Promoted Cd Accumulation Research Articles

Microplastics have additive effects on cadmium accumulation and toxicity in Rice flower carp (Procypris merus)

Procypris merus, a local fish species found in Guangxi, China is often exposed to both microplastics (MPs) and Cd. However, it remains unclear how these two pollutants affect P. merus. Therefore, we investigated the effects of MPs on Cd accumulation in P. merus. To this end, P. merus was separately exposed to Cd and MPs (500 μg/L) or their combination for 14 days. We found that MPs enhanced Cd accumulation in liver and gills of P. merus. Further, both the single-contaminant (MP and Cd) and combined treatments resulted in lesions in these two tissues, with more severe damage associated with the combined treatment. Even though the effect of MP on the antioxidant defense system of P. merus was limited, the Cd-only and combined treatments considerably affected the antioxidant parameters of P. merus, with the combined treatment showing a stronger effect. GO and KEGG analyses revealed that the differentially expressed genes (DEGs; TNF-related apoptosis-inducing ligand receptor, trail-r) in the Cd-only treatment group were enriched for immune-related GO terms and cell growth and death related pathways, indicating that Cd toxicity affected immune defense in P. merus. The MP-only treatment downregulated DEGs (acyl-CoA synthetase long chain family member 1a, acsl1a) related to lipid metabolism, possibly leading to lipid accumulation in the liver. The combined treatment also upregulated DEGs (aspartate aminotransferase 1, ast 1) associated with immune-related GO terms and amino acid metabolism pathways, suggesting that it affected immune function in P. merus, thereby negatively impacting its health. Results indicated that MPs have additive effects on Cd accumulation and toxicity in rice flower carp. Consequently, MPs ingested by P. merus can promote Cd accumulation, more adverse effects on the health may occur after combined exposure, which can eventually reach humans through the food chain and pose potential risks to human health.

The plasma membrane-localized transporter VrNramp5 of Vigna radiata L. governs cadmium tolerance and accumulation in Arabidopsis thaliana

Cadmium (Cd) is a highly toxic non-essential element, which requires the transporters of essential and beneficial elements to enter the plant, and poses threat to plant growth and development. However, the mechanism of Cd uptake and accumulation in mungbean is limited. Here, we reported a Cd transporter VrNramp5 in mungbean, and its functional roles in response to Cd toxicity were conducted. The expression of VrNramp5 was down-regulated by Cd toxicity. VrNramp5 localized at plasma membrane based on subcellular localization analysis in epidermal cells of Nicotiana benthamiana. Heterologous expression of VrNramp5 in Arabidopsis thaliana promoted Cd accumulation, displayed the Cd sensitive phenotype including decreased root elongation and fresh weight, and VrNramp5 could diminish the Cd tolerance phenotype of AtNramp1-deficient mutant (atnramp1). Non–invasive micro–test showed that VrNramp5-overexpressing lines possessed higher Cd absorption capacity in root tips. Moreover, the Cd fluorescence probe staining revealed that more Cd accumulated in the leaf protoplasts of VrNramp5-overexpressing Arabidopsis. Those were consistent with the plants grown in the absence or presence of Cd (10 mg kg−1 or 20 mg kg−1) in soil. Taken together, VrNramp5 is responsible for plant Cd tolerance via regulating the Cd absorption capacity of roots and altering the intracellular distribution of Cd. Our findings provide a theoretical basis for further exploring the mechanism of Cd tolerance and breeding variety of mungbean with low Cd accumulation.

