Metal binding properties and structure of a type III metallothionein from the metal hyperaccumulator plant Noccaea caerulescens

Metallothioneins (MT) are low molecular weight proteins with cysteine-rich sequences that bind heavy metals with remarkably high affinities. Plant MTs differ from animal ones by a peculiar amino acid sequence organization consisting of two short Cys-rich terminal domains (containing from 4 to 8 Cys each) linked by a Cys free region of about 30 residues. In contrast with the current knowledge on the 3D structure of animal MTs, there is a striking lack of structural data on plant MTs. We have expressed and purified a type III MT from Noccaea caerulescens (previously Thlaspi caerulescens). This protein is able to bind a variety of cations including Cd(2+), Cu(2+), Zn(2+) and Pb(2+), with different stoichiometries as shown by mass spectrometry. The protein displays a complete absence of periodic secondary structures as measured by far-UV circular dichroism, infrared spectroscopy and hydrogen/deuterium exchange kinetics. When attached onto a BIA-ATR biosensor, no significant structural change was observed upon removing the metal ions.     

Demographic history of the trace metal hyperaccumulator Noccaea caerulescens (J. Presl and C. Presl) F. K. Mey. in Western Europe

Noccaea caerulescens (Brassicaceae) is a major pseudometallophyte model for the investigation of the genetics and evolution of metal hyperaccumulation in plants. We studied the population genetics and demographic history of this species to advance the understanding of among‐population differences in metal hyperaccumulation and tolerance abilities. Sampling of seven to 30 plants was carried out in 62 sites in Western Europe. Genotyping was carried out using a combination of new chloroplast and nuclear neutral markers. A strong genetic structure was detected, allowing the definition of three genetic subunits. Subunits showed a good geographic coherence. Accordingly, distant metallicolous populations generally belonged to distinct subunits. Approximate Bayesian computation analysis of demographic scenarios among subunits further supported a primary isolation of populations from the southern Massif Central prior to last glacial maximum, whereas northern populations may have derived during postglacial recolonization events. Estimated divergence times among subunits were rather recent in comparison with the species history, but certainly before the establishment of anthropogenic metalliferous sites. Our results suggest that the large‐scale genetic structure of N. caerulescens populations pre‐existed to the local adaptation to metalliferous sites. The population structure of quantitative variation for metal‐related adaptive traits must have established independently in isolated gene pools. However, features of the most divergent genetic unit (e.g. extreme levels of Cd accumulation observed in previous studies) question the putative relationships between adaptive evolution of metal‐related traits and subunits isolation. Finally, admixture signals among distant metallicolous populations suggest a putative role of human activities in facilitating long‐distance genetic exchanges.     

超累积植物与高生物量植物提取镉效率的比较

利用植物修复污染的土壤已受到广泛的关注.采用土壤盆栽试验,比较了超累积植物遏蓝菜与3种高生物量植物印度芥菜、烟草和向日葵对长期施用含镉有机、无机肥料污染的土壤(总Cd,2.87mg·kg-1)的提取效率.研究结果表明,遏蓝菜富集镉的能力明显高于其他3种植物,其地上部镉含量可达43.7mg·kg-1,分别是烟草、印度芥菜和向日葵(叶)的10、27和56倍;而地上部生物量最高的植物烟草,其生物量干重为24.8g· pot-1,分别是遏蓝菜、印度芥菜、向日葵的35倍、3倍、2倍.4种植物提取镉最多的是烟草,每盆可以提取117μg,遏蓝菜和印度芥菜提取镉量分别为35μg·pot-1和30μg·pot-1,向日葵提取量最少,每盆仅为10μg左右.植物对土壤中镉的提取效率分别为:烟草 1%,遏蓝菜0.6%,印度芥菜 0.5%,向日葵0.08%.4种植物种植后,土壤总镉和有效态镉含量没有显著的变化.     

