稳定同位素技术在植物水分利用研究中的应用

近20a稳定同位素技术在植物生态学研究中的应用得到了长足发展,使得对植物与水分关系也有了更深一步的了解。介绍稳定同位素性碳、氢、氧同位素在研究植物水分关系中的应用及进展,以期能为国内植物水分利用研究提供参考。由于植物根系从土壤中吸收水分时并不发生同位素分馏,对木质部水分同位素分析有助于对植物利用水分来源,生态系统中植物对水分的竞争和利用策略的研究,更好地了解生态系统结构与功能。稳定碳同位素作为植物水分利用效率的一个间接指标,在不同水分梯度环境中,及植物不同代谢产物与水分关系中有着广泛的应用。同位素在土壤-植被-大气连续体水分中的应用,有助于了解生态系统的水分平衡。随着稳定同位素方法的使用,植物与水分关系的研究将取得更大的进展。     

Biohydrogen production from microalgae—Major bottlenecks and future research perspectives

The imprudent use of fossil fuels has resulted in high greenhouse gas (GHG) emissions, leading to climate change and global warming. Reduction in GHG emissions and energy insecurity imposed by the depleting fossil fuel reserves led to the search for alternative sustainable fuels. Hydrogen is a potential alternative energy carrier and is of particular interest because hydrogen combustion releases only water. Hydrogen is also an important industrial feedstock. As an alternative energy carrier, hydrogen can be used in fuel cells for power generation. Current hydrogen production mainly relies on fossil fuels and is usually energy and CO₂-emission intensive, thus the use of fossil fuel-derived hydrogen as a carbon-free fuel source is fallacious. Biohydrogen production can be achieved via microbial methods, and the use of microalgae for hydrogen production is outstanding due to the carbon mitigating effects and the utilization of solar energy as an energy source by microalgae. This review provides comprehensive information on the mechanisms of hydrogen production by microalgae and the enzymes involved. The major challenges in the commercialization of microalgae-based photobiological hydrogen production are critically analyzed and future research perspectives are discussed. Life cycle analysis and economic assessment of hydrogen production by microalgae are also presented.     

Photoproduction of hydrogen by photosynthetic bacteria from sewage and waste water

Numerous prokaryotes, belonging to physiologically and taxonomically different groups, are able to produce hydrogen. Some photosynthetic bacteria have the property of light-dependent production of hydrogen from organic substrates. We isolated several photosynthetic purple and green bacteria from enrichment cultures made from the water of a waste-water pond of a cool-drink refilling station. After testing them for their ability to use various organic compounds as carbon source, and sulphide, thiosulphate and organic compounds as electron donor, we selected the fastest-growing isolate, aRhodopseudomonas, for a study of its ability to produce molecular hydrogen in presence of light. Immobilized cells of this isolate produced significant amounts of hydrogen from both sewage and waste water     

Usefulness of the hydrogen sulfide test for assessment of water quality in Bangladesh

Aim: To evaluate the usefulness of the hydrogen sulfide (H₂S) test for assessing water quality in Bangladesh. Methods and Results: We tested 382 water samples from a variety of sources using locally produced H₂S test kits and laboratory‐based membrane filtration for the detection of Escherichia coli. Compared with membrane filtration, H₂S tests, when incubated for 24 h, had both a sensitivity and positive predictive value (PPV) of <40% when analysis was restricted to water samples with E. coli levels below 100 colony forming units (CFU) per 100 ml. In contrast, for E. coli levels from 1000 to 9999 CFU per 100 ml, sensitivity was 94% and PPV 88%; specificity was 97% and negative predictive value was 99%. Conclusions: The hydrogen sulfide test, when incubated at 24 h, is a promising alternative for assessing water quality where E. coli levels may be high. An improved understanding of the incremental impact of contamination level on health is needed to better determine its usefulness. Significance and Impact of the Study: The hydrogen sulfide test is inexpensive, easy to use and portable. Its use may allow rapid assessment of water quality in situations where cost or logistics prevent use of other testing methods, such as in remote areas or during floods and other natural disasters.     

