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1.
Carbon isotope composition in relation to leaf gas exchange and environmental conditions in Hawaiian Metrosideros polymorpha populations 总被引:3,自引:0,他引:3
Summary Carbon isotope composition, photosynthetic gas exchange, and nitrogen content were measured in leaves of three varieties of Metrosideros polymorpha growing in sites presenting a variety of precipitation, temperature and edaphic regimes. The eight populations studied could be divided into two groups on the basis of their mean foliar 13C values, one group consisting of three populations with mean 13C values ca.-26 and another group with 13C values ca.-28. Less negative 13C values appeared to be associated with reduced physiological availability of soil moisture resulting from hypoxic conditions at a poorly drained high elevation bog site and from low precipitation at a welldrained, low elevation leeward site. Gas exchange measurements indicated that foliar 13C and intrinsic wateruse efficiency were positively correlated. Maximum photosynthetic rates were nearly constant while maximum stomatal conductance varied substantially in individuals with foliar 13C ranging from-29 to-24. In contrast with the patterns of 13C observed, leaf nitrogen content appeared to be genetically determined and independent of site characteristics. Photosynthetic nitrogenuse efficiency was nearly constant over the range of 13C observed, suggesting that a compromise between intrinsic water- and N-use efficiency did not occur. In one population variations in foliar 13C and gas exchange with leaf cohort age, caused the ratio of intercellular to atmospheric partial pressure of CO2 predicted from gas exchange and that calculated from 13C to be in close agreement only in the two youngest cohorts of fully expanded leaves. The results indicated that with suitable precautions concerning measurement protocol, foliar 13C and gas exchange measurements were reliable indicators of potential resource use efficiency by M. polymorpha along environmental gradients. 相似文献
2.
Evanilde Benedito cecilio Alexandre Leandro pereira Cássia Mônica sakuragui 《Environmental Biology of Fishes》2004,71(4):313-320
In this paper we analysed autotrophic sources of the carbon (
13C) and the trophic position (
15N) of Leporinus friderici in the influence area of Corumbá Reservoir, Brazil. We collected samples of muscles of fish from different sizes riparian vegetation, C4 grasses, zooplankton, periphyton and particulate organic carbon (POC). There were significant differences for the carbon isotope proportion found in muscles of L.friderici in the different size groups analysed. The highest values of
13C recorded for middle sized individuals is attributed to the large contribution of C4 plants in their diet. Small individuals sampled upstream also receive similar contribution from C4 plants. In contrast the same size group sampled downstream from the reservoir, has a much smaller of C4 plants. The
13C negative character of small individuals from downstream is due to the larger contribution of C3 plants (except periphyton). At larger sizes we found intermediate
13C values. The
15N proportions we found for each size group were not significantly different, however we found decreasing mean values with increasing size. The trophic level calculated from the dietary data was higher than that found with the
13C concentration in the muscle, except for small individuals, when the values were equal. 相似文献
3.
The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in 15N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in 15N was found in the mysid. The annual averages of 15N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of15N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of 15N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year. 相似文献
4.
This report describes a method for quantifying -endotoxin contents in spray-dried preparations ofBacillus thuringiensis strain GC-91. -Endotoxin is solubilized in the pro-toxin form and separated from other soluble compounds by ion exchange chromatography. The method does not discriminate between the different -endotoxins produced by strain GC-91. It is suitable for quality control, since -endotoxin concentrations found in different preparations correlate inversely with the LC 50 in bioassays on artificial diet against freshly hatched larvae ofSpodoptera littoralis. A typical batch of spray-dried material contains 1.22%±0.08% -endotoxin. The method is most accurate with preparations containing 0.5 to 2.0% toxin, for which triplicate estimations give standard errors close to±0.2%. 相似文献
5.
Summary The 13C values of submerged aquatic plants from contrasting but relatively defined habitats, and the 13C values of emergent, floating and submerged leaves of dimorphic aquatic plants, were measured. In many instances the 13C values of dissolved inorganic carbon in the water were also measured. Plant 13C values in the vicinity of-40 to-50 were found in rapidly flowing spring waters with carbonate 13C values of-16 to-21, consistent with the notion that species such as Fontinalis antipyretica almost exclusively assimilate free CO2 via RuP2 carboxylase. Plant 13C values in the vicinity of-10 to-15 in sluggish water with carbonate 13C values of about-5 were observed, consistent with the notion that boundary layer diffusion and/or HCO3
- uptake may determine the 13C value of submerged aquatic plants in these circumstances. Comparisons of 13C values of the same or related species growing in waters of similar carbonate 13C value but different flow rates confirmed this view; more negative 13C values were frequently associated with plants in fast moving water. In Britain, but not in Finland, the 13C values of submerged leaves of dimorphic plants were almost invariably more negative than in aerial leaves. The 13C value of carbonate from chalk streams and in acid springs indicate substantial inputs of respiratory CO2, as opposed to atmospheric carbon. The contributions of these variations in 13C of the carbon source, and of isotope fractionation in diffusion, to the 13C value of submerged parts of dimorphic plants is discussed. 相似文献
6.