The use of the three-ridge clam (Amblema perplicata) to monitor trace metal contamination

The three-ridge clamAmblema perplicata was used to monitor two streams for the presence of zinc (Zn) and cadmium (Cd) derived from an industrial source. Clams were collected from a relatively uncontaminated area in one river and transported to four study sites in the two contaminated streams. The clams were placed into polyethylene cages and left in these streams for one week. Control clams were treated in a similar manner and left in the uncontaminated river.The highest mean concentration of Zn (956 µg/g dry wt) was found in the gill tissue of clams from the most contaminated site. The highest mean Cd concentration (18.6 µg/ g dry wt) was found in digestive glands of clams, also from the most contaminated site. Mean concentrations at contaminated sites were significantly higher than background and control levels; the findings suggest that these particular organs of clams may be useful in monitoring levels of Zn and Cd in other freshwater systems.     

Effect of thallium fractions in the soil and pollution origins on Tl uptake by hyperaccumulator plants: a key factor for the assessment of phytoextraction

Phytoremediation is often discussed as a means of extracting trace metals in excess in the soil, but to increase its efficiency a better understanding of the factors controlling plant uptake is required. The main objective of this study was to examine the effect of origin (anthropogenic vs. geogenic) and mobility of thallium (Tl) in the rhizosphere on Tl uptake. Two Tl-hyperaccumulating Brassicaceae species, kale (Brassica oleracea acephala L. cv. Winterbor F1) and candytuft (Iberis intermedia Guers.), were grown in a rhizobox system to investigate the dynamics of Tl in the rhizosphere soil. Four different soils were used. Two soils contained high Tl amounts due to anthropogenic sources (emissions from a cement plant and mining activities). High Tl content in the two other soils was due to a high rock content (geogenic origin). On completion of growth in the rhizoboxes, the depletion of Tl in seven different chemical fractions, determined by sequential extraction, was compared to the plant uptake. Most of the Tl taken up was derived from the so-called "easily accessible" fractions in both soils with geogenic Tl as well as in the soils polluted by mining activities. Due to the small amounts of easily accessible Tl in the geogenic soils, Tl uptake by Brassicaceae was low. On the other hand, for the air emission-polluted soil, a high depletion of Tl from "less accessible" fractions was observed in addition to depletion of the easily accessible fractions. Hence, the latter soil demonstrated the highest potential for effective soil decontamination by phytoextraction within an appropriate time frame.     

A kinetic approach to predict soil trace metal bioavailability: preliminary results

The presence of large amounts of trace metals creates a hazard in some soils that is strongly related to the speciation of these metals. The aim of this work was to apply an operationally defined fractionation based on kinetics, which could distinguish “labile” (quickly extracted) and “non-labile” (or slowly labile i.e. slowly extracted) cations by using the extraction kinetics of trace metals by EDTA. This kinetic fractionation was applied to 10 unpolluted soil samples from Burgundy (France) in order to determine their labile concentrations of lead and cadmium. According to this method, cadmium was found to be more mobile than lead, with respect to both labile concentration and the kinetic constants. Moreover, it was also found that the labile concentration of cadmium was related (R ²=0.6) to its concentration in wheat shoots; however, no such correlation was found for lead.     

Plant availability of thallium in the rhizosphere of hyperaccumulator plants: a key factor for assessment of phytoextraction

The dynamics of thallium (Tl) fractions in the rhizosphere of two Tl hyperaccumulator plants, kale (Brassica oleracea acephala L. cv. Winterbor) and candytuft (Iberis intermedia Guers.), were examined to evaluate the efficiency of their possible use in phytoextraction. Plants were grown in a rhizobox system with a soil contaminated by Tl deposits from a cement plant in Leimen, Germany (1300 g Tl kg^–1 soil (aqua regia extraction) and 106 g Tl kg^–1 soil NH₄NO₃-extractable Tl). After 6 and 8 weeks growth of kale and candytuft, respectively, Tl fractions were sequentially extracted and compared with Tl uptake by plants. The uptake from `plant-available' Tl (fraction 1 – 4) in the rhizosphere (0–2 mm distance from root compartment) of both hyperaccumulator plants kale and candytuft accounted for 18 and 21% of the Tl accumulated in their shoots, respectively. The uptake from the `non-plant available' Tl (fraction 5 – 7) accounted for 50 and 40% of the mass of Tl accumulated by kale and candytuft, respectively. The high uptake capacity for Tl and the subsequent marked depletion in the rhizosphere soil might have resulted in a rapid shift in the equilibrium between the various Tl fractions. In addition, the high depletion in the rhizosphere indicates that the transport of Tl to roots is mainly diffusion driven. In conclusion, the easy access of the so called `non-plant available' Tl fraction in the rhizosphere soil by both hyperaccumulator plants indicates a high efficacy of possible phytoremediation of Tl contaminated soils such as the soil at the site in Leimen.     

