Foliar application of selenium nanoparticles alleviates cadmium toxicity in maize (Zea mays L.) seedlings: Evidence on antioxidant, gene expression, and metabolomics analysis

Integrated physiological, transcriptomic, and metabolomic investigation reveals that MgO NPs mediate the alleviation of cadmium stress in tobacco seedlings through ABA-regulated lignin synthesis

The harmful influence caused by cadmium (Cd) to agriculture is severe and enduring. Efforts to reduce the damage by Cd to crop is an important topic. In this study, we investigated the effect of MgO NPs on tobacco seedlings' growth under Cd stress and explored its mechanism. Results showed Cd inhibited seedling growth, but MgO NPs alleviated this toxicity. With MgO NPs, shoot and root fresh weight increased by 35.12 % and 45.73 %. This was mainly due to MgO NPs reducing Cd accumulation by 40 % in root and 20.48 % in shoot compared to Cd treatment. MgO NPs not only reduced Cd accumulation but redistributed it to inactive cell walls: up to 55 % in shoot and 22 % in root (compared to 47 % and 22 % in Cd treatment). The primary mechanism was the change in cell wall's main ingredient: lignin. MgO NPs increased lignin content by 50.62 % compared to Cd treatment. To further investigate the underlying molecular mechanism, multi-omics analysis was conducted. Comparing Cd + MgO NPs with Cd, 1358 DEGs (694 up, 664 down) and 160 DEMs (44 up, 116 down) were identified. Furthermore, we identified ABA-regulated phenylpropanoid pathway as the key mechanism for lignin synthesis. MgO NPs boosted ABA levels by 6.72 % compared to Cd treatment. The multi-omics analysis revealed upregulation of ABA synthesis and signal transduction, leading to increased phenylpropanoid pathway metabolites and gene expressions. Notably, POD, a key enzyme, increased by 92.05 %. It was concluded that MgO NPs represent a highly efficient alternative for enhancing plant resistance to Cd.

Selenium absorption, translocation and biotransformation in pak choi (Brassica chinensis L.) after foliar application of selenium nanoparticles

Diets consisting of selenium-deficient crops are associated with immune disorders and cardiomyopathy. Compared to the extensively used but highly toxic selenite (SeO32-), low-toxicity selenium nanoparticles (SeNPs) have emerged as a promising nanoplatform for Se biofortification in agriculture; however, the mechanisms underlying their transportation and biotransformation within crops remain elusive. In this study, SeNPs were successfully prepared using liquid-phase laser irradiation. We conducted a comparative study on the effects of foliar application of SeO32- and SeNPs on the growth of pak choi (Brassica chinensis L.), and investigated the absorption, translocation, and biotransformation mechanisms of Se in pak choi. The recommended dietary intake can be effectively achieved by applying SeNPs using leaf-spraying techniques. Our findings suggested that foliar application of SeNPs might be an efficient way to produce Se fortified crops, especially leafy vegetables, which are favorable for human health.

Cadmium translocation combined with metabolomics analysis revealed potential mechanisms of MT@MSN-CS and GSH@MSN-CS in reducing cadmium accumulation in rice (Oryza sativa L.) grains

Applying nano-delivery systems for phytohormones via foliar application has proven effective in reducing grain cadmium (Cd) levels in crops. However, the mechanisms underlying this reduction remain inadequately understood. This study integrated the determination of leaf photosynthetic parameters, Cd translocation analysis, and metabolomics to elucidate the effects of reduced glutathione (GSH) and melatonin (MT), delivered with or without chitosan-encapsulated mesoporous silica nanoparticles (MSN-CS), on grain Cd levels in rice. Our findings revealed that the foliar application of MT@MSN-CS significantly outperformed MT alone in reducing grain Cd levels and enhancing leaf photosynthesis under Cd stress. Conversely, GSH@MSN-CS showed comparable effects to GSH alone. Foliar-applied GSH@MSN-CS and MT@MSN-CS both decreased the Cd transport coefficients from panicle nodes to brown rice by 26.2-53.3%, with MT@MSN-CS demonstrating superior efficiency in reducing Cd concentrations across roots, stems, leaves, panicle nodes, and grains. Metabolomic analysis revealed substantial shifts in rice metabolite profiles following GSH@MSN-CS and MT@MSN-CS treatments. Foliar application of MT@MSN-CS or GSH@MSN-CS may rapidly and effectively activate the primary antioxidant defense system and alleviate membrane lipid peroxidation in rice grown on low-to-moderately Cd-contaminated soils by upregulating amino acid metabolism. The secondary defense mechanism, phenylpropanoid biosynthesis, was reprogrammed to reduce energy expenditure and decrease Cd translocation.

