黏着箭菌JB19对菊苣幼苗铅镉抗性及黄酮生物合成的影响

【目的】探讨耐重金属细菌对铅(lead, Pb)和镉(cadmium, Cd)胁迫下菊苣(Cichorium intybus L.)幼苗Pb、Cd抗性和黄酮生物合成的调控作用。【方法】在不同浓度Pb和Cd [(200+20) mg/kg、(400+40) mg/kg、(800+80) mg/kg]处理下,接种菌株JB19并测定菊苣幼苗生长指标、Pb和Cd含量、抗氧化酶活性、总黄酮含量和黄酮生物合成相关基因表达量。【结果】菌株JB19可显著提高不同浓度Pb和Cd处理下菊苣的生物量和叶绿素含量;减少氧化损伤,地上部和根部Pb、Cd含量均降低,其中在(Pb200+Cd20) mg/kg处理下H₂O₂和丙二醛(malondialdehyde, MDA)含量分别比对照降低了25.7%和26.1%,地上部Pb、Cd含量降低的幅度最大,分别降低了53.2%和54.1%;加强了菊苣幼苗的抗氧化酶防御系统,黄酮生物合成相关基因均显著上调,其中在(Pb400+Cd40) mg/kg处理下黄酮类化合物的含量增加了105.2%,查尔酮异构酶基因上调最显著,达458....     

Cadmium(II) Removal by a Hyperaccumulator Fungus <Emphasis Type="Italic">Phoma</Emphasis> sp. F2 Isolated from Blende Soil

A cadmium(II)-resistant fungus, strain F2, isolated from blende soil was identified as Phoma sp. by morphological study and internal transcribed spacer sequencing. This strain could accumulate 280 mg of Cd(II)/g dry weight mycelium. In liquid medium containing 163.8 mg Cd(II)/L, 96% of Cd(II) was removed by the actively growing mycelium. In addition, both oven-dried and lyophilized mycelium could effectively adsorb Cd(II). There were removed 91% and 46.2% of Cd(II) from 51.6 mg Cd(II)/L solution by lyophilized biomass and oven-dried biomass respectively. Transmission electron microscopy and energy-dispersive X-ray analysis showed the accumulation of Cd(II) in the mycelium cell walls. Our results demonstrated that Phoma sp. F2 was a hyperaccumulator for the removal of Cd(II) from contaminated soil and water.     

Effects of inoculation of a plant growth promoting rhizobacterium <Emphasis Type="Italic">Burkholderia</Emphasis> sp. D54 on plant growth and metal uptake by a hyperaccumulator <Emphasis Type="Italic">Sedum alfredii</Emphasis> Hance grown on multiple metal contaminated soil

Batch experiments were designed to characterize a multiple metal resistant bacterium Burkholderia sp. D54 isolated from metal contaminated soils in the Dabaoshan Mine in South China, and a follow-up experiment was conducted to investigate the effects of inoculating the isolate on plant growth and metal uptake by Sedum alfredii Hance grown on soils collected from a heavily contaminated paddy field in Daxing County, Guangxi Zhuang Automounous Region, Southwest China. Our experiments showed that strain D54 produced indole acetic acid (IAA), siderophores, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and solubilizing inorganic phosphate and solubilized insoluble metal bearing minerals. Bacterial inoculation significantly enhanced S. alfredii biomass production, and increased both shoot and root Cd concentration, but induced little variation in root/shoot Pb concentration and shoot Zn concentration. Despite this, the total shoot and root uptake of Cd, Pb and Zn in S. alfredii inoculated with D54 increased greatly compared to the non-inoculated controls. It was concluded that inoculation with strain D54 could help S. alfredii grow better on metal contaminated soils, produce more biomass, and remove more metals from soil, which implies improved efficiency of phytoextraction from metal contaminated soil. The knowledge gained from the present experiments constitutes an important advancement in understanding of the interaction between plant growth-promoting bacteria and hyperaccumulators with regard to plant ability to grow and remove the multiple heavy metals from soils.     

