Leaching losses of inorganic N and DOC following repeated drying and wetting of a spruce forest soil

Forest soils are frequently subjected to dry–wet cycles, but little is known about the effects of repeated drying and wetting and wetting intensity on fluxes of , and DOC. Here, undisturbed soil columns consisting of organic horizons (O columns) and organic horizons plus mineral soil (O + M columns) from a mature Norway spruce stand at the Fichtelgebirge; Germany, were repeatedly desiccated and subsequently wetted by applying different amounts of water (8, 20 and 50 mm day⁻¹) during the initial wetting phase. The constantly moist controls were not desiccated and received 4 mm day⁻¹ during the entire wetting periods. Cumulative inorganic N fluxes of the control were 12.4 g N m⁻² (O columns) and 11.4 g N m⁻² (O + M columns) over 225 days. Repeated drying and wetting reduced cumulative and fluxes of the O columns by 47–60 and 76–85%, respectively. Increasing (0.6–1.1 g N m⁻²) and decreasing fluxes (7.6–9.6 g N m⁻²) indicate a reduction in net nitrification in the O + M columns. The negative effect of dry–wet cycles was attributed to reduced net N mineralisation during both the desiccation and wetting periods. The soils subjected to dry–wet cycles were considerably drier at the final wetting period, suggesting that hydrophobicity of soil organic matter may persist for weeks or even months. Based on results from this study and from the literature we hypothesise that N mineralisation is mostly constrained by hydrophobicity in spruce forests during the growing season. Wetting intensity did mostly not alter N and DOC concentrations and fluxes. Mean DOC concentrations increased by the treatment from 45 mg l⁻¹ to 61–77 mg l⁻¹ in the O tlsbba columns and from 12 mg l⁻¹ to 21–25 mg l⁻¹ in the O + M columns. Spectroscopic properties of DOC from the O columns markedly differed within each wetting period, pointing to enhanced release of rather easily decomposable substrates in the initial wetting phases and the release of more hardly decomposable substrates in the final wetting phases. Our results suggest a small additional DOC input from organic horizons to the mineral soil owing to drying and wetting.     

Effects of common soil anions and pH on the uptake and accumulation of perchlorate in lettuce

A mechanistic understanding of perchlorate () entry into plants is important for establishing the human health risk associated with consumption of contaminated produce and for assessing the effectiveness of phytoremediation. To determine whether common soil anions affect uptake and accumulation in higher plants, a series of competition experiments using lettuce (Lactuca sativa L.) were conducted between (50 nM) and (4–12 mM), (1–10 mM), or Cl⁻ (5–15 mM) in hydroponic solution. The effects of (0–5 mM) and pH (5.5–7.5) on uptake were also examined. Increasing in solution significantly reduced the amount of taken up by green leaf, butter head, and crisphead lettuces. Sulfate and Cl⁻ had no significant effects on uptake in lettuce over the concentrations tested. Increasing pH significantly reduced the amount of taken up by crisphead and green leaf lettuces, whereas increasing significantly reduced uptake in butter head lettuce. The inhibition by across all lettuce genotypes suggests that may share an ion carrier with , and the decrease in uptake with increasing pH or provides macroscopic evidence for cotransport across the plasma membrane.     

Can biological nitrification inhibition (BNI) genes from perennial Leymus racemosus (Triticeae) combat nitrification in wheat farming?