Developments and Perspectives in 3d Transition‐Metal‐Based Electrocatalysts for Neutral and Near‐Neutral Water Electrolysis

Technology for producing highly pure hydrogen (99.999%) by water electrolysis is a field of importance in terms of the planets' current energy scenario. A much needed transition from a carbon economy to a hydrogen economy further adds importance to the field of hydrogen generation from water for a sustainable future. To avoid energy losses in the production process, the use of highly acidic (Proton Exchange Membrane (PEM) water electrolyzer) and alkaline (alkaline water electrolyzer) electrolytes is conventional practice in this field. Unfortunately, there are several other issues associated with the use of acidic and alkaline electrolytes such as the requirement of specific ion exchanging membranes with good stability, acid or alkali stable catalysts and corrosive environment withstanding cell stacks, etc. To overcome these issues, researchers have shown interest in the field of electrochemical water splitting in neutral and near‐neutral conditions. In this review, the chronological development of 3d transition‐metal‐based electrocatalysts for neutral and near‐neutral water splitting is extensively discussed with emphases on screening methodologies, mechanisms, structure‐activity correlations, and detailed catalyst specific evolution. In addition, catalysts reported so far, are also benchmarked based on their performance separately for different electrolytes used.     

Increased snowfall weakens complementarity of summer water use by different plant functional groups

Winter snowfall is an important water source for plants during summer in semiarid regions. Snow, rain, soil water, and plant water were sampled for hydrogen and oxygen stable isotopes analyses under control and increased snowfall conditions in the temperate steppe of Inner Mongolia, China. Our study showed that the snowfall contribution to plant water uptake continued throughout the growing season and was detectable even in the late growing season. Snowfall versus rainfall accounted for 30% and 70%, respectively, of the water source for plants, on the basis of hydrogen stable isotope signature (δD) analysis, and accounted for 12% and 88%, respectively, on the basis of oxygen stable isotope signature (δ¹⁸O) analysis. Water use partitioning between topsoil and subsoil was found among species with different rooting depths. Increased snowfall weakened complementarity of plant water use during summer. Our study provides insights into the relationships between precipitation regimes and species interactions in semiarid regions.     

Water uptake by plants: perspectives from stable isotope composition

Stable isotope studies of hydrogen and oxygen stable isotope ratios of water within plants are providing new information on water sources, competitive interactions and water use patterns under natural conditions. Variation in the utilization of summer rain by aridland species and limited use of stream water by mature riparian trees are two examples of how stable isotope studies have modified our understanding of plant water relations. Analyses of xylem sap and tree rings have the potential of providing both short-term and long-term information on plant water use patterns.     

Thermodynamics of amide hydrogen bond formation in polar and apolar solvents

We present the initial findings of a theoretical study of hydrogen bond formation between two formamide molecules in water and in carbon tetrachloride. These systems were chosen as the simplest models for secondary structure formation in the polar environment near the protein surface and the apolar environment of the protein interior. We have employed thermodynamic simulation methods to obtain absolute binding free energies and free energy profiles for the formation of peptide hydrogen bonds in the two solvents. We find that the amide hydrogen bond is stable by 8.4 kcal/mol in CCl4, and by 0.3 kcal/mol in water. Our results indicate also that the hydrogen-bonded dimer is 2.2 kcal/mol more stable in water than it is in CCl4. We compare our results with those from experiment, and discuss their use in interpreting mechanisms of protein folding.     

Identification of by-products in hydrogen producing bacteria; Rhodobacter sphaeroides O.U. 001 grown in the waste water of a sugar refinery

Rhodobacter sphaeroides O.U. 001 is able to produce hydrogen anaerobically upon illumination. The cells were screened for the presence of valuable by-products such as poly-β-hydroxy (PHB) butyric acid aiming to improve the feasibility of the system. Also waste water from a sugar refinery was used for bacterial growth to further increase the feasibility. Under aerobic conditions the standard growth media containing -malic acid and sodium glutamate in 7.5/10 and 15/2 molar ratios and a medium containing 30% waste water from sugar refinery were used. In this case the maximum concentration of PHB produced were approximately 0.2 g l⁻¹ in both of the standard media whereas it was 0.3 g l⁻¹ in medium containing 30% waste water. By using the medium containing 30% waste water, PHB and hydrogen productions were determined under anaerobic conditions. The maximum concentration of PHB produced was around 0.5 g l⁻¹ and the amount of gas collected was 35 ml in 108 h. From these results it can be concluded that PHB can be collected during hydrogen production. The use of waste water from sugar refinery increased the yield.     