Assessing stress responses in potherb mustard (Brassica juncea var. multiceps) exposed to a synergy of microplastics and cadmium: Insights from physiology, oxidative damage, and metabolomics

Both microplastics (MPs) and cadmium (Cd) are common contaminants in farmland systems, is crucial for assessing their risks for human health and environment, and little research has focused on stress responses mechanisms of crops exposed to the combined pollution. The present study investigated the impact of polyethylene (PE) and polypropylene (PP) microplastics (MPs), in combination with Cd, on the physiological and metabolomic changes as well as rhizosphere soil of potherb mustard. Elevated levels of PEMPs and PPMPs were found to impede nutrient uptake in plants while promoting premature flowering, and the concomitant effect is lower crop yields. The substantial improvement in Cd bioavailability facilitated by MPs in rhizosphere soil, especially in high concentrations of MPs, then elevated bioavailability of Cd contributed to promoted Cd accumulation in plants, with distinct effects depending on the type and concentration of MPs. The presence of MPs Combined exposure to high concentrations of MPs and Cd resulted in alterations in plant physiology and metabolomics, including decreased biomass and photosynthetic parameters, elevated levels of reactive oxygen species primarily H2O2, increased antioxidant enzyme activities, and modifications in metabolite profiles. Overall, our study assessed the potential impact on food security (the availability of cadmium to plant) and crops stress responses regarding the contamination of MPs and Cd, providing new insights for future risk assessment in agriculture.

Exogenous ATP triggers antioxidant defense system and alleviates Cd toxicity in maize seedlings

The role of exogenous adenosine 5′-triphosphate (ATP) in the regulation of antioxidant response in plants under heavy metal stress is unclear. Here, we investigated the effects of exogenous ATP application on plant growth, antioxidant response, and Cd accumulation in maize seedlings. Treatment with 0.1 mM CdCl2 moderately reduced dry weight, decreased chlorophyll content, impaired photosynthesis, and increased lipid peroxidation in maize seedlings compared with controls. However, toxicity due to Cd was alleviated after 10–200 µM ATP treatment. Subsequently, the activity of Cd-regulated antioxidant enzymes, antioxidant metabolite accumulation, and total antioxidant capacity were drastically enhanced after 50 µM ATP treatment. Similar patterns were observed in the ADP-treated group but not in the AMP-treated group under Cd stress. However, the ATP-induced elevation in antioxidant defense ability was decreased by the inhibition of NADPH oxidase (NOX). ATP-induced elevation in NOX activity and H2O2 production was partly reversed by the inhibition of NOX in maize seedlings under Cd stress. Furthermore, ATP promoted Cd accumulation in the roots and shoots of maize seedlings. However, the ATP-induced increase in Cd accumulation was partly abolished by the inhibition of NOX. To our knowledge, this is the first report on the role and mechanism of exogenous ATP in regulating plant growth, antioxidant response, and heavy metal phytoextraction. The study provides a new method based on exogenous ATP for enhancing heavy metal tolerance in plants.

Microplastics promoted cadmium accumulation in maize plants by improving active cadmium and amino acid synthesis

Combined pollution from microplastics (MPs) and cadmium (Cd) can influence soil environment and soil biota, altering plant growth and development, and Cd mobilization. We investigated the effects of polystyrene (PS) and polypropylene (PP) MPs alongside Cd on soil Cd bioavailability, rhizosphere soil metabolomics, bacterial community structure, and maize (Zea mays L.) growth in two soil types (red soil and cinnamon soil). Although the addition of PS/PP-Cd promoted Cd accumulation in maize plants overall, there were large-particle-size- and small-particle-size-dependent effects in the red soil and cinnamon soil, respectively. The difference is mainly due to the capacity of the large particle size MPs to significantly reduce soil pH, improve soil electrical conductivity (EC), promote active Cd, and intensify Cd mobilization in red soil. In contrast, small-size MPs in cinnamon soil promoted the synthesis and secretion of rhizosphere amino acids and soil metabolites, thus promoting Cd absorption by maize roots. Soil microorganisms also improved Cd bioavailability via C-related functional bacteria. Overall, our study provides novel insights on the potential effects of combined MPs and Cd pollution on soil ecology and agricultural production, enhancing our understanding of rhizosphere metabolites in different soils.

