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1.
Here we present the within-site, seasonal, and interannual variations of the carbon (δ13C) and nitrogen (δ15N) isotope ratios of leaves, wood, bark and litter from four sites in the Amazon region, Brazil. Samples were collected in Manaus (3° 06′07′′ S; 60°01′30′′ W), Ji-Paraná (10°53′07′′ S; 61°57′06′′ W), and Santarém (2°26′35′′ S; 54°42′30′′ W) with mean annual precipitation of 2207, 2040 and 1909 mm respectively. The overall average for all leaf samples was for δ13C and for δ15N (n=756). The leaf δ values at these sites were often but not always statistically distinct from each other. The δ13C values varied from to . Pronounced differences in δ13C values occurred with height associated with differences in forest structure. The δ13C of leaf dry matter showed seasonal variations associated with the length of the dry season, despite the fact that total annual precipitation was similar among the studied sites. Leaf δ15N values ranged from to a maximum value of , and the Santarém sites showed more enriched values than Manaus and Ji-Paraná sites. No seasonal variation was detected in the δ15N of leaves, but significant differences were observed among sites and with changes in canopy height. The isotope ratio data are consistent with our current understanding of the roles of light, water availability, and recycling of soil-respired CO2 influences on δ13C and consistent with our understanding that an open nitrogen cycle can lead to high δ15N values despite a significant number of legumes in the vegetation.  相似文献   

2.
Pan BS  Wolyniak CJ  Brenna JT 《Amino acids》2007,33(4):631-638
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 Δ15Np − s = δ15Npeptide − δ15Nsidechain = +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.  相似文献   

3.
Biocycling of sulfur (S) has been proposed to play an important role in the recovery of ecosystems following anthropogenic S deposition. Here, we investigated the importance of the humus layer in the biocycling of S in three forested catchments in the Gårdsjön area of southwestern Sweden with differing S inputs and S isotope signature values. These experimental sites consisted of two reference catchments and the Gårdsjön roof experiment catchment (G1), where anthropogenic deposition was intercepted from 1991 until May 2002 by a roof placed over the entire catchment area. Under the roof, controlled levels of deposition were applied, using a sprinkler system, and the only form of S added was marine SO42− with a δ of +19.5‰.We installed ion exchange resin bags at the interface between the humus layer and mineral soil at each of the catchments to collect SO42− passing through the humus. The resin bags were installed on four occasions, in 1999 and 2000, covering two summer and two winter periods. The ions collected by each bag during these sampling periods were then eluted and their δ values and SO42− concentrations determined. The most striking result is that the average δ value in the resin bags was more than 12‰ lower compared to that of the sprinkler water in the G1 roof catchment. There was no increasing trend in the isotope value in the resin bag SO42− despite that the roof treatment has been on-going for almost 10 years; the average value for all resin bags was +7.1‰. The highest δ values found in the G1 roof catchment were between +11‰ and +12‰. However, these values were all obtained from resin bags installed at a single sampling location. Throughfall and resin bag δ values were more similar in the two reference catchments: about +7.5‰ in both cases. There was, however, an increase in resin bag δ values during the first winter period, from about +7‰ to +9‰. The resin bag δ value was linearly and positively related (r2 = 0.26, p < 0.001) to the amount of SO42− extracted from the resin bags, if relatively high amounts (>50 mmol m−2) were excluded. High amounts of resin bag SO42− seemed to be related to groundwater inputs, as indicated by the δ value. Our results suggest that rapid immobilization of SO42− into a large organic S pool may alter the S isotope value and affect the δ values measured in the mineral soil and runoff.  相似文献   

4.
Four whole-lake inorganic 13C addition experiments were conducted in lakes of differing trophic status. Inorganic 13C addition enriched algal carbon in 13C and changed the C-DOC by +1.5‰ to +9.5‰, depending on the specific lake. This change in C-DOC represented a significant input of algal DOC that was not completely consumed by bacteria. We modeled the dynamics in C-DOC to estimate the fluxes of algal and terrestrial carbon to and from the DOC pool, and determine the composition of the standing stock. Two experiments in lightly stained, oligotrophic lakes indicated that algal production was the source of about 20% of the DOC pool. In the following year, the experiment was repeated in one of these lakes under conditions of nutrient enrichment, and in a third, more humic lake. Algal contributions to the DOC pool were 40% in the nutrient enriched lake and 5% in the more humic lake. Spectroscopic and elemental analyses corroborated the presence of increased algal DOC in the nutrient enriched lake. Natural abundance measurements of the C of DOC in 32 lakes also revealed the dual contributions of both terrestrial and algal carbon to DOC. From these results, we suggest an approach for inferring the contribution of algal and terrestrial DOC using easily measurable parameters.  相似文献   

