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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.
The C-terminal region of sulfate transporters from plants and animals belonging to the SLC26 family members shares a weak but significant similarity with the Bacillus sp. anti-anti-sigma protein SpoIIAA, thus defining the STAS domain (sulfate transporter and anti-sigma antagonist). The present study is a structure/function analysis of the STAS domain of SULTR1.2, an Arabidopsis thaliana sulfate transporter. A three-dimensional model of the SULTR1.2 STAS domain was built which indicated that it shares the SpoIIAA folds. Moreover, the phosphorylation site, which is necessary for SpoIIAA activity, is conserved in the SULTR1.2 STAS domain. The model was used to direct mutagenesis studies using a yeast mutant defective for sulfate transport. Truncation of the whole SULTR1.2 STAS domain resulted in the loss of sulfate transport function. Analyses of small deletions and mutations showed that the C-terminal tail of the SULTR1.2 STAS domain and particularly two cysteine residues plays an important role in sulfate transport by SULTR1.2. All the substitutions made at the putative phosphorylation site Thr-587 led to a complete loss of the sulfate transport function of SULTR1.2. The reduction or suppression of sulfate transport of the SULTR1.2 mutants in yeast was not due to an incorrect targeting to the plasma membrane. Both our three-dimensional modeling and mutational analyses strengthen the hypothesis that the SULTR1.2 STAS domain is involved in protein-protein interactions that could control sulfate transport. 相似文献
4.
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
5.
Compartmental analysis of 35SO 42− exchange kinetics is used to obtain SO 42− fluxes and compartment contents in carrot ( Daucus carota L.) storage root cells, where 2 to 5% of the SO 42− taken up is reduced to organic form. The necessary curve fitting is verified by (a) consistency between `content versus time' and `rate versus time' plots of washout data; (b) agreement between loading and washout kinetics; and (c) correct identification of the fastest exchange phase as being from extracellular spaces. Sulfate is actively transported up an electrochemical potential gradient at both plasmalemma and tonoplast. The plasmalemma influx is from 2 to 10 times higher than the tonoplast influx, is much greater than the SO42− reduction rate, and would not limit the rate of either. This is consistent with the finding that the plasmalemma influx is not regulated by internal SO42− or cysteine (Cram 1982 Plant Sci Lett, in press). Both SO42− influxes rise with only limited saturation as the external SO42− concentration increases up to 50 millimolarity. Both effluxes appear to be passive, with extensive recycling in the plasmalemma influx pump. SO42− permeability is about 10−11 meter per second at both membranes. The high, nonlimiting fluxes of SO42− at the plasmalemma relative to the tonoplast (found also in Lemna; Thoiron, Thoiron, Demarty, Thellier 1981 Biochim Biophys Acta 644: 24-35) contrasts with SO42− fluxes in bacteria and with Cl− fluxes in plant cells. Their implications for work on characteristics and regulation of SO42− uptake in roots and tissue cultures are discussed. 相似文献
6.
The population composition and biogeochemistry of sulfate-reducing bacteria (SRB) in the rhizosphere of the marsh grass Spartina alterniflora was investigated over two growing seasons by molecular probing, enumerations of culturable SRB, and measurements of SO 42− reduction rates and geochemical parameters. SO 42− reduction was rapid in marsh sediments with rates up to 3.5 μmol ml −1 day −1. Rates increased greatly when plant growth began in April and decreased again when plants flowered in late July. Results with nucleic acid probes revealed that SRB rRNA accounted for up to 43% of the rRNA from members of the domain Bacteria in marsh sediments, with the highest percentages occurring in bacteria physically associated with root surfaces. The relative abundance (RA) of SRB rRNA in whole-sediment samples compared to that of Bacteria rRNA did not vary greatly throughout the year, despite large temporal changes in SO 42− reduction activity. However, the RA of root-associated SRB did increase from <10 to >30% when plants were actively growing. rRNA from members of the family Desulfobacteriaceae comprised the majority of the SRB rRNA at 3 to 34% of Bacteria rRNA, with Desulfobulbus spp. accounting for 1 to 16%. The RA of Desulfovibrio rRNA generally comprised from <1 to 3% of the Bacteria rRNA. The highest Desulfobacteriaceae RA in whole sediments was 26% and was found in the deepest sediment samples (6 to 8 cm). Culturable SRB abundance, determined by most-probable-number analyses, was high at >10 7 ml −1. Ethanol utilizers were most abundant, followed by acetate utilizers. The high numbers of culturable SRB and the high RA of SRB rRNA compared to that of Bacteria rRNA may be due to the release of SRB substrates in plant root exudates, creating a microbial food web that circumvents fermentation. 相似文献
8.
