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1.
Hafiza Samra Younas Muhammad Abid Muhammad Shaaban Muhammad Ashraf 《Physiology and Molecular Biology of Plants》2021,27(2):387
Soil salinity is the main constraint for crop productivity in many parts of the world. Application of silicon (Si) and chitosan (Chi) can improve crop growth under saline soil conditions. The current study was aimed to examine the effects of Si and Chi on mitigation of salinity, morphological and physiological attributes as well as the antioxidant system of maize (Zea mays L.) under saline soil conditions. A field experiment was conducted that comprised of nine treatments as follows: (i) Control (no amendment), (ii) Silicon 40 kg ha−1 (Si1), (iii) Chitosan 15 kg ha−1 (Chi1), (iv) Si1 + Chi1, (v) Silicon 80 kg ha−1 (Si2), (vi) Chitosan 30 kg ha−1 (Chi2), (vii) Si2 + Chi2, (viii) Si1 + Chi2 and (ix) Si2 + Chi1. Application of Si and Chi substantially improved the morphological and physiological attributes as well as antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of maize plants, and combined application of Si and Chi was more effective when compared with Si and Chi treatments separately. Membrane stability index was improved by 25%, relative water content by 26%, chlorophyll a by 69% and b by 56% with combined application of Si and chitosan (Si2 + Chi2) compared with control. The SOD, POD and CAT increased by 36%, 38% and 65% with Si2 + Chi2 compared with control. The results suggest that Si and Chi application is the possible option for alleviating salinity stress in maize plant. Further research is suggested to examine Si and Chi effects on various crop''s growth. 相似文献
2.
Ashok Aspatwar Harlan Barker Heidi Aisala Ksenia Zueva Marianne Kuuslahti Martti Tolvanen Craig R. Primmer Jaakko Lumme Alessandro Bonardi Amit Tripathi Seppo Parkkila Claudiu T. Supuran 《Journal of enzyme inhibition and medicinal chemistry》2022,37(1):1577
A β-class carbonic anhydrase (CA, EC 4.2.1.1) was cloned from the genome of the Monogenean platyhelminth Gyrodactylus salaris, a parasite of Atlantic salmon. The new enzyme, GsaCAβ has a significant catalytic activity for the physiological reaction, CO2 + H2O ⇋ HCO3− + H+ with a kcat of 1.1 × 105 s−1 and a kcat/Km of 7.58 × 106 M−1 × s−1. This activity was inhibited by acetazolamide (KI of 0.46 µM), a sulphonamide in clinical use, as well as by selected inorganic anions and small molecules. Most tested anions inhibited GsaCAβ at millimolar concentrations, but sulfamide (KI of 81 µM), N,N-diethyldithiocarbamate (KI of 67 µM) and sulphamic acid (KI of 6.2 µM) showed a rather efficient inhibitory action. There are currently very few non-toxic agents effective in combating this parasite. GsaCAβ is subsequently proposed as a new drug target for which effective inhibitors can be designed. 相似文献
3.
Vieira SA Alves LF Duarte-Neto PJ Martins SC Veiga LG Scaranello MA Picollo MC Camargo PB do Carmo JB Neto ES Santos FA Joly CA Martinelli LA 《Ecology and evolution》2011,1(3):421-434
We estimated carbon and nitrogen stocks in aboveground biomass (AGB) and belowground biomass (BGB) along an elevation range in forest sites located on the steep slopes of the Serra do Mar on the north coast of the State of São Paulo, southeast Brazil. In elevations of 100 m (lowland), 400 m (submontane), and 1000 m (montane) four 1-ha plots were established, and above- (live and dead) and belowground (live and dead) biomass were determined. Carbon and nitrogen concentrations in each compartment were determined and used to convert biomass into carbon and nitrogen stocks. The carbon aboveground stock (CAGB) varied along the elevation range from approximately 110 to 150 Mg·ha−1, and nitrogen aboveground stock (NAGB), varied from approximately 1.0 to 1.9 Mg·ha−1. The carbon belowground stock (CBGB) and the nitrogen belowground stock (NBGB) were significantly higher than the AGB and varied along the elevation range from approximately 200–300 Mg·ha−1, and from 14 to 20 Mg·ha−1, respectively. Finally, the total carbon stock (CTOTAL) varied from approximately 320 to 460 Mg·ha−1, and the nitrogen total stock (NTOTAL) from approximately 15 to 22 Mg·ha−1. Most of the carbon and nitrogen stocks were found belowground and not aboveground as normally found in lowland tropical forests. The above- and belowground stocks, and consequently, the total stocks of carbon and nitrogen increased significantly with elevation. As the soil and air temperature also decreased significantly with elevation, we found a significantly inverse relationship between carbon and nitrogen stocks and temperature. Using this inverse relationship, we made a first approach estimate that an increase of 1°C in soil temperature would decrease the carbon and nitrogen stocks in approximately 17 Mg·ha−1 and 1 Mg·ha−1 of carbon and nitrogen, respectively. 相似文献
4.
