Lower Cd Uptake Research Articles

The transcription factor OsNAC5 regulates cadmium accumulation in rice

Cadmium (Cd) is a hazardous heavy metal that threatens human health through the consumption of contaminated rice. To mitigate Cd accumulation in rice grains, it is crucial to reduce Cd uptake. Nevertheless, the transcriptional mechanisms governing Cd uptake in rice remain largely unknown. This research identifies the transcription factor OsNAC5 in Oryza sativa as a positive regulator of the Cd transporter gene OsNRAMP1, thereby influencing Cd uptake. OsNAC5 is predominantly expressed in the roots, resides in the nucleus, and is upregulated by Cd-induced hydrogen peroxide (H2O2). Knocking out OsNAC5 results in lower Cd concentrations in both shoots and roots and heightens sensitivity to Cd. The expression of OsNRAMP1, enhanced by Cd stress, is dependent on OsNAC5. OsNAC5 binds to "CATGTG" motifs in the OsNRAMP1 promoter, activating its expression. The loss of OsNAC5 function leads to reduced Cd accumulation in rice grains. Our findings provide insights into the transcriptional regulation of Cd stress response in rice and propose biotechnological strategies to lower Cd uptake in crops.

Cadmium stress responses under white or blue light are influenced by putrescine pre-treatment in wheat

Blue light plays an important role in most plant functions: it influences plant morphology, photosynthesis, primary and secondary metabolism. Although certain studies have already revealed that blue light may have positive effects under certain stress conditions, its exact mechanism is largely unknown. The importance of polyamines in stress tolerance has been widely investigated; however, their interaction with the dependent processes is still poorly understood. In addition, the quality of light can also affect the polyamine metabolism, thus it can influence their roles and relationships with other protective compounds. According to these, the main question of the present work was that whether blue light induces different responses during Cd stress, especially which are related to polyamine metabolism, and whether it may be able to modify the protective effect of exogenous putrescine compared to white light conditions in wheat. It has been demonstrated that less pronounced Cd stress was detected under blue light than at white light conditions. Blue light had its own effect at metabolite and gene expression levels and the lower Cd uptake was accompanied by lower phytochelatin but higher conjugated polyamine accumulation at the same time. Putrescine pre-treatment had protective effect especially under white light conditions, and it highlighted certain differences observed under Cd stress between blue light and white light conditions, especially in phytochelatin synthesis, polyamine metabolism, and accumulation of phenolic compounds and plant hormones. Our data demonstrated that blue light regulated Cd tolerance in wheat and modified defence strategy when excess putrescine was present.

An arbuscular mycorrhizal fungus differentially regulates root traits and cadmium uptake in two maize varieties

Arbuscular mycorrhizal fungi (AMF) are symbiotic fungi that colonize plant roots, and they are more common in Cd-polluted habitats. However, there is limited understanding of the response of root traits and cadmium (Cd) uptake to AMF in different crop varieties. Two maize varieties, Panyu 3 and Ludan 8, with high and low Cd uptake capacities, respectively, were cultivated as host plants in a pot experiment with Cd-polluted soil (17.1 mg/kg Cd). The effects of AMF on the growth, mineral nutrient concentration, root traits, phytohormone concentrations and Cd uptake of the two maize varieties and their comprehensive response to AMF fungal inoculation were investigated. AMF improved growth, mineral nutrient levels and root morphology and increased lignin and phytohormone concentrations in roots and Cd uptake in the two maize varieties. However, the two maize varieties, Panyu 3 and Ludan 8, had different responses to AMF, and their comprehensive response indices were 753.6% and 389.4%, respectively. The root biomass, branch number, abscisic acid concentrations, lignin concentrations and Cd uptake of maize Panyu 3 increased by 151.1%, 28.6%, 139.7%, 99.5% and 84.7%, respectively. The root biomass, average diameter, auxin concentration, lignin concentration and Cd uptake of maize Ludan 8 increased by 168.7%, 31.8%, 31.4%, 41.7% and 136.7%, respectively. Moreover, Cd uptake in roots presented very significant positive correlations with the average root diameter and abscisic acid concentration. A structural equation model indicated that the root abscisic acid concentration and root surface area had positive effects on Cd uptake by the Panyu 3 maize roots; the root abscisic acid concentration and root tip number had positive effects on Cd uptake by the Ludan 8 maize roots. Thus, AMF differentially regulated Cd uptake in the two maize varieties, and the regulatory effect was closely related to root traits and phytohormone concentrations.