Chloride application weakens cadmium immobilization by lime in paddy rice soil

Contamination of agricultural products by cadmium (Cd) is a global health problem, causing chronic abnormalities. The consumption of rice, the most-consumed foods, is an important exposure route of Cd to human body. Chloride (Cl-) is reported to increase Cd uptake by rice; however, the effect on Cd uptake and accumulation by rice in the presence of lime is not clear. Therefore, a pot culture experiment was performed to explore the influence of Cl- on the absorption and accumulation of Cd in rice plants under lime remediation and its possible mechanisms. The results showed that Cl- promoted Cd accumulation in rice grains, mainly because of increased Cd bioavailability in the soil and by impeding the formation of iron plaques on rice roots, which reduced chelating and precipitation of Cd. Moreover, increased overexpression of the main transporters of Cd in rice roots, including OsNramp5, OsNramp1, OsIRTs and OsHMA2, favored the upward translocation of Cd from the root to shoot and increased the transfer factors (TFs) from soil to root, root-stem, leaf to grain, and soil to grain. Therefore, the application of Cl-rich materials to Cd-contaminated rice fields should be avoided during liming of the soil for Cd immobilization.

Identification of StAP2/ERF genes of potato (Solanum tuberosum) and their multiple functions in detoxification and accumulation of cadmium in yest: Implication for Genetic-based phytoremediation

The discovery of genes responsible for the tolerance to heavy metals is critical for genome-based phytotechnologies. In this study, we exposed potato (Solanum tuberosum L.) to Cd/Pb/Zn/Ni/Cu as an approach to explore the potential genes associated with stress tolerance. Using genome-wide analysis, we identified 181 potential StAP2/ERF genes that were classified into three subgroups. These StAP2/ERF genes were significantly related to heavy metal stress and are more specifically related to Cd tolerance in yeast. Yeast complementation tests showed that the StAP2/ERF129/139 genes (Subgroup 1) decreased Cd accumulation (Cd reduction-type), whilst the StAP2/ERF044/180 genes (Subgroup 2) promoted Cd accumulation in yeast which showed inhibited growth (Cd accumulation-type). The StAP2/ERF075/077/126 genes (Subgroup 3) promoted Cd accumulation and yeast growth (Cd detoxification-type). We used phylogenetic analysis to classify the 181 genes into three Cd tolerant types defined above in which the numbers of Cd reduction, accumulation, and detoxification type genes were 81, 65 and 35 respectively. Also, we performed tandem duplication, phylogenetic, and conserved motifs analysis to characterization the StAP2/ERF genes and results supported their functions in Cd tolerance. Our study showed that StAP2/ERFs is indispensable in Cd uptake and tolerance, and may be useful towards designing gene-modified plants with improved Cd tolerances.

Physiological, metabolomic, and transcriptomic analyses reveal the dynamic redox homeostasis upon extended exposure of Dunaliella salina GY-H13 cells to Cd

The study was done to elucidate the molecular mechanisms underlying the steady maintenance of the green microalga Dunaliella salina GY-H13 in successive subcultures in F/2 medium supplemented with the high cadmium (Cd) concentration (5 mg L−1) for 3 months or 84 days using physiological, metabolomic, and transcriptomic methodologies. Physiological analysis indicated that Cd suppressed growth rate, photosynthetic efficiency, and pigment contents and promoted Cd accumulation, reactive oxygen species (ROS) generation and lipid peroxidation. UPLC-MS/MS-based metabolic analysis identified the top most upregulated and downregulated metabolites, the 5′-dehydroxyadenosine and thiamine acetic acid that were associated with the formation and removal of H2O2. RNA-seq-based transcriptomic analysis showed the overrepresentation of low-CO2-inducible genes in the most downregulated gene set. Metabolomic and transcriptomic analyses further showed that the decreased GSSG/GSH-based redox potential, increased oxidative-phosphorylation gene expression, and reduced activity of TCA cycle in cells after extended exposure to Cd. Taken together, our results imply that cellular defense to Cd in D. salina is achieved by upregulation of ROS-scavenging activities including depletion of thiamine acetic acid. Dynamic redox homeostasis is maintained in cells with extended exposure to Cd by production of both oxidants and antioxidants through multiple pathways.

