Shoot Cd Concentrations Research Articles

Organic acids in conjunction with various oilseed sunflower cultivars promote Cd phytoextraction through regulating micro-environment in root zone

Exogenous chelates in conjunction with phytoextraction have been demonstrated as a prominent potential for remediating Cd-contaminated soils. Among bath chelates, low molecular-weight organic acids have the advantages of smaller impact on plant growth and lower negative effects on soil environment. In this research, oilseed sunflowers were selected as the main extraction plants, and the Cd phytoextraction effects of different cultivars, varies organic acid types and concentrations combinations were systematically examined. Results showed that adding exogenous organic acids improved biomass of all issues, but the increase varied with the cultivar. For both cultivars, their biomass increase with acid application concavely, with the acid application rate at which the biomass peaked differed between the two cultivars. Adding exogenous acids boosted Cd concentration in roots and shoots in general, but it reduced the Cd content in seeds as well as the rhizosphere and bulk soil. In addition to its impact on Cd, application of organic acids also reduced nutrient and salinity in the rhizosphere and promoted root uptake of nutrients as a result. Cd content plant an soil was closely related to nutrients in soil and plant. The organic acids reduced soil Cd and nutrients in soil proximal to the roots. It was also found that adding acids reduced Cd content in the top 0–10 cm soil but increased the Cd content in the 10–30 cm soil, alluding a potential leaching. Therefore, adding organic acids to improve phytoremediation of Cd needs to proceed with care.

Knockout of OsNRAMP5 enhances rice tolerance to cadmium toxicity in response to varying external cadmium concentrations via distinct mechanisms

OsNRAMP5 is a transporter responsible for cadmium (Cd) and manganese (Mn) uptake and root-to-shoot translocation of Mn in rice plants. Knockout of OsNRAMP5 is regarded as an effective approach to minimize Cd uptake and accumulation in rice. It is vital to evaluate the effects of knocking out OsNRAMP5 on Cd and Mn accumulation, as well as Cd tolerance of rice plants in response to varying environmental Cd concentrations, and to uncover the underlying mechanism, which until now, has remained largely unexplored. This study showed that knockout of OsNRAMP5 decreased Cd uptake, but simultaneously facilitated Cd translocation from roots to shoots. The effect of OsNRAMP5 knockout on reducing root Cd uptake weakened, however its effect on improving root-to-shoot Cd translocation was constant with increasing environmental Cd concentrations. As a result, its mutation dramatically reduced Cd accumulation in shoots under low and moderate Cd stress, but inversely increased that under high Cd conditions. Interestingly, Cd tolerance of its knockout mutants was persistently enhanced, irrespective of lower or higher Cd concentrations in shoots, compared with that of wild-type plants. Knockout of OsNRAMP5 mitigated Cd toxicity by dramatically diminishing Cd uptake at low or moderate external Cd concentrations. Remarkably, its knockout effectively complemented deficient mineral nutrients in shoots, thereby indirectly enhancing rice tolerance to severe Cd stress. Additionally, its mutation conferred preferential delivery of Mn to young leaves and grains. These results have important implications for the application of the OsNRAMP5 mutation in mitigating Cd toxicity and lowering the risk of excessive Cd accumulation in rice grains.

Boron supplying alters cadmium retention in root cell walls and glutathione content in Capsicum annuum

Large areas of farmland in southern China are facing environmental problems such as cadmium (Cd) contamination and boron (B) deficiency. The aim of this study was to investigate the biochemical and molecular mechanisms underlying the reduction in Cd accumulation in hot pepper (Capsicum annuum) by B application. A hydroponic experiment was conducted to compare the subcellular distribution of Cd, transcriptome profile, degree of pectin methylation, and glutathione (GSH) synthesis in the roots of hot pepper under different B and Cd conditions. Boron supply promoted root cell wall biosynthesis and pectin demethylation by upregulating related genes and increasing cell wall Cd concentration by 28%. In addition, with the application of B, the proportion of Cd in root cell walls increased from 27% to 37%. Boron supplementation upregulated sulfur metabolism-related genes but decreased cysteine and GSH contents in the roots. As a result, shoot Cd concentration decreased by 27% due to the decrease in GSH, a critical long-distance transport carrier of Cd. Consequently, B supply could reduce the uptake, translocation, and accumulation of Cd in hot pepper by retaining Cd in the root cell walls and decreasing GSH content.

