Soil-Weathered CuO Nanoparticles Compromise Foliar Health and Pigment Production in Spinach (Spinacia oleracea).

In this study, spinach plants exposed to fresh/unweathered (UW) or weathered (W) copper compounds in soil were analyzed for growth and nutritional composition. Plants were exposed for 45 days to freshly prepared or soil-aged (35 days) nanoparticulate CuO (nCuO), bulk-scale CuO (bCuO), or CuSO4 at 0 (control), 400, 400, and 40 mg/kg of soil, respectively. Foliar health, gas exchange, pigment content (chlorophyll and carotenoid), catalase and ascorbate peroxidase enzymes, gene expression, and Cu bioaccumulation were evaluated along with SEM imagery for select samples. Foliar biomass was higher in UW control (84%) and in UW ionic treatment (87%), compared to the corresponding W treatments (p ≤ 0.1). Root catalase activity was increased by 110% in UW bCuO treatment as compared to the W counterpart; the value for the W ionic treatment was increased by 2167% compared to the UW counterpart (p ≤ 0.05). At 20 days post-transplantation, W nCuO-exposed plants had ∼56% lower carotenoid content compared to both W control and the UW counterpart (p ≤ 0.05). The findings indicate that over the full life cycle of spinach plant the weathering process significantly deteriorates leaf pigment production under CuO exposure in particular and foliar health in general.

Recent insights into the impact, fate and transport of cerium oxide nanoparticles in the plant-soil continuum.

The advent of the nanotechnology era offers a unique opportunity for sustainable agriculture provided that the exposure and toxicity are adequately assessed and properly controlled. The global production and application of cerium oxide nanoparticles (CeO2-NPs) in various industrial sectors have tremendously increased. Most of the nanoparticles end up in water and soil where they interact with soil microorganisms and plants. Investigating the uptake, translocation and accumulation of CeO2-NPs is critical for its safe application in agriculture. Plant uptake of CeO2-NPs may lead to their accumulation in different plant tissues and interference with key metabolic processes of plants. Soil microbes can also be affected by increasing CeO2-NPs in soil, leading to changes in the physiology and enzymatic activity of soil microorganisms. The interactions between CeO2-NPs, microbes and plants in the agricultural system need systemic research in ecologically relevant conditions. In the present review, The uptake pathways and in-planta translocation of CeO2-NPs,and their impact on plant morphology, nutritional values, antioxidant enzymes and molecular determinants are presented. The role of CeO2-NPs in modifying soil microbial community in plant rhizosphere is also discussed. Overall, the review aims to provide a comprehensive account on the behaviour of CeO2-NPs in soil-plant systems and their potential impacts on the soil microbial community and plant health.

C60 Fullerols Enhance Copper Toxicity and Alter the Leaf Metabolite and Protein Profile in Cucumber.

Abiotic and biotic stress induce the production of reactive oxygen species (ROS), which limit crop production. Little is known about ROS reduction through the application of exogenous scavengers. In this study, C60 fullerol, a free radical scavenger, was foliar applied to three-week-old cucumber plants (1 or 2 mg/plant) before exposure to copper ions (5 mg/plant). Results showed that C60 fullerols augmented Cu toxicity by increasing the influx of Cu ions into cells (170% and 511%, respectively, for 1 and 2 mg of C60 fullerols/plant). We further use metabolomics and proteomics to investigate the mechanism of plant response to C60 fullerols. Metabolomics revealed that C60 fullerols up-regulated antioxidant metabolites including 3-hydroxyflavone, 1,2,4-benzenetriol, and methyl trans-cinnamate, among others, while it down-regulated cell membrane metabolites (linolenic and palmitoleic acid). Proteomics analysis revealed that C60 fullerols up-regulated chloroplast proteins involved in water photolysis (PSII protein), light-harvesting (CAB), ATP production (ATP synthase), pigment fixation (Mg-PPIX), and electron transport ( Cyt b6f). Chlorophyll fluorescence measurement showed that C60 fullerols significantly accelerated the electron transport rate in leaves (13.3% and 9.4%, respectively, for 1 and 2 mg C60 fullerols/plant). The global view of the metabolic pathway network suggests that C60 fullerols accelerated electron transport rate, which induced ROS overproduction in chloroplast thylakoids. Plant activated antioxidant and defense pathways to protect the cell from ROS damaging. The revealed benefit (enhance electron transport) and risk (alter membrane composition) suggest a cautious use of C60 fullerols for agricultural application.

