重金属镉(Cd)在植物体内的转运途径及其调控机制

重金属镉(Cd)的毒害效应与其由土壤向植物地上部分运输有关,揭示Cd~(2+)转运途径及其调控机制可为提高植物抗镉性以及镉污染的植物修复提供依据。对Cd~(2+)在植物体内的转运途径,特别是限制Cd~(2+)移动的细胞结构和分子调控机制研究进展进行了回顾。Cd~(2+)通过共质体和质外体途径穿过根部皮层进入木质部的过程中,大部分在皮层细胞间沉积,少部分抵达中柱后转移到地上部分。为了免受Cd~(2+)的危害,植物体产生了多种限制Cd~(2+)吸收和转移的生理生化机制:1)环绕在内皮层径向壁和横向壁上的凯氏带阻止Cd~(2+)以质外体途径进入木质部;2)螯合剂与进入根的Cd~(2+)螯合形成稳定化合物并区隔在液泡中;3)通过H+/Cd~(2+)离子通道等将Cd~(2+)逆向转运出根部。植物共质体和质外体途径转运重金属镉的能力以及两条途径的串扰尚待进一步明晰和阐明。     

Relationship between cadmium sensitivity and degree of plasma membrane fatty acid unsaturation in Saccharomyces cerevisiae

The sensitivity of Saccharomyces cerevisiae to the redox-active metal copper has recently been found to be influenced by cellular fatty acid composition. This study sought to investigate whether fatty acid composition affected plasma membrane permeabilisation and whole-cell toxicity induced by the redox-inactive metal cadmium. S. cerevisiae NCYC 1383 was enriched with the polyunsaturated fatty acids linoleate (18:2) and linolenate (18:3) by growth in 18:2- or 18:3-supplemented medium. Incorporation of the exogenous fatty acids resulted in them comprising more than 65% of the total fatty acids in plasma membrane lipids. Inhibition of cell division in the presence of Cd(NO₃)₂ was accentuated by growth in the presence of a polyunsaturated fatty acid. Furthermore, susceptibility to Cd²⁺-induced plasma membrane permeabilisation increased with the degree of fatty acid unsaturation. Thus, during exposure to Cd²⁺, K⁺ efflux from 18:2- and 18:3-enriched cells was up to 2.5-fold or 3-fold greater, respectively than that from unsupplemented cells. In addition, reductions in cell viability during exposure to Cd²⁺ were most marked in polyunsaturated-fatty-acid-supplemented cells. At certain times, unsupplemented Cd²⁺-exposed cells displayed up to 7-fold greater viability than supplemented Cd²⁺-exposed cells. The study demonstrates that the toxicity of the redox-inactive metal Cd²⁺ towards S. cerevisiae becomes markedly amplified with increased cellular and plasma membrane fatty acid unsaturation. Received: 14 March 1997 / Received revision: 4 June 1997 / Accepted: 7 June 1997     

Cadmium interactions with ATPase activity in the euryhaline alga Dunaliella bioculata

To further study the toxicity of cadmium in the euryhaline alga, Dunaliella bioculata, ATPase activity and Cd²⁺ interactions were investigated in this species.Ultracytochemical studies showed the presence of ATPase reaction after incubation with Ca²⁺ and Mg²⁺, on different cell structures, the cytoplasm, the nucleoplasm, the axoneme and the membrane of the flagellae. In the cytoplasm, the localization of the lead precipates suggests that they are associated with the endoplasmic reticulum.The in vitro measurement of enzyme activity in crude cell extracts obtained by a partial solubilization of deflagellated algae with Triton X100, revealed a high Mg²⁺ dependent pyrophosphatase activity, a weak Mg²⁺-ATPase and a Ca²⁺-ATPase (Km = 0.12 mM) which was little sensitive to vanadate. In these extracts, a Ca²⁺ dependent ATPase was detected at the level of a double band by a non-denaturing electrophoresis. The same activity was found in the supernatant of sonicated cells in the absence of detergent, which suggests that this ATPase could be a cytosolic enzyme.In plasma membrane fractions, vanadate-sensitive ATPase activity was measured. This reaction was activated either by Mg²⁺ at relatively low concentrations (Km = 150µm) or by Ca² +, but required unusually high concentrations of this ion, 50–100 mM.The inhibitory effects of Cd²⁺ on Ca²⁺ ATPase activity in cell extracts were compared with those of other cations. The range of toxicity was: Zn²⁺ > Cd²⁺ > Cu²⁺ > La³⁺ > Co²⁺. For Cd²⁺, the IC₅₀ was 42 µM. The nature of inhibition, though, mixed was for the most part competitive, since the competitive constant value (Ki = 7 µM) was lower than the non-competitive constant value (Ki = 35 µM).In plasma membrane fractions, ATPase activity showed a high sensitivity to the heavy metal. It was non-competitively inhibited by cadmium in a narrow range of micromolar concentrations.     