A view of the three dimensional structure of globular proteins

A view of the three dimensional structure of globular proteins based on continuous networks of hydrogen bonds is proposed. Active sites of enzymes and ion sites are prominent and, within the networks, there are islands of hydrophobic regions giving an overall piebald effect to the appearance of the molecule. This point of view was originally suggested by the results of quantum mechanical computations on the coupling between hydrogen bonds. A formalism for the total energy of a globular protein in water is also suggested.The study of five lines of experimental evidence supports this suggestion. The analysis of the experimental X-ray data for ten globular proteins, using the NETWORK program, revealed the existence of these hydrogen bond networks; X-ray data showed that water molecules tend to occupy fixed positions relative to the protein molecule; a survey has shown that water molecules tend to occupy specific positions relative to the hydrogen bonding side chains; experimental evidence on the bulk properties of lysozyme showed that there exist tightly bound water molecules; graphics studies of the ribonucleaseA molecule demonstrated the networks and the piebald effect. This point of view is pictorially simple and, to illustrate the use of such networks, we discuss the simple ion pairs which occur as substructures within the networks.     

Monte Carlo studies on water in the dCpG/proflavin crystal hydrate

The extensive water network identified in the crystallographic studies of the dCpG/Proflavin hydrate by Neidle, Berman and Shieh (Nature 288, 129, 1980) forms an ideal test case for a) assessing the accuracy of theoretical calculations on nucleic acid--water systems based on statistical thermodynamic computer simulation, and b) the possible use of computer simulation in predicting the water positions in crystal hydrates for use in the further refinement and interpretation of diffraction data. Monte Carlo studies have been carried out on water molecules in the unit cell of dCpG/proflavin, with the nucleic acid complex fixed and the condensed phase environment of the system treated by means of periodic boundary conditions. Intermolecular interactions are described by potential functions representative of quantum mechanical calculations developed by Clementi and coworkers, and widely used in recent studies of the aqueous hydration of various forms of DNA fragments. The results are analyzed in terms of hydrogen bond topology, hydrogen bond distances and energies, mean water positions, and water crystal probability density maps. Detailed comparison of calculated and experimentally observed results are given, and the sensitivity of results to choice of potential is determined by comparison with simulation results based on a set of empirical potentials.     

N-H...O, O-H...O, and C-H...O hydrogen bonds in protein-ligand complexes: strong and weak interactions in molecular recognition

The characteristics of N-H...O, O-H...O, and C-H...O hydrogen bonds are examined in a group of 28 high-resolution crystal structures of protein-ligand complexes from the Protein Data Bank and compared with interactions found in small-molecule crystal structures from the Cambridge Structural Database. It is found that both strong and weak hydrogen bonds are involved in ligand binding. Because of the prevalence of multifurcation, the restrictive geometrical criteria set up for hydrogen bonds in small-molecule crystal structures may need to be relaxed in macromolecular structures. For example, there are definite deviations from linearity for the hydrogen bonds in protein-ligand complexes. The formation of C-H...O hydrogen bonds is influenced by the activation of the C(alpha)-H atoms and by the flexibility of the side-chain atoms. In contrast to small-molecule structures, anticooperative geometries are common in the macromolecular structures studied here, and there is a gradual lengthening as the extent of furcation increases. C-H...O bonds formed by Gly, Phe, and Tyr residues are noteworthy. The numbers of hydrogen bond donors and acceptors agree with Lipinski's "rule of five" that predicts drug-like properties. Hydrogen bonds formed by water are also seen to be relevant in ligand binding. Ligand C-H...O(w) interactions are abundant when compared to N-H...O(w) and O-H...O(w). This suggests that ligands prefer to use their stronger hydrogen bond capabilities for use with the protein residues, leaving the weaker interactions to bind with water. In summary, the interplay between strong and weak interactions in ligand binding possibly leads to a satisfactory enthalpy-entropy balance. The implications of these results to crystallographic refinement and molecular dynamics software are discussed.     

