Assimilate partitioning affects 13C fractionation of recently assimilated carbon in maize

Coupling ¹³C natural abundance and ¹⁴C pulse labelling enabled us to investigate the dependence of ¹³C fractionation on assimilate partitioning between shoots, roots, exudates, and CO₂ respired by maize roots. The amount of recently assimilated C in these four pools was controlled by three levels of nutrient supply: full nutrient supply (NS), 10 times diluted nutrient supply (DNS), and deionised water (DW). After pulse labelling of maize shoots in a ¹⁴CO₂ atmosphere, ¹⁴C was traced to determine the amounts of recently assimilated C in the four pools and the δ¹³C values of the four pools were measured. Increasing amounts of recently assimilated C in the roots (from 8% to 10% of recovered ¹⁴C in NS and DNS treatments) led to a 0.3‰ ¹³C enrichment from NS to DNS treatments. A further increase of C allocation in the roots (from 10% to 13% of recovered ¹⁴C in DNS and DW treatments) resulted in an additional enrichment of the roots from DNS to DW treatments by 0.3‰. These findings support the hypothesis that ¹³C enrichment in a pool increases with an increasing amount of C transferred into that pool. δ¹³C of CO₂ evolved by root respiration was similar to that of the roots in DNS and DW treatments. However, if the amount of recently assimilated C in root respiration was reduced (NS treatment), the respired CO₂ became 0.7‰ ¹³C depleted compared to roots. Increasing amounts of recently assimilated C in the CO₂ from NS via DNS to DW treatments resulted in a 1.6‰ δ¹³C increase of root respired CO₂ from NS to DW treatments. Thus, for both pools, i.e. roots and root respiration, increasing amounts of recently assimilated C in the pool led to a δ¹³C increase. In DW and DNS plants there was no ¹³C fractionation between roots and exudates. However, high nutrient supply decreased the amount of recently assimilated C in exudates compared to the other two treatments and led to a 5.3‰ ¹³C enrichment in exudates compared to roots. We conclude that ¹³C discrimination between plant pools and within processes such as exudation and root respiration is not constant but strongly depends on the amount of C in the respective pool and on partitioning of recently assimilated C between plant pools. Section Editor: H. Lambers     

Effects of D-glucose upon D-fuctose metabolism in rat hepatocytes: A 13C NMR study

Isolated hepatocytes from fed rats were exposed for 120 min to D-glucose (10 mM) and either D-[1-¹³C]fructose, D-[2-¹³C]fructose or D-[6-¹³C]fructose (also 10 mM) in the presence of D₂O. The identification and quantification of ¹³C-enriched D-fructose and its metabolites (D-glucose, L-lactate, L-alanine) in the incubation medium and the measurement of their deuterated isotopomers indicated, by comparison with a prior study conducted in the absence of exogenous D-glucose, that the major effects of the aldohexose were to increase the recovery of ¹³C-enriched D-fructose, decrease the production of ¹³C-enriched D-glucose, restrict the deuteration of the ¹³C-enriched isotopomers of D-glucose to those generated by cells exposed to D-[2-¹³C]fructose, and to accentuate the lesser deuteration of the C₂ (as compared to C₅) of ¹³C-enriched D-glucose derived from D-[2-¹³C]fructose. The ratio between C2-deuterated and C₂-hydrogenated L-lactate, as well as the relative amounts of the CH₃-, CH₂D-, CHD₂ and CD₃- isotopomers of ¹³C-enriched L-lactate were not significantly different, however, in the absence or presence of exogenous D-glucose. These findings indicate that exogenous D-glucose suppressed the deuteration of the C₁ of D-[1-¹³C]glucose generated by hepatocytes exposed to D-[1-¹³C]fructose or D-[6-¹³C]fructose, as otherwise attributable, in part at least, to gluconeogenesis from fructose-derived [3-¹³C]pyruvate, and apparently favoured the phosphorylation of D-fructose by hexokinase isoenzymes, probably through stimulation of D-fructose phosphorylation by glucokinase.     

