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1.
Discrimination between12C and13C by marine plants 总被引:2,自引:0,他引:2
Summary The natural abundance13C/12C ratios (as δ13C) of organic matter of marine macroalgae from Fife and Angus (East Scotland) were measured for comparison with the species'
ability to use CO2 and HCO
3
-
for photosynthesis, as deduced from previously published pH-drift measurements. There was a clear difference in δ13C values for species able or unable to use HCO
3
-
. Six species of Chlorophyta, 12 species of Phaeophyta and 8 species of Rhodophyta that the pH-drift data suggested could
use HCO
3
-
had δ13C values in the range -8.81‰ to -22.55‰. A further 6 species of Rhodophyta which the pH-drift data suggested could only use
CO2 had δ13C values in the range -29.90‰ to-34.51‰. One of these six species (Lomentaria articulata) is intertidal; the other five are subtidal and so have no access to atmospheric CO2 to complicate the analysis. For these species, calculations based on the measured δ13C of the algae, the δ13C of CO2 in seawater, and the known13C/12C discrimination of CO2 diffusion and RUBISCO carboxylation suggest that only 15–21% of the limitation to photosynthesisin situ results from CO2 diffusion from the bulk medium to the plastids; the remaining 79–85% is associated with carboxylation reactions (and, via
feedback effects, down-stream processes). This analysis has been extended for one of these five species,Delesseria sanguinea, by incorporating data onin situ specific growth rates, respiratory rates measured in the laboratory, and applying Fick's law of diffusion to calculate a
boundary layer thickness of 17–24 μm. This value is reasonable for aDelesseria sanguinea frondin situ. For HCO
3
-
-using marine macroalgae the range of δ13C values measured can be accommodated by a CO2 efflux from algal cells which range from 0.306 of the gross HCO
3
-
influx forEnteromorpha intestinalis (δ13C=-8.81‰) in a rockpool to 0.787 forChondrus crispus (δ13C=-22.55‰). The relatively high computed CO2 efflux for those HCO
3
-
-users with the more negative δ13C values implies a relatively high photon cost of C assimilation; the observed photon costs can be accommodated by assuming
coupled, energy-independent inorganic carbon influx and efflux. The observed δ13C values are also interpreted in terms of water movement regimes and obtaining CO2 from the atmosphere. Published δ13C values for freshwater macrophytes were compared with the ability of the species to use CO2 and HCO
3
-
and again there was an apparent separation in δ13C values for these two groups. δ13C values obtained for marine macroalgae for which no pH-drift data are available permit predictions, as yet untested, as to
whether they use predominantly CO2 or HCO
3
- 相似文献
2.
R. Guilluy F. Billion-Rey J.L. Brazier 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1991,562(1-2)
A differential kinetic study of 13CO2 enrichment of breath after the intake of specific 13C-labelled substrates and co-administration of a drug allows the drug's ability for enzyme induction to be evaluated in vivo. A method and a gas chromatograph—isotope ratio mass spectrometer device for on-line measurements of 13CO2 enrichment in the breath of small animals are described. This system allows on-line breath sample collection from a metabolic cage, purification by gas chromatography, determination of CO2 by thermal conductivity detection and measurement of 13CO2 enrichment by isotope ratio mass spectrometry. Two protocols for phenobarbital-inducible P450 and 3-methylcholanthrene-inducible P1-450 isoenzymes are described. 相似文献
3.
