Cultivar variations in cadmium and lead accumulation and distribution among 30 wheat (Triticum aestivum L.) cultivars

Comparison of soil addition, foliar spraying, seed soaking, and seed dressing of selenium and silicon nanoparticles effects on cadmium reduction in wheat (Triticum turgidum L.)

Wheat cadmium (Cd) contamination is a critical food security issue worldwide, and selenium (Se) and silicon (Si) are widely reported to reduce Cd accumulation in cereal crops. However, few studies have compared the most effective pathway to reduce Cd accumulation in crops using Se nanoparticles (nano-Se), Si nanoparticles (nano-Si), and their mixtures. Here, we investigated the concentrations of Cd in wheat using four application modes: soil addition, foliar spraying, seed soaking, and seed dressing combined with three different materials. The concentration of Cd in wheat grains can be significantly reduced by 31.30-62.99% and 36.96-51.04% through four applications of nano-Se and soil application and seed soaking of nano-Si, respectively. However, all treatments involving mixtures of nano-Si and nano-Se did not show a reduction in Cd concentration. The applications of both nano-Se and nano-Si can enhance antioxidant enzyme systems and regulate Cd-related gene expression to safeguard wheat tissues from Cd stress. Downregulation of the influx transporter from soil to root (TaNramp5) and from root to shoot (TaLCT1), along with the upregulation of the efflux transporter from cytoplasm to vacuole (TaHMA3), contributed to the nano-Si/nano-Se dependent Cd transport and reduced Cd accumulation in wheat grains. Overall, the application of nano-Se instead of nano-Si, and soil addition rather than foliar spraying, seed soaking, and seed dressing, can be efficiently utilized to reduce grain Cd accumulation from Cd-contaminated soils.

The accumulation of cadmium and lead in wheat grains is primarily determined by the soil-reducible cadmium level during wheat tillering

The significant increase in cadmium (Cd) and lead (Pb) pollution in agricultural soil has greatly heightened environmental contamination issues and the risk of human diseases. However, the mechanisms underlying the transformation of Cd and Pb in soil as well as the influencing factors during their accumulation in crop grains remain unclear. Based on the analysis of the distribution trend of Cd and Pb in soil during the growth and development stages of wheat (tillering, filling, and maturity) in alkaline heavy metal-polluted farmland in northern China, this study investigated the response mechanism of soil heavy metal form transformation to soil physicochemical properties, and elucidated the main determining periods and influencing factors for Cd and Pb enrichment in wheat grains. The results showed that an increase in CEC and SOM levels, along with a decrease in pH level, contributed to enhancing the bioavailability of Cd in the soil. This effect was particularly evident during the tillering stage and grain filling stage of wheat. Nevertheless, the effects of soil physicochemical properties on bioavailable Pb was opposite to that on bioavailable Cd. The enrichment of Cd and Pb in grain was significantly influenced by soil pH (r = -0.786, p < 0.01), SOM (r = 0.807, p < 0.01), K (r = -0.730, p < 0.01), AK (r = 0.474, p = 0.019), and AP (r = -0.487, p = 0.016). The reducible form of Cd in soil during the wheat tillering stage was identified as the primary factor contributing to the accumulation of Cd and Pb in wheat grains, with a significant contribution rate of 84.5%. This study provides a greater scientific evidence for the management and risk control of heavy metal pollution in alkaline farmland.

Effect of Genotype on Cadmium and Trace Element Accumulation in Wheat from Weakly Alkaline Cadmium-contaminated Soil

Cadmium (Cd) contamination of farmland soils leads to Cd accumulation in crops and reduced micronutrient uptake, posing grave risks to food safety. Herein, we investigated the enrichment and transportation patterns of Cd and trace elements in different parts of six wheat genotypes grown in weakly alkaline Cd-contaminated soils via pot experiments. The results revealed that the wheat grain variety with high Cd accumulation (Ningmai13) demonstrated a 1.94-fold increase compared to the variety with low accumulation (Yanong0428). The transfer factor of Cd from wheat straw to grain ranged from 0.319 to 0.761, while the transfer factor of Cd from root to straw ranged from 0.167 to 0.461. Furthermore, the concentrations of other metals in wheat grains followed the order of Zn > Mn > Fe > Cu. There was a significant positive correlation between Cd and Mn in grains, indicating a potential synergistic effect. Overall, this study provides valuable insights into the regulation of micronutrient intake to modulate Cd uptake in wheat.

Variations in Cadmium and Lead Bioaccessibility in Wheat Cultivars and Their Correlations with Nutrient Components

To reduce the health risks of exposure to Cd and Pb in wheat, a field experiment was conducted to investigate the differences in Cd and Pb bioaccessibility among the grains of 11 wheat cultivars and their relationships with the nutrient compositions of grains. The grain concentrations (Cd: 0.14-0.56 mg kg-1, Pb: 0.08-0.39 mg kg-1) and bioaccessibility (5.28-57.43% and 0.72-7.72% for Cd and Pb in the intestinal phase, respectively) of Cd and Pb differed significantly among the 11 cultivars. A safe wheat cultivar (Shannong16) with a relatively low health risk and the lowest grain Cd and Pb concentrations was selected. Ca, Mg, phytate, and methionine played key roles in affecting Cd and Pb bioaccessibility in wheat, with Ca and phytate significantly negatively correlated with Cd and Pb bioaccessibility. These findings can be used to optimize the selection strategy for safe wheat cultivars for healthy grain production in Cd-polluted farmland.

Molecular-Assisted Breeding of Cadmium Pollution-Safe Cultivars

Cadmium (Cd) contamination in edible agricultural products, especially in crops intended for consumption, has raised worldwide concerns regarding food safety. Breeding of Cd pollution-safe cultivars (Cd-PSCs) is an effective solution to preventing the entry of Cd into the food chain from contaminated agricultural soil. Molecular-assisted breeding methods, based on molecular mechanisms for cultivar-dependent Cd accumulation and bioinformatic tools, have been developed to accelerate and facilitate the breeding of Cd-PSCs. This review summarizes the recent progress in the research of the low Cd accumulation traits of Cd-PSCs in different crops. Furthermore, the application of molecular-assisted breeding methods, including transgenic approaches, genome editing, marker-assisted selection, whole genome-wide association analysis, and transcriptome, has been highlighted to outline the breeding of Cd-PSCs by identifying critical genes and molecular biomarkers. This review provides a comprehensive overview of the development of Cd-PSCs and the potential future for breeding Cd-PSC using modern molecular technologies.