《Saudi Journal of Biological Sciences》2021,28(11):6209-6217
Avoidable or inappropriate nitrogen (N) fertilizer rates harmfully affect the yield production and ecological value. Therefore, the aims of this study were to optimize the rate and timings of N fertilizer to maximize yield components and photosynthetic parameter of soybean. This field experiment consists of five fertilizer N rates: 0, 75, 150, 225 and 300 kg N ha−1 arranged in main plots and four N fertilization timings: V5 (trifoliate leaf), R2 (full flowering stage) and R4 (full poding stage), and R6 (full seeding stage) growth stages organized as subplots. Results revealed that 225 kg N ha−1 significantly enhanced grain yield components, total chlorophyll (Chl), photosynthetic rate (PN), and total dry biomass and N accumulation by 20%, 16%, 28%, 7% and 12% at R4 stage of soybean. However, stomatal conductance (gs), leaf area index (LAI), intercellular CO2 concentration (Ci) and transpiration rate (E) were increased by 12%, 88%, 10%, 18% at R6 stage under 225 kg N ha−1. Grain yield was significantly associated with photosynthetic characteristics of soybean. In conclusion, the amount of nitrogen 225 kg ha−1 at R4 and R6 stages effectively promoted the yield components and photosynthetic characteristics of soybean. 相似文献
5.
Nora Gallarotti Matti Barthel Elizabeth Verhoeven Engil Isadora Pujol Pereira Marijn Bauters Simon Baumgartner Travis W. Drake Pascal Boeckx Joachim Mohn Manon Longepierre John Kalume Mugula Isaac Ahanamungu Makelele Landry Cizungu Ntaboba Johan Six 《The ISME journal》2021,15(11):3357
Primary tropical forests generally exhibit large gaseous nitrogen (N) losses, occurring as nitric oxide (NO), nitrous oxide (N2O) or elemental nitrogen (N2). The release of N2O is of particular concern due to its high global warming potential and destruction of stratospheric ozone. Tropical forest soils are predicted to be among the largest natural sources of N2O; however, despite being the world’s second-largest rainforest, measurements of gaseous N-losses from forest soils of the Congo Basin are scarce. In addition, long-term studies investigating N2O fluxes from different forest ecosystem types (lowland and montane forests) are scarce. In this study we show that fluxes measured in the Congo Basin were lower than fluxes measured in the Neotropics, and in the tropical forests of Australia and South East Asia. In addition, we show that despite different climatic conditions, average annual N2O fluxes in the Congo Basin’s lowland forests (0.97 ± 0.53 kg N ha−1 year−1) were comparable to those in its montane forest (0.88 ± 0.97 kg N ha−1 year−1). Measurements of soil pore air N2O isotope data at multiple depths suggests that a microbial reduction of N2O to N2 within the soil may account for the observed low surface N2O fluxes and low soil pore N2O concentrations. The potential for microbial reduction is corroborated by a significant abundance and expression of the gene nosZ in soil samples from both study sites. Although isotopic and functional gene analyses indicate an enzymatic potential for complete denitrification, combined gaseous N-losses (N2O, N2) are unlikely to account for the missing N-sink in these forests. Other N-losses such as NO, N2 via Feammox or hydrological particulate organic nitrogen export could play an important role in soils of the Congo Basin and should be the focus of future research.Subject terms: Microbiology, Biogeochemistry 相似文献
6.