GUILLAUME TCHERKEZ RUDI SCHÄUFELE SALVADOR NOGUÉS CLÉMENT PIEL ARNOUD BOOM GARY LANIGAN CÉCILE BARBAROUX CATARINA MATA SLIMAN ELHANI DEBBIE HEMMING CHRISTINA MAGUAS DAN YAKIR FRANZ W. BADECK HOWARD GRIFFITHS HANS SCHNYDER JALEH GHASHGHAIE 《Plant, cell & environment》2010,33(6):900-913
While there is currently intense effort to examine the 13C signal of CO2 evolved in the dark, less is known on the isotope composition of day‐respired CO2. This lack of knowledge stems from technical difficulties to measure the pure respiratory isotopic signal: day respiration is mixed up with photorespiration, and there is no obvious way to separate photosynthetic fractionation (pure ci/ca effect) from respiratory effect (production of CO2 with a different δ13C value from that of net‐fixed CO2) at the ecosystem level. Here, we took advantage of new simple equations, and applied them to sunflower canopies grown under low and high [CO2]. We show that whole mesocosm‐respired CO2 is slightly 13C depleted in the light at the mesocosm level (by 0.2–0.8‰), while it is slightly 13C enriched in darkness (by 1.5–3.2‰). The turnover of the respiratory carbon pool after labelling appears similar in the light and in the dark, and accordingly, a hierarchical clustering analysis shows a close correlation between the 13C abundance in day‐ and night‐evolved CO2. We conclude that the carbon source for respiration is similar in the dark and in the light, but the metabolic pathways associated with CO2 production may change, thereby explaining the different 12C/13C respiratory fractionations in the light and in the dark. 相似文献
4.
Rhizodeposition, i.e. the release of carbon into the soil by growing roots, is an important part of the terrestrial carbon
cycle. However thein situ nature and dynamics of root-derived carbon in the soil are still poorly understood. Here we made an investigation of the
latter in laboratory experiments using13CO2 pulse chase labelling of wheat (Triticum aestivum L.). We analyzed the kinetics of13C-labelled carbon and more specially13C carbohydrates in the rhizosphere. Wheat seedlings-soil mesocosms were exposed to13CO2 for 5 hours in controlled chambers and sampled repeatedly during two weeks for13C/C analysis of organic carbon. After a two-step separation of the soil from the roots, the amount of total organic13C was determined by isotope ratio mass spectrometry as well as the amounts of13C in arabinose, fructose, fucose, glucose, galactose, mannose, rhamnose and xylose. The amount and isotopic ratio of monosaccharides
were obtained by capillary gas chromatography coupled with isotope ratio mass spectrometry (GC/C/IRMS) after trimethyl-silyl
derivatization. Two fractions were analyzed : total (hydrolysable) and soluble monomeric (water extractable) soil sugars.
The amount of organic13C found in the soil, expressed as a percentage of the total photosynthetically fixed13C at the end of the labelling period, reached 16% in the day following labelling and stabilised at 9% after one week. We concluded
that glucose under the form of polymers was the dominant moietie of rhizodeposits. Soluble glucose and fructose were also
present. But after 2 days, these soluble sugars had disappeared. Forty percent of the root-derived carbon was in the form
of neutral sugars, and exhibited a time-increasing signature of microbial sugars. The composition of rhizospheric sugars rapidly
tended towards that of bulk soil organic matter. 相似文献
5.
Biogenic isoprene substantially affects atmospheric chemistry, but it is not known how or why many plants, especially trees, make isoprene. We fed 13CO2 to leaves of Quercus rubra and monitored the incorporation of 13C into isoprene by mass spectrometry. After feeding 13CO2 for 9 min we found all possible labelling patterns from completely unlabelled to fully labelled isoprene. By 18 min, 84% of the carbon atoms in isoprene were 13C. Labelling of the last 20% of the carbon atoms was much slower than labelling of the first 80%. The rate of labelling of isoprene was similar to that reported for phosphoglyceric acid indicating that there is a close linkage between the carbon source for isoprene synthesis and the photosynthetic carbon reduction pathway. 相似文献
6.