Takusaburo Ebina Yoshiaki Fujimiya Tomohiro Yamaguchi Naoko Ogama Hiroko Sasaki Noriko Isono Youichi Suzuki Ryuichi Katakura Kazuya Tanaka Kinya Nagata Shoichi Takano Keiji Tamura Kazuko Uno Tsunataro Kishida 《Biotherapy》1998,11(4):241-253
Adoptive immunotherapy using MHC-nonrestricted-lymphocytes, peripheral blood T cells and NK cells was devised. Peripheral blood mononuclear cells (3 x 107) were selected by immobilization to anti-CD3 monoclonal antibody for 4 days and cultured for 2 weeks in the presence of IL-2. Thereafter they were reactivated by 500 U/ml of IFN- and 1000 U/ml of IL-2 for 1 hour. Enhancement of NK and LAK activities was confirmed. Peripheral blood T cells proliferated in response to immobilized anti-CD3 antibody (3% to 30%). Approximately 6 x 109 BRM-activated killer (BAK) cells composed of CD56+ T cells and CD56+ NK cells, were dispensed to cancer patients via intravenous drip infusion. Nine patients were treated with BAK cells every 2 weeks or every month on an outpatient basis. During the course of adoptive immunotherapy, the crossed affinity immunoelectrophoresis (CAIE) pattern of serum immunosuppressive acidic protein (IAP) was analysed. Both the production and glycosylation pattern of IAP is changed in response to tumor enlargement and may therefore act as a marker of the disease progression. During the course of BAK therapy, the glycosylation IAP pattern of 6 patients changed from tumor (T) to normal (N). In addition, the performance status of all patients was maintained at 90–100% of the Karnofsky scale and any side effects including fever were not observed during treatments with BAK cells. Moreover, the overall quality of life (QOL) of the patients, scored at the Face scale was favorable. In addition, blood levels of activated T cells producing IFN- were assayed as an indication marker of BAK therapy. The normal range of IFN- producing T cells comprised 6.9 ± 0.9% of peripheral blood mononuclear cells (PBMC), according to a single cell FACScan analyses of PBMCs derived from normal individuals. IFN- producing T cells of Patients No. 8 and 9, who received extensive chemotherapy before initiation of BAK therapy, comprised only 0.2% and 2% of PBMC, respectively. These patients died 3 and 6 months after beginning BAK therapy. Peripheral blood T cells of Patients Nos. 1–7 proliferated in response to immobilized anti-CD3 antibody and the frequency of IFN- producing T cells in PBMC preparation of these patients were over 3% before initiation of BAK therapy. Since our data show a positive correlation between survival time and initial T cell counts, a low frequency of these cells may contraindicate BAK therapy. 相似文献
7.
The measurement of natural 15N abundance is a well-established technique for the identification and quantification of biological N2 fixation in plants. Associative N2 fixing bacteria have been isolated from sugarcane and reported to contribute potentially significant amounts of N to plant growth and development. It has not been established whether Australian commercial sugarcane receives significant input from biological N2 fixation, even though high populations of N2 fixing bacteria have been isolated from Australian commercial sugarcane fields and plants. In this study, 15N measurements were used as a primary measure to identify whether Australian commercial sugarcane was obtaining significant inputs of N via biological N2 fixation. Quantification of N input, via biological N2 fixation, was not possible since suitable non-N2 fixing reference plants were not present in commercial cane fields. The survey of Australian commercially grown sugarcane crops showed the majority had positive leaf 15N values (73% >3.00, 63% of which were >5.00), which was not indicative of biological N2 fixation being the major source of N for these crops. However, a small number of sites had low or negative leaf 15N values. These crops had received high N fertiliser applications in the weeks prior to sampling. Two possible pathways that could result in low 15N values for sugarcane leaves (other than N2 fixation) are proposed; high external N concentrations and foliar uptake of volatilised NH3. The leaf 15N value of sugarcane grown in aerated solution culture was shown to decrease by approximately 5 with increasing external N concentration (0.5–8.0 mM), with both NO3
– and NH4
+ nitrogen forms. Foliar uptake of atmospheric NH3 has been shown to result in depleted leaf 15N values in many plant species. Acid traps collected atmospheric N with negative 15N value (–24.45±0.90) from above a field recently surface fertilised with urea. The 15N of leaves of sugarcane plants either growing directly in the soil or isolated from soil in pots dropped by 3.00 in the same field after the fertiliser application. Both the high concentration of external N in the root zone (following the application of N-fertilisers) and/or subsequent foliar uptake of volatilised NH3 could have caused the depleted leaf 15N values measured in the sugarcane crops at these sites. 相似文献
8.