Biodegradation of Chloromethane by Pseudomonas aeruginosa Strain NB1 under Nitrate-Reducing and Aerobic Conditions
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David L. Freedman Meghna Swamy Nathan C. Bell Mathew F. Verce 《Applied microbiology》2004,70(8):4629-4634
Pseudomonas aeruginosa strain NB1 uses chloromethane (CM) as its sole source of carbon and energy under nitrate-reducing and aerobic conditions. The observed yield of NB1 was 0.20 (±0.06) (mean ± standard deviation) and 0.28 (±0.01) mg of total suspended solids (TSS) mg of CM−1 under anoxic and aerobic conditions, respectively. The stoichiometry of nitrate consumption was 0.75 (±0.10) electron equivalents (eeq) of NO3− per eeq of CM, which is consistent with the yield when it is expressed on an eeq basis. Nitrate was stoichiometrically converted to dinitrogen (0.51 ± 0.05 mol of N2 per mol of NO3−). The stoichiometry of oxygen use with CM (0.85 ± 0.21 eeq of O2 per eeq of CM) was also consistent with the aerobic yield. Stoichiometric release of chloride and minimal accumulation of soluble metabolic products (measured as chemical oxygen demand) following CM consumption, under anoxic and aerobic conditions, indicated complete biodegradation of CM. Acetylene did not inhibit CM use under aerobic conditions, implying that a monooxygenase was not involved in initiating aerobic CM metabolism. Under anoxic conditions, the maximum specific CM utilization rate (k) for NB1 was 5.01 (±0.06) μmol of CM mg of TSS−1 day−1, the maximum specific growth rate (μmax) was 0.0506 day−1, and the Monod half-saturation coefficient (Ks) was 0.067 (±0.004) μM. Under aerobic conditions, the values for k, μmax, and Ks were 10.7 (±0.11) μmol of CM mg of TSS−1 day−1, 0.145 day−1, and 0.93 (±0.042) μM, respectively, indicating that NB1 used CM faster under aerobic conditions. Strain NB1 also grew on methanol, ethanol, and acetate under denitrifying and aerobic conditions, but not on methane, formate, or dichloromethane. 相似文献
7.
Characterization of Two Inducible Phosphate Transport Systems in Rhizobium tropici 总被引:2,自引:0,他引:2
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Rhizobium tropici forms nitrogen-fixing nodules on the roots of the common bean (Phaseolus vulgaris). Like other legume-Rhizobium symbioses, the bean-R. tropici association is sensitive to the availability of phosphate (Pi). To better understand phosphorus movement between the bacteroid and the host plant, Pi transport was characterized in R. tropici. We observed two Pi transport systems, a high-affinity system and a low-affinity system. To facilitate the study of these transport systems, a Tn5B22 transposon mutant lacking expression of the high-affinity transport system was isolated and used to characterize the low-affinity transport system in the absence of the high-affinity system. The Km and Vmax values for the low-affinity system were estimated to be 34 ± 3 μM Pi and 118 ± 8 nmol of Pi · min−1 · mg (dry weight) of cells−1, respectively, and the Km and Vmax values for the high-affinity system were 0.45 ± 0.01 μM Pi and 86 ± 5 nmol of Pi · min−1 · mg (dry weight) of cells−1, respectively. Both systems were inducible by Pi starvation and were also shock sensitive, which indicated that there was a periplasmic binding-protein component. Neither transport system appeared to be sensitive to the proton motive force dissipator carbonyl cyanide m-chlorophenylhydrazone, but Pi transport through both systems was eliminated by the ATPase inhibitor N,N′-dicyclohexylcarbodiimide; the Pi transport rate was correlated with the intracellular ATP concentration. Also, Pi movement through both systems appeared to be unidirectional, as no efflux or exchange was observed with either the wild-type strain or the mutant. These properties suggest that both Pi transport systems are ABC type systems. Analysis of the transposon insertion site revealed that the interrupted gene exhibited a high level of homology with kdpE, which in several bacteria encodes a cytoplasmic response regulator that governs responses to low potassium contents and/or changes in medium osmolarity. 相似文献
8.
Root-Associated N2 Fixation (Acetylene Reduction) by Enterobacteriaceae and Azospirillum Strains in Cold-Climate Spodosols 总被引:11,自引:8,他引:3
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N2 fixation by bacteria in associative symbiosis with washed roots of 13 Poaceae and 8 other noncultivated plant species in Finland was demonstrated by the acetylene reduction method. The roots most active in C2H2 reduction were those of Agrostis stolonifera, Calamagrostis lanceolata, Elytrigia repens, and Phalaris arundinacea, which produced 538 to 1,510 nmol of C2H4·g−1 (dry weight)· h−1 when incubated at pO2 0.04 with sucrose (pH 6.5), and 70 to 269 nmol of C2H4· g−1 (dry weight)·h−1 without an added energy source and unbuffered. Azospirillum lipferum, Enterobacter agglomerans, Klebsiella pneumoniae, and a Pseudomonas sp. were the acetylene-reducing organisms isolated. The results demonstrate the presence of N2-fixing organisms in associative symbiosis with plant roots found in a northern climatic region in acidic soils ranging down to pH 4.0. 相似文献
9.