UV-B and cadmium induced changes in pigments,photosynthetic electron transport activity,antioxidant levels and antioxidative enzyme activities of <Emphasis Type="Italic">Riccia</Emphasis> sp.

UV-B and cadmium, alone and together, induced changes in photosynthetic pigment levels, photosynthetic electron transport activity, enzymatic and non-enzymatic (low molecular weight) antioxidants, level of hydrogen peroxide and lipid peroxidation in Riccia sp. were evaluated. Chlorophyll content was found to decrease with the rising concentration of cadmium and UV-B exposure alone and its level further declined when both the stresses were applied together. In contrast to this, carotenoids exhibited varied response, as it showed enhancement with UV-B (15, 30 and 45 min exposure) and low concentration of Cd (1 and 10 μM) treatment alone and in combination. Both the stresses caused strong inhibitory effect on PS II activity (H₂O → p-BQ), while PS I activity (DCPIP/ASC → MV) appeared to be less sensitive. Total peroxide content increased with simultaneous increase in lipid peroxidation. The level of non-enzymatic antioxidant ascorbate and enzymatic antioxidants superoxide dismutase and peroxidase activity were found to increase with simultaneous decrease in catalase activity following UV-B and Cd treatments. These results indicate that 45 min of UV-B exposure and 10, 100 and 1000 μM cadmium alone and together, strongly arrested electron flow through PS II which caused accelerated generation of reactive oxygen species (H₂O₂) and excess accumulation of H₂O₂ due to significant inhibition of catalase activity, led to the oxidative damage in Riccia sp.     

Bacteria associated with yellow lupine grown on a metal‐contaminated soil: in vitro screening and in vivo evaluation for their potential to enhance Cd phytoextraction

In order to stimulate selection for plant‐associated bacteria with the potential to improve Cd phytoextraction, yellow lupine plants were grown on a metal‐contaminated field soil. It was hypothesised that growing these plants on this contaminated soil, which is a source of bacteria possessing different traits to cope with Cd, could enhance colonisation of lupine with potential plant‐associated bacteria that could then be inoculated in Cd‐exposed plants to reduce Cd phytotoxicity and enhance Cd uptake. All cultivable bacteria from rhizosphere, root and stem were isolated and genotypically and phenotypically characterised. Many of the rhizobacteria and root endophytes produce siderophores, organic acids, indole‐3‐acetic acid (IAA) and aminocyclopropane‐1‐carboxylate (ACC) deaminase, as well as being resistant to Cd and Zn. Most of the stem endophytes could produce organic acids (73.8%) and IAA (74.3%), however, only a minor fraction (up to 0.7%) were Cd or Zn resistant or could produce siderophores or ACC deaminase. A siderophore‐ and ACC deaminase‐producing, highly Cd‐resistant Rhizobium sp. from the rhizosphere, a siderophore‐, organic acid‐, IAA‐ and ACC deaminase‐producing highly Cd‐resistant Pseudomonas sp. colonising the roots, a highly Cd‐ and Zn‐resistant organic acid and IAA‐producing Clavibacter sp. present in the stem, and a consortium composed of these three strains were inoculated into non‐exposed and Cd‐exposed yellow lupine plants. Although all selected strains possessed promising in vitro characteristics to improve Cd phytoextraction, inoculation of none of the strains (i) reduced Cd phytotoxicity nor (ii) strongly affected plant Cd uptake. This work highlights that in vitro characterisation of bacteria is not sufficient to predict the in vivo behaviour of bacteria in interaction with their host plants.     

