超积累植物吸收重金属的根际效应研究进展

阐述近年来国内外在超积累植物吸收重金属的根际微生态效应这一领域的最新研究成果 ,介绍了根际微生态效应在植物修复中的应用 ,并对当前超积累植物在根际微生态效应研究中的不足之处和需要进一步深入研究的方向进行讨论。     

浅析植物吸收矿质盐与根际pH变化

1881年,Mayer根据植物吸收矿质盐时根际PH的变化,提出了生理酸碱性盐理论。植物吸收矿质盐时,根际PH为什么会发生变化？现行的植物生理学教材”·’,’－”伙都归结为植物对矿质盐的阴阳离子不均等吸收后残留离子的作用。一些讨论生理酸碱性盐的文章p’‘’恰当地否定了残留离子的作用,认为是由于植物不均等吸收了矿质盐的阴阳离子,为保持细胞PH恒定和电行平衡而分泌或吸收十”的结果。对此问题,笔者也想谈一点粗浅的看法。要阐明植物吸收矿质盐时根际PH变化的原因,首先应从根如何吸收矿质盐开始。矿质盐是以离子形式被吸收进入…     

植物超积累重金属的生理机制研究进展

土壤重金属污染已经成为一个全球性问题。重金属超积累植物在修复土壤重金属污染中具有重要的应用前景。重金属超积累植物通常具备三个基本特征,即：根系具有从土壤中吸收重金属的强大能力、能从根到地上部分高效转运重金属、在叶片中能解毒和隔离大量重金属。本文总结了重金属超积累植物吸收、转运、隔离和解毒重金属的生理机制研究进展,以期为进一步阐明植物超积累重金属的机制及其在植物修复中的应用提供参考。     

铜矿区超积累Cu植物的研究

1　引　　言土壤重金属污染一直是环境污染问题之一 ,而且土壤中的重金属污染具有严重性、长期性和广泛性的特点[1 ,6] .但常规的一些物理化学方法因费用过高、对土壤性质破坏等一系列问题而难以广泛应用 ,植物修复为重金属污染带来了希望[5,7,9,1 3] .植物修复主要是基于重金属超积累植物 (ｈｙｐｅｒ ａｃｃｕｍｕｌａｔｏｒ)的研究而兴起的 .超积累植物是指地上部分能富集重金属占干重的 1 0 0ｍｇ·ｋｇ-1 (Ｃｕ、Ｐｂ、Ｃｄ)或 1 0 0 0 0ｍｇ·ｋｇ-1 (如Ｚｎ)的一类植物[2～ 4,8] .在过去 2 0年内 ,已报道的超积累植物已有 4 0 0余种 …     

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.     

镉超积累植物及植物镉积累特性转基因改良研究进展

植物提取修复技术是一项既经济又环保的土壤镉(Cd)污染修复技术,该技术的关键是筛选Cd超积累植物或利用基因工程手段改良植物以提高其Cd积累能力。人们已发现遏兰菜等7种Cd超积累植物及美人蕉等潜在的Cd超积累植物。还发现了许多与Cd耐受和积累能力有关的基因:(1)编码与Cd积累、耐受有关酶的基因,如细菌中的ACC(1-aminocyclopropane-1-carboxylic acid),植物中的PCS(Phytochelatin Synthase)基因;(2)编码金属结合蛋白的基因:MT(Metallothionein)、转运蛋白(P-type ATPase、ABC型转运器)基因;(3)其它相关基因:Hvhsp17、PvSR2(Phaseolus vulgaris stress-related gene number 2)等。并将其中的一些基因转入到其它生物中,提高了其对Cd的耐受性和积累量,为实现Cd污染土壤修复的目标奠定基础。     

植物对重金属的吸收和分布

植物修复是利用植物来清除污染土壤中重金属的一项技术。该技术成功与否取决于植物从土壤中吸取金属以及向地上部运输金属的能力。植物对金属的吸收主要取决于自由态离子活度。许多螯合剂能诱导植物对重金属的吸收。金属离子在液泡中的区域化分布是植物耐重金属的主要原因。同时,细胞内的金属硫蛋白、植物螯合脓等蛋白质以及有机酸、氨基酸等在金属贮存和解毒方面也起重要作用。本文还论述了重金属在植物体内运输的生理及分子方面的研究进展。     