Upland rice (Oryza sativa L.) was grown at both ambient (350 μmol mol?1) and elevated (700 μmol mol?1) CO2 in either the presence or absence of the root hemi‐parasitic angiosperm Striga hermonthica (Del) Benth. Elevated CO2 alleviated the impact of the parasite on host growth: biomass of infected rice grown at ambient CO2 was 35% that of uninfected, control plants, while at elevated CO2, biomass of infected plants was 73% that of controls. This amelioration occurred despite the fact that O. sativa grown at elevated CO2 supported both greater numbers and a higher biomass of parasites per host than plants grown at ambient CO2. The impact of infection on host leaf area, leaf mass, root mass and reproductive tissue mass was significantly lower in plants grown at elevated as compared with ambient CO2. There were significant CO2 and Striga effects on photosynthetic metabolism and instantaneous water‐use efficiency of O. sativa. The response of photosynthesis to internal [CO2] (A/Ci curves) indicated that, at 45 days after sowing (DAS), prior to emergence of the parasites, uninfected plants grown at elevated CO2 had significantly lower CO2 saturated rates of photosynthesis, carboxylation efficiencies and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) contents than uninfected, ambient CO2‐grown O. sativa. In contrast, infection with S. hermonthica prevented down‐regulation of photosynthesis in O. sativa grown at elevated CO2, but had no impact on photosynthesis of hosts grown at ambient CO2. At 76 DAS (after parasites had emerged), however, infected plants grown at both elevated and ambient CO2 had lower carboxylation efficiencies and Rubisco contents than uninfected O. sativa grown at ambient CO2. The reductions in carboxylation efficiency (and Rubisco content) were accompanied by similar reductions in nitrogen concentration of O. sativa leaves, both before and after parasite emergence. There were no significant CO2 or infection effects on the concentrations of soluble sugars in leaves of O. sativa, but starch concentration was significantly lower in infected plants at both CO2 concentrations. These results demonstrate that elevated CO2 concentrations can alleviate the impact of infection with Striga on the growth of C3 hosts such as rice and also that infection can delay the onset of photosynthetic down‐regulation in rice grown at elevated CO2. 相似文献
7.
Carbon dioxide biofixation by Chlorella vulgaris at different CO2 concentrations and light intensities
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Barbara Clément‐Larosière Filipa Lopes Ana Gonçalves Behnam Taidi Marc Benedetti Michel Minier Dominique Pareau 《Engineering in Life Science》2014,14(5):509-519
In order to develop an effective CO2 mitigation process using microalgae for potential industrial application, the growth and physiological activity of Chlorella vulgaris in photobioreactor cultures were studied. C. vulgaris was grown at two CO2 concentrations (2 and 13% of CO2 v/v) and at three incident light intensities (50, 120 and 180 μmol m?2 s?1) for 9 days. The measured specific growth rate was similar under all conditions tested but an increase in light intensity and CO2 concentration affected the biomass and cell concentrations. Although carbon limitation was observed at 2% CO2, similar cellular composition was measured in both conditions. Light limitation induced a net change in the growth behavior of C. vulgaris. Nitrogen limitation seemed to decrease the nitrogen quota of the cells and rise the intracellular carbon:nitrogen ratio. Exopolysaccharide production per cell appeared to be affected by light intensity. In order to avoid underestimation of the CO2 biofixation rate of the microalgae, exopolysaccharide production was taken into account. The maximum CO2 removal rate (0.98 g CO2 L?1 d?1) and the highest biomass concentration (4.14 g DW L?1) were determined at 13% (v/v) CO2 and 180 μmol m?2 s?1. Our results show that C. vulgaris has a real potential for industrial CO2 remediation. 相似文献
8.
