium oxyanions from wastewaters and also offer an explanation for the presence of selenite in oxic waters. 相似文献
2.
The effects of several amino-reactive disulfonic stilbene derivatives and N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate on Cl −, SO 42−, and inorganic phosphate (Pi) uptake in protoplasts isolated from corn root tissue were studied. 4-Acetamido-4′-isothiocyano-2,2′-stilbenedisulfonic acid, 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid, 4,4′-diamino-2,2′-stilbenedisulfonic acid, and NAP-taurine inhibited Cl − and SO 42− but not Pi and K + uptake in corn root protoplasts; whereas mersalyl inhibited Pi but not Cl − or SO 42− uptake. The rate of uptake of all anions decreased with increasing external pH. In addition, these reagents markedly inhibited plasmalemma ATPase activity isolated from corn root tissue. Excised root segments were less sensitive to Cl − and SO 42− transport inhibitors. 相似文献
3.
We measured potential rates of bacterial dissimilatory reduction of 75SeO 42− to 75Se 0 in a diversity of sediment types, with salinities ranging from freshwater (salinity = 1 g/liter) to hypersaline (salinity = 320 g/liter and with pH values ranging from 7.1 to 9.8. Significant biological selenate reduction occurred in all samples with salinities from 1 to 250 g/liter but not in samples with a salinity of 320 g/liter. Potential selenate reduction rates (25 nmol of SeO 42− per ml of sediment added with isotope) ranged from 0.07 to 22 μmol of SeO 42− reduced liter −1 h −1. Activity followed Michaelis-Menten kinetics in relation to SeO 42− concentration ( Km of selenate = 7.9 to 720 μM). There was no linear correlation between potential rates of SeO 42− reduction and salinity, pH, concentrations of total Se, porosity, or organic carbon in the sediments. However, potential selenate reduction was correlated with apparent Km for selenate and with potential rates of denitrification ( r = 0.92 and 0.81, respectively). NO 3−, NO 2−, MoO 42−, and WO 42− inhibited selenate reduction activity to different extents in sediments from both Hunter Drain and Massie Slough, Nev. Sulfate partially inhibited activity in sediment from freshwater (salinity = 1 g/liter) Massie Slough samples but not from the saline (salinity = 60 g/liter) Hunter Drain samples. We conclude that dissimilatory selenate reduction in sediments is widespread in nature. In addition, in situ selenate reduction is a first-order reaction, because the ambient concentrations of selenium oxyanions in the sediments were orders of magnitude less than their Kms. 相似文献
4.
Two strains of E. coli K-12 which grew in 0.01 m Na 2SeO 4 were compared to Wild E. coli K-12 which does not grow in 0.01 m Na 2SeO 4. Although the growth and SO 42? uptake in the absence of SeO 42? were similar in the three strains, the growth and uptake of SO 42? in the presence of SeO 42? were severely restricted in the Wild while not being affected at all in the tolerant strains. On the other hand, the uptake of SeO 42? took place to a much greater extent in the Wild than in the tolerant strains in either the absence or presence of SO 42?. The tolerant strains seemed to be able to control their SeO 42? contents. Efflux of both SO 42? and SOe 42? took place in the tolerant strains but not in the Wild indicating that both SO 42? and SeO 42? are quickly tied up into a nondiffusible form in the Wild but not in the other strains. Proteins of the Wild strain were found to be about 2.5× as high in Se as were the proteins of the tolerant strains. Studies with initial rates of SO 42? and SeO 42? uptake into sulfur-starved E. coli indicated that the initial uptake of SO 42? seemed to be an active transport process in all three strains while initial SeO 42? uptake seemed to be a diffusion process. The transport of SO 42? was strongly inhibited by SeO 42? in the Wild but only weakly in the tolerant strains. Sulfur amino acids and peptides were able to overcome SeO 42? toxicity in the Wild. 相似文献
5.
