Cd Accumulation In Shoots Research Articles

Modulation of Cd carriers by innovative nanocomposite (Ca+Mg) and Cd-resistance microbes (Bacillus pumilus): a mechanistic approach to enhance growth and yield of rice (Oryza sativa L.).

Cadmium (Cd) is a well-known pollutant in agricultural soil, affecting human health through the food chain. To combat this issue, Ca + Mg (25 mg L-1) nanocomposite and Bacillus pumilus, either alone or combined, were applied to rice plants under Cd (5 mg kg-1, 10 mg kg-1) contamination. In our study, growth and yield traits demonstrated the beneficial influence of Ca + Mg and B. pumilus application in improving rice defense mechanism by reducing Cd stress. Combined Ca + Mg and B. pumilus application increased SPAD (15), total chlorophyll (18), chlorophyll a (11), chlorophyll b (22), and carotenoids (21%) with Cd (10 mg kg-1), compared to the application alone. Combined Ca + Mg and B. pumilus application significantly regulated MDA (15), H2O2 (13), EL (10), and O2 •- (24%) in shoots under Cd (10 mg kg-1), compared to the application alone. Cd (10 mg kg-1) increased the POD (22), SOD (21), APX (12), and CAT (13%) in shoots with combined Ca + Mg and B. pumilus application, compared to the application alone. Combined Ca + Mg and B. pumilus application significantly reduced Cd accumulation in roots (22), shoots (13), and grains (20%) under Cd (10 mg kg-1), compared to the application alone. Consequently, the combined application of Ca + Mg and B. pumilus is a sustainable solution to enhance crop production under Cd stress.

Transcriptome analysis of potassium-mediated cadmium accumulation in sweet sorghum

Cadmium (Cd) pollution in the soil is a serious environmental issue worldwide. Phytoextraction of Cd-polluted soil is a cost-effective, sustainable and environmentally-friendly strategy. Agricultural fertilizer management is beneficial for promoting the Cd phytoremediation efficiency. Potassium (K) is the nutrient required in the largest amount cation by plants. Sweet sorghum exhibits a substantial phytoremediation potential of Cd-polluted soil. Clarifying the mechanism of K-mediated Cd accumulation in sweet sorghum is imperative. Sweet sorghum plants were grown hydroponically with an extra K supply in the presence or absence of Cd treatment. An extra K application significantly increased plant growth under non-Cd addition, while K lost the profitable effect under Cd stress. K supplementation remarkably enhanced Cd concentrations and Cd accumulation in shoots and roots of sweet sorghum. Transcriptome analysis demonstrated that zinc ion transport, cysteine and methionine metabolism, flavonoid biosynthesis and phenylpropanoid biosynthesis pathways might contribute to the increased Cd accumulation as affected by an extra K supply. Furthermore, SbZIP9, SbSTP8, SbYS1, SbMAG and SbFOMT-like were targeted as they closely correlated with both plant growth and Cd stress in sweet sorghum. SbFOMT-like showed an independent pathway, while SbZIP9, SbSTP8, SbYS1 and SbMAG displayed positive correlations mutually. Notably, SbZIP9 and SbFOMT-like were highly expressed when compared with other target genes. Taken together, SbZIP9 and SbFOMT-like were upregulated and downregulated by an extra K supply under Cd stress, suggesting that SbZIP9 and SbFOMT-like enhances and declines Cd accumulation as regulated by K addition in sweet sorghum respectively.

Performance and mechanistic study of biochar and magnesium-enhanced phytoremediation in cadmium-contaminated soil by alfalfa

Recently, phytoremediation has been regarded as a green and environment friendly technique to treat metals contaminated soils. Thus, in this study, pot experiments were designed to investigate the combine effects of biochar and magnesium (MPs) to purify cadmium (Cd)-contaminated soils by Medicago sativa L. (alfalfa). The results showed that the combined use of biochar and Mg significantly increased the accumulation of Cd and promoted the transport of Cd from root to shoot in alfalfa, simultaneously. Importantly, the combined use of biochar and Mg could increase the accumulation of Cd in shoot and whole plant (shoot + root) of alfalfa up-to 59.1% and 23.1%, respectively. Moreover, the enhancement mechanism can be analyzed from several aspects. Firstly, the photosynthesis was enhanced, which was beneficial to plant growth. The product of photosynthesis provided energy for uptake and transport of Cd. Meanwhile, its transport in phloem could promote the transport of Cd. Secondly, the enhancement of antioxidant capacity of alfalfa effectively protected the membrane structure of alfalfa, which indicated that Cd could enter alfalfa from the channel on the cell membrane. Lastly, the chemical form of Cd and microbial community structure in soil were changed. Overall, these changes reduced the Cd toxicity in soil, enhanced the resistance capability of alfalfa, increased the Cd uptake by alfalfa and promoted the growth of alfalfa. Thus, the obtained results suggested that the combined use of biochar and Mg is an effective approach to enhance phytoremediation performance for purifying Cd-contaminated soils.