The role of swelling-activated currents in cell volume regulation is unclear. Currents elicited by swelling rabbit ventricular myocytes in solutions with 0.6–0.9× normal osmolarity were studied using amphotericin perforated patch clamp techniques, and cell volume was examined concurrently by digital video microscopy. Graded swelling caused graded activation of an inwardly rectifying, time-independent cation current (ICir,swell) that was reversibly blocked by Gd3+, but ICir,swell was not detected in isotonic or hypertonic media. This current was not related to IK1 because it was insensitive to Ba2+. The PK/PNa ratio for ICir,swell was 5.9 ± 0.3, implying that inward current is largely Na+ under physiological conditions. Increasing bath K+ increased gCir,swell but decreased rectification. Gd3+ block was fitted with a K
0.5 of 1.7 ± 0.3 μM and Hill coefficient, n, of 1.7 ± 0.4. Exposure to Gd3+ also reduced hypotonic swelling by up to ∼30%, and block of current preceded the volume change by ∼1 min. Gd3+-induced cell shrinkage was proportional to ICir,swell when ICir,swell was varied by graded swelling or Gd3+ concentration and was voltage dependent, reflecting the voltage dependence of ICir,swell. Integrating the blocked ion flux and calculating the resulting change in osmolarity suggested that ICir,swell was sufficient to explain the majority of the volume change at –80 mV. In addition, swelling activated an outwardly rectifying Cl− current, ICl,swell. This current was absent after Cl− replacement, reversed at ECl, and was blocked by 1 mM 9-anthracene carboxylic acid. Block of ICl,swell provoked a 28% increase in swelling in hypotonic media. Thus, both cation and anion swelling-activated currents modulated the volume of ventricular myocytes. Besides its effects on cell volume, ICir,swell is expected to cause diastolic depolarization. Activation of ICir,swell also is likely to affect contraction and other physiological processes in myocytes. 相似文献
10.
Joseph A. Tabcharani Paul Linsdell John W. Hanrahan 《The Journal of general physiology》1997,110(4):341-354
Permeation of cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channels by halide ions was studied in stably transfected Chinese hamster ovary cells by using the patch clamp technique. In cell-attached patches with a high Cl− pipette solution, the CFTR channel displayed outwardly rectifying currents and had a conductance near the membrane potential of 6.0 pS at 22°C or 8.7 pS at 37°C. The current–voltage relationship became linear when patches were excised into symmetrical, N-tris(hydroxymethyl)methyl-2-aminomethane sulfonate (TES)-buffered solutions. Under these conditions, conductance increased from 7.0 pS at 22°C to 10.9 pS at 37°C. The conductance at 22°C was ∼1.0 pS higher when TES and HEPES were omitted from the solution, suggesting weak, voltage-independent block by pH buffers. The relationship between conductance and Cl− activity was hyperbolic and well fitted by a Michaelis-Menten–type function having a K
m of ∼38 mM and maximum conductance of 10 pS at 22°C. Dilution potentials measured with NaCl gradients indicated high anion selectivity (PNa/PCl = 0.003–0.028). Biionic reversal potentials measured immediately after exposure of the cytoplasmic side to various test anions indicated PI (1.8) > PBr (1.3) > PCl (1.0) > PF (0.17), consistent with a “weak field strength” selectivity site. The same sequence was obtained for external halides, although inward F− flow was not observed. Iodide currents were protocol dependent and became blocked after 1–2 min. This coincided with a large shift in the (extrapolated) reversal potential to values indicating a greatly reduced I−/Cl− permeability ratio (PI/PCl < 0.4). The switch to low I− permeability was enhanced at potentials that favored Cl− entry into the pore and was not observed in the R347D mutant, which is thought to lack an anion binding site involved in multi-ion pore behavior. Interactions between Cl− and I− ions may influence I− permeation and be responsible for the wide range of PI/PCl ratios that have been reported for the CFTR channel. The low PI/PCl ratio usually reported for CFTR only occurred after entry into an altered permeability state and thus may not be comparable with permeability ratios for other anions, which are obtained in the absence of iodide. We propose that CFTR displays a “weak field strength” anion selectivity sequence. 相似文献
11.