Using a recombinant luminescent Nitrosomonas europaea assay to quantify biological nitrification inhibition (BNI), we found that a wild relative of wheat (Leymus racemosus (Lam.) Tzvelev) had a high BNI capacity and releases about 20 times more BNI compounds (about 30 ATU g⁻¹ root dry weight 24 h⁻¹) than Triticum aestivum L. (cultivated wheat). The root exudate from cultivated wheat has no inhibitory effect on nitrification when applied to soil; however, the root exudate from L. racemous suppressed formation and kept more than 90% of the soil’s inorganic-N in the -form for 60 days. The high-BNI capacity of L. racemosus is mostly associated with chromosome Lr#n. Two other chromosomes Lr#J, and Lr#I also have an influence on BNI production. Tolerance of L. racemosus to is controlled by chromosome 7Lr#1-1. Sustained release of BNI compounds occurred only in the presence of in the root environment. Given the level of BNI production expressed in DALr#n and assuming normal plant growth, we estimated that nearly 87,500,000 ATU of BNI activity ha⁻¹ day⁻¹ could be released in a field of vigorously growing wheat; this amounts to the equivalent of the inhibitory effect from the application of 52.5 g of the synthetic nitrification inhibitor nitrapyrin (one AT unit of BNI activity is equivalent to 0.6 μg of nitrapyrin). At this rate of BNI production it would take only 19 days for a BNI-enabled wheat crop to produce the inhibitory power of a standard commercial application of nitrapyrin, 1 kg ha⁻¹. The synthetic nitrification inhibitor, dicyandiamide, blocked specifically the AMO (ammonia monooxygenase) pathway, while the BNI from L. racemosus blocked the HAO (hydroxylamine oxidoreductase) pathway in Nitrosomonas. Here we report the first finding of high production of BNI in a wild relative of any cereal and its successful introduction and expression in cultivated wheat. These results demonstrate the potential for empowering the new generation of wheat cultivars with high-BNI capacity to control nitrification in wheat-production systems. Responsible Editor: Hans Lambers.     

Light affects competition for inorganic and organic nitrogen between maize and rhizosphere microorganisms

Effects of light on the short term competition for organic and inorganic nitrogen between maize and rhizosphere microorganisms were investigated using a mixture of amino acid, ammonium and nitrate under controlled conditions. The amount and forms of N added in the three treatments was identical, but only one of the three N forms was labeled with ¹⁵N. Glycine was additionally labeled with ¹⁴C to prove its uptake by maize and incorporation into microbial biomass in an intact form. Maize out-competed microorganisms for during the whole experiment under low and high light intensity. Microbial uptake of ¹⁵N and ¹⁴C was not directly influenced by the light intensity, but was indirectly related to the impact the light intensity had on the plant. More was recovered in microbial biomass than in plants in the initial 4 h under the two light intensities, although more ¹⁵N-glycine was incorporated into microbial biomass than in plants in the initial 4 h under low light intensity. Light had a significant effect on uptake by maize, but no significant effects on the uptake of or ¹⁵N-glycine. High light intensity significantly increased plant uptake of and glycine ¹⁴C. Based on ¹⁴C to ¹⁵N recovery ratios of plants, intact glycine contributed at least 13% to glycine-derived nitrogen 4 h after tracer additions, but it contributed only 0.5% to total nitrogen uptake. These findings suggest that light intensity alters the competitive relationship between maize roots and rhizosphere microorganisms and that C4 cereals such as maize are able to access small amounts of intact glycine. We conclude that roots were stronger competitor than microorganisms for inorganic N, but microorganisms out competed plants during a short period for organic N, which was mineralized into inorganic N within a few hours of application to the soil and was thereafter available for root uptake.     

The root–soil system of Norway spruce subjected to turning moment: resistance as a function of rotation

The reactions of trees to wind, rockfall, and snow and debris flow depend largely on how strong and deformable their anchorage in the soil is. Here, the resistive turning moment M of the root–soil system as a function of the rotation ϕ at the stem base plays the major role. M(ϕ) describes the behavior of the root–soil system when subject to rotational moment, with the maximum M(ϕ) indicating the anchorage strength M _a of the tree. We assessed M(ϕ) of 66 Norway spruce (Picea abies L. Karst) by pulling them over with a winch. These 45- to 170-year-old trees grew at sites of low and high elevation, with a diameter at breast height DBH = 14–69 cm and a height H = 9–42 m. M(ϕ) displayed a strong nonlinear behavior. M _a was reached at a lower ϕ for large trees than for small trees. Thus overhanging tree weight contributed less to M _a for the large trees. Overturning also occurred at a lower ϕ for the large trees. These observations show that the rotational ductility of the root–soil system is higher for small trees. M _a could be described by four monovariate linear regression equations of tree weight, stem weight, stem volume and DBH ² ·H (0.80 < R ² < 0.95), and ϕ at M _a, ϕ _a, by a power law of DBH²·H (R ² = 0.85). We found significantly higher M _a for the low-elevation spruces than for the high-elevation spruces, which were more shallowly anchored, but no significant difference in ϕ _a. The 66 curves of M(ϕ), normalized (_n) by M _a in M-direction and by ϕ _a in ϕ-direction, yielded one characteristic average curve: . Using and the predictions of M _a and ϕ _a, it is shown that M(ϕ) and the curves associated with M(ϕ) can be predicted with a relative standard error ≤25%. The parameterization of M(ϕ) by tree size and weight is novel and provides useful information for predicting with finite-element computer models how trees will react to natural hazards.     