植物对重金属的吸收和分布

植物修复是利用植物来清除污染土壤中重金属的一项技术。该技术成功与否取决于植 物从土壤中吸取金属以及向地上部运输金属的能力。植物对金属的吸收主要取决于自由态离子活度。许多螯合剂能诱导植物对重金属的吸收。金属离子在液泡中的区域化分布是植物耐 重金属的主要原因。同时,细胞内的金属硫蛋白、植物螯合肽等蛋白质以及有机酸、氨基酸等在金属贮存和解毒方面也起重要作用。本文还论述了重金属在植物体内运输的生理及分子 方面的研究进展。     

水稻不同品种对Cd吸收累积的差异和机理研究

采用盆栽和水培试验研究了华南地区水稻的主要品种对Ｃｄ吸收累积的差异和引起差异的原因。盆栽试验结果表明,供试的２０多个品种生长在同一污染土壤上,汕优６３,汕优６４等杂交稻,产量较高,但糙米Ｃｄ含量也较高,野奥丝苗,增城丝苗,黑糯等优质稻糙米重金属含量较低;常规稻则变幅较大,作物品种间差异可达１倍以上,在同一Ｃｄ浓度和营养液配方条件下的水培试验显示,与汕优６３相比,糙米Ｃｄ含量较低的野奥丝苗其单位产量     

超积累植物的金属配位体及其在植物修复中的应用

综述了超积累植物体内金属配位体（包括植物螯合肽、植物金属硫蛋白、有机酸和氨基酸）的生物合成,参与的植物体内金属的吸收、运输、积累的解毒过程的生理及分子机制,并对金属配位体在植物修复中的应用作了评述。     

Influence of root-induced pH on the solubility of soil aluminium in the rhizosphere

Increase in solubility of soil aluminium (Al) as a result of root-induced decrease of soil pH was studied. Soil samples of known distances from the roots of NH₄-N fertilized Ryegrass were analyzed for pH and aluminium extractable with 0.01 M CaCl₂. Results showed that though no Al was found in bulk soil (pH 6.8), its concentration in the vicinity of roots increased to 0.023 mM with a concomitant decrease of soil pH from 6.8 to 4.4.     

Comparison of the chemical changes in the rhizosphere of the nickel hyperaccumulator Alyssum murale with the non-accumulator Raphanus sativus

Changes in pH and redox potential were studied in the rhizosphere soil of a nickel hyperaccumulator plant (Alyssum murale) and of a crop plant, radish (Raphanus sativus). Differences in rhizosphere pH and reducing activity were found between the lateral and the main roots of both species, but the pH changes in the rhizosphere were similar in both species. Changes in pH were associated with the relative uptakes of cations and anions; whether the concentrations of heavy metals in the growth medium did not have any effect on the rhizosphere pH. The source of nitrogen (ammonium or nitrate) was the major factor determining the pH of the rhizosphere of both species. The redox potential of the rhizosphere was influenced by both the N-source and the concentrations of heavy metals. When heavy metals were not present in the growth medium, and nitrate was the N-source, the reducing capacity of A. murale roots was enhanced. However, the reducing activity of A. murale was always smaller than that of radish. Therefore, the mechanism of metal solubilization by the hyperaccumulator plant does not involve either the reduction of pH in the rhizosphere or the release of reductants from roots. The acidification and reducing activity of the roots of A. murale was always smaller than that of R. sativus.     