Soil amendments to reduce cadmium in cacao (Theobroma cacao L.): A comprehensive field study in Ecuador.

The new EU regulations on maximum levels of cadmium (Cd) in cacao products sparked research on countermeasures to reduce Cd concentrations in cacao beans. This study was set up to test the effects of soil amendments in two established cacao orchards (soil pH 6.6 and 5.1) in Ecuador. Soil amendments included: 1) agricultural limestone at 2.0 and 4.0 Mg ha−1 y−1, 2) gypsum at 2.0 and 4.0 Mg ha−1 y−1 and 3) compost at 12.5 and 25 Mg ha−1 y−1, all amendments were applied at the surface during two subsequent years. Lime application increased the soil pH by one unit down to 20 cm depth. On the acid soil, leaf Cd concentrations decreased by lime application and the reduction factor gradually rose to 1.5 after 30 months. No effects of liming or gypsum on leaf Cd was found in the pH neutral soil. Compost application in the pH neutral soil reduced leaf Cd concentration with factor 1.2 at 22 months but that effect was absent at 30 months after application. Bean Cd concentrations were unaffected by any of the treatments at 22 months after application (acid soil) or 30 months (pH neutral soil) suggesting that any treatment effects on bean Cd might be even more delayed than in leaves. Soil columns experiments in the laboratory showed that mixing lime with compost largely enhanced the depth of lime penetration compared to lime only. Compost + lime reduced 10−3 M CaCl2 extractable Cd in soil without lowering extractable Zn. Our results suggest that soil liming has the potential to lower Cd uptake in cacao in the long term in acid soils and that the compost + lime treatment should be tested at field scale to accelerate the effects of the mitigation.

Potential use of hydroxyapatite combined with hydrated lime or zeolite to promote growth and reduce cadmium transfer in the soil-celery-human system.

Although hydroxyapatite (HAP) can prominently lower Cd uptake by celery from Cd-polluted soil, its high application rates in reality may lead to high cost and potential environmental risk. Therefore, we aimed to clarify whether combined amendments of HAP and another low-cost material (hydrated lime, corn straw-derived biochar, or zeolite) with reduced application rate of each single amendment could significantly decrease Cd transfer in soil-celery-human system without side effect on celery growth through a pot experiment. Results revealed that adding biochar, HAP, zeolite, or combined amendments had no obvious side effect on celery growth, while adding 0.3% hydrated lime significantly decreased fresh edible celery yield by 69.0%. Conversely, adding 0.5% HAP + 0.05% hydrated lime increased fresh edible celery yield by 39.8%. Additionally, adding HAP, zeolite, or hydrated lime rather than adding biochar effectively decreased total and bioaccessible Cd in edible celery. Similarly, HAP + hydrated lime and HAP + zeolite were much more efficient than HAP + biochar in lowering Cd transfer in soil-celery-human system. The total and bioaccessible Cd in edible celery were even reduced by over 50.0% after adding HAP + hydrated lime or HAP + zeolite at low rates. Considering the effects on celery growth and Cd transfer, HAP + hydrated lime and HAP + zeolite have the potential in remediating soil Cd contamination.

Difference in Cd2+ flux around the root tips of different soybean (Glycine max L.) cultivars and physiological response under mild cadmium stress

The purpose of the study was to compare differences in Cd2+ flux in the vicinity of root tips of 20 soybean cultivars under mild Cd stress conditions using non-invasive micro-test technology (NMT). The results indicated that Cd2+ influx to the root tips under mild Cd treatment was higher compared to controls. Cd2+ influx showed an obvious spatial distribution, with the highest Cd2+ influx measured 300 μm from the root tips, and a gradually decrease above and below this site. The cultivar Liaodou32 had a lower Cd uptake (3.40 pmol cm−2 s−1), while Liaodou23 had a relatively higher Cd uptake (66.37 pmol cm−2 s−1). Cluster analysis showed that the order of the average Cd2+ influx of the cultivars at a distance of 300 μm from the root tips was as follows: high-uptake cultivars (61.80 pmol cm−2 s−1)>medium-high-uptake cultivars (33.92 pmol cm−2 s−1)>medium-low-uptake cultivars (19.78 pmol cm−2 s−1)>low-uptake cultivars (4.84 pmol cm−2 s−1). We also analyzed physiological responses of different soybean cultivars to mild Cd stress. The results indicated that mild Cd stress could inhibit soluble protein production and root vigor among individual soybean cultivars. Moreover, stress increased SOD, CAT and POD activities and MDA content in root tissues. It should be noted that the physio-biochemical indicators of low-uptake cultivars did not change significantly after exposure to mild Cd stress compared to controls. Pearson's correlation analyses showed that all physio-biochemical indicators were significantly positively associated with influx, except of root SP and biomass. PCA analysis demonstrated that root vigor was a dominant factor causing the differences in Cd tolerance among different soybean seedling cultivars. NMT is of great significance for safe utilization of contaminated soil to distinguish the cultivars with different enrichment capacity for heavy metals from different crop cultivars.

