Studies on the accumulation of cadmium by a strain of Proteus mirabilis

Abstract A bacterium isolated from a wastewater plant sludge, identified as Proteus mirabilis , was tested for cadmium tolerance and accumulation capacity. The organism was able to grow in the presence of Cd²⁺ up to 300 mg l⁻¹.
Accumulation of cadmium is reported for growing and non-growing cells of the organism. In non-growing cultures a 70% removal of cadmium was observed when the initial concentration of Cd²⁺ was 1 mg l⁻¹ whereas at the same concentration the removal by growing cells was only 22%. The metal was shown to be associated with the cell envelope (80%) and accumulated in the cytoplasm (20%).     

Transport of cadmium across the apical membrane of epithelial cell lines

Cadmium (Cd) uptake and secretion across the apical membrane of epithelial cells was studied using LLC-PK1 cells cultured on Petri dishes and permeable membranes, respectively. Cd accumulation in cells from the apical medium was decreased by low temperature and metabolic inhibitors. A saturable tendency was observed between initial Cd accumulation and increased concentrations of Cd in the apical medium at 37 degrees C, but not at 4 degrees C. Co-incubation with ZnCl2 or CuCl2 competitively decreased Cd accumulation at 37 degrees C. A decrease in the pH of the apical medium markedly decreased Cd accumulation. Pretreatment of cells with an inorganic anion-exchange inhibitor significantly decreased Cd uptake at pH 7.4 in the presence of bicarbonate, but only marginally in its absence. A decrease in the pH of the apical medium increased the secretory (basolateral-to-apical) transport of Cd, with a concomitant decrease in the cellular accumulation of Cd. Co-incubation with Cd and tetraethylammonium, a typical substrate of the organic cation transporter, decreased Cd transport, with a concomitant increase in cellular Cd accumulation. The uptake and secretion of Cd across the apical membrane appear to be partly mediated via an inorganic anion exchanger and a H+ antiport of the organic cation transport system, respectively. Therefore, a decrease in pH of the apical medium markedly decreases Cd accumulation, possibly as a result of not only the decrease in Cd uptake via an inorganic anion exchanger, but also the increase in Cd secretion via the Cd2+/H+ antiport. Further evidence of the antiport was obtained from experiments using brush border membrane vesicles isolated from rat kidney and small intestine. In addition, passive diffusion of Cd appears to be decreased by low temperature and a decrease in pH.     

Manganese is highly effective in protecting cells from cadmium intoxication

Cadmium poisoning results in cell death. Although several intracellular pathways have been identified in this response, transport systems responsible for cadmium entry into cells remain poorly understood and controversial. Here, we analyzed the effects of several divalent cations on cadmium toxicity in different cell types. We found that zinc, previously reported as a protective agent against cadmium poisoning, is actually much less efficient than manganese. We show that manganese dramatically reduces cadmium intake, and that this is associated with the inhibition of our recently reported sustained activation of ERK, characteristic of cadmium intoxication. Finally, we show that this inhibition of cadmium entry and ERK-sustained activation perfectly correlates with a high cellular resistance to cadmium exposure. Our results, together with previously published data, support the idea that the yet to be characterized manganese transporter system(s) may be responsible for cadmium entry into cells.     

Enhancing plant uptake of polychlorinated biphenyls and cadmium using tea saponin

The potential of natural surfactant tea saponin to enhance uptake of polychlorinated biphenyls (PCBs) and cadmium (Cd) by Zea Mays L. and Saccharum officinarum L. was investigated. With addition of tea saponin at 0.01% in solution culture, the concentrations of PCB 14, PCB 18, PCB 77 and PCB 156 in root of corn seedling were 2.72, 2.68, 1.94 and 2.40 times as those of treatments without adding any surfactant, respectively. Application of tea saponin to the soil significantly elevated PCB 5 accumulation in shoots and roots (p < 0.05) by sugarcanes. With addition of 0.3% tea saponin, Cd concentration was increased by 96.9% in roots, 156.8% in stems and 30.1% in leaves compared with the treatment without addition of surfactant in sugarcane grown in soil. Tea saponin had potential of assisting the uptake of PCBs and Cd by plants from water solution and soil.     