Temporal Comparative Transcriptome Analysis on Wheat Response to Acute Cd Toxicity at the Seedling Stage

Cadmium (Cd) is a non-essential and toxic metal that accumulates in plant's tissues and diminishes plant growth and productivity. In the present study, differential root transcriptomic analysis was carried out to identify Cd stress-responsive gene networks and functional annotation under Cd stress in wheat seedlings. For this purpose, the Yannong 0428 wheat cultivar was incubated with 40 µm/L of CdCl₂·2.5H₂O for 6 h at three different seedling growth days. After the quality screening, using the Illumina Hiseq 2000 platform, more than 2482 million clean reads were retrieved. Following this, 84.8% to 89.3% of the clean reads at three time points under normal conditions and 86.5% to 89.1% of the reads from the Cd stress condition were mapped onto the wheat reference genome. In contrast, at three separate seedling growth days, the data analysis revealed a total of 6221 differentially expressed genes (DEGs), including 1543 (24.8%) up-regulated genes and 4678 (75.8%) down-regulated genes. In total, 120 DEGs were co-expressed throughout all the growth days, whereas 1096, 1088, and 2265 DEGs were found to be selectively up-/down-regulated at 7d, 14d, and 30d, respectively. However, the clustering of DEGs, through utilizing the Kyoto Encyclopedia of Genes and Genomes (KEGG), revealed that the DEGs in the metabolic category were frequently annotated for phenylpropanoid biosynthesis. In comparison, a considerable number of DEGs were linked to protein processing in the endoplasmic reticulum under the process of genetic information processing. Similarly, in categories in organismal systems and cellular processes, DEGs were found in plant hormone signal transduction pathways, and DEGs were identified in the plant-pathogen interaction pathway, respectively. However, DEGs in "endocytosis pathways" were enriched in environmental information processing. In addition, in-depth annotations of roughly specific heavy metal stress-response genes and pathways were also mined, and the expression patterns of eight DEGs were studied using quantitative real-time PCR. The results were congruent with the findings of RNA sequencing regarding transcript abundance in the studied wheat cultivar.

Heterologous expression of the tobacco metallothionein gene NtMT2F confers enhanced tolerance to Cd stress in Escherichia coli and Arabidopsis thaliana

Heavy metal pollution in the soil is a serious threat to crop growth and human health. Metallothionein (MT) is a low molecular weight protein that is rich in cysteine, which can effectively alleviate the toxicity of heavy metals in plants. In this study, a novel metallothionein encoding gene, NtMT2F, was cloned from the Cd-hyperaccumulator tobacco and heterologously expressed in E. coli and A. thaliana to verify its biological function. Recombinant E. coli incubated with NtMT2F effectively resisted heavy metal stress, particularly Cd. The recombinant strain grew significantly faster and had a higher content of Cd than the control. Mutations in the C-terminal Cys residues of NtMT2F significantly reduced its ability to chelate heavy metals. The overexpression of NtMT2F significantly enhanced resistance to Cd toxicity in transgenic A. thaliana. The germination rate, root length, and fresh weight of transgenic plants under Cd stress were higher than those of the wild type (WT). The contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) were lower than those of the WT. In addition, the activities of anti-peroxidase enzymes including glutathione reductase (GR), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), were significantly increased in the transgenic plants. The results of this study indicate that NtMT2F significantly improved the tolerance of microorganisms and plants to Cd and could be an important candidate protein for phytoremediation.

Effect of boron on cadmium uptake and expression of Cd transport genes at different growth stages of wheat (Triticum aestivum L.)

Boron (B) is an essential microelement for plant growth and has been shown to reduce cadmium (Cd) toxicity in wheat through modulating gene expression. However, there is not enough information about the effects of different applications of B fertilizer on the accumulation of Cd, particularly throughout the wheat growth period. This experiment employed two different B fertilization methods. The soil application method utilized 1.5 mg B kg^-1 soil (Cd+B) and foliar application utilized 0.1% (F0.1%), 0.3% (F0.3%), and 0.6% (F0.6%) B concentrations along with 4 mg kg^-1 Cd. The results showed that B application in the soil reduced Cd concentrations per plant by 43.9% at the seedling stage, 74.59% in the roots, and 52.11% in the shoots at the elongation stage. At the same time, Cd concentrations in the roots were higher by B application at the anthesis and maturity stages, suggesting that B retains more Cd in the roots. The gray correlation analysis showed that the gray relational coefficients followed the following order: F0.3% > F0.1% > Cd+B > F0.6%. According to quantitative real-time PCR analysis, the six Cd transporters were mostly expressed in the roots at the seedling stage and anthesis stage. In addition, the expression of TCONS1113, TRIAE1060, and TRIAE5370 showed a negative correlation relationship with Cd concentration at the seedling stage, both in roots and shoots. At the anthesis stage, the expression of TCONS1113 and TRIAE5370 in roots was higher in Cd-treated plants compared to B-treated plants, and a similar tendency was noted for the expression of TRIAE5770 and TRIAE1060 in shoots as well. These results suggest that B application could significantly inhibit Cd uptake and translocation by regulating the expression of Cd transporter genes, especially at the seedling stage and the elongation phase in wheat.

Comparative responses of cadmium accumulation and subcellular distribution in wheat and rice supplied with selenite or selenate

Cadmium (Cd) contamination of crop plants has aroused a worldwide concern because of the threats posed to human health through accumulation in the food chains. Selenium (Se) can alleviate the Cd-induced phytotoxicity, but the relevant underlying mechanisms are not fully understood. Therefore, with wheat (Triticum aestivum L.) and rice (Oryza sativa L.) chosen as the target plants in this study, the effects of selenite or selenate on Cd accumulation and subcellular distribution were investigated through greenhouse hydroponic experiments; and simultaneously, the effects of pre-Se treatment with selenite or selenate on Cd accumulation and root-to-shoot translocation in the studied plants were also included. Results showed the addition of Se slightly changed the Cd content in plant roots in a time-dependent manner; however, with the obvious decreasing trend on the Cd transfer factor (TF), its content in plant shoots was significantly reduced by selenite or selenate in a plant species-dependent manner. At 48 h of exposure, the supplementation of selenite and selenate significantly decreased the Cd content by 40.4% and 38.0% in wheat shoots, and by 72.2% and 40.9% in rice shoots, respectively. Additionally, the order of Cd proportion distributed to the different subcellular fractions of plant tissues was as follows: cell wall > soluble cytosol > organelle, irrespective of the Se treatments or the plant species. However, selenate increased the Cd percentage in soluble cytosol of wheat shoots, while selenite increased that percentage in the cell wall of rice shoots; and the Cd proportion in soluble cytosol of the studied plant roots was significantly enhanced owing to selenite or selenate addition. Moreover, similar to the co-application, the pre-Se treatment with inorganic Se also reduced the Cd accumulation and translocation both in wheat and rice. Our results proved that the inorganic Se could decline the Cd accumulation and translocation in the crop plants, although selenite was found more effective than selenate regarding such effects.