Nickel and cobalt phytoextraction by the hyperaccumulator Berkheya coddii: implications for polymetallic phytomining and phytoremediation

We investigated the potential of the South African high-biomass Ni hyperaccumulator Berkheya coddii to phytoextract Co and/or Ni from artificial metalliferous media. Plant accumulation of both metals from single-element substrates indicate that the plant/media metal concentration quotient (bioaccumulation coefficient) increases as total metal concentrations increase. Cobalt was readily taken up by B. coddii with and without the presence of Ni. Nickel uptake was, however, inhibited by the presence of an equal concentration of Co. Bioaccumulation coefficients of Ni and Co for the single element substrates (total metal concentration of 1000 micrograms g-1) were 100 and 50, respectively. Cobalt phytotoxicity was observed above a total Co concentration in plant growth media of 20 micrograms g-1. Elevated Co concentrations significantly decreased the biomass production of B. coddii without affecting the bioaccumulation coefficients. The mixed Ni-Co substrate produced bioaccumulation coefficients of 22 for both Ni and Co. Cobalt phytotoxicity in mixed Ni-Co substrate occurred above a total Co concentration of 15 micrograms g-1. When grown in the presence of both Ni and Co, the bioaccumulation coefficients of each metal were reduced, as compared to single-element substrate. This may indicate competition for binding sites in the root zone. The interference relationship between Ni and Co uptake demonstrated by B. coddii suggests a significant limitation to phytoextraction where both metals are present.     

Effect of an artificial metal pollution on nematode assemblage of a calcareous loamy chernozem soil

Heavy metal pollution in soils constitutes an acute problem threatening various groups of living organisms. Nematode samples were taken in the framework of a complex food-chain experiment which is being carried out after artificially contaminating a part of an agrobiotope. The 13 heavy metals and microelements involved in the study are the following: Al, As, Ba, Cd, Cr, Cu, Hg, Mo, Ni, Pb, Se, Sr, and Zn. Parallel plots receiving maximum concentrations equal to approx. 270 ppm were sampled twice during a complete vegetation period of winter wheat. Nematode abundance and richness as well as Maturity Index data revealed that Se and Cr had significantly negative effects on assemblages, while Zn appeared to have a generally positive influence on these parameters. Impacts by the other elements are less obvious or quite neutral (like that of Al). Favorable soil conditions and time elapsed (over 5 years) since the contamination, both resulting in a decrease of available element concentrations, may account for the not very pronounced effects. This revised version was published online in June 2006 with corrections to the Cover Date.     

SNP分子标记及其在木本植物遗传育种的应用

木本植物因其生命周期长、基因组杂合度高、基因组较大、遗传背景不清晰等特性,制约了其研究进程。随着现代生物技术的发展,DNA分子标记技术在木本植物研究领域的应用越来越多,其中单核苷酸多态性(SNP)作为第三代分子标记技术以其高效、快速、稳定、可靠等诸多优点得到广泛应用。本文简述SNP标记的特点、开发方法、检测方法及其在木本植物遗传多样性和亲缘关系分析、品种鉴定、连锁图谱构建和辅助育种等方面的研究进展,为更好地应用SNP技术开展木本植物研究提供参考。     