5.
The electrochemical potential differences for potassium, between excised barley (Hordeum vulgare L.) roots and external media containing 0.05 mM KCl+0.5 mM CaSO4, were determined over a 4-h period during which initially low-K+ roots accumulated K+ by pretreatment in 50 mM KCl plus 0.5 mM CaCl2. This pretreatment resulted in increased internal [K+], decreased K+ influx (as measured from 0.05 mM KCl+0.5 mM CaSO4) and decreased values of . These observations indicate that the decline of K+ influx associated with increased internal K+ concentration cannot be accounted for by passive adjustment to the electrochemical gradient for this ion.  相似文献   

6.
N saturation induced by atmospheric N deposition can have serious consequences for forest health in many regions. In order to evaluate whether foliar may be a robust, regional-scale measure of the onset of N saturation in forest ecosystems, we assembled a large dataset on atmospheric N deposition, foliar and root and N concentration, soil C:N, mineralization and nitrification. The dataset included sites in northeastern North America, Colorado, Alaska, southern Chile and Europe. Local drivers of N cycling (net nitrification and mineralization, and forest floor and soil C:N) were more closely coupled with foliar than the regional driver of N deposition. Foliar increased non-linearly with nitrification:mineralization ratio and decreased with forest floor C:N. Foliar was more strongly related to nitrification rates than was foliar N concentration, but concentration was more strongly correlated with N deposition. Root was more tightly coupled to forest floor properties than was foliar . We observed a pattern of decreasing foliar values across the following species: American beech>yellow birch>sugar maple. Other factors that affected foliar included species composition and climate. Relationships between foliar and soil variables were stronger when analyzed on a species by species basis than when many species were lumped. European sites showed distinct patterns of lower foliar , due to the importance of ammonium deposition in this region. Our results suggest that examining values of foliage may improve understanding of how forests respond to the cascading effects of N deposition.  相似文献   

7.
N saturation induced by atmospheric N deposition can have serious consequences for forest health in many regions. In order to evaluate whether foliar may be a robust, regional-scale measure of the onset of N saturation in forest ecosystems, we assembled a large dataset on atmospheric N deposition, foliar and root and N concentration, soil C:N, mineralization and nitrification. The dataset included sites in northeastern North America, Colorado, Alaska, southern Chile and Europe. Local drivers of N cycling (net nitrification and mineralization, and forest floor and soil C:N) were more closely coupled with foliar than the regional driver of N deposition. Foliar increased non-linearly with nitrification:mineralization ratio and decreased with forest floor C:N. Foliar was more strongly related to nitrification rates than was foliar N concentration, but concentration was more strongly correlated with N deposition. Root was more tightly coupled to forest floor properties than was foliar . We observed a pattern of decreasing foliar values across the following species: American beech>yellow birch>sugar maple. Other factors that affected foliar included species composition and climate. Relationships between foliar and soil variables were stronger when analyzed on a species by species basis than when many species were lumped. European sites showed distinct patterns of lower foliar , due to the importance of ammonium deposition in this region. Our results suggest that examining values of foliage may improve understanding of how forests respond to the cascading effects of N deposition.  相似文献   

8.
The vertical distribution of dissolved greenhouse gases (CH4,CO2 and N2O), NO ,and 13C of CO2 in Lake Biwa during a stagnantperiod was precisely determined. CO2 as well as NO was accumulated in the hypolimnion, whereas NO and CH4concen\-trations were generally higher in theepilimnion than in the hypolimnion. In August, NO andCH4 were ephemerally accumulated at the thermocline. Theconcentration of CH4 always exceeded equilibrium with respectto air/water exchange. N2O was rather uniformly distributed inboth time and space, and remained near equilibrium with respect toair/water exchange. All of these observations are similar to otherstratified, oligotrophic lakes, in which the hypolimnia were welloxygenated. The 13C of CO2 became morenegative with increasing depth, and showed a strong negativecorrelation with apparent oxygen utilization. From the data, the 13Cvalue of organic matter decomposed into CO2 inthe hypolimnion was calculated by isotope mass-balance, and found tobe in a similar range to 13C of phytoplankton and benthic algaeand distinctively higher than 13C of both terrestrial andsedimentary organic matters. This suggests that autochthonous organicmatter was the major source of CO2.  相似文献   