Epiphytic Cyanobacteria on Chara vulgaris Are the Main Contributors to N2 Fixation in Rice Fields
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Yoanna Ariosa Antonio Quesada Juan Aburto David Carrasco Ramn Carreres Francisco Legans Eduardo Fernndez Valiente 《Applied microbiology》2004,70(9):5391-5397
The distribution of nitrogenase activity in the rice-soil system and the possible contribution of epiphytic cyanobacteria on rice plants and other macrophytes to this activity were studied in two locations in the rice fields of Valencia, Spain, in two consecutive crop seasons. The largest proportion of photodependent N2 fixation was associated with the macrophyte Chara vulgaris in both years and at both locations. The nitrogen fixation rate associated with Chara always represented more than 45% of the global nitrogenase activity measured in the rice field. The estimated average N2 fixation rate associated with Chara was 27.53 kg of N ha−1 crop−1. The mean estimated N2 fixation rates for the other parts of the system for all sampling periods were as follows: soil, 4.07 kg of N ha−1 crop−1; submerged parts of rice plants, 3.93 kg of N ha−1 crop−1; and roots, 0.28 kg of N ha−1 crop−1. Micrographic studies revealed the presence of epiphytic cyanobacteria on the surface of Chara. Three-dimensional reconstructions by confocal scanning laser microscopy revealed no cyanobacterial cells inside the Chara structures. Quantification of epiphytic cyanobacteria by image analysis revealed that cyanobacteria were more abundant in nodes than in internodes (on average, cyanobacteria covered 8.4% ± 4.4% and 6.2% ± 5.0% of the surface area in the nodes and internodes, respectively). Epiphytic cyanobacteria were also quantified by using a fluorometer. This made it possible to discriminate which algal groups were the source of chlorophyll a. Chlorophyll a measurements confirmed that cyanobacteria were more abundant in nodes than in internodes (on average, the chlorophyll a concentrations were 17.2 ± 28.0 and 4.0 ± 3.8 μg mg [dry weight] of Chara−1 in the nodes and internodes, respectively). These results indicate that this macrophyte, which is usually considered a weed in the context of rice cultivation, may help maintain soil N fertility in the rice field ecosystem. 相似文献
12.
Mechanism of Stimulation and Inhibition of Tonoplast H-ATPase of Beta vulgaris by Chloride and Nitrate 总被引:2,自引:1,他引:1
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The H+-ATPase of tonoplast vesicles isolated from red beet (Beta vulgaris L.) storage tissue was studied with respect to the kinetic effects of Cl− and NO3−. N-Ethylmaleimide (NEM) was employed as a probe to investigate substrate binding and gross conformational changes of the enzyme. Chloride decreased the Km of the enzyme for ATP but caused relatively little alteration of the Vmax. Nitrate increased Km only. Michaelis-Menten kinetics applied throughout with respect to ATP concentration. Nitrate yielded similar kinetics of inhibition in both the presence and absence of Cl−. Other monovalent anions that specifically increased the Km of the ATPase for ATP were, in order of increasing Ki, SCN−, ClO4−, and ClO3−. Sulfate, although inhibitory, manifested noncompetitive kinetics with respect to ATP concentration. ADP, like NO3−, was a competitive inhibitor of the ATPase but ADP and NO3− did not interact cooperatively nor did either interfere with the inhibitory action of the other. It is concluded that NO3− does not show competitive kinetics because of its stereochemical similarity to the terminal phosphoryl group of ATP. NEM was an irreversible inhibitor of the tonoplast ATPase. Both Mg·ADP and Mg·ATP protected the enzyme from inactivation by NEM but Mg·ADP was the more potent of the two. Chloride and NO3− exerted little or no effect on the protective actions of Mg·ADP and Mg·ATP suggesting that neither Cl− nor NO3− are involved in substrate binding. 相似文献
13.