重金属Cd2+和Cu2+胁迫下泥蚶消化酶活性的变化

为了探讨重金属Cd²⁺和Cu²⁺胁迫对泥蚶消化酶活性的影响,运用酶学分析的方法,按《渔业水质标准》（GB 11607）规定的Cd²⁺、Cu²⁺最高限量值的1、2、5、10倍设置重金属离子Cd²⁺、Cu²⁺浓度及其组合,研究了在重金属Cd²⁺、Cu²⁺胁迫下,30d内泥蚶3种消化酶活性的变化规律。结果表明：与空白对照组相比,在重金属Cd²⁺、Cu²⁺或其组合的胁迫下,较低浓度组泥蚶的淀粉酶活性实验前期增强（即被诱导）,实验后期减弱（即被抑制）,较高浓度组泥蚶的淀粉酶活性从实验一开始就减弱,并保持在较低水平,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合Cu²⁺ > （Cd²⁺+Cu²⁺）组合 > Cd²⁺;泥蚶脂肪酶的活性实验前期增强,实验后期转为微减弱或减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合（Cd²⁺+Cu²⁺）组合 > Cu²⁺ > Cd²⁺;泥蚶胃蛋白酶的活性实验前期增强,且活性呈现升高-降低-再升高-再降低的变化,实验后期分别表现微增强、微减弱和减弱,毒性比较,同一重金属高浓度 > 低浓度,不同重金属及其组合（Cd²⁺+Cu²⁺）组合 > Cu²⁺ > Cd²⁺。可见：环境中的Cd²⁺和Cu²⁺对泥蚶的消化酶活性起着明显的影响作用。     

Heavy Metal-Activated Synthesis of Peptides in Chlamydomonas reinhardtii

In this study, we have addressed the capacity of the green alga Chlamydomonas reinhardtii to produce metal-binding peptides in response to stress induced by the heavy metals Cd²⁺, Hg²⁺, and Ag⁺. Cells cultured in the presence of sublethal concentrations of Cd²⁺ synthesized and accumulated oligopeptides consisting solely of glutamic acid, cysteine, and glycine in an average ratio of 3:3:1. Cadmium-induced peptides were isolated in their native form as higher molecular weight peptide-metal complexes with an apparent molecular weight of approximately 6.5 × 10³. The isolated complex bound cadmium (as evidenced by absorption spectroscopy) and sequestered (with a stoichiometry of 0.7 moles of cadmium per mole of cysteine) up to 70% of the total cadmium found in extracts of cadmium-treated cells. In Hg²⁺-treated cells, the principal thiol-containing compound induced by Hg²⁺ ions was glutathione. It is possible that glutathione functions in plant cells (as it does in animal cells) to detoxify heavy metals. Cells treated with Ag⁺ ions also synthesized a sulfur-containing component with a charge to mass ratio similar to Cd²⁺-induced peptides. But, in contrast to the results obtained using Cd²⁺ as an inducer, these molecules did not accumulate to significant levels in Ag⁺-treated cells. The presence of physiological concentrations of Cu²⁺ in the growth medium blocked the synthesis of the Ag⁺-inducible component(s) and rendered cells resistant to the toxic effects of Ag⁺, suggesting competition between Cu²⁺ and Ag⁺ ions, possibly at the level of metal uptake.     