9.
Interactions of structurally dissimilar anionic compounds with the plasma membrane of HEK293 cells were analyzed by patch clamp and electrorotation. The combined approach provides complementary information on the lipophilicity, preferential affinity of the anions to the inner/outer membrane leaflet, adsorption depth and transmembrane mobility. The anionic species studied here included the well-known lipophilic anions dipicrylamine (DPA), tetraphenylborate (TPB) and [W2(CO)10(S2CH)], the putative lipophilic anion and three new heterocyclic W(CO)5 derivatives. All tested anions partitioned strongly into the cell membrane, as indicated by the capacitance increase in patch-clamped cells. The capacitance increment exhibited a bell-shaped dependence on membrane voltage. The midpoint potentials of the maximum capacitance increment were negative, indicating the exclusion of lipophilic anions from the outer membrane leaflet. The adsorption depth of the large organic anions DPA, TPB and increased and that of W(CO)5 derivatives decreased with increasing concentration of mobile charges. In agreement with the patch-clamp data, electrorotation of cells treated with DPA and W(CO)5 derivatives revealed a large dispersion of membrane capacitance in the kilohertz to megahertz range due to the translocation of mobile charges. In contrast, in the presence of TPB and no mobile charges could be detected by electrorotation, despite their strong membrane adsorption. Our data suggest that the presence of oxygen atoms in the outer molecular shell is an important factor for the fast translocation ability of lipophilic anions.  相似文献   

10.
During the last 60 years, pollution of the groundwater with has greatly increased in many parts of Europe, as a consequence of excessive use of manure and synthetic fertilisers. Monitoring of groundwater-fed wetlands indicated that sediments with high concentrations had the lowest Fe and concentrations in the pore water. A comparison of two restored open water fens, differing in supply via the groundwater, indicated that the redox potential and the sulphate ( ) reduction rate were lower when the groundwater contained not only but also high concentrations. The lower reduction rates in the -rich open water fen were associated with lower concentrations and the presence of plant species characteristic of clear water. In contrast, the higher reduction rates in the -poor open water fen were associated with very high concentrations and massive development of plant species characteristic of eutrophic environments. Investigations at -rich seepage sites in black alder carrs, showed that high concentrations in the pore water caused chlorosis in the alder carr vegetation, due to lower availability of Fe in the pore water and less Fe uptake by the plants. Experimental desiccation of sediments proved that the -rich seepage sites contained no oxidisable FeS x , contrary to -poor locations, which became acidified and mobilised extremely high amounts of due to FeS x oxidation. A laboratory experiment showed that addition to sediments led to reduced releases of Fe, and S2–, very likely due to the oxidation of reduced Fe and S compounds. Overall, the results confirmed that is an energetically more favourable electron acceptor in anaerobic sediments than Fe and , and that high loads function as a redox buffer, preventing reduction of Fe and . Limited reduction prevents S2– -mediated mobilisation of from Fe- complexes. At a higher redox potential, reduced Fe, including FeS x , was oxidised, increasing the content of Fe(III) capable of binding . This prevented increased availability and the concomitant massive development of plant species characteristic of eutrophic environments.  相似文献   

11.
R Glasser  E J Gabbay 《Biopolymers》1968,6(2):243-254
The synthesis of spermine derivatives (II), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_1 {\rm R}_{\rm 2} {\rm R}_{\rm 3} \mathop {\rm N}\limits^ + \left( {{\rm CH}_2 } \right)_3 \mathop {\rm N}\limits^ + {\rm R}_{\rm 1} {\rm R}_{\rm 2} \left( {{\rm CH}_2 } \right)_2 ]_2 \cdot 4{\rm X}^ - $\end{document}, and spermidine derivatives (III), \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}_1 {\rm R}_{\rm 2} {\rm R}_{\rm 3} \mathop {\rm N}\limits^ + \left( {{\rm CH}_2 } \right)_4 \mathop {\rm N}\limits^ + {\rm R}_{\rm 1} {\rm R}_{\rm 2} \left( {{\rm CH}_2 } \right)_3 \mathop {\rm N}\limits^ + {\rm R}_{\rm 1} {\rm R}_{\rm 2} {\rm R}_3 \cdot 3{\rm X}^ - $\end{document}, are reported. The effects of these salts on the helix–coil transition of rA–rU and rI–rC helices were examined. Increasing the size of the hydrophobic substituents, R1, R2, and R3 lowers the degree of stabilization of the helical structure. The disproportionation reaction, 2rA–rU→rA–rU2 + rA occurs readily with salts II and III, especially when the substituents, R1, R2, and R3 are small, i.e., H or Me. Spermine is found to stabilize the rA–rU2 and rI–rC helices to approximately the same extent; however, large differences between the degree of stabilization of rA–rU2 and rI-rC helices are observed when the substituents R1, R2, and R3 are large hydrophobic groups. Similar results are also obtained for the spermidine series. Finally, differences in the interactions of the salts II and III with rA–rU2 and rI–rC helices suggest that the latter helix is denser.  相似文献   

