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991.
Mercury(II) bridge complexes of the type [Nuc-Hg-Nuc] (Nuc = thymidine or guanosine), and methylmercury(II) complexes of thymidine and guanosine of the type [CH3Hg(Nuc)], have been prepared under appropriate conditions of pH and reactant's stochiometry in acqueous soluton. The various complexes have been characterized by 1H and 13C NMR and used as probes, in competition and exchange studies, to establish the relative affinities of Hg(II) and CH3Hg(II) towards the nucleosides guanosine and thymidine. These studies have confirmed that Hg(II) and CH3Hg(II) bind to N3 of thymidine in preference to N1 of guanosine. The studies further show that reactions of mercury(II) with the nucleosides are thermodynamically controlled; the preperential binding reflects the relative stabilities of the respective complexes. 相似文献
992.
In vitro labeling of tissue sections with [3H]sulpiride has been utilized in the present study to autoradiographically localize D2-dopamine receptors in the rat brain. Preliminary biochemical studies, using slide-mounted tissue sections, were performed to define the optimal labeling conditions for this binding. Autoradiograms were generated by apposition of the labeled tissue sections to tritium-sensitive film. Specific binding sites for [3H]sulpiride were localized to the caudate-putamen, nucleus accumbens, olfactory tubercle, glomerular layer of the olfactory bulb, pituitary, laminae I and III of the entorhinal cortex, substantia nigra, lateral mammillary nucleus and the stratum-lacunosum moleculare of the hippocampus. The high selectivity of [3H]sulpiride for the D2-dopamine receptor indicates that it is a valuable tool for the autoradiographic localization and quantitation of neuroleptic receptors. 相似文献
993.
Terrance B. Murphy Norman J. Rose Verner Schomaker Alejandro Aruffo 《Inorganica chimica acta》1985,108(3):183-194
Iron(III) complexes of three aroyl hydrazones, pyridoxal isonicotinoyl hydrazone (H2pih), pyridoxal benzoyl hydrazone (H2pbh), and salicylaldehyde benzoyl hydrazone (H2sbh), were synthesized and characterized. In aqueous medium at pH 7, [Fe(pih)(Hpih)]·3H2O is formed. In acidic methanol, a 1:1 ligand-to-metal complex is formed, [FeCl2(H2pih)]Cl (1), whereas in aqueous medium at low pH cis-[FeCl2(H2pih)(H2O)]Cl·H2O (2) is formed. Compounds 1 and 2 are high-spin d5 with μeff = 5.88 μB and 5.93 μB (298 K). The crystal structures of 1 and 2 show that H2pih acts as a tridentate neutral ligand in which the phenolic and hydrazidic protons have shifted to the pyridine nitrogen atoms. The co- ordination polyhedron of 1 is ‘square’ pyramidal, whereas that of 2 is pseudo-octahedral. Compound 1 is triclinic, space group P, with a = 12.704(2) Å, b = 8.655(2) Å, c = 8.820(2) Å, α = 105.42(1)°, β = 89.87(1)°, γ = 107.60(1)°, V = 888 Å3, and Z = 2; 2 is monoclinic, space group P21/c, with a = 15.358(4) Å, b = 7.304(3) Å, c = 17.442(4) Å, β = 101.00(2)°, V = 1921 Å3, and Z = 4. 相似文献
994.
Three new saponins, melongosides N, O and P, have been isolated from the methanolic extract of seeds of Solanum melongena and their structures elucidated. Melongoside N is 3-O-[β-D-glucopyranosy l-(1 → 2)-β-D-glucopyranosyl]-26-O-(β-D-glucopyranosyl)-(25R)-5α-furostan-3β,22 α,26-triol, whereas melongoside O is 3-O-[β-D-glucopyranosyl-(1 → 2)β-D-glucopyranosyl]- 26-O-(β-D-glucopyranosyl)-(25R)-furost-5-en-3β,22α,26-triol and melongoside P is 3-O- [β-D-glucopyranosyl-(1 → 2)]-[α-L-rhamnopyranosyl-(1 → 3)]-β-D-glucopyranosyl)-26-O- (β-D-glucopyranosyl)-(25 R)-5α-furostan-3β,22α,26-triol. 相似文献
995.