Addition of nickel stimulated growth and nitrogenase activity of Pseudomonas saccharophila under nitrogen-limited chemolithotrophic conditions, apparently because of a significant increase in expression of uptake hydrogenase activity. Inhibition of hydrogenase expression by 50 μM EDTA was relieved by nickel over a wide concentration range (1 to 200 μM). Co 2+, Zn 2+, Mn 2+, and Cu 2+ stimulated expression of hydrogenase activity, but to a much lesser degree than nickel, and Fe 2+, Mg 2+, SeO 42−, and SeO 32− did not increase expression. Nickel in individual combination with Mg 2+, Fe 2+, SeO 32−, and SeO 42− resulted in activities that were essentially the same as that with nickel alone. Hydrogenase synthesis required the presence of nickel, and repression by O 2 was alleviated by increasing the concentration of added nickel. Cells placed under hydrogenase derepression conditions showed progressive incorporation of radioactive nickel to a much greater extent than did cells which were not derepressed. 相似文献
6.
Exposure (30 minutes) of leaf-free mesophyll cells from the C-3 plant, Papaver somniferum, to concentrations of sulfite (SO 2 + HSO 3− + SO 3−) up to 20 millimolar stimulated the rate of CO 2 incorporation as much as 30%. The sulfite rapidly affects the metabolism of newly incorporated CO 2. Ammonia incorporation into glutamine and subsequent transamination reactions were stimulated during the short term exposure periods while glycolate metabolism apparently was inhibited by bisulfite at two points in the pathway. The results further indicate that glycolate is the major precursor of glycine in these cells. Prolonged periods of exposure (24 hours) to sulfite had somewhat different effects on carbon metabolism: the high concentrations (10 to 20 millimolar) severely inhibited all aspects of cellular metabolism while lower concentrations (1 millimolar) appeared to inhibit ammonia incorporation but stimulated synthesis of sucrose and starch. 相似文献
7.
Chlorsulfuron, an inhibitor of acetolactate synthase (EC 4.1.3.18) (TB Ray 1984 Plant Physiol 75: 827-831), markedly inhibited the growth of Lemna minor at concentrations of 10 −8 molar and above, but had no inhibitory effects on growth at 10 −9 molar. At growth inhibitory concentrations, chlorsulfuron caused a pronounced increase in total free amino acid levels within 24 hours. Valine, leucine, and isoleucine, however, became smaller percentages of the total free amino acid pool as the concentration of chlorsulfuron was increased. At concentrations of chlorsulfuron of 10 −8 molar and above, a new amino acid was accumulated in the free pool. This amino acid was identified as α-amino- n-butyrate by chemical ionization and electron impact gas chromatography-mass spectrometry. The amount of α-amino- n-butyrate increased from undetectable levels in untreated plants, to as high as 840 nanomoles per gram fresh weight (2.44% of the total free pool) in plants treated with 10 −4 molar chlorsulfuron for 24 hours. The accumulation of this amino acid was completely inhibited by methionine sulfoximine. Chlorsulfuron did not inhibit the methionine sulfoximine induced accumulations of valine, leucine, and isoleucine, supporting the idea that the accumulation of the branched-chain amino acids in methionine sulfoximine treated plants is the result of protein turnover rather than enhanced synthesis. Protein turnover may be primarily responsible for the failure to achieve complete depletion of valine, leucine, and isoleucine even at concentrations of chlorsulfuron some 10 4 times greater than that required to inhibit growth. Tracer studies with 15N demonstrate that chlorsulfuron inhibits the incorporation of 15N into valine, leucine, and isoleucine. The α-amino- n-butyrate accumulated in the presence of chlorsulfuron and [ 15N]H 4+ was heavily labeled with 15N at early time points and appeared to be derived by transamination from a rapidly labeled amino acid such as glutamate or alanine. We propose that chlorsulfuron inhibition of acetolactate synthase may lead to accumulation of 2-oxobutyrate in the isoleucine branch of the pathway, and transamination of 2-oxobutyrate to α-amino- n-butyrate by a constitutive transaminase utilizing either glutamate or alanine as α-amino- N donors. 相似文献
8.