Exogenous spermidine and spermine enhance cadmium tolerance of <Emphasis Type="Italic">Potamogeton malaianus</Emphasis>

In order to investigate the effects of spermidine (Spd) and spermine (Spm) on cadmium stress, the content of chlorophyll, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), soluble protein and proline, the rate of O₂^·− generation, and activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)) in Potamogeton malaianus Miq. were measured. Exogenous application of Spd or Spm significantly enhanced the level of proline, retarded the loss of chlorophyll, enhanced photosynthesis, decreased the rate of O₂^·− generation and H₂O₂ content, and prevented Cd-induced lipid peroxidation. Spd and Spm also effectively maintained the balance of antioxidant enzyme activities under Cd stress; however, GR activity was found to increase only slightly in response to polyamines (PAs). The antioxidant systems, which were modified by PAs, were able to moderate the radical-scavenging system and to lessen in this way the oxidative stress. These results suggest that both Spd and Spm can enhance Cd tolerance of P. malaianus.     

Exogenous Application of Selenium Mitigates Cadmium Toxicity in <Emphasis Type="Italic">Brassica juncea</Emphasis> L. (Czern &amp; Cross) by Up-Regulating Antioxidative System and Secondary Metabolites

The main aim of the present study was to examine the role of selenium (Se) in ameliorating the toxic effect of cadmium (Cd) in mustard (Brassica juncea) plants. The plants exposed to elevated levels of Cd exhibited reduced biomass, pigment content, and relative water content (RWC). However, supplementation of Se restores the negative effect of Cd and increases biomass, pigment content, and RWC. Osmolyte (proline and glycine betaine) and sugar content were increased under Cd stress and further increase was observed with addition of Se. Cd decreased protein content and supplementation of Se increases it to appreciable levels. Cd also increased production of H₂O₂ and lipid peroxidation, electrolyte leakage, and the activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, and glutathione reductase. Supplementation of Se decreased accumulation of H₂O₂ and lipid peroxidation, increased the activities of antioxidant enzymes to greater levels, and regulates Cd accumulation in roots and shoots. Ascorbic acid (AsA) and flavonoids decreased with elevated concentrations of Cd; however, tocopherol and total phenols were increased with the same concentrations of Cd. Se application maintains AsA and flavonoid content, and further increase in tocopherol and total phenols were observed with Se in the present study. Overall the results confirm that exogenous application of Se mitigates the negative effects of Cd stress in mustard plants through the regulation of osmoprotectants, antioxidant enzymes, and secondary metabolites.     

Changes in the population of seed bacteria of transgenerationally Cd‐exposed Arabidopsis thaliana

Plant‐associated bacteria can have beneficial effects on the growth and health of their host. Nevertheless, the role of endophytic bacteria present in seeds has not been investigated in depth. In this study, the cultivable endophytic population of seeds from Arabidopsis thaliana exposed to 2 μm cadmium for several generations (Cd seeds) was compared with a population isolated from seeds of plants that were never exposed to Cd (control seeds). We observed obvious differences between the two types of seed concerning genera present and phenotypic characteristics of the different isolates. Sinorhizobium sp. and Micrococcus sp. were only found in control seeds, while Pseudomonas sp., Bosea sp. and Paenibacillus sp. were only found in Cd seeds. Sphingomonas sp., Rhizobium sp., Acidovorax sp., Variovorax sp., Methylobacterium sp., Bacillus sp. and Staphylococcus sp. occurred in varying numbers in both types of seed. Metal tolerance and 1‐aminocyclopropane‐1‐carboxylate deaminase activity were predominantly found in strains isolated from Cd seeds, while the production of siderophores, indole‐3‐acetic acid and organic acids was more prevalent in endophytes isolated from control seeds. These data support the hypothesis that certain endophytes are selected for transfer to the next generation and that their presence might be important for subsequent germination and early seedling development.     

