Sorghum roots are inefficient in uptake of EDTA-chelated lead

BACKGROUND AND AIMS: Ethylene diamine tetraacetic acid (EDTA)-assisted phytoremediation has been developed to clean up lead (Pb)-contaminated soil; however, the mechanism responsible for the uptake of EDTA-Pb complex is not well understood. In this study, the accumulation process of Pb from EDTA-Pb is characterized in comparison to ionic Pb [Pb(NO(3))(2)] in sorghum (Sorghum bicolor). METHODS: Sorghum seedlings were exposed to a 0.5 mM CaCl(2) (pH 5.0) solution containing 0, 1 mM Pb(NO(3))(2) or EDTA-Pb complexes at a molar ratio of 1:0.5, 1:1, 1:2 and 1:4 (Pb:EDTA). The root elongation of sorghum at different ratios of Pb:EDTA was measured. Xylem sap was collected after the stem was severed at different times. The concentration of Pb in the shoots and roots were determined by an atomic absorption spectrometer. In addition, the roots were stained with Fluostain I for observation of the root structure. KEY RESULTS: Lead accumulation in the shoots of the plants exposed to EDTA-Pb at 1:1 ratio was only one-fifth of that exposed to ionic Pb at the same concentration. Lead accumulation decreased when transpiration was suppressed. The concentration of Pb in the xylem sap from the EDTA-Pb-treated plants was about 1/25,000 of that in the external solution. Root elongation was severely inhibited by ionic Pb, but not by EDTA-Pb at a 1:1 ratio. Root staining showed that a physiological barrier was damaged in the roots exposed to ionic Pb, but not in the roots exposed to EDTA-Pb. CONCLUSIONS: All these results suggest that sorghum roots are inefficient in uptake of EDTA-chelated Pb and that enhanced Pb accumulation from ionic Pb was attributed to the damaged structure of the roots.     

Lead induced changes in the growth and antioxidant metabolism of the lead accumulating and non-accumulating ecotypes of Sedum alfredii

The phytotoxicity and antioxidative adaptations of lead （Pb） accumulating ecotype （AE） and non-accumulating ecotype （NAE） of Sedum alfredii Hance were investigated under different Pb treatments involving 0, 0.02 mmol/L Pb, 0.1 mmol/L Pb and 0.1 mmol/L Pb/0.1 mmol/L ethylenediaminetetraacetic acid （EDTA） for 6days. With the increasing Pb level, the Pb concentration in the shoots of AE plants enhanced accordingly, and EDTA supply helped 51% of Pb translocation to shoots of AE compared with those treated with 0.1 mmol/L Pb alone. Moreover, the presence of EDTA alleviated Pb phytotoxicity through changes in plant biomass, root morphology and chlorophyll contents. Lead toxicity induced hydrogen peroxide （H2O2） accumulation and lipid peroxidation in both ecotypes of S. alfredii. The activities of superoxide dismutase （SOD）, guaiacol peroxidase （G-POD）, ascorbate peroxidase, and dehydroascorbate reductase elevated in both leaves and roots of AE as well as in leaves of NAE with the increasing Pb levels, but SOD and G-POD declined in roots of NAE. Enhancement in glutathione reductase activity was only detected in roots of NAE while a depression in catalase activity was recorded in the leaves of NAE. A significant enhancement in glutathione and ascorbic acid （AsA） levels occurred in both ecotypes exposed to Pb and Pb/EDTA treatment compared with the control, however, the differences between these two treatments were insignificant. The dehydroascorbate （DHA） contents in roots of both ecotypes were 1.41 to 11.22-fold higher than those in leaves, whereas the ratios of AsA to DHA （1.38 to 6.84） in leaves altering more to the reduced AsA form were much higher than those in roots. These results suggested that antioxidative enzymes and antioxidants play an important role in counteracting Pb stress in S. alfredii.     