Comparative studies of zinc metabolism in cultured chinese hamster cells with differing metallothionein-induction capacities

Previous work in our laboratory led to the isolation of a cadmium (Cd)-resistant variant (Cd^r2C10) of the line CHO Chinese Hamster cell having a 10-fold greater resistance to the cytotoxic action of Cd²⁺ compared with the CHO cell. This resistance was attributed to an increased capacity of the Cd²⁺-resistant Cd^r2C10 subline to induce synthesis of the Cd²⁺- and Zn²⁺-binding protein(s), metallothionein(s) (MT). Evidence that Cd²⁺ behaves as an analog of the essential trace metal, Zn²⁺, especially as an inducer of MT synthesis, suggested that the Cd^r and CHO cell types could be employed to investigate cellular Zn²⁺ metabolism. In the present study, measurements were made to compare CHO and Cd^r cell types for (a) growth as a function of the level of ZnCl₂ added to the culture medium, (b) uptake and subcellular distribution of Zn²⁺, and (c) capacity to induce MT synthesis. The results of these measurements indicated that (a) both CHO and Cd^r cell types grew normally (T _d≊16–18 h) during exposures to Zn²⁺ at levels up to 100 μM added to the growth medium, but displayed abrupt growth inhibition at higher Zn²⁺ levels, (b) Cd^r cells incorporate fourfold more Zn²⁺ during a 24-h exposure to the maximal subtoxic level of Zn²⁺ and (c) the CHO cell lacks the capacity to induce MT synethesis while the Cd^r cell is proficient in this response during exposure to the maximal subtoxic Zn²⁺ level. These findings suggest that (a) the CHO and Cd^r cell systems will be useful in further studies of cellular Zn²⁺ metabolism, especially in comparisons of Zn²⁺ metabolism in the presence and absence of induction of the Zn²⁺-sequestering MT and (b) a relationship exists between cellular capacity to induce MT synthesis and capacity for cellular Zn²⁺ uptake.     

Comparison of Physiological Changes in Euglena gracilis During Exposure to Heavy Metals of Heterotrophic and Autotrophic Cells

The effect of different concentrations of Hg²⁺, Cd²⁺, and Pb²⁺ on ultrastructure, growth, respiration, photosynthesis, chlorophyll content, and metal accumulation in Euglena gracilis was examined. The toxicity of the heavy metals was dependent on the culture medium used and whether cells were grown in the dark or under illumination. Hg²⁺ was the most toxic metal, which showed effects at a concentration as low as 1.5 μM; Cd²⁺ showed an intermediate toxicity (effects observed above 50 μM); and Pb²⁺ was almost ineffective up to 1 mM. Cells grown for several weeks in the dark, in the presence of 1.5 μM Hg²⁺ showed a reduced sensitivity to subsequent exposure to Cd²⁺ or Pb²⁺. The Hg²⁺-pretreated cells also presented an enhanced capacity to accumulate other metals. In comparison, light-grown cells showed a greater Cd²⁺ accumulation, but a lower Pb²⁺ uptake than Hg²⁺-pretreated dark-grown cells. Pretreatment of light-grown cells with Hg²⁺ did not enhance the accumulation of Cd²⁺. These results suggest that the capacity to tolerate heavy metals by Euglena may have mechanistic differences when cells are grown in the dark or under illumination.     

Endoplasmic reticulum is a major target of cadmium toxicity in yeast

Cadmium (Cd²⁺) is a very toxic metal that causes DNA damage, oxidative stress and apoptosis. Despite many studies, the cellular and molecular mechanisms underlying its high toxicity are not clearly understood. We show here that very low doses of Cd²⁺ cause ER stress in Saccharomyces cerevisiae as evidenced by the induction of the unfolded protein response (UPR) and the splicing of HAC1 mRNA. Furthermore, mutant strains (Δire1 and Δhac1) unable to induce the UPR are hypersensitive to Cd²⁺, but not to arsenite and mercury. The full functionality of the pathways involved in ER stress response is required for Cd²⁺ tolerance. The data also suggest that Cd²⁺‐induced ER stress and Cd²⁺ toxicity are a direct consequence of Cd²⁺ accumulation in the ER. Cd²⁺ does not inhibit disulfide bond formation but perturbs calcium metabolism. In particular, Cd²⁺ activates the calcium channel Cch1/Mid1, which also contributes to Cd²⁺ entry into the cell. The results reinforce the interest of using yeast as a cellular model to study toxicity mechanisms in eukaryotic cells.     