Rhizosphere bacteria affect growth and metal uptake of heavy metal accumulating willows

A variety of plants growing on metalliferous soils accumulate metals in their harvestable parts and have the potential to be used for phytoremediation of heavy metal polluted land. There is increasing evidence that rhizosphere bacteria contribute to the metal extraction process, but the mechanisms of this plant–microbe interaction are not yet understood. In this study ten rhizosphere isolates obtained from heavy metal accumulating willows affiliating with Pseudomonas, Janthinobacterium, Serratia, Flavobacterium, Streptomyces and Agromyces were analysed for their effect on plant growth, Zn and Cd uptake. In plate assays Zn, Cd and Pb resistances and the ability of the bacteria to produce indole-3-acetic acid (IAA), 1-amino-cyclopropane-1-carboxylic acid deaminase (ACC deaminase) and siderophores were determined. The isolates showed resistance to high Zn concentrations, indicating an adaptation to high concentrations of mobile Zn in the rhizosphere of Salix caprea. Four siderophore producers, two IAA producers and one strain producing both siderophores and IAA were identified. None of the analysed strains produced ACC deaminase. Metal mobilization by bacterial metabolites was assessed by extracting Zn and Cd from soil with supernatants of liquid cultures. Strain Agromyces AR33 almost doubled Zn and Cd extractability, probably by the relase of Zn and Cd specific ligands. The remaining strains, immobilized both metals. When Salix caprea plantlets were grown in γ-sterilized, Zn/Cd/Pb contaminated soil and inoculated with the Zn resistant isolates, Streptomyces AR17 enhanced Zn and Cd uptake. Agromyces AR33 tendentiously promoted plant growth and thereby increased the total amount of Zn and Cd extracted from soil. The IAA producing strains did not affect plant growth, and the siderophore producers did not enhance Zn and Cd accumulation. Apparently other mechanisms than the production of IAA, ACC deaminase and siderophores were involved in the observed plant–microbe interactions.     

In Vitro and In Vivo Antioxidant Activity of <Emphasis Type="Italic">Bifidobacterium animalis</Emphasis> 01 Isolated from Centenarians

Several studies reported the antioxidant activity of bifidobacteria using assays in vitro. In present study, the in vitro and in vivo antioxidant activity of Bifidobacterium animalis 01 was investigated. Culture supernatant, intact cells, and intracellular cell-free extracts of B. animalis 01 were involved in this study. The antioxidant assays in vitro included lipid peroxidation assay, 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, hydroxyl radical ( ^• OH) assay and superoxide anion ( \textO₂ ^- {\text{O}}_{2}^{ - } ) assay. The antioxidant assays in vivo were conducted using mice model. Activities of antioxidative enzymes, malondialdehyde (MDA) content in serums and livers of aging mice were evaluated. Monoamine oxidase (MAO) activity and lipofuscin level in brains of aging mice were also characterized. Results showed that culture supernatant, intact cells and intracellular cell-free extracts of B. animalis 01 could effectively scavenge free radicals, significantly enhance mice’s activities of antioxidative enzymes and reduce mice’s MDA content, lipofuscin level and MAO activity. Our results indicated that B. animalis 01 has the potential to be developed into a dietary antioxidant supplements.     

Studies on lead and cadmium toxicity in Dianthus carthusianorum calamine ecotype cultivated in vitro

• Information on metallophytes during reclamation of land contaminated with heavy metals is sparse. We investigated the response of D. carthusianorum calamine ecotype to Pb and Cd stress. We focused on in vitro selection of tolerant plant material for direct use in chemically degraded areas.
• Shoot cultures were treated with various concentrations of Pb or Cd ions. Plantlet status was estimated as micropropagation efficiency, growth tolerance index (GTI) and through physiological analysis. Moreover, determination of plant Pb, Cd and other elements was performed.
• The application of Pb(NO₃)₂ resulted in stronger growth inhibition than application of CdCl₂. In the presence of Pb ions, a reduction was observed of both, the micropropagation coefficient to 1.1–1.8 and the GTI to 48%. In contrast, Cd ions had a positive influence on tested cultures, expressed as an increase of GTI up to 243% on medium enriched with 1.0 μm CdCl₂. Moreover, photosynthetic pigment content in shoots cultivated on media with CdCl₂ was higher than in control treatment. The adaptation to Cd was associated with decreased accumulation of phenols in the order: 0.0 μm  > 1.0 μm > 3.0 μm  > 5.5 μm CdCl₂. It seems that high tolerance to Cd is related to K uptake, which is involved in antioxidant defence.
• This work presents an innovative approach to the impact of Cd ions on plant growth and suggests a potential biological role of this metal in species from metalliferous areas.