Regulatory effects and mechanism of different selenium species on cadmium accumulation in Triticum aestivum L. (microbial response, gene expression and element accumulation)

Decreasing cadmium (Cd) accumulation in wheat grain is significant for human health. This study compared the effect of soil applied different selenium (Se) species on Cd accumulation in wheat. In Cd-contaminated soil, the applications of inorganic Se species, organic Se species, and selenium nanoparticles (SeNPs) had little effect on physicochemical properties, available Cd content, and Cd fractions in soil, but changed the β diversity and relative abundance of bacteria at genus level. The application of different Se species reduced Cd concentration in wheat grain, and inorganic Se species had the best effect on reducing Cd, with a decrease of 24.1%-57.0%. Under Cd stress, selenite (Se(IV)) application inhibited the expression of Cd transport-related genes; selenate (Se(VI)) application mainly prompted the expression of gene associated with Cd sequestration in vacuole; and seleno-L-methionine (SeMet) and SeNPs application inhibited the expression of genes related to Cd uptake and transport. Further, Se application alleviated the toxicity of Cd stress on chloroplast. Correlation and stepwise regression equation indicated that different Se species had different crucial part affecting grain Cd accumulation. When Cd was absorbed by plant root, different Se species differentially affected the synergistic effect between nutrient elements and Cd. In all, Se application, especially Se(IV) can be effectively used to reduce grain Cd accumulation.

Brassica rapa selenium transporter NPF2.20 (BrNPF2.20) accounts for Se-enrichment in Chinese cabbage

Selenium (Se) is an essential nutrient for the human body and breeding highly Se-enriched Chinese cabbage varieties is an important means of addressing Se deficiency in individuals in certain regions. The genus Brassica has a strong ability to enrich Se; however, the primary molecular mechanism of Se enrichment remains unclear. We screened for high- and low-Se-enriched Chinese cabbage varieties from 39 different genotypes and identified a key candidate gene for Se enrichment, namely, BrNPF2.20 (BraA07g035670.3.1 C), located on the cell membrane. The expression level of BrNPF2.20 in the high-Se-enriched Chinese cabbage variety P2 was significantly higher than that in the low-Se-enriched variety P6. Heterologous expression of BrNPF2.20 increased the sensitivity of yeast to Se. The overexpression of BrNPF2.20 significantly increased the Se content in Arabidopsis plants, whereas silencing BrNPF2.20 in Chinese cabbage leaves reduced the Se content. Cell selenium mainly in the cell wall may be the physiological and biochemical mechanism of the high-Se-enriched vareity in response to selenium stress. BrNPF2.20 promoted the transport and accumulation of Se from root to shoot in Chinese cabbage maybe by increasing GSH-Px activity or regulating sulfate transporter family genes related to Se absorption and transport. This study not only deepens our understanding of Se transport from Chinese cabbage root to the ground part, but also provides a new idea for breeding Se-rich Chinese cabbage varieties by promoting SeMet transport.

Organic foliar spraying: A method that synchronously reduces mercury methylation in soil and accumulation in vegetable