A Novel Approach for Bioremediation of a Coastal Marine Wastewater Effluent Based on Artificial Microbial Mats

A novel alternative for wastewater effluent bioremediation was developed using constructed microbial mats on low-density polyester. This biotechnology showed high removal efficiencies for nitrogen and phosphorous in a short retention time (48 h): 94% for orthophosphate (7.78 g m³ d⁻¹), 79% for ammonium (11.30 g m⁻³ d⁻¹), 78% for nitrite (7.46 g m⁻³ d⁻¹), and 83% for nitrate (8.55 g m⁻³ d⁻¹). The microbial mats were dominated by Cyanobacteria genera such as Chroococcus sp., Lyngbya sp., and bacteria of the subclass Proteobacteria representative of the Eubacteria Domain. Nitzschia sp. was the dominant Eukaryote Domain. Various N and P substrates in the wastewater permit the growth of self-forming and self-sustaining bacterial, microalgal, and cyanobacterial communities on a polyester support. The result is the continuous, self-sufficient growth of microbial mats. This is an innovative, economical, and environmentally safe alternative for the treatment of wastewater effluents in coastal marine environments.     

Modification of the data-processing method for the turbidimetric bioassay of nisin

The data processing method of the turbidimetric bioassay of nisin was modified to facilitate its industrial application. The influence of the initial indicator concentration was minimized by a redefined specific dose of the bacteriocin as the quotient between the titer of the added bacteriocin and the initial population density of the indicator in the suspension. It was found that d _c = 0.125 μg ml⁻¹ was the critical dose of nisin that can cause a complete inhibition of the indicator, Pediococcus acidilactici UL5, with an initial OD of 0.135. To eliminate the interference of the cell debris, an equation, , exploiting d _c, was formulated to obtain the intrinsic survival proportion. The use of the specific dose of the bacteriocin and the intrinsic survival proportion as parameters of the dose/response curve greatly enhanced its repeatability and feasibility. A dual-dosage approach was developed to further simplify the conventional standard dose/response curve method.     

Alternate-site isotopic labeling of ribonucleotides for NMR studies of ribose conformational dynamics in RNA

Heteronuclear NMR spin relaxation studies of conformational dynamics are coming into increasing use to help understand the functions of ribozymes and other RNAs. Due to strong magnetic interactions within the ribose ring, however, these studies have thus far largely been limited to ¹³C and ¹⁵N resonances on the nucleotide base side chains. We report here the application of the alternate-site ¹³C isotopic labeling scheme, pioneered by LeMaster for relaxation studies of amino acid side chains, to nucleic acid systems. We have used different strains of E. coli to prepare mononucleotides containing ¹³C label in one of two patterns: Either C1′ or C2′ in addition to C4′, termed (1′/2′,4′) labeling, or nearly complete labeling at the C2′ and C4′ sites only, termed (2′,4′) labeling. These patterns provide isolated H spin systems on the labeled carbon atoms and thus allow spin relaxation studies without interference from scalar or dipolar coupling. Using relaxation studies of AMP dissolved in glycerol at varying temperature to produce systems with correlation times characteristic of different size RNAs, we demonstrate the removal of errors due to interaction in T ₁ measurements of larger nucleic acids and in T _1ρ measurements in RNA molecules. By extending the applicability of spin relaxation measurements to backbone ribose groups, this technology should greatly improve the flexibility and completeness of NMR analyses of conformational dynamics in RNA.     