Measurement of amino acid metabolism derived from [1-13C]glucose in the rat brain using13C magnetic resonance spectroscopy

To clarify the unique characteristics of amino acid metabolism derived from glucose in the central nervous system (CNS), we injected [1-¹³C]glucose intraperitoneally to the rat, and extracted the free amino acids from several kinds of tissues and measured the amount of incorporation of¹³C derived from [1-¹³C]glucose into each amino acid using¹³C-magnetic resonance spectroscopy (NMR). In the adult rat brain, the intensities of resonances from¹³C-amino acids were observed in the following order: glutamate, glutamine, aspartate, -aminobutyrate (GABA) and alanine. There seemed no regional difference on this labeling pattern in the brain. However, only in the striatum and thalamus, the intensities of resonances from [2-¹³C]GABA were larger than that from [2,3-¹³C]aspartate. In the other tissues, such as heart, kidney, liver, spleen, muscle, lung and small intestine, the resonances from GABA were not detected and every intensity of resonances from¹³C-amino acids, except¹³C-alanine, was much smaller than those in the brain and spinal cord. In the serum,¹³C-amino acid was not detected at all. When the rats were decapitated, in the brain, the resonances from [1-¹³C]glucose greatly reduced and the intensities of resonances from [3-¹³C]lactate, [3-¹³C]alanine, [2, 3, 4-¹³C]GABA and [2-¹³C]glutamine became larger as compared with those in the case that the rats were sacrificed with microwave. In other tissues, the resonances from [1-¹³C]glucose were clearly detected even after the decapitation. In the glioma induced by nitrosoethylurea in the spinal cord, the large resonances from glutamine and alanine were observed; however, the intensities of resonances from glutamate were considerably reduced and the resonances from GABA and aspartate were not detected. These results show that the pattern of¹³C label incorporation into amino acids is unique in the central nervous tissues and also suggest that the metabolic compartmentalization could exist in the CNS through the metabolic trafficking between neurons and astroglia.Abbreviations NMR nuclear magnetic resonance - GABA -aminobutyrate - GFAP glial fibrillary acidic protein Special issue dedicated to Dr. Bernard W. Agranoff.     

Variation in the export of 13C and 15N from soybean leaf: the effects of nitrogen application and sink removal

Translocation of carbon and nitrogen within a single source-sink unit, comprising a trifoliated leaf, the axillary pod and the subtending internode, and from this unit to the rest of the plant was examined in soybean (Glycine max L. cv. Akishirome) plant by feeding ¹³CO₂ and ¹⁵NO₃. The plants were grown at two levels of nitrogen in the basal medium, i.e. low-N (2 g N m^–2) and high-N (35 g N m^–2) and a treatment of depodding was imposed by removing all the pods from the plant, except the pod of the source sink unit, 13 days after flowering. The plants at high-N accumulated more biomass in its organs compared to low-N and pod removal increased the weight of the vegetative organs. When the terminal leaflet of the source-sink unit was fed with ¹³CO₂, almost all of the radioactive materials were retained inside the source-sink unit and translocation to rest of the plants was insignificant under any of the treatments imposed. Out of the¹³C exported by the terminal leaflet, less than half went into the axillary pod, as the lateral leaflets claimed equal share and very little material was deposited in the petiole. Pod removal decreased ¹³C export at high-N , but not at low-N. Similar to ¹³C, the source-sink unit retained all the ¹⁵N fed to the terminal leaflet at high-N. At low-N, the major part of ¹⁵N partitioning occurred in favour of the rest of the plant outside the source-sink unit, but removal of the competitve sinks from the rest of the plants nullified any partitioning outside the unit. Unlike the situation in ¹³C, no partitioning of ¹⁵N occurred in favour of the lateral leaflets from the terminal leaflet inside the unit. It is concluded that sink demand influences partitioning of both C and N and the translocation of carbon is different from that of nitrogen within a source-sink unit. The translocation of the N is more adjustive to a demand from other sink units compared to the C.     