Water-soluble chitosan and phytoremediation efficiency of two Brassica napus L. cultivars in cadmium-contaminated farmland soils

Pot and field trials were conducted to investigate Cd uptake and phytoremediation efficiency of two Brassica napus cultivars (QY-1 and SYH) with applied water-soluble chitosan (WSC, Pot: 0, 2% and 4%; Field: 0 and 10 g·m−2) grown in Cd-contaminated soils. The results from the pot and field trials generally showed that WSC treatments significantly increased Cd concentrations in shoot and root tissues by 33.77–159.71% (except for SYH/JY) and 7.42–168.71% of two B. napus cultivars compared with the control (p < 0.05). The uptake of Cd by shoots of SYH was obviously higher than by shoots of QY-1 treated with WSC under pot and field conditions, which was 1.54–2.22 times than that of QY-1 (p < 0.05). The results indicated that 2% WSC treatment significantly increased the water-soluble and acid extractable Cd in rhizosphere soils of both B. napus cultivars. Furthermore, Cd concentrations in the oils of two B. napus cultivars with applied WSC (10 g·m−2) grown under field conditions were not significantly different from commercial rapeseed oils. Rapeseed oil of B. napus is not only an edible oil with high nutritional value, but it can also be converted into biomass diesel that can be used as a substitute for petroleum diesel.

Cadmium Accumulation Characteristics of Different Heat Varieties Under Cadmium Stress

In order to provide technical support for the safe utilization of heavy metal-polluted farmland, we screened wheat varieties with a low accumulation of Cd in grain via a pot experiment. For this purpose, we respectively investigated the enrichment and transport characteristics of Cd in various plant parts of 119 wheat varieties under the conditions of 1.5 mg·kg-1 (low content) and 4.0 mg·kg-1 (high content) Cd-contaminated soil and explored the correlation between the Cd content of different organs of wheat and the relationship between Cd content in soil and the uptake of Cd by wheat. The results showed that:① there were significant differences in the ability to accumulate and transport Cd in roots, stems, leaves, and grains of tested wheat varieties (P<0.05). Under the condition of low Cd content, the Cd enrichment ability of each part of the wheat plant was as follows:leaf>stem ≈root>grain; under high-content stress conditions, the Cd enrichment ability of each part of the wheat plant was:leaf>root>stem>grain; under different content conditions, the Cd transport ability of each part of the wheat plant was:leaf>stem>grain. Cd content in the wheat shoot was positively correlated with total Cd content and ion-exchangeable Cd content in soil (P<0.01) and was closely related to strong transpiration under the pot experiment. ② The correlation coefficient r of BCFCd of wheat roots, stems, leaves, and grain was -0.267 to -0.645, showing a very significant negative correlation (P<0.01), indicating that with the increase in soil Cd content, the migration and accumulation degree of Cd in wheat plant organs showed a downward trend. Moreover, the negative correlation between BCFCd and soil Cd content in stems was significantly higher than that in roots, leaves, and grains, indicating that the enrichment of Cd in wheat plants largely depended on the accumulation and transportation of stems. ③ The correlation coefficient r of Cd content between the root and stem, root and leaf, root and grain, stem and leaf, stem and grain, and leaf and grain in low-and high-content groups was 0.450-0.763, showing a very significant positive correlation (P<0.01), indicating that there was a close transport relationship among the wheat organs, and the degree of translocation from the root to stem and stem to leaf was higher than that from the stem to grain and leaf to grain. ④ Using cluster analysis and enrichment and translocation coefficient sequencing, this study screened 16 and 11 wheat varieties with low Cd accumulation under the soil cadmium content of 1.5 mg·kg-1and 4.0 mg·kg-1, respectively. Among them, Luohan 7 could be used as the optimal wheat variety with low Cd accumulation under the conditions of low-, medium-, and high-Cd content.

Effects of aqueous Moringa oleifera leaf extract on growth performance and accumulation of cadmium in a Thai jasmine rice-Khao Dawk Mali 105 variety.