Monte Carlo Studies on Water in the dCpG/Proflavin Crystal Hydrate

Abstract

The extensive water network identified in the crystallographic studies of the dCpG/Proflavin hydrate by Neidle, Berman and Shieh (Nature 288, 129, 1980) forms an ideal test case for a) assessing the accuracy of theoretical calculations on nucleic acid—water systems based on statistical thermodynamic computer simulation, and b) the possible use of computer simulation in predicting the water positions in crystal hydrates for use in the further refinement and interpretation of diffraction data. Monte Carlo studies have been carried out on water molecules in the unit cell of dCpG/proflavin, with the nucleic acid complex fixed and the condensed phase environment of the system treated by means of periodic boundary conditions. Intermolecular interactions are described by potential functions representative of quantum mechanical calculations developed by Clementi and coworkers, and widely used in recent studies of the aqueous hydration of various forms of DNA fragments. The results are analyzed in terms of hydrogen bond topology, hydrogen bond distances and energies, mean water positions, and water crystal probability density maps. Detailed comparison of calculated and experimentally observed results are given, and the sensitivity of results to choice of potential is determined by comparison with simulation results based on a set of empirical potentials.     

Using the amide proton signals of intracellular proteins and peptides to detect pH effects in MRI

In the past decade, it has become possible to use the nuclear (proton, 1H) signal of the hydrogen atoms in water for noninvasive assessment of functional and physiological parameters with magnetic resonance imaging (MRI). Here we show that it is possible to produce pH-sensitive MRI contrast by exploiting the exchange between the hydrogen atoms of water and the amide hydrogen atoms of endogenous mobile cellular proteins and peptides. Although amide proton concentrations are in the millimolar range, we achieved a detection sensitivity of several percent on the water signal (molar concentration). The pH dependence of the signal was calibrated in situ, using phosphorus spectroscopy to determine pH, and proton exchange spectroscopy to measure the amide proton transfer rate. To show the potential of amide proton transfer (APT) contrast for detecting acute stroke, pH effects were noninvasively imaged in ischemic rat brain. This observation opens the possibility of using intrinsic pH contrast, as well as protein- and/or peptide-content contrast, as diagnostic tools in clinical imaging.     

Utilization of a palladium-metal oxide semiconductor (Pd-MOS) sensor for on-line monitoring of dissolved hydrogen in anaerobic digestion

The use of a hydrogen-sensitive palladium-metal oxide semiconductor (Pd-MOS) sensor in combination with a membrane for liquid-to-gas transfer for the detection of dissolved hydrogen was investigated. The system was evaluated with known concentrations of dissolved hydrogen in water. The lowest concentration detected with this set-up was 160 nM. The method was applied to monitoring of a laboratory-scale anaerobic digestion process employing mixed sludge containing mainly food/industrial waste. Pulse loads of glucose were added to the system at different levels of microbial activity, and the microbial status of the culture was reflected in the dissolved hydrogen response. Simultaneous headspace hydrogen measurements were performed, and at the lower levels of dissolved hydrogen no corresponding headspace hydrogen could be detected. When glucose was added to a resting culture the dissolved hydrogen response was rapid and the first response could be detected 9 min after addition of glucose, whereas headspace hydrogen concentrations increased only after 80 to 110 min. This indicates limitations in the liquid-to-gas hydrogen transfer and illustrates the importance of hydrogen monitoring in the liquid. The sensor system developed is flexible, the membrane is easily replaceable, and the probe for liquid-to-gas hydrogen transfer can be adjusted easily to large-scale applications.     