Polystyrene microplastics enhanced the toxicity of cadmium to rice seedlings: Evidence from rice growth, physiology, and element metabolism

Microplastics (MPs) and cadmium (Cd) are toxic to rice; however, the effects and mechanisms of their combined exposure are unclear. The combined exposure effects of polystyrene microplastics (PS-MPs) with different particle sizes (1–10 μm, 50–150 μm) and concentrations (50, 500 mg·L−1) and Cd on rice were explored. PS-MPs combined with Cd amplifies the inhibition of each individual exposure on the height and biomass of rice seedlings, and they showed antagonistic effects. PS-MPs reduced the content of chlorophyll and increased the content of carotenoid rice seedlings significantly. High concentrations of PS-MPs enhanced the inhibition of Cd on chlorophyll content. Cd, PS-MPs single and combined exposures significantly altered the antioxidant enzyme (POD, CAT, SOD) activities in rice seedlings. Under PS-MPs exposure, overall, the MDA content in shoots and roots exhibited opposite trends, with a decrease in the former and an increase in the latter. In comparison with Cd treatment, the combined exposures' shoot and root MDA content was reduced. Cd and PS-MPs showed “low concentration antagonism, high concentration synergism” on the composite physiological indexes of rice seedlings. PS-MPs significantly increased the Cd accumulation in shoots. PS-MPs promoted the root absorption of Cd at 50 mg·L−1 while inhibited at 500 mg·L−1. Cd and PS-MPs treatments interfered with the balance of microelements (Mn, Zn, Fe, Cu, B, Mo) and macroelements (S, P, K, Mg, Ca) in rice seedlings; Mn was significantly inhibited. PS-MPs can enhance of Cd's toxicity to rice seedlings. The combined toxic effects of the two contaminants appear to be antagonistic or synergistic, relying on the particle size and concentration of the PS-MPs. Our findings offer information to help people understanding the combined toxicity of Cd and MPs on crops.

Differential reduction in cadmium accumulation in barley under cadmium-salt co-exposure involves specific HMA genes and antioxidative responses

Salinity and heavy metal accumulation adversely affect agricultural productivity and environmental sustainability. Little information exists about the combinatory effect of various stresses on plants, but it is assumed that stress interaction may trigger a specific response. Here, we assessed the combinatory effect of salinity and cadmium on various physiological and molecular traits in two cultivated barley genotypes with contrasting salinity tolerance; Rihane (RH, salt tolerant) and Lemsi (LM, salt sensitive). Studied genotypes were hydroponically exposed to CdCl2 (30 µM), NaCl (300 mM) or the combined Cd-NaCl stresses for 15 days. Salinity and to a lesser degree Cd-NaCl stress significantly reduced growth, leaf water content, chlorophyll pigments, and K uptake, and increased Na and Cl contents for both genotypes, with LM being more affected than RH. Cd content in roots was higher than in shoots for both genotypes either under Cd alone or when combined with NaCl. Interestingly, NaCl addition reduced Cd accumulation in both roots and shoots of the two barley genotypes, suggesting that the interaction of NaCl and Cd on their uptake and accumulation is antagonistic. The tolerant genotype (RH) accumulated lower Cd levels in shoots and roots than the salt-sensitive one (LM). Cd-NaCl stress significantly lowered H2O2 and MDA contents relative to NaCl treatment alone. The activity of several antioxidant enzymes was essentially higher in RH than in LM, under the different stresses. These responses were in concomitant with an enhanced expression of specific Heavy Metal ATPases (HvHMA) genes, mainly in RH, which can partially, explain the reduced Cd accumulation in this genotype. Overall, these findings suggest the possibility of cultivating salt-tolerant barley genotypes in saline soils slightly contaminated with Cd, whereas barley sensitive genotypes could be assessed for phytoremediation purposes.

