Silicon inhibits the upward transport of Cd in the first internode of different rice varieties in a Cd stressed farm land

Manganese oxide application reduces cadmium bioavailability in rice rhizosphere: Insights from desorption kinetics and high-resolution imaging

Cadmium (Cd) contamination in paddy soils threatens global food safety. While manganese (Mn)-based materials show promise in reducing soil Cd bioavailability, their efficacy requires further evaluation. Traditional ex situ sampling methods often overlook metal desorption kinetics and rhizosphere biochemical heterogeneity, potentially misinterpreting Mn's regulatory influence on Cd dynamics. This study employed in situ monitoring tools, including diffusive gradients in thin-films (DGT) measurements, DIFS (DGT-induced fluxes in soils) modeling, and high-resolution DGT and planar optode (PO) imaging, to assess the impact of two Mn oxides (MnO2 and Mn2O3) on Cd bioavailability in rice rhizosphere. Application of MnO2 and Mn2O3 reduced bioavailable Cd by 28.9 % and 15.3 %, respectively, attributed to elevated soil Mn and Fe levels fostering Cd immobilization. DGT-DIFS results revealed that Mn oxide application prolonged Cd replenishment time and reduced its desorption rate from soil solids. PO imaging identified pH heterogeneity in rice rhizosphere, confirming that Mn oxides mediated Cd bioavailability reduction by increasing pH. High-resolution DGT imaging revealed distinct spatial distribution patterns of Cd, Mn, and Fe fluxes, demonstrating Mn's inhibitory effects on Cd bioavailability. These findings highlight the potential of Mn oxides to mitigate Cd uptake by rice, offering a promising strategy for managing Cd-contaminated soils.

Exogenous nano-silicon enhances the ability of intercropped faba bean to alleviate cadmium toxicity and resist Fusarium wilt

Excessive soil cadmium (Cd) and the accumulation of pathogens pose serious threats to legume growth. However, it remains unclear whether intercropping (IFcd) and its combined treatment with silicon nanoparticles (Si-NPs) (IFcd + Si) can alleviate these challenges under Cd stress, as well as the underlying mechanisms involved. This study systematically elucidated the mechanism of faba bean-wheat intercropping and Si-NPs regulating faba bean growth under Cd stress using rhizosphere metabolomics and 16 S rRNA microbiome analysis. The results showed that IFcd and IFcd + Si treatments significantly reduced Cd accumulation by 17.3% and 56.2%, and Fusarium wilt incidence by 11.1% and 33.3%, respectively, compared with monoculture faba bean (MFcd) while promoting root and plant growth. These treatments reduced oxidative stress markers, including H2O2, MDA, and O2-, and increased the activity of defense enzymes, such as SOD, APX, and POD in plants. Furthermore, they increased NH4+-N and available potassium levels in rhizosphere soils. Interestingly, the NH4+-N content increased and was significantly positively correlated with urease (URE) activity and negatively correlated with Cd. Beneficial bacteria and functional metabolites were enriched in the rhizosphere of faba bean. Joint analysis revealed increased relative abundances of Sphingomonas, Intrasporangium, and Streptomyces, which were positively correlated with antibacterial metabolites, such as sordarin, lactucin, and 15-methylpalmate. This explains the reduced Cd accumulation and Fusarium wilt in plants. These findings provide mechanistic insights into how intercropping with Si-NPs mitigates Cd stress and controls soil-borne diseases by regulating rhizosphere metabolites, bacterial communities, and plant resistance.

The protective roles of Oryza glumaepatula and phytohormone in enhancing rice tolerance to cadmium stress by regulating gene expression, morphological, physiological, and antioxidant defense system

The heavy metal cadmium (Cd) is highly poisonous and has received significant attention from environmental scientists due to its harmful impacts on plants. Oryza glumaepatula is a wild rice that contains useful genes against biotic and abiotic stresses. Therefore, the current study used SG007, a single-segment substitution line (SSSL), generated by crossing O. glumaepatula with an elite rice cultivar (HJX74), to evaluate the resistance potential against Cd. Moreover, we assessed the efficacy of strigolactone GR24 (1 μM) against Cd toxicity (100 μM) by investigating physiological, biochemical, and molecular mechanisms in both cultivars (i.e., SG007 and HJX74). The findings of this study revealed that Cd toxicity declined the chlorophyll a, chlorophyll b, and carotenoids by 50%, 20%, and 44% in SG007, and 58%, 39%, and 59% in HJX74 by enhancing electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2) by 113%, 184%, and 119% in SG007 and 248%, 273% and 195% in HJX74, respectively. GR24 improved growth under Cd stress in both cultivars, and SG007 exhibited better plant growth parameters, antioxidant enzymatic activities, nitric oxide synthase (NOS), and nitric oxide (NO) levels than HJX74 under Cd toxicity. GR24 with SG007 regulated expressions of Cd transporters and reduced the cytological disruptions in cell organelles. The combined utilization of SG007 and GR24 reduced Cd accumulation and oxidative stress and improved plant growth parameters and enzymatic activities. In conclusion, our study highlights the potential of utilizing SG007 in conjunction with GR24 as a practical strategy to mitigate Cd pollution in rice. The results not only underscore the beneficial effects of strigolactone GR24 in alleviating Cd-induced stress but also emphasize the valuable genetic traits of O. glumaepatula in developing rice lines with enhanced tolerance to heavy metals, offering broader implications for sustainable agriculture and crop improvement in contaminated environments.