Copper bioavailability and rhizosphere pH changes as affected by nitrogen supply for tomato and oilseed rape cropped on an acidic and a calcareous soil

Vineyard soils have been contaminated by long-term applications of copper salts as fungicides against mildew, raising the question of the bioavailability (and toxicity) of such accumulated Cu to cultivated plants which can replace vines. The aim of this study was to assess, in an acidic and a calcareous Cu-contaminated soil, how the extractability and bioavailability of soil Cu was affected by pH changes in the rhizosphere of two plant species (oilseed rape and tomato), in response to various forms of nitrogen supply (nitrate only or both nitrate and ammonium). Besides shoot analysis, the experimental approach used in the present work provided an easy access to both roots and rhizosphere soil. Roots of tomato and rape induced a systematic acidification in the calcareous soil while root-induced alkalinization occurred in the acidic soil. Whilst few differences were found between treatments in the calcareous soil, oilseed rape took up more Cu and also alkalinized its rhizosphere more strongly than tomato in the acidic soil. The growth of tomato roots was restricted in the acidic soil, while that of oilseed rape was not, suggesting that tomato was either more sensitive to soil acidity and/or Cu toxicity. A major finding was that, in the acidic soil, Cu bioavailability increased with increasing rhizosphere pH. This was largely due to the enhanced accumulation of Cu in the root compartment of both species with increasing rhizosphere pH. The hypothetical explanation proposed here is that Cu binding to root cell walls played a major role in the accumulation of Cu into the plant. Apoplasmic Cu (Cu bound to cell walls) would indeed be expected to increase with increasing pH as a consequence of the pH-dependency of the charges of cell wall constituents.     

Involvement of multiple aluminium exclusion mechanisms in aluminium tolerance in wheat

The goal of this study was to determine if Al-chelators other than malate are released from root apices and are involved in Al-tolerance in different wheat (Triticum aestivum L.) genotypes. Also we wanted to establish if root exudates contribute to increases in rhizosphere pH around the root tip. In seedlings of Al-tolerant Atlas, we have documented a constitutive phosphate exudation from the root apex. Because phosphate can complex Al and bind protons, it could play an important role in Al tolerance, both via complexation of Al³⁺ and by contributing to the alkalinization of rhizosphere pH observed at the apex of Atlas. This study suggests that in wheat, Al-tolerance can be mediated by multiple exclusion mechanisms controlled by different genes.     

不同耐盐植物根际土壤盐分的动态变化

以甘肃秦王川引大灌区盐渍化土壤为研究背景,用盆栽根袋法对4种耐盐植物根际和非根际土壤pH和盐分离子的动态变化进行了分析比较。结果表明:4种待测植物随着培养时间的延长土壤pH和EC值呈降低趋势。新疆大叶(Medicago Sativa L.cv.Xinjiangdaye)、向日葵(Helianthus annuus)和霸王(Zygophyllum xanthoxylum)生长90 d后根际土壤pH明显低于非根际,而裸麦(Hordeum vulgare var. vulgare)根际较非根际pH差异不大。霸王和新疆大叶根际土壤EC值较非根际高,而裸麦和向日葵的根际与非根际差异不大。4种供试植物根际K⁺均出现亏缺,Ca²⁺、Na⁺、Mg²⁺、SO^2-₄和Cl^-在新疆大叶、霸王和向日葵3种植物根际均出现富集,对于裸麦:Ca²⁺、Mg²⁺和SO^2-₄ 3种离子在植物根际富集,而Cl^-和Na⁺在根际亏缺。随着待测植物培养时间的增加Na⁺/K⁺、Na⁺/Ca²⁺和Na⁺/Mg²⁺ 这3个比值呈降低趋势,说明Na⁺相对于K⁺、Ca²⁺和Mg²⁺的含量降低,生物措施对Na⁺的移除效果较显著。     

The Carbon Cost of Protecting the Root Apex from Soil Acidity: A Theoretical Framework