GABA-mediated inhibition of cadmium uptake and accumulation in apples

GABA, a four-carbon non-protein amino acid, plays an important role in animals and plants. We previously found GABA could alleviate alkali stress in apple seedlings. However, its physiological mechanism under heavy metal cadmium (Cd) stress need to be further studied. Thus, we explored its biological role in response to Cd stress. It was verified that 0.5 mM GABA could effectively alleviate Cd toxicity. Using NMT technique, we found that exogenous GABA could significantly reduce the net Cd2+ fluxes in apple roots, and Cd content was significantly lower than that in roots under Cd stress. Further analysis indicated exogenous GABA could significantly reduce the expression of genes related to the uptake and transport of Cd in apples under Cd stress. In addition, exogenous GABA could significantly increase the content of amino acids in apple roots under Cd stress. GAD is a key enzyme in GABA synthesis, we obtained transgenic apple roots of overexpression MdGAD1. Compared with the control, transgenic roots accumulated less Cd, maintained lower Cd uptake by roots, and lower expression of related transport genes. These results showed that GABA could effectively alleviate Cd toxicity in apple seedlings and provide a new perspective of GABA to alleviate Cd stress.

Cadmium concentrations in Idaho wheat grain and soil

AbstractCurrent efforts to reduce the maximum allowable cadmium (Cd) concentrations in wheat (Triticum aestivum L.) for at‐risk populations such as infants require sourcing wheat with low concentrations of Cd. Since Idaho (USA) is a major wheat supplier, there is a need to understand which varieties and locations in Idaho produce wheat containing low Cd. Therefore, the main objective of this paper is to report on a survey of total Cd concentrations in 469 wheat grain samples and 216 soil samples from several varieties and locations throughout Idaho. Total Cd concentrations in wheat grain ranged from <0.01 to 0.28 mg kg−1, varying by both wheat variety and location grown. Total soil Cd ranged from 0.450 to 1.85 mg kg−1. Bioaccumulation factor (BAF) was calculated by dividing the grain total Cd concentration by the soil total Cd concentration and ranged from 0.05 to 0.5. The variety ‘UI Sparrow’ had the lowest mean BAF (0.06), and several other varieties were also relatively low. Overall, almost all wheat varieties meet European Food Safety Authority (EFSA) requirements for Cd concentration for adult consumption. However, meeting the EFSA maximum allowable limit of Cd in infant food requires planting varieties noted for low Cd uptake, like UI Sparrow, and careful selection of growing regions with the lowest total soil Cd, such as northern, central, or western Idaho.

Comparing soil-to-plant cadmium (Cd) transfer and potential human intake among rice cultivars with different Cd tolerance levels grown in a tropical contaminated soil.

With its accumulation in upland rice, cadmium (Cd) can easily enter the human food chain, which poses a global health threat considering nearly half of the human population depends on rice as a staple food source. A study was conducted to (1) evaluate Cd accumulation by rice cultivars, grown in Cd-polluted Tropical Oxisols, with different levels of Cd tolerance; (2) quantify Cd transfer from soil to rice shoots and grain; and (3) estimate daily Cd intake by humans. Three rice cultivars, characterized by low (Cateto Seda-CS), medium (BRSMG Talento-BT), and high (BRSMG Caravera-BC) Cd uptake capacity, were investigated. Rice cultivars were exposed to increasing soil Cd concentrations (0.0, 0.7, 1.3, 3.9, 7.8, and 11.7mgkg-1). Analysis was performed on soil, shoots, and grain. Shoot biomass and grain yield decreased with increasing Cd supply, suggesting the following Cd tolerance: CS > BT > BC. Cadmium concentrations in shoots and grain increased when exposed to Cd. Only CS did not exceed the maximum Cd limit permitted in food (0.40mgkg-1), when rates up to 1.3mgkg-1 of Cd were applied to soil. Considering daily rice consumption levels in Brazil, Cd intake often exceeds maximum tolerable levels. Continuous monitoring of soil Cd concentrations is a pivotal step in avoiding hazards to humans. Such monitoring is important on a global scale since outside of Asia, Brazil is the leading rice-producing and rice-consuming country.