双酚A与镉对植物光合作用的复合微生态效应

近年来,国内外学者研究了双酚A (BPA)及重金属镉(Cd)单一因子对植物光合作用的影响.但在自然背景下,污染多呈复合型,因此研究BPA和Cd对二者叠加的空间内植物光合作用的复合影响意义重大.本文综述了BPA对植物光合作用的影响及机制,及Cd对植物光合作用的影响及其机制,其中单一BPA和Cd对植物光合作用的影响均表现为:低浓度促进光合作用,高浓度反之.根据相关研究推测了植物在受到复合胁迫时的生态响应,相应的生理生化反应,及光合过程的响应机制.最后提出了BPA与Cd对植物复合胁迫可能开展的相关研究方向.     

The uptake of cadmium,lead and selenium by barley and cabbage grown on soils amended with refuse incinerator fly ash

Summary Barley and cabbage plants grown in the greenhouse on soils amended with refuse incinerator fly ash contained significantly elevated levels of Cd, Pb and Se, with Cd uptake being greatest in both plant species. Cabbage grown on 20% ash amended soil contained 146 times more Cd than controls. Cadmium and Se appeared to be less available in a successive barley crop after overwintering the pots of soil outside, but elemental concentrations still remained elevated. Comparisons with data from other studies indicated that Cd availability was greater from refuse fly ash than from sewage sludge.     

Transcriptome profiling reveals similarities and differences in plant responses to cadmium and lead

We analyzed the influence of salts of two heavy metals—lead and cadmium (Pb²⁺ and Cd²⁺) on plants, including plant and root size, plant genome stability as well as global genome expression. Measurement of the metal uptake showed that there was a significantly higher incorporation of Cd than of Pb, 0.6 and 0.15 uM per gram of dry weight, respectively. The analysis of the root length and plant size showed a dose dependent decrease in plants exposed to cadmium. In contrast there was little difference in the size of plants exposed to lead, although there was nearly four-fold increase of the root length. Analysis of the genome stability revealed that cadmium led to a dose dependent increase of homologous recombination whereas lead had no effect.

Analysis of the global genome expression of plants chronically exposed to 50 uM of Cd and Pb revealed 65 and 338 up- and down-regulated genes by Cd and 19 and 76 by Pb, respectively. Interestingly, half of the genes that changed their expression in Pb-treated plants also changed their expression in Cd-treated ones. The greater number of genes regulated by Cd reflects generally higher genome instability of plants as well as higher uptake as compared to Pb.     

Subcellular distribution,chemical forms,and physiological response to cadmium stress in Hydrilla verticillata

This study investigated the subcellular distribution and chemical forms of cadmium (Cd) in Hydrilla verticillata and the physiological mechanism underlying H. verticillata responses to Cd stress. Hydrilla verticillata was grown in a hydroponic system and was treated with various Cd concentrations (0, 10, 50, 100, 125, and 150?µM) for 7?days. Cadmium analysis of the leaves at the subcellular level showed that Cd was mainly stored in the soluble fraction (77.98–83.62%) and in smaller quantities in the cell wall fraction (11.99–17.30%) and the cell organelles (4.30–4.88%). The Cd taken up by H. verticillata was in different chemical forms. In the leaves and stems, the Cd was mostly extracted using 1?M NaCl and smaller amounts of Cd were extracted using 2% acetic acid. The malondialdehyde content significantly increased at all Cd concentrations, which indicated oxidative stress. The superoxide dismutase, guaiacol peroxidase, and catalase activities were enhanced. The proline, ascorbate, and glutathione contents increased at lower Cd concentrations, but decreased consistently as the Cd concentration rose. These results suggest that H. verticillata can be successfully used in the phytoremediation of Cd-contaminated water.     

Experimental and mathematical simulation of plant growth promoting rhizobacteria and plant interaction under cadmium stress

Bacterial inoculants of the commercially available plant growth promoting rhizobacteria (PGPR) Arthrobacter mysorens 7, Flavobacterium sp. L30, and Klebsiella mobilis CIAM 880 were selected to obtain ecologically safe barley crop production on cadmium (Cd) polluted soils. All the PGPR immobilized 24–68% soluble cadmium from soil suspension. A. mysorens 7 and K. mobilis CIAM 880 were highly resistant to Cd and grew in up to 1 and 3 mmol CdCl₂ on DAS medium respectively. All PGPR were able to fix nitrogen (276–1014 nmol mg^–1 bacterial DW) and to produce indole acetic acid (IAA) (126–330 nmol mg^–1 bacterial DW) or ethylene (4.6–13.5 nmol bacterial DW). All the PGPR actively colonized barley root system and rhizosphere and significantly stimulated root elongation of barley seedlings (up to 25%), growing on soil containing 5 or 15 mg Cd kg^–1 of soil. Created in the simulation mathematical model confirms our hypothesis that PGPR beneficial effect on barley growing under Cd-stress is a complex process. One of mechanisms underlying this effect might be increase of bacterial migration from rhizoplane to rhizosphere, where PGPR bind soluble free Cd ions in biologically unavailable complex forms. Among the studied PGPR K. mobilis CIAM 880 was the most effective inoculant. Inoculation with K. mobilis CIAM 880 of barley plants growing on Cd contaminated soil (5 mg Cd kg^–1 of soil) under field conditions increased by 120% grain yield and 2-fold decreased Cd content in barley grain. The results suggest that the using K. mobilis CIAM 880 is an effective way to increase the plant yield on poor and polluted areas.     