Exogenous silicon facilitates safe crop production in cadmium-contaminated soils: A comprehensive meta-analysis

Soil contamination by cadmium (Cd) is an increasing environmental concern that potentially jeopardizes both crop productivity and human health. Silicon (Si), the Earth's second most abundant element, has shown a significant potential in reducing Cd uptake by crops. However, there is still a lack of quantitative data on the beneficial effects of Si in reducing Cd toxicity, thereby making it more difficult to ensure safe crop production. We conducted a comprehensive meta-analysis of 105 studies to assess the impact of exogenous Si on Cd accumulation in three major cereal crops (wheat, maize, and rice) and elucidate the key factors governing the Si effects. We found that Si supplementation significantly mitigated Cd toxicity in crops, reducing Cd accumulation in maize, rice, and wheat by 37 %, 30 %, and 45 %, respectively. This reduction was most pronounced in all three crop grains (reductions reaching 40-51 %). The four different forms of Si applied all increased crop yield, with nano-silicon resulting in an average yield increase of 19 %, surpassing silicate, Si-based fertilizer, and other silica-based materials. The effects of Si were primarily influenced by application rate and methods, soil pH, Cd concentration, and the effects of foliar and field application. Based on Cd inhibition levels and overall economic benefits, we recommend a Si application rate of ≤ 250 mg/kg, preferably using nano-silicon or silicate. Overall, our study provides valuable globally relevant guidance on Si amendments selection and application thereby ensuring safer and higher crop production in Cd-contaminated soils.

Effects of foliar spraying different sizes of zinc fertilizer on the growth and cadmium accumulation in rice

BACKGROUND

Nanotechnology has been widely applied in agricultural science. During the process of reducing metal toxicity and accumulation in rice, nanomaterials exhibit size effects. However, there is limited knowledge regarding these size effects. We aim to explore the impact of fertilizer with various sizes of ZnO nanoparticles (ZnO-NPs) on rice growth and cadmium (Cd) accumulation and to elucidate the potential mechanism of Cd reduction in rice. Foliar applications of different concentrations (0.5 and 2 mmol L-1) and different sizes (30 and 300 nm ZnO-NPs) of zinc (Zn) fertilizer (Zn(NO3)2) were performed to investigate the effects on rice growth, Cd accumulation and subcellular distribution, and the expression of Zn-Cd transport genes.

RESULTS

The results suggested that all the foliar sprayings can significantly reduce the Cd concentrations in rice grains by 41-61% with the highest reduction in the application of ZnO-NPs with large size and low concentration. This is related to the enhancement of Cd fixation in leaf cell walls and downregulation of Cd transport genes (OsZIP7, OsHMA2, OsHMA3) in stem nodes. Foliar ZnO-NPs applications can increase the Zn concentration in grains by 9-21%. Foliar applications of Zn(NO3)2 and small-sized ZnO-NPs promoted plant growth and rice yield, while the application of large-sized ZnO-NPs significantly reduced rice growth and yield.

CONCLUSION

The study suggests that the rice yield and Cd reduction are dependent on the size and concentration of foliar spraying and the use of large-sized ZnO-NPs is the most effective strategy when considering both yield and Cd reduction comprehensively. © 2024 Society of Chemical Industry.

Hydroxamate Siderophores Intensify the Co-Deposition of Cadmium and Silicon as Phytolith-Like Particulates in Rice Stem Nodes: A Natural Strategy to Mitigate Grain Cadmium Accumulation

Sequestration of cadmium (Cd) in rice phytolith can effectively restrict its migration to the grains, but how hydroxamate siderophore (HDS) affects phytolith formation within rice plants especially the fate of Cd and silicon (Si) remains poorly understood. Here, we found that the addition of HDS increased the content of dissolved Si and Cd in soil pore water as well as its absorption by the rice roots during the reproductive growth stage. HDS effectively trapped orthosilicic acid and Cd ions at the third stem nodes of rice plants via hydrogen bonds and chelation interactions, which then rapidly deposited on the xylem cell wall through hydrophobic interactions. Ultimately, Cd was immobilized as phytolith-like particulates in the form of CdSiO3. Field experiments verified that Cd accumulation was significantly reduced by 46.4% in rice grains but increased by 41.2% in rice stems after HDS addition. Overall, this study advances our understanding of microbial metabolites enhancing the instinctive physiological barriers within rice plants.