Soil temperature and biotic factors drive the seasonal variation of soil respiration in a maize (Zea mays L.) agricultural ecosystem

The diurnal and seasonal variation of soil respiration (SR) and their driving environmental factors were studied in a maize ecosystem during the growing season 2005. The diurnal variation of SR showed asymmetric patterns, with the minimum occurring around early morning and the maximum around 13:00 h. SR fluctuated greatly during the growing season. The mean SR rate was 3.16 μmol CO₂ m⁻² s⁻¹, with a maximum of 4.87 μmol CO₂ m⁻² s⁻¹ on July 28 and a minimum of 1.32 μmol CO₂ m⁻² s⁻¹ on May 4. During the diurnal variation of SR, there was a significant exponential relationship between SR and soil temperature (T) at 10 cm depth: . At a seasonal scale, the coefficient α and β fluctuated because the biomass (B) increased α, and the net primary productivity (NPP) of maize markedly increased β of the exponential equation. Based on this, we developed the equation to estimate the magnitude of SR and to simulate its temporal variation during the growth season of maize. Most of the temporal variability (93%) in SR could be explained by the variations in soil temperature, biomass and NPP of maize. This model clearly demonstrated that soil temperature, biomass and NPP of maize combined to drive the seasonal variation of SR during the growing season. However, only taking into account the influence of soil temperature on SR, an exponential equation over- or underestimated the magnitude of SR and resulted in an erroneous representation of the seasonal variation in SR. Our results highlighted the importance of biotic factors for the estimation of SR during the growing season. It is suggested that the models of SR on agricultural sites should not only take into account the influence of soil temperature, but also incorporate biotic factors as they affect SR during the growing season.     

Soil algal communities inhabiting zinc and lead mine spoils

Algal communities inhabiting four calamine mine spoils differing in time since cessation of exploitation and loaded with high concentrations of zinc (20,284–61,599 μg g⁻¹ soil DW), lead (2,620–3,885 μg g⁻¹ DW) and cadmium (104–232 μg g⁻¹ DW) were studied. In dump soils of slightly alkaline pH (7.28–7.52) and low nutrient (, , ) concentrations, chlorophyll a content ranged from 0.41 to 2.27 μg g⁻¹ soil DW. In total, 23 algal species were recorded. Chlorophyta were the dominant taxonomic group (42–55% of all identified species) followed by Cyanobacteria (28–36%) and Heterokontophyta (13–21%). The highest species richness (18) was observed in the oldest dump (120 years old) with natural succession, while in younger dumps it was lower (11–15). Total algal abundance ranged between 5.5 and 19.1 × 10² ind. g⁻¹ soil DW, and values of Margalef’s diversity indices (1.59–2.25) were low. These results may suggest that both high concentrations of heavy metals and low nutrient content influenced the algal communities in all the dumps studied. The differences in algal microflora observed between tailing dumps may indicate that habitat quality improved with time and that algae isolated from Zn/Pb-loaded soils may be Zn/Pb-resistant ecotypes of ubiquitous species.     

Do oaks have different strategies for uptake of N, K and P depending on soil depth?

The uptake of nutrients from deep soil layers has been shown to be important for the long-term nutrient sustainability of forest soils. When modelling nutrient uptake in forest ecosystems, the nutrient uptake capacity of trees is usually defined by the root distribution. However, this leads to the assumption that roots at different soil depths have the same capacity to take up nutrients. To investigate if roots located at different soil depths differ in their nutrient uptake capacity, here defined as the nutrient uptake rate under standardized conditions, a bioassay was performed on excised roots (<1 mm) of eight oak trees (Quercus robur L.). The results showed that the root uptake rate of ⁸⁶Rb⁺ (used as an analogue for K⁺) declined with increasing soil depth, and the same trend was found for . The root uptake rate of , on the other hand, did not decrease with soil depth. These different physiological responses in relation to soil depth indicate differences in the oak roots, and suggest that fine roots in shallow soil layers may be specialized in taking up nutrients such as K⁺ and which have a high availability in these layers, while oak roots in deep soil layers are specialized in taking up other resources, such as P, which may have a high availability in deep soil layers. Regardless of the cause of the difference in uptake trends for the various nutrients, these differences have consequences for the modelling of the soil nutrient pool beneath oak trees and raise the question of whether roots can be treated uniformly, as has previously been done in forest ecosystem models. Responsible Editor: Herbert Johannes Kronzucker.     