Copper-dependent control of uptake, translocation and accumulation of cadmium in hyperaccumlator Sedum alfredii

Cadmium (Cd) is detrimental to plant growth and threatens human health. Here, we investigated the potential for remediation of Cd-contaminated soil with high copper (Cu) background using Cd hyperaccumulator ecotype (HE) Sedum alfredii. We assessed effects of Cu on Cd accumulation, compartmentation and translocation in HE S. alfredii, and compared with those in a related non-accumulator ecotype (NHE). We found that Cu supply significantly induced Cd accumulation in roots and shoots of long-term soil-cultivated HE S. alfredii. A large fraction of root Cd was accumulated in the organelles, but a small fraction was stored in the cell wall. Importantly, Cu addition reduced Cd accumulation in the cell wall and the organelles in root cells. Furthermore, leaf cell capacity to sequestrate Cd in the organelles was greatly improved upon Cu exposure. We also found that genes involving metal transport and cell wall remodeling were distinctly regulated to mediate Cd accumulation in HE S. alfredii. These findings indicate that Cu-dependent decrease of root cell-wall-bound Cd, and stimulation of efflux/influx of organelle Cd transport in root and leaf cells plays a role in the dramatic Cd hyperaccumulation expressed in naturally survived HE S. alfredii.

Effect of brackish water irrigation on cadmium migration in a soil-maize system.

Phytoremediation is an effective way to reduce heavy metal content in agricultural soil. The effects of brackish water irrigation on phytoremediation efficiency of plants have not yet been completely understood. In this study, the effects of brackish water irrigation on cadmium (Cd) uptake by maize as the phytoremediator were investigated. In a pot experiment, maize seedlings were grown in soil with exogenously added Cd (0, 5, 10, or 15mgkg-1) and irrigated with deionized water (T1), natural brackish water (T2), or water with NaCl with salinity equal to that of natural brackish water (T3). Salt stress and cation antagonism caused by brackish water affected maize plant growth and Cd uptake. Under 5, 10, and 15mgkg-1 Cd, Cd accumulation in maize shoots was 5.55, 7.08, and 5.71μg plant-1; 4.08, 3.04, and 5.38μg plant-1; and 2.48, 3.44, and 5.33μg plant-1 under the T1, T2, and T3 treatments, respectively. Cd accumulation in the shoots was significantly lower under the T2 and T3 treatments than under the T1 treatment at 5 and 10mgkg-1 Cd; however, no significant differences were observed among all treatments at 15mgkg-1 Cd. These findings indicated that phytoremediation efficiency decreased in response to both salt stress and cation antagonism caused by brackish water under low soil-Cd concentrations; however, this effect was negligible under high soil-Cd concentration. Therefore, brackish water irrigation can be considered for the phytoremediation of soils contaminated with high Cd levels to save freshwater resources.

Insight into the mechanism of nano-TiO2-doped biochar in mitigating cadmium mobility in soil-pak choi system

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

Elevated carbon dioxide concentrations increase the risk of Cd exposure in rice.

Since the Industrial Revolution, crops have been exposed to various changes in the environment, including elevated atmospheric carbon dioxide (CO2) concentration and cadmium (Cd) pollution in soil. However, information about how combined changes affect crop is limited. Here, we have investigated the changes of japonica and indica rice subspecies seedlings under elevated CO2 level (1200 ppm) and Cd exposure (5 μM Cd) conditions compared with ambient CO2 level (400 ppm) and without Cd exposure in CO2 growth chambers with hydroponic experiment. The results showed that elevated CO2 levels significantly promoted seedling growth and rescued the growth inhibition under Cd stress. However, the elevated CO2 levels led to a significant increase in the shoot Cd accumulation of the two rice subspecies. Especially, the increase of shoot Cd accumulation in indica rice was more than 50% compared with control. Further investigation revealed that the decreases in the photosynthetic pigments and photosynthetic rates caused by Cd were attenuated by the elevated CO2 levels. In addition, elevated CO2 levels increased the non-enzymatic antioxidants and significantly enhanced the ascorbate peroxidase (APX) and glutathione reductase (GR) activities, alleviating the lipid peroxidation and reactive oxygen species (ROS) accumulation induced by Cd. Overall, the research revealed how rice responded to the elevated CO2 levels and Cd exposure, which can help modify agricultural practices to ensure food security and food safety in a future high-CO2 world.