Raising Climate-Resilient Crops: Journey From the Conventional Breeding to New Breeding Approaches

BackgroundIn order to meet the demands of the ever-increasing human population, it has become necessary to raise climate-resilient crops. Plant breeding, which involves crossing and selecting superior gene pools, has contributed tremendously towards achieving this goal during the past few decades. The relatively newer methods of crop improvement based on genetic engineering are relatively simple, and targets can be achieved in an expeditious manner. More recently emerged genome editing technique using CRISPR has raised strong hopes among plant scientists for precise integration of valuable traits and removal of undesirable ones.ConclusionGenome editing using Site-Specific Nucleases (SSNs) is a good alternative to the plant breeding and genetic engineering approaches as it can modify the genomes specifically and precisely at the target site in the host genome. Another added advantage of the genome editing approach is the simpler biosafety regulations that have been adopted by many countries for commercialization of the products thus generated. This review provides a critical assessment of the available methods for improving the stress tolerance in crop plants. Special emphasis has been given on genome editing approach in light of the diversity of tools, which are being discovered on an everyday basis and the practical applications of the same. This information will serve as a beginner’s guide to initiate the crop improvement programs as well as giving technical insight to the expert to plan the research strategically to tackle even multigenic traits in crop plants.     

人工诱变技术在植物抗病育种中的应用(综述)

介绍人工诱变技术在植物抗病育种中的主要成就,并探讨其发展方向及前景。人工诱变技术与杂交育种、基因转移及离体筛选等手段相结合,提高了育种效率,拓宽了抗病育种的范围。该技术在植物抗病育种中的成功应用,将有利于培育植物抗病新品种,促进农业的增产增收及可持续发展。     

桂北典型锰矿区周边土壤重金属污染状况及主要植物富集特征

为探究桂北某典型锰矿尾库区周边土壤和农作物重金属污染状况,筛选适合该地区污染土壤修复的植物材料,该研究在矿区周边采集了9种农作物和23种主要植物及其根际土壤,并测定了Cd、Mn、Cr、Pb和Zn 5种重金属含量,采用单因子污染指数法和综合污染指数法评价了矿区农田土壤、农作物中重金属的生态风险,通过计算植物对重金属的富集和转运系数评估其应用潜力。结果表明:(1)研究区土壤Cd、Mn污染最为严重,单因子污染指数分别为18.53、147.09,达到重度污染级别。(2)研究区花生和小白菜等作物可食用部位中的Cd、Cr、Pb含量均超过食品国家安全标准(GB 2762—2017)中的阈值,具有较高健康风险。(3)23种主要植物中青葙、鬼针草、一点红、蜈蚣草等对多种重金属转运系数大于1,具备富集型植物特征; 一把伞南星、蓖麻、千里光等根部重金属含量较高,转运系数较低,具备根部囤积型植物特征; 响铃豆、筒轴茅、苣荬菜等富集的重金属含量相对较低,且在重金属污染土壤中能健康生长,具备规避型植物特征。该研究结果表明,研究区土壤存在较严重的Cd/Mn复合污染,青葙等植物用于修复该复合污染土壤极具应用潜力。     

Zinc and cadmium uptake by the hyperaccumulator Thlaspi caerulescens in contaminated soils and its effects on the concentration and chemical speciation of metals in soil solution