Cu2+对拟南芥根的局部毒性及诱导DNA损伤和细胞死亡

该文探讨了不同浓度的Cu²⁺胁迫对拟南芥(Arabidopsis thaliana)根生长、活性氧(ROS)积累、抗氧化酶活性、质膜完整性和细胞活性的影响, 通过分根实验初步分析了Cu²⁺毒性效应的影响范围。结果表明, Cu²⁺胁迫可显著抑制拟南芥主根伸长, 诱导ROS积累及DNA损伤, 促发抗氧化酶活性升高, 破坏质膜完整性, 且Cu²⁺浓度越高, 毒性效应越明显, 在高浓度Cu²⁺胁迫下细胞活性显著降低。分析各参数之间的关系, 表明ROS的积累与超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)及抗坏血酸过氧化物酶(APX)的活性呈显著正相关; ROS积累与DNA损伤、质膜完整性、细胞活性之间具有显著的近线性关系。分根实验结果表明, 只有在添加重金属Cu²⁺(75 μmol·L^–1)一侧培养基中的根生长受抑制, 并出现ROS积累、细胞死亡, 暗示Cu²⁺对拟南芥根系的局部毒性效应可能是由于ROS的局部性积累导致受胁迫根系一侧的细胞死亡所引起的。     

Depletion of extracellular calcium increases cadmium toxicity in barley root tip via enhanced Cd uptake-mediated superoxide generation and cell death

Whereas severe Cd stress (150 µM Cd) causes root growth arrest as a consequence of marked superoxide generation leading to extensive cell death in the root tips, mild Cd stress (15 µM Cd) evokes morphogenic responses, such as reduced root elongation and radial root expansion, resulting in shorter and thicker roots. Similar to the low Cd concentration-caused mild stress, treatment of roots with either Ba to remove exchangeable or EDTA to remove both exchangeable and tightly bound cations, including Ca and Mg, from the apoplast, induced root growth inhibition and swelling. However, pre-treatment of roots with Ba had a synergistic effect on the development of these mild Cd stress-induced morphogenic responses, but without the development of any other symptoms in the root tips. In turn, EDTA pre-treatment markedly increased the toxicity of Cd in barley root tips via enhanced Cd uptake-mediated superoxide generation, which evoked extensive cell death in the transition zone of root tips identically to the high Cd concentration-induced severe stress. While the mild stress-induced responses were alleviated by the inhibition of auxin signalling pathway, the severe stress-induced symptoms were prevented by Ca, but not Mg, supplementation or by the inhibition of Cd uptake into the root symplasm. Therefore, the appropriate concentration of Ca in the apoplast is crucial to prevent the rapid accumulation of Cd in the symplasm, which above a certain threshold level leads to the huge superoxide generation and cell death.     

Influence of EDTA on lead transportation and accumulation by Sedum alfredii hance

Hydroponics and pot experiments were conducted to study the effects of ethylenediaminetetraacetic acid (EDTA) on Pb transportation and accumulation by two contrasting ecotypes of Sedum alfredii Hance. In hydroponics experiments, the accumulating ecotype (AE) showed more ability to tolerate Pb toxicity compared with the non-accumulating ecotype (NAE). When treated with equimolar mixtures of EDTA and Pb, maximum Pb accumulation occurred without any phytotoxicity symptoms. Pot experiments with Pb contents of 400 mg kg-1 showed that 5 mM EDTA is the optimum dose for the phytoextraction of soils contaminated with relatively low Pb levels; in contrast, increasing EDTA addition resulted in increased Pb accumulation in the shoots of AE in soils with high Pb content (1200 mg kg(-1)). The post-harvest effects of EDTA on available Pb were strong compared with those without addition of EDTA (CK). Within the initial 7 days almost no differences of water-soluble Pb were noted in soils contaminated with both levels of Pb but after 2 weeks, water-soluble Pb started to decrease significantly compared with before. Considering the toxicity and biodegradability of synthetic chelators, it can be concluded that the chelate-assisted technique is more suitable for soils contaminated with low Pb levels and to avoid environment risks; a suitable dose of chelators must be considered before application.     

The Influence of Selenium on Root Growth and Oxidative Stress Induced by Lead in Vicia faba L. minor Plants

The effect of selenium (Se) on Vicia faba L. minor roots subjected to lead (Pb) stress was studied by investigating root growth, root viability, and antioxidant enzyme activity. The experiments were carried out on plants grown for 2 weeks on Hoagland medium supplied with 50 μM Pb in the form of lead nitrate Pb(NO(3))(2) and/or Se concentrations of 1.5 and 6 μM in the form of sodium selenite Na(2)SeO(3). It was shown that Pb reduced the root growth and caused serious damage in the roots, which was accompanied by metal accumulation in these tissues. The exposition of roots to Pb led to significant changes in the biochemical parameters: the MDA and T-SH content and glutathione peroxidase (GSH-Px) activity increased but the guaiacol peroxidase (GPOX) activity decreased. Moreover, Pb intensified O(2)(·-) production in the roots. Selenium at a lower concentration alleviated Pb toxicity which was accompanied by a decreased O(2)(·-) production in the apical parts of roots and increased the T-SH content and GPOX activity. However, higher Se concentration intensified MDA and T-SH accumulation and GPOX and GSH-Px activity in Pb-treated plant roots. At low concentration, Se improved cell viability whereas at high concentration it was pro-oxidant and enhanced the lipid peroxidation and cell membrane injury.     