A preliminary study of the bioremediation potential of Codium fragile applied to seaweed integrated multi-trophic aquaculture (IMTA) during the summer

In integrated multi-trophic aquaculture (IMTA), seaweeds have the capacity to reduce the environmental impact of nitrogen-rich effluents in coastal ecosystems. To establish such bioremediation systems, selection of suitable seaweed species is important. The distribution and productivity of seaweeds vary seasonally based on water temperature and photoperiod. In Korea, candidate genera such as Pophyra, Laminaria, and Undaria grow from autumn to spring. In contrast, Codium grows well at relatively high water temperatures in summer. Thus, aquaculture systems potentially could capitalize on Codium’s capacity for rapid growth in the warm temperatures of late summer and early fall. In this study, we investigated ammonium uptake and removal efficiency by Codium fragile. In laboratory experiments, we grew C. fragile under various water temperatures (10, 15, 20, and 25°C), irradiances (dark, 10, and 100 μmol photons m⁻² s⁻¹), and initial ammonium concentrations (150 and 300 μM); in all cases, C. fragile exhausted the ammonium supply for 6 h. At 150 μM of , ammonium removal efficiency was greatest (99.5 ± 2.6%) when C. fragile was incubated at 20°C under 100 μmol photons m⁻² s⁻¹. At 300 μM of , removal efficiency was greatest (86.3 ± 2.1%) at 25°C under 100 μmol photons m⁻² s⁻¹. Ammonium removal efficiency was significantly greater at 20 and 25°C under irradiance of 100 μmol photons m⁻² s⁻¹ than under other conditions tested.     

Regulation of mineral nitrogen uptake in plants

In the biosphere plants are exposed to different forms of N, which comprise mineral and organic N forms in soils as well as gaseous NH3, NOx, and molecular N2 in the atmosphere. The form of N uptake is mainly determined by its abundance and accessibility, which make and the most important N forms for plant nutrition under agricultural conditions. With minor importance, the form of N uptake is also subject to plant preferences, by which plants maintain their cation/anion balance during uptake. However, some species seem to have an obligatory preference which even prevents their growth on certain other N sources. In general, uptake of a certain N form closely matches the growth-related demand of the plant, at least when N transport to the root surface is not limiting. In addition, many plants accumulate large pools of N during vegetative growth which are remobilized in the generative stage. As a consequence, systems responsible for N transport need to be tightly regulated in their expression and activity upon sensing N availability and plant demand. Employing the tools of molecular genetics, the first plant genes encoding transporters for inorganic N have recently been isolated and characterized. These data can now complete the wealth of physiological and nutritional studies on N uptake. The present article will focus on the uptake of and into root cells and tries to link data derived from physiological, genetic and molecular studies.     

The intramolecular δ<Superscript>15</Superscript>N of lysine responds to respiratory status in <Emphasis Type="Italic">Paracoccus denitrificans</Emphasis>