A promising crop for cadmium-contamination remediation: Broomcorn millet

Cadmium (Cd) pollution highly threatens food security and human health, and phytoremediation with Cd-tolerant plants is a cost-effective in situ method for remediation of Cd contamination. Broomcorn millet is known for its strong abiotic stress resistance and can be used as a pioneer crop in both marginal regions and newly reclaimed land. To evaluate their potential in remediation of Cd contamination, a total of 288 broomcorn millet core collections were investigated under hydroponic conditions to compare their capabilities in Cd tolerance, translocation, and accumulation. The core collections varied considerably in their growth parameters, Cd concentration, Cd translocation factor, Cd bioaccumulation factor, and Cd accumulation under Cd stress. According to the Cd tolerance index (TI) values, 160 varieties were Cd tolerant. The Cd TI was significantly positively correlated with Cd accumulation, and the shoot Cd concentrations of five Cd-tolerant varieties were more than 100 mgkg-1, the threshold for being Cd hyperaccumulators. Moreover, the concentrations of essential metal elements were significantly decreased in shoots, and Cd concentration had a significantly positive relationship with magnesium (Mg) and zinc (Zn) concentrations in roots under Cd stress. These results demonstrate that broomcorn millet shows considerable tolerance to Cd stress and great differences in Cd accumulation abilities among varieties. Accordingly, broomcorn millet is a promising plant species for Cd bioremediation, with valuable varieties that have been identified for further study on Cd tolerance mechanisms and the remediation of Cd contamination.

Phytoavailability, translocation and soil thresholds derivation of cadmium for food safety through soil-wheat (Triticum aestivum L.) system

Cadmium (Cd) pollution in cultivated soils has posed a great risk to human health through the soil-plant-human pathway. Therefore, it is important to derive soil thresholds for the low-Cd accumulating genotype of wheat (Triticum aestivum L.) to promote its application in agricultural production on Cd-contaminated sites. Here, a pot experiment was performed to explore the transfer characteristics of Cd in two contrasting wheat genotypes at three different soils and the effect of soil parameters together with soil safety Cd thresholds derivation. Generally, grain Cd highly accumulating wheat genotype (Zhenmai10, HT) showed higher Cd accumulation in grains than grain Cd weakly accumulating wheat genotype (Aikang58, LT). Stepwise multiple linear regression (SMLR) analysis (log-transformed Freundlich-type) indicated that Cd accumulation in wheat grains was strongly related to soil total Cd concentration and pH for both genotypes (R2 = 0.907*** for HT; R2 = 0.910*** for LT). Combining the simple regression model of soil-plant transfer system with the risk assessment method based on human health, soil total Cd thresholds for three soils were calculated with the values of 0.62, 0.82, and 0.62 mg kg-1 in LT genotype and 0.31, 0.77, and 0.49 mg kg-1 in HT genotype. Therefore, we suggested that when deducing soil thresholds, the ability of wheat genotypes to accumulate Cd and soil properties should be considered because of the large differences in soil thresholds between different genotypes and types of soils. We believe our results will promote the application of low-Cd wheat genotypes to agricultural production, thereby ensuring the safety of their products.

Effects of mercapto-palygorskite on Cd distribution in soil aggregates and Cd accumulation by wheat in Cd contaminated alkaline soil

Cadmium (Cd) contamination in alkaline soils is a serious issue in China. As the basic structural units of soil, soil aggregates play an important role in the migration and transformation of heavy metal. However, there are few studies on the effects of adding amendments on Cd distribution in soil aggregates in alkaline soils. In this study, pot experiments were conducted to assess the effects of mercapto-palygorskite (MPAL) on soil aggregates and Cd accumulation in wheat. The results showed that MPAL application had no effect on wheat yield but significantly reduced the Cd uptake by the roots and the Cd transport to the adjacent internode. Application of 0.1% MPAL reduced the Cd concentration in two wheat grains (0.57 and 0.44 mg/kg, control) to 0.10 and 0.09 mg/kg in moderately Cd-contaminated soil, which are below the China national standard limit of 0.1 mg/kg (GB 2762-2017). MPAL application had no effect on soil pH, cation exchange capacity, mass proportion and mean weight diameter of soil aggregates, but increased soil organic matter content. Importantly, MPAL application promoted the migration of Cd from large particles (>0.25 mm) to small particles (<0.048 mm), reduced the unstable Cd fractions in >0.25 mm soil particles of clay soil and in >0.075 mm soil particles of sandy soil, and increased the stable Cd fractions in bulk soils and soil aggregates. The effects of MPAL addition on soil aggregates (grain size fraction metals loading and accumulation factor) of sandy soil were more prominent than on those of clay soil. Under MPAL treatments, wheat grains Cd concentration was significantly positively correlated with the available Cd in >0.075 mm soil particles and the total Cd in >0.25 mm soil particles. These results indicated that MPAL application in alkaline soils promoted the migration of Cd to micro-aggregates and inhibited the uptake and transport of Cd by wheat roots, thus reducing the Cd concentration in wheat grains.

Nitrate supply decreases uptake and accumulation of ciprofloxacin in Brassica parachinensis

How nitrate (NO₃^-) fertilization influences ciprofloxacin (CIP) uptake by crops remains unsolved. Here, two Brassica parachinensis cultivars differing in CIP accumulation were cultivated to investigate the effects of NO₃^- supply on CIP uptake and the underlying mechanism. The results showed that NO₃^- supply effectively reduced CIP toxicity and accumulation in the two cultivars, especially in the low CIP cultivar. Moreover, NO₃^- supply induced different mechanisms of coping with CIP stress in the two cultivars through influencing subcellular distribution of CIP. The uptake of CIP by root was demonstrated to be a carrier-mediated, energy-consuming, and proton motive force-dependent influx process. Consequently, a mechanism of nitrate supply decreasing CIP uptake was proposed that uptake of CIP and NO₃- into root cell would compete for the proton motive force and share a common energy source provided by plasma membrane H⁺-ATPase. Besides, regulating the concentration balances of cytoplasmic NO₃- and proton by inhibiting the activities of NRase and two tonoplast proton pumps (V-ATPase and V-PPase) led to opposite effect on CIP uptake, further supporting this inference. Our results provide a novel insight into CIP uptake by plant roots, and improve the strategy of minimizing CIP accumulation in crops for food safety by fertilization management.

Bioaccumulation of cadmium in different genotypes of wheat crops irrigated with different sources of water in agricultural regions

The study was carried out to evaluate the health risks associated with accumulation of cadmium in the different genotypes of wheat, grown in agricultural regions of Punjab, Pakistan. Five genotypes irrigated with three varied water sources were selected randomly from each region. Among all sources of water, types of soil, and grain samples, the cadmium (Cd) quantities were found (2.24-2.82 mg/L, 1.75-4.16 mg/kg, 0.86-1.90, respectively), exceeding the maximum permissible limits (0.01 mg/L, 1.1 mg/kg, 0.2 mg/kg, respectively) described by FAO/WHO. The pollution load index (PLI) exhibited by all of the samples was higher than 1.00, the permissible limit; however, other factors including bioaccumulation, translocation, bio-concentration, daily intake, and enrichment values of Cd were less than 1.00. Moreover, the health risk index for cadmium in all types of wheat grain samples was less than 1.00. The study concluded that the continuous use of wastewater resources may lead to the accumulation of cadmium in the vital body organs that may cause severe health hazards.