Metabolomics Reveals How Cucumber ( Cucumis sativus) Reprograms Metabolites To Cope with Silver Ions and Silver Nanoparticle-Induced Oxidative Stress.

Due to their well-known antifungal activity, the intentional use of silver nanoparticles (AgNPs) as sustainable nanofungicides is expected to increase in agriculture. However, the impacts of AgNPs on plants must be critically evaluated to guarantee their safe use in food production. In this study, 4-week-old cucumber ( Cucumis sativus) plants received a foliar application of AgNPs (4 or 40 mg/plant) or Ag+ (0.04 or 0.4 mg/plant) for 7 days. Gas chromatography-mass spectrometry (GC-MS)=based nontarget metabolomics enabled the identification and quantification of 268 metabolites in cucumber leaves. Multivariate analysis revealed that all the treatments significantly altered the metabolite profile. Exposure to AgNPs resulted in metabolic reprogramming, including activation of antioxidant defense systems (upregulation of phenolic compounds) and downregulation of photosynthesis (upregulation of phytol). Additionally, AgNPs enhanced respiration (upregulation of tricarboxylic acid cycle intermediates), inhibited photorespiration (downregulation of glycine/serine ratio), altered membrane properties (upregulation of pentadecanoic and arachidonic acids, downregulation of linoleic and linolenic acids), and reduced inorganic nitrogen fixation (downregulation of glutamine and asparagine). Although Ag ions induced some of the same metabolic changes, alterations in the levels of carbazole, lactulose, raffinose, citraconic acid, lactamide, acetanilide, and p-benzoquinone were AgNP-specific. The results of this study offer new insight into the molecular mechanisms by which cucumber responds to AgNP exposure and provide important information to support the sustainable use of AgNPs in agriculture.

Cerium Biomagnification in a Terrestrial Food Chain: Influence of Particle Size and Growth Stage.

Mass-flow modeling of engineered nanomaterials (ENMs) indicates that a major fraction of released particles partition into soils and sediments. This has aggravated the risk of contaminating agricultural fields, potentially threatening associated food webs. To assess possible ENM trophic transfer, cerium accumulation from cerium oxide nanoparticles (nano-CeO2) and their bulk equivalent (bulk-CeO2) was investigated in producers and consumers from a terrestrial food chain. Kidney bean plants (Phaseolus vulgaris var. red hawk) grown in soil contaminated with 1000-2000 mg/kg nano-CeO2 or 1000 mg/kg bulk-CeO2 were presented to Mexican bean beetles (Epilachna varivestis), which were then consumed by spined soldier bugs (Podisus maculiventris). Cerium accumulation in plant and insects was independent of particle size. After 36 days of exposure to 1000 mg/kg nano- and bulk-CeO2, roots accumulated 26 and 19 µg/g Ce, respectively, and translocated 1.02 and 1.3 µg/g Ce, respectively, to shoots. The beetle larvae feeding on nano-CeO2 exposed leaves accumulated low levels of Ce since ∼98% of Ce was excreted in contrast to bulk-CeO2. However, in nano-CeO2 exposed adults, Ce in tissues was higher than Ce excreted. Additionally, Ce content in tissues was biomagnified by a factor of 5.3 from the plants to adult beetles and further to bugs.

Physiological and Biochemical Changes Imposed by CeO2 Nanoparticles on Wheat: A Life Cycle Field Study.