Fractionation of stable isotopes in the Arctic marine copepod Calanus glacialis: Effects on the isotopic composition of marine particulate organic matter

Fractionation of δ¹³C and δ¹⁵N between food, consumer, and faecal pellets was studied in the Arctic marine copepod Calanus glacialis Jaschnov, fed with isotopically distinct algal monocultures. Temporal variations in δ¹³C and δ¹⁵N of copepods that were fed ice algae and phytoplankton followed those of a control group consisting of starved animals. There were no significant trends in the δ¹³C and δ¹⁵N values of copepods that were starved for 42 days, suggesting that the isotopic composition of non-lipid body tissues is unaffected by the metabolic processes during prolonged periods of starvation. The stable isotopic composition of starved copepods therefore seems to reflect food consumed during the previous period of feeding and growth. Faecal pellets produced by feeding copepods were depleted in ¹³C and ¹⁵N by 6.3-11.2‰ and 0.7-9.1‰, respectively, relative to the food ingested. These results indicate that faecal pellet production is an important pathway for the trophic fractionation of δ¹³C, whereas other fractionation pathways, such as excretion of ammonia, may be relatively more important for δ¹⁵N. The strong depletion of ¹³C in faecal pellets compared to the food suggests that grazing by herbivorous copepods on primary production adds to the variability of δ¹³C in marine particulate organic matter.     

C isotopomer analysis of glutamate by heteronuclear multiple quantum coherence-total correlation spectroscopy (HMQC-TOCSY)

¹³C has become an important tracer isotope for studies of intermediary metabolism. Information about relative flux through pathways is encoded by the distribution of ¹³C isotopomers in an intermediate pool such as glutamate. This information is commonly decoded either by mass spectrometry or by measuring relative multiplet areas in a ¹³C NMR spectrum. We demonstrate here that groups of glutamate ¹³C isotopomers may be quantified by indirect detection of protons in a 2D HMQC-TOCSY NMR spectrum and that fitting of these data to a metabolic model provides an identical measure of the ¹³C fractional enrichment of acetyl-CoA and relative anaplerotic flux to that given by direct ¹³C NMR analysis. The sensitivity gain provided by HMQC-TOCSY spectroscopy will allow an extension of ¹³C isotopomer analysis to tissue samples not amenable to direct ¹³C detection (∼10 mg soleus muscle) and to tissue metabolites other than glutamate that are typically present at lower concentrations.     

Simple and rapid quantitative assay of C-labelled urea in human serum using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry

A simple and rapid quantitative method for ¹³C-labelled urea ([¹³C]urea) in human serum was developed by using high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS). This method is used to establish and normalize the [¹³C]urea breath test, which is considered as an effective diagnostic method for Helicobacter pylori infection. HPLC-APCI-MS, involving a simple pretreatment process such as diluting serum with water, was shown to be able to discriminate the extrinsic [¹³C]urea from intrinsic urea present at high concentration in serum. In addition, a ¹³C nuclear magnetic resonance spectroscopic quantitative method for [¹³C]urea in human urine is also described. The precision and accuracy of measured concentrations in these two methods were found to be within the acceptable limit. An application of these methods to investigate the pharmacokinetic profile of orally administered [¹³C]urea in human serum and urine is also presented.     

Translocation and conservation of organic nitrogen within the coral-zooxanthella symbiotic system of Acropora pulchra, as demonstrated by dual isotope-labeling techniques

Carbon (C) and nitrogen (N) metabolism of the hermatypic coral Acropora pulchra and its symbiotic algae (zooxanthellae) was investigated using ¹³C and ¹⁵N isotope tracers. A. pulchra was incubated in seawater containing ¹³C-labeled bicarbonate and ¹⁵N-labeled nitrate (NO₃⁻) for 24 h (pulse period), and subsequently ¹³C and ¹⁵N isotopic ratios of the host coral and the zooxanthellae were followed in ¹³C- and ¹⁵N-free seawater for 2 weeks (chase period). Under our experimental condition of NO₃⁻ (12 μM), C and N were absorbed by the coral-algal symbiotic system with the C:N ratio of 23 during the pulse period. Taking account of concentration dependence of NO₃⁻ uptake rates determined by a separate experiment, C:N uptake ratios under supposed in situ NO₃⁻ conditions (< 1.0 μM) would be > 3.0 times higher, if the photosynthetic rate did not change. During the pulse period, more than half of the absorbed ¹³C and ¹⁵N appeared in the host fraction in organic forms. ¹³C:¹⁵N ratio at the end of the pulse period was similar between the host and the algal fraction, suggesting that algal photosynthetic products were translocated to the host. It is also implied that C:N ratios of the translocated products change depending on N availability for the zooxanthellae. During the chase period, atom % excess (APE) ¹⁵N of the zooxanthellae constantly declined, while that of the host slightly increased. Consequently, APE ¹⁵N of the both fractions appeared to approach a common steady state value, suggesting that ¹⁵N was recycled within the coral-algal symbiotic system. As for C, > 86% of C photosynthetically fixed by the zooxanthellae accumulated in the host at the end of the pulse period, and had a turnover time of ca. 20 days for the host C pool during the following chase period. C:N ratios of organic matter newly synthesized with NO₃⁻ exponentially declined and converged into 5.7 and 4.5 for the host and the zooxanthellae, respectively. This suggests that organic compounds of high C:N ratios such as lipids and carbohydrates were selectively consumed more rapidly than those of low C:N ratios such as proteins and nucleic acids.     