Theoretical considerations predict that the cell N:P ratio at transition from nitrogen limitation to phosphorus limitation of phytoplankton growth (critical ratio, Rc) varies, as a function of population growth rate. This prediction is confirmed by experimental, data from the literature along with new experimental data for the marine, prymnesiophyte Pavlova lutheri (Droop) Green. Rc passes through a maximum at intermediate growth rates for the three phytoplankton species for which data, are available, but there is significant interspecific variability in its value. There is no theoretical or experimental evidence to support the idea that the ratio of subsistence N and P cell quotas is equal to Rc over the range of growth rates, or that the subsistence quota ratio equals the ratio of the N and P cell quotas minus a storage fraction. Examination of N:P composition ratios can be used to determine which nutrient is limiting, but cannot be used to determine relative growth rates or competitive advantage between species limited by the same nutrient. Growth rates are determined by environmental conditions and by the cell quota of the limiting nutrient, without reference to the cell quota of the non-limiting nutrient. 相似文献
996.
Algal nutrient enrichment bioassays were conducted between May 1975 and August 1978 using water samples collected from Chautauqua Lake, New York. Photosynthetic fixation rates of natural phytoplankton assemblages were enhanced by additions of phosphorus and nitrogen, although enrichment with other nutrients had no significant stimulatory effect on algal photosynthesis. Whereas phosphorus stimulated in spring and early summer, both nitrogen and phosphorus enhanced photosynthesis in midsummer and fall. Relative to the effect of phosphorus enrichment, enhancement of photosynthesis by nitrogen during the summer and fall was highest in the northern part of the lake. During the period of ice cover, photosynthesis did not appear to be limited by nutrients in that nutrient additions (P, N, Si, C, Fe, trace metals) did not enhance fixation rates. Observed temporal fluctuations in the response of the algae to P and N correlated with changes in the lake water N:P ratio as well as with temporal changes in dissolved orthophosphate and nitrate-nitrite nitrogen. The N:P ratio decreased drastically in the summer and remained at ca. 10 or less through mid-fall, suggesting that N concentrations were inadequate for the non-N-fixing phytoplankton. Studies over 3 yr indicate that states of P and N limitation undergo time-space fluctuations that occur in a cyclic pattern in the surface waters of Chautauqua Lake. 相似文献
997.
Photosynthesis and nitrogenase activity (acetylene reduction) in Oscillatoria (Trichodesmium) thiebautii were significantly reduced after its gas vesicles were collapsed by pressurizing to 6·2 MPa (62 bars). The reduction in nitrogenase activity was observed with both intact and disrupted colonies, and under both aerobic and microaerobic conditions. It is unlikely, therefore, that the reduction in either process results solely from loss of gas diffusion pathways, and may simply originate from disturbance of the cellular architecture as gas vesicles are destroyed. Since nitrogenase activity of the samples was affected by gas vesicle collapse, the process presumably resides in the gas vacuolate organism (Oscillatoria) rather than in any associated bacteria which might be present. 相似文献
998.
Nitrogen and carbon isotope responses of Chinese cabbage and chrysanthemum to the application of liquid pig manure 总被引:2,自引:0,他引:2
Sang-Sun Lim Woo-Jung Choi Jin-Hyeob Kwak Jae-Woon Jung Scott X. Chang Han-Yong Kim Kwang-Sik Yoon Soo-Myung Choi 《Plant and Soil》2007,295(1-2):67-77
The effects of the liquid pig manure (LM) used in organic farming on the natural abundance of 15N and 13C signatures in plant tissues have not been studied. We hypothesized that application of LM will (1) increase δ15N of plant tissues due to the high δ15N of N in LM as compared with soil N or inorganic fertilizer N, and (2) increase δ13C of plant tissues as a result of high salt concentration in LM that decreases stomatal conductance of plants. To test these
hypotheses, variations in the δ15N and δ13C of Chinese cabbage (Brassica campestris L.) and chrysanthemum (Chrysanthemum morifolium Ramatuelle) with two different LMs (with δ15N of +15.6 and +18.2‰) applied at two rates (323 and 646 kg N ha-1 for cabbage and 150 and 300 kg N ha-1 for chrysanthemum), or urea (δ15N = -2.7‰) applied at the lower rate above for the respective species, in addition to the control (no N input) were investigated
through a 60-day pot experiment. Application of LM significantly increased plant tissue δ15N (range +9.4 to +14.9‰) over the urea (+3.2 to +3.3‰) or control (+6.8 to 7.7‰) treatments regardless of plant species, strongly
reflecting the δ15N of the N source. Plant tissue δ13C were not affected by the treatments for cabbage (range −30.8 to −30.2‰) or chrysanthemum (−27.3 to −26.8‰). However, cabbage
dry matter production decreased while its δ13C increased with increasing rate of LM application or increasing soil salinity (P < 0.05), suggesting that salinity stress caused by high rate of LM application likely decreased stomatal conductance and
limited growth of cabbage. Our study expanded the use of the δ15N technique in N source (organic vs. synthetic fertilizer) identification and suggested that plant tissue δ13C maybe a sensitive indicator of plant response to salinity stress caused by high LM application rates. 相似文献
999.