Interactions of nCeO2 with plants have been mostly evaluated at seedling stage and under controlled conditions. In this study, the effects of nCeO2 at 0 (control), 100 (low), and 400 (high) mg/kg were monitored for the entire life cycle (about 7 months) of wheat plants grown in a field lysimeter. Results showed that at high concentration nCeO2 decreased the chlorophyll content and increased catalase and superoxide dismutase activities, compared with control. Both concentrations changed root and leaf cell microstructures by agglomerating chromatin in nuclei, delaying flowering by 1 week, and reduced the size of starch grains in endosperm. Exposed to low concentration produced embryos with larger vacuoles, while exposure to high concentration reduced number of vacuoles, compared with control. There were no effects on the final biomass and yield, Ce concentration in shoots, as well as sugar and starch contents in grains, but grain protein increased by 24.8% and 32.6% at 100 and 400 mg/kg, respectively. Results suggest that more field life cycle studies are needed in order to better understand the effects of nCeO2 in crop plants.

Monitoring the environmental effects of CeO2 and ZnO nanoparticles through the life cycle of corn (Zea mays) plants and in situ µ-XRF mapping of nutrients in kernels.

Information about changes in physiological and agronomic parameters through the life cycle of plants exposed to engineered nanoparticles (NPs) is scarce. In this study, corn (Zea mays) plants were cultivated to full maturity in soil amended with either nCeO2 or nZnO at 0, 400, and 800 mg/kg. Gas exchange was monitored every 10 days, and at harvest, bioaccumulation of Ce and Zn in tissues was determined by ICP-OES/MS. The effects of NPs exposure on nutrient concentration and distribution in ears were also evaluated by ICP-OES and µ-XRF. Results showed that nCeO2 at both concentrations did not impact gas exchange in leaves at any growth stage, while nZnO at 800 mg/kg reduced net photosynthesis by 12%, stomatal conductance by 15%, and relative chlorophyll content by 10% at day 20. Yield was reduced by 38% with nCeO2 and by 49% with nZnO. Importantly, µ-XRF mapping showed that nCeO2 changed the allocation of calcium in kernels, compared to controls. In nCeO2 treated plants, Cu, K, Mn, and Zn were mainly localized at the insertion of kernels into cobs, but Ca and Fe were distributed in other parts of the kernels. Results showed that nCeO2 and nZnO reduced corn yield and altered quality of corn.

Environmental Effects of Nanoceria on Seed Production of Common Bean (Phaseolus vulgaris): A Proteomic Analysis.

The rapidly growing literature on the response of edible plants to nanoceria has provided evidence of its uptake and bioaccumulation, which delineates a possible route of entry into the food chain. However, little is known about how the residing organic matter in soil may affect the bioavailability and resulting impacts of nanoceria on plants. Here, we examined the effect of nanoceria exposure (62.5-500 mg/kg) on kidney bean (Phaseolus vulgaris) productivity and seed quality as a function of soil organic matter content. Cerium accumulation in the seeds produced from plants in organic matter enriched soil showed a dose-dependent increase, unlike in low organic matter soil treatments. Seeds obtained upon nanoceria exposure in soils with higher organic matter were more susceptible to changes in nutrient quality. A quantitative proteomic analysis of the seeds produced upon nanoceria exposure provided evidence for upregulation of stress-related proteins at 62.5 and 125 mg/kg nanoceria treatments. Although the plants did not exhibit overt toxicity, the major seed proteins primarily associated with nutrient storage (phaseolin) and carbohydrate metabolism (lectins) were significantly down-regulated in a dose dependent manner upon nanoceria exposure. This study thus suggests that nanoceria exposures may negatively affect the nutritional quality of kidney beans at the cellular and molecular level. More confirmatory studies with nanoceria along different species using alternative and orthogonal "omic" tools are currently under active investigation, which will enable the identification of biomarkers of exposure and susceptibility.

Evidence of translocation and physiological impacts of foliar applied CeO2 nanoparticles on cucumber (Cucumis sativus) plants.