T-cell clones expressing the T-cell receptor (Tcr) were generated from peripheral blood lymphocytes (PBLs) and from a thymus sample. In the panel of ten thymus-derived clones, four Tcr phenotypes [as defined by the reaction of monoclonal antibodies (mAbs) directed against known V and V regions] were identified. All the clones lacked expression of the V3 V region, while seven clones were V1+ . V1 was found in combination with V9 or with undefined VVregions. In addition, two other Tcr phenotypes were identified on these clones: V9+ V1– V3– and V9– V1– V3– One of the clones expressed CD4 and another was CD8positive. The remaining clones were CD4– CD8–. In the panel of 76 PBL-derived, Tcr-bearing clones, five Tcr phenotypes could be identified. In contrast to the thymus-derived clones, 30% of the clones were V3+ whereas V1 was expressed by a minority of the clones only. One clone was CD4-positive and approximately 30% of the clones were CD8-positive. Four of the five mAb-defined Tcr phenotypes could be identified on both thymus and PBL-derived T-cell clones. However, biochemical analysis of the Tcrs demonstrates differences in the usage of Ct- and C2-encoded y chains by T cells derived from the thymus and PBLs. The results therefore indicate that, at the clonal level, similarities and differences exist between the Tcr repertoires expressed in the thymus and by PBLs. Furthermore, they indicate that combinatorial Tcr heterogeneity is larger than has so far been described. The receptor diversity, combined with the potential of Tcr+ cells to express CD4 or CD8, indicates that these cells are a heterogeneous population that might mediate a number of immune functions. 相似文献
9.
Iren Vollenweider Eva Vrbka Walter Fierz Peter Groscurth 《Cancer immunology, immunotherapy : CII》1993,36(5):331-336
Effector-target conjugates, formed by coincubation of lymphokine-activated killer (LAK) cells with either K562 or Daudi cells, were separated from single cells by Percoll sedimentation. The occurrence of various CD molecules (CD3, CD56, CD57, CD16, /-TCR) was compared in both fractions. Only LAK cells expressing the / T cell receptor (TCR) were found in a significantly increased percentage in fractions containing conjugates indicating that /-TCR+ LAK cells were preferably bound to target cells at the time of separation. In order to determine whether /-TCR+ LAK cells also show a preferred killing activity against the targets, cultures enriched with or depleted of /-TCR+ cells were established. Against K562 cells, /-TCR+-enriched cultures showed a greatly reduced killing activity compared to LAK bulk cultures or cultures depleted of /-TCR+ cells. Using Daudi cells as targets the enriched fraction revealed a slightly increased killing activity compared to bulk cultures or depleted fractions. Preincubation of /-TCR+ LAK cells with anti-/ or anti-CD3 mAb resulted in a distinct increase of the killing activity against K562 cells, but in only a slightly enhanced activity against Daudi cells. It is postulated that /-TCR+ LAK cells use the same adhesion mechanism for both targets but that only Daudi cells express a specific ligand for the /-TCR. Occupation of the /-TCR/CD3 complex by mAb, however, seems to substitute for the absent epitope on K562 cells by eliciting stimulatory signals in /-TCR+ LAK cells which, in combination with the binding stimulus, trigger cytolytic activity.This work was supported by the Hartmann-Müller Foundation, Zürich 相似文献
10.