One arm of Lake Anna, Va., receives acid mine drainage (AMD) from Contrary Creek (SO 42− concentration = 2 to 20 mM, pH = 2.5 to 3.5). Acid-volatile sulfide concentrations, SO 42− reduction rates, and interstitial SO 42− concentrations were measured at various depths in the sediment at four stations in four seasons to assess the effects of the AMD-added SO 42− on bacterial SO 42− reduction. Acid-volatile sulfide concentrations were always an order of magnitude higher at the stations receiving AMD than at a control station in another arm of the lake that received no AMD. Summer SO 42− reduction rates were also an order of magnitude higher at stations that received AMD than at the control station (226 versus 13.5 mmol m −2 day −1), but winter values were inconclusive, probably due to low sediment temperature (6°C). Profiles of interstitial SO 42− concentrations at the AMD stations showed a rapid decrease with depth (from 1,270 to 6 μM in the top 6 cm) due to rapid SO 42− reduction. Bottom-water SO 42− concentrations in the AMD-receiving arm were highest in winter and lowest in summer. These data support the conclusion that there is a significant enhancement of SO 42− reduction in sediments receiving high SO 42− inputs from AMD. 相似文献
9.
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
10.
Corn shoot mitochondria possess an energy-linked transport system for sulfate uptake as demonstrated by osmotic swelling and [ 35S]SO 42− accumulation. Maximum uptake is secured in the presence of Mg 2+ and oligomycin with sucrose for osmotic support. Neither phosphate nor dicarboxylate anions are required. When added simultaneously, millimolar concentrations of phosphate block [ 35S]SO 42− uptake after the initial minute. Mersalyl, N-ethylmaleimide, and 2,4-dinitrophenol are strong inhibitors of sulfate uptake; n-butylmalonate is a weak inhibitor. These inhibitors act in the same fashion on phosphate uptake. It is concluded that sulfate uptake in the absence of phosphate is by the phosphate transporter. 相似文献
11.
Aureobasidium pullulans (de Bary) Arnaud isolated from the phylloplane of sycamore exposed to heavy atmospheric pollution oxidized S 0 to S 2O 32−, S 4O 62−, and SO 42− in vitro. The intermediates S 2O 32− and S 4O 62− were also oxidized to SO 42−. Cell-free extracts of A. pullulans also oxidized reduced forms of S, the oxidation increasing linearly with increasing protein concentration, showing that the process is enzymatic. The possible role of fungi in S oxidation in soils is discussed. 相似文献
12.
The structure and intrinsic activities of conserved STAS domains of the ubiquitous SulP/SLC26 anion transporter superfamily have until recently remained unknown. Here we report the heteronuclear, multidimensional NMR spectroscopy solution structure of the STAS domain from the SulP/SLC26 putative anion transporter Rv1739c of Mycobacterium tuberculosis. The 0.87-Å root mean square deviation structure revealed a four-stranded β-sheet with five interspersed α-helices, resembling the anti-σ factor antagonist fold. Rv1739c STAS was shown to be a guanine nucleotide-binding protein, as revealed by nucleotide-dependent quench of intrinsic STAS fluorescence and photoaffinity labeling. NMR chemical shift perturbation analysis partnered with in silico docking calculations identified solvent-exposed STAS residues involved in nucleotide binding. Rv1739c STAS was not an in vitro substrate of mycobacterial kinases or anti-σ factors. These results demonstrate that Rv1739c STAS binds guanine nucleotides at physiological concentrations and undergoes a ligand-induced conformational change but, unlike anti-σ factor antagonists, may not mediate signals via phosphorylation. 相似文献
13.