Investigation of Arbuscular mycorrhizal Fungus and EDTA Efficiencies on Lead Phytoremediation by Sunflower in a Calcareous Soil

Lead (Pb) contamination of soils is a widespread problem. Mycorrhizal inoculation and synthetic chelators such as ethylenediaminetetraacetic acid (EDTA) may be useful for improving phytoremediation efficiency in Pb-contaminated soils. A greenhouse experiment was performed to study the influence of inoculation with arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and addition of EDTA on phytoremediation of Pb by sunflowers (Helianthus annuus) in a calcareous soil. The experiment was a completely randomized design in a factorial arrangement with five levels of Pb, two levels of mycorrhizal treatments, and two levels of EDTA. Inoculation increased root colonization as Pb levels increased, but the addition of EDTA decreased it. Shoot and root dry matter yields increased by inoculation; however, they decreased with EDTA and Pb levels in co-application treatments. Pb concentration in shoots was significantly higher than that in roots, indicating a translocation factor greater than 1. Inoculation or addition of EDTA significantly increased Pb in roots and its translocation to shoots. The uptake index (UI) value increased in co-application of EDTA and AMF and the individual application of them; it is, therefore, concluded that both AMF and EDTA are effective in phytoremediation of Pb by sunflowers in the studied soil.     

How phytohormone IAA and chelator EDTA affect lead uptake by Zn/Cd hyperaccumulator Picris divaricata

In this paper, the effects of indole-3-acetic acid (IAA) and/or ethylenediaminetetraacetic acid (EDTA) on lead uptake by a Zn/Cd hyperaccumulator Picris divaricata were studied. P. divaricata responded to Pb by better root system and increased biomass in presence of phytohormone IAA, which was able to reduce the inhibiting effects of Pb on transpiration without reducing the uptake of Pb The application of 100 microM IAA increased plant transpiration rate by about 20% and Pb concentration in leaves by about 37.3% as compared to treatment exposed to Pb alone. The enhanced phytoextraction efficiency could be attributed to the mechanisms played by IAA through alleviating Pb toxicity, creating better root system and plant biomass, promoting a higher transpiration rate as well as regulating the level of nutrient elements. On the contrary, inefficiency of phytoextraction was found with EDTA or the combination of IAA and EDTA probably because most Pb was in the form of Pb-EDTA complex which blocked the uptake by P. divaricata. The present study demonstrated that IAA was able to enhance the phytoextraction of Pb by Zn/Cd hyperaccumulator P. divaricata, providing a feasible method for the phytoremediation of polymetallic contaminated soils.     

Root Morphology and Zn2+ Uptake Kinetics of the Zn Hyperaccumulator of Sedum alfredii Hance

Root morphology and Zn2 uptake kinetics of the hyperaccumulating ecotype (HE) and nonhyperaccumulating ecotype (NHE) of Sedum alfredii Hance were investigated using hydroponic methods and the radiotracer flux technique. The results indicate that root length, root surface area, and root volume of NHE decreased significantly with increasing Zn2 concentration in growth media, whereas the root growth of HE was not adversely affected, and was even promoted, by 500 μmol/L Zn2 . The concentrations of Zn2 in both ecotypes of S. alfredii were positively correlated with root length, root surface area and root volumes, but no such correlation was found for root diameter. The uptake kinetics for 65Zn2 in roots of both ecotypes of S. alfredii were characterized by a rapid linear phase during the first 6 h and a slower linear phase during the subsequent period of investigation. The concentration-dependent uptake kinetics of the two ecotypes of S. alfredii could be characterized by the Michaelis-Menten equation, with the Vmax for 65Zn2 influx being threefold greater in HE compared with NHE, indicating that enhanced absorption into the root was one of the mechanisms involved in Zn hyperaccumulation. A significantly larger Vmax value suggested that there was a higher density of Zn transporters per unit membrane area in HE roots.     

Comparison of EDTA- and Citric Acid-Enhanced Phytoextraction of Heavy Metals in Artificially Metal Contaminated Soil by Typha Angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.     