The contamination of paddy fields and rice grains by cadmium (Cd) adversely affects human health. Thus, many approaches have been proposed to reduce the accumulation of Cd in rice. Here, we investigate the potential of aqueous Moringa oleifera leaf extract (AMOLE) in decreasing uptake and toxicity of Cd in a popular Thai jasmine rice variety, Khao Dawk Mali 105 (KDML105). Plants were grown in Petri dishes, a hydroponic system, and a pot system under different concentrations of Cd, in the presence and absence of AMOLE. In Petri dishes, Cd reduced the percentage of germination by 79%, but the treatment with 0.5mgmL-1 AMOLE significantly increased the germination percentage. Moreover, AMOLE significantly decreased Cd accumulation in rice seedlings by 97%. In the hydroponics system, 0.5mgmL-1 AMOLE decreased Cd content in shoots by 48%. Although no significant physiological changes in response to Cd treatments were observed in the pot system, a large amount of Cd was accumulated in rice roots. The AMOLE treatments significantly reduced Cd accumulation in rice shoots and decreased Cd content in milled grain by half compared to those without AMOLE treatment. We conclude that AMOLE reduced Cd toxicity, enhanced seedling growth, and reduced Cd accumulation in rice grains.

A new technique for reducing accumulation, transport, and toxicity of heavy metals in wheat (Triticum aestivum L.) by bio-filtration of river wastewater

The occurrence of contaminants such as heavy metals in an aqueous environment has become a global concern. In the present study, a bio-filter was designed to eliminate heavy metals from river wastewater contaminated with industrial effluents. Moreover, we analyzed simple tap water, bio-filtered water, and unfiltered river wastewater and measured the concentrations of different heavy metals in the samples, such as cadmium (Cd), nickel (Ni), lead (Pb), and copper (Cu). The current experiment explored irrigation effects of three water regimes (tap water, bio-filtered water, and wastewater) on two wheat (Triticum aestivum L.) varieties (NARC-2009 and NARC-2011). Results of the present study indicated that wastewater negatively influenced the growth parameters and photosynthetic contents along with a significant increase in oxidative damage in terms of electrolyte leakage (EL) (50 and 61%), hydrogen peroxide (H2O2) (52 and 61 μmol/g), and malondialdehyde (MDA) (16 and 17.7 μmol/g) contents in NARC-2009 and NARC-2011 respectively. However, bio-filtered water positively regulated the growth profile, activities of antioxidants such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), total soluble sugars, amino acids, total protein, and proline contents in wheat as compared with untreated wastewater. In addition, bio-filtered water had significant impacts on the reduction of Cd, Ni, Pb, and Cu concentrations in roots, shoots, and grains of both wheat varieties as compared to wastewater. The concentrations (mg/kg) of Cd (15 and 18), Ni (35 and 57), Pb (5 and 7), and Cu (69 and 72) in roots, Cd (5 and 6), Ni (24 and 43), Pb (3 and 4), and Cu (16 and 19) in shoots, and Cd (0.7 and 1.0), Ni (11 and 26), Pb (2 and 3), and Cu (1.6 and 1.5) in grains of NARC-2009 and NARC-2011 were found under river wastewater treatment. Overall, wastewater treatment through bio-filtration process is an effective strategy for the reduction of toxic elements in bio-filtered water and their accumulation by plants.

Effect of rice residue biochar on bioavailability of cadmium to indian mustard under combined lead and cadmium spiking in a loamy sand soil

A screen house experiment was conducted to study the effect of rice residue biochar (0, 0.5, 1 and 2% w/w) on the bioavailability and accumulation of Cd by Indian mustard (Brassica juncea) in a loamy sand soil spiked with three levels each of Cd (0, 10 & 25 mg Kg−1 soil) and Pb (0, 25 & 50 mg Kg−1 soil) in all possible combinations. Immobilization of Cd by rice residue biochar was assessed by DTPA-extractable Cd in soil and Cd concentrations in shoots of Indian mustard. Mean DTPA-Cd after harvest of crop decreased with increasing rates of applied rice residue biochar. Addition of biochar at its highest level of 2% decreased the mean DTPA-Cd in soil and its concentrations in plant by 59% and 36% over control, respectively. Biochar addition increased dry matter yield (DMY) of Indian mustard and a maximum increase of 18% over control was observed at a level of 1%. However, DMY decreased by 19% with addition of biochar at 2%. It was concluded that rice residue biochar can be used as an amendment for amelioration of Cd contaminated sites as its concentration in plants decreased with increasing levels of biochar application.

Effects of Auxin at Different Concentrations on the Growth, Root Morphology and Cadmium Uptake of Maize (Zea mays L.)