In this paper we investigate the hypothesis that long-term sulphate (SO 4
2−) deposition has made peatlands a larger source of methyl mercury (MeHg) to remote boreal lakes. This was done on experimental plots at a boreal, low sedge mire where the effect of long-term addition of SO 4
2− on peat pore water MeHg concentrations was observed weekly throughout the snow-free portion of 1999. The additions of SO 4
2− started in 1995. The seasonal mean of the pore water MeHg concentrations on the plots with 17 kg ha −1 yr −1 of sulphur (S) addition (1.3±0.08 ng L −1, SE; n = 44) was significantly (p<0.0001) higher than the mean MeHg concentration on the plots with 3 kg ha −1 yr −1 of ambient S deposition (0.6±0.02 ng L −1, SE; n = 44). The temporal variation in pore water MeHg concentrations during the snow free season was larger in the S-addition plots, with an amplitude of >2 ng L −1 compared to +/−0.5 ng L −1 in the ambient S deposition plots. The concentrations of pore water MeHg in the S-addition plots were positively correlated (r 2 = 0.21; p = 0.001) to the groundwater level, with the lowest concentrations of MeHg during the period with the lowest groundwater levels. The pore water MeHg concentrations were not correlated to total Hg, DOC concentration or pH. The results from this study indicate that the persistently higher pore water concentrations of MeHg in the S-addition plots are caused by the long-term additions of SO 4
2− to the mire surface. Since these waters are an important source of runoff, the results support the hypothesis that SO 4
2− deposition has increased the contribution of peatlands to MeHg in downstream aquatic systems. This would mean that the increased deposition of SO 4
2− in acid rain has contributed to the modern increase in the MeHg burdens of remote lakes hydrologically connected to peatlands. 相似文献
14.
The cut ends of excised Zea mays roots were sealed to a pressure transducer and their root pressures recorded. These rose approximately hyperbolically to a maximum value of 4.21 ± 0.34 bar after 30 to 40 minutes. Xylem exudate could not be collected at this pressure since the flow rate was zero. Samples of exudate were collected at lower applied pressures (Δ P), however, and Δπ, the osmotic pressure difference between them and the solution bathing the root, was measured by freezing point depression. A plot of Δ P/Δπ against Jv/Δπ, where Jv is the volume flux, proved to be a straight line whose intercept, equal to σ, the reflection coefficient, was 0.853 ± 0.016. The maximum xylem concentrations of various chemical species were found by a similar extrapolative method and compared with those in the cell sap. This indicated that (a) Ca 2+, Mg 2+, NO 32−, SO 42−, and most amino acids move from the cells to the xylem down an electrochemical potential gradient; (b) relative to these ions H +, NH 4+, glutamine and asparagine are actively transported into the xylem; and (c) H 2PO 4−, and K + are actively retained in the symplasm. 相似文献
15.
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
17.
The patterns of molybdenum (MoO 42−) absorption and transport were investigated in intact bean ( Phaseolus vulgaris L.) and rice ( Oryza sativa L. cv. I.R.8) plants. The mobility of MoO 42− absorbed by roots and by leaves was compared with that of a freely mobile element, Rb +. Although MoO 42− absorption by bean roots was nearly as high as that of Rb +, its transport to the shoot was considerably less. When MoO 42− was fed to one of the primary leaves, most of it was transported to the stem and root. Evidence obtained here showed that MoO 42− was mobile. Experiments with intact rice seedlings revealed large differences in the absorption and transport of MoO 42− between the plants grown in CaSO 4 and those in Hoagland solution. Molybdate uptake by excised rice roots was suggested to be an active process since it was greatly inhibited by a metabolic inhibitor. The presence of Mn 2+, Zn 2+, Cu 2+, CI −, or SO 42− in the absorption medium reduced MoO 42− uptake which was markedly enhanced by the presence of Fe 2+. 相似文献
18.
