同位素示踪技术在丛枝菌根真菌生态学研究中的应用

丛枝菌根(arbuscular mycorrhizal,AM)真菌是生态系统中重要的土壤微生物之一。AM真菌菌丝体网络是由AM真菌菌丝体在土壤生态系统中连接两株或两株以上植物根系所形成的菌丝体网络。随着菌根学研究的深入,如何直观的揭示AM真菌的生态学功能已经成为相关领域关注的热点问题。研究发现,利用同位素示踪技术可以开展AM真菌与宿主植物对土壤矿质营养的吸收、转运等方面的研究,以及菌丝体网络对不同宿主植物之间营养物质的分配研究和AM真菌在生态系统生态学中的功能研究。基于此,为了阐明同位素示踪技术在AM真菌研究中的价值,围绕菌根学最新研究进展,系统回顾了利用同位素示踪技术探究AM共生体对不同元素吸收和转运的机制、同位素示踪技术在AM真菌菌丝体网络研究中的价值和利用同位素示踪技术研究AM真菌在生态系统中的功能,为AM真菌生态学功能的研究提供理论基础,并对本领域未来的研究方向和应用前景进行展望。     

同位素示踪技术在高中生物学实验中的应用小结

同位素示踪技术是生物学实验中常用的技术手段。将高中教材中所涉及到的利用同位素示踪技术研究的相关内容进行了归纳总结,便于学生对同位素示踪技术的理解和掌握。     

Pu同位素示踪技术在土壤侵蚀研究中的应用

土壤侵蚀是地球表面物质迁移的重要形式,也是造成土壤肥力下降和生态环境退化的重要诱因之一,对土壤侵蚀速率的定量研究是进行区域土壤侵蚀治理的前提和基础。大气核试验产生的Pu同位素具有较长的半衰期,其沉降到土壤中易被土壤中的黏土矿物和有机质吸附,近年来被认为是定量研究土壤侵蚀速率的重要示踪元素,尤其是质谱技术的发展,缩短了Pu同位素的测量时间并提高了其测量灵敏度,大力推动了土壤侵蚀核素示踪技术的发展。本文在梳理已有相关研究的基础上,总结土壤中Pu同位素的分布特征及吸附与迁移行为,阐述了应用Pu同位素示踪土壤侵蚀的基本原理和应用研究进展,并对Pu同位素和¹³⁷Cs示踪技术在土壤侵蚀研究中的适用性进行比较分析,对未来研究方向提出展望,以期为科学应用Pu同位素示踪技术研究土壤侵蚀提供参考。     

碳同位素示踪技术及其在陆地生态系统碳循环研究中的应用与展望

碳同位素示踪技术具有高度的专一性和灵敏度, 经过几十年的发展, 形成了一系列成熟的标记方法, 在陆地生态系统碳循环过程的研究中已得到广泛应用。目前, 自然丰度法、与¹³C贫化示踪技术结合的自由空气中气体浓度增加(FACE)实验、脉冲与连续标记法以及碳同位素高丰度底物富集标记法是研究陆地生态系统碳循环过程常用的碳同位素示踪方法; 通过将长期定位实验和室内模拟实验结合, 量化光合碳在植物-土壤系统的传输与分配特征, 明确植物光合碳对土壤有机质的来源、稳定化过程的影响及其微生物驱动机制; 阐明土壤碳动态变化(迁移与转化)和新碳与老碳对土壤碳库储量的相对贡献, 评估有机碳输入、转化与稳定的生物与非生物微观界面过程机制。然而, 生态系统碳循环受气候、植被、人为活动等多因素影响, 碳同位素技术需要结合质谱、光谱技术实现原位示踪, 结合分子生物学技术阐明其微生物驱动机制, 从而构建灵敏、准确、多尺度、多方位的同位素示踪技术体系。因此, 该文以稳定碳同位素为主, 综述了碳同位素示踪技术的原理、分析方法和在陆地生态系统碳循环过程中的应用进展, 归纳总结了碳同位素示踪技术结合原位检测技术和分子生物学技术的研究进展和应用前景, 并对碳同位素示踪技术存在的问题进行了分析和展望。     