Bivalent Metal Ions Modulate Cd2+ Effects on Isolated Rat Liver Mitochondria

We have studied Cd²⁺-induced effects on mitochondrial respiration and swelling in various media as a function of the [Cd²⁺] in the presence or absence of different bivalent metal ions or ruthenium red (RR). It was confirmed by monitoring oxygen consumption by isolated rat liver mitochondria that, beginning from 5 M, Cd²⁺ decreased both ADP and uncoupler-stimulated respiration and increased their basal respiration when succinate was used as respiratory substrate. At concentrations higher than 5 M, Cd²⁺ stimulated ion permeability of the inner mitochondrial membrane, which was monitored in this study by swelling of both nonenergized mitochondria in 125 mM KNO₃ or NH₄NO₃ medium and succinate-energized mitochondria incubated in a medium containing 25 mM K-acetate and 100 mM sucrose. We have found substantial changes in the above-mentioned Cd²⁺ effects on mitochondria treated in sequence with 100 M of Ca²⁺, Sr²⁺, Mn²⁺ or Ba²⁺(Me²⁺) and 7.5 M RR, as well as the alterations in Cd²⁺ action on the uptake of ¹³⁷Cs⁺ by succinate-energized mitochondria in the presence or absence of valinomycin in acetate medium (50 mM Tris-acetate and 140 mM sucrose) with or without Ca²⁺ or RR. The evidence obtained indicate that Ca²⁺ exhibits a synergestic action on all Cd²⁺ effects examined, whereas Sr²⁺ and Mn²⁺, conversely, are antagonistic. In the presence of RR, the Cd²⁺ effects on respiration [stimulation of State 4 respiration and inhibition of 2,4-dinitrophenol (DNP)-uncoupled respiration] still exist, but are observed at concentrations of cadmium more than one order higher; the inhibition of State 3 respiration by Cd²⁺, conversely, takes place under even lower cadmium concentrations than those determined without RR in the medium. In addition, RR added simultaneously with cadmium in the incubation medium prevents any swelling in the nitrate media, but induces an increment both in Cd²⁺-stimulated swelling and ¹³⁷Cs⁺ (analog of K⁺) uptake in the acetate media. For the first time, we have shown that Cd²⁺-induced swelling in all media under study is susceptible to cyclosporin A (CSA), a high-potency inhibitor of the mitochondrial permeability transition (PT) pore. The observations are interpreted in terms of a dual effect of cadmium on respiratory chain activity and permeability transition.     

Heavy metal uptake capacities by the common freshwater green alga Cladophora fracta

Macroalgae have received much attention for heavy metal removal in treatment of domestic wastewater. In this report, the uptake capacity of a common freshwater green alga, Cladophora fracta, for heavy metal ions (copper, zinc, cadmium, and mercury) was evaluated. The equilibrium adsorption capacities were 2.388?mg Cu²⁺, 1.623?mg Zn²⁺, 0.240?mg Cd²⁺, and 0.228?mg Hg²⁺ per gram of living algae at 18°C and pH?5.0. The removal efficiency for Cu²⁺, Zn²⁺, Cd²⁺, and Hg²⁺ were 99, 85, 97, and 98%, respectively. Greater removal efficiency was achieved when the concentrations of metal ions were at very low level. The results indicated that living algae are suitable for removal and recovery of heavy metal ions from aqueous solutions and can be a potential tool to treat industrial wastewater.     