12.
A new 3D, spin-state-selective coherence transfer NMR experiment is described that yields accurate measurements for eight scalar or dipolar couplings within a spin system composed of a methylene adjacent to a methine group. Implementations of the experiment have been optimized for proteins and for nucleic acids. The experiments are demonstrated for C–C moieties of the third IgG-binding domain from Streptococcal Protein G (GB3) and for C –C groups in a 24-nt RNA oligomer. Chemical shifts of C, C and H (respectively C , C and H ) are dispersed in the three orthogonal dimensions, and the absence of heteronuclear decoupling leads to distinct and well-resolved E.COSY multiplet patterns. In an isotropic sample, the E.COSY displacements correspond to 1JCH, 2JCH2+2JCH3, 2JCH, 1JCH2+1JCH3, 1JCH22JH2H3, 1JCH32JH2H3, 3JHH2 and 3JHH3 for proteins, and 1J , 2J J , 2J , 1J +1J , 1J J , 1J J , 3J and 3J in nucleic acids. The experiment, based on relaxation-optimized spectroscopy, yields best results when applied to residues where the methine–methylene group corresponds to a reasonably isolated spin system, as applies for C, F, Y, W, D, N and H residues in proteins, or the C –C groups in nucleic acids. Splittings can be measured under either isotropic or weakly aligned conditions, yielding valuable structural information both through the 3J couplings and the one-, two- and three-bond dipolar interactions. Dipolar couplings for 10 out of 13 sidechains in GB3 are found to be in excellent agreement with its X-ray structure, whereas one residue adopts a different backbone geometry, and two residues are subject to extensive 1 rotamer averaging. The abundance of dipolar couplings can also yield stereospecific assignments of the non-equivalent methylene protons. For the RNA oligomer, dipolar data yielded stereospecific assignments for six out of the eight C H2 groups in the loop region of the oligomer, in all cases confirmed by 1J ^{1} $$" align="middle" border="0"> J , and H resonating downfield of H .Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s10858-005-0175-z.  相似文献   

13.
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 1Hα spin resonating close to the H2O signal, a modified HNCA experiment can be employed to measure the vicinal 1HN,1Hα 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.  相似文献   

14.
Summary The cellular dynamics of HIV interaction with the immune system is explored in three-dimensions using a direct Monte Carlo simulation. Viral mutation with probability, Pmut, is considered with immobile and mobile cells. With immobile cells, the viral population becomes larger than that of the helper cells beyond a latency period Tcrit and above a mutation threshold Pcrit. That is at Pmut ≥ Pcrit, { }, with γ ⋍ 0.73 in three dimensions and γ ⋍ 0.88 in 2-D. Very little difference in Pcrit is observed between two and three dimensions. With mobile cells, no power-law is observed for the period of latency, but the difference in Pcrit between two and three dimensions is increased. The time-dependency of the density difference between Viral and Helper cell populations (ρV − ρH) is explored and follows the basic pattern of an immune response to infection. This is markedly more defined than in the 2-D case, where no clear pattern emerges.  相似文献   