Indoleacetic acid (IAA) is an important regulator that plays a crucial role in plant growth and responses to abiotic stresses. In the present study, a sand cultivation experiment was carried out to investigate the effects of IAA at different concentrations (0, 0.01, 0.1, 0.5, 1, and 2.5 mmol/L) on maize growth, root morphology, mineral elements (Ca, Mg) and Cd uptake under 20 mg/kg Cd stress. The results showed that 0.01 mmol/L is the optimal IAA concentration for enhancing the Cd tolerance of maize. Compared with the control treatment, 0.01 mmol/L IAA promoted maize growth, with significant increases in the height, shoot and root biomass by 34.6%, 25.0% and 16.3%; altered the root morphology, with increases in root length, root tip number, and root tip density by 8.9%, 31.4% and 20.7%, respectively; and enhanced the mineral element uptake of maize, resulting in signifi- cant increases in the Ca content in shoots and roots by 640.6% and 1036.4% and in the Mg content in shoots by 205.8%, respectively. In addition, 0.01 mmol/L IAA decreased the Cd content and uptake in the shoots by 51.9% and 39.6%, respectively. Furthermore, the Cd content and uptake exhibited a significant negative correlation with Ca content in roots and a significantly positive correlation with root morphology, and the Cd content in shoots was significantly and negatively correlated with root tip number. Thus, 0.01 mmol/L IAA was effective in enhancing the Cd tolerance and plant growth of maize.

Mechanisms of Stress Alleviation after Lime and Biochar Applications for Brassica napus L. in Cadmium-Contaminated Soil

Lime and biochar amendments are widely used to immobilize cadmium (Cd) in agricultural soils and to ensure food security. However, the effects of these two soil amendments on the mechanisms of Cd stress alleviation in crops are unclear. Therefore, the effects of lime and biochar applications on Cd uptake, transport, subcellular distribution, antioxidant system, N metabolism, and related factors were examined in a soil- Brassica napus L. ( B. napus) system. We found that lime application significantly increased the root Cd content by 41.5% but decreased Cd TF and shoot Cd by 81.0% and 74.3%, respectively, whereas biochar amendment decreased root and shoot Cd contents by 67.6% and 34.3%, respectively, but increased Cd TF by 104.1%. Lime treatment immobilized Cd in the cell wall of the root to reduce Cd transport, but biochar treatment increased the soluble fraction of Cd in root cells to improve the migration capacity of Cd. The significant negative relationship between the soil exchangeable Cd and Ca and the positive relationships between Cd and Ca both in shoot and root indicated that the Ca mediated Cd transport from soil to B. napus after lime and biochar applications. Additionally, lime amendment increased Cd proportion in the root cell walls to immobilize Cd, but biochar amendment increased Cd proportion in the soluble fraction to enhance Cd migration. Furthermore, biochar application significantly increased SOD, CAT, and POD by 17.5%, 95.4%, and 26.6%, whereas lime amendment only significantly enhanced CAT by 51.0%. Besides, both of biochar and lime applications increased shoot N content and GDH activity, but only the shoot NO3 - content and nitrate reductase under biochar treatment were significantly altered. Overall, these findings suggested that lime is more efficient in reducing the transport of Cd from underground to aboveground and in improving Cd tolerance, whereas biochar tends to improve the antioxidant capacity and facilitate N metabolism. These results will provide significant strategies for selecting appropriate amendments to ensure the crops safety.

Interactive Effects of Soil Lead and Cadmium on Dry Matter Yield and Metal Content of Indian Mustard (Brassica juncea (L.) Czern)

Lead (Pb) and cadmium (Cd) are known to influence each other’s uptake by plants when they coexist in the soil in significant amounts. This influence can be useful if it is antagonistic but may be detrimental if synergistic. In a screenhouse, interactive effects of soil Cd (0, 10, 25, 50 and 100 mg kg-1) and Pb (0, 25, 50, 100 and 200 mg kg-1) were studied on dry matter yield (DMY), Cd and Pb content in Indian mustard (Brassica juncea (L.) Czern) grown for 60 days in a loamy sand soil. The DMY was recorded and plants were analyzed for total Cd and Pb contents. In equilibrated soil there was significant increase in the mean DTPA-Cd and DTPA-Pb with increase in levels of their respective spiking. The content of DTPA-Cd increased significantly where different combinations of Cd and Pb were applied whereas, DTPA-Pb significantly decreased when Pb was applied in combination with Cd. At Cd+200 mg Pb kg-1 soil and Pb+100 mg Cd kg-1 soil, the mean shoot DMY of Indian mustard decreased by 55.8 and 57.7 per cent, respectively as compared to control. The mean shoot Cd content of Indian mustard increased by 9.9 per cent with application of Cd+200 mg Pb kg-1 soil while the mean Pb content decreased by 10.4 per cent with application of Pb+100 mg Cd kg-1 soil as compared to their respective single treatments. The post-harvest soil DTPA-Cd and Pb decreased as compared to their pre-sowing contents but considerable residual contents still remained in soil. An additive adverse effect of the metals on DMY, Pb and Cd content of the crop was observed.