碳同位素示踪技术及其在陆地生态系统碳循环研究中的应用与展望

碳同位素示踪技术具有高度的专一性和灵敏度,经过几十年的发展,形成了一系列成熟的标记方法,在陆地生态系统碳循环过程的研究中已得到广泛应用。目前,自然丰度法、与13C贫化示踪技术结合的自由空气中气体浓度增加(FACE)实验、脉冲与连续标记法以及碳同位素高丰度底物富集标记法是研究陆地生态系统碳循环过程常用的碳同位素示踪方法;通过将长期定位实验和室内模拟实验结合,量化光合碳在植物-土壤系统的传输与分配特征,明确植物光合碳对土壤有机质的来源、稳定化过程的影响及其微生物驱动机制;阐明土壤碳动态变化(迁移与转化)和新碳与老碳对土壤碳库储量的相对贡献,评估有机碳输入、转化与稳定的生物与非生物微观界面过程机制。然而,生态系统碳循环受气候、植被、人为活动等多因素影响,碳同位素技术需要结合质谱、光谱技术实现原位示踪,结合分子生物学技术阐明其微生物驱动机制,从而构建灵敏、准确、多尺度、多方位的同位素示踪技术体系。因此,该文以稳定碳同位素为主,综述了碳同位素示踪技术的原理、分析方法和在陆地生态系统碳循环过程中的应用进展,归纳总结了碳同位素示踪技术结合原位检测技术和分子生物学技术的研究进展和应用前景,并对碳同位素示踪技术存在的问题进行了分析和展望。     

对“同位素示踪技术在高中生物学实验中的应用小结”一文的商榷

同位素示踪技术是生物学实验中常用的一项技术,在人教版高中生物学教材中多处有所涉及。但在教学中,许多教师、教辅资料等并未对放射性同位素和稳定同位素进行严格的区分,以致出现了错误表述。针对《生物学通报》,2010年,第12期上“同位素示踪技术在高中生物学实验中的应用小结”一文,对同位素及其示踪技术进行了简要介绍,以期引起同行的注意。     

稳定性碳同位素在植物生理生态研究中的应用

稳定性碳同位素~(13)C/~(12)C比率是研究植物光合作用及有关的物质代谢、水分关系和生态系统中种间关系、进化及对环境的响应等的有效指标。δ~(13)C值与细胞间CO_2浓度及水分利用效率之间有一定的数量关系。光合作用过程中对碳同位素的辨别力主要是不同的CO_2扩散阻抗和羧化反应速率引起的结果。     

基于15N示踪技术的植物-土壤系统氮循环研究进展

同位素示踪技术是指外源添加与生物体内的元素或物质完全共同运行的示踪物,用来指示生物体内某元素或物质变化过程的一种方法。利用氮稳定同位素示踪技术,能从本质上揭示生态学过程发生的机理,从而成为生态学科研工作十分重要的工具之一。对近年来15N示踪技术应用于土壤氮素固定、植物氮素营养和植物-土壤系统氮迁移的研究进展进行了综述,并对稳定氮同位素技术在解决相关生态学难题可能的前景和不足方面进行了展望。     

稳定性碳同位素技术在生态学研究中的应用

 植物光合作用是自然界产生碳同位素分馏的最重要过程,也是碳同位素技术在生态学研究中应用的基础。最初,碳同位素主要应用于光合途径的鉴别。随着技术的不断完善和研究的不断深入,目前此项技术在生态学研究的许多领域都得到了广泛的应用。作者从植物叶片、功能群、群落冠层、生态系统以及全球等几个不同的尺度上,对碳同位素技术在生态学研究中的主要应用进行了简要的总结。     

固氮酶催化乙炔还原的色谱测定

一般认为(15)~N_2同位素示踪技术是研究固氮作用最可靠的方法。Dilworth 1965年发现乙炔也是固氮微生物的一种底物,报道了巴氏梭菌粗提液能还原乙炔为乙烯。Hardy和Knight最先用氢火焰离子化气相色谱法测定了还原反应的产物。此后,这一方法便成了研究固氮活性的有效方法。由于气相色谱法较之(15)~N_2同位素示踪法具有简单、迅速,灵敏等优点,并能适应江河、湖泊、土壤测定的需要,得到了广泛的应用。 (一) 在固氮研究中,无论是土壤肥力调查,固氮资源开发以及对于固氮酶分子水平的结构与功能,底物反应动力学等的研究,都是一项工作量     

Determination of stable molybdenum isotopes by thermionic mass spectrometry for tracer studies of molybdenum plant metabolism

A tracer technique based on multiple stable Mo isotopes and thermionic quadrupole mass spectrometry for isotopic analysis of plant tissue was developed and has been applied in the long-term study of foliar absorption of Mo by potato plants. As several tracers have been used the multivariate linear regression methods has been applied to calculate the portions of tracer Mo present in the potato samples from the isotopic ratios measured and to estimate their reproducibilities.In this paper solely the tracer portions transferred from the leaf into the tuber of the potato have been determined. Dependent on the time of contamination, tracer portions of 0.2 to 12% have been measured, corresponding to a maximum of 2.3% of the foliar application of the tracer molybdate. The reproducibilities of the tracer method as a whole (analytical determination and calculation of the tracer portions in the tracer plant samples) amounted to 7% at the maximum (with one exception); by contrast, the individual differences between the three plants investigated were much larger (up to 80%).     