15.
Qilian juniper (Sabina przewalskii Kom.) and Qinghai spruce (Picea crassifolia Kom.) represent different tree functional types, which can be found extensively in northwestern China. The former is drought-tolerant, whereas the latter is hygrophilous and shade-tolerant. We compared their intrinsic water-use efficiency (iWUE, inferred from carbon isotopic discrimination, δ13C, in their wood) as a function of atmospheric CO2 concentration, [CO2], and climate. δ13C of spruce was consistently about higher than that of juniper in semi-arid areas but was lower in arid areas. This difference was stable over time and demonstrated strong cross-correlations between species, although some subtle high-frequency (2 or 3 years) variations existed in both species, suggesting that regional climate may control carbon isotope discrimination. The ratio (the [CO2] values in leaf intercellular and the atmosphere, respectively) of the juniper increased steadily over time, whereas that of the spruce showed a long-term downward trend. IWUE increased at all sites over the 150-year study period, mainly caused by increasing [CO2]. The relationship between iWUE and [CO2] reveals that the spruce was more sensitive than the juniper to increasing [CO2], suggesting a species-specific adaptation to long-term environmental changes. Correlations between the high-frequency variations in stable carbon discrimination (Δ) and climate indicate similar intra-site responses to climate in both species, but different response strengths. Overall, complex interactions of temperature and moisture on stable carbon discrimination during current growth seasons of both species were environmental-determined. Regulation of gas exchange and reduced transpiration may influence water and energy budgets directly; therefore species-dependent responses of trees to elevated CO2 should be considered in future research on global plant physiological ecology.  相似文献   

16.
Zusammenfassung Bei Röntgenbestrahlung von L-Leucin·HCl bei Zimmertemperatur wird das >C-H-Proton unter Bildung des Radikals (CH3)2 C-CH2-CHNH3 +-COOH abgetrennt. Das von acht -Protonen stammende ESR-Spektrum wurde wegen nur schwacher Anisotropie der -Protonen-Hfs auch im polykristallinen Zustand vollständig aufgelöst, und es wurden folgende isotrope Aufspaltungen ermittelt: bei Messung bei Zimmertemperatur = 23.5±1 Gauß für sechs äquivalente CH3-Protonen und =8,0±1 Gauß und = 38,8±1 Gauß für die zwei Methylenprotonen, bei Messung bei 77 °K entsprechend = 22,6±1 Gauß =8,8±1 Gauß und =45,2±1 Gauß (Temperaturabhängigkeit der CH2-Protonenkopplung). Das bei Zimmertemperatur beobachtete Radikal wird bereits durch Bestrahlung bei 77 °K gebildet.
ESR-studies on the structure of radicals in X-irradiated L-leucine hydrochloride
Summary The structure of radicals in X-irradiated polycrystalline L-leucine·HCl has been studied by ESR. At room temperature the radical (CH3)2 > C-CH2-CHNH 3 + -COOH is formed by abstraction of the >C-H-proton. The isotropic part of hyperfine interaction with eight -protons has been measured even in polycrystalline state with following values: at 300 °K =23,5±1 gauss for six equivalent CH3-protons and =8.0±1 gauss and =38.8±1 gauss for two CH2-protons, at 77 °K =22.6±1 gauss, =8.8±1 gauss and =45-2±1 gauss respectively (the coupling of the CH2-protons is dependent from temperature). This radical is present already following irradiation at 77 °K.


Herrn Prof. Dr. habil. Kh.Lohs möchten wir an dieser Stelle für die Unterstützung dieser Arbeit und wertvolle Diskussionen danken. Herrn Ing. N.Klimes, Frl. G.Klein und Herrn J.Benkert gilt unser Dank für die technische Assistenz, Herrn Ing. M.Kresse für die Bestrahlung der verwendeten Proben.  相似文献   

17.
Intermittent drainage of rice fields isdiscussed as an option to mitigate emission ofCH4, an important greenhouse gas. HoweverN2O, a potentially more effective greenhouse gas,may be emitted during the aeration phase. Therefore,the metabolism of NO, N2O, NH ,NO and NO and the kinetics ofCH4 oxidation were measured after aeration ofmethanogenic rice field soil. Before aeration, thesoil contained NH in relatively highconcentrations (about 4 mM), while NO andNO were almost undetectable. Immediatelyafter aeration both NO and N2O were produced withrates of about 15 pmol h-1 gdw-1 and 5 pmolh-1 gdw-1, respectively. Simultaneously,NH decreased while NO accumulated. Later on, NO was depletedwhile NO concentrations increased.Characteristic phases of nitrogen turnover wereassociated with the activities of ammonium oxidizers,nitrite oxidizers and denitrifiers. Oxidation ofNH and production of NO and N2O wereinhibited by 10 Pa acetylene demonstrating thatnitrification was obligatory for the initiation ofnitrogen turnover and production of NO and N2O.Ammonium oxidation was not limited by the availableNH and thus, concomittant production of NOand N2O was not stimulated by addition ofNH . However, addition of NO stimulated production of NO and N2O in bothanoxic and aerated rice soil slurries. In this case,10 Pa acetylene did not inhibit the production of NOand N2O demonstrating that it was due todenitrification which was obviously limited by theavailability of NO . In the aerated soilslurries CH4 was only oxidized if present atelevated concentrations >50 ppmv CH4). Atatmospheric CH4 concentrations (1.7 ppmv)CH4 was not consumed, but was even slightly produced.CH4 oxidation activity increased afterpreincubation at 20% CH4, and then CH4was also oxidized at atmospheric concentrations. CH4oxidation kinetics exhibited sigmoid characteristicsat low CH4 concentrations presumably because ofinhibition of CH4 oxidation by NH .  相似文献   