Influence of Clay Application and Water Management on Ability of Rice to Resist Cadmium Stress

A high percentage of available Cadmium (Cd) in acid rice fields in south China promoted Cd accumulation in rice plant and caused a grain Cd content above the national standard GB 2762-2012 guidelin...

Effect of cornstalk biochar on phytoremediation of Cd-contaminated soil by Beta vulgaris var. cicla L

Cadmium (Cd) contamination is the most common and extensive heavy metal pollution in the farmland of China. Phytoremediation is considered as a promising measure for Cd-contaminated soil remediation, but the remediation efficiency still needs to be enhanced. Biochar as an effective amendment medium is widely manufactured and studied for the soil remediation of heavy metals. In this study, a greenhouse pot trial was conducted to investigate the effects of cornstalk biochar on Cd accumulation of Beta vulgaris var. cicla L. (Beta vulgaris) in Cd contaminated soil. The Cd availability, speciation and nutrients in soil, biomass and Cd chemical forms in the Beta vulgaris root were studied to explore the mechanism that how the cornstalk biochar promoted Cd accumulation in Beta vulgaris. Biochar amendment reduced the DTPA-extractable Cd concentration and stimulated the growth of root. Compared to the Beta vulgaris without biochar treatment, the results of 5% biochar amendment showed that the root dry weight of Beta vulgaris increased to 267%, Cd accumulation in Beta vulgaris increased to 206% and the Cd concentration in leaves and roots increased by 36% and 52%, respectively. Additionally, after 5% biochar was applied to soil, the total content of organic matter-bound Cd and residual Cd increased by 38%, while the content of Fe–Mn oxides-bound Cd decreased by 40%. Meanwhile, Cd may mainly bind to the root cell wall and the ratio of NaCl-extracted Cd to HAc-extracted Cd increased to 166% with 5% biochar amendment. According to our study, Cd in soil can be removed by Beta vulgaris and phytoremediation efficiency can be improved with biochar amendment. The combination of phytoremediation and biochar amendment is a promising strategy for the Cd-contaminated soil remediation.

Migration and transformation of cadmium in rice - soil under different nitrogen sources in polymetallic sulfide mining areas

We conducted pot experiments to assess the bioavailability of cadmium (Cd) in contaminated rhizosphere soil and accumulation in rice organs in response to nitrogen (N) supply ((NH4)2SO4, NH4NO3, NH4Cl). The results showed that the concentration of bioavailable Cd in rice rhizosphere soil was (NH4)2SO4 treatment > NH4Cl treatment > NH4NO3 treatment at the same level of N application and growth period; the Cd concentration in rice roots was (NH4)2SO4 treatment > NH4NO3 treatment > NH4Cl treatment; and the Cd concentration in rice straw was NH4NO3 treatment > NH4Cl. The Cd concentration in rice roots, straws, and seeds at the maturity stage was (NH4)2SO4 treatment > NH4Cl treatment. With the same N fertilizer, excessive N promoted Cd accumulation in rice at later growth stages. This suggested that sulfate (SO42−) influenced Cd concentration in rice. NH4Cl application maintained a low Cd level in different rice organs with the same N level. This confirmed that NH4Cl is a safe N source for rice planting in polymetallic sulfide mining areas. The study concludes that appropriate NH4Cl levels for Cd-contaminated paddy soil with high-S-content could obtain rice grains with Cd concentrations below the food safety standards (0.2 or 0.4 mg·kg−1).

Magnesium reduces cadmium accumulation by decreasing the nitrate reductase-mediated nitric oxide production in Panax notoginseng roots

Panax notoginseng is a traditional medicinal herb in China. However, the high capacity of its roots to accumulate cadmium (Cd) poses a potential risk to human health. Our previous study showed that nitrate reductase (NR)-dependent nitric oxide (NO) production promoted Cd accumulation in P. notoginseng root cell walls. In this study, the role of Mg in the regulation of NO production and Cd accumulation in P. notoginseng roots was characterized. Exposure of P. notoginseng roots to increasing concentrations of Cd resulted in a linear increase in NO production. The application of 2 mM Mg for 24 h significantly alleviated Cd-induced NO production and Cd accumulation in roots, which coincided with a significant decrease in the NR activity. Western analysis suggested that Mg increased the interaction between the 14-3-3 protein and NR, which might have been a reason for the Mg-mediated decrease in NR activity and NO production under Cd stress. These results suggested that Mg-mediated alleviation of Cd-induced NO production and Cd accumulation is achieved by enhancement of the interaction between the 14-3-3 protein and NR in P. notoginseng roots.