Differences in Cadmium Accumulation, Detoxification and Antioxidant Defenses between Contrasting Maize Cultivars Implicate a Role of Superoxide Dismutase in Cd Tolerance.

Cadmium (Cd), a readily absorbed and translocated toxic heavy metal, inhibits plant growth, interrupts metabolic homeostasis and induces oxidative damage. Responses towards Cd-stress differ among plant cultivars, and the complex integrated relationships between Cd accumulation, detoxification mechanisms and antioxidant defenses still need to be unraveled. To this end, 12 Egyptian maize cultivars were grown under Cd-stress to test their Cd-stress tolerance. Out of these cultivars, tolerant (TWC360 and TWC321), moderately sensitive (TWC324) and sensitive (SC128) cultivars were selected, and we determined their response to Cd in terms of biomass, Cd accumulation and antioxidant defense system. The reduction in biomass was highly obvious in sensitive cultivars, while TWC360 and TWC321 showed high Cd-tolerance. The cultivar TWC321 showed lower Cd uptake concurrently with an enhanced antioxidant defense system. Interestingly, TWC360 accumulated more Cd in the shoot, accompanied with increased Cd detoxification and sequestration. A principal component analysis revealed a clear separation between the sensitive and tolerant cultivars with significance of the antioxidant defenses, including superoxide dismutase (SOD). To confirm the involvement of SOD in Cd-tolerance, we studied the effect of Cd-stress on a transgenic maize line (TG) constitutively overexpressing AtFeSOD gene in comparison to its wild type (WT). Compared to their WT, the TG plants showed less Cd accumulation and improved growth, physiology, antioxidant and detoxification systems. These results demonstrate the role of SOD in determining Cd-tolerance.

Comparative morpho-physiological analyses revealed H2O2-Induced different cadmium accumulation in two wheat cultivars (Triticum aestivum L.)

Different wheat cultivars have their individual defense response to heavy metal stress, exploring which is beneficial to using targeted and effective agronomic practice to reduce cadmium (Cd) accumulation in plants. Our previous study shows Cd concentration is higher in the Cd-tolerant cultivar Bainong 160 than the sensitive one Pingan 8. In this experiment, Bainong 160 showed stronger Cd uptake capacity and lower Cd translocation than Pingan 8, leading to its higher Cd concentration in roots and shoots, as verified by both dose- and time-dependent experiments. This study aims at exploring the factors underpinning Cd resistance and accumulation in wheat, and whether there is an interaction between them. There was a positive correlation between Cd distribution in organelle and H2O2 concentration in both shoot (r = 0.7) and root (r = 0.94**), suggesting that the less Cd distribution in organelle of Bainong 160 contributes to its lower H2O2 concentration than Pingan 8. For Pingan 8, lower expression of TaNramp6 and Cd-induced programmed cell death in cortex lead to its weaker Cd uptake capacity; while for Bainong 160, there are stronger positive cellular responses to Cd stress, including severe lignification in cortex cell, casparian strip formation, increment of both GSH and phytochelatins, and significant increased expression of TaHMA3 and repressed expression of TaHMA2, which together result in its stronger Cd retention in root and so as to inhibit Cd root-to-shoot transfer. Correlation analysis shows most of these reactions are associated with H2O2 concentration. In conclusion, Cd stress induced higher H2O2 concentration in sensitive cultivar Pingan 8 than tolerant one Bainong 160. The excessive H2O2-associated passive reaction in sensitive cultivar caused its lower Cd uptake ability, and moderate H2O2-induced stronger active response in tolerant cultivar, promoting Cd retention in root.

Effect of soil cadmium on root organic acid secretion by forage crops.