Bioremediation of cadmium induced renal toxicity in Rattus norvegicus by medicinal plant Catharanthus roseus

Cadmium is the second most hazardous metals with bio-concentration factor (BCF)?>?100 Although WHO permitted cadmium concentration in drinking water is 0.005?mg/L, yet the reality is far above to this limit because of industrial utility of this metal. Oral exposure of cadmium to human results in dreadful symptoms of metabolic disorders especially in liver and kidneys. Endogenous protection could be supported by some exogenous herbal supplement (viz., Catharanthus roseus in this case) to overcome the toxic effects. Present Study has been designed to find out the functional renal changes under the effect of cadmium and Catharanthus roseus in the model organism albino rats. Cadmium significantly (p?>?0.01) increases the level of nitrogenous waste (Urea, BUN, Uric Acid and Creatinin), while decreases the serum protein profile in acute and sub-acute sets. Urea concentration of control ranged from 16.56 to 17.72?mg/dl while that of Group-B and D were 19.84 to 20.87?mg/dl and 17.56 to 17.59?mg/dl respectively. Similarly uric acid concentration ranged in control form 6.98 to 8.01?mg/dl in group-B from 7.58 to 10.25?mg/dl, in Group-D 8.02 to 8.59?mg/dl respectively. Creatinin concentration ranged in control 0.57 to 0.65?mg/dl, in group-B 0.97 to 1.02?mg/dl, in group-D – 0.95 to 0.98?mg/dl respectively.These results might be due to altered filtration rate of kidney because of protein disruption. The studies conclude the efficient nephro-protection offered by Catharanthus roseus extract against Cadmium toxicity.     

Subtypes of Sodium-Dependent High-Affinity L-[3H]Glutamate Transport Activity: Pharmacologic Specificity and Regulation by Sodium and Potassium

Abstract: Some data suggest that the sodium-dependent, high-affinity L-glutamate (Glu) transport sites in forebrain are different from those in cerebellum. In the present study, sodium-dependent transport of L-[³H]Glu was characterized in cerebellum and cortex. In both cerebellar and cortical tissue, activity was enriched in synaptosomes. Approximately 100 excitatory amino acid analogues were tested as potential inhibitors of transport activity. Many of the compounds tested inhibited transport activity by <65% at 1 mM and were not studied further. One group of compounds exhibited inhibition conforming to theoretical curves with Hill coefficients of 1 and were <10-fold selective as inhibitors of transport activity. These included three of the putative endogenous substrates for transport: L-Glu, L-aspartate, and L-cysteate. Four of the compounds exhibited inhibition conforming to theoretical curves with Hill coefficients of 1 and were > 10-fold selective as inhibitors. These included β-N-oxalyl-L-α,β-diaminopropionate, α-methyl-DL-glutamate, (2S, 1′S,2′S)-2-(carboxycyclopropyl)glycine, and (2S, 1′S,2′S,3′S)-2-(2-carboxy-3-methoxymethylcyclopropyl)glycine. Data obtained with a few of the inhibitors were consistent with two sites in one or both of the brain regions. (2S, 1′R,2′R)-2-(Carboxycyclopropyl)glycine (L-CCG-II) was identified as the most potent (IC₅₀= 5.5 μM) and selective (60–100-fold) inhibitor of transport activity in cerebellum. One of the potential endogenous substrates, L-homocysteate, was also a selective inhibitor of cerebellar transport activity. The data for inhibition of transport activity in cortex by both L-CCG-II and L-homocysteate were best fit to two sites. Kainate was equipotent as an inhibitor of transport activity, and in both brain regions the data for inhibition were best fit to two sites. The possibility that there are four subtypes of excitatory amino acid transport is discussed. Altering sodium and potassium levels affects cerebellar and cortical transport activity differently, suggesting that the differences extend to other recognition sites on these transporters.     