Mitigating cadmium accumulation in dicotyledonous vegetables by iron fertilizer through inhibiting Fe transporter IRT1-mediated Cd uptake

The solubility of cadmium (Cd) in soil and its transfer to plants are influenced by soil pH. While increasing soil pH reduces Cd solubility and accumulation in rice plants grown in acidic soils, its effect on Cd accumulation in vegetables remains inconclusive. Here, we investigated the impact of soil pH on Cd accumulation in dicotyledonous vegetables and elucidated the underlying molecular mechanisms. Soils collected from various locations were supplemented with varying quantities of lime to achieve soil pH values of around 5.0, 6.0, 7.0, and 8.0. Raising soil pH from around 5.0 to 8.0 markedly decreased extractable Cd. However, increasing soil pH tended to promote shoot Cd accumulation in dicotyledonous vegetable species including lettuce, pakchoi, and Chinese cabbage, and the model dicotyledonous plant Arabidopsis thaliana. Conversely, soil pH increase resulted in a monotonic decrease in rice Cd accumulation. In our hydroponic experiments, we discovered that iron (Fe) deficiency substantially increased Cd uptake and accumulation in dicotyledonous plants but not in rice. Increasing soil pH reduced soil Fe availability and induced the Fe transporter gene IRT1 expression in dicotyledonous vegetables roots, which led to an increase in IRT1-mediated Cd uptake and subsequently increased Cd accumulation as soil pH increases. A comprehensive model incorporating extractable Cd and root IRT1 expression better explained Cd accumulation in vegetable shoots. The application of 50 mg/kg of Fe fertilizer in neutral or alkaline soils resulted in a significant reduction in Cd accumulation by 34–58% in dicotyledonous vegetables. These findings reveal that increasing soil pH has two opposite effects, decreasing soil Cd availability while promoting Cd uptake through IRT1 upregulation, reconciling the inconsistency in its effect on Cd accumulation in dicotyledonous plants. Our findings provide important insights for understanding the factors affecting Cd uptake in plants and offer a practical solution to mitigate Cd contamination in vegetables.

Expression in A. thaliana and cellular localization reveal involvement of BjNRAMP1 in cadmium uptake.

Although Brassica juncea has demonstrated potential as a hyperaccumulator crop, it was not entirely clear how cadmium (Cd) accumulates in plants. Here, we found that BjNRAMP1 (Natural Resistance-Associated Macrophage Protein 1) plays a crucial role in the accumulation of Cd and manganese (Mn) through its expression in yeast and Arabidopsis thaliana. The high concentration of Cd exposure could induce the expression of BjNRAMP1. The ectopic expression of BjNRAMP1 in yeast led to higher accumulation of Cd and Mn compared to the vector control. BjNARAMP1 was localized to the plasma membrane and expressed in the vascular system of roots, leaves, and flowers. The overexpression of BjNRAMP1 in A. thaliana resulted in an increased accumulation of Cd in both roots and shoots, which inhibited the normal growth of transgenic lines. Moreover, Mn uptake in roots was activated by the increase in Cd stress. Together, our results indicated that BjNRAMP1 significantly contributes to the uptake of Mn and Cd in B. juncea.

Enhancement of Phytoremediation of Heavy Metal Pollution Using an Intercropping System in Moso Bamboo Forests: Characteristics of Soil Organic Matter and Bacterial Communities

Heavy metal pollution in soil is a major global issue, and one effective method for addressing it is phytoremediation through bamboo planting. Nevertheless, there is a notable gap in our knowledge as no studies have explored the characteristics of soil organic matter (SOM) and the bacterial communities in bamboo forests during the remediation process. To bridge this knowledge gap, we conducted research to investigate the impact of different bamboo planting patterns on the SOM characteristics and microbial communities in soils contaminated with heavy metals. The contents of SOM and dissolved organic matter (DOM) in rhizosphere and non-rhizosphere soils differed significantly between monocropping and intercropping systems, with DOM accounting for only 1.7%–2.5% of SOM. Fourier transform infrared spectra showed that the contents of SOM polysaccharides C-O, carbonate C-O, aliphatic methyl, and methylene increased, while the aromatic C=C abundance decreased in the intercropping rhizosphere soil. The differences between bamboo cultivation patterns in the rhizosphere and non-rhizosphere soils were elucidated using the biomarkers, including MND1 and Nitrospira (non-rhizosphere), and Sphingomonas (rhizosphere). Heavy metals, DOM, SOM, and refined organic functional groups, especially C-O in polysaccharides and symmetric carboxylate, were the determining factors of soil bacterial communities. Compared to monocropping, intercropping increased the accumulation of Zn and Cd in bamboo shoots by 35% and 40%, respectively, and hence, intercropping soil, with a low toxicity, was suitable for bamboo shoot sprouting. Intercropping can alter the characteristics of SOM and bacterial communities and plays a vital role in phytoremediation and shoot growth in bamboo forests. Future studies on soil carbon dynamics and nutrient status during heavy metal remediation will improve our knowledge of soil transformation and its impact on soil ecosystem health and productivity.