In grassland ecosystems, N and P fertilization often increase plant productivity, but there is no concensus if fertilization affects soil C fractions. We tested effects of N, P and N+P fertilization at 5, 10, 15 g m−2 yr−1 (N5, N10, N15, P5, P10, P15, N5P5, N10P10, and N15P15) compared to unfertilized control on soil C, soil microbial biomass and functional diversity at the 0–20 cm and 20–40 cm depth in an alpine meadow after 5 years of continuous fertilization. Fertilization increased total aboveground biomass of community and grass but decreased legume and forb biomass compared to no fertilization. All fertilization treatments decreased the C:N ratios of legumes and roots compared to control, however fertilization at rates of 5 and 15 g m−2 yr−1 decreased the C:N ratios of the grasses. Compared to the control, soil microbial biomass C increased in N5, N10, P5, and P10 in 0–20 cm, and increased in N10 and P5 while decreased in other treatments in 20–40 cm. Most of the fertilization treatments decreased the respiratory quotient (qCO2) in 0–20 cm but increased qCO2 in 20–40 cm. Fertilization increased soil microbial functional diversity (except N15) but decreased cumulative C mineralization (except in N15 in 0–20 cm and N5 in 20–40 cm). Soil organic C (SOC) decreased in P5 and P15 in 0–20 cm and for most of the fertilization treatments (except N15P15) in 20–40 cm. Overall, these results suggested that soils will not be a C sink (except N15P15). Nitrogen and phosphorus fertilization may lower the SOC pool by altering the plant biomass composition, especially the C:N ratios of different plant functional groups, and modifying C substrate utilization patterns of soil microbial communities. The N+P fertilization at 15 g m−2 yr−1 may be used in increasing plant aboveground biomass and soil C accumulation under these meadows. 相似文献
14.
Biological N2 fixation is the dominant supply of new nitrogen (N) to the oceans, but is often inhibited in the presence of fixed N sources such as nitrate (NO3
−). Anthropogenic fixed N inputs to the ocean are increasing, but their effect on marine N2 fixation is uncertain. Thus, global estimates of new oceanic N depend on a fundamental understanding of factors that modulate N source preferences by N2-fixing cyanobacteria. We examined the unicellular diazotroph Crocosphaera watsonii (strain WH0003) to determine how the light-limited growth rate influences the inhibitory effects of fixed N on N2 fixation. When growth (µ) was limited by low light (µ = 0.23 d−1), short-term experiments indicated that 0.4 µM NH4
+ reduced N2-fixation by ∼90% relative to controls without added NH4
+. In fast-growing, high-light-acclimated cultures (µ = 0.68 d−1), 2.0 µM NH4
+ was needed to achieve the same effect. In long-term exposures to NO3
−, inhibition of N2 fixation also varied with growth rate. In high-light-acclimated, fast-growing cultures, NO3
− did not inhibit N2-fixation rates in comparison with cultures growing on N2 alone. Instead NO3
− supported even faster growth, indicating that the cellular assimilation rate of N2 alone (i.e. dinitrogen reduction) could not support the light-specific maximum growth rate of Crocosphaera. When growth was severely light-limited, NO3
− did not support faster growth rates but instead inhibited N2-fixation rates by 55% relative to controls. These data rest on the basic tenet that light energy is the driver of photoautotrophic growth while various nutrient substrates serve as supports. Our findings provide a novel conceptual framework to examine interactions between N source preferences and predict degrees of inhibition of N2 fixation by fixed N sources based on the growth rate as controlled by light. 相似文献
15.
M. Oshiki S. Ishii K. Yoshida N. Fujii M. Ishiguro H. Satoh S. Okabe 《Applied and environmental microbiology》2013,79(13):4087-4093
We examined nitrate-dependent Fe2+ oxidation mediated by anaerobic ammonium oxidation (anammox) bacteria. Enrichment cultures of “Candidatus Brocadia sinica” anaerobically oxidized Fe2+ and reduced NO3− to nitrogen gas at rates of 3.7 ± 0.2 and 1.3 ± 0.1 (mean ± standard deviation [SD]) nmol mg protein−1 min−1, respectively (37°C and pH 7.3). This nitrate reduction rate is an order of magnitude lower than the anammox activity of “Ca. Brocadia sinica” (10 to 75 nmol NH4+ mg protein−1 min−1). A 15N tracer experiment demonstrated that coupling of nitrate-dependent Fe2+ oxidation and the anammox reaction was responsible for producing nitrogen gas from NO3− by “Ca. Brocadia sinica.” The activities of nitrate-dependent Fe2+ oxidation were dependent on temperature and pH, and the highest activities were seen at temperatures of 30 to 45°C and pHs ranging from 5.9 to 9.8. The mean half-saturation constant for NO3− ± SD of “Ca. Brocadia sinica” was determined to be 51 ± 21 μM. Nitrate-dependent Fe2+ oxidation was further demonstrated by another anammox bacterium, “Candidatus Scalindua sp.,” whose rates of Fe2+ oxidation and NO3− reduction were 4.7 ± 0.59 and 1.45 ± 0.05 nmol mg protein−1 min−1, respectively (20°C and pH 7.3). Co-occurrence of nitrate-dependent Fe2+ oxidation and the anammox reaction decreased the molar ratios of consumed NO2− to consumed NH4+ (ΔNO2−/ΔNH4+) and produced NO3− to consumed NH4+ (ΔNO3−/ΔNH4+). These reactions are preferable to the application of anammox processes for wastewater treatment. 相似文献
16.