Uptake of six heavy metals by oat as influenced by soil type and additions of cadmium,lead, zinc and copper

Summary The influence of heavy metal additions on availability and uptake of cadmium, lead, zinc, copper, manganese and iron by oat was studied. The experiments were carried out as pot experiments using sandy loam, sandy soil and organic soil. Selective extractants were used to remove metals held in different soil fractions.Lead and copper were preferently bound by organics and oxides, zinc by oxides and inorganics, and cadmium by inorganics and organics.Addition of cadmium to the soils resulted in higher cadmium concentrations in all plant parts but lower concentrations of lead, zinc, copper, manganese and iron, and the accumulation indexes of these metals were also lower when cadmium was added to the soil.Addition of cadmium plus lead, zinc and copper resulted in higher cadmium concentrations in leaves and straw of plants grown in sandy loam and sandy soil, but lower concentrations when plants were grown in organic soil as compared with the results when cadmium was added separately. The transfer of cadmium, lead, zinc and copper from soil to plant was greatest from sandy soil, and zinc and cadmium were more mobile in the plant than were lead and copper.Cadmium concentrations in leaves correlated significantly with CaCl₂ and CH₃COOH extractions in sandy loam and sandy soil and with CH₃COOH extractions in organic soil.Generally, the total metal uptake was lowest from organic soil.     

Inhibition of DNA demethylation enhances plant tolerance to cadmium toxicity by improving iron nutrition

Although the alteration of DNA methylation due to abiotic stresses, such as exposure to the toxic metal cadmium (Cd), has been often observed in plants, little is known about whether such epigenetic changes are linked to the ability of plants to adapt to stress. Herein, we report a close linkage between DNA methylation and the adaptational responses in Arabidopsis plants under Cd stress. Exposure to Cd significantly inhibited the expression of three DNA demethylase genes ROS1/DML2/DML3 (RDD) and elevated DNA methylation at the genome-wide level in Col-0 roots. Furthermore, the profile of DNA methylation in Cd-exposed Col-0 roots was similar to that in the roots of rdd triple mutants, which lack RDD, indicating that Cd-induced DNA methylation is associated with the inhibition of RDD. Interestingly, the elevation in DNA methylation in rdd conferred a higher tolerance against Cd stress and improved cellular Fe nutrition in the root tissues. In addition, lowering the Fe supply abolished improved Cd tolerance due to the lack of RDD in rdd. Together, these data suggest that the inhibition of RDD-mediated DNA demethylation in the roots by Cd would in turn enhance plant tolerance to Cd stress by improving Fe nutrition through a feedback mechanism.     

Influence of cadmium on penetration of the root-knot nematode,Meloidogyne incognita and plant growth parameters of tomato

The results of experiment clearly reveal that cadmium inhibited root penetration by the second stage juveniles (J₂) of Meloidogyne incognita which subsequently affected the development of root galls in tomato. The heavy metal was highly injurious to tomato plants at all the concentrations tested for (7.5, 15.0, 30.0 and 60.0?ppm). The inhibitory effect on plant growth and other parameters (fresh and dry weight of plant, chlorophyll content of leaves, water absorption capability of roots) significantly increased with an increase in the concentration of the metal. It was further increased in the presence of the nematode.     

Distribution of cadmium and lead in a stream ecosystem

Cadmium and lead were detected in all components of the stream that were examined. Cadmium was present in similar concentrations in both fishes and sediments. Aquatic insects, however, exhibited higher concentrations of cadmium than did sediments. Lead concentrations in sediments and aquatic insects were similar, but higher than concentrations in fishes. Snails contained the highest level of lead and had noticeably greater amounts of the metal than did aquatic insects. In general, concentrations of both metals increased successively from water to fish to sediments to aquatic invertebrates.     

The effects of biochars produced in different pyrolsis temperatures from agricultural wastes on cadmium uptake of tobacco plant