Currently, most of the nanotoxicity studies in plants involve exposure to the nanoparticles (NPs) through the roots. However, plants interact with atmospheric NPs through the leaves, and our knowledge on their response to this contact is limited. In this study, hydroponically grown cucumber (Cucumis sativus) plants were aerially treated either with nano ceria powder (nCeO2) at 0.98 and 2.94 g/m(3) or suspensions at 20, 40, 80, 160, and 320 mg/L. Fifteen days after treatment, plants were analyzed for Ce uptake by using ICP-OES and TEM. In addition, the activity of three stress enzymes was measured. The ICP-OES results showed Ce in all tissues of the CeO2 NP treated plants, suggesting uptake through the leaves and translocation to the other plant parts. The TEM results showed the presence of Ce in roots, which corroborates the ICP-OES results. The biochemical assays showed that catalase activity increased in roots and ascorbate peroxidase activity decreased in leaves. Our findings show that atmospheric NPs can be taken up and distributed within plant tissues, which could represent a threat for environmental and human health.

Alginate modifies the physiological impact of CeO2 nanoparticles in corn seedlings cultivated in soil.

Alginates are naturally occurring components of organic matter in natural soil whose effects on nanoparticle (NP) toxicity to plants is not well understood. In the present study, corn plants were grown for one month in soil spiked with 400 mg/kg CeO2 NPs with various alginate concentrations. After one month of growth in the NPs impacted soil, plants were harvested and analyzed for Ce and mineral element concentrations. Chlorophyll concentration and heat shock protein 70, used as biomarkers for oxidative stress, were also evaluated. Results showed that, compared to CeO2 NPs treatment, alginate at 10, 50, and 100 mg/kg increased Ce concentration in roots by approximately 46%, 38%, and 29% and by 115%, 45%, and 56% in shoots, respectively. CeO2 NPs without alginate increased Mn accumulation in roots by 34% compared to control. CeO2 NPs with low and medium alginate increased Mn by ca. 92% respect to NPs without alginate and by ca. 155% respect to control. CeO2 NPs without/with alginate significantly increased accumulation of Fe and Al in roots. In addition, alginate at 50 mg/kg increased Zn accumulation in roots by 52% compared to control. In shoots, K increased at all NP treatments but the accumulation of other elements was not affected. Alginate enlarged the impact of CeO2 NPs to corn plants by reducing chlorophyll a content and triggering overexpression of heat shock protein 70.

Effect of cerium oxide nanoparticles on rice: a study involving the antioxidant defense system and in vivo fluorescence imaging.

Previous studies have reported the uptake of cerium oxide nanoparticles (nCeO2) by plants, but their physiological impacts are not yet well understood. This research was aimed to study the impact of nCeO2 on the oxidative stress and antioxidant defense system in germinating rice seeds. The seeds were germinated for 10 days in nCeO2 suspension at 62.5, 125, 250, and 500 mg L(-1) concentrations. The Ce uptake, growth performance, stress levels, membrane damage, and antioxidant responses in seedlings were analyzed. Ce in tissues increased with increased nCeO2 concentrations, but the seedlings showed no visible signs of toxicity. Biochemical assays and in vivo imaging of H2O2 revealed that, relative to the control, the 62.5 and 125 mg nCeO2 L(-1) treatments significantly reduced the H2O2 generation in both shoots and roots. Enhanced electrolyte leakage and lipid peroxidation were found in the shoots of seedlings grown at 500 mg nCeO2 L(-1). Altered enzyme activities and levels of ascorbate and free thiols resulting in enhanced membrane damage and photosynthetic stress in the shoots were observed at 500 mg nCeO2 L(-1). These findings demonstrate a nCeO2 concentration-dependent modification of oxidative stress and antioxidant defense system in rice seedlings.

Synchrotron verification of TiO2 accumulation in cucumber fruit: a possible pathway of TiO2 nanoparticle transfer from soil into the food chain.