The hyperaccumulator Thlaspi caerulescens J & C Presl. was grown in seven different soils collected from around Europe that had been contaminated with heavy metals by industrial activity or the disposal of sewage sludge to land. Zinc accumulation factors (shoot concentration/initial soil solution concentration) ranged from 3500–85 000 with a mean value of around 36 000. This compares with mean accumulation factors of 636, 66 and 122 for Cd, Ca and Mg, respectively. The concentration of Zn in the shoots was much greater than in the roots. The total removal of Zn and Cd ranged from 8 to 30 and from 0.02 to 0.5 mg kg^-1 soil, respectively. The Zn concentration in shoots of T. caerulescens correlated, using a curvilinear relationship, with the initial Zn concentration in soil solution (R² = total Zn 0.78; Zn²+ 0.80). There was no relationship between the uptake of Zn and the total Zn concentration in the soil. In most soils, solution pH increased only slightly after growth of T. caerulescens, indicating that acidification was not the mechanism used to mobilise Zn in the soil. Dissolved organic carbon concentrations generally increased but characterisation of the component organic compounds was not attempted. The concentrations of Zn and Cd in soil solution decreased considerably after growth of T. caerulescens. The percentages of Zn and Cd in soil solution present as free ions also decreased. However, the decrease of Zn in soil solution after growth accounted for only about 1% of the total Zn uptake by T. caerulescens. This was much lower than for Cd, Ca and Mg. The results suggest that either T. caerulescens was highly efficient at mobilising Zn which was not soluble initially, or the soils used had large buffering capacities to replenish soil solution Zn within a short time. This work highlights the need to investigate the role of root exudates on the mobilisation of Zn and Cd in soils by the hyperaccumulator T. caerulescens.     

Plant-associated bacteria and their role in the success or failure of metal phytoextraction projects: first observations of a field-related experiment

Phytoextraction has been reported as an economically and ecologically sound alternative for the remediation of metal-contaminated soils. Willow is a metal phytoextractor of interest because it allows to combine a gradual contaminant removal with production of biomass that can be valorized in different ways. In this work two willow clones growing on a metal-contaminated site were selected: ‘Belgisch Rood’ (BR) with a moderate metal extraction capacity and ‘Tora’ (TO) with a twice as high metal accumulation. All cultivable bacteria associated with both willow clones were isolated and identified using 16SrDNA ARDRA analysis followed by 16SrDNA sequencing. Further all isolated bacteria were investigated for characteristics that might promote plant growth (production of siderophores, organic acids and indol acetic acid) and for their metal resistance. The genotypic and phenotypic characterization of the isolated bacteria showed that the TO endophytic bacterial population is more diverse and contains a higher percentage of metal-resistant plant growth promoting bacteria than the endophytic population associated with BR. We hypothesize that the difference in the metal accumulation capacity between BR and TO clones might be at least partly related to differences in characteristics of their associated bacterial population.     

Enhanced phytoextraction: I. Effect of EDTA and citric acid on heavy metal mobility in a calcareous soil

Phytoextraction, the use of plants to extract heavy metals from contaminated soils, could be an interesting alternative to conventional remediation technologies. However, calcareous soils with relatively high total metal contents are difficult to phytoremediate due to low soluble metal concentrations. Soil amendments such as ethylene diaminetetraacetate (EDTA) have been suggested to increase heavy metal bioavailability and uptake in aboveground plant parts. Strong persistence of EDTA and risks of leaching of potentially toxic metals and essential nutrients have led to research on easily biodegradable soil amendments such as citric acid. In our research, EDTA is regarded as a scientific benchmark with which degradable alternatives are compared for enhanced phytoextraction purposes. The effects of increasing doses of EDTA (0.1,1,10 mmol kg(-1) dry soil) and citric acid (0.01, 0.05, 0.25, 0.442, 0.5 mol kg(-1) dry soil) on bioavailable fractions of Cu, Zn, Cd, and Pb were assessed in one part of our study and results are presented in this article. The evolution of labile soil fractions of heavy metals over time was evaluated using water paste saturation extraction (approximately soluble fraction), extraction with 1 M NH4OAc at pH 7 (approximately exchangeable fraction), and extraction with 0.5 M NH4OAc + 05 M HOAc + 0.02 M EDTA at pH 4.65 (approximately potentially bioavailable fraction). Both citric acid and EDTA produced a rapid initial increase in labile heavy metal fractions. Metal mobilization remained constant in time for soils treated with EDTA, but a strong exponential decrease of labile metal fractions was noted for soils treated with citric acid. The half life of heavy metal mobilization by citric acid varied between 1.5 and 5.7 d. In the following article, the effect of heavy metal mobilization on uptake by Helianthus annuus will be presented.