We assessed the effects of doubling atmospheric CO2 concentration, [CO2], on C and N allocation within pedunculate oak plants (Quercus robur L.) grown in containers under optimal water supply. A short-term dual 13CO2 and 15NO3? labelling experiment was carried out when the plants had formed their third growing flush. The 22-week exposure to 700 μl l?1 [CO2] stimulated plant growth and biomass accumulation (+53% as compared with the 350 μl l?1 [CO2] treatment) but decreased the root/shoot biomass ratio (-23%) and specific leaf area (-18%). Moreover, there was an increase in net CO2 assimilation rate (+37% on a leaf dry weight basis; +71% on a leaf area basis), and a decrease in both above- and below-ground CO2 respiration rates (-32 and -26%, respectively, on a dry mass basis) under elevated [CO2]. 13C acquisition, expressed on a plant mass basis or on a plant leaf area basis, was also markedly stimulated under elevated [CO2] both after the 12-h 13CO2 pulse phase and after the 60-h chase phase. Plant N content was increased under elevated CO2 (+36%), but not enough to compensate for the increase in plant C content (+53%). Thus, the plant C/N ratio was increased (+13%) and plant N concentration was decreased (-11%). There was no effect of elevated [CO2] on fine root-specific 15N uptake (amount of recently assimilated 15N per unit fine root dry mass), suggesting that modifications of plant N pools were merely linked to root size and not to root function. N concentration was decreased in the leaves of the first and second growing flushes and in the coarse roots, whereas it was unaffected by [CO2] in the stem and in the actively growing organs (fine roots and leaves of the third growth flush). Furthermore, leaf N content per unit area was unaffected by [CO2]. These results are consistent with the short-term optimization of N distribution within the plants with respect to growth and photosynthesis. Such an optimization might be achieved at the expense of the N pools in storage compartments (coarse roots, leaves of the first and second growth flushes). After the 60-h 13C chase phase, leaves of the first and second growth flushes were almost completely depleted in recent 13C under ambient [CO2], whereas these leaves retained important amounts of recently assimilated 13C (carbohydrate reserves?) under elevated [CO2]. 相似文献
9.
I. Emma Huertas Brian Colman George S. Espie Luis M. Lubian 《Journal of phycology》2000,36(2):314-320
The occurrence of an active CO2 transport system and of carbonic anhydrase (CA) has been investigated by mass spectrometry in the marine, unicellular rhodophyte Porphyridium cruentum (S.F. Gray) Naegeli and two marine chlorophytes Nannochloris atomus Butcher and Nannochloris maculata Butcher. Illumination of darkened cells incubated with 100 μM H13CO3? caused a rapid initial drop, followed by a slower decline in the extracellular CO2 concentration. Addition of bovine CA to the medium raised the CO2 concentration by restoring the HCO3?–CO2 equilibrium, indicating that cells were taking up CO2 and were maintaining the CO2 concentration in the medium below its equilibrium value during photosynthesis. Darkening the cell suspensions caused a rapid increase in the extracellular CO2 concentration in all three species, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. CA activity was detected by monitoring the rate of exchange of 18O from 13C18O2 into water. Exchange of 18O was rapid in darkened cell suspensions, but was not inhibited by 500 μM acetazolamide, a membrane‐impermeable inhibitor of CA, indicating that external CA activity was not present in any of these species. In all three species, the rate of exchange was completely inhibited by 500 μM ethoxyzolamide, a membrane‐permeable CA‐inhibitor, showing that an intracellular CA was present. These results demonstrate that the three species are capable of CO2 uptake by active transport for use as a carbon source for photosynthesis. 相似文献
10.
Atmospheric CO2 mole fraction affects stand‐scale carbon use efficiency of sunflower by stimulating respiration in light
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Xiao Ying Gong Rudi Schäufele Christoph Andreas Lehmeier Guillaume Tcherkez Hans Schnyder 《Plant, cell & environment》2017,40(3):401-412
Plant carbon‐use‐efficiency (CUE), a key parameter in carbon cycle and plant growth models, quantifies the fraction of fixed carbon that is converted into net primary production rather than respired. CUE has not been directly measured, partly because of the difficulty of measuring respiration in light. Here, we explore if CUE is affected by atmospheric CO2. Sunflower stands were grown at low (200 μmol mol?1) or high CO2 (1000 μmol mol?1) in controlled environment mesocosms. CUE of stands was measured by dynamic stand‐scale 13C labelling and partitioning of photosynthesis and respiration. At the same plant age, growth at high CO2 (compared with low CO2) led to 91% higher rates of apparent photosynthesis, 97% higher respiration in the dark, yet 143% higher respiration in light. Thus, CUE was significantly lower at high (0.65) than at low CO2 (0.71). Compartmental analysis of isotopic tracer kinetics demonstrated a greater commitment of carbon reserves in stand‐scale respiratory metabolism at high CO2. Two main processes contributed to the reduction of CUE at high CO2: a reduced inhibition of leaf respiration by light and a diminished leaf mass ratio. This work highlights the relevance of measuring respiration in light and assessment of the CUE response to environment conditions. 相似文献
11.