Although the use of foliar spraying with organic matter has been extensively studied and applied to reduce heavy metals in plants, research on its application for reducing mercury (Hg) accumulation in plants, particularly the more toxic methylmercury (MeHg), remains scarce. Furthermore, previous researches on the barrier mechanisms of foliar spraying primarily concentrated on the effects of spraying agents on plant physiological and biochemical indicators, with limited focus on their impacts on soil environment. Herein, the dynamic effects and mechanisms of organic foliar spraying materials, including earthworm liquid fertilizer (ELF), Tween 80 (T80), and citric acid (CA), on soil Hg methylation and accumulation in lettuce were investigated using pot experiment. The findings revealed that foliar spraying significantly reduced the total mercury (THg) and MeHg concentrations in mature lettuce stems and leaves, with CA demonstrating the highest efficacy, achieving reduction rates of 24-60% for THg and 64-69% for MeHg. Spraying CA and T80 also simultaneously reduced the dissolved Hg and MeHg in the soil during the lettuce maturity period. The reductions of soil Hg methylation and bioaccumulation in lettuce were related to the increased abundance of Hg-reducing bacteria, decreased tartaric acid content and Hg-methylating bacteria abundance in soils, as well as enhanced nutrient absorption by lettuce. Additionally, foliar spraying lessened Hg toxicity to the plant and facilitated Hg sequestration in cell walls and vacuoles. Thus, foliar organic spraying impacted Hg enrichment in plant through altering plant physiological and biochemical indices, soil environment and Hg methylation processes.

Endophytic Colletotrichum fructicola KL19 and Its Derived SeNPs Mitigate Cd-Stress-Associated Damages in Spinacia oleracea L

The application of nanotechnology in agriculture has received much attention in order to improve crop yield, quality and food safety. In the present study, a Cd-tolerant endophytic fungus Colletotrichum fructicola KL19 was first ever reported to produce SeNPs, and the production conditions were optimized using the Box-Behnken design in the Response Surface Methodology (RSM-BBD), achieving a peak yield of 1.06 mM under optimal conditions of 2.62 g/20 mL biomass, 4.56 mM Na2SeO3, and pH 6.25. Following this, the properties of the biogenic SeNPs were elucidated by using TEM, DLS, and FTIR, in which the 144.8 nm spherical-shaped SeNPs were stabilized by different functional groups with a negative zeta potential of -18.3 mV. Furthermore, strain KL19 and SeNPs (0, 5, 10, 20 and 50 mg/L) were inoculated in the root zone of small-leaf spinach (Spinacia oleracea L.) seedlings grown in the soil with 33.74 mg/kg Cd under controlled conditions for seven weeks. Impressively, compared with Cd stress alone, the strain KL19 and 5 mg/L SeNPs treatments significantly (p < 0.05) exhibited a reduction in Cd contents (0.62 and 0.50 folds) within the aboveground parts of spinach plants and promoted plants' growth by improving the leaf count (0.92 and 1.36 folds), fresh weight (2.94 and 3.46 folds), root dry weight (4.00 and 5.60 folds) and root length (0.14 and 0.51 folds), boosting total chlorophyll synthesis (0.38 and 0.45 folds), enhancing antioxidant enzymes (SOD, POD) activities, and reducing the contents of reactive oxygen species (MDA, H2O2) in small-leaf spinach under Cd stress. Overall, this study revealed that utilizing endophytic fungus C. fructicola or its derived SeNPs could mitigate reactive oxygen species generation by enhancing antioxidant enzyme activity as well as diminish the absorption and accumulation of Cd in small-leaf spinach, promoting plant growth under Cd stress.

Common metabolism and transcription responses of low-cadmium-accumulative wheat (Triticum aestivum L.) cultivars sprayed with nano-selenium

Cadmium (Cd) contamination in soils threatens food security, while cultivating low-Cd-accumulative varieties, coupled with agro-nanotechnology, offers a potential solution to reduce Cd accumulation in crops. Herein, foliar application of selenium nanoparticles (SeNPs) was performed on seedlings of two low-Cd-accumulative wheat (Triticum aestivum L.) varieties grown in soil spiked with Cd at 3 mg/kg. Results showed that foliar application of SeNPs at 0.16 mg/plant (SeNPs-M) significantly decreased the Cd content in leaves of XN-979 and JM-22 by 46.4 and 40.8 %, and alleviated oxidative damage. The wheat leaves treated with SeNPs-M underwent significant metabolic and transcriptional reprogramming. On one hand, four specialized antioxidant metabolites such as L-Tyrosine, beta-N-acetylglucosamine, D-arabitol, and monolaurin in response to SeNPs in JM-22 and XN-979 is the one reason for the decrease of Cd in wheat leaves. Moreover, alleviation of stress-related kinases, hormones, and transcription factors through oxidative post-translational modification, subsequently regulates the expression of defense genes via Se-enhanced glutathione peroxidase. These findings indicate that combining low-Cd-accumulative cultivars with SeNPs spraying is an effective strategy to reduce Cd content in wheat and promote sustainable agricultural development.