The transfer of nanoparticles (NPs) into the food chain through edible plants is of great concern. Cucumis sativus L. is a freshly consumed garden vegetable that could be in contact with NPs through biosolids and direct agrichemical application. In this research, cucumber plants were cultivated for 150 days in sandy loam soil treated with 0 to 750 mg TiO2 NPs kg(-1). Fruits were analyzed using synchrotron µ-XRF and µ-XANES, ICP-OES, and biochemical assays. Results showed that catalase in leaves increased (U mg(-1) protein) from 58.8 in control to 78.8 in 750 mg kg(-1) treatment; while ascorbate peroxidase decreased from 21.9 to 14.1 in 500 mg kg(-1) treatment. Moreover, total chlorophyll content in leaves increased in the 750 mg kg(-1) treatment. Compared to control, FTIR spectra of fruit from TiO2 NP treated plants showed significant differences (p ≤ 0.05) in band areas of amide, lignin, and carbohydrates, suggesting macromolecule modification of cucumber fruit. In addition, compared with control, plants treated with 500 mg kg(-1) had 35% more potassium and 34% more phosphorus. For the first time, µ-XRF and µ-XANES showed root-to-fruit translocation of TiO2 in cucumber without biotransformation. This suggests TiO2 could be introduced into the food chain with unknown consequences.

Cerium oxide nanoparticles modify the antioxidative stress enzyme activities and macromolecule composition in rice seedlings.

Cerium oxide nanoparticles (nCeO2) have been shown to have significant interactions in plants; however, there are limited reports on their impacts in rice (Oryza sativa). Given the widespread environmental dispersal of nCeO2, it is paramount to understand its biochemical and molecular impacts on a globally important agricultural crop, such as rice. This study was carried out to determine the impact of nCeO2 on the oxidative stress, membrane damage, antioxidant enzymes' activities, and macromolecular changes in the roots of rice seedlings. Rice seeds (medium amylose) were grown for 10 days in nCeO2 suspensions (0-500 mg L(-1)). Results showed that Ce in root seedlings increased as the external nCeO2 increased without visible signs of toxicity. Relative to the control, the 62.5 mg nCeO2 L(-1) reduced the H2O2 generation in the roots by 75%. At 125 mg nCeO2 L(-1), the roots showed enhanced lipid peroxidation and electrolyte leakage, while at 500 mg L(-1), the nCeO2 increased the H2O2 generation in roots and reduced the fatty acid content. The lignin content decreased by 20% at 500 mg nCeO2 L(-1), despite the parallel increase in H2O2 content and peroxidase activities. Synchrotron µ-XRF confirmed the presence of Ce in the vascular tissues of the roots.

Prosopis pubescens (screw bean mesquite) seedlings are hyperaccumulators of copper.

Due to health reasons, toxic metals must be removed from soils contaminated by mine tailings and smelter activities. The phytoremediation potential of Prosopis pubescens (screw bean mesquite) was examined by use of inductively-coupled plasma optical emission spectroscopy. Transmission electron microscopy was used to observe ultrastructural changes of parenchymal cells of leaves in the presence of copper. Elemental analysis was used to localize copper within leaves. A 600-ppm copper sulfate exposure to seedlings for 24 days resulted in 31,000 ppm copper in roots, 17,000 ppm in stems, 11,000 in cotyledons and 20 ppm in the true leaves. For a plant to be considered a hyperaccumulator, the plant must accumulate a leaf-to-root ratio <1. Screw bean mesquite exposed to copper had a leaf-to-root ratio of 0.355 when cotyledons were included. We showed that P. pubescens grown in soil is a hyperaccumulator of copper. We recommend that this plant should be field tested.

Advanced Analytical Techniques for the Measurement of Nanomaterials in Food and Agricultural Samples: A Review.