Summary. Presented here is the first experimental evidence that natural, intramolecular, isotope ratios are sensitive to physiological status, based on observations of intramolecular δ¹⁵N of lysine in the mitochondrial mimic Paracoccus denitrificans. Paracoccus denitrificans, a versatile, gram-negative bacterium, was grown either aerobically or anaerobically on isotopically-characterized ammonium as sole cell-nitrogen source. Nitrogen isotope composition of the biomass with respect to source ammonium was = −6.2 ± 1.2‰ for whole cells under aerobic respiration, whereas cells grown anaerobically produced no net fractionation ( = −0.3 ± 0.23‰). Fractionation of ¹⁵N between protein nitrogen and total cell nitrogen increased during anaerobic respiration and suggests that residual nitrogen-containing compounds in bacterial cell membranes are isotopically lighter under anaerobic respiration. In aerobic cells, the lysine intramolecular difference between peptide and sidechain nitrogen is negligible, but in anaerobic cells was a remarkable Δ¹⁵N_{p − s} = δ¹⁵N_peptide − δ¹⁵N_sidechain = +11.0‰, driven predominantly by enrichment at the peptide N. Consideration of known lysine pathways suggests this to be likely due to enhanced synthesis of peptidoglycans in the anaerobic state. These data indicate that distinct pathway branching ratios associated with microbial respiration can be detected by natural intramolecular Δδ¹⁵N measurements, and are the first in vivo observations of position-specific measurements of nitrogen isotope fractionation.     

In Situ pH Measurement in Partly Frozen Aqueous Solution Using the Fluorescent Probe 8-Hydroxypyrene-1,3,6-Trisulfonic Acid

A method based on the fluorescence probe 8-hydroxypyrene-1,3,6-trisulfonic acid for in situ measurement of pH in partly frozen aqueous solutions was developed using multifrequency, phase-modulated fluorescence spectroscopy inherently correcting for light scattering. The probe was determined to have pK _a = 7.72 ± 0.03 at 25.0 °C extrapolated to zero ionic strength with as derived from temperature dependence (5 to 25 °C investigated). Ionic strength dependence of pK _a determined experimentally was described using Debye–Hückel formalism for ionic strength up to 3 M. Temperature and ionic strength dependence were combined to yield for determination of pH at subzero temperatures with α experimentally determined from the ratio between fluorescence intensity after excitation at 454 and 415 nm, α = FI(454 nm)/2.5·FI(415 nm). Fluorescence could be described as a decay of a single excited state with a fluorescence life time of 5.40 ± 0.05 ns at 25 °C, and excited state acid–base equilibration was shown not to interfere with the pH measurement. Using the method, pH of a 0.25 M phosphate buffer with pH = 6.8 at 25 °C was shown to decrease gradually to pH = 4.2 in the ice slurry at −13 °C.     

The effect of temperature on post-feeding ammonia excretion and oxygen consumption in the southern catfish

The post-prandial rates of ammonia excretion (TAN) and oxygen consumption in the southern catfish (Silurus meridionalis) were assessed at 2 h intervals post-feeding until the rates returned to those of the fasting rates, at 17.5, 22.5, 27.5, and 32.5°C, respectively. Both fasting TAN and increased with temperature, and were lower than those previously reported for many fish species. The relationship between fasting TAN (mmol NH₃–N kg⁻¹ h⁻¹) and temperature (T, °C) was described as: fasting TAN = 0.144e ^0.0266T (r = 0.526, n = 27, P < 0.05). The magnitude of ammonia excretion and its ratio to total N intake during the specific dynamic action (SDA) tended to increase initially, and then decrease with increasing temperature. The ammonia quotient (AQ), calculated as mol NH₃–N/mol O₂, following feeding decreased as temperature increased. The relationship between AQ during SDA and temperature was described as: AQ_{during SDA} = 0.303e ^−0.0143T (r = 0.739, n = 21, P < 0.05). Our results suggest that ammonia excretion and oxygen consumption post-feeding are operating independently of each other. Furthermore, it appears that the importance of protein as a metabolic substrate in postprandial fish decreases with temperature.     

Purinergic junctional transmission and propagation of calcium waves in cultured spinal cord microglial networks

In order to elucidate the mechanisms of purinergic transmission of calcium (Ca^2 +) waves between microglial cells, we have employed micro-photolithographic methods to form discrete patterns of microglia that allow quantitative measurements of Ca^2 + wave propagation. Microglia were confined to lanes 20–100 wide and Ca^2 + waves propagated from a point of mechanical stimulation, with a diminution in amplitude, for about 120 . The number of cells participating in propagation also decreased over this distance. Ca^2 + waves could propagate across a cell-free lane from one microglia lane to another if this distance of separation was less than about 60 , indicating that propagation involved diffusion of a chemical transmitter. This transmitter was identified as ATP since all Ca^2 + wave propagation was blocked by the purinoceptor antagonist suramin, which blocks P2Y₂ and P2Y₁₂ at relatively low concentrations. Antibodies to P2Y₁₂ showed these at very high density compared with P2Y₂, indicating a role for P2Y₁₂ receptors. These observations were quantitatively accounted for by a model in which the main determinants are the diffusion of ATP released from a stimulated microglial cell and differences in the dissociation constant of the purinoceptors on the microglial cells.     