The two forage species used in New Zealand pastoral agricultural systems, chicory (Cichorium intybus) and plantain (Plantago lanceolata) show differential ability to absorb and translocate cadmium (Cd) from roots to shoots. Chicory can accumulate Cd from even low Cd soils to levels that might exceed regulatory guidelines for Cd in fodder crops and food. Chicory and plantain were grown in soil-filled rhizocolumns under increasing Cd levels (0 (Control), 0.4, 0.8 and 1.6mg Cd/kg soil) for 60 days and showed variable secretion of oxalic, fumaric, malic and acetic acids as a function of Cd treatment. Plant roots secrete such Low Molecular Weight Organic Acids into the rhizosphere soil, which can influence Cd uptake. Chicory showed significantly (P<0.05) lower secretion of fumaric acid, and higher secretion of acetic acid than plantain at all Cd treatments. We propose that the significant secretion differences between the two species can explain the significantly (P<0.05) higher shoot Cd concentration in chicory for all Cd treatments. Understanding the mechanism for increased uptake in chicory may lead to breeding or genetic modification which yield low Cd uptake cultivars needed to mitigate the risk of Cd accumulation in pastoral agricultural food chains from this increasingly important fodder crop.

Low endogenous NO levels in roots and antioxidant systems are determinants for the resistance of Arabidopsis seedlings grown in Cd

Cadmium (Cd), which is a toxic non-essential heavy metal capable of entering plants and thus the food chain, constitutes a major environmental and health concern worldwide. An understanding of the tools used by plants to overcome Cd stress could lead to the production of food crops with lower Cd uptake capacity and of plants with greater Cd uptake potential for phytoremediation purposes in order to restore soil efficiency in self-sustaining ecosystems. The signalling molecule nitric oxide (NO), whose function remains unclear, has recently been involved in responses to Cd stress. Using different mutants, such as nia1nia2, nox1, argh1-1 and Atnoa1, which were altered in NO metabolism, we analysed various parameters related to reactive oxygen and nitrogen species (ROS/RNS) metabolism and seedling fitness following germination and growth under Cd treatment conditions for seven days. Seedling roots were the most affected, with an increase in ROS and RNS observed in wild type (WT) seedling roots, leading to increased oxidative damage and fitness loss. Mutants that showed lower NO levels in seedling roots under Cd stress were more resistant than WT seedlings due to the maintenance of antioxidant systems which protect against oxidative damage.

Soil-indigenous arbuscular mycorrhizal fungi and zeolite addition to soil synergistically increase grain yield and reduce cadmium uptake of bread wheat (through improved nitrogen and phosphorus nutrition and immobilization of Cd in roots).

Soil pollution with heavy metals is a major problem in industrial areas. Here, we explored whether zeolite addition to soil and indigenous arbuscular mycorrhizal fungi (AMF) can reduce cadmium (Cd) uptake from soil by bread wheat. We conducted a pot experiment, in which the effects of indigenous soil AMF, zeolite addition, and Cd spiking to soil [0, 5, 10, and 15 mg (kg soil)-1] were tested. Zeolite addition to soil spiked with 15 mg Cd kg-1 decreased the Cd uptake to grains from 11.8 to 8.3 mg kg-1 and 8.9 to 3.3 mg kg-1 in the absence and presence of indigenous AMF, respectively. Positive growth, nitrogen (N), and phosphorous (P) uptake responses to mycorrhization in Cd-spiked soils were consistently magnified by zeolite addition. Zeolite addition to soil stimulated AMF root colonization. The abundance of AMF taxa changed in response to zeolite addition to soil and soil Cd spiking as measured by quantitative polymerase chain reaction. With increasing Cd spiking, the abundance of Funneliformis increased. However, when less Cd was spiked to soil and/or when zeolite was added, the abundance of Claroideoglomus and Rhizophagus increased. This study showed that soil-indigenous AMF and addition of zeolite to soil can lower Cd uptake to the grains of bread wheat and thereby reduce Cd contamination of the globally most important staple food.