     

Protective Effect of Enzymatic Extracts from Microalgae Against DNA Damage Induced by H<Subscript>2</Subscript>O<Subscript>2</Subscript>

The enzymatic extracts from seven species of microalgae (Pediastrum duplex, Dactylococcopsis fascicularis, Halochlorococcum porphyrae, Oltmannsiellopsis unicellularis, Achnanthes longipes, Navicula sp. and Amphora coffeaeformis) collected from three habitats (freshwater, tidal pool, and coastal benthic) at Jeju Island in Korea were investigated for their antioxidant activity. Of the extracts tested, the AMG 300 L (an exo 1, 4-α-d-glucosidase) extract of P. duplex, the Viscozyme extract of Navicula sp., and the Celluclast extract of A. longipes provided the most potential as antioxidants. Meanwhile, the Termamyl extract of P. duplex in an H₂O₂ scavenging assay exhibited an approximate 60% scavenging effect. In this study, we report that the DNA damage inhibitory effects of P. duplex (Termamyl extract) and D. fascicularis (Kojizyme extract) were nearly 80% and 69% respectively at a concentration of 100 μg/ml. Thus, it is suggested that the microalgae tested in this study yield promising DNA damage inhibitory properties on mouse lymphoma L 5178 cells that are treated with H₂O₂. Therefore, microalgae such as P. duplex may be an excellent source of naturally occurring antioxidant compounds with potent DNA damage inhibition potential.     

Effect of mycorrhizal inoculations on heavy metal uptake and stress alleviation of Cajanus cajan (L.) Millsp. genotypes grown in cadmium and lead contaminated soils

The aim of the present study was to evaluate the role of arbuscular mycorrhizal (AM) fungi on metal uptake, oxidative effects and antioxidant defence mechanisms under cadmium (Cd) and lead (Pb) stresses in Cajanus cajan (L.) Millsp. (pigeonpea). Treatments consisted of two concentrations each of Cd (25 and 50 mg/kg of soil) and Pb (500 and 800 mg/kg of soil) singly as well as in combination. Both metals induced oxidative damage through increased lipid peroxidation, electrolyte leakage and hydrogen peroxide levels, but Cd was found to be more toxic than Pb. Compared with the effects of Cd or Pb alone, the combination of Cd and Pb acted synergistically; however, Pb immobilisation in soil controlled the uptake of Cd in plants. There was a direct correlation between the type of genotype, heavy metal content and oxidative damage in concentration dependent manner. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) increased under stress. The toxicity symptoms of the metal stress were significantly higher in Sel-141-97 genotype when compared with Sel-85 N. The high ratio of glutathione to its oxidised form, glutathione disulfide (GSH/GSSG), could be restored by means of higher glutathione reductase (GR) activity and increased GSH synthesis in mycorrhizal stressed plants. AM inoculations with Glomus mosseae significantly arrested uptake of Cd and Pb into the root system and further translocation into the above ground parts and led to decreased lipid peroxidation and electrolyte leakage. Increased activities of SOD, CAT, POX as well as GR were observed in all mycorrhizal stressed plants.     

Cadmium-induced changes in antioxidant enzymes from the marine alga Nannochloropsis oculata

Cadmium-induced oxidative stress symptoms such as lipid peroxidation and H₂O₂ production were examined in the marine alga Nannochloropsis oculata. Changes in antioxidant enzyme levels and isozyme patterns were also examined. Increasing concentrations of Cd produced growth inhibition. Among the responses to added Cd, the H₂O₂ content and malonyldialdehyde accumulation increased significantly, indicating a state of oxidative stress. In the case of ascorbate peroxidase activity the increase was about 2.5 times and a marked induction of the isozyme APX2 contributed to this increase. Guaiacol peroxidase activity increased about 4-fold, this being due mainly to the isozyme GPX3. Catalase activity increased slightly, whereas superoxide dismutase and glutathione reductase activity decreased markedly. Alterations of antioxidant enzyme levels and isozyme pattern changes in Cd-treated alga suggest that they might be involved in the heavy metal tolerance in this alga.     