The Effects of Calcium and Sulfur Fertilizers Accompanied by Different Side Elements on the Growth and Cd Uptake of Spinacia oleracea Grown in Cd-Contaminated Alkaline Soil

The detoxification of crops grown in Cadmium (Cd)-contaminated acid soil has been widely studied, but for contaminated alkaline soil, there is still inadequate research or information. In order to investigate the effects of calcium and sulfur fertilizers, accompanied by different side elements, on the growth and Cd uptake of Spinacia oleracea grown in Cd-contaminated alkaline soil, the plants were subjected to five treatments, including calcium silicate (Ca-Si), calcium biphosphate (Ca-P), magnesium sulfate (S-Mg), ferric sulfate (S-Fe), and zinc sulfate (S-Zn), and a control group. The results showed that the S-Fe achieved the highest shoot fresh mass and dry mass and the highest shoot Cd concentration and accumulation, which were 30%, 68%, 4.6%, and 73% higher than the control group, respectively. The Ca-Si, Ca-P, S-Mg, and S-Zn reduced the root Cd concentration by 18%, 42%, 7%, and 49%, respectively, and reduced the shoot Cd concentration by 25%, 36%, 15%, and 27%, respectively, as compared to the control. S-Fe increases plant N uptake and photosynthesis, which is beneficial to biomass accumulation. Ca-P improves soil and plant P nutrition status, as well as plant K and Ca status, and helps alleviate plant Cd stress. Overall, calcium fertilizers accompanied by phosphorus have the potential to reduce plant Cd contamination risk, while sulfur fertilizers accompanied by iron show potential for enhancing Cd extraction.

Soil water stress alters differentially relative metabolic pathways affecting growth performance and metal uptake efficiency in a cadmium hyperaccumulator ecotype of Sedum alfredii.

Modeling plants for biomass production and metal uptake from surrounding environment is strongly dependent on the moisture content of soil. Therefore, experiments were conducted to find out how soil moisture affects the phenotypic traits, photosynthetic efficiency, metabolic profile, and metal accumulation in the hyperaccumulating ecotype of Sedum alfredii (S. alfredii). A total of six water potential gradients were set: 0 ~ -15 kPa (T1), -15 ~ -30 kPa (T2), -30 ~ -45 kPa (T3), -45 ~ -60 kPa (T4), -60 ~ -75 kPa (T5), and -75 ~ -90 kPa (T6). Different water potential treatments had a significant effect on plant growth and metal uptake efficiency. Compared to T3, T2 was more effective in promoting plant growth and development, with an increase in biomass of 23% and 17% in both fresh weight (FW) and dry weight (DW), respectively. T2 and T3 had the highest cadmium (Cd) content in the shoot (280.2 mg/kg) and (283.3 mg/kg), respectively, whereas T1 had the lowest values (204.7 mg/kg). Cd availability for plants in the soil was affected by moving soil moisture cycles. Changes in soil moisture that were either too high or too low compared to the ideal soil water content for S. alfredii growth resulted in a significant reduction in Cd accumulation in shoots. Tryptophan, phenylalanine, and other amino acids were accumulated in T5, whereas only tryptophan and phenylalanine slightly increased in T1. Sugars and alcohols such as sucrose, trehalose, mannitol, galactinol, and mannobiose increased in T5, while they decreased significantly in T1. Interestingly, in contrast to T1, the two impaired metabolic pathways in T5 (galactose and starch metabolism) were identified to be glucose metabolic pathways. These findings provide scientific information (based on experiments) to improve biomass production and metal uptake efficiency in hyperaccumulating ecotype of S. alfredii for phytoremediation-contaminated agricultural fields.