Three species of the reef coral genus Madracis display skeletal isotopic characteristics that relate to depth, colony topography, and consequently to coral physiology. The joint interpretation of skeletal 13C and 18O provides information on the ecological plasticity and adaptation to depth of a coral species. Isotopic results are most easily understood in terms of kinetic effects, which reduce both 18O and 13C below isotopic equilibrium values, and metabolic effects, which only influence the skeletal 13C. Madracis mirabilis is adapted to depths shallower than 20 m, and shows the greatest range in kinetic effects and the strongest metabolic 13C enrichments caused by symbiont photosynthesis. Madracis formosa lives deeper than 40 m, and shows a reduced range of kinetic effects and relatively weak metabolic 13C enrichments. Madracis pharensis inhabits depths from 5 to >60 m, and does not attain the strength of kinetic effects of either of the other two species, apparently because it is not quite as well adapted to rapid growth at either extreme. 相似文献
11.
Mean oxygen-isotope signatures in Porites spp. corals: inter-colony variability and correction for extension-rate effects 总被引:1,自引:1,他引:0
The assessment of inter-colony variability in the mean skeletal 18O signatures of modern Porites spp. corals is a prerequisite for the estimation of past mean climate conditions based on fossil colonies. Here we show that the mean 18O signatures of Porites spp. corals from the northern end of the Gulf of Aqaba (Red Sea) with mean extension rates between 0.2 and 1.5 cm/year can have an inter-colony variability as large as 1.28. At extension rates of less than 0.6 cm/year the mean coral 18O values of the individual colonies are strongly dependent on the mean extension rate, with increasingly higher 18O values corresponding to decreasing extension rate. This suggests that extension-rate-related kinetic isotope disequilibrium effects are responsible for a large proportion of the inter-colony differences in the mean coral 18O signatures. A correction procedure for these effects based on the relationship between mean 18O values and mean extension rate reduces the variability of mean coral 18O values among the individual colonies to 0.43. Although certainly not perfect, the correction procedure enables a better assessment of mid-Holocene climate conditions at this location based on Porites spp. with mean extension rates of less than 0.6 cm/year. 相似文献
12.
In order to assess the ability of Porites corals to accurately record environmental variations, high-resolution (weekly/biweekly) coral 18O records were obtained from four coral colonies from the northern Gulf of Aqaba, which grew at depths of 7, 19, 29, and 42 m along one transect. Adjacent to each colony, hourly temperatures, biweekly salinities, and monthly 18O of seawater were continuously recorded over a period of 14 months (April 1999 to June 2000). Contrary to water temperature, which shows a regular and strong seasonal variation and change with depth, seawater 18O exhibits a weak seasonality and little change with depth. Positive correlations between seawater 18O and salinity were observed. The two parameters were related to each other by the equation 18O
Seawater
(, VSMOW) = 0.281 × Salinity – 9.14. The high-resolution coral 18O records from this study show a regular pattern of seasonality and are able to capture fine details of the weekly average temperature records. They resolve more than 95% of the weekly average temperature range. On the other hand, attenuation and amplification of coral seasonal amplitudes were recorded in deep, slow-growing corals, which were not related to environmental effects (temperature and/or seawater 18O) or sampling resolution. We propose that these result from a combined effect of subannual variations in extension rate and variable rates of spine thickening of skeletal structures within the tissue layer. However, no smoothing or distortion of the isotopic signals was observed due to calcification within the tissue layer in shallow-water, fast-growing corals. The calculations from coral 18O calibrations against the in situ measurements show that temperature (T) is related to coral 18O (
c
) and seawater 18O (
w
) by the equation T (°C) = –5.38 (
c
–
w
) –1.08. Our results demonstrate that coral 18O from the northern Gulf of Aqaba is a reliable recorder of temperature variations, and that there is a minor contribution of seawater 18O to this proxy, which could be ignored. 相似文献
13.
G. G. Chestukhina S. A. Tyurin L. I. Kostina A. L. Osterman I. A. Zalunin O. A. Khodova V. M. Stepanov 《Journal of Protein Chemistry》1990,9(4):501-507
N-Terminal domain (65 kD) of -endotoxin produced byBacillus thuringiensis ssp.alesti, as shown by limited proteolysis, consists of two subdomains of molecular mass 30 and 33 kD that correspond, respectively, to conservative and variable regions of the -endotoxin primary structure. Furthermore, proteolysis of these subdomains leads to their conversion into at least two fragments of molecular mass 10 kD stable to proteinase action. Such a pattern of molecular organization appears to be common for several structurally related -endotoxins that belong to thekurstaki group. Entomicidal protein produced by ssp.israelensis (70 kD), which differs strongly fromalesti and otherkurstaki group -endotoxins, retains a similar type of molecular organization and consists of two subdomains with molecular mass of 35 kD. Apparently, the characteristic pattern of the -endotoxins' molecular structure reflects separation of functions (e.g., host recognition and toxicityper se) between domains and subdomains of these proteins. 相似文献
14.