18.
The archaeogastropod Haliotis iris possesses paired bipectinate gills and normally four to six shell holes. In still water, endogenous water flow entered the branchial chamber anteriorly to the left of the head and was exhaled primarily from the three most posterior holes. The first or second anterior aperture was occasionally weakly inhalant. Cardiac interaction superimposed an oscillatory component upon ciliary ventilation but did not augment mean flow. At normal endogenous flow rates 49% of oxygen was extracted from the branchial flow, increasing to 71% at lower flows. In still water, normoxic was 0.47 μmol g−1 h−1. Oxyregulation occurred down to with partial oxyregulation down to 45 Torr (P crit), and oxyconformity below this. The oxyregulatory plateau was absent in artificially ventilated animals but normoxic was higher (0.65 μmol g−1 h−1). Endogenous ventilation was unaffected by hypoxia to 15 Torr. Heart rate decreased by ~20% at 26 Torr before falling more steeply. Oxygen uptake from the branchial ventilation stream fully accounted for normoxic In hypoxia (<30 Torr), no uptake occurred from the head or foot despite extensive eversion of the epipodium. Blood oxygen measurements excluded the right mantle as a significant gas exchange organ. Changes in oxygen uptake caused by changes in the velocity of external water currents support the concept of induced ventilation and suggest that in still water aerobic respiration was ventilation-limited. Although ciliary ventilation appears adequate to support resting aerobic metabolism, induced ventilation may provide increased aerobic scope for activity and repayment of oxygen debt. An erratum to this article can be found at  相似文献   

19.
Influence of 100 μM Ni on growth, Ni accumulation,, H2O2 and lipid peroxides contents as well as the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POD) and glutathione peroxidase (GSH-Px) were studied in the leaves of wheat plants on the 3rd, 6th and 9th days after treatment. Exposure of the plants to Ni for only 3 days led to almost 200-fold increase in this metal concentration in the leaf tissue but later the rate of Ni accumulation was much slower. Length and fresh weight of the leaves were substantially reduced, up to 25% and 39%, respectively at the end of experiment. Visible symptoms of Ni toxicity: chlorosis and necrosis were observed following the 3rd day. Treatment with Ni resulted in the increase in and H2O2 contents in the leaves. Both showed their highest values, approximately 250% of those of the control, on the 3rd day and then their levels decreased but still markedly exceeded the control values. SOD and CAT activities decreased significantly in response to Ni treatment, however a several-fold increase in APX and POD activities was found. No significant changes in lipid peroxides content were observed in the leaves after Ni application. The activity of GSH-Px showed a 29% induction on the 3rd day. Our results indicated that despite prolonged increases in and H2O2 levels, oxidative damage, measured as the level of lipid peroxidation, did not occur in the leaves of Ni-treated wheat.  相似文献   

20.
Analysis of linkage disequilibrium (=mean squared correlation of allele frequencies at different gene loci) provides a means of estimating effective population size (N e) from a single sample, but this method has seen much less use than the temporal method (which requires at least two samples). It is shown that for realistic numbers of loci and alleles, the linkage disequilibrium method can provide precision comparable to that of the temporal method. However, computer simulations show that estimates of N e based on for unlinked, diallelic gene loci are sharply biased downwards ( in some cases) if sample size (S) is less than true N e. The bias is shown to arise from inaccuracies in published formula for when S and/or N e are small. Empirically derived modifications to for two mating systems (random mating and lifetime monogamy) effectively eliminate the bias (residual bias in % in most cases). The modified method also performs well in estimating N e in non-ideal populations with skewed sex ratio or non-random variance in reproductive success. Recent population declines are not likely to seriously affect , but if N has recently increased from a bottleneck can be biased downwards for a few generations. These results should facilitate application of the disequilibrium method for estimating contemporary N e in natural populations. However, a comprehensive assessment of performance of with highly polymorphic markers such as microsatellites is needed.The US Governmentȁ9s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.  相似文献   

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