Exogenous abscisic acid (ABA) promotes cadmium (Cd) accumulation in Sedum alfredii Hance by regulating the expression of Cd stress response genes.

Sedum alfredii Hance is a zinc (Zn) and cadmium (Cd) hyperaccumulator plant. However, the regulatory role of plant hormones in the Zn or Cd uptake and accumulation of S. alfredii remains unclear. In this work, the growth, Cd accumulation, abscisic acid (ABA) synthesis and catabolism, malonaldehyde (MDA) content, and transcriptional level of some Cd stress response genes under ABA and Cd co-treatment were investigated to reveal the impact of ABA on Cd resistance and Cd accumulation of S. alfredii. The results show that 0.2mg/L ABA and 100μmol/L Cd co-treatment enhanced Cd accumulation and growth in S. alfredii, whereas lower or higher ABA concentrations weaken or even reverse this effect, which was positively correlated with endogenous ABA content. The increase in endogenous ABA content might be the results of the increasing ABA synthetase activities and decreasing ABA lytic enzyme, which was induced by the application of 0.2mg/L ABA under 100μmol/L Cd treatment. Principal component analysis (PCA) indicated that ABA impacted the expression pattern of Cd stress response genes, which coincided with the Cd accumulation pattern in the shoots of S. alfredii. Cross-over analysis of partial least squares-discriminant analysis (PLS-DA) and correlation analysis indicated that HsfA4c, HMA4 expression in roots, and HMA2, HMA3, CAD, NAS expression in shoots were correlated with endogenous ABA, which suggests that endogenous ABA improves Cd resistance of seedlings, switches the root-to-shoot transporter from HMA2 to HMA4, and transports more Cd into apoplasts to promote Cd accumulation in the shoots of S. alfredii. Taken together, ABA plays an essential role not only in Cd resistance but also in Cd transport from root to shoot in S. alfredii under Cd stress.

Effects of sulfate on cadmium uptake in wheat grown in paddy soil - pot experiment

Rice-wheat rotation is common in China. Cadmium (Cd) and sulfur (S) are added to rice fields through various activities. The sulfur amendment has been recommended to control the uptake of Cd in rice. However, the effect of S on Cd uptake in winter wheat cultivated in paddy soil is rarely reported. A greenhouse pot experiment including two Cd levels (0, 10 mg Cd/kg, as CdCl<sub>2</sub>) combined with three S rates (0, 30, 60 mg S/kg, as Na<sub>2</sub>SO<sub>4</sub>) was performed to investigate the effect of S application on uptake and allocation of Cd in wheat cultivated in paddy soil. Cadmium concentrations in wheat grain significantly (P < 0.05) increased by 37% at 30 mg S/kg, and the percentage of Cd allocation to grain significantly (P < 0.05) increased by 7% at 60 mg S/kg compared with non-S addition treatment when wheat was grown in Cd-added soil. For the low Cd soil, a similar trend was seen, but Cd increases were insignificant for grain while significant (P < 0.05) for root at 60 mg S/kg. In conclusion, S fertiliser may promote Cd accumulation in wheat grain and should be considered when it is used for wheat in paddy soils.

Overexpression of Three Duplicated BnPCS Genes Enhanced Cd Accumulation and Translocation in Arabidopsis thaliana Mutant cad1-3.