The Fragile culm19 (FC19) mutation largely improves plant lodging resistance, biomass saccharification, and cadmium resistance by remodeling cell walls in rice

Cell wall is essential for plant upright growth, biomass saccharification, and stress resistance. Although cell wall modification is suggested as an effective means to increase biomass saccharification, it is a challenge to maintain normal plant growth with improved mechanical strength and stress resistance. Here, we reported two independent fragile culm mutants, fc19–1 and fc19–2, resulting from novel mutations of OsIRX10, produced by the CRISPR/Cas9 system. Compared to wild-type, the two mutants exhibited reduced contents of xylose, hemicellulose, and cellulose, and increased arabinose and lignin without significant alteration in levels of pectin and uronic acids. Despite brittleness, the mutants displayed increased breaking force, leading to improved lodging resistance. Furthermore, the altered cell wall and increased biomass porosity in fc19 largely increased biomass saccharification. Notably, the mutants showed enhanced cadmium (Cd) resistance with lower Cd accumulation in roots and shoots. The FC19 mutation impacts transcriptional levels of key genes contributing to Cd uptake, sequestration, and translocation. Moreover, transcriptome analysis revealed that the FC19 mutation resulted in alterations of genes mainly involved in carbohydrate and phenylpropanoid metabolism. Therefore, a hypothetic model was proposed to elucidate that the FC19 mutation-mediated cell wall remodeling leads to improvements in lodging resistance, biomass saccharification, and Cd resistance.

Assessment of the capability of cadmium accumulation and translocation among 31 willows: four patterns of willow biomass variation response to cadmium.

Cadmium (Cd) pollution threatens food security and the environment. Willow species (Salix, Salicaceae) exhibit a remarkable potential to restore Cd-polluted sites due to their high biomass production and high Cd accumulation capacities. This study examined the Cd accumulation and tolerance in 31 genotypes of shrub willow in hydroponic conditions at varying Cd levels (0μM Cd, 5μM Cd, and 20μM Cd). The root, stem, and leaf biomass of 31 shrub willow genotypes showed significant differences to Cd exposure. Among 31 willow genotypes, four patterns of biomass variation response to Cd were identified: insensitive to Cd; growth inhibition due to excessive Cd supply (high Cd inhibition); low Cd causing inhibited growth, whereas high Cd leading to increased biomass (U-shape); and growth increment with excessive Cd exposure (high Cd induction). The genotypes belonging to the "insensitive to Cd" and/or "high Cd induction" were candidates for the utilization of phytoremediation. Based on the analysis of Cd accumulation of 31 shrub willow genotypes at high and low Cd levels, genotypes 2372, 51-3, and 1052 obtained from a cross between S. albertii and S. argyracea grew well and accumulated relatively more Cd levels than other genotypes. In addition, for Cd-treated seedlings, root Cd accumulation was positively correlated with shoot Cd accumulation and total Cd uptake, demonstrating that Cd accumulation in roots could serve as a biomarker for evaluating the Cd extraction capacity of willows, especially in hydroponics screening. The results of this study screened out willow genotypes with high Cd uptake and translocation capacities, which will provide valuable approaches for restoring Cd-contaminated soils with willows.

Plant Defensin-Dissimilar Thionin OsThi9 Alleviates Cadmium Toxicity in Rice Plants and Reduces Cadmium Accumulation in Rice Grains.

Thionins are important antibacterial peptides in plants. However, the roles of plant thionins, especially the defensin-dissimilar thionins, in alleviating heavy-metal toxicity and accumulation remain unclear. Here, cadmium (Cd)-related functions and mechanisms of the defensin-dissimilar rice thionin OsThi9 were investigated. OsThi9 was significantly upregulated in response to Cd exposure. OsThi9 was localized to the cell wall and was shown to bind Cd; these characters help to increase Cd tolerance. In Cd-exposed rice plants, OsThi9 overexpression significantly increased cell wall Cd binding, decreasing upward Cd translocation and subsequent Cd accumulation in shoots and straw, while OsThi9 knockout had inverse effects. Importantly, in rice plants grown in Cd-contaminated soils, OsThi9 overexpression significantly reduced Cd accumulation in brown rice (decrease of ≥ 51.8%) without negatively impairing the crop yield and essential elements. Thus, OsThi9 plays an important role in the alleviation of Cd toxicity and accumulation and has significant potential for developing low-Cd rice.