A 13C/12C mass spectrometer was interfaced with a open gas exchange system including four growth chambers to investigate CO2 exchange components of perennial ryegrass (Lolium perenne L.) stands. Chambers were fed with air containing CO2 with known δ13C (δCΟ2?2.6 or ?46.8‰). The system did not fractionate C isotopes and no extraneous CO2 leaked into chambers. The on‐line 13C discrimination (Δ) of ryegrass stands in light was independent of δCΟ2 when δCΟ2 was constant. The δ of CO2 exchanged by the stands in light (δNd) and darkness (δRn) differed by 0.7‰, suggesting some Δ in dark respiration at the stand‐level. However, Δ decreased by ~ 10‰ when δCΟ2 was switched from ?46.8 to ?2.5‰, and increased by ~ 10‰ following a shift from ?2.6 to ?46.7‰ due to isotopic disequilibria between photosynthetic and respiratory fluxes. Isotopic imbalances were used to assess (non‐photorespiratory) respiration in light and the replacement of the respiratory substrate pool(s) by new photosynthate. Respiration was partially inhibited by light, but increased during the light period and decreased in darkness, in association with temperature changes. The labelling kinetics of respiratory CO2 indicated the existence of two major respiratory substrate pools: a fast pool which was exchanged within hours, and a slow pool accounting for ~ 60% of total respiration and having a mean residence time of 3.6 d. 相似文献
12.
Plants may be more sensitive to carbon dioxide (CO2) enrichment at subambient concentrations than at superambient concentrations, but field tests are lacking. We measured soil‐water content and determined xylem pressure potentials and δ13C values of leaves of abundant species in a C3/C4 grassland exposed during 1997–1999 to a continuous gradient in atmospheric CO2 spanning subambient through superambient concentrations (200–560 µmol mol2?1). We predicted that CO2 enrichment would lessen soil‐water depletion and increase xylem potentials more over subambient concentrations than over superambient concentrations. Because water‐use efficiency of C3 species (net assimilation/leaf conductance; A/g) typically increases as soils dry, we hypothesized that improvements in plant‐water relations at higher CO2 would lessen positive effects of CO2 enrichment on A/g. Depletion of soil water to 1.35 m depth was greater at low CO2 concentrations than at higher CO2 concentrations during a mid‐season drought in 1998 and during late‐season droughts in 1997 and 1999. During droughts each year, mid‐day xylem potentials of the dominant C4 perennial grass (Bothriochloa ischaemum (L.) Keng) and the dominant C3 perennial forb (Solanum dimidiatum Raf.) became less negative as CO2 increased from subambient to superambient concentrations. Leaf A/g—derived from leaf δ13C values—was insensitive to feedbacks from CO2 effects on soil water and plant water. Among most C3 species sampled—including annual grasses, perennial grasses and perennial forbs—A/g increased linearly with CO2 across subambient concentrations. Leaf and air δ13C values were too unstable at superambient CO2 concentrations to reliably determine A/g. Significant changes in soil‐ and plant‐water relations over subambient to superambient concentrations and in leaf A/g over subambient concentrations generally were not greater over low CO2 than over higher CO2. The continuous response of these variables to CO2 suggests that atmospheric change has already improved water relations of grassland species and that periodically water‐limited grasslands will remain sensitive to CO2 enrichment. 相似文献
13.