Accumulation of Cd by three forage mulberry (Morus atropurpurea Roxb.) cultivars in heavy metal-polluted farmland: a field experiment

A 3-year field experiment was conducted to evaluate the accumulation ability of 3 forage mulberry (Morus atropurpurea Roxb.) varieties (Guisangyou 62, Guisangyou 12, Yuesang 11) for Cadmium (Cd). The results showed that the shoot biomass of forage mulberry could reach to 64.51~69.58 t/ha in 2018. The total production of Guisangyou 12 was the highest among the tested 3 cultivars in each year. However, the biomass of the 3 varieties displayed without significant differences at every sampling time. In addition, the concentrations of Cd in the roots of the 3 mulberry cultivars were higher than those in the corresponding shoots in 2018. But in 2019, the Cd content in roots was near to that of shoots. The Cd concentrations in the roots of the forage mulberry showed Guisangyou 62 > Yuesang 11 > Guisangyou 12. And the Cd concentrations in shoots of all the 3 tested forage mulberry varieties were less than 1 mg/kg, meeting the hygienical standard for feeds (China). Though the 3 forage mulberry varieties were not hyperaccumulators for Cd, they could be used as alternative plants to make use of the Cd-polluted (< 1.0 mg/kg) paddy soils.

A comparative study of root cadmium radial transport in seedlings of two wheat (Triticum aestivum L.) genotypes differing in grain cadmium accumulation

The radial transport of cadmium (Cd) is essential for Cd influx in roots. The role of radial transport pathway on the Cd translocation from root to shoot among wheat genotypes are still poorly understood. This study explored the role of apoplastic and symplastic pathway on root Cd uptake and root-to-shoot translocation in Zhenmai 10 (ZM10, high Cd in grains) and Aikang 58 (AK58, low Cd in grains). Under Cd treatment, the deposition of Casparian strips (CSs) and suberin lamellae (SL) initiated closer to the root apex in ZM10 than that in AK58, which resulted in the lower Cd concentration in apoplastic fluid of ZM10. Simultaneously, Cd-induced expression levels of genes related to Cd uptake in roots were significantly higher in AK58 by contrast with ZM10, contributing to the symplastic Cd accumulation in AK58 root. Moreover, the addition of metabolic inhibitor CCCP noticeably decreased the Cd accumulation in root of both genotypes. Intriguingly, compared to ZM10, greater amounts of Cd were sequestrated in the cell walls and vacuoles in roots of AK58, limiting the translocation of Cd from root to shoot. Furthermore, the elevated TaHMA2 expression in ZM10 indicates that ZM10 had a higher capacity of xylem loading Cd than AK58. All of these results herein suggest that the radial transport is significant for Cd accumulation in roots, but it cannot explain the difference in root-to-shoot translocation of Cd in wheat genotypes with contrast Cd accumulation in grains.

Insights into the mechanisms underlying the remediation potential of earthworms in contaminated soil: A critical review of research progress and prospects

In recent years, soil pollution is a major global concern drawing worldwide attention. Earthworms can resist high concentrations of soil pollutants and play a vital role in removing them effectively. Vermiremediation, using earthworms to remove contaminants from soil or help to degrade non-recyclable chemicals, is proved to be an alternative, low-cost technology for treating contaminated soil. However, knowledge about the mechanisms and framework of the vermiremediation various organic and inorganic contaminants is still limited. Therefore, we reviewed the research progress of effects of soil contaminants on earthworms and potential of earthworm used for remediation soil contaminated with heavy metals, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), pesticides, as well as crude oil. Especially, the possible processes, mechanisms, advantages and limitations, and how to boost the efficiency of vermiremediation are well addressed in this review. Finally, future prospects of vermiremediation soil contamination are listed to promote further studies and application of vermiremediation in contaminated soils.

Differences in absorption of cadmium and lead among fourteen sweet potato cultivars and health risk assessment

Planting sweet potato (Ipomoea batatas (L.) Lam.) instead of rice in the area contaminated with heavy metals is one of the measures to ensure people's health and agricultural economy. Therefore, it is important to screen the low accumulation cultivars of sweet potato and to find out the concentration rule of cadmium (Cd) and lead (Pb) in edible parts along with the associated health risks to humans. A field experiment was performed with fourteen of three main types (starch, purple, and edible-type) of sweet potato cultivars grown on farmland polluted with Cd and Pb in eastern Hunan Province, China. The Cd and Pb concentrations in the sweet potato tissues as well as the yield were measured. The yield of the shoot and tuberous root of the fourteen sweet potato cultivars ranged from 14.59 to 68.57 and 26.35-50.76 t ha^-1 with mean values of 33.09 and 33.46 t ha^-1, respectively. Compared with purple and edible-type cultivars, the starch-type cultivar had lower Cd and Pb concentrations in the flesh, but higher in the shoot. The Cd and Pb concentrations in the flesh of cultivars Shangshu 19, Sushu 24, Yushu 98, and Xiangshu 98 were lower than MCL provided in Chinese National Food Safety Standards GB2762-2017. Based on the hazard index (HI), the consumption of sweet potato flesh is lower health risk, while shoots pose a greater health risk to local people and Cd is the main cause of the risk. As a result, sweet potato cultivars Shangshu 19, Sushu 24, Yushu 98 and Xiangshu 98 can be plant in serve Cd and Pb contaminated soils with the advantages of easy cultivation, high yield and economic benefits without stopping agricultural production.

Optimal voltage and treatment time of electric field with assistant Solanum nigrum L. cadmium hyperaccumulation in soil

We have attempted to obtain optimal conditions of direct current electrical field with switching polarity to increase Cd accumulation of the hyperaccumulator Solanum nigrum L. from soil. The effects of different voltages and treatment times on S. nigrum accumulating Cd were determined. The results showed that Cd concentration in S. nigrum under all electrical field conditions were significantly higher (p < 0.05) than that of the CK. The Cd concentration in shoot and root of treatment T3 (3 V cm^-1) were higher than the equal results of treatment T2 (2 V cm^-1) and T1 (1 V cm^-1) under the same condition of 6 h d^-1 treatment time. In different treatments concerning time of T1 (6 h d^-1), T4 (10 h d^-1) and T5 (14 h d^-1) under same voltage of 1 V cm^-1, the S. nigrum Cd concentration were with similar trend to the different voltage treatments (T5 with the highest Cd concentration). These results might be caused by positive change trends of pH, EC and extractable Cd concentration in soil. However, the S. nigrum biomasses of T3 were the lowest and the highest biomass happened in treatment of T4. Finally, the highest Cd accumulation in S. nigrm (μg pot^-1) was the T4 with the condition of 1 V cm^-1 and 10 h d^-1, which was also the optimal voltage and treatment time of the electric field. The optimal conditions were important references in the practice of combined use of electrokinetic remediation and phytoremediation.