Nanotechnology offers substantial prospects for the development of state-of-the-art products and applications for agriculture, water treatment, and food industry. Profuse use of nanoproducts will bring potential benefits to farmers, the food industry, and consumers, equally. However, after end-user applications, these products and residues will find their way into the environment. Therefore, discharged nanomaterials (NMs) need to be identified and quantified to determine their ecotoxicity and the levels of exposure. Detection and characterization of NMs and their residues in the environment, particularly in food and agricultural products, have been limited, as no single technique or method is suitable to identify and quantify NMs. In this review, we have discussed the available literature concerning detection, characterization, and measurement techniques for NMs in food and agricultural matrices, which include chromatography, flow field fractionation, electron microscopy, light scattering, and autofluorescence techniques, among others.

Environmental implication of MoS2 nanosheets: Effects on maize plant growth and soil microorganisms.

Molybdenum disulfide (MoS2) nanosheets have been used extensively in a variety of fields including medical and industrial. However, little is known about their toxicity effects, especially to edible plants. In this greenhouse study, maize (Zea mays) seedlings were exposed for 4 weeks, through the soil route, to 10 and 100 mg/kg of 2H MoS2 nanosheets. Plant growth, physiological parameters (chlorophyll, antioxidants, and MDA), along with Mo and nutrient element contents were determined in plant tissues. Results showed that at both doses, the nanosheets decreased plant growth. Inductively coupled plasma-mass spectrometry data also showed that both 2H MoS2 concentrations allowed Mo absorption and translocation by maize plants. Additionally, at 100 mg/kg the nanosheets significantly reduced Ca, Mg, Mn, and Zn in leaves, and Na in roots. Gene sequencing data of 16S rRNA showed, that MoS2 nanosheets changed the soil microbial community structure, compared with the untreated control. In addition, nitrogen-fixing microorganisms such as Burkholderiales, Rhizobiales and Xanthobacteraceae were enriched. Overall, the data suggest that, even at low dose (10 mg/kg), the 2H MoS2 nanosheets perturbed both the nutrient uptake by maize plants and the soil microbial communities.

Selenium nanoparticles reduce Ce accumulation in grains and ameliorate yield attributes in mung bean (Vigna radiata) exposed to CeO2.

Exposure of crops to CeO2 nanoparticles (nCeO2) in agricultural environments impact crop quality and human health. In this regard, the effects of selenium nanoparticles (nSe) on the yield and quality of Vigna radiata (L.) exposed to nCeO2 were investigated. The experiment was carried out as a factorial with two factors: NPs (nCeO2, and nSe) as factor one and concentrations as factor two [(0, 250, 500 and 1000 mg/L nCeO2; 0, 25, 50 and 75 mg/L nSe)]. Nanoparticles were foliar applied to 45-day old mung bean shoot in two steps and one-week interval. At 250-1000 mg/L, nCeO2 increased P, protein and Ce accumulation in grain. Additionally, at 1000 mg/L, the nCeO2, significantly decreased seed number, yield, Fe, and Zn storage in seeds. Conversely, at 25 and 50 mg/L, nSe stimulated the growth and yield of mung bean, and significantly increased P, Fe, Zn, and Se in seeds, but reduced the protein content in seeds. The Se25+Ce250 and Se50+Ce250 significantly increased pod number, seed number, grain weight, yield, Fe, Zn and Se storage in grains. In contrast, the Ce accumulation in seeds decreased in all combination treatments (nCeO2 + nSe) compared to their respective single nCeO2 treatments. Moreover, in the plants exposed to high nCeO2 concentrations, nSe application resulted in undamaged vacuoles, less starch granules' accumulation, significant yield improvement, and elevated Fe, Se, and Zn in seeds. Data suggest that selenium nanoparticles prevent nCeO2 stress in mung bean and improve grain production and quality.

Synchrotron micro-XRF and micro-XANES confirmation of the uptake and translocation of TiO2 nanoparticles in cucumber (Cucumis sativus) plants.