Abiotic stresses caused by cadmium (Cd) contamination in soil retard plant growth and decline the quality of food. Amendment of biochar was reported effective in reduction of mobility, plant uptake and toxicity of Cd in plants. The aim of this study was to investigate the effect of biochar applications produced from corn cob and rice husk at three different pyrolysis temperatures (400, 500 and 600 °C) on Cd uptake of tobacco plants. The results showed that the shoot Cd concentration and content of tobacco plants significantly increased with the application of Cd in increasing doses. The results showed that increasing Cd dosescaused significant increase (P < 0.01) in shoot Cd concentration and content of the tobacco plant at three different pyrolysis temperatures of both corn cob and rice husk biochars. The concentration of Cd was 0.48 mg kg⁻¹ in Cd0 dose of corn cob biochar produced at 500 °C and increased to 61.6 mg kg⁻¹ at Cd5, while Cd concentration increased to 72.3 mg kg⁻¹ with rice husk biochar. Despite the increase in Cd concentrations and content, shoot Cd concentrations and contents were significantly (P < 0.01) reduced with the treatments of corn cob and rice husk biochars produced at different pyrolysis temperatures. The Cd concentration at Cd5 dose in the absence of biochar addition was 90.5 mg kg⁻¹, while Cd concentration at Cd5 dose in 400, 500 and 600 °C treatments of corn cob biochar was reduced to 66.5, 61.6 and 67.3 mg kg⁻¹ respectively, and to 77.0, 72.3 and 70.2 mg kg⁻¹ in rice husk biochar. The results also revealed that corn cob biochar treatments were more effective in reducing Cd uptake of tobacco plants compared to rice husk biochar. Higher specific surface area of corncob biochar compared to rice husk biochar caused to the difference between two biochar sources on Cd uptake of tobacco plants.     

Physiological mechanism of hypertolerance of cadmium in Kentucky bluegrass and tall fescue: Chemical forms and tissue distribution

Kentucky bluegrass (Poa pratensis) and tall fescue (Festuca arundinacea) are hypertolerant grasses to soil cadmium contamination. Little information is available on their tolerance mechanism. A sand culture and a hydroponic culture experiment were designed to investigate the Cd chemical form changes and its translocation in different tissues. The results showed that Kentucky bluegrass and tall fescue can tolerate 50–200 mg kg⁻¹ of soil Cd stresses and accumulate as high as 4275 and 2559 mg Cd kg⁻¹ DW, respectively, in their shoots without the loss of shoot biomass. Their Cd hypertolerance was correlated with an increase of the undissolved Cd phosphates in the leaves in both grass species, as determined by sequential solvent extraction procedures. The superior Cd tolerance of tall fescue to Kentucky bluegrass was associated with less Cd translocation into the stele of roots and less Cd transported to leaves. The pectate- and protein-integrated Cd forms may be involved in the symplastic translocation of Cd from cortex into stele, and this may lead the higher Cd concentrations in the stele of roots and then above ground leaves via long-distance transport in Kentucky bluegrass.     

Effects of ionic and complexed metal concentrations on plant uptake of cadmium and micronutrient metals from solution

Summary Uptake of Cd and micronutrient metals by intact tomato plants (Lycopersicon esculentum, cv. Wisconsin-55) from solution cultures was investigated by establishing four levels of Cd-ion activity in the presence or absence of a metal-complexing agent (±EDTA). Activity ratios of Cd, Cu, Mn, Ni, and Zn were controlled with chelating resin while activity ratios of K, Ca, and Mg were controlled with a strong-acid cation-exchange resin. Hydrogen ion activity was controlled with a weak-acid cation-exchange resin and P activity by a cation-exchange resin containing adsorbed polynuclear hydroxy-Al. The concentrations of all nutrients and Cd were maintained at concentrations similar to those occuring in solutions of sludge-amended soils. The EDTA treatments increased the concentrations of Cu and Ni in hydroponic solution by approximately four orders of magnitude, Zn by two orders of magnitude, Cd by a factor of 50, Mn by a factor of 2.4, and Fe by a factor of 1.6 Neither the Cd nor the EDTA treatments affected plant yield, and Cd treatments did not significantly affect uptake of other elements. EDTA treatments inhibited Fe uptake, enhanced Cu uptake, and had little effect on the uptake of Cd, Zn, and Mn. Accumulation of Cd, Zn, Mn, and Cu in plant shoots appears to be related to their respective ionic activities rather than their concentrations in hydroponic solution. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and by the United States Environmental Protection Agency through Grant CR807270010.     

Some physiological and biochemical aspects of plant resistance to cadmium effect. I. Antioxidative system

The hitherto studies on the effect of cadmium on plants have shown that it causes intensification of two types of unfavorable processes in plants: inactivation of macromolecules and cellular structures and induction of oxidative stress. In response, the plant organism activates processes restoring its homeostasis, i.e. those which remove reversible and irreversible changes. In removing the former a particular role is played by the antioxidative system containing enzymatic and nonenzymatic antioxidants, and removing the active forms of oxygen. The strategy of stress tolerance plays an important role in the plant resistance to cadmium and other toxic metals.