Effect of different concentration of exogenous proline applications on cadmium accumulation and mineral nutrition (K, Mg, Na and Ca) of common wheat (Triticum aestivum)

The present study investigates the role of exogenously applied proline on cadmium (Cd) accumulation in common wheat (Triticum aestivum L.) tissues. Seedlings were subjected for 4 days to different exogenous proline levels (0, 1, 10, and 20 mM) under Cd stress (1000 μM of Cd(NO3)2·4H2O). The concentration of Cd, Ca, Mg, and K was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). Exogenous proline caused significant changes in the growth of wheat cultivar under Cd stress. In addition, the growth of wheat under Cd stress increased by the addition of 1 mM proline. According to the analysis results, Cd accumulation in wheat seedlings showed that the increment of exogenous proline treatments (except Cd+Pr1) in the water resulted in a decrease of Cd content in roots and shoots. Under Cd treatment (not applied proline), the contents of Ca, K, Mg, and Na decreased in roots by 22.1, 70, 17.7, and 10.1% and in shoots by 29.6, 32.2, 19.1, and 5.3%, respectively. Nevertheless, K content decreased in roots and shoots under all Cd and exogenous proline treatments.

Response of Prosopis farcta to gradually increased soil copper and cadmium levels based on an integrated investigation

The impact of gradually increased soil levels of copper (Cu) and cadmium (Cd) on the medicinal plant, Prosopis farcta, irrigated with metal-enriched water was determined. Plants were treated with 2.54, 5.08, 10.16, and 20.32 µg mL−1 for Cu2+ and 6.13, 12.26, 24.52, and 49 µg mL−1 for Cd2+. The rate of phytoremediation was measured by bioconcentration factor (BCF) and the relative bioconcentration factor (RBCF). The movement of metal ions from roots to shoots was calculated as the Translocation Factor (TF). The exposure of plants to Cd or Cu decreased plant growth and increased Cd and Cu concentration in their shoots and roots. The weight of both shoots and roots decreased linearly with the increase of Cu and Cd contents in roots and shoots. Cd was more toxic than Cu as expected. The water content of shoots and roots decreased linearly as heavy metal levels increased. Prosopis farcta can take up Cu and Cd in both Cu- and Cd-contaminated soils but was more capable for transporting Cd from roots to shoots rather than Cu although more Cu is taken up by roots. Prosopis farcta is a natural accumulator of Cu and Cd and can be used in phytoremediation. CONCISE NOVEL ASPECTS OF THIS STUDY This is the first report to show that the medicinal plant Prosopis farcta is an accumulator for Cu and Cd. This was determined by gradual addition of the metals to the soil via irrigation by heavy metal-polluted water which can provide an opportunity for the plant to develop a metal-resistance mechanism. Choosing suitable plant species for heavy metal accumulation is a critical step for successful phytoremediation of heavy metal pollutants. CORE IDEAS Prosopis farcta is of interest as a medicinal plant. P. farcta can take up Cu and Cd in both Cu- and Cd-contaminated soils. P. farcta transports more Cd from roots to shoots but more Cu is taken up.