Mengli Cai Ying Huang Jianhua Liu Ramaswamy Krishnamoorthi 《Journal of biomolecular NMR》1995,6(2):123-128
Summary Three different conformations of proline rings in a protein in solution, Up, Down and Twist, have been distinguished, and stereospecific assignments of the pyrrolidine -, - and -hydrogens have been made on the basis of 1H-1H vicinal coupling constant patterns and intraresidue NOEs. For all three conformations, interhydrogen distances in the pairs -3, 3-3, 2-2, 2-2, and 3-3 (2.3 Å) are shorter than those in the pairs -2, 2-3, 3-2, 2-3, and 3-2 (2.7–3.0 Å), resulting in stronger NOESY cross peaks. For the Up conformation, the 3-2 and 2-3 spin-spin coupling constants are small (<3 Hz), and weak cross peaks are obtained in a short-mixing-time (10 ms) TOCSY spectrum; all other vicinal coupling constants are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. For the Down form, the -2, 2-3, and 3-2 vicinal coupling constants are small, leading to weak TOCSY cross peaks; all other couplings again are in the range 5–12 Hz, and result in medium to strong TOCSY cross peaks. In the case of a Twist conformation, dynamically averaged coupling constants are anticipated. The procedure has been applied to bovine pancreatic trypsin inhibitor and Cucurbita maxima trypsin inhibitor-V, and ring conformations of all prolines in the two proteins have been determined. 相似文献
15.
Summary Two double heterozygous 0/0 thalassemic sibs of Mexican descent were studied. The father had a 0/0 genotype, while the mother, one sib and several maternal relatives were 0/0 heterozygotes. Parental consanguinity and an apparently low frequency of thalassemia among Mexicans suggested a possible common origin of both 0 and 0 genes. A hypothesis to explain such a possibility is proposed on the basis of a partial mispairing between 0 and genes followed by a crossing-over which would results in a 0 recombinant gene. This hypothesis could also be extended to explain the 22 gluala, 22 alaglu and 116 arghis Hb variants as recombinants from double crossing-over between and mispaired genes for which the name interstitial-Lepore is proposed. 相似文献
16.
Changes in carbon isotope composition(13C) and leaf morphology associated withvegetative phase change were monitored in Metrosiderosexcelsa Sol. ex Gaertn. (family Myrtaceae). Plants of threeontogenetic states were used: juvenile seedlings, micropropagated plants in arejuvenated state, and reproductively mature plants bearing leaves with adultcharacteristics. The effects of temperature regime (32/24 °C,24/16 °C, and 16/8 °C day/night) and plantarchitecture (branched and single-stemmed plants) were studied in two separateexperiments. Although both juvenile and rejuvenated plants exhibited juvenileleaf morphology at the start of the experiments, there was no differencebetweenleaf 13C in these plants and that in adultplantsat this time (mean ca. –27%). Vegetative phase change occurred injuvenileand rejuvenated plants grown at 24/16 °C, and there was acorresponding increase in leaf 13C (from ca.–27% to –23%) in these two groups of plants. Leaf13C in adult plants remained relatively constant(ca. –26%) at 24/16 °C. There was little change in leaf13C in all plant states maintained at 32/24°C or 16/8 °C, and vegetative phase change didnot occur in juvenile and rejuvenated plants grown under these two temperatureregimes. Rejuvenated plants grown in a greenhouse also exhibited a progressivedevelopment of adult leaf morphology, accompanied by an increase in leaf13C, an effect that was more pronounced insingle-stemmed (from –26.4% to ca. –24%) than in branched plants. Itis suggested that increasing 13C in juvenile andrejuvenated plants undergoing phase change is a result of reduced sink strengthin single-stemmed plants, and to a lesser extent within each branch of branchedplants, causing reduced stomatal conductance and photosynthesis. 相似文献
17.