Effect of cadmium uptake and heat stress on root ultrastructure, membrane damage and antioxidative response in rice seedlings

Excess cadmium (Cd²⁺) in the soil environment is taken up by plants and can cause phytotoxicity. Elevated temperatures also lead to deleterious effects on plants. Plants are very often exposed to a combination of stresses rather than a single stress. The effect of Cd²⁺ and heat stress (HS) on the growth, root ultrastructure, lipid peroxidation (MDA), hydrogen peroxide accumulation and the activities of antioxidant enzymes peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) of rice roots from sensitive cv. DR-92 and tolerant cv. Bh-1 were investigated at 10 and 20 day of growth under controlled conditions. At day 10 under all Cd²⁺ treatments, the Cd²⁺ content between the two rice cultivars were almost similar. Application of 500 μM Cd²⁺ significantly increased metal concentrations at day 20 in the roots of rice seedlings resulting in a maximum accumulation of 44.25 μg Cd²⁺ g^-1 dry wt in cv. DR-92 and 30 μg Cd²⁺ g^-1 dry wt in cv. Bh-1 with a ~25 % decline in Relative Growth Index (RGI) in cv. DR-92. TEM studies revealed slight disorganization with cell wall ingrowths in root tissues from cv. DR-92 grown in 100 μM Cd²⁺ + HS. Uptake and accumulation of Cd²⁺ increased upon heat treatment in parenchyma, vacuoles and vascular cylinder of root tissues. Peroxidase primarily located in cell walls, the intensity being higher in sensitive cv. DR-92. Under Cd²⁺ stress alone, plants of sensitive cv. DR-92 significantly increased the H₂O₂ and MDA levels together with increased activities of the enzymes POD, CAT and APX at day 10 but remained almost stable at day 20. A strong increase in MDA levels was noted at day 20 in tolerant cv. Bh-1. Cd²⁺ + HS treatments in tolerant cv.Bh-1 led to a decreased H₂O₂ and MDA levels and decreased activities of the enzymes POD, CAT and APX. Results suggest stimulation of root antioxidant system under combination of two stresses and that heat stress seem to have a direct protective role by mitigating the effect of mild Cd²⁺ toxicity largely by enhanced Cd²⁺-MT formation contributing thereby towards the management of Cd²⁺ toxicity at cellular level that confers Cd²⁺ tolerance to rice cv. Bh-1.     

Toxicity of heavy metals to Asellus aquaticus (L.) (Crustacea,Isopoda)

Effects of heavy metals on the isopod Asellus aquaticus (L.) are studied by static toxicity tests. Results demonstrate that the species is sensitive to Cd⁺², Cr⁺⁶, Cu⁺², Fe⁺³, Hg⁺², Ni⁺² Pb⁺² and Zn⁺², but the toxicity of each metal is different. Differences are also found between adults and between adults and juveniles. The comparative analysis of all data on the toxicity has been performed on the concentrations of metal ions and not on metal compound concentrations.Criteria for establishing water quality in order to guarantee protection of the environment are discussed.     

Hg2+ and Cd2+ interact differently with biomimetic erythrocyte membranes

In order to characterize the potentially deleterious effects of toxic Hg²⁺ and Cd²⁺ on lipid membranes, we have studied their binding to liposomes whose composition mimicked erythrocyte membranes. Fluorescence spectroscopy utilizing the concentration dependent quenching of Phen Green™ SK by Hg²⁺ and Cd²⁺ was found to be a sensitive tool to probe these interactions at metal concentrations ≤1 μM. We have systematically developed a metal binding affinity assay to screen for the interactions of Hg²⁺ or Cd²⁺ with certain lipid classes. A biomimetic liposome system was developed that contained four major lipid classes of erythrocyte membranes (zwitterionic lipids: phosphatidylcholine and phosphatidylethanolamine; negatively charged: phosphatidylserine and neutral: cholesterol). In contrast to Hg²⁺, which preferentially bound to the negatively charged phosphatidylserine compared to the zwitterionic components, Cd²⁺ bound stronger to the two zwitterionic lipids. Thus, the observed distinct differences in the binding affinity of Hg²⁺ and Cd²⁺ for certain lipid classes together with their known effects on membrane properties represent an important first step toward a better understanding the role of these interactions in the chronic toxicity of these metals.     

Effects of heavy metals on microbial activity of water and sediment communities

The effects of Cd²⁺, Cr³⁺ and Zn²⁺ on the microbial activity of water and sediment samples from a contaminated stream were studied. The maximum [¹⁴C]glucose uptake (V_max) and the mineralization (¹⁴CO₂) rates were determined. A 10% reduction in V_max was obtained at lower metal concentrations in water samples than in sediment ones. Moreover, a 10% decrease in ¹⁴CO₂ was observed at significantly minor metal levels, so ¹⁴CO₂ was more sensitive to evaluated heavy metal pollution. On the basis of MICs obtained for both communities, they were more sensitive to Cd²⁺ than to Cr³⁺ and Zn²⁺. Zinc was less inhibitory to V_max and ¹⁴CO₂ rates; Cr³⁺ showed an intermediate toxicity, and Cd²⁺ was 10–100 times more inhibitory than the other metals.     