The leakage of various inorganic carbon species from air-grown cells of Synechococcus UTEX 625 was investigated after a light to dark transition or during a light period using a mass spectrometer under a wide variety of experimental conditions. Total inorganic carbon efflux and CO2 efflux during the initial period of darkness were measured with or without carbonic anhydrase in the reaction medium respectively. The HCO3? efflux after a light to dark transition was estimated by difference. Carbon dioxide efflux in the light was measured by inhibiting CO2 transport with either Na2S or COS3 or quenching the 13C inorganic carbon transport by the addition of 12C inorganic carbon in excess. In cells in which CO2 fixation was inhibited, when only the HCO3? transport system was fully operative, CO2 effluxed continuously during the light period at a rate equal to about 25% of that in darkness. When only the CO2 transport system was operative, HCO3? effluxed during the light period. The difference between the light and dark efflux rates was consistent with a 0.6 unit decrease in the intracellular pH upon darkening the cells. The permeabilities of the cell for CO2 (2.94 ± 0.14 ± 10?8ms?1; mean ± SE, n=137) and HCO3? (1.4–1.7 ± 10?9 ms?1) were calculated. 相似文献
14.
The unicellular green alga Chlamydomonas reinhardtii possesses a CO2-concentrating mechanism. In order to measure the CO2 permeability coefficients of the plasma membranes (PMs), carbonic anhydrase (CA) loaded vesicles were isolated from C. reinhardtii grown either in air enriched with 50 mL CO2 · L?1} (high-Ci cells) or in ambient air (350 μL CO2 · L?1}; low-Ci cells). Marker-enzyme measurements indicated less than 1% contamination with thylakoid and mitochondrial membranes, and that more than 90% of the PMs from high and low-Ci cells were orientated right-side-out. The PMs appeared to be sealed as judged from the ability of vesicles to accumulate [14C]acetate along a proton gradient for at least 10 min. Carbonic anhydrase-loaded PMs from high and low-Ci cells of C. reinhardtii were used to measure the exchange of 18O between doubly labelled CO2 (13C18O2) and H2O in stirred suspensions by mass spectrometry. Analysis of the kinetics of the 18O depletion from 13C18O2 in the external medium provides a powerful tool to study CO2 diffusion across the PM to the active site of CA which catalyses 18O exchange only inside the vesicles but not in the external medium (Silverman et al., 1976, J Biol Chem 251: 4428–4435). The activity of CA within loaded PM vesicles was sufficient to speed-up the 18O loss to H2O to 45360–128800 times the uncatalysed rate, depending on the efficiency of CA-loading and PM isolation. From the 18O-depletion kinetics performed at pH 7.3 and 7.8, CO2 permeability coefficients of 0.76 and 1.49·10?3} cm·s?1}, respectively, were calculated for high Ci cells. The corresponding values for low-Ci cells were 1.21 and 1.8·10?3} cm·s?1}. The implications of the similar and rather high CO2 permeability coefficients (low CO2 resistance) in high and low-Ci cells for the COi-concentrating mechanism of C. reinhardtii are discussed. 相似文献
15.
P. A. M. Claassen C. Dijkema J. Visser A. J. B. Zehnder 《Archives of microbiology》1986,146(3):227-232
The disappearance of 2-13C-acetate and the subsequent incorporation of label into cellular metabolites were followed in denitrifying cells of Thiobacillus versutus by 13C NMR spectroscopy. In cells grown under acetate-limitation, the specific rate of consumption was idependent of the density of the cell suspension. An isotopic steady state was reached within 30 min if sufficient substrate was added to the cell suspension. In cells grown under nitrate-limitation, the consumption of 2-13C-acetate proceeded at a significantly lower rate. The decrease and final disappearance of 2-13C-acetate were accompanied by incorporation of 13C into glutamate, glutamine, and by the release of labeled HCO
3
–
and CO2. The appearance of a broad resonance being the methyl endgroup of poly-3-hydroxybutyrate (PHB) was indicative for PHB mobilization during the incubation. The sequence of label incorporation and the distribution among the various carbon nuclei were consistent with the operation of the tricarboxylic acid cycle. 相似文献
16.
Inorganic carbon (Ci) uptake and efflux has been investigated in the marine microalga Nannochloropsis gaditana Lubian by monitoring CO2 fluxes in cell suspensions using mass spectrometry. Addition of H13CO3
− to cell suspensions in the dark caused a transient increase in the CO2 concentration in the medium far in excess of the equilibrium CO2 concentration. The magnitude of this release was dependent on the length of time the cells had been kept in the dark. Once
equilibrium between the Ci species had been achieved, a CO2 efflux was observed after saturating light intensity was applied to the cells. External carbonic anhydrase (CA) was not detected
nor does this species demonstrate a capacity to take up CO2 by active transport. Photosynthetic O2 evolution and the release CO2 in the dark depend on HCO3
− uptake since both were inhibited by the anion exchange inhibitor, 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS).