Root Morphology and Anatomy Affect Cadmium Translocation and Accumulation in Rice

Paddy fields contaminated with cadmium (Cd) present decreased grain yield and produce Cd-contaminated grains. Screening for low-Cd-accumulating cultivars is a useful method to reduce the amount of Cd in the grains. The present study aimed to examine the roles of the root morphology and anatomy in Cd translocation and accumulation in rice plants. Twenty-two rice cultivars were used in the first experiment, after which two cultivars [Zixiangnuo (ZXN) and Jinyou T36 (JYT36)] were selected and used in subsequent experiments under hydroponic conditions. The results showed that there were significant differences in Cd concentrations in the shoots (ranging from 4 to 100mg/kg) and the Cd translocation rates (shoot/root) (from 7% to 102%) among the 22 cultivars, and the shoot Cd concentration was significantly correlated with the Cd translocation rate of the 22 cultivars under 0.1mg/L Cd treatment. Compared with cultivar ZXN, JYT36 had greater root Cd uptake and accumulation but lower shoot Cd accumulation and Cd translocation rate. The number of root tips per surface area of cultivar ZXN was greater than that of JYT36, while the average root diameter was lower than that of JYT36. Compared with ZXN, JYT36 had stronger apoplastic barriers, and the Casparian bands and suberin lamellae in the root endodermis and exodermis were closer to the root apex in both the control and Cd treatments, especially for suberin lamellae in the root exodermis with Cd treatments, with a difference of 25mm. The results also showed that, compared with ZXN, JYT36 had greater percentages of Cd bound in cell walls and intracellular Cd but lower Cd concentrations in the apoplastic fluid under the Cd treatment. The results suggested that Cd translocation, rather than root Cd uptake, is a key process that determines Cd accumulation in the rice shoots. The root morphological and anatomical characteristics evidently affect Cd accumulation in the shoots by inhibiting Cd translocation, especially via the apoplastic pathway. It was possible to pre-screen low-Cd-accumulating rice cultivars on the basis of their root morphology, anatomical characteristics and Cd translocation rate at the seedling stage.

The role of silicon in cadmium alleviation by rice root cell wall retention and vacuole compartmentalization under different durations of Cd exposure

Silicon (Si) plays a pivotal role in mitigating phytotoxicity caused by cadmium (Cd). However, few former reports focused on the internal mechanism how Si assisted in alleviating Cd stress in rice under different durations of Cd exposure. Herein, the effects of Si on subcellular distribution of Cd in rice roots under short-term (12 h) and long-term (20 d) Cd exposure were explored. Results showed that Si decreased shoot Cd concentration but had little impact on root Cd levels. Under short-term Cd exposure, subcellular distribution analysis showed that Si increased the ratio of Cd in root cell wall by 23.2~24.0%, and decreased the ratio of Cd in root soluble fraction by 20.6~21.5%. This suggested that Si supply improved root retention of Cd by fixing it on the cell wall and thus restricted intracellular transportation of Cd. Further analysis unraveled that pectin (especially ionic-soluble pectin) of the cell wall was the main binding component, and Si supply induced more Cd accumulation in covalent-soluble pectin and hemicellulose. Moreover, the overexpression of germin-like proteins (GLPs) proved the role of cell wall in moderating Cd toxicity. Under long-term Cd exposure, Si promoted phytochelatin 2 (PC2) and phytochelatin 3 (PC3) synthesis in cytosol, at the same time, Si down-regulated the expression of the Cd efflux-related protein multidrug resistance-associated protein-like ATP-binding cassette transporters (MRP-like ABC transporters) and limited Cd transportation from vacuole to cytosol. Taken together, Si rather predominates in limiting Cd translocation by the cell wall of root under short-term Cd exposure and promoting vacuole compartmentalization to mitigate the Cd toxicity under long-term exposure, instead of reducing the absorption of Cd in rice roots, thereby decreasing Cd delivery into shoots.

Transcriptome analysis and physiological indicators reveal the role of sulfur in cadmium accumulation and transportation in water spinach (Ipomoea aquatica Forsk.)

Cadmium (Cd) contamination of croplands has become a threat to crop food safety and human health. In this study, we investigated the effect of sulfur on the growth of water spinach under Cd stress and the amount of Cd accumulation by increasing the soil sulfate content. We found that the biomass of water spinach significantly increased after the application of sulfur while the shoot Cd concentration was considerably reduced (by 31%). The results revealed that sulfur could promote the expression of PME and LAC genes, accompanied by an increase in PME activity and lignin content. Also, the cell wall Cd content of water spinach roots was significantly increased under sulfur treatment. This finding suggests that sulfur could enhance the adsorption capacity of Cd by promoting the generation of cell wall components, thereby inhibiting the transportation of Cd via the apoplastic pathway. In addition, the higher expression of Nramp5 under the Cd1S0 (concentration of Cd and sulfur are 2.58 and 101.31 mg/kg respectively) treatment led to increased Cd uptake. The CAX3 and ABC transporters and GST were expressed at higher levels along with a higher cysteine content and GSH/GSSR value under Cd1S1 (concentration of Cd and sulfur are 2.60 and 198.36 mg/kg respectively) treatment, which contribute to the Cd detoxification and promotion of Cd compartmentalization in root vacuoles, thereby reducing the translocation of Cd to the shoot via the symplastic pathway.