13C–13C NOESY spectra of a 480 kDa protein: solution NMR of ferritin

Molecular size has limited solution NMR analyses of proteins. We report ¹³C–¹³C NOESY experiments on a 480 kDa protein, the multi-subunit ferritin nanocage with gated pores. By exploiting ¹³C-resonance-specific chemical shifts and spin diffusion effects, we identified 75% of the amino acids, with intraresidue C–C connectivities between nuclei separated by 1–4 bonds. These results show the potential of ¹³C–¹³C NOESY for solution studies of molecular assemblies >100 kDa.     

Dictyostelium discoideum as Expression Host: Isotopic Labeling of a Recombinant Glycoprotein for NMR Studies

The advantages of the organism Dictyostelium discoideum as an expression host for recombinant glycoproteins have been exploited for the production of an isotopically labeled cell surface protein for NMR structure studies. Growth medium containing [¹⁵N]NH₄Cl and [¹³C]glycerol was used to generate isotopically labeled Escherichia coli, which was subsequently introduced to D. discoideum cells in simple Mes buffer. A variety of growth conditions were screened to establish minimal amounts of nitrogen and carbon metabolites for a cost-effective protocol. Following single-step purification by anion-exchange chromatography, 8 mg of uniformly ¹³C,¹⁵N-labeled protein secreted by approximately 10¹⁰D. discoideum cells was isolated from 3.3 liters of supernatant. Mass spectrometry showed the recombinant protein of 16 kDa to have incorporated greater than 99.9% isotopic label. The two-dimensional ¹H-¹³C HSQC spectrum confirms ¹³C labeling of both glycan and amino acid residues of the glycoprotein. All heteronuclear NMR spectra showed a good dispersion of cross-peaks essential for high-quality structure determination.     

Conformation and dynamics changes of bacteriorhodopsin and its D85N mutant in the absence of 2D crystalline lattice as revealed by site-directed C NMR

¹³C NMR spectra of [3-¹³C]Ala- and [1-¹³C]Val-labeled D85N mutant of bacteriorhodopsin (bR) reconstituted in egg PC or DMPC bilayers were recorded to gain insight into their secondary structures and dynamics. They were substantially suppressed as compared with those of 2D crystals, especially at the loops and several transmembrane α_II-helices. Surprisingly, the ¹³C NMR spectra of [3-¹³C]Ala-D85N turned out to be very similar to those of [3-¹³C]Ala-bR in lipid bilayers, in spite of the presence of globular conformational and dynamics changes in the former as found from 2D crystalline preparations. No further spectral change was also noted between the ground (pH 7) and M-like state (pH 10) as far as D85N in lipid bilayers was examined, in spite of their distinct changes in the 2D crystalline state. This is mainly caused by that the resulting ¹³C NMR peaks which are sensitive to conformation and dynamics changes in the loops and several transmembrane α_II-helices of the M-like state are suppressed already by fluctuation motions in the order of 10⁴-10⁵ Hz interfered with frequencies of magic angle spinning or proton decoupling. However, ¹³C NMR signal from the cytoplasmic α-helix protruding from the membrane surface is not strongly influenced by 2D crystal or monomer. Deceptively simplified carbonyl ¹³C NMR signals of the loop and transmembrane α-helices followed by Pro residues in [1-¹³C]Val-labeled bR and D85N in 2D crystal are split into two peaks for reconstituted preparations in the absence of 2D crystalline lattice. Fortunately, ¹³C NMR spectral feature of reconstituted [1-¹³C]Val and [3-¹³C]Ala-labeled bR and D85N was recovered to yield characteristic feature of 2D crystalline form in gel-forming lipids achieved at lowered temperatures.     