The Bioadsorption of Cadmium and Lead by Bacteria in Root Exudates Culture

Microorganisms are important for phytoremediation of soil contaminated with heavy metals. In the present study, bacteria Bacillus sp., Pseudomonas sp., Alcaligenes sp., and Flavobacterium sp. isolated from the Zhangshi Irrigation Area were applied to bioadsorbed Cd and Pb in liquid cultures with root exudates of sunflower as a sole carbon source. The experimental data demonstrated that these bacteria had a high potential of enrichment of Cd and Pb, and Bacillus sp. and Alcaligenes sp. had better ability to accumulate Cd or Pb than the others; the distinct bioadsorption of Cd and Pb by bacteria might depend on the physiology of bacteria, categories of heavy metals, and environmental factors (such as pH). In addition, root exudates of sunflower could not only support the growth of these bacteria, but also influence the toxicity and bioavailability of Cd and Pb. Our results indicated that amendment with bacteria isolated from heavy-metal-polluted soil and root exudates could be considered as a potential approach to enhance the phytoremediation of Cd- or Pb-contaminated soil.     

Effects of Cadmium,Chromium and Lead on Growth,Metal Uptake and Antioxidative Capacity in <Emphasis Type="Italic">Typha angustifolia</Emphasis>

This study investigates the modulation of antioxidant defence system of Typha angustifolia after 30 days exposure of 1 mM chromium (Cr), cadmium (Cd), or lead (Pb). T. angustifolia showed high tolerance to heavy metal toxicity with no visual toxic symptom when exposed to metal stress, and Cd/Pb addition also increased plant height and biomass especially in Pb treatment. Along with increased Cr, Cd, and Pb uptake in metal treatments, there was enhanced uptake of plant nutrients including Ca and Fe, and Zn in Pb treatment. A significant increase in malondialdehyde (MDA) content and superoxide dismutase (SOD) and peroxidase (POD) activities were recorded in plants subjected to Cr, Cd, or Pb stress. Furthermore, Pb stress also improved catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) activities; whereas Cr stress depressed APX and GPX. The results indicate that enzymatic antioxidants and Ca/Fe uptake were important for heavy metal detoxification in T. angustifolia, stimulated antioxidative enzymes, and Ca, Fe, and Zn uptake could partially explain its hyper-Pb tolerance.     

Antioxidant Properties of Selected <Emphasis Type="Italic">Boletus</Emphasis> Mushrooms

Considering the growing interest for mushrooms and the demand search of natural antioxidants sources, the aim of this study was to investigate the antioxidant properties of two edible widely used Boletus species, Boletus edulis, and Boletus auranticus, collected from Istra region in Croatia in late summer 2007. To evaluate the antioxidant properties and content of antioxidant compounds, scavenging capacity on DPPH˙, OH˙, and O₂˙⁻ radicals, reducing power and capacity to inhibit lipid peroxidation has been investigated. It is determined that content of total phenols (41.82 ± 0.08 mg gallic acid equivalent per gram of dry extract) was higher for B. edulis. Using high performance liquid chromatography/diode array detector analysis, the main antioxidant compound, variegatic acid, has been detected and quantified. 1,1-Diphenyl-2-picryl-hydrazyl-hydrate assay was used as a preliminary free radical–scavenging evaluation. By this assay, it has been found that B. edulis dry mushroom extract exhibits 50% of inhibition value at the extract concentration of 0.016 ± 0.0003 mg/ml. The extracts were capable of reducing iron(III) and, thus, are capable of donating electrons. Using electron paramagnetic resonance spin-trapping and spin-probing techniques, activity against relevant reactive species, ˙OH and O₂˙⁻ radical, was analyzed for both mushroom extracts. Both investigated extracts are determined as good inhibitors for ˙OH radical reduction, and both exhibited significant capacity for scavenging O₂˙⁻ radical and for that could help to prevent or meliorate oxidative damage. Only B. edulis extract prevents lipid peroxidation. Investigated mushroom extracts could represent easily accessible natural antioxidant resource.     