Aquaporin mediated silicon-enhanced root hydraulic conductance is benefit to cadmium dilution in tobacco seedlings

Numerous studies shown that silicon (Si) enhanced plants' resistance to cadmium (Cd). Most studies primarily focused on investigating the impact of Si on Cd accumulation. However, there is a lack of how Si enhanced Cd resistance through regulation of water balance. The study demonstrated that Si had a greater impact on increasing fresh weight compared to dry weight under Cd stress. This effect was mainly attributed to Si enhanced plant relative water content (RWC). Plant water content depends on the dynamic balance of water loss and water uptake. Our findings revealed that Si increased transpiration rate and stomatal conductance, leading to higher water loss. This, in turn, negatively impacted water content. The increased water content caused by Si could ascribe to improve root water uptake. The Si treatment significantly increased root hydraulic conductance (Lpr) by 131 % under Cd stress. This enhancement was attributed to Si upregulation genes expression of NtPIP1;1, NtPIP1;2, NtPIP1;3, and NtPIP2;1. Through meticulously designed scientific experiments, this study showed that Si enhanced AQP activity, leading to increased water content that diluted Cd concentration and ultimately improved plant Cd resistance. These findings offered fresh insights into the role of Si in bolstering plant resistance to Cd.

In-situ remediation of cadmium contamination in paddy fields: from rhizosphere soil to rice kernel

Cadmium (Cd) has become an important heavy metal pollutant because of its strong migration and high toxicity. The industrial production process aggravated the Cd pollution in rice fields. Human exposure to Cd through rice can cause kidney damage, emphysema, and various cardiovascular and metabolic diseases, posing a grave threat to health. As modern technology develops, the Cd accumulation model in rice and in-situ remediation of Cd pollution in cornfields have been extensively studied and applied, so it is necessary to sort out and summarize them systematically. Therefore, this paper reviewed the primary in-situ methods for addressing heavy metal contamination in rice paddies, including chemical remediation (inorganic-organic fertilizer remediation, nanomaterials, and composite remediation), biological remediation (phytoremediation and microbial remediation), and crop management remediation technologies. The factors that affect Cd transformation in soil and Cd migration in crops, the advantages and disadvantages of remediation techniques, remediation mechanisms, and the long-term stability of remediation were discussed. The shortcomings and future research directions of in situ remediation strategies for heavily polluted paddy fields and genetic improvement strategies for low-cadmium rice varieties were critically proposed. To sum up, this review aims to enhance understanding and serve as a reference for the appropriate selection and advancement of remediation technologies for rice fields contaminated with heavy metals.

Foliar spraying of Zn/Si affects Cd accumulation in paddy grains by regulating the remobilization and transport of Cd in vegetative organs

The reduction of cadmium (Cd) accumulation in rice grains through biofortification of essential nutrients like zinc (Zn) and silicon (Si) is an area of study that has gained significant attention. However, there is limited understanding of the mechanism of Zn/Si interaction on Cd accumulation and remobilization in rice plants. This work used a pot experiment to examine the effects of Zn and Si applied singly or in combination on the physiological metabolism of Cd in different rice organs under Cd stress. The results revealed that: Zn/Si application led to a significant decrease in root Cd concentration and reduce the value of Tf Soil-Root in filling stage. The content of phytochelatin (PCs, particularly PC2) and glutathione (GSH) in roots, top and basal nodes were increased with Zn/Si treatment application. Furthermore, Zn/Si treatment promoted the distribution of Cd in cell wall during Cd stress. These findings suggest that Zn/Si application facilitates the compartmentalization of Cd within subcellular structures and enhances PCs production in vegetative organs, thereby reducing Cd remobilization. Zn/Si treatment upregulated the metabolism of amino acid components involved in osmotic regulation, secondary metabolite synthesis, and plant chelating peptide synthesis in vegetative organs. Additionally, it significantly decreased the accumulation of Cd in globulin, albumin, and glutelin, resulting in an average reduction of 50.87% in Cd concentration in milled rice. These results indicate that Zn/Si nutrition plays a crucial role in mitigating heavy metal stress and improving the nutritional quality of rice by regulating protein composition and coordinating amino acid metabolism balance.