Soil salinization is a growing threat to global agriculture and carbon sequestration, but to date it remains unclear how microbial processes will respond. We studied the acute response to salt exposure of a range of anabolic and catabolic microbial processes, including bacterial (leucine incorporation) and fungal (acetate incorporation into ergosterol) growth rates, respiration, and gross N mineralization and nitrification rates. To distinguish effects of specific ions from those of overall ionic strength, we compared the addition of four salts frequently associated with soil salinization (NaCl, KCl, Na 2SO 4, and K 2SO 4) to a nonsaline soil. To compare the tolerance of different microbial processes to salt and to interrelate the toxicity of different salts, concentration-response relationships were established. Growth-based measurements revealed that fungi were more resistant to salt exposure than bacteria. Effects by salt on C and N mineralization were indistinguishable, and in contrast to previous studies, nitrification was not found to be more sensitive to salt exposure than other microbial processes. The ion-specific toxicity of certain salts could be observed only for respiration, which was less inhibited by salts containing SO 42− than Cl − salts, in contrast to the microbial growth assessments. This suggested that the inhibition of microbial growth was explained solely by total ionic strength, while ion-specific toxicity also should be considered for effects on microbial decomposition. This difference resulted in an apparent reduction of microbial growth efficiency in response to exposure to SO 42− salts but not to Cl − salts; no evidence was found to distinguish K + and Na + salts. 相似文献
9.
Osmotic adjustment was studied in cultured cells of tomato ( Lycopersicon esculentum Mill cv VFNT-Cherry) adapted to different levels of external water potential ranging from −4 bar to −28 bar. The intracellular concentrations of reducing sugars, total free amino acids, proline, malate, citrate, quaternary ammonium compounds, K +, NO 3−, Na +, and Cl − increased with decreasing external water potential. At any given level of adaptation, the maximum contribution to osmotic potential was from reducing sugars followed by potassium ions. The sucrose levels in the cells were 3- to 8-fold lower than reducing sugar levels and did not increase beyond those observed in cells adapted to −16 bar water potential. Concentrations of total free amino acids were 4- to 5-fold higher in adapted cells. Soluble protein levels declined in the adapted cell lines, but the total reduced nitrogen was not significantly different after adaptation. Uptake of nitrogen (as NH 4+ or NO 3−) from the media was similar for adapted and unadapted cells. Although the level of quaternary ammonium compounds was higher in the nonadapted cells than that of free proline, free proline increased as much as 500-fold compared to only a 2- to 3-fold increase observed for quaternary ammonium compounds. Although osmotic adjustment after adaptation was substantial (up to −36 bar), fresh weight (volume increase) was restricted by as much as 50% in the adapted cells. Altered metabolite partitioning was evidenced by an increase in the soluble sugars and soluble nitrogen in adapted cells which occurred at the expense of incorporation of sugar into cell walls and nitrogen into protein. Data indicate that the relative importance of a given solute to osmotic adjustment may change depending on the level of adaptation. 相似文献
10.
Experiments were designed to study the importance of organic acids as counterions for K + translocation in the xylem during excess cation uptake. A comparison was made of xylem exudate from wheat seedlings treated 72 hours with either 1.0 millimolar KNO 3 or 0.5 millimolar K 2SO 4, both in the presence of 0.2 millimolar CaSO 4. Exudation from KNO 3 plants had twice the volume and twice the K + and Ca 2+ fluxes or rate of delivery to shoots, as K 2SO 4 plants. Malate flux was 25% higher in K 2SO 4 than in KNO 3 exudate. Malate was the principal anion accompanying K + or Ca 2+ in K 2SO 4 treatment, while in the KNO 3 treatment, NO 3− was the principal anion. The contribution of SO 42− was negligible in both treatments. In a second experiment, exudate was collected every 4 hours during the daytime throughout a 72-hour treatment with KNO 3. Malate was the only anion present in exudate at first, just after the CaSO 4 pretreatment had ended. Malate concentration decreased and NO 3− concentration increased with time and these concentrations were negatively correlated. By 62 hours, NO 3− represented 80% of exudate anions. K + and NO 3− concentrations in exudate were strongly correlated with K + and NO 3− uptake, respectively. The first 36 hours of absorption from KNO 3 solution resembled the continuous absorption of K 2SO 4, in that malate was the principal counterion for translocation of K +. 相似文献
11.