3D-QSAR study of microsomal prostaglandin E<Subscript>2</Subscript> synthase(mPGES-1) inhibitors

Microsomal prostaglandin E₂ synthase (mPGES-1) has been identified recently as a novel target for treating pain and inflammation. The aim of this study is to understand the binding affinities of reported inhibitors for mPGES-1 and further to design potential new mPGES-1 inhibitors. 3D-QSAR-CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis) - techniques were employed on a series of indole derivatives that act as selective mPGES-1 inhibitors. The lowest energy conformer of the most active compound obtained from systematic conformational search was used as a template for the alignment of 32 compounds. The models obtained were used to predict the activities of the test set of eight compounds, and the predicted values were in good agreement with the experimental results. The 3D-QSAR models derived from the training set of 24 compounds were all statistically significant (CoMFA; q ² = 0.89, r ² = 0.95, , and CoMSIA; q ² = 0.84, r ² = 0.93, , ). Contour plots generated for the CoMFA and CoMSIA models reveal useful clues for improving the activity of mPGES-1 inhibitors. In particular, substitutions of an electronegative fluorine atom or a bulky hydrophilic phenoxy group at the meta or para positions of the biphenyl rings might improve inhibitory activity. A plausible binding mode between the ligands and mPGES-1 is also proposed.     

Factors affecting denitrification in agricultural headwater streams in Northeast Ohio,USA

As a result of increased anthropogenic nitrogen (N) loading in surface waters of agricultural watersheds, there is enhanced interest to understand and quantify N removal mechanisms. Denitrification, an important N removal mechanism in aquatic systems, may contribute to reducing N pollution in agricultural headwater streams. However, the key factors controlling this process in lotic systems remain unclear. The objective of our study was to examine the factors regulating rates of denitrification in the sediments of agricultural headwater streams in the mid-western USA. Denitrification rates were variable among streams and treatments (<0.1–28.0 μg N g AFDM⁻¹ h⁻¹) and on average, were higher than those reported for similar headwater streams. Carbon quantity and quality, and pH had no effect on denitrification, while temperature and nitrate ( ) concentrations had a positive effect on rates of denitrification. Specifically, controlled denitrification following Michaelis-Menten kinetics. We calculated a value of k_m (1.0 mg -N L^-1) that was comparable to other studies in aquatic sediments but was well below the median in-stream concentrations (5.2–17.4 mg -N L⁻¹) observed at the study sites. Despite high rates of denitrification, this removal mechanism is most likely saturated in the agricultural headwater streams we examined, suggesting that these systems are not effective at removing in-stream N. Handling editor: D. Ryder     

(H)NCAHA and (H)CANNH experiments for the determination of vicinal coupling constants related to the ϕ-torsion angle

Summary A set of three-dimensional triple-resonance experiments is described which provide , , and coupling constants. The pulse sequences generate E.COSY-like multiplet patterns and comprise a magnetization transfer from the amide proton to the α-proton or vice versa via the directly bound heteronuclei. For residues with the ¹H^α spin resonating close to the H₂O signal, a modified HNCA experiment can be employed to measure the vicinal ¹H^N,¹H^α couplings. Ambiguities associated with the conversion of values into ϕ-angle constraints for protein structure determination can be resolved with the knowledge of the heteronuclear ³J-couplings. In favourable cases, stereospecific assignments of glycine α-protons can be obtained by employing the experiments described here in combination with NOE data. The methods are applied to flavodoxin from Desulfovibrio vulgaris.