Synthetic and natural polymers are often used as drug delivery systems in vitro and in vivo. Biodegradable chitosan of different sizes were used to encapsulate antitumor drug tamoxifen (Tam) and its metabolites 4-hydroxytamoxifen (4-Hydroxytam) and endoxifen (Endox). The interactions of tamoxifen and its metabolites with chitosan 15, 100 and 200 KD were investigated in aqueous solution, using FTIR, fluorescence spectroscopic methods and molecular modeling. The structural analysis showed that tamoxifen and its metabolites bind chitosan via both hydrophilic and hydrophobic contacts with overall binding constants of K
tam-ch-15 = 8.7 (±0.5)×103 M−1, K
tam-ch-100 = 5.9 (±0.4)×105 M−1, K
tam-ch-200 = 2.4 (±0.4)×105 M−1 and K
hydroxytam-ch-15 = 2.6(±0.3)×104 M−1, K
hydroxytam – ch-100 = 5.2 (±0.7)×106 M−1 and K
hydroxytam-ch-200 = 5.1 (±0.5)×105 M−1, K
endox-ch-15 = 4.1 (±0.4)×103 M−1, K
endox-ch-100 = 1.2 (±0.3)×106 M−1 and K
endox-ch-200 = 4.7 (±0.5)×105 M−1 with the number of drug molecules bound per chitosan (n) 2.8 to 0.5. The order of binding is ch-100>200>15 KD with stronger complexes formed with 4-hydroxytamoxifen than tamoxifen and endoxifen. The molecular modeling showed the participation of polymer charged NH2 residues with drug OH and NH2 groups in the drug-polymer adducts. The free binding energies of −3.46 kcal/mol for tamoxifen, −3.54 kcal/mol for 4-hydroxytamoxifen and −3.47 kcal/mol for endoxifen were estimated for these drug-polymer complexes. The results show chitosan 100 KD is stronger carrier for drug delivery than chitosan-15 and chitosan-200 KD. 相似文献
17.
Current-voltage curves for DIDS-insensitive Cl− conductance have been determined in human red
blood cells from five donors. Currents were estimated from the rate of cell shrinkage using flow cytometry and differential laser light scattering. Membrane potentials were estimated from the extracellular pH of unbuffered suspensions using the proton ionophore FCCP. The width of the Gaussian distribution of cell volumes remained invariant during cell shrinkage, indicating a homogeneous Cl− conductance among the cells. After pretreatment for
30 min with DIDS, net effluxes of K+ and Cl− were induced by valinomycin and were measured in the continued
presence of DIDS; inhibition was maximal at ∼65% above 1 μM DIDS at both 25°C and 37°C. The nonlinear current-voltage curves for DIDS-insensitive net Cl− effluxes, induced by valinomycin or gramicidin at varied [K+]o,
were compared with predictions based on (1) the theory of electrodiffusion, (2) a single barrier model, (3) single
occupancy, multiple barrier models, and (4) a voltage-gated mechanism. Electrodiffusion precisely describes the
relationship between the measured transmembrane voltage and [K+]o. Under our experimental conditions (pH
7.5, 23°C, 1–3 μM valinomycin or 60 ng/ml gramicidin, 1.2% hematocrit), the constant field permeability ratio
PK/PCl is 74 ± 9 with 10 μM DIDS, corresponding to 73% inhibition of PCl. Fitting the constant field current-voltage equation to the measured Cl− currents yields P
Cl = 0.13 h−1 with DIDS, compared to 0.49 h−1 without DIDS,
in good agreement with most previous studies. The inward rectifying DIDS-insensitive Cl− current, however, is inconsistent with electrodiffusion and with certain single-occupancy multiple barrier models. The data are well described either by a single barrier located near the center of the transmembrane electric field, or, alternatively, by a
voltage-gated channel mechanism according to which the maximal conductance is 0.055 ± 0.005 S/g Hb, half the
channels are open at −27 ± 2 mV, and the equivalent gating charge is −1.2 ± 0.3. 相似文献
18.