Evaluation of lead toxicity in Erica andevalensis as an alternative species for revegetation of contaminated soils

Although revegetation using native flora is a low cost way to stabilize soil and restore the landscape contaminated with metals, little is known regarding the Pb-tolerance of many of these species. For this purpose, we evaluated the tolerance of Erica andevalensis to Pb by growing plants in nutrient solutions with increasing concentrations of Pb (up to 100 microM). Plant growth and different physiological parameters were determined to ascertain tolerance to metal stress. Additionally, an electron microscopy study coupled with EDX-analysis was performed to get clues on the Pb uptake and translocation from roots into stem and leaves. The LOEC (the lowest observed effect concentration) of Pb was 40 microM while the IC50 (inhibition concentration) was 80 microM Pb. Chemical analysis revealed a root > stem > leaf accumulation pattern. There was a severe reduction in fresh biomass and chlorophyll concentration at the highest Pb dose. The SEM-EDX study indicated that Pb was mostly located in root epidermal tissues. The blockage of Pb on the root probably avoided its toxic effects by limiting Pb transport to other tissues.     

不同生态型东南景天对土壤中Cd的生长反应及吸收积累的差异性

 采用盆栽方法研究了两种生态型东南景天(Sedum alfredii)对土壤中不同含量Cd(即对照, 12.5, 25, 50, 100, 200, 300, 400 mg&;#8226;kg^－1)的生 长反应、吸收和积累Cd的差异性。结果表明,土壤添加重金属Cd后,矿山生态型东南景天生长正常,地上部和根系Cd含量随着土壤中Cd含量的 增加而增加,在400 mg&;#8226;kg^－1 Cd处理下含量分别高达2 900和500 mg&;#8226;kg^－1,其地上部显著大于根部;然而,土壤添加Cd后,非矿山生态型东 南景天的生长受到抑制,地上部和根部的生物量显著降低。当土壤Cd含量为50～100 mg&;#8226;kg^－1 时,非矿山生态型东南景天的地上部和根系Cd含 量随着土壤中Cd含量的增加而增加,而且根系Cd含量则大于地上部。当土壤Cd≤50 mg&;#8226;kg^－1时,矿山生态型东南景天根系Cd含量比非矿山生态 型高 ,但当土壤Cd≥100 mg&;#8226;kg^－1,两者之间无显著差异;然而,但在同一Cd处理水平下,矿山生态型东南景天地上部Cd含量总是高于非矿山 生态型。这些结果表明,矿山生态型东南景天有很强的忍耐和吸收土壤Cd的能力,再次证明其为一种Cd超积累植物。     

Effects of exogenous nitric oxide on cadmium toxicity, element contents and antioxidative system in perennial ryegrass

The effects of sodium nitroprusside (SNP, a donor of NO) on cadmium (Cd) toxicity in ryegrass seedlings (Lolium perenne L.) were studied by investigating the symptoms, plant growth, chlorophyll content, lipid peroxidation, H⁺-ATPase enzyme and antioxidative enzymes. Addition of 100???M CdCl₂ caused serious chlorosis and inhibited the growth of ryegrass seedlings, and dramatically increased accumulation of Cd in both shoots and roots, furthermore, the absorption of macro and micronutrients were inhibited. Addition of 50, 100, 200???M SNP significantly decreased the transport of Cd from roots to shoots, alleviated the inhibition of K, Ca, Mg and Fe, Cu, Zn absorption induced by Cd, reduced the toxicity symptoms and promoted the plant growth. The accumulation of reactive oxygen species (ROS) significantly increased in ryegrass seedlings exposed to Cd, and resulted in the lipid peroxidation, which was indicated by accumulated concentration of thiobarbituric acid-reactive substances. Addition of 50, 100, 200???M SNP significantly decreased the level of ROS and lipid peroxidation. Activities of antioxidant enzymes also showed the same changes. Addition of 50, 100, 200???M SNP increased activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase in ryegrass seedlings exposed to Cd. Addition of 100???M SNP had the most significant alleviating effect against Cd toxicity while the addition of 400???M SNP had no significant effect with Cd treatment.     