While fertigation can increase fertilizer use efficiency, there is an uncertainly as to whether the fertilizer should be introduced
at the beginning of the irrigation or at the end, or introduced during irrigation. Our objective was to determine the effect
of different fertigation schemes on nitrogen (N) uptake and N use efficiency (NUE) in cotton plants. A pot experiment was
conducted under greenhouse conditions in year 2004 and 2005. According to the application timing of nitrogen (N) fertilizer
solution and water (W) involved in an irrigation cycle, four nitrogen fertigation schemes [nitrogen applied at the beginning
of the irrigation cycle (N–W), nitrogen applied at the end of the irrigation cycle (W–N), nitrogen applied in the middle of
the irrigation cycle (W–N–W) and nitrogen applied throughout the irrigation cycle (N&W)] were employed in a completely randomized
design with four replications. Cotton was grown in plastic containers with a volume of 84 l, which were filled with a clay
loam soil and fertilized with 6.4 g of N per pot as unlabeled and 15N-labeled urea for 2004 and 2005, respectively. Plant total dry matter (DM) and N content in N–W was significantly higher
than in N&W in both seasons, but these were not consistent for W–N and W–N–W treatments. In year 2005, a significantly higher
nitrogen derived from fertilizer (NDFF) for the whole plant was found in W–N and N–W than that in W–N–W and N&W. Fertigation
scheme had a consistent effect on total NUE: N–W had the highest NUE for the whole plant, but this was not significantly different
from W–N. Treatments W–N and W–N–W had similar total NUE, and N&W had the lowest total NUE. After harvesting, the total residual
fertilizer N in the soil was highest in W–N, lowest in N–W, but this was not significantly different from N&W and W–N–W treatments.
Total residual NO3–N in the soil in N&W and W–N treatments was 20.7 and 21.2% higher than that in N–W, respectively. The total 15N recovery was not statistically significant between the four fertigation schemes. In this study, the fertigation scheme N–W
(nitrogen applied at the beginning of an irrigation cycle) increased DM accumulation, N uptake and NUE of cotton. This study
indicates that Nitrogen application at the beginning of an irrigation cycle has an advantage on N uptake and NUE of cotton.
Therefore, NUE could be enhanced by optimizing fertilization schemes with drip irrigation. 相似文献
1000.
Altitudinal gradients of grassland carbon and nitrogen isotope composition are recorded in the hair of grazers 总被引:1,自引:0,他引:1
Tobias Tassilo Männel Karl Auerswald Hans Schnyder 《Global Ecology and Biogeography》2007,16(5):583-592
Aim The hair of grazers provides an isotopic record of environmental and nutritional signals. Here, we assess the effect of altitude on the carbon and nitrogen isotope composition of the hair of ruminant grazers and its relation to grassland vegetation, to evaluate the use of hair isotope data for ecosystem reconstruction, animal nutritional ecology and biogeochemical studies in montane environments. Location European Alps. Methods We sampled grassland vegetation (pure C3) and the hair of ruminants along an altitudinal gradient (400–2500 m), and analysed their isotope composition (δ13C and δ15N). Results were compared with published effects of altitude on 13C in C3 plants at the species level and on 15N at the community level. The study was complemented with a comparison of diet and hair isotope composition in ruminants held in confinement. Results δ13C of hair increased (c. 1.1‰ km−1) and δ15N decreased (c. 1.1‰ km−1) with altitude. The same changes occurred in local grassland vegetation, and in regional to global grassland data sets. Offsets between hair and vegetation 13C or 15N (‘diet–hair shift’) were independent of altitude. Sheep (Ovis aries) and cattle (Bos taurus) exhibited a 13C shift near +3‰, but that of goats (Capra hircus) was larger (+4.2‰) in alpine environments and in confinement. The diet–hair shift for 15N was more variable (+2.1 to +3.6‰). Main conclusions Grazer hair provides a faithful spatially and temporally integrated record of grassland isotope composition, useful for ecosystem and environment reconstruction. The effect of altitude on hair 15N is important for studies of trophic relationships: an altitude shift of 2000 m produced the same effect in hair 15N as would a shift from an animal tissue‐based to a plant‐based diet. The similarity of altitude effects on δ13C of individual plant species, vegetation and hair indicates that the effect of altitude on species‐level ‘intrinsic water use efficiency’ scales up linearly to the community and landscape level. 相似文献