Antioxidant defense system in leaves of Indian mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis>) and rape (<Emphasis Type="Italic">Brassica napus</Emphasis>) under cadmium stress

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from environment. Using two brassica species (Brassica juncea and Brassica napus), nutrient solution experiments were conducted to study variation in tolerance to cadmium (Cd) toxicity based on (1) lipid peroxidation and (2) changes in antioxidative defense system in leaves of both plants (i.e., superoxide dismutase (SOD EC 1.15.1.1), catalase (CAT EC 1.11.1.6), ascorbate peroxidase (APX EC 1.11.1.11), guaiacol peroxidase (GPX EC 1.11.1.7), glutathione reductase (GR EC 1.6.4.2), levels of phytochelatins (PCs), non-protein thiols (NP-SH), and glutathione. Plants were grown in nutrient solution under controlled environmental conditions, and subjected to increasing concentrations of Cd (0, 10, 25 and 50 μM) for 15 days. Results showed marked differences between both species. Brassica napus under Cd stress exhibited increased level of lipid peroxidation, as was evidenced by the increased malondialdehyde (MDA) content in leaves. However, in Brassica juncea treated plants, MDA content remained unchanged. In Brassica napus, with the exception of GPX, activity levels of some antioxidant enzymes involved in detoxification of reactive oxygen species (ROS), including SOD, CAT, GR, and APX, decreased drastically at high Cd concentrations. By contrast, in leaves of Brassica juncea treated plants, there was either only slight or no change in the activities of the antioxidative enzymes. Analysis of the profile of anionic isoenzymes of GPX revealed qualitative changes occurring during Cd exposure for both species. Moreover, levels of NP-SH and PCs, monitored as metal detoxifying responses, were much increased in leaves of Brassica juncea by increasing Cd supply, but did not change in Brassica napus. These results indicate that Brassica juncea plants possess the greater potential for Cd accumulation and tolerance than Brassica napus.     

Expression of Arabidopsis acyl‐CoA‐binding proteins AtACBP1 and AtACBP4 confers Pb(II) accumulation in Brassica juncea roots

In Arabidopsis thaliana, the expression of two genes encoding acyl‐CoA‐binding proteins (ACBPs) AtACBP1 and AtACBP4, were observed to be induced by lead [Pb(II)] in shoots and roots in qRT‐PCR analyses. Quantitative GUS (β‐glucuronidase) activity assays confirmed induction of AtACBP1pro::GUS by Pb(II). Electrophoretic mobility shift assays (EMSAs) revealed that Pas elements in the 5′‐flanking region of AtACBP1 were responsive to Pb(II) treatment. AtACBP1 and AtACBP4 were further compared in Pb(II) uptake using Brassica juncea, a potential candidate for phytoremediation given its rapid growth, large roots, high biomass and good capacity to accumulate heavy metals. Results from atomic absorption analyses on transgenic B. juncea expressing AtACBP1 or AtACBP4 indicated Pb(II) accumulation in roots. Subsequent Pb(II)‐tracing assays demonstrated Pb(II) accumulation in the cytosol of root tips and vascular tissues of transgenic B. juncea AtACBP1‐overexpressors (OXs) and AtACBP4‐OXs and transgenic Arabidopsis AtACBP1‐OXs. Transgenic Arabidopsis AtACBP1‐OXs sequestered Pb(II) in the trichomes and displayed tolerance to hydrogen peroxide (H₂O₂) treatment. In addition, AtACBP1 and AtACBP4 were H₂O₂‐induced in the roots of wild‐type Arabidopsis, while lipid hydroperoxide (LOOH) measurements of B. juncea AtACBP1‐OX and AtACBP4‐OX roots suggested that AtACBP1 and AtACBP4 can protect lipids against Pb(II)‐induced lipid peroxidation.