PM 2.5 and PM 10 samples were collected simultaneously in each season in Beijing, Tianjin and Shijiazhuang to identify the characteristics of water-soluble ion compositions in the North China Plain. The water-soluble ions displayed significant seasonal variation. The dominant ions were NO 3
−, SO 4
2−, NH 4
+ and Cl −, accounting for more than 90% and 86% to the mass of total water-soluble ions in PM 2.5 and PM 10, respectively. The anion/cation ratio indicated that the ion acidity of each city varied both between sites and seasonally. Over 50% of the ion species were enriched in small particles ≤1 µm in diameter. The [NO 3
−]/[SO 4
2−] ratio indicated that vehicles accounted for the majority of the particulate pollution in Beijing. Shijiazhuang, a city highly reliant on coal combustion, had a higher SO 4
2− concentration. 相似文献
12.
Isolated cells from leaves of Spinacia oleracea have been maintained in a state capable of high rates of photosynthetic CO 2 fixation for more than 60 hours. The incorporation of 14CO 2 under saturating CO 2 conditions into carbohydrates, carboxylic acids, and amino acids, and the effect of ammonia on this incorporation have been studied. Total incorporation, specific radioactivity, and pool size have been determined as a function of time for most of the protein amino acids and for γ-aminobutyric acid. The measurements of specific radio-activities and of the approaches to 14C “saturation” of some amino acids indicate the presence and relative sizes of metabolically active and passive pools of these amino acids. 相似文献
13.
The effect of NaCl and Na 2SO 4 salinity on NO 3− assimilation in young barley ( Hordeum vulgare L. var Numar) seedlings was studied. The induction of the NO 3− transporter was affected very little; the major effect of the salts was on its activity. Both Cl − and SO 42− salts severely inhibited uptake of NO 3−. When compared on the basis of osmolality of the uptake solutions, Cl − salts were more inhibitory (15-30%) than SO 42− salts. At equal concentrations, SO 42− salts inhibited NO 3− uptake 30 to 40% more than did Cl − salts. The absolute concentrations of each ion seemed more important as inhibitors of NO 3− uptake than did the osmolality of the uptake solutions. Both K + and Na + salts inhibited NO 3− uptake similarly; hence, the process seemed more sensitive to anionic salinity than to cationic salinity. Unlike NO3− uptake, NO3− reduction was not affected by salinity in short-term studies (12 hours). The rate of reduction of endogenous NO3− in leaves of seedlings grown on NaCl for 8 days decreased only 25%. Nitrate reductase activity in the salt-treated leaves also decreased 20% but its activity, determined either in vitro or by the `anaerobic' in vivo assay, was always greater than the actual in situ rate of NO3− reduction. When salts were added to the assay medium, the in vitro enzymic activity was severely inhibited; whereas the anaerobic in vivo nitrate reductase activity was affected only slightly. These results indicate that in situ nitrate reductase activity is protected from salt injury. The susceptibility to injury of the NO3− transporter, rather than that of the NO3− reduction system, may be a critical factor to plant survival during salt stress. 相似文献
14.
1. dl-Cysteine decreases the uptake of 35SO 42− by Euglena gracilis but does not decrease the relative incorporation of the isotope into sulpholipid; cysteic acid, on the other hand, does not affect the uptake of 35SO 42− but does dilute out its incorporation into the sulpholipid. 2. Both l-[ 35S]cysteic acid and dl-+ meso-[3- 14C]cysteic acid appear almost exclusively in 6-sulphoquinovose. 3. Molybdate inhibits the incorporation of 35SO 42− into sulpholipid but not its uptake into the cells; this suggests that adenosine 3′-phosphate 5′-sulphatophosphate may be concerned with the biosynthesis of sulpholipid, and it was shown to be formed by chloroplast fragments. 4. An outline scheme for sulpholipid biosynthesis based on these observations is discussed. 相似文献
15.