Additive effects of metal excess and superoxide,a highly toxic mixture in bacteria

Heavy metal contamination is a serious environmental problem. Understanding the toxicity mechanisms may allow to lower concentration of metals in the metal-based antimicrobial treatments of crops, and reduce metal content in soil and groundwater. Here, we investigate the interplay between metal efflux systems and the superoxide dismutase (SOD) in the purple bacterium Rubrivivax gelatinosus and other bacteria through analysis of the impact of metal accumulation. Exposure of the Cd²⁺-efflux mutant ΔcadA to Cd²⁺ caused an increase in the amount and activity of the cytosolic Fe-Sod SodB, thereby suggesting a role of SodB in the protection against Cd²⁺. In support of this conclusion, inactivation of sodB gene in the ΔcadA cells alleviated detoxification of superoxide and enhanced Cd²⁺ toxicity. Similar findings were described in the Cu⁺-efflux mutant with Cu⁺. Induction of the Mn-Sod or Fe-Sod in response to metals in other bacteria, including Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida, Vibrio cholera and Bacillus subtilis, was also shown. Both excess Cd²⁺ or Cu⁺ and superoxide can damage [4Fe-4S] clusters. The additive effect of metal and superoxide on the [4Fe-4S] could therefore explain the hypersensitive phenotype in mutants lacking SOD and the efflux ATPase. These findings underscore that ROS defence system becomes decisive for bacterial survival under metal excess.     

Dye decolorization by sub-tropical basidiomycetous fungi and the effect of metals on decolorizing ability

White-rot basidiomycetous fungi from sub-tropical forests plus a Phanerochaete chrysosporium control were able to decolorize several azo, triphenylmethane and heterocyclic/polymeric dyes over 14 days. The effects of metal ions on decolorizing ability towards the dye Poly-R varied. Two sub-tropical strains were capable of decolorization in the presence of up to 0.25 mM Cd²⁺, Cu²⁺ and Zn²⁺, whereas decolorization by P. chrysosporium was completely inhibited by all metals at concentrations as low as 0.1 mM. In all cases decolorizing ability was more sensitive than biomass production to metal inhibition.     

Effects of heavy metals on pollen tube growth and ultrastructure

Summary The influence of different concentrations of the heavy metals cadmium (Cd²⁺), cobalt (Co²⁺), copper (Cu²⁺), iron (Fe²⁺ and Fe³⁺), mercury (Hg²⁺), manganese (Mn²⁺), and zinc (Zn²⁺), plus aluminium (Al³⁺) (a toxic metal in polluted areas), on pollen germination and tube growth ofLilium longiflorum was investigated using light microscopy. Effects could be observed with 3 M and 100 M of heavy metal, added as chloride salts to the medium. Cd²⁺, Cu²⁺, and Hg²⁺, showed the greatest toxicity, whereas germination and growth rate was less affected by Mn²⁺. Affected tubes showed swelling of the tip region. Tubes treated with Cd²⁺, Co²⁺, Fe²⁺, Fe³⁺, Hg²⁺, and Mn²⁺ were also prepared for ultrastructural studies. In all cases, the main effect was abnormal cell wall organization, mostly at the tip, where round, fibrillar aggregates, the shape and size of secretory Golgi vesicles were formed. They built up a loose network which could be up to 10 m thick compared to untreated tubes where the cell wall was composed of thin layers of long fibrils and about 100 nm thick. Cd²⁺ was the only metal which produced effects at the intracellular level: organelle distribution within the tip region appeared disorganized. A general mechanism of heavy metal action on pollen tube growth is discussed.     