~(13)C-标记秸秆添加对DNA稳定性同位素探针试验结果的影响

【目的】稳定性同位素探针技术(stable isotope probing,SIP)是采用稳定性同位素示踪复杂环境中具有代谢活性微生物的有力工具。然而,在近期利用SIP技术的研究当中,我们发现~(13)C-标记物对试验本身有一定程度影响。例如研究土壤秸秆降解微生物,需将~(13)C-标记作物秸秆添加到土壤,利用微域培养实验和DNA-SIP技术解析主导降解微生物物种。但是~(13)C秸秆的添加以及不同土壤肥力水平是否会影响土壤微生物群落有待商榷。【方法】本研究采集江西鹰潭红壤试验站3种施肥处理(Control、NPK、OM)水稻土壤,分别添加自然丰度(12C)和~(13)C-标记的高丰度水稻秸秆,进行微域培养试验,研究两种秸秆添加下的响应物种以及不同丰度C对生物质气体的累积排放、细菌a-多样性以及群落结构的影响。【结果】研究发现,3种施肥土壤下,2种丰度秸秆处理间C累计排放无差异。但是,寡营养条件(Control)下,~(13)C-标记秸秆处理的细菌a-多样性高,12C秸秆处理群落异质性高,稳定性较差,无差异性物种;与~(12)C秸秆处理相比,富营养条件(NPK和OM)下,~(13)C-标记秸秆处理的细菌a-多样性和群落结构无差异,但存在差异物种,主要集中于变形菌门和稀有物种。【结论】本研究的结果表明~(13)C标记秸秆对微生物群落有一定影响,因此在后续的SIP试验中,高丰度秸秆虽可被用来作为标记底物,但需慎用。     

The dynamics of neutral sugars in the rhizosphere of wheat. An approach by13C pulse-labelling and GC/C/IRMS

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.     

A13C NMR study of the hinge region of a mouse monoclonal antibody

Summary A¹³C NMR study is reported of the hinge region of an intact mouse monoclonal antibody with a molecular weight of 150 K. Cys, Ile, and Pro analogs of the antibody labeled with¹³C at the carbonyl carbon were prepared by growing hybridoma cells in the serum-free media. Resonance assignments have been performed as described previously [Kato, K., Matsunaga, C., Igarashi, T., Kim, H., Odaka, A., Shimada, I. and Arata, Y. (1991)Biochemistry,30, 270–278]. The spectral data obtained show that¹³C NMR can give detailed information about the structure of the hinge region of the intact antibody molecule. Prospects for the future role of¹³C NMR in the structural analyses of larger proteins are briefly discussed.Dedicated to the memory of Professor V.F. Bystrov     

Application of <Superscript>13</Superscript>C mineral carbon for assessment of the primary production of organic matter in aquatic environments

The possibility of measuring the rates of light and dark CO₂ assimilation using ¹³C carbonate was demonstrated on Lake Kichier (Marii El). The application of methods utilizing the stable ¹³C and the radioactive ¹⁴C isotopes resulted in comparable values of the rates of light and dark CO₂ fixation. Due to its absolute environmental safety, the method with ¹³C mineral carbon can be recommended as an alternative to radioisotope methods for qualitative measurements of CO₂ fixation rates in aquatic ecosystems.     

Estimates of methyl 13C and 1H CSA values (Δσ) in proteins from cross-correlated spin relaxation

Simple pulse schemes are presented for the measurement of methyl ¹³C and ¹H CSA values from ¹H–¹³C dipole/¹³C CSA and ¹H–¹³C dipole/¹H CSA cross-correlated relaxation. The methodology is applied to protein L and malate synthase G. Average ¹³C CSA values are considerably smaller for Ile than Leu/Val (17 vs 25 ppm) and are in good agreement with previous solid state NMR studies of powders of amino acids and dipeptides and in reasonable agreement with quantum-chemical DFT calculations of methyl carbon CSA values in peptide fragments. Small averaged ¹H CSA values on the order of 1 ppm are measured, consistent with a solid state NMR determination of the methyl group ¹H CSA in dimethylmalonic acid.     