Citrate transport across the membrane of tomato fruit tonoplast vesicles was investigated. In the tonoplast vesicles, [ 14C]methylamine uptake was stimulated 10-fold by MgATP and strongly inhibited by NO 3−. Under identical experimental conditions, [ 14C]citrate uptake was inhibited by 5 millimolar free Mg 2+, and this inhibition was reversed in the presence of ATP, presumably by ATP chelation of free Mg 2+. No evidence was obtained in support of energy-linked ATP stimulation of citrate uptake. Citrate uptake showed saturation kinetics, and was inhibited by 4,4′-diisothiocyano-2,2′-stilbenedisulfonic acid and by other organic acids. The pH-dependence of uptake suggested that citrate 3− was the transported species. Our results indicate that citrate transport across the tomato fruit tonoplast occurs by facilitated diffusion of citrate 3−. The carrier shares some features in common with anion channels in that it is relatively nonspecific for organic acids and is inhibitable by 4,4′-diisothyocyano-2,2′-stilbenedisulfonic acid. 相似文献
16.
Net uptakes of K + and NO 3− were monitored simultaneously and continuously for two barley ( Hordeum vulgare) cultivars, Prato and Olli. The cultivars had similar rates of net K + and NO 3− uptake in the absence of NH 4+ or Cl −. Long-term exposure (over 6 hours) to media which contained equimolar mixtures of NH 4+, K +, Cl −, or NO 3− affected the cultivars very differently: (a) the presence of NH 4+ as NH 4Cl stimulated net NO 3− uptake in Prato barley but inhibited net NO 3− uptake in Olli barley; (b) Cl − inhibited net NO 3− uptake in Prato but had little effect in Olli; and (c) NH 4+ as (NH 4) 2SO 4 inhibited net K + uptake in Prato but had little effect in Olli. Moreover, the immediate response to the addition of an ion often varied significantly from the long-term response; for example, the addition of Cl − initially inhibited net K + uptake in Olli barley but, after a 4 hour exposure, it was stimulatory. For both cultivars, net NH 4+ and Cl − uptake did not change significantly with time after these ions were added to the nutrient medium. These data indicate that, even within one species, there is a high degree of genotypic variation in the control of nutrient absorption. 相似文献
17.
The trace metal selenium is in demand for health supplements to human and animal nutrition. We studied the reduction of selenite (SeO 3
−2) to red elemental selenium by Rhodopseudomonas palustris strain N. This strain was cultured in a medium containing SeO 3
−2 and the particles obtained from cultures were analyzed using transmission electron microscopy (TEM), energy dispersive microanalysis (EDX) and X ray diffraction analysis (XRD). Our results showed the strain N could reduce SeO 3
−2 to red elemental selenium. The diameters of particles were 80–200 nm. The bacteria exhibited significant tolerance to SeO 3
−2 up to 8.0 m mol/L concentration with an EC 50 value of 2.4 m mol/L. After 9 d of cultivation, the presence of SeO 3
2− up to 1.0 m mol/L resulted in 99.9% reduction of selenite, whereas 82.0% (p<0.05), 31.7% (p<0.05) and 2.4% (p<0.05) reduction of SeO 3
−2 was observed at 2.0, 4.0 and 8.0 m mol/L SeO 3
2− concentrations, respectively. This study indicated that red elemental selenium was synthesized by green technology using Rhodopseudomonas palustris strain N. This strain also indicated a high tolerance to SeO 3
−2. The finding of this work will contribute to the application of selenium to human health. 相似文献
18.