Exogenous nitric oxide improves antioxidative capacity and reduces auxin degradation in roots of Medicago truncatula seedlings under cadmium stress

The effects of nitric oxide (NO) on cadmium toxicity in Medicago truncatula seedlings were studied by investigating root growth and uptake of antioxidants, IAA and ions. Exposure to cadmium reduced root growth and NO accumulation, and increased the production of reactive oxygen species (ROS) in roots. Supplementation with NO improved root growth and reduced ROS accumulation in roots. The NO-scavenger cPTIO, the nitrate reductase (NR) inhibitor tungstate, and the NO synthase (NOS) inhibitor L-NAME all inhibited the accumulation of NO in roots and reversed the effects of NO in promoting the root growth and accumulation of proline and glutathione. Application of NO reduced auxin degradation by inhibiting the activity of IAA oxidase. Exogenous NO also enhanced the uptake of K⁺ and Ca²⁺. These results suggest that NO improves cadmium tolerance in plants by reducing oxidative damage, maintaining the auxin equilibrium and enhancing ion absorption.     

The effect of EDTA and EDDS on lead uptake and localization in hydroponically grown Pisum sativum L.

Pisum sativum plants were treated for 3 days with an aqueous solution of 100 μM Pb(NO₃)₂ or with a mixture of lead nitrate and ethylenediaminetetraacetic acid (EDTA) or [S,S]-ethylenediaminedisuccinic acid (EDDS) at equimolar concentrations. Lead decline from the incubation media and its accumulation and localization at the morphological and ultrastructural levels as well as plant growth parameters (root growth, root and shoot dry weight) were estimated after 1 and 3 days of treatment. The tested chelators, especially EDTA, significantly diminished Pb uptake by plants as compared to the lead nitrate-treated material. Simultaneously, EDTA significantly enhanced Pb translocation from roots to shoots. In the presence of both chelates, plant growth parameters remained considerably higher than in the case of uncomplexed Pb. Considerable differences between the tested chelators were visible in Pb localization both at the morphological and ultrastructural level. In Pb+EDTA-treated roots, lead was mainly located in the apical parts, while in Pb+EDDS-exposed material Pb was evenly distributed along the whole root length. Transmission electron microscopy and EDS analysis revealed that in meristematic cells of the roots incubated in Pb+EDTA, large electron-dense lead deposits were located in vacuoles and small granules were rarely noticed in cell walls or cytoplasm, while after Pb+EDDS treatment metal deposits were restricted to the border between plasmalemma and cell wall. Such results imply different ways of transport of those complexed Pb forms.     

The mobilisation and fate of soil and rock phosphate in the rhizosphere of ectomycorrhizal Pinus radiata seedlings in an Allophanic soil

A pot experiment was conducted to investigate the uptake of Zn from experimentally contaminated calcareous soil of low nutrient status by maize inoculated with the arbuscular mycorrhizal (AM) fungus Glomus caledonium. EDTA was applied to the soil to mobilize Zn and thus maximize plant Zn uptake. The highest plant dry matter (DM) yields were obtained with a moderate Zn addition level of 300 mg kg^?1. Plant growth was enhanced by mycorrhizal colonization when no Zn was added and under the highest Zn addition level of 600 mg kg^?1, while application of EDTA to the soil generally inhibited plant growth. EDTA application also increased plant Zn concentration, and Zn accumulation in the roots increased with increasing EDTA addition level. The effects of inoculation with G. caledonium on plant Zn uptake varied with Zn addition level. When no Zn was added, Zn translocation from roots to shoots was enhanced by mycorrhizal colonization. In contrast, when Zn was added to the soil, mycorrhizal colonization resulted in lower shoot Zn concentrations in mycorrhizal plants. The P nutrition of the maize was greatly affected by AM inoculation, with mycorrhizal plants showing higher P concentrations and P uptake. The results indicate that application of EDTA mobilized soil Zn, leading to increased Zn accumulation by the roots and subsequent plant toxicity and growth inhibition. Mycorrhizal colonization alleviated both Zn deficiency and Zn contamination, and also increased host plant growth by influencing mineral nutrition. However, neither EDTA application nor arbuscular mycorrhiza stimulated Zn translocation from roots to shoots or metal phytoextraction under the experimental conditions. The results are discussed in relation to the environmental risk associated with chelate-enhanced phytoextraction and the potential role of arbuscular mycorrhiza in soil remediation.     