Perfusion Method for Assaying Microbial Activities in Sediments: Applicability to Studies of N2 Fixation by C2H2 Reduction
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A perfusion method for assaying nitrogenase activity (acetylene reduction) in marine sediments was developed. The method was used to assay sediment cores from Spartina alterniflora (salt marsh), Zostera marina (sea grass), and Thalassia testudinum (sea grass) communities, and the results were compared with those of conventional sealed-flask assays. Rates of ethylene production increased progressively with time in the perfusion assays, reaching plateau values of 2 to 3 nmol · g of dry sediment−1 · h−1 by 10 to 20 h. Depletion of interstitial NH4+ was implicated in this stimulation of nitrogenase activity. Initial acetylene reduction rates determined by the perfusion assay of cores from the Spartina community ranged from 0.15 to 0.60 nmol of C2H4 · g of dry sediment−1 · h−1. These rates were similar to those for sediments assayed in sealed flasks without seawater when determined over linear periods of C2H4 production. Initial values obtained by using the perfusion method were 0.66 nmol of C2H4 · g of dry sediment−1 · h−1 for sediments from Zostera communities and 0.70 nmol of C2H4 · g of dry sediment−1 · h−1 for sediments from Thalassia communities. In all cases, rates determined by simultaneous slurry assays were lower than those determined by the perfusion method. 相似文献
19.
1. The polychaete worm Marphysa sanguinea has a circulating erythrocruorin of mol.wt. about 2·4×106 (S020,w 58·2s, D20,w 2·06×10−7 cm.2/sec). This is the predominant form existing at pH 6–8 and (non-protein) I 0·10–0·21, and also at approx. pH 6·7 and I 0·15–3·00. 2. The pigment contains 2·24% of protohaem. 3. The 58s protein has an electrophoretic mobility of 8·08×10−5 cm.2/v/sec. at pH 8·12, I 0·21 and 0°. The isoelectric point of suspended particles is 4·63 at I 0·16 and 21·5°. 4. At very low ionic strength and pH 6·7 (unbuffered) the 58s pigment associates reversibly to 97s and 150s forms, which are probably dimer and tetramer species. 5. At pH 10·0 and I 0·025, it dissociates irreversibly to give a small amount of 2–4s non-haem-containing protein and much 9s haem-enriched protein. These and the 58s pigment may correspond to structures found in Levin's (1963) electron-microscope studies of other erythrocruorins. 6. Absorption spectra of the 58s oxygenated erythrocruorin and the deoxygenated and carbon monoxide derivatives have been obtained. 相似文献
20.
Steady-State Effects of 2,5,2′,5′-Tetrachlorobiphenyl on Growth, Photosynthesis, and P Uptake in Selenastrum capricornutum
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The steady-state effect of 2,5,2′,5′-tetrachlorobiphenyl (TCBP) on the green alga Selenastrum capricornutum was investigated in a P-limited two-stage chemostat system. The partition coefficient of this polychlorinated biphenyl congener was 5.9 × 104 in steady-state cultures. At a cellular TCBP concentration of 12.2 × 10−8 ng · cell−1, growth rate was not affected. However, photosynthetic capacity (Pmax) was significantly enhanced by TCBP (56 × 10−9 μmol of C · cell−1 · h−1 versus 34 × 10−9 μmol of C · cell−1 · h−1 in the control). Photosynthetic efficiency, or the slope of the photosynthesis-irradiance curve, was also significantly higher. There was little difference in the cell chlorophyll a content, and therefore the difference in these photosynthetic characteristics was the same even when they were expressed on a per-chlorophyll a basis. Cell C content was higher in TCBP-containing cells than in TCBP-free cells, but approximately 36% of the C fixed by cells with TCBP was not incorporated as cell C. The maximum P uptake rate was also enhanced by TCBP, but the half-saturation concentration appeared to be unaffected. 相似文献