Screening of Foliar Barrier Agents and Reduces the Absorption and Transport of Cd in Wheat.

Different foliar barrier agents (FBA) were used by foliar spraying in first season field and pot experiments to compare their effects on Cadmium (Cd) reduction in wheat grains. The best two FBA (50 µM SNP and 2 mM Na2EDTA) can significantly reduce Cd concentration in wheat grains, and the filling period was the most effective period for FBA application. Compared with the control (H2O), foliar spraying 50 µM SNP or 2 mM Na2EDTA inhibited the moving of Cd from the lower tissue to upper tissue in stem and also significantly reduced the Cd accumulation in grains. Furthermore, compared with normal wheat variety (AK58), foliar spraying 50 µmol SNP or 2 mM Na2EDTA as the best two FBA significantly reduced Cd concentration in shoots of Cd low accumulation varieties (HZB and HJBY), which can be used for the safe production of wheat in Cd-contaminated farmlands.

Selenium inhibits cadmium uptake and accumulation in the shoots of winte wheat by altering the transformation of chemical forms of cadmium in soil.

This study aimed to investigate the effects of selenium application on cadmium absorption, transport, and soil cadmium forms of winter wheat at different stages. A pot experiment with one Cd application (6 mg·kg-1) and five Se application levels (0, 1, 2, 5, and 10 mg·kg-1) was conducted. The results showed that Se application increased the grain yield of winter wheat, especially at 5 mg·kg-1 under Cd stress. As Se was supplied at 5 (Se5) and 10 (Se10) mg·kg-1, the Cd concentrations in roots and shoots, including stems, spikes, glumes, and grains, decreased at different growth stages, and the decreases in grain were 46.1% and 70.9% respectively. Se5 and Se10 also significantly decreased the translocation factors of Cd from roots to shoots, roots to stems, stems to spikes, and glumes to grains, promoted the accumulation of Cd in roots, and inhibited the accumulation of Cd in shoots and final grains at different growth stages, and the accumulation of Cd in grains decreased by 16.9% and 68.1%, respectively. High levels of Se application (Se5 and Se10) decreased the concentrations and proportions of exchangeable Cd (EXC-Cd) and iron (Fe)-manganese (Mn) oxide-bound Cd (R2O3-Cd) but increased the concentration and proportion of residual Cd (RES-Cd) in both soils with wheat and fallow soil at different growth stages. Therefore, under Cd stress, high levels of Se application reduced the shoot Cd concentration by inhibiting the uptake and transport of Cd from roots to shoots, and decreased the bioavailability of Cd in both soil with wheat and fallow by enhancing the transformation and distribution of RES-Cd from EXC-Cd and R2O3-Cd.

Additions of different accumulator straws affect the growth and cadmium uptake of Ziziphus acidojujuba seedlings

ABSTRACT This study examined the effects of straw from cadmium (Cd)-accumulator plant species on the growth and Cd uptake of Ziziphus acidojujuba seedlings grown in Cd-containing soil. The treatments were independent applications of straw from seven Cd-accumulator plant species (Cardamine hirsuta, Gnaphalium polycaulon, Pterocypsela laciniata, Malachium aquaticum, Galium aparine, Conyza canadensis, and Stellaria media) and a no-straw control. The whole-plant biomass, total chlorophyll and soluble sugar contents, and antioxidant enzymes activities in Z. acidojujuba seedlings under the different straw treatments showed the following trend: P. laciniata > M. aquaticum > S. media > C. canadensis > G. polycaulon > control > G. aparine > C. hirsuta. Compared with the control, the Cd contents in roots of Z. acidojujuba seedlings after any straw application significantly decreased by 19.05%-43.76%, and the Cd contents in shoots decreased by 31.58%-54.39%, except after G. aparine, G. polycaulon, and C. hirsuta straws applications. Therefore, the application of P. laciniata, M. aquaticum, and S. media straws promoted the growth and reduced the Cd uptake of Z. acidojujuba seedlings most significantly, making them ideal remediation materials for Cd-contaminated jujuba orchards.

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.