生态系统光合与呼吸拆分的同位素理论、方法和应用进展

生态系统光合和呼吸是构成净生态系统CO₂交换量(NEE)的重要组分。涡度相关技术可直接观测生态系统NEE,并通过建立温度回归或光响应曲线等函数将NEE统计拆分为生态系统光合和呼吸,但是存在自相关和高估白天呼吸等问题。稳定同位素红外光谱技术的进步使高时间分辨率大气CO₂及其稳定碳同位素组成(δ¹³C)的连续观测成为可能,与涡度相关技术观测的NEE数据相结合,可实现昼夜和季节尺度生态系统光合和呼吸拆分。本文系统阐述了生态系统光合与呼吸的同位素通量拆分方法的基本理论与假设,阐述了同位素通量观测技术的发展及其应用进展,综述了同位素通量拆分理论解析生态系统光合与呼吸过程的新机制认识,最后总结并展望了同位素通量拆分理论的不确定性以及开展多种拆分方法综合比较的必要性。     

The phosphoenolpyruvate carboxykinase also catalyzes C3 carboxylation at the interface of glycolysis and the TCA cycle of Bacillus subtilis

Quantitative physiological characterization and isotopic tracer experiments revealed that pyruvate kinase mutants of Bacillus subtilis produced significantly more CO(2) from glucose in the tricarboxylic acid cycle than is explained by the remaining conversion of phosphoenolpyruvate (PEP) to pyruvate catalyzed by the phosphotransferase system. We show here that this additional catabolic flux into the tricarboxylic acid cycle was catalyzed by the PEP carboxykinase. In contrast to its normal role in gluconeogenesis, PEP carboxykinase can operate in the reverse direction from PEP to oxaloacetate upon knockout of pyruvate kinase in a riboflavin-producing B. subtilis strain and in wild-type 168. At least in the industrial strain, we demonstrate the additional capacity of PEP carboxykinase to function as a substitute anaplerotic reaction when the normal pyruvate carboxylase is inactivated. Presumably as a consequence of the unfavorable kinetics of an ATP-synthesizing anaplerotic PEP carboxykinase reaction, such pyruvate carboxylase mutants grow slowly or, as in the case of wild-type 168, not at all.     

Calculation of stable isotope enrichment tracer kinetic procedures

The choice of method of expressing isotopic enrichment in tracer kinetic experiments utilizing stable isotopes was found to affect the calculation of tracee pool size and half-life. The most commonly used definition, the difference between enriched and natural abundance, i.e. atom percent excess, was found to result in significant error in model systems when the dose of tracer was 10% of the pool size. Errors in determining first-order rate constants of efflux and in pool sizes decreased with decreasing ratio of tracer to tracee. Error in determining pool size increased with longer 'sampling' periods, while error in determining the rate constant increased with shorter sampling periods. Of three less frequently used expressions of isotopic enrichment two were found to yield the exact answers in model systems. The correct expressions of isotopic enrichment were linear functions of the quantity of tracer in the system. A practical example demonstrated the effect of choice of expression of enrichment on estimates of whole body copper pool size and turnover in dairy cattle.     

18O and mass spectrometry in chlorophyll research: Derivation and loss of oxygen atoms at the periphery of the chlorophyll macrocycle during biosynthesis,degradation and adaptation

Chlorophylls, magnesium-containing tetrapyrrolic pigments of photosynthesis, are widely-distributed in Nature and participate in both light harvesting and in the transduction of light energy to chemical energy for the photosynthetic fixation of carbon dioxide. We briefly discuss the extensive role of various isotopic labelling techniques in elucidating the pathway of tetrapyrrole-pigment biosynthesis and we acknowledge the classic and meticulous research of David Shemin who, approximately 50 years ago, introduced isotopic tracer techniques with ¹⁵N and ¹⁴C isotopes to study the biosynthesis of the carbon/nitrogen macrocycle of haem, an iron tetrapyrrole. The main focus of this review is the application of mass spectrometry and ¹⁸O labelling to the study of the incorporation of oxygen atoms from molecular oxygen or water into the periphery of the chlorophyll macrocycle during biosynthesis and their loss during degradation and light acclimation. In particular, we review the mechanism of formation of the isocyclic ring of chlorophylls, in higher plants, green algae and various photosynthetic bacteria, which concomitantly incurs formation of the 13¹-oxo group that is present in all photosynthetically-active chlorophylls. In addition we discuss the formation of the ubiquitous 13³- and 17³-carboxyl groups and also the formation of the 7-formyl group of chlorophyll b and the 3-acetyl group of bacteriochlorophyll a. This revised version was published online in June 2006 with corrections to the Cover Date.     