Cataloging of Cd Allocation in Late Rice Cultivars Grown in Polluted Gleysol: Implications for Selection of Cultivars with Minimal Risk to Human Health

Cadmium (Cd) is a toxic trace metal that has polluted 20% of agricultural land in China where its concentration exceeds the standards for Chinese farmland. Plants are capable of accumulating Cd and other trace metals, but this capacity varies with species and cultivars within a species. Rice is a staple food consumed by half of the global population. In order to select safe late rice cultivars that are suitable late rice cultivars that can be cultivated in for growing in slightly contaminated soil, a two-year field experiment was conducted with 27 in the first year and 9 late rice cultivars in the second year. The results showed that plant Cd concentrations varied among the cultivars, with high magnitudes of variation occurred in straw and grains. Five genotypes including LR-12, LR-17, LR-24, LR-25 and LR-26 were identified as low accumulators for the first year while LR-15 and LR-17 were identified as promising cultivars based on Cd concentration in the polished rice grains (<0.02 mg kg⁻¹ DW). In addition, these cultivars had favorable traits, including mineral nutrition and grain yield. Therefore, these genotypes should be considered for cultivation in slightly or moderately Cd contaminated soils.

Translocation and accumulation of cadmium and lead in the tissues of 39 rape cultivars grown in a polluted farmland

To investigate the differences in cadmium (Cd) and lead (Pb) uptake and translocation among rape cultivars and genotypes and select suitable rape cultivars for both safe production and soil remediation, a field experiment was carried out with 39 rape cultivars of three genotypes on a farmland polluted with Cd and Pb in eastern Hunan Province, China. The Cd and Pb contents in rape tissues were measured, and the amount of Cd and Pb removed was calculated. The results showed that Cd in rape plants accumulated mostly in stems, while Pb accumulated mostly in roots. The Cd accumulation in various rape tissues followed the sequence stem > root > husk > rapeseed, while the Pb accumulation followed the sequence root > stem > husk > rapeseed. The total Cd and Pb removed by planting rape were 4.50-23.6 g ha^-1 and 5.85-13.7 g ha^-1, respectively, and the Cd and Pb contents in rapeseeds were in the range 0.11-0.47 mg kg^-1 and 0.03-0.84 mg kg^-1, respectively. Only the Pb content in rapeseed of "Youyan 9" exceeded the limit of the maximum levels of contaminants in foods (GB2762-2017, Pb ≤ 0.2 mg kg^-1). In this experiment, the roots of most rape cultivars showed a greater capacity for Cd transport, while the stems showed a greater capacity for Pb transport. Except for the TF_stem-husk for Cd, there were no significant differences in the TFs and BAFs of 39 rape cultivars, and clear variations in Cd content were found in the stems of the three genotypes, while there was no significant difference in the Cd and Pb contents in the other tissues. In the farmland polluted with Cd and Pb, planting "Xiangzayou 695" and "Youyan 2013" not only reduced soil pollution but also allowed the production of safe rapeseed.

Identification of wheat (Triticum aestivum L.) genotypes for food safety on two different cadmium contaminated soils

Over the last decade, human population has been facing great challenges in ensuring appropriate supply of food free from cadmium (Cd) contamination. Selection of genetically low-Cd wheat (Triticum aestivum L.) genotypes, with a large biomass and high accumulation of Cd in straw but low-Cd concentration in grains, is an inventive approach of phytoremediation while keeping agricultural production in moderately contaminated soils. In this study, variations in Cd uptake and translocation among the 30 wheat genotypes in two different sites were investigated in field experiments. Significant differences in grain Cd concentration were observed between the two sites, with averaged values of 0.048 and 0.053 mg kg^-1 DW, respectively. Based on straw Cd accumulation, grain Cd concentration, and TF_rs, Bainong207 and Aikang58 for site A and Huaimai23 and Yannong21 for site B are promising candidates of low-Cd genotypes, which have considerable potential in achieving phytoremediation while keeping agricultural production on moderately or slightly Cd-polluted soil. The results indicate that it is possible to select the optimal low-Cd genotypes of wheat for different soil types by taking consideration of the effect of soil-wheat genotype interaction on grain Cd concentration.

The mobility of cadmium and lead in the soil-mulberry-silkworm system

Evaluation of the transportation of heavy metals in food chain has received a great deal of attention. In this study, the mobility of cadmium (Cd) and lead (Pb) in soil-mulberry-silkworm system was assessed. The results showed that bioconcentration factors for Cd and Pb were lower than 1 for all the three mulberry cultivars. Higher translocation factors (TFs) were observed in the levels from branch to leaf, larvae to excrement. The BCFs of Pb in root and silkworm excrement were higher than those in the other parts. Meanwhile, most of Cd accumulated from soils located in the root (48.00-54.40%) and only about 10% was in the leaf. But the Cd and Pb had significant effects on the ratios of cocoon shell with Yuesang 11 under different planting densities. For Yuesang 11 and Qiangsang 1, the Pb percentages were roots > branches > leaves > stems. The rates of ingestion (IR) and digestion (DR) were a little higher than those in the control at first and then decreased gradually with time. The IR reached the lowest values on 8th day while the DR arrived at the highest. Planting mulberry and raising silkworm could be a reasonable method for the utilization of heavy metal contaminated paddy soils.

Accumulation and distribution of cadmium and lead in 28 oilseed rape cultivars grown in a contaminated field

Heavy metal pollution in soils has become an important concern for human health. Therefore, it is vital to develop suitable remediation strategies for contaminated soils. Oilseed rape tolerates high concentrations of heavy metals and is a promising candidate for the phytoextraction of cadmium (Cd) and lead (Pb) from metal-contaminated soils. A field experiment was conducted to evaluate 28 oilseed rape cultivars including Brassica napus L. and Brassica juncea L. for their ability to accumulate Cd and Pb. These cultivars were grown in a field co-contaminated with Cd (0.78 mg kg^-1) and Pb (330 mg kg^-1). The results showed that concentrations in shoots ranged from 1.22 to 3.01 mg kg^-1 for Cd and from 10.8 to 29.5 mg kg^-1 for Pb. Cadmium and Pb accumulations in shoots could reach 83.4 and 799 μg plant^-1, respectively. The majority of translocation factors (TFs) for Cd (> 1.0) were higher than for Pb (≤ 1.0). However, concentrations of Cd and Pb in seeds were much lower, in the range of 0.04 to 0.21 mg kg^-1 and 0.04 to 0.51 mg kg^-1, respectively. The seed yields of oilseed rape varied from 1238 to 2904 kg ha^-1, with a mean value of 2289 kg ha^-1. Among the cultivars, three (OS-9, OS-12, and OS-15) were selected as Cd and Pb potential accumulators, with Cd accumulation in shoots being 2.74-3.70 times higher and Pb accumulation in shoots being 3.37-5.23 times higher as compared with the lowest accumulating cultivar. These selected cultivars (B. napus) have application potential for phytoextraction of Cd and Pb from polluted soils without stopping agricultural activities and accompanying food safety issues.