Gene identification and transcriptome analysis of low cadmium accumulation rice mutant (lcd1) in response to cadmium stress using MutMap and RNA-seq

BackgroundCadmium (Cd) is a widespread toxic heavy metal pollutant in agricultural soil, and Cd accumulation in rice grains is a major intake source of Cd for Asian populations that adversely affect human health. However, the molecular mechanism underlying Cd uptake, translocation and accumulation has not been fully understood in rice plants.ResultsIn this study, a mutant displaying extremely low Cd accumulation (lcd1) in rice plant and grain was generated by EMS mutagenesis from indica rice cultivar 9311 seeds. The candidate SNPs associated with low Cd accumulation phenotype in the lcd1 mutant were identified by MutMap and the transcriptome changes between lcd1 and WT under Cd exposure were analyzed by RNA-seq. The lcd1 mutant had lower Cd uptake and accumulation in rice root and shoot, as well as less growth inhibition compared with WT in the presence of 5 μM Cd. Genetic analysis showed that lcd1 was a single locus recessive mutation. The SNP responsible for low Cd accumulation in the lcd1 mutant located at position 8,887,787 on chromosome 7, corresponding to the seventh exon of OsNRAMP5. This SNP led to a Pro236Leu amino acid substitution in the highly conserved region of OsNRAMP5 in the lcd1 mutant. A total of 1208 genes were differentially expressed between lcd1 and WT roots under Cd exposure, and DEGs were enriched in transmembrane transport process GO term. Increased OsHMA3 expression probably adds to the effect of OsNRAMP5 mutation to account for the significant decreases in Cd accumulation in rice plant and grain of the lcd1 mutant.ConclusionsAn extremely low Cd mutant lcd1 was isolated and identified using MutMap and RNA-seq. A Pro236Leu amino acid substitution in the highly conserved region of OsNRAMP5 is likely responsible for low Cd accumulation in the lcd1 mutant. This work provides more insight into the mechanism of Cd uptake and accumulation in rice, and will be helpful for developing low Cd accumulation rice by marker-assisted breeding.

Metal resistant PGPR lowered Cd uptake and expression of metal transporter genes with improved growth and photosynthetic pigments in Lycopersicon esculentum under metal toxicity

Plant growth promoting rhizobacteria (PGPRs) are very effective in immobilization of heavy metals and reducing their translocation in plants via precipitation, complex formation and adsorption. The present study was therefore designed to understand the role of Pseudomonas aeruginosa and Burkholderia gladioli in mitigation of Cd stress (0.4 mM) in 10-days old L. esculentum seedlings. The present work investigated growth characteristics, photosynthetic pigments, metal tolerance index, metal uptake and the contents of metal chelating compounds (protein bound and non-protein bound thiols, total thiols) in microbes inoculated Cd treated L. esculentum seedlings. The gene expression profiling of different metal transporters was conducted in order to investigate the quantitative analysis. Our results revealed Cd generated toxicity in seedlings in terms of reduced growth (root length, shoot length and fresh weight) and photosynthetic pigments (chlorophyll, carotenoid and xanthophyll) which enhanced upon inoculations of P. aeruginosa and B. gladioli. Further, the metal uptake along with levels of protein and non-protein bound thiols was also enhanced in Cd-treated seedlings. Gene expression studies suggested enhanced expression in the metal transporter genes which were further declined in the microbe supplemented seedlings. Therefore, micro-organisms possess growth promoting traits that enable them to reduce metal toxicity in plants.

Glutathione Might Attenuate Cadmium-Induced Liver Oxidative Stress and Hepatic Stellate Cell Activation

The liver is a major organ involved in cadmium (Cd)-induced oxidative damage. Following liver injury, hepatic stellate cells (HSCs) are activated to participate in the wound healing process, but also facilitate liver fibrosis. Previous studies have observed fibrogenic effects of Cd on liver. However, the oxidative stress mechanisms of Cd-induced HSC activation as well as whether administration of glutathione (GSH) alleviates this activation, remain unclear. In this study, 24 rats were divided randomly into four experimental groups: control, GSH-treated, Cd-treated, and Cd + GSH-treated. After 4weeks, the liver injury index, HSC-specific activation markers, oxidative stress-related antioxidants, and enzyme activities and signals were measured. Cd uptake and the generation of reactive oxygen species (ROS) in hepatocytes were detected by mass cytometry and fluorescence microscopy, respectively. Levels of aspartate aminotransferase, xanthine oxidase, γ-glutamyl transpeptidase, and α-smooth muscle actin (αSMA) were significantly increased in Cd-treated rats. Activated HSCs positive for αSMA expression and excess collagen deposition were detected in the Cd-treated group. In contrast, activities of the antioxidant enzymes superoxide dismutase, glutathione peroxidase, and catalase were reduced. Supplementation with GSH reversed some of the Cd-induced effects and increased the protein level of phosphorylated (p)-P65 while decreasing p-JNK. Pretreatment with GSH lowered Cd uptake and ROS generation in hepatocytes in vitro. These results indicate that administration of GSH was effective in attenuating Cd-induced oxidative stress via decreasing Cd uptake, restoring the activities of oxidative enzymes, activating NF-κB, inhibiting the JNK signaling pathway, and preventing excessive ROS generation and HSC activation.