Phytochelatins are widely known to chelate heavy metal in vacuole and decrease plant damage. Phytochelatin synthase gene (PCS), which is involved in phytochelatins synthesis, is commonly designated as a key gene for phytoremediation. In our study, we cloned three duplicated BnPCS genes from Brassica napus and transformed them into Arabidopsis thaliana AtPCS1 mutant cad1-3, respectively. Three transgene lines and cad1-3 were subjected to a cascade of concentrations of cadmium (Cd) treatment. Evaluation of morphological and physiological measurement results show that transgene lines possess higher Cd tolerance and resistance than A. thaliana mutant cad1-3. The analysis of PCs and Cd contents in root and shoot collectively indicated that transgenic plants promoted Cd accumulation and translocation. In conclusion, all the three BnPCS transgene lines enhanced Cd tolerance, accumulation and translocation, which could provide gene resources for phytoremediation.

Cd and Pb accumulation characteristics of phytostabilizer Athyrium wardii (Hook.) grown in soils contaminated with Cd and Pb.

Interactions between heavy metals in soil could affect soil heavy metal availability and plant uptake. Thus, in this study, Cd and Pb accumulation as well as plant growth of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii (Hook.) in response to the exposure of Cd and Pb was investigated by a pot experiment. Although the exposure of Cd in combination with Pb further inhibited the growth of the two ecotypes in comparison with the exposure of single Cd or Pb, the ME presented lower biomass decline for the whole plant (22.0%-70.0%) than the NME among most treatments. The presence of Pb promoted Cd accumulation both in above-ground and under-ground parts of the ME. Cd concentrations in under-ground parts of the ME decreased when exposed to higher concentrations of Pb (> 600mgkg-1). Meanwhile, the presence of Cd inhibited Pb accumulation in above-ground parts of the ME and promoted Pb accumulation in under-ground parts of the ME. Pb concentrations in under-ground parts of the ME decreased when soil Cd concentrations were more than 25mgkg-1. The partial correlation analysis further demonstrated that the interactions between Cd and Pb stimulated Cd accumulation both in above-ground and under-ground parts of the ME and Pb accumulation in under-ground parts of the ME, while inhibited Pb accumulation in above-ground parts of the ME, showing great benefit for Pb phytostabilization by the ME. Among treatments, the bioaccumulation coefficients for Cd and Pb of the ME, varying from 2.71-31.05 and 20.09-78.06, were much higher than those of the NME. The translocation factors for Cd and Pb of the ME, varying from 0.26-0.52 and 0.01-0.10, were lower than those of the NME. These results indicate that the ME presented greater potential for the phytostabilization of soil contamination with Cd and Pb, especially for Pb.

Rhizosphere characteristics of phytostabilizer Athyrium wardii (Hook.) involved in Cd and Pb accumulation

Soil contamination with Cd and Pb shows interactive effects on rhizosphere microenvironment and further uptake of Cd and Pb by plants. Thus, the rhizosphere characteristics of the mining ecotype (ME) and non-mining ecotype (NME) of Athyrium wardii in response to Cd and Pb was investigated through a pot experiment in this study. Compared with Cd or Pb alone, the contamination of Cd and Pb inhibited the growth of the two ecotypes of A. wardii, and ME presented lower decrease of 56.22% and 55.07% for above-ground part biomass than NME. The combination of Cd and Pb promoted Cd accumulation both in above-ground and under-ground parts of ME, as well as Pb accumulation in under-ground parts of ME, with the increase of 92.68%, 102.77% and 35.87%, respectively. As a result, increased bioaccumulation coefficients (BCF) for Cd and Pb and decreased translocation factors (TF) for Pb of ME were observed when exposed Cd and Pb. ME presented much greater BCF values for Cd and Pb, and much lower TF values for Cd and Pb than NME. The rhizosphere soil pH of ME with the exposure of Cd and Pb reduced by 0.12–0.13 units compared with single Cd or Pb. The dissolved organic carbon (DOC) concentrations in rhizosphere soils of ME exposed to Cd and Pb increased in comparison with single Cd or Pb, and ME showed greater increase (53.31–59.00%) than NME. These suggested that pH reduction and exudation of greater amounts of DOC may have contributed to the promotion of Cd and Pb accumulation in ME. In addition, the combination of Cd and Pb inhibited soil microbial biomass carbon (MBC) and soil respiration (SR) of A. wardii compared with Cd or Pb alone. However, greater MBC and SR, and lower metabolic quotients were found in rhizosphere soils of ME when exposed to Cd and Pb. ME showed better soil biophysical conditions in rhizosphere soils when exposed to Cd and Pb. These improvements presented great benefit for ME to phytostabilize soils co-contaminated with Cd and Pb.