Ricinus communis L. plants were grown in nutrient solutions in which N was supplied as NO 3− or NH 4+, the solutions being maintained at pH 5.5. In NO 3−-fed plants excess nutrient anion over cation uptake was equivalent to net OH − efflux, and the total charge from NO 3− and SO 42− reduction equated to the sum of organic anion accumulation plus net OH − efflux. In NH 4+-fed plants a large H + efflux was recorded in close agreement with excess cation over anion uptake. This H + efflux equated to the sum of net cation (NH 4+ minus SO 42−) assimilation plus organic anion accumulation. In vivo nitrate reductase assays revealed that the roots may have the capacity to reduce just under half of the total NO 3− that is taken up and reduced in NO 3−-fed plants. Organic anion concentration in these plants was much higher in the shoots than in the roots. In NH 4+-fed plants absorbed NH 4+ was almost exclusively assimilated in the roots. These plants were considerably lower in organic anions than NO 3−-fed plants, but had equal concentrations in shoots and roots. Xylem and phloem saps were collected from plants exposed to both N sources and analyzed for all major contributing ionic and nitrogenous compounds. The results obtained were used to assist in interpreting the ion uptake, assimilation, and accumulation data in terms of shoot/root pH regulation and cycling of nutrients. 相似文献
19.
The distribution of S to sulfate, glucosinolates, glutathione, and the insoluble fraction within oilseed rape ( Brassica napus L.) leaves of different ages was investigated during vegetative growth. The concentrations of glutathione and glucosinolates increased from the oldest to the youngest leaves, whereas the opposite was observed for SO 42−. The concentration of insoluble S was similar among all of the leaves. At sufficient S supply and in the youngest leaves, 2% of total S was allocated to glutathione, 6% to glucosinolates, 50% to the insoluble fraction, and the remainder accumulated as SO 42−. In the middle and oldest leaves, 70% to 90% of total S accumulated as SO 42−, whereas glutathione and glucosinolates together accounted for less than 1% of S. When the S supply was withdrawn (minus S), the concentrations of all S-containing compounds, particularly SO 42−, decreased in the youngest and middle leaves. Neither glucosinolates nor glutathione were major sources of S during S deficiency. Plants grown on nutrient solution containing minus S and low N were less deficient than plants grown on solution containing minus S and high N. The effect of N was explained by differences in growth rate. The different responses of leaves of different ages to S deficiency have to be taken into account for the development of field diagnostic tests to determine whether plants are S deficient. 相似文献
20.
A greatly improved most-probable-number (MPN) method for selective enumeration of sulfate-reducing bacteria (SRB) is described. The method is based on the use of natural media and radiolabeled sulfate ( 35SO 42−). The natural media used consisted of anaerobically prepared sterilized sludge or sediment slurries obtained from sampling sites. The densities of SRB in sediment samples from Kysing Fjord (Denmark) and activated sludge were determined by using a normal MPN (N-MPN) method with synthetic cultivation media and a tracer MPN (T-MPN) method with natural media. The T-MPN method with natural media always yielded significantly higher (100- to 1,000-fold-higher) MPN values than the N-MPN method with synthetic media. The recovery of SRB from environmental samples was investigated by simultaneously measuring sulfate reduction rates (by a 35S-radiotracer method) and bacterial counts by using the T-MPN and N-MPN methods, respectively. When bacterial numbers estimated by the T-MPN method with natural media were used, specific sulfate reduction rates (qSO 42−) of 10 −14 to 10 −13 mol of SO 42− cell −1 day −1 were calculated, which is within the range of qSO 42− values previously reported for pure cultures of SRB (10 −15 to 10 −14 mol of SO 42− cell −1 day −1). qSO 42− values calculated from N-MPN values obtained with synthetic media were several orders of magnitude higher (2 × 10 −10 to 7 × 10 −10 mol of SO 42− cell −1 day −1), showing that viable counts of SRB were seriously underestimated when standard enumeration media were used. Our results demonstrate that the use of natural media results in significant improvements in estimates of the true numbers of SRB in environmental samples. 相似文献
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