On-line mass spectrometry: membrane inlet sampling

Significant insights into plant photosynthesis and respiration have been achieved using membrane inlet mass spectrometry (MIMS) for the analysis of stable isotope distribution of gases. The MIMS approach is based on using a gas permeable membrane to enable the entry of gas molecules into the mass spectrometer source. This is a simple yet durable approach for the analysis of volatile gases, particularly atmospheric gases. The MIMS technique strongly lends itself to the study of reaction flux where isotopic labeling is employed to differentiate two competing processes; i.e., O₂ evolution versus O₂ uptake reactions from PSII or terminal oxidase/rubisco reactions. Such investigations have been used for in vitro studies of whole leaves and isolated cells. The MIMS approach is also able to follow rates of isotopic exchange, which is useful for obtaining chemical exchange rates. These types of measurements have been employed for oxygen ligand exchange in PSII and to discern reaction rates of the carbonic anhydrase reactions. Recent developments have also engaged MIMS for online isotopic fractionation and for the study of reactions in inorganic systems that are capable of water splitting or H₂ generation. The simplicity of the sampling approach coupled to the high sensitivity of modern instrumentation is a reason for the growing applicability of this technique for a range of problems in plant photosynthesis and respiration. This review offers some insights into the sampling approaches and the experiments that have been conducted with MIMS.

     

Concerning the equilibrium exchange kinetics and mechanism of the sheep brain glutamine synthetase reaction

Isotope exchange measurements of sheep brain glutamine synthetase have yielded conflicting experimental findings and interpretation, leaving in doubt the question of whether the enzyme operates via ordered or random pathways of enzyme-substrate interactions. We now report new experimental evidence that demonstrates the earlier discrepant results may be attributed to the choice of reaction conditions used to achieve equilibration of the chemical reaction prior to addition of isotopic tracer. A random kinetic mechanism, perhaps not of the rapid-equilibrium type, is most compatible with the exchange data. We also discuss other potential time-dependent processes that may compromise the equilibration of reaction systems and affect the outcome of exchange experiments, and criteria for equilibration are suggested for the aid of other workers.     

光合作用研究进展:从分子机理到绿色革命

根据国际科学期刊Nature,Science和PhotosynthesisResearch等近年发表的60多篇文献评论了过去5年来光合作用研究领域的研究进展.这篇评论由光合机构的精细结构与光合作用的反应机理、光合作用的调节机制与环境胁迫和光合机理知识的应用与绿色革命三部分组成.第一部分包括天线和反应中心的结构、放氧机理和ATP合成的分子机理;第二部分涉及二磷酸核酮糖羧化酶/加氧酶,光抑制,氧化还原调节和光合作用的高温抑制;第三部分讨论新绿色革命的特点和艰巨性,指出新绿色革命的中心问题是作物光合效率的改善,锐利武器是基因工程,新绿色革命的成功有赖于对光合作用的深入理解和分子生物学家、植物生理学家、生物化学家与农学家们的协同努力.     

Double isotope tracer method for measuring fractional zinc absorption: theoretical analysis

Several approaches for estimation of fractional zinc absorption (FZA) by calculating the ratio of oral to intravenous stable isotopic tracer concentrations (at an appropriate time) in urine or plasma after their simultaneous administration have been proposed in the last decade. These simple-to-implement approaches, often referred to as the double isotopic tracer ratio (DITR) method, are more attractive than the classical "deconvolution" method and the more commonly used single-tracer methods based on fecal monitoring and indicator dilution, after oral or intravenous tracer administration, respectively. However, the domain of validity of DITR for measuring FZA has recently been questioned. In this paper, we provide a theoretical justification of the validity of four different "approximate" formulations of the DITR technique by demonstrating mathematically that their accuracy is a consequence of the particular properties of zinc kinetics.     

Antiquity of the biological sulphur cycle: evidence from sulphur and carbon isotopes in 2700 million-year-old rocks of the Belingwe Belt, Zimbabwe

Sulphur and carbon isotopic analyses on small samples of kerogens and sulphide minerals from biogenic and non-biogenic sediments of the 2.7 x 10(9) years(Ga)-old Belingwe Greenstone Belt (Zimbabwe) imply that a complex biological sulphur cycle was in operation. Sulphur isotopic compositions display a wider range of biological fractionation than hitherto reported from the Archaean. Carbon isotopic values in kerogen record fractionations characteristic of rubisco activity methanogenesis and methylotrophy and possibly anoxygenic photosynthesis. Carbon and sulphur isotopic fractionations have been interpreted in terms of metabolic processes in 2.7 Ga prokaryote mat communities, and indicate the operation of a diverse array of metabolic processes. The results are consistent with models of early molecular evolution derived from ribosomal RNA.