The bicarbonate uptake mechanism requires light but can also continue for short periods in the dark. Ethoxyzolamide, a CA
inhibitor, markedly inhibited CO2 efflux in the dark, indicating that CO2 efflux was dependent upon the intracellular dehydration of HCO3
−. These results indicate that Nannochloropsis possesses a bicarbonate uptake system which causes the accumulation of high intracellular Ci levels and an internal CA which
maintains the equilibrium between CO2 and HCO3
− and thus causes a subsequent release of CO2 to the external medium.
Received: 20 September 1999 / Accepted: 25 October 1999 相似文献
17.
R. B. Thompson 《Plant and Soil》1996,180(1):49-55
A preliminary study was conducted using the stable isotope 13C to pulse label the cover crop phacelia (Phacelia tanacetifolia) to examine its decomposition in soil, under field conditions. Plants were grown, in pots, in the greenhouse and after four weeks of growth were labelled with 13CO2 six times, at 1–2 week intervals. A single chamber was placed over the pots, and 13CO2 was generated, inside the chamber, by injecting lactic acid into sodium carbonate (99 atom % 13C). For calculating the quantity of Na2CO3 required, a target enrichment of 5 atom% 13C within the shoots of plants, assuming no respiration losses, was used. When harvested, at flowering, the mean enrichment of the shoot material was 3.0466 atom% 13C, or 1.9654 atom% excess 13C. To assess uniformity of labelling within plants, the shoot of a single plant was divided into leaves and stem from three sections of equal length. Ninety-three percent of this plant's dry matter had a 13C enrichment within 20 % of the weighted mean. At a field site with sandy soil, 13C labelled shoot and root material were combined and mixed with soil (0–15 cm). The soil was sampled 16 and 179 days later to determine the recovery of the added excess 13C in soil total C. The recoveries in soil (0–30 cm) were, respectively, 78 and 40 % at 16 and 179 days; there was appreciable variation associated with the recovery data from day 16, much less so at day 179. Methodological procedures for (i) enhancing the uniformity of labelling with 13C within plants, and (ii) minimising variability in the recovery of 13C from soil are suggested. ei]R Merckx 相似文献
18.
Helge Holo 《Archives of microbiology》1989,151(3):252-256
Chloroflexus aurantiacus OK-70 fl secreted 3-hydroxypropionate (3HP) during phototrophic growth. The greatest amounts were secreted by cells grown on propionate (0.35 mM 3HP) while the lowest levels were found in autotrophically grown cultures (1.5 M). Large amounts of 2-fluoro,3-hydroxypropionate were formed by autotrophically grown cells exposed to fluoroacetate (FAc). Increased levels of 3HP were observed in these cultures when incubated with acctate. The secretion of 3HP was further stimulated by 0.2 mM KCN, an inhibitor of CO2 fixation, but only in the presence of acetate. The pathway of 3HP formation was studied by using 13C-labelled substrates and NMR. The 3HP formed in the presence of C1-labelled acetate and FAc was labelled at C3 and somewhat less at C2 while with C2-labelled acetate as the tracer 3HP was labelled predominantly at C2. The carboxyl group was derived from CO2. The 3HP formed by cells grown on propionate and 13CO2 was labelled at all carbon atoms, the label content of C2 and C3 was about 25 and 65% of that of C1 respectively. It is suggested that 3HP is an intermediate in a pathway for acetate assimilation and in a new reductive carboxylic acid cycle for autotrophic CO2 fixation.Abbreviations 3HP
3-hydroxypropionate
- 2F3HP
2,fluoro,3-hydroxypropionate
- FAc
fluoroacetate
- GC
gas chromatography
- MS
mass spectrometry
- NMR
nuclear magnetic resonance 相似文献
19.