Effects of Foliar Dressing with Chemical Nano-Selenum and Na2SeO3 on the Antioxidant System and Accumulation of Se and Bioactive Components in Cyclocarya paliurus (Sweet Tea Tree)

Selenium (Se)-rich Cyclocarya paliurus is popular for its bioactive components, and exogenous Se fortification is the most effective means of enrichment. However, the effects of exogenous Se fortification on the nutritional quality of C. paliurus are not well known. To investigate the nutrient contents and antioxidant properties of C. paliurus following Se treatment, we used a foliar spray to apply Se in two forms-chemical nano-Se (Che-SeNPs) and sodium selenite (Na2SeO3). Sampling began 10 days after spraying and was conducted every 5 days until day 30. The Se, secondary metabolite, malondialdehyde contents, antioxidant enzyme activity, Se speciation, and Se-metabolism-related gene expression patterns were analyzed in the collected samples. Exogenous Se enhancement effectively increased the Se content of leaves, reaching a maximum on days 10 and 15 of sampling, while the contents of flavonoids, triterpenes, and polyphenols increased significantly during the same period. In addition, the application of Se significantly enhanced total antioxidant activity, especially the activity of the antioxidant enzyme peroxidase. Furthermore, a positive correlation between the alleviation of lipid peroxidation and Se content was observed, while methylselenocysteine formation was an effective means of alleviating Se stress. Finally, Na2SeO3 exhibited better absorption and conversion efficiency than Che-SeNPs in C. paliurus.

The role and transcriptomic mechanism of cell wall in the mutual antagonized effects between selenium nanoparticles and cadmium in wheat

Selenium nanoparticles (SeNPs) has been reported as a beneficial role in alleviating cadmium (Cd) toxicity in plant. However, underlying molecular mechanisms about SeNPs reducing Cd accumulation and alleviating Cd toxicity in wheat are not well understood. A hydroponic culture was performed to evaluate Cd and Se accumulation, cell wall components, oxidative stress and antioxidative system, and transcriptomic response of wheat seedlings after SeNPs addition under Cd stress. Results showed that SeNPs application notably reduced Cd concentration in root and in shoot by 56.9% and 37.3%, respectively. Additionally, SeNPs prompted Cd distribution in root cell wall by 54.7%, and increased lignin, pectin and hemicellulose contents by regulating cell wall biosynthesis and metabolism-related genes. Further, SeNPs alleviated oxidative stress caused by Cd in wheat through signal transduction pathways. We also observed that Cd addition reduced Se accumulation by downregulating the expression level of aquaporin 7. These results indicated that SeNPs alleviated Cd toxicity and reduced Cd accumulation in wheat, which were associated with the synergetic regulation of cell wall biosynthesis pathway, uptake transporters, and antioxidative system via signaling pathways.

Mitigating cadmium exposure risk in rice with foliar nano-selenium: Investigations through Caco-2 human cell line in-vivo bioavailability assay

The contamination of paddy fields by cadmium and lead is a major issue in China. The consumption of rice grown in heavy metals contaminated areas poses severe health risks to humans, where bioavailability and bioaccessibility remains the critical factor for risk determination. Selenium nanoparticles (Se-NPs) can mitigate the toxicity of heavy metals in plants. However, there exists limited information regarding the role of Se-NPs in dictating cadmium (Cd) toxicity in rice for human consumption. Moreover, the impact of Se-NPs under simultaneous field and laboratory controlled conditions is rarely documented. To address this knowledge gap, a field experiment was conducted followed by laboratory scale bioavailability assays. Foliar application of Se-NPs and selenite (at 5, 10 mg L-1) was performed to assess their efficiency in lowering Cd accumulation, promoting Se biofortification in rice grains, and evaluating Cd exposure risk from contaminated rice. Obtained results indicate that foliar treatments significantly reduced the heavy metal accumulation in rice grains. Specifically, Se-NP 10 mg L-1 demonstrated higher efficiency, reducing Cd and Pb by 56 and 32 % respectively. However, inconsistent trends for bioavailable Cd (0.03 mg kg-1) and bioaccessible (0.04 mg kg-1) were observed while simulated human rice intake. Furthermore, the foliage application of Se-NPs and selenite improved rice quality by elevating Se, Zn, Fe, and protein levels, while lowering phytic acid content in rice grains. In summary, this study suggests the promising potential of foliage spraying of Se-NPs in lowering the health risks associated with consuming Cd-contaminated rice.