There is an assumption in much recent literature that secreted organic anions (OAs) protect the root meristem from Al toxicity by complexation of Al ions. In fact, several possible mechanisms exist by which common OA might afford some degree of protection. Plants can excrete OA which undergo chemical association with protons (hereafter referred to as protonation) in the soil and increase rhizosphere pH. The cost in reduced carbon relative to protons consumed, C:H⁺, ranges from 2–6. The efficiency of this mechanism can be enhanced in the presence of soil organisms which can oxidise the OA that remain dissociated at soil pH to CO₂ and H₂O, thereby consuming protons which associate with lower pK functional groups (pK 1.2 to ~ 4). For fully dissociated organic acids the C:H⁺ ratio decreases to the range 1–3. The C cost to plants is further minimised if MnO₂ is the terminal electron acceptor rather than O₂, resulting in C:H⁺<1. OA might also complex or chelate Al. Complexes of Al³⁺ with oxalate appear to be effective, with some C:H⁺≤1. However, citrate complexation appears to be more stable in pure solutions and might offer the additional benefit of enhanced P acquisition. Our assessment is that the most efficient strategy for a plant to employ to protect itself from Al toxicity is to increase pH near the root apex by secreting OA into soil where the microbial oxidation of reduced C could be coupled with the reduction of MnO₂. This would consume 0.2–0.67 mole of C per H⁺, which is the order of magnitude better than the C:H⁺ ratio of 2–6 that would occur if only protonation of OA was to be relied upon. These mechanisms have implications for the effectiveness of programs aimed at selecting cultivars for resistance to acidic soils.     

The effects of root-induced pH changes on the depletion of inorganic and organic phosphorus in the rhizosphere

A new method allowing control of rhizosphere pH and mineral nutrition was applied to study depletion of various organic and inorganic phosphorus fractions extractable sequentially with 0.5M KHCO₃ (pH 8.5), 0.1M NaOH and residual P extractable with 6M H₂SO₄ from the rhizosphere soil.Soil pH was affected about 2 mm from the root mat. Depletion zones of inorganic P (KHCO₃-P_i) extractable with 0.5M KHCO₃ extended up to about 4 mm but the depletion zones of all other P fractions were about 1 mm only. The root-induced decrease of soil pH from 6.7 to 5.5 increased the depletion of total P from all fractions by 20% and depletion of KHCO₃-P_i and residual P by 34% and 43%, respectively. Depletion of organic P (KHCO₃-P_o) extractable with 0.5M KHCO₃ was not affected by a change in rhizosphere pH. With constant or increased pH, depletion of inorganic P (NaOH-P_i) was 17% and organic P (NaOH-P_o) was 22% higher than with decreased pH. Only 54–60% of total P withdrawn from all fractions was from KHCO₃-P_i. Substantial amounts of KHCO₃-P_o and NaOH-P_o were mineralized and withdrawn from the rhizosphere within 1 mm from the root mat, as 11–15% of total P withdrawn originated from the organic P fractions. A remaining 11–16% was derived from NaOH-P_i, and 15–18% from residual P fractions likely to be rather immobile. Thus, 40–46% of the P withdrawn near the root mat of rape originated from non-mobile P fractions normally not included in 0.5M NaHCO₃ extraction used to obtain an index of plant-available soil P.     

Origins of root-mediated pH changes in the rhizosphere and their responses to environmental constraints: A review

The aim of the present review is to define the various origins of root-mediated changes of pH in the rhizosphere, i.e., the volume of soil around roots that is influenced by root activities. Root-mediated pH changes are of major relevance in an ecological perspective as soil pH is a critical parameter that influences the bioavailability of many nutrients and toxic elements and the physiology of the roots and rhizosphere microorganisms. A major process that contributes root-induced pH changes in the rhizosphere is the release of charges carried by H⁺ or OH^– to compensate for an unbalanced cation–anion uptake at the soil–root interface. In addition to the ions taken up by the plant, all the ions crossing the plasma membrane of root cells (e.g., organic anions exuded by plant roots) should be taken into account, since they all need to be balanced by an exchange of charges, i.e., by a release of either H⁺ or OH^–. Although poorly documented, root exudation and respiration can contribute some proportion of rhizosphere pH decrease as a result of a build-up of the CO₂ concentration. This will form carbonic acid in the rhizosphere that may dissociate in neutral to alkaline soils, and result in some pH decrease. Ultimately, plant roots and associated microorganisms can also alter rhizosphere pH via redox-coupled reactions. These various processes involved in root-mediated pH changes in the rhizosphere also depend on environmental constraints, especially nutritional constraints to which plants can respond. This is briefly addressed, with a special emphasis on the response of plant roots to deficiencies of P and Fe and to Al toxicity. Finally, soil pH itself and pH buffering capacity also have a dramatic influence on root-mediated pH changes.