关于生物制氢

简述了生物制氢发展过程及现今取得的成果。经济发展和人类对能源需求造成了诸如环境污染、常规能源短缺等一系列问题。因此 ,作为一种新型、可再生能源 ,氢能研究已经受到了人们高度重视。与其它制氢方法相比 ,生物制氢有着突出的优点 ,尤其是藻类利用太阳能光解水制氢 ,使人们看到了解决能源问题的希望。     

Development and application of a two-tier multiple-choice diagnostic test for high school students’ understanding of cell division and reproduction

Department of Physiological Botany, Uppsala University, Uppsala, Sweden Hydrogen gas is regarded as a potential candidate for a future energy economy. Research and development in the field of hydrogen energy is greatly encouraged on all continents. A wide range of microorganisms are able to produce hydrogen gas, among them photosynthetically active organisms that use light as their sole energy source. These organisms are good candidates for the photobiological production of hydrogen gas. Green algae are of particular interest since they are capable of splitting water during photosynthesis and of releasing hydrogen gas under certain conditions. This article describes a small bioreactor that can be run in the classroom and used to demonstrate the concept of photohydrogen production.     

The influence of environmental water on the hydrogen stable isotope ratio in aquatic consumers

Aquatic food webs are subsidized by allochthonous resources but the utilization of these resources by consumers can be difficult to quantify. Stable isotope ratios of hydrogen (deuterium:hydrogen; δD) potentially distinguish allochthonous inputs because δD differs between terrestrial and aquatic primary producers. However, application of this tracer is limited by uncertainties regarding the trophic fractionation of δD and the contributions of H from environmental water (often called “dietary water”) to consumer tissue H. We addressed these uncertainties using laboratory experiments, field observations, modeling, and a literature synthesis. Laboratory experiments that manipulated the δD of water and food for insects, cladoceran zooplankton, and fishes provided strong evidence that trophic fractionation of δD was negligible. The proportion of tissue H derived from environmental water was substantial yet variable among studies; estimates of this proportion, inclusive of lab, field, and literature data, ranged from 0 to 0.39 (mean 0.17 ± 0.12 SD). There is a clear need for additional studies of environmental water. Accounting for environmental water in mixing models changes estimates of resource use, although simulations suggest that uncertainty about the environmental water contribution does not substantially increase the uncertainty in estimates of resource use. As long as this uncertainty is accounted for, δD may be a powerful tool for estimating resource use in food webs.     

Advances in the biotechnology of hydrogen production with the microalga Chlamydomonas reinhardtii

Biological hydrogen production is being evaluated for use as a fuel, since it is a promising substitute for carbonaceous fuels owing to its high conversion efficiency and high specific energy content. The basic advantages of biological hydrogen production over other “green” energy sources are that it does not compete for agricultural land use, and it does not pollute, as water is the only by-product of the combustion. These characteristics make hydrogen a suitable fuel for the future. Among several biotechnological approaches, photobiological hydrogen production carried out by green microalgae has been intensively investigated in recent years. A select group of photosynthetic organisms has evolved the ability to harness light energy to drive hydrogen gas production from water. Of these, the microalga Chlamydomonas reinhardtii is considered one of the most promising eukaryotic H₂ producers. In this model microorganism, light energy, H₂O and H₂ are linked by two excellent catalysts, the photosystem 2 (PSII) and the [FeFe]-hydrogenase, in a pathway usually referred to as direct biophotolysis. This review summarizes the main advances made over the past decade as an outcome of the discovery of the sulfur-deprivation process. Both the scientific and technical barriers that need to be overcome before H₂ photoproduction can be scaled up to an industrial level are examined. Actual and theoretical limits of the efficiency of the process are also discussed. Particular emphasis is placed on algal biohydrogen production outdoors, and guidelines for an optimal photobioreactor design are suggested.     

植物水分利用策略研究进展

水分是影响植物生长发育的重要因子之一。地球上大多数生态系统中的植物都会经历一个降水相对稀少的干旱季节,植物在不同的季节与不同的生态系统中究竟如何利用水分,利用哪些水分去获得生存,成为一个人们关注的问题。在过去的20年,稳定同位素技术在植物生态学中的应用得到了稳定长足的发展。因为陆地植物(少数排盐种类除外)在水分吸收过程中不发生同位素分馏,因此可以利用δD与δ18O数据进行水分获取方式的研究。对植物木质部水分以及其潜在水源的稳定同位素进行分析,并参考土壤水势、叶片水势、土壤含水量等数据,同时运用二元或三元混合模型,可以定量确定植物的水分利用来源。大量的研究表明,不同功能型、生长阶段、季节的植物以及不同物种往往具有不同的水分利用策略。