The addition of 20 mM MoO 42− (molybdate) to a reduced marine sediment completely inhibited the SO 42− reduction activity by about 50 nmol g −1 h −1 (wet sediment). Acetate accumulated at a constant rate of about 25 nmol g −1 h −1 immediately after MoO 42− addition and gave a measure of the preceding utilization rate of acetate by the SO 42−-reducing bacteria. Similarly, propionate and butyrate (including isobutyrate) accumulated at constant rates of 3 to 7 and 2 to 4 nmol g −1 h −1, respectively. The rate of H 2 accumulation was variable, and a range of 0 to 16 nmol g −1 h −1 was recorded. An immediate increase of the methanogenic activity by 2 to 3 nmol g −1 h −1 was apparently due to a release of the competition for H 2 by the absence of SO 42− reduction. If propionate and butyrate were completely oxidized by the SO 42−-reducing bacteria, the stoichiometry of the reactions would indicate that H 2, acetate, propionate, and butyrate account for 5 to 10, 40 to 50, 10 to 20, and 10 to 20%, respectively, of the electron donors for the SO 42−-reducing bacteria. If the oxidations were incomplete, however, the contributions by propionate and butyrate would only be 5 to 10% each, and the acetate could account for as much as two-thirds of the SO 42− reduction. The presence of MoO 42− seemed not to affect the fermentative and methanogenic activities; an MoO 42− inhibition technique seems promising in the search for the natural substrates of SO 42− reduction in sediments. 相似文献
19.
Illuminated intact pea chloroplasts in the presence of O-acetylserine ( OAS) catalysed incorporation of SeO 32- and SO 32- into selenocysteine and cysteine at rates of ca 0.36 and 6 μmol/mg Chl per hr respectively. Sonicated chloroplasts catalysed SeO 32- and SO 32- incorporation at ca 3.9 and 32% respectively of the rates of intact chloroplasts. Addition of GSH and NADPH increased the rates to ca 91 and 98% of the intact rates, but SeO 32- incorporation under these conditions was essentially light-independent. In the absence of OAS, intact chloroplasts catalysed reduction of SO 32- to S 2- at rates of ca 5.8 μmol/mg Chl per hr. In the presence of OAS, S 2- did not accumulate. Glutathione (GSH) reductase was purified from peas and was inhibited by ZnCl 2. This enzyme, in the presence of purified clover cysteine synthase, OAS, GSH and NADPH, catalysed incorporation of SeO 32- into selenocysteine (but not SO 32- into cysteine). The reaction was inhibited by ZnCl 2. Incorporation of SeO 32- into selenocysteine by illuminated intact chloroplasts and sonicated chloroplasts (with NADPH and GSH) was also inhibited by ZnCl 2 but not by KCN. Conversely, incorporation of SO 32- into cysteine was inhibited by KCN but not by ZnCl 2. It was concluded that SeO 32- and SO 32- are reduced in chloroplasts by independent light-requiring mechanisms. It is proposed that SeO 32- is reduced by light-coupled GSH reductase and that the Se 2- produced is incorporated into selenocysteine by cysteine synthase. 相似文献
20.
The correlation between the extractable activities of three key enzymes of assimilatory sulfate reduction and the in vivo incorporation of 35SO 42− into amino acids, proteins, and sulfolipids was investigated from greening to senescence in primary leaves of beans ( Phaseolus vulgaris L.). The total extractable activity of ATP sulfurylase (EC 2.7.7.4) and of adenosine 5′-phosphosulfate sulfotransferase reached a maximum in the leaves of approximately 7- and 11-day-old seedlings, respectively. During senescence, there was a decrease in both enzyme activities. After approximately 17 days, no appreciable activities remained. In contrast, total O-acetyl- l-serine sulfhydrylase (EC 4.3.99.8) activity decreased to only approximately 50% of the maximal value during the same period. The in vivo incorporation of 35SO 42− into amino acid and protein fractions showed a time-course similar to that of the total extractable adenosine 5′-phosphosulfate sulfotransferase activity. Both cysteine and sulfate markedly decreased during senescence. The total extractable activity of ribulosebisphosphate carboxylase (EC 4.1.1.39) was maximal in the primary leaves of 13-day-old seedlings, and approximately 40% of this value was still detectable after 17 days. Taken together with results from the literature, these results show that assimilatory sulfate reduction in primary leaves of P. vulgaris L. stops before CO 2 and nitrate assimilation. 相似文献
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