Effects of ZnO nanoparticles on the toxicity of cadmium to duckweed Lemna minor

Release of nanoparticles into the aquatic environment will inevitably influence the behavior and toxicities of other existing pollutants. In the present study, 10 mg/L of nano-ZnO (diameter 20–30 nm) was used to evaluate its impacts on cadmium (Cd) toxicity on duckweed Lemna minor based on IC50 values and four biological parameters including percent inhibition of growth rate (Ir), ratio of chlorophyll/pheophytin (D665/D665a), antioxidant enzymes, and H+-ATPase. Results of the 96-h IC50 values of Cd with or without nano-ZnO indicate no additional toxicological effects of nano-ZnO to plants. Further examinations using two Cd concentrations (0.1 and 1 mg/L) showed that nano-ZnO did not influence the inhibitory effect of 0.1 mg/L Cd, but significantly (P < 0.05) reduced the stress of 1 mg/L Cd to the duckweed. The index D665/D665a reflected that the toxic effect of 1 mg/L Cd was significantly (P < 0.05) suppressed by nano-ZnO. H+-ATPase was also sensitive to reveal the protective effects of nano-ZnO on the duckweed under Cd exposure. However, the responses of the antioxidant enzymes SOD and CAT failed to reflect the effects of nano-ZnO on Cd toxicity. Hysteretic addition of nano-ZnO for 24 h showed that the protective effects of nano-ZnO were weakened. Our results suggest that the adsorption of Cd to nano-ZnO may result in lower Cd uptake by L. minor, thus reducing its toxicity.

Root system architecture influencing cadmium accumulation in rice (Oryza sativa L.)

Cadmium (Cd) contamination in paddy fields affects human health because of the consumption of Cd-contaminated rice. In the current study, we demonstrated that variation in root system architecture (RSA) influenced Cd uptake by rice. Rice cultivars consisting of KDML105, Mali Dang, Pitsanulok2 and Niaw San-pah-tawng were assessed in hydroponics and mesocosms while KDML 105, Pitsanulok2, and RD53 were used in field experiments. In hydroponics, root number and root weight were positively correlated with Cd uptake. In mesocosms, we found that the effects of Cd on RSA depended on rice varieties. Among different rice varieties, Mali Dang consistently accumulated high concentration of Cd, while Niaw San-pah-tawng tended to accumulate much lower amount in its shoot in both hydroponics and mesocosms. Correlation analysis indicates that Cd concentrations in shoot was positively correlated with root weight (R2 = 0.95), crown root number (R2 = 0.74), and negatively correlated with root depth (R2 = 0.86). In the field, Cd is most abundant at a depth of 10–20 cm. and root distribution influenced Cd uptake as evidenced by high root Cd content in the RD53 variety. We propose that low crown root number and deep RSA could be promising traits for selection and breeding for low Cd uptake rice.

Reactive oxygen and nitrogen species as key indicators of plant responses to Cd stress

Although cadmium (Cd), an extremely toxic non-essential heavy metal, has no biological function, it is capable of entering plant roots. Cd not only presents a problem for plants, which have developed specific Cd detection, transport and detoxification mechanisms, but also for humans as it can enter the food chain. After entering the root, Cd can be loaded into the xylem and then into the leaves and fruits, thus constituting a major environmental and health hazard worldwide. Understanding the mechanisms involved in plant responses to Cd stress would facilitate the production of crops with a lower Cd uptake and accumulation capacity as well as plants with greater Cd uptake potential for phytoremediation. One of the most common symptoms of Cd toxicity is the induction of oxidative stress in plants, which have developed various strategies to avoid this toxicity, including the early production of reactive oxygen and nitrogen species (ROS and RNS) with signalling functions. This review focuses on the dual role of ROS and RNS in plant responses to Cd stress: in low concentrations, as signalling molecules capable of orchestrating plant responses on the one hand, and at higher concentrations, as oxidative stress inducers on the other.