Foliar spray of TiO2 nanoparticles prevails over root application in reducing Cd accumulation and mitigating Cd-induced phytotoxicity in maize (Zea mays L.)

Cadmium (Cd) pollution is considered one of the global environmental issues due to its adverse effects on plant and human health. With the rapid development of nanotechnology and the practical application of engineered nanoparticles (ENPs) in agriculture, the mechanisms underlying the interactions between NPs and heavy metal on their uptake, accumulation, and phytotoxicity in crops are still not fully understood. Therefore, the impact of TiO₂ NPs (0, 100, 250 mg/L) and Cd (0, 50 μM) co-exposure on hydroponic maize (Zea mays L.) was determined under two exposure modes. Results showed that root co-exposure to TiO₂ NPs and 100 mg/L Cd significantly enhanced Cd uptake and produced greater phytotoxicity in maize than foliar exposure to TiO₂ NPs. Meanwhile, plant dry weight and chlorophyll content showed a reduction of 45.3% and 50.5%, respectively, when compared with single Cd treatment. In addition, the accumulation of Ti in shoots and roots increased by 1.61 and 4.29 times, respectively when root exposure to 250 mg/L TiO₂ NPs. By contrast, foliar exposure of TiO₂ NPs could markedly decrease shoot Cd contents from 15.2% to 17.8% and had a stronger influence on alleviating Cd-induced toxicity via increasing superoxide dismutase (SOD) and glutathione S-transferase (GST) activities and upregulating several metabolic pathways, including galactose metabolism and citrate cycle, alanine, aspartate and glutamate metabolism, as well as glycine, serine and threonine metabolism. This study provides a new strategy for the application of TiO₂ NPs in crop safety production in Cd contaminated soils.

Differences in root surface adsorption, root uptake, subcellular distribution, and chemical forms of Cd between low- and high-Cd-accumulating wheat cultivars

The differences in the mechanism of cadmium (Cd) accumulation in the grains of different wheat (Triticum aestivum L.) cultivars remain unclear. Thus, we conducted a hydroponic experiment in a greenhouse to compare root surface adsorption, root uptake, subcellular distribution, and chemical forms of Cd between low- and high-Cd-accumulating wheat cultivars at seedling stage, to improve our understanding of the differences between cultivars. The results showed that Cd adsorbed on the root surface was mainly in a complexed form, and the total amount of Cd on the Yaomai16 (YM, high-Cd-accumulating genotypes) root surface was higher (p < 0.05) than that on Xinmai9817 (XM, low-Cd-accumulating genotypes). A large amount of Cd ions adsorbed on root surface would cause plant damage and inhibit growth. Comparing the root-to-shoot translocation factors of Cd, the transfer coefficients of YM were 1.017, 1.446, 1.464, and 1.030 times higher than those of XM under 5, 10, 50, and 100 μmol L^-1 Cd treatments, respectively. The subcellular distribution of Cd under Cd exposure is mainly in the cell wall and soluble fraction. The proportions of Cd in YM shoot soluble fraction were higher than those in XM, which was the main detoxification mechanism limiting the activity of Cd and may be responsible for low Cd accumulation in grains, while the effects of the chemical forms of Cd on migration and detoxification were not found to be related to Cd accumulation in the kernels.

The zinc-regulated protein (ZIP) family genes and glutathione s-transferase (GST) family genes play roles in Cd resistance and accumulation of pak choi (Brassica campestris ssp. chinensis)

The molecular mechanisms of the differences among the Cd tolerance and accumulation of different pak choi cultivars are essential to further breed Cd-safe genotypes pak choi. In our research, via morphological comparison, qRT-PCR and yeast function complementary approaches, we explored the differences of Cd tolerance and capacity for Cd uptake in nine various pak choi varieties. Results showed that higher expressions of BcZIPs involved in Cd uptake in 'Kang Re605' may lead to its higher capacity for Cd accumulation. The lowest expressions of transporter gene in 'Wu Yueman' were consistent with its fewest ability to uptake Cd. Beyond that, the difference of resistance was very great among varieties. Meanwhile, the expressions of the BcGSTUs were differentially induced by Cd exposure in different pak choi varieties, and 'Kang Re605' performed the highest BcGSTUs expression overall. To verify the role of GSTUs played in Cd resistance of pak choi, four BcGSTUs, BcGSTU4, BcGSTU11, BcGSTU12 and BcGSTU22 in a high-Cd accumulation and tolerance variety 'Kang Re605' were cloned, quantitated and transferred to Cd-sensitive yeast mutant strain. And finally found that BcGSTU11 increased the Cd tolerance of yeast, which may associate with a high Cd resistance of 'Kang Re605'. Simultaneously, less BcGSTUs abundance in 'Shang Haiqing' may result in its weak tolerance to Cd. These findings will help us to comprehend the roles of BcZIPs and BcGSTUs in Cd absorption and detoxification as well as promote our understanding of the Cd-resistant and Cd-accumulated mechanisms in pak choi.

Effect and mechanism of commonly used four nitrogen fertilizers and three organic fertilizers on Solanum nigrum L. hyperaccumulating Cd

Solanum nigrum L. is a hyperaccumulator and shows very high phytoremediation potential for Cd-contaminated soil. Fertilizer addition to soil is an effective pathway to improve Cd hyperaccumulation. This article compared the strengthening roles of commonly used four nitrogen fertilizers with three organic fertilizers on S. nigrum hyperaccumulating Cd at the same total nitrogen level. The results showed that Cd concentrations in roots and shoots of S. nigrum were not affected by the addition of inorganic nitrogen like NH₄HCO₃, NH₄Cl, (NH₄)₂SO₄, and CH₄N₂O compared with the control without nitrogen addition. However, Cd concentrations in S. nigrum roots and shoots were significantly decreased (p < 0.05) when the organic nitrogen was added in the form of chicken manure, pig manure, and commercial organic fertilizer (by 15.6% and 15.1%, 30.1% and 23.6%, 20.3% and 16.8%, respectively). On the other hand, of all nitrogen treatments, the addition of (NH₄)₂SO₄ and CH₄N₂O to the soil enormously increased S. nigrum biomass, i.e., S. nigrum shoot biomass increased 2.0- and 2.1-fold compared with the control. Correspondingly, Cd loads in S. nigrum shoots were also the highest in former two treatments and amounted to 79.91 μg pot^-1 and 80.17 μg pot^-1, respectively. Compared with the control, the addition of three organic fertilizers significantly increased (p < 0.05) pH and decreased (p < 0.05) available Cd concentrations in the soil, which could be the main reasons for their negative effects on S. nigrum accumulating Cd. (NH₄)₂SO₄ and CH₄N₂O significantly increased S. nigrum biomasses and exerted no effects on the available soil Cd concentration, which made them more better fertilizers in practice. In general, the same fertilizer may show different effects on different hyperaccumulators. The selection of fertilizer should be decided in accordance with the specific conditions in the phytoremediation practice of contaminated soil.