Biosynthetic selenium nanoparticles (Bio-SeNPs) mitigate the toxicity of antimony (Sb) in rice (Oryza sativa L.) by limiting Sb uptake, improving antioxidant defense system and regulating stress-related gene expression

Nanotechnology offers a promising and innovative approach to mitigate biotic and abiotic stress in crop production. In this study, the beneficial role and potential detoxification mechanism of biogenic selenium nanoparticles (Bio-SeNPs) prepared from Psidium guajava extracts in alleviating antimony (Sb) toxicity in rice seedlings (Oryza sativa L.) were investigated. The results revealed that exogenous addition of Bio-SeNPs (0.05 g/L) into the hydroponic-cultured system led to a substantial enhancement in rice shoot height (73.3%), shoot fresh weight (38.7%) and dry weight (28.8%) under 50 μM Sb(III) stress conditions. Compared to Sb exposure alone, hydroponic application of Bio-SeNPs also greatly promoted rice photosynthesis, improved cell viability and membrane integrity, reduced reactive oxygen species (ROS) levels, and increased antioxidant activities. Meanwhile, exogenous Bio-SeNPs application significantly lowered the Sb accumulation in rice roots (77.1%) and shoots (35.1%), and reduced its root to shoot translocation (55.3%). Additionally, Bio-SeNPs addition were found to modulate the subcellular distribution of Sb and the expression of genes associated with Sb detoxification in rice, such as OsCuZnSOD2, OsCATA, OsGSH1, OsABCC1, and OsWAK11. Overall, our findings highlight the great potential of Bio-SeNPs as a promising alternative for reducing Sb accumulation in crop plants and boosting crop production under Sb stress conditions.

Foliar Application of Nanoparticles Reduced Cadmium Content in Wheat (Triticum aestivum L.) Grains via Long-Distance "Leaf-Root-Microorganism" Regulation

Foliar application of beneficial nanoparticles (NPs) exhibits potential in reducing cadmium (Cd) uptake in crops, necessitating a systematic understanding of their leaf-root-microorganism process for sustainable development of efficient nano-enabled agrochemicals. Herein, wheat grown in Cd-contaminated soil (5.23 mg/kg) was sprayed with different rates of four commonly used NPs, including nano selenium (SeNPs)/silica (SiO2NPs)/zinc oxide/manganese dioxide. SeNPs and SiO2NPs most effectively reduced the Cd concentration in wheat grains. Compared to the control, Cd concentration in grains was significantly decreased by 35.0 and 33.3% by applying 0.96 mg/plant SeNPs and 2.4 mg/plant SiO2NPs, and the grain yield was significantly increased by 33.9% with SeNPs application. Down-regulated gene expression of Cd transport proteins (TaNramp5 and TaLCT1) and up-regulated gene expression of vacuolar Cd fixation proteins (TaHMA3 and TaTM20) were observed with foliar SeNPs and SiO2NPs use. SeNPs increased the levels of leaf antioxidant metabolites. Additionally, foliar spray of SeNPs resulted in lower abundances of rhizosphere organic acids and reduced Cd bioavailability in rhizosphere soil, and soil microorganisms related to carbon and nitrogen (Solirubrobacter and Pedomicrobium) were promoted. Our findings underscore the potential of the foliar application of SeNPs and SiO2NPs as a plant and rhizosphere soil metabolism-regulating approach to reduce Cd accumulation in wheat grains.