Effect of hemoglobin on the growth and Cd accumulation of pea plants (Pisum sativum L.)

This study was set to investigate the effect of the presence of hemoglobin (Hb) in cadmium (Cd)-contaminated soil on phytotoxicity and Cd accumulation. The effect of Hb on the Cd accumulation by Pisum sativum L. (pea) and seed germination and growth was studied using pot tests with the artificially Cd-contaminated soil. The results show that the externally applied Hb to Cd-contaminated soil samples did not promote Cd accumulation by P. sativum. However, the Fe accumulation was greater in the presence of Hb. The seed germination was not affected, but the adverse effects on the plant growth increased with increasing Hb/Cd molar ratio from 0 to 0.015. This can be attributed to toxic effects of the Fe added with the Hb application. The results suggest that the presence of Hb may have harmful effects on pea plants used in phytoremediation of Cd-contaminated soil due to toxic effects imposed by Fe.

Stabilized Nanoscale Zerovalent Iron Mediated Cadmium Accumulation and Oxidative Damage of Boehmeria nivea (L.) Gaudich Cultivated in Cadmium Contaminated Sediments.

Nanoparticles can be absorbed by plants, but their impacts on phytoremediation are not yet well understood. This study was carried out to determine the impacts of starch stabilized nanoscale zerovalent iron (S-nZVI) on the cadmium (Cd) accumulation and the oxidative stress in Boehmeria nivea (L.) Gaudich (ramie). Plants were cultivated in Cd-contaminated sediments amended with S-nZVI at 100, 500, and 1000 mg/kg, respectively. Results showed that S-nZVI promoted Cd accumulation in ramie seedlings. The subcellular distribution result showed that Cd content in cell wall of plants reduced, and its concentration in cell organelle and soluble fractions increased at S-nZVI treatments, indicating the promotion of Cd entering plant cells by S-nZVI. In addition, the 100 mg/kg S-nZVI alleviated the oxidative damage to ramie under Cd-stress, while 500 and 1000 mg/kg S-nZVI inhibited plant growth and aggravated the oxidative damage to plants. These findings demonstrate that nanoparticles at low concentration can improve the efficiency of phytoremediation. This study herein develops a promising novel technique by the combined use of nanotechnology and phytoremediation in the remediation of heavy metal contaminated sites.

Differential effects of citric acid on cadmium uptake and accumulation between tall fescue and Kentucky bluegrass

Organic acids play an important role in cadmium availability, uptake, translocation, and detoxification. A sand culture experiment was designed to investigate the effects of citric acid on Cd uptake, translocation, and accumulation in tall fescue and Kentucky bluegrass. The results showed that two grass species presented different Cd chemical forms, organic acid components and amount in roots. The dormant Cd accumulated in roots of tall fescue was the pectate- and protein- integrated form, which contributed by 84.85%. However, in Kentucky bluegrass, the pectate- and protein- integrated Cd was only contributed by 35.78%, and the higher proportion of Cd form was the water soluble Cd-organic acid complexes. In tall fescue, citric acid dramatically enhanced 2.8 fold of Cd uptake, 3 fold of root Cd accumulation, and 2.3 fold of shoot Cd accumulation. In Kentucky bluegrass, citric acid promoted Cd accumulation in roots, but significantly decreased Cd accumulation in shoots. These results suggested that the enhancements of citric acid on Cd uptake, translocation, and accumulation in tall fescue was associated with its promotion of organic acids and the water soluble Cd-organic acid complexes in roots.