Advances in nanotechnology have raised concerns about possible effects of engineered nanomaterials (ENMs) in the environment, especially in terrestrial plants. In this research, the impacts of TiO(2) nanoparticles (NPs) were evaluated in hydroponically grown cucumber (Cucumis sativus) plants. Seven day old seedlings were treated with TiO(2) NPs at concentrations varying from 0 to 4000 mg L(-1). At harvest, the size of roots and shoots were measured. In addition, micro X- ray fluorescence (micro-XRF) and micro X-ray absorption spectroscopy (micro-XAS), respectively, were used to track the presence and chemical speciation of Ti within plant tissues. Results showed that at all concentrations, TiO(2) significantly increased root length (average >300%). By using micro-XRF it was found that Ti was transported from the roots to the leaf trichomes, suggesting that trichomes are possible sink or excretory system for the Ti. The micro-XANES spectra showed that the absorbed Ti was present as TiO(2) within the cucumber tissues, demonstrating that the TiO(2) NPs were not biotransformed.

Exploring the significance of nanomaterials and organic amendments - Prospect for phytoremediation of contaminated agroecosystem.

Emerging micro-pollutants have rapidly contaminated the agro-ecosystem, posing serious challenges to a sustainable future. The vast majority of them have infiltrated the soil and damaged agricultural fields and crops after being released from industry. These pollutants and their transformed products are also transported in vast quantities which further exacerbate the damage. Sustainable remediation techniques are warranted for such large amounts of contaminants. As aforementioned, many of them have been detected at very high concentrations in soil and water which adversely affect crop physiology by disrupting different metabolic processes. To combat this situation, nanomaterials and other organic amendments assisted phytoremediation ware considered as a viable alternative. It is a potent synergistic activity between the biological system and the supplied organic or nanomaterial material to eliminate emerging contaminants and micropollutants from crop fields. This can be effectively be applied to degraded crop fields and could potentially embody a green technology for sustainable agriculture.

A comprehensive study of selenium and cerium oxide nanoparticles on mung bean: Individual and synergistic effect on photosynthesis pigments, antioxidants, and dry matter accumulation.

In this study, the interaction effects of CeO2 NPs (250, 500 and 1000 mg L-1) and Se NPs (25, 50 and 75 mg L-1) were evaluated in mung bean (Vigna radiata). Single NPs and their combinations were foliar applied to 45-day old mung bean plants under greenhouse conditions. In each pot, a total volume of 100 mL of NPs suspension was sprayed on the plants shoot in two steps and one-week interval. After 94 days of growth, membrane degradation, antioxidant activity, photosynthetic pigments, and dry matter accumulation were assessed. At 250 and 500 mg CeO2-NPs L-1, there was partial increase of dry matter, stimulated activity of antioxidant enzymes (p ≤ 0.05), and reactive oxygen species (ROS). However, at 1000 mg L-1, CeO2-NPs caused strong accumulation of ROS (p ≤ 0.05), enlargement of starch granules and swelling of chloroplasts. In addition, at such concentration, there was accumulation of starch granules, reduction of photosynthetic pigments, biological nitrogen fixation, chlorosis, and a significant retardation in plant growth, compared with control, (p ≤ 0.05). Combination of Se-NPs (25 and 50 mg L-1) with 250 mg L-1 of CeO2 NPs decreased hydrogen peroxide, improved CAT, Chla, Chlb, and increased dry matter (p ≤ 0.05). At 1000 mg CeO2 NPs L-1, foliar spray of Se-NPs led to Ce accumulation in the cell wall and increased levels of SOD and proline (p ≤ 0.05). Results showed that 25 and 50 mg Se NPs L-1 ameliorate the stress of CeO2 NPs by upregulating photosynthesis pigments, antioxidants, and dry matter accumulation. Therefore, depending on the CeO2 NPs concentration, the mechanisms of Se NPs in modulating CeO2 NPs stress varied; low concentrations of Se NPs may strengthen the metabolism of legumes, and protect them against foliar toxicity of CeO2 NPs in semi-arid ecosystems.