Spectral analysis of a series of partially protected and deprotected tetrapeptides, analogues of AS-I phytotoxin

Summary A series of six tetrapeptides, analogues of AS-I phytotoxin, pathogenic to sunflower, have been synthesized either in solution and/or by solid phase methods and have been tested for phytotoxic activity in various plants and cytotoxic activity in three cancer cell lines. These peptides were identified as model compounds by fast atom bombardment (FAB), plasma desorption (PD), electrospray ionization (ESI) mass spectrometry and by¹H,¹H-¹H,¹³C and¹H-¹³C NMR. The data presented show that in protected tetrapeptides the molecular ion was easily identified whereas some difficulties appeared with the fully deprotected peptides. NMR spectra are given.     

Simultaneous <Superscript>1</Superscript>H- or <Superscript>2</Superscript>H-, <Superscript>15</Superscript>N- and multiple-band-selective <Superscript>13</Superscript>C-decoupling during acquisition in <Superscript>13</Superscript>C-detected experiments with proteins and oligonucleotides

Significant resolution improvement in ¹³C,¹³C-TOCSY spectra of uniformly deuterated and ¹³C, ¹⁵N-labeled protein and ¹³C,¹⁵N-labeled RNA samples is achieved by introduction of multiple-band-selective ¹³C-homodecoupling applied simultaneously with ¹H- or ²H- and ¹⁵N-decoupling at all stages of multidimensional experiments including signal acquisition period. The application of single, double or triple band-selective ¹³C-decoupling in 2D-[¹³C,¹³C]-TOCSY experiments during acquisition strongly simplifies the homonuclear splitting pattern. The technical aspects of complex multiple-band homonuclear decoupling and hardware requirements are discussed. The use of this technique (i) facilitates the resonance assignment process as it reduces signal overlap in homonuclear ¹³C-spectra and (ii) possibly improves the signal-to-noise ratio through multiplet collapse. It can be applied in any ¹³C-detected experiment.     

西北油松叶片δ13C特征与环境因子和叶片矿质元素的关系

选取甘肃、宁夏及内蒙古油松(Pinus tabulaeformis)10个天然种群, 通过测定油松叶片稳定碳同位素组成(δ¹³C)和元素含量等特征, 分析了油松叶片δ¹³C特征及其与环境气候因子和叶片矿质元素含量之间的关系。研究结果表明, 油松叶片δ¹³C的变化范围在-28.68‰ - -25.02‰之间, 平均值为-26.82‰; 油松叶片δ¹³C值与海拔、经度之间相关性不显著, 与纬度之间呈显著正相关, 与年降水量、年平均温度之间均呈显著负相关, 说明年平均温度和年降水量是决定油松¹³C分馏能力差别及生长的主要限制因子; 叶片元素N、P、K、Si、Ca、Fe含量与δ¹³C值有明显的相关性, 其中叶片N、P、K含量与δ¹³C值显著负相关, Si、Ca、Fe含量与δ¹³C值显著正相关, 可见不同种群间δ¹³C组成差异可反映植物营养元素含量的变化状况。不同生境条件下环境气候因子和矿质元素含量的这种响应模式在一定程度上反映和影响了以油松为建群种和优势种的生态系统的δ¹³C变化特性。     

Fractional <Superscript>13</Superscript>C enrichment of isolated carbons using [1-<Superscript>13</Superscript>C]- or [2-<Superscript>13</Superscript>C]-glucose facilitates the accurate measurement of dynamics at backbone C<Superscript>α</Superscript> and side-chain methyl positions in proteins

A simple labeling approach is presented based on protein expression in [1-¹³C]- or [2-¹³C]-glucose containing media that produces molecules enriched at methyl carbon positions or backbone C^α sites, respectively. All of the methyl groups, with the exception of Thr and Ile(δ1) are produced with isolated ¹³C spins (i.e., no ¹³C–¹³C one bond couplings), facilitating studies of dynamics through the use of spin-spin relaxation experiments without artifacts introduced by evolution due to large homonuclear scalar couplings. Carbon-α sites are labeled without concomitant labeling at C^β positions for 17 of the common 20 amino acids and there are no cases for which ¹³C^α−¹³CO spin pairs are observed. A large number of probes are thus available for the study of protein dynamics with the results obtained complimenting those from more traditional backbone ¹⁵N studies. The utility of the labeling is established by recording ¹³C R _1ρ and CPMG-based experiments on a number of different protein systems.