Characterization of fava bean (Vicia faba L.) genotypes for phytoremediation of cadmium and lead co-contaminated soils coupled with agro-production

The identification of high yield genotypes that are capable of accumulating multiple heavy metals in the non-edible parts (roots and shoots), but not in the edible parts (seeds) and have desired nutritional value is necessary for accomplishing phytoremediation coupled with agro-production. In this study, 17 fava bean genotypes were screened in two different field conditions to examine their phytoremediation potential in terms of uptake and translocation of Cd and Pb. Ten genotypes, LBAO, JNJX, DCAN, QXCJ, QIKM, LXYC, YDL6, RBCD, QPID and ZHW6 were found as the best accumulators for Cd and Pb with permissible limit of metals in seeds. The concentration of plant nutrients were genotype and soil type dependent and there was a significant correlation between these two factors. Furthermore, the three genotypes DCAN, LBAO and LXYC showed best performance in alluvial soil type while QPID, RBCD and LXYC were the best in red soil type. Genotype LXYC was similar for both soil types and appeared to be the best fit for phytoremediation coupled with agro-production for slightly or moderately Cd and Pb co-contaminated soil. Therefore, fava bean LXYC genotype is suggested as a potential candidate for phytoremediation of Cd/Pb co-contaminated soils coupled with agro-production.

Cultivar-Dependent Accumulation and Translocation of Perfluorooctanesulfonate among Lettuce ( Lactuca sativa L.) Cultivars Grown on Perfluorooctanesulfonate-Contaminated Soil

Perfluorooctanesulfonate (PFOS) is a toxic and persistent organic pollutant that can be widely detected in agricultural soils. In this study, two lettuce cultivars with low PFOS accumulation were screened out to reduce the exposure of PFOS to the human body via vegetable consumption. The screened low-PFOS cultivars may help to ensure food safety, despite planting in highly PFOS-polluted soils (1.0 mg/kg), due to their high tolerance to PFOS and 4.4-5.7 times lower shoot PFOS concentration than the high-PFOS cultivars. Protein content and protein-mediated transpiration played key roles in regulating PFOS accumulation in the lettuce cultivars tested. Lower protein content, lower stomatal conductance, and lower transpiration rate resulted in low PFOS accumulation. This study reveals the mechanism of forming low-PFOS accumulation of lettuce cultivars at physiological and biochemical levels and lays a foundation for developing a cost-effective and safe approach to grow vegetables in PFOS-polluted soils.

Breeding Low-Cadmium Wheat: Progress and Perspectives

Farmland cadmium (Cd) contamination has adverse impacts on both wheat grain yield and people’s well-being through food consumption. Safe farming using low-Cd cultivars has been proposed as a promising approach to address the farmland Cd pollution problem. To date, several dozen low-Cd wheat cultivars have been screened worldwide based on a Cd inhibition test, representing candidates for wheat Cd minimization. Unfortunately, the breeding of low-Cd wheat cultivars with desired traits or enhanced Cd exclusion has not been extensively explored. Moreover, the wheat Cd inhibition test for variety screening and conventional breeding is expensive and time-consuming. As an alternative, low-Cd wheat cultivars that were developed with molecular genetics and breeding approaches can be promising, typically by the association of marker-assisted selection (MAS) with conventional breeding practices. In this review, we provide a synthetics view of the background and knowledge basis for the breeding of low-Cd wheat cultivars.

Ornamental hyperaccumulator Mirabilis jalapa L. phytoremediating combine contaminated soil enhanced by some chelators and surfactants

Mirabilis jalapa L. is an ornamental plant of the composite family, which was found hyperaccumulating Cd. Due to its larger biomass, developed root system, root exudation, and microbial interactions, certain organic pollutants in its rhizosphere can be effectively degraded. Thus, M. jalapacan be used to co-remediate heavy metal and organic pollutant co-contaminated soil. The aim of this paper is to explore the remediation capacity of M. jalapa for Cd-PAHs co-contaminated soil in the presence of five chelators or surfactants. The concentrations of Cd and PAHs in collected soil samples were 0.85 mg kg^-1 Cd and 1.138 mg kg^-1 PAHs (16 kinds of priority control polycyclic aromatic hydrocarbons by USEPA). The chelators or surfactants of EDTA, EGTA, CA, TW80, and SA were respectively spiked to the pots according to the experiment design at 1 month before the plant harvested. The results showed that the capacity of Cd in shoot of M. jalapa was 7.99 μg pot^-1 without any addition (CK4, M. jalapa in original soil without amendment). However, Cd capacity in shoot of M. jalapa was increased (p < 0.05) by 31.7%, 181.7%, and 107.4% in treatment of R_EGTA, R_CA and R_{EGTA + SA}, respectively. As for the degradation of PAHs in soil, there was no significant decrease (p < 0.05) in the treatment of CK2 (original soil spiked with 0.9 SA without M. jalapa), CK3 (original soil spiked with 0.3 TW80 without M. jalapa), and CK4 compared to the control CK1 (original soil without M. jalapa and amendment). When amendments were added to soils with M. jalapa,the PAHs concentrations in soils significantly decreased (p < 0.05) by 21.7%, 23.8%, 27.0%, 19.8%, 21.8%, 31.2%, and 25.5% for the treatment of R_{EDTA + SA}, R_{EDTA + T80}, R_{EGTA + SA}, R_{EGTA + T80}, R_{CA + T80}, R_{SA + T80 + EDTA}, and R_{SA + T80 + CA}, respectively. Basically, Cd capacity in shoot of M. jalapa was improved by chelators. PAHs degradation was caused by the existence of surfactants in rhizosphere of M. jalapa. But the roles of different chelators or surfactants were quite distinct. In short, the Cd capacity in the shoot and PAHs degradation in the rhizosphere of M. jalapa in the treatment of R_{EGTA + SA} were all significantly increased (p < 0.05), which was more practical for M. jalapa phytoremediating Cd-PAHs co-contaminated soil.