Cadmium uptake and xylem loading are active processes in the hyperaccumulator Sedum alfredii

Sedum alfredii is a well known cadmium (Cd) hyperaccumulator native to China; however, the mechanism behind its hyperaccumulation of Cd is not fully understood. Through several hydroponic experiments, characteristics of Cd uptake and translocation were investigated in the hyperaccumulating ecotype (HE) of S. alfredii in comparison with its non-hyperaccumulating ecotype (NHE). The results showed that at Cd level of 10 microM measured Cd uptake in HE was 3-4 times higher than the implied Cd uptake calculated from transpiration rate. Furthermore, inhibition of transpiration rate in the HE has no essential effect on Cd accumulation in shoots of the plants. Low temperature treatment (4 degrees C) significantly inhibited Cd uptake and reduced upward translocation of Cd to shoots for 9 times in HE plants, whereas no such effect was observed in NHE. Cadmium concentration was 3-4-fold higher in xylem sap of HE, as compared with that in external uptake solution, whereas opposite results were obtained for NHE. Cadmium concentration in xylem sap of HE was significantly reduced by the addition of metabolic inhibitors, carbonyl cyanide m-chlorophenylhydrazone (CCCP) and 2,4-dinitrophenol (DNP), in the uptake solutions, whereas no such effect was noted in NHE. These results suggest that Cd uptake and translocation is an active process in plants of HE S. alfredii, symplastic pathway rather than apoplastic bypass contributes greatly to root uptake, xylem loading and translocation of Cd to the shoots of HE, in comparison with the NHE plants.     

Evaluation of DNA damage and mutagenicity induced by lead in tobacco plants

Tobacco (Nicotiana tabacum L. var. xanthi) seedlings were treated with aqueous solutions of lead nitrate (Pb2+) at concentrations ranging from 0.4 mM to 2.4 mM for 24 h and from 25 microM to 200 microM for 7 days. The DNA damage measured by the comet assay was high in the root nuclei, but in the leaf nuclei a slight but significant increase in DNA damage could be demonstrated only after a 7-day treatment with 200 microM Pb2+. In tobacco plants growing for 6 weeks in soil polluted with Pb2+ severe toxic effects, expressed by the decrease in leaf area, and a slight but significant increase in DNA damage were observed. The tobacco plants with increased levels of DNA damage were severely injured and showed stunted growth, distorted leaves and brown root tips. The frequency of somatic mutations in tobacco plants growing in the Pb2+-polluted soil did not significantly increase. Analytical studies by inductively coupled plasma optical emission spectrometry demonstrate that after a 24-h treatment of tobacco with 2.4 mM Pb2+, the accumulation of the heavy metal is 40-fold higher in the roots than in the above-ground biomass. Low Pb2+ accumulation in the above-ground parts may explain the lower levels or the absence of Pb2+-induced DNA damage in leaves.     

Aluminium alleviates manganese toxicity to rice by decreasing root symplastic Mn uptake and reducing availability to shoots of Mn stored in roots

Background and Aims Manganese (Mn) and aluminium (Al) phytotoxicities occur mainly in acid soils. In some plant species, Al alleviates Mn toxicity, but the mechanisms underlying this effect are obscure.Methods Rice (Oryza sativa) seedlings (11 d old) were grown in nutrient solution containing different concentrations of Mn²⁺ and Al³⁺ in short-term (24 h) and long-term (3 weeks) treatments. Measurements were taken of root symplastic sap, root Mn plaques, cell membrane electrical surface potential and Mn activity, root morphology and plant growth.Key Results In the 3-week treatment, addition of Al resulted in increased root and shoot dry weight for plants under toxic levels of Mn. This was associated with decreased Mn concentration in the shoots and increased Mn concentration in the roots. In the 24-h treatment, addition of Al resulted in decreased Mn accumulation in the root symplasts and in the shoots. This was attributed to higher cell membrane surface electrical potential and lower Mn²⁺ activity at the cell membrane surface. The increased Mn accumulation in roots from the 3-week treatment was attributed to the formation of Mn plaques, which were probably related to the Al-induced increase in root aerenchyma.Conclusions The results show that Al alleviated Mn toxicity in rice, and this could be attributed to decreased shoot Mn accumulation resulting from an Al-induced decrease in root symplastic Mn uptake. The decrease in root symplastic Mn uptake resulted from an Al-induced change in cell membrane potential. In addition, Al increased Mn plaques in the roots and changed the binding properties of the cell wall, resulting in accumulation of non-available Mn in roots.     

镉、铅及其相互作用对小白菜根系生理生态效应的研究

采用溶液培养方法,以镉,铅作为胁迫因子,研究了不同镉,铅浓度对小白菜根系生理生态的影响。实验结果表明;培养液中镉超过０．１ｍｇ／Ｌ,侧根数目减少,根的分枝程度降低,根系生物量和体积下降,根系生长发育受阻,根系不发达,根系对锰,锌的吸收受到抑制,根系活动降低,对硝酸盐吸收能力下降,蛋白质分解加快,游离氨基酸积累,氮代谢紊乱,失调。