Microanalysis of C and O isotopes of azooxanthellate and zooxanthellate corals by ion microprobe 总被引:1,自引:0,他引:1
We have determined the 18O and 13C values of azooxanthellate (Lophelia pertusa) and zooxanthellate (Porites lutea) corals at a micrometer scale using an ion microprobe (SIMS—secondary ion mass spectrometry). In P. lutea, centers of calcification are small (10 to 15 m) and difficult to locate during measurements. In L. pertusa, they are large (50 m) and arranged in lines of centers of calcification. Our results show that centers of calcification in L. pertusa have a restricted range of variation in 18O [-2.8±0.3 (PDB)], and a larger range in 13C [14.3 to 10.9 (PDB)]. Surrounding skeletal fibers exhibit large isotopic variation both for C and O (up to 12), and 13C and 18O are positively correlated. The C and O isotopic compositions of the center of calcification deviate from this linear trend at the lightest 18O values of the surrounding fibers. Ion microprobe results on P. lutea demonstrate also a large range of variation for the 18O values (up to 10). No correlation is found with C isotopes that exhibit, in comparison with L. pertusa, a small range of variation (2). This variation of 18O at a micrometer scale is probably the result of two processes: (1) an isotopic equilibrium calcification with 1 pH unit variation in the calcification fluid as indicated by direct measurements of coelenteron pH in the coral Galaxea fascicularis (Al-Horani et al. 2003) and (2) a kinetic fractionation. The 13C apparent disequilibrium in P. lutea may be the result of mixing between metabolic CO2 (respiration) and dissolved inorganic carbon (DIC) coming directly from seawater. 相似文献
18.
Zyakun A. M. Kosheleva I. A. Zakharchenko V. N. Kudryavtseva A. I. Peshenko V. A. Filonov A. E. Boronin A. M. 《Microbiology》2003,72(5):592-596
The study deals with a comparative analysis of the relative abundances of the carbon isotopes 12C and 13C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (13C = –44.6 ± 0.2) were characterized by the values of 13CCO
2 = –50.2 ± 0.4, 13Cbiom = –46.6 ± 0.4, and 13Cexo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (13C = –21 ± 0.4) were characterized by the isotope effects 13CCO
2 = –24.1 ± 0.4, 13Cbiom = –19.2 ± 0.4, and 13Cexo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed. 相似文献
19.
Stable isotope analyses are often used to calculate relative contributions of multiple food sources in an animals diet. One prerequisite for a precise calculation is the determination of the diet-tissue fractionation factor. Isotopic ratios in animals are not only affected by the composition of the diet, but also by the amount of food consumed. Previous findings regarding the latter point are controversial. As stable isotope analyses have often been used to investigate aquatic food webs, an experiment with carp (Cyprinus carpio L.) was carried out to test the influence of the feeding level and individual metabolic rate on 13C and 15N values of the whole body. After an initial phase, 49 carp were assigned randomly to four groups and fed the same diet at different levels for 8 weeks. For 15 fish, the energy budget was determined by indirect calorimetry. Feed and individual fish were analysed for their proximate composition, gross energy content and 13C and 15N values. 13C and 15N values differed significantly at different feeding levels. While 13C values of the lipids and 15N values decreased with increasing feeding rate, 13C values of the lipid-free matter showed a non-linear pattern. Data obtained from fish held in the respirometric system revealed a relationship between 13C values and the percentage retention of metabolizable energy. Our results show that reconstructing the diets of fish from the isotopic ratios when the feeding level and individual metabolic rates are unknown would introduce an error into the data used for back-calculation of up to 1 for both 13C and 15N values and may have substantial effects on the results of calculated diets. As other workers have pointed out, the development and application of stable isotopes to nutritional ecology studies is a field in its infancy and gives rise to erroneous, misleading results without nutritional, physiological and ecological knowledge. 相似文献
20.
The selfassociation of N6,N9-dimethyladenine and N6-dimethyl-N9-ethyladenine has been studied by means of NMR technique. The thermodynamic quantities have been calculated using an isodesmic NMR model with three NMR parameters (the monomer shift M and two complex shifts
2 and
3).The dependence of the thermodynamic quantities on the NMR parameters is discussed. Special attention is given to the determination of
M
and its temperature dependence.Calculations with
3=2·
2 and
M
taken independently of temperature result in an average entropy
S
=–17.9±1.8 e.u. for N6,N9-dimethyladenine and
S
=–16.7±1.7 e.u. for N6-dimethyl-N9-ethyladenine and in an average enthalpy H=–7.2±0.6 kcal· mol–1 for both substances investigated.Part of the Ph.D. Theses of W. Schimmack and H. Sapper.Dedicated to Professor Dr. A. Schraub on the occasion of his 65th birthday. 相似文献