Ethylene glycol tetra-acetic acid and salicylic acid improve anti-oxidative ability of maize seedling leaves under heavy-metal and polyethylene glycol 6000-simulated drought stress

Stress caused by divalent heavy metal ions and drought exert many toxic and adverse effects on seedling growth and development of plants, especially on leave growth. Organic acids such as ethylene glycol tetra-acetic acid (EGTA) and salicylic acid (SA) have been shown to alleviate the unfavorable effects exerted by these stresses on seedling growth and metabolism. In order to reveal the physiological mechanism underlying these toxic effects and the alleviated effects exerted by organic acids, maize seedling leaves (genotype “Zhengdan958”) were exposed for 7 days to different concentrations of cadmium (Cd²⁺), mercury (Hg²⁺), and lead (Pb²⁺) ions and to the drought stress-inducing polymer polyethylene glycol (PEG) 6000. The same experiments were also carried out in the presence of EGTA or SA. Treated leaves were analyzed for activities of the anti-oxidative enzymes catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) and for the content of malondialdehyde (MDA). The results showed that stress treatments with the heavy metals Cd²⁺, Hg²⁺, and Pb²⁺ and with PEG all affected the activities of CAT, POD, and SOD, although the extent and patterns of these changes were different under different stress conditions. Both heavy metal and drought stress caused a concentration-dependent increase in MDA content. Treatments in the presence with EGTA or SA showed that both these compounds exerted certain alleviative effects on seedling growth under Cd²⁺, Hg²⁺, and Pb²⁺ stresses and PEG-simulated drought stress, with SA generally showing better effects than EGTA.     

Laboratory simulation of a mining accident: acute toxicity, hsc/hsp70 response, and recovery from stress in Gammarus fossarum (Crustacea, Amphipoda) exposed to a pulse of cadmium

The rate of survival and stress protein (hsc/hsp70) response were investigated in the freshwater amphipod, Gammarus fossarum Koch, 1835, during a 20-day stress and recovery experiment. Adult females and males, were separately exposed to 9 different cadmium concentrations for 5 days to simulate a short-term pulse of xenobiotics in an aquatic environment, followed by a recovery period of 15 days. In terms of mortality, females were much more sensitive to cadmium than males; 4.28±2.45 g Cd²⁺/l resulted in strong effects on the rate of survival of females but not males. In both sexes, mortality occurred predominantly within the first 5 days of the recovery period. At the cellular level, cadmium induced an hsc/hsp70 response. The lower Cd²⁺ concentrations we used led to an induction of stress proteins while higher Cd²⁺ concentrations resulted in a proportionately reduced hsc/hsp70 response, most likely due to pathological damage. Surviving individuals retained their capacity to induce stress protein production in the recovery period, even if the stress protein response system was overwhelmed by cadmium during the exposure period.     

Effects of Cadmium on Chlorophyll Content,Photochemical Efficiency,and Photosynthetic Intensity of Canna indica Linn.

The effects of cadmium (Cd²⁺) on growth status, chlorophyll (Chl) content, photochemical efficiency, and photosynthetic intensity were studied on Canna indica Linn. Plant specimens that were produced from a constructed wetland and precultivated hydroponically in 20 L of 1/10 Hoagland solution under greenhouse conditions for 1 week were exposed to cadmium in concentrations of 0, 0.4, 0.8, 1.6 and 3.2 mg L^―1 Cd²⁺, respectively. The results show that leaves were injured in the Cd²⁺ solution by the third day of exposure and the injury became more serious with an increase in the applied heavy metal. Under 3.2 mg L^―1 Cd²⁺ treatment, growth retardation, the decrease of chlorophyll content from 0.70 to 0.43 mg g^―1 FW, and a decrease in Chl a/b ratio from 2.0 to 1.2 were observed. Chl a was more sensitive than Chl b to Cd²⁺ stress. The decrease was the same with photochemical efficiency. Photosynthetic intensity decreased by 13.3% from 1.5×10⁴ μmol m^―2s^―1 CO₂ in control to 1.3×10⁴ μmol m^―2s^―1 CO₂ in the treatment of 3.2 mg L^―1. Because Canna species are used in heavy metal phytoremediation, these results show that C. indica can tolerate 0.4 to 0.8 mg L^―1 Cd²⁺. Therefore, it is a potential species for phytoremediation of cadmium with some limitations only at higher concentrations.