Inorganic carbon acquisition has been investigated in the marine haptophyte Isochrysis galbana. External carbonic anhydrase (CA) was present in air‐grown (0.034% CO2) cells but completely repressed in high (3%) CO2‐grown cells. External CA was not inhibited by 1.0 mM acetazolamide. The capacity of cells to take up bicarbonate was examined by comparing the rate of photosynthetic O2 evolution with the calculated rate of spontaneous CO2 supply; at pH 8.2 the rates of O2 evolution exceeded the CO2 supply rate 14‐fold, indicating that this alga was able to take up HCO3 ? . Monitoring CO2 concentrations by mass spectrometry showed that suspensions of high CO2‐grown cells caused a rapid drop in the extracellular CO2 in the light and addition of bovine CA raised the CO2 concentration by restoring the HCO3 ? ‐CO2 equilibrium, indicating that cells were maintaining the CO2 in the medium below its equilibrium value during photosynthesis. A rapid increase in extracellular CO2 concentration occurred on darkening the cells, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. Active CO2 uptake was blocked by the photosynthetic electron transport inhibitor 3‐(3′,4′‐dichlorphenyl)‐1,1‐dimethylurea, indicating that CO2 transport was supported by photosynthetic reactions. These results demonstrate that this species has the capacity to take up HCO3 ? and CO2 actively as sources of substrate for photosynthesis and that inorganic carbon transport is not repressed by growth on high CO2, although external CA expression is regulated by CO2 concentration. 相似文献
20.
Abstract. A new technique for the precise measurement of 13C-abundance and concentration is described. It is based on the differences in infra-red spectra between 12CO2 and 13CO2 and can be applied to gas mixtures or organic materials which have been oxidized to CO2. The gas mixture is first dried and then passed through two infra-red gas analysers (IRGAs) connected in parallel. The two IRGAs are fitted with different optical filters so they differ in their relative sensitivities to 12CO2 and 13CO2. Once these sensitivities are known then simple algebra allows the concentrations of 12CO2 and 13CO2 to be calculated from the two readings. Two variants of this basic system have been tested. In both, one IRGA was a normal commercial instrument with a narrow band pass interference filter making it highly specific for 12CO2; the second instrument was fitted with either a wide-band pass filter covering both the 12CO2 and 13CO2 absorption bands, or a narrow band pass filter specific for 13CO2. These variations convey different advantages in operation. The wide-band system can be easily calibrated using a single natural abundance 12CO2 standard but is only moderately precise at low abundances. It is particularly valuable for continuous monitoring of the relatively high abundance sources used in plant photosynthesis experiments. The narrow-band system gives high precision but requires a more complex standardization procedure. It is recommended for measurements on low-abundance samples resulting from tracer experiments. Here, its high sensitivity permits measurements on samples as small as 3 μmole C, thus enabling plant fractions and individual metabolites to be investigated. While the wide-band system can be manually operated under field conditions, it is necessary for highest precision to use computerized data collection and linearization. These processes are described, as are novel techniques for standardization, the preparation of small quantities of CO2 of known abundance, and the transfer of gas samples from oxidizer to analyser. Determinations by the wide band system of % abundance in standard gas mixtures gave a standard error of ±0.03% but this increased to over ±0.1% for abundances below 20%. Corresponding values for the narrow-band system were ±0.01% over the whole abundance range an accuracy almost identical to that observed with an organic mass spectrometer. Two pulse-chase experiment with 13CO2 are described in which the technique was used for studies on growth and metabolism of Lemna minor. The first demonstrated that 13C-accumulation within the plants matched closely the predictions from the net assimilation rate and measurements of 13C-abundance in the gas phase. The second revealed the rapid changes in the 13C-labelling of some plant components during pulse and chase phases. These examples demonstrate the potential of the method for studies in plant physiology and biochemistry. In view of its relative cheapness, ease of maintenance and operation, accuracy, and sensitivity, it is suggested that this new method may encourage a wider use of the safe stable 13C for biological and medical applications. 相似文献