Low-Cd tomato cultivars (Solanum lycopersicum L.) screened in non-saline soils also accumulated low Cd, Zn, and Cu in heavy metal-polluted saline soils

Many reclaimed tidal flat soils feature high salinity and heavy metal (HM) accumulation. Consumption of vegetables cultivated in this type of cropland may cause health risks. Low-Cd tomato cultivars (Solanum lycopersicum L.) were identified in non-saline soil in our previous studies (Tan et al. 2014). However, further research should determine whether these low-Cd cultivars will maintain in the repeatability and stability in saline soil and whether they have low accumulation abilities for accompanying metals (such as Zn and Cu). A soil-pot trial was implemented to measure Cd, Zn, and Cu concentrations in low- and high-Cd cultivars of both common and cherry-type tomatoes grown on HM-polluted reclaimed tidal flat saline soil. Then, cultivar differences in dissolution of Cd, Zn, and Cu in soil and their uptake and redistribution in plants were analyzed. Results showed that the cherry type accumulated more Cd, Zn, and Cu than the common type. Low-Cd cultivars of both types in saline soil accumulated low concentrations of Cd, Zn, and Cu in fruits. Low HM accumulation in fruits is partly attributed to a low root/shoot (R/S) biomass ratio. Low amounts of soil HMs were dissolved because of the low level of rhizosphere organic compounds, which possibly decreased HM uptake by the roots. Low-Cd cultivars of both tomato types had a higher ability to retain HMs in the roots than their high-Cd cultivars. These findings may provide a scientific guidance for the safe cultivation of HM-polluted saline soils.

Low-molecular-weight organic acids correlate with cultivar variation in ciprofloxacin accumulation in Brassica parachinensis L

To understand the mechanism controlling cultivar differences in the accumulation of ciprofloxacin (CIP) in Chinese flowering cabbage (Brassica parachinensis L.), low-molecular-weight organic acids (LMWOAs) secreted from the roots of high- and low-CIP cultivars (Sijiu and Cutai, respectively) and their effects on the bioavailability of CIP in soil were investigated. Significant differences in the content of LMWOAs (especially maleic acid) between the two cultivars played a key role in the variation in CIP accumulation. Based on the Freundlich sorption coefficient (K_f) and distribution coefficient (K_d), the presence of LMWOAs reduced the CIP sorption onto soil particles, and higher concentrations of LMWOAs led to less CIP sorption onto soil. On the other hand, LMWOAs enhanced CIP desorption by lowering the solution pH, which changed the surface charge of soil particles and the degree of CIP ionization. LMWOAs promoted CIP desorption from soil by breaking cation bridges and dissolving metal cations, particularly Cu²⁺. These results implied that the LMWOAs (mainly maleic acid) secreted from Sijiu inhibited CIP sorption onto soil and improved CIP desorption from soil to a greater extent than those secreted from Cutai, resulting in higher bioavailability of CIP and more uptake and accumulation of CIP in the former.

Cross-Species Extrapolation of Models for Predicting Lead Transfer from Soil to Wheat Grain

The transfer of Pb from the soil to crops is a serious food hygiene security problem in China because of industrial, agricultural, and historical contamination. In this study, the characteristics of exogenous Pb transfer from 17 Chinese soils to a popular wheat variety (Xiaoyan 22) were investigated. In addition, bioaccumulation prediction models of Pb in grain were obtained based on soil properties. The results of the analysis showed that pH and OC were the most important factors contributing to Pb uptake by wheat grain. Using a cross-species extrapolation approach, the Pb uptake prediction models for cultivar Xiaoyan 22 in different soil Pb levels were satisfactorily applied to six additional non-modeled wheat varieties to develop a prediction model for each variety. Normalization of the bioaccumulation factor (BAF) to specific soil physico-chemistry is essential, because doing so could significantly reduce the intra-species variation of different wheat cultivars in predicted Pb transfer and eliminate the influence of soil properties on ecotoxicity parameters for organisms of interest. Finally, the prediction models were successfully verified against published data (including other wheat varieties and crops) and used to evaluate the ecological risk of Pb for wheat in contaminated agricultural soils.

Cadmium accumulation characteristics and removal potentials of high cadmium accumulating rice line grown in cadmium-contaminated soils

Phytoextraction is a promising technique to remove cadmium (Cd) from contaminated soils. In this research, the two different Cd accumulation rice lines of Lu527-8 (the high Cd accumulating rice line) and Lu527-4 (the normal rice line) were grown in soils with different Cd treatments (0, 5, 10, and 20 mg kg(-1) soil) to evaluate Cd accumulation characteristics and Cd removal potentials. When the concentration of Cd in soil increased, Lu527-8 showed less symptoms of phytotoxicity when compared to Lu527-4. Furthermore, Lu527-8 demonstrated greater shoot Cd accumulation (321.17-964.95 mg plant(-1)) than Lu527-4 (50.37-201.66 μg plant(-1)) at the jointing and filling stages. The soil available Cd content of Lu527-8 significantly decreased by 26.92-38.97 and 27.77-63.44 % at the jointing and filling stages, respectively. Meanwhile, the total Cd content in soil also reduced by 11.64-46.75 and 21.41-54.11 % at jointing and filling stages, respectively. When the Cd concentration in soil was 20 mg kg(-1), the Cd extraction rate in shoots of Lu527-8 reached 2.12 and 2.85 % which increased 10.60 and 6.48 times compared with that of Lu527-4 at the jointing and filling stages, respectively. In conclusion, this study demonstrates that Lu527-8 shows great abilities of Cd accumulation and Cd removal potential from contaminated soils with different Cd treatments and it is a promising species for phytoextraction of Cd-contaminated soils.

Cadmium minimization in wheat: A critical review

Cadmium (Cd) accumulation in wheat (Triticum aestivum L.) and its subsequent transfer to food chain is a major environmental issue worldwide. Understanding wheat response to Cd stress and its management for aiming to reduce Cd uptake and accumulation in wheat may help to improve wheat growth and grain quality. This paper reviewed the toxic effects, tolerance mechanisms, and management of Cd stress in wheat. It was concluded that Cd decreased germination, growth, mineral nutrients, photosynthesis and grain yield of wheat and plant response to Cd toxicity varies with cultivars, growth conditions and duration of stress applied. Cadmium caused oxidative stress and genotoxicity in wheat plants. Stimulation of antioxidant defense system, osmoregulation, ion homeostasis and over production of signalling molecules are important adaptive strategies of wheat under Cd stress. Exogenous application of plant growth regulators, inorganic amendments, proper fertilization, silicon, and organic, manures and biochar, amendments are commonly used for the reduction of Cd uptake in wheat. Selection of low Cd-accumulating wheat cultivars, crop rotation, soil type, and exogenous application of microbes are among the other agronomic practices successfully employed in reducing Cd uptake by wheat. These management practices could enhance wheat tolerance to Cd stress and reduce the transfer of Cd to the food chain. However, their long-term sustainability in reducing Cd uptake by wheat needs further assessment.