Cadmium Reduction in Spring Wheat: Root Exudate Composition Affects Cd Partitioning Between Roots and Shoots

Cadmium (Cd) in cereals is one of the major sources of Cd intake by human diets, and solutions to reduce Cd concentrations in wheat still need to be developed. Plant breeding, by selecting low-Cd varieties, can be an important tool to reduce Cd in crops. Knowing the genotypic variation in Cd accumulation and furthering our understanding of the impact of root exudates composition on Cd accumulation in crops may provide valuable information for plant breeding. In this study, we selected nine spring wheat varieties and analysed the accumulation and distribution of Cd in shoots, roots, root surfaces and kernels in relation to their qualitative and quantitative composition of root exudates, determined by 1H-NMR (Proton Nuclear Magnetic Resonance). Results showed that the Cd concentration in shoots at an early stage could be used as a predictor for Cd concentration in kernels. Total Cd uptake was not correlated to the mobility of Cd in the rhizosphere, but total Cd was negatively correlated to Cd adsorbed at the root surface. Furthermore, (i) exudation of organic acids (primarily succinate and acetate) increased Cd concentration in shoots, and (ii) exudation of nucleosides, DNA (deoxyribonucleic acid) degradation products, increased Cd adsorption at the root surface. Therefore, root exudates composition should be taken into account when selecting for low-Cd wheat traits.

Hydrogen peroxide reduces root cadmium uptake but facilitates root-to-shoot cadmium translocation in rice through modulating cadmium transporters

Cadmium (Cd) contamination in agricultural soils has become a serious worldwide environmental problem threatening crop production and human health. Hydrogen peroxide (H2O2) is a critical second messenger in plant response to Cd exposure. However, its role in Cd accumulation in various organs of plants and the mechanistic basis of this regulation remains to be elucidated. In this study, we used electrophysiological and molecular approaches to understand how H2O2 regulates Cd uptake and translocation in rice plants. Our results showed that the pretreatment of H2O2 significantly reduced Cd uptake by rice roots, which was associated with the downregulation of OsNRAMP1 and OsNRAMP5. On the other hand, H2O2 promoted the root-to-shoot translocation of Cd, which might be attributed to the upregulation of OsHMA2 critical for Cd2+ phloem loading and the downregulation of OsHMA3 involved in the vacuolar compartmentalization of Cd2+, leading to the increased Cd accumulation in rice shoots. Furthermore, such regulatory effects of H2O2 on Cd uptake and translocation were notably amplified by the elevated level of exogenous calcium (Ca). Collectively, our results suggest that H2O2 can inhibit Cd uptake but increase root to shoot translocation through modulating the transcriptional levels of genes encoding Cd transporters, furthermore, application of Ca can amplify this effect. These findings will broaden our understanding of the regulatory mechanisms of Cd transport in rice plants and provide theoretical foundation for breeding rice for low Cd accumulation.

Three Different Fertilizers Enhance Spinach Growth and Reduce Spinach Cd Concentration in Cd Contaminated Alkaline Soil

In order to investigate the impact of peach branch derived fertilizer (PB), cow manure derived fertilizer (CM) and silicon liquid fertilizer (Si) on the growth and Cd uptake of the Spinacia oleracea L. in the Cd contaminated soil, a pot experiment was conducted. The fertilizers were applied with low (L), medium (M) or high (H) levels, leading to nine treatments and a control group (CK). As a result, compared to CK, PB increased shoot dry mass by 15 to 46% and reduced shoot Cd by 19 to 56%; CM increased shoot dry mass by 6.1 to 162% and reduced shoot Cd by 38 to 55%; Si showed no effect on plant biomass but significantly reduced the root Cd bioconcentration factor. The CMM and CMH significantly reduced soil-available Cd by 6.5 and 7.5%, respectively, compared to CK. The CM enhanced the plant biomass dilution of Cd and decreased soil-available Cd, but led to higher total shoot Cd accumulation. PB led to simultaneous decline of the shoot Cd and total shoot Cd accumulation, indicating a stronger plant Cd “rejection” effect, independent from biomass accumulation. Si reduced plant root Cd with the sacrifice of biomass accumulation.