Vitamin E: An assistant for black soldier fly to reduce cadmium accumulation and toxicity

Cadmium (Cd) is a toxic heavy metal associated with osteoporosis, liver, and kidney disease. The black soldier fly (BSF) Hermetia illucens may be exposed to Cd during the transformation of livestock manure. The BSF has a high tolerance to Cd. In the previous work of the laboratory, we found that vitamin E (VE) may play a role in the tolerance of BSF to Cd exposure. The main findings are as follows: The BSF larvae pretreated with exogenous VE had heavier body weight, lower content and toxicity of Cd under similar Cd exposure. Even in high Cd exposure at the concentrations of 300 and 700 mg/kg, the BSF larvae pretreated with exogenous VE at a concentration of 100 mg/kg still reduced the Cd toxicity to 85.33 % and 84.43 %, respectively. The best-fitting models showed that metallothionein (MT) content, oxidative damage (8-hydroxydeoxyguanosine content, malondialdehyde content), antioxidant power (total antioxidant power, peroxidase activity) had a great influence on content and toxicity of Cd bioaccumulated in the larvae. The degree of oxidative damage was reduced in the larvae with exogenous VE pretreatments. This variation can be explained by their changed MT content and increased antioxidant power because of exogenous VE. These results reveal the roles of VE in insects defense against Cd exposure and provide a new option for the prevention and therapy of damage caused by Cd exposure.

Mitigating cadmium accumulation and toxicity in plants: The promising role of nanoparticles

Cadmium (Cd) is a highly toxic heavy metal that adversely affects humans, animals, and plants, even at low concentrations. It is widely distributed and has both natural and anthropogenic sources. Plants readily absorb and distribute Cd in different parts. It may subsequently enter the food chain posing a risk to human health as it is known to be carcinogenic. Cd has a long half-life, resulting in its persistence in plants and animals. Cd toxicity disrupts crucial physiological and biochemical processes in plants, including reactive oxygen species (ROS) homeostasis, enzyme activities, photosynthesis, and nutrient uptake, leading to stunted growth and reduced biomass. Although plants have developed defense mechanisms to mitigate these damages, they are often inadequate to combat high Cd concentrations, resulting in yield losses. Nanoparticles (NPs), typically smaller than 100 nm, possess unique properties such as a large surface area and small size, making them highly reactive compared to their larger counterparts. NPs from diverse sources have shown potential for various agricultural applications, including their use as fertilizers, pesticides, and stress alleviators. Recently, NPs have emerged as a promising strategy to mitigate heavy metal stress, including Cd toxicity. They offer advantages, such as efficient absorption by crop plants, the reduction of Cd uptake, and the enhancement of mineral nutrition, antioxidant defenses, photosynthetic parameters, anatomical structure, and agronomic traits in Cd-stressed plants. The complex interaction of NPs with calcium ions (Ca2+), intracellular ROS, nitric oxide (NO), and phytohormones likely plays a significant role in alleviating Cd stress. This review aims to explore the positive impacts of diverse NPs in reducing Cd accumulation and toxicity while investigating their underlying mechanisms of action. Additionally, it discusses research gaps, recent advancements, and future prospects of utilizing NPs to alleviate Cd-induced stress, ultimately promoting improved plant growth and yield.

Impact of nanopollution on plant growth, photosynthesis, toxicity, and metabolism in the agricultural sector: An updated review

Nanotechnology provides distinct benefits to numerous industrial and commercial fields, and has developed into a discipline of intense interest to researchers. Nanoparticles (NPs) have risen to prominence in modern agriculture due to their use in agrochemicals, nanofertilizers, and nanoremediation. However, their potential negative impacts on soil and water ecosystems, as well as plant growth and physiology, have caused concern for researchers and policymakers. Concerns have been expressed regarding the ecological consequences and toxicity effects associated with nanoparticles as a result of their increased production and usage. Moreover, the accumulation of nanoparticles in the environment poses a risk, not only because of the possibility of plant damage but also because nanoparticles may infiltrate the food chain. In this review, we have documented the beneficial and detrimental effects of NPs on seed germination, shoot and root growth, plant biomass, and nutrient assimilation. Nanoparticles exert toxic effects by inducing ROS generation and stimulating cytotoxic and genotoxic effects, thereby leading to cell death in several plant species. We have provided possible mechanisms by which nanoparticles induce toxicity in plants. In addition to the toxic effects of NPs, we highlighted the importance of nanomaterials in the agricultural sector. Thus, understanding the structure, size, and concentration of nanoparticles that will improve plant growth or induce plant cell death is essential. This updated review reveals the multifaceted connection between nanoparticles, soil and water pollution, and plant biology in the context of agriculture.