Divergent effects of cerium oxide nanoparticles alone and in combination with cadmium on nutrient acquisition and the growth of maize (Zea mays)

IntroductionThe increasing use of cerium nanoparticles (CeO2-NPs) has made their influx in agroecosystems imminent through air and soil deposition or untreated wastewater irrigation. Another major pollutant associated with anthropogenic activities is Cd, which has adverse effects on plants, animals, and humans. The major source of the influx of Cd and Ce metals in the human food chain is contaminated food, making it an alarming issue; thus, there is a need to understand the factors that can reduce the potential damage of these heavy metals.MethodsThe present investigation was conducted to evaluate the effect of CeO2-10-nm-NPs and Cd (alone and in combination) on Zea mays growth. A pot experiment (in sand) was conducted to check the effect of 0, 200, 400, 600, 1,000, and 2,000 mg of CeO2-10 nm-NPs/kg-1 dry sand alone and in combination with 0 and 0.5 mg Cd/kg-1 dry sand on maize seedlings grown in a partially controlled greenhouse environment, making a total of 12 treatments applied in four replicates under a factorial design. Maize seedling biomass, shoot and root growth, nutrient content, and root anatomy were measured.Results and discussionThe NPs were toxic to plant biomass (shoot and root dry weight), and growth at 2,000 ppm was the most toxic in Cd-0 sets. For Cd-0.5 sets, NPs applied at 1,000 ppm somewhat reverted Cd toxicity compared with the contaminated control (CC). Additionally, CeO2-NPs affected Cd translocation, and variable Ce uptake was observed in the presence of Cd compared with non-Cd applied sets. Furthermore, CeO2-NPs partially controlled the elemental content of roots and shoots (micronutrients such as B, Mn, Ni, Cu, Zn, Mo, and Fe and the elements Co and Si) and affected root anatomy

Effects Of Cerium Oxide Nanoparticles In Cereals: Insights Into The Toxicity Mechanisms And Macromolecular Modifications

Despite the inundation of studies on the interaction of engineered nanomaterials (ENMs) with plants, investigations involving complete life cycle (i.e from seedling establishment to full maturity) are still lacking. Assessments on the nutritional value of plants cultivated to full maturity in ENMs-treated soil are also missing. Cerium oxide nanoparticles (nCeO2) have significant interactions with plants; however, there are no life cycle studies yet on their implications in cereals like rice (Oryza sativa L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.). These cereals are globally important crops that support the economic activity, and nutritional and health needs of billions of people around the world. This research project was performed to determine the changes in the macromolecular and biochemical processes and their impacts on the physiological, yield, and nutritional properties in cereals. Experiments were completed in four parts: Parts I and II were conducted at germination stage and Parts III and IV included life cycle evaluations. Part I was devoted to rice seeds only. Rice seeds were germinated in nCeO2 suspensions (0, 62.5, 125, 250, 500 mg L-1) and biochemical assays, ICP-OES, GC-MS, and synchrotron micro-XRF analyses were performed on roots to measure the relationships between parameters like Ce uptake, oxidative stress, radical scavenging activities, and macromolecular contents. Results showed that Ce uptake increased as the external nCeO2 increased without visible signs of toxicity. The nCeO2 treatment (500 mg L-1) decreased the fatty acid contents which resulted in reduced membrane damage, and reduced the lignin content despite the parallel increase in H2O2 content and peroxidase activities. Synchrotron micro-XRF also revealed the presence of Ce in the vascular tissues of the roots. In Part II rice, wheat, and barley seeds were exposed to the same nCeO2 suspensions and the structural integrity of intact root xylem was analyzed using FTIR spectromicroscopy and principal component analysis (PCA). The PCA of FTIR spectra showed that nCeO2 induced modifications in the biomolecular compositions of root xylem. Part III involved cultivation of low, medium, and high amylose rice varieties (LA, MA, and HA, respectively) in nCeO2-treated soil (0 and 500 mg kg-1) and the grains were analyzed for nutrient content, antioxidant property, and nutritional quality. The nCeO2 treatment increased the accumulation of Ce in the grains of LA and MA by 997 and 1126%, respectively, compared to controls. The nCeO2 treatment did not affect the sugar content but decreased the starch content in HA and LA by 9 and 8%, respectively, compared to control, with concomitant reduction in the phenolic content and DPPH scavenging ability. In case of the protein fractions, glutelin was not detected in the treated grains. Relative to the untreated, globulin and prolamin decreased significantly in both treated MA and LA grains while albumin decreased in the treated LA grains only. On the other hand, the treated MA grains had dramatic reduction in lauric, valeric, palmitic, oleic, and total fatty acids contents. Similarly, the treated MA grains had improved K, Na, Fe, and Al contents compared to the untreated. In contrast, treated MA grains had reduced S content while treated LA grains had low Fe content. Part IV of this Dissertation research was accomplished by growing wheat and barley to grain production in soil amended with nCeO2 (0, 125, 250 and 500 mg kg-1) and the agronomic, yield, and nutritional properties were examined. The nCeO2 treatment promoted the growth and shoot biomass in both plants, but induced negative effects on yield parameters with wheat showing a more apparent delay in grain formation than barley. Despite the initial poor yield performance, grain yield in both nCeO2-exposed plants was greatly improved at harvest. However, the highest nCeO2 treatment completely halted the grain production in barley. Ce accumulation in wheat grains was not recorded but was tremendously enhanced in barley; Ce content in nCeO2-treated barley grains registered up to 294% increase relative to control. In case of mineral content, the nCeO2 treatment modified only the storage S and Mn in wheat grains but enhanced the accumulations of all elements, except for Na and B, in barley grains. Similarly, nCeO2 modified the amino acid and fatty acid contents in both wheat and barley grains. This study provided insights on several issues and knowledge gaps in the current literature. The result showed that nCeO2 impacted the growth and productivity of cereals which could entail adaptations of new planting and cultivation practices. nCeO2 could enhance Ce accumulation in grains and compromise their nutritional value which may have unknown implications on human health and nutrition. In general, the findings afforded a more comprehensive understanding on the impacts of nCeO2 on globally important agricultural crops

Cerium oxide nanoparticles transformation at the root–soil interface of barley ( Hordeum vulgare L.)

The transformation of cerium oxide nanoparticles (CeO2-NPs) in soil and its role in plant uptake is a critical knowledge gap in the literature. This study investigated the reduction and speciation of CeO2-NPs in barley (Hordeum vulgare L.) cultivated in soil amended with 250 mg CeO2-NPs kg-1 soil. Synchrotron micro-X-ray fluorescence (μXRF) was employed for spatial localization and speciation of CeO2-NPs in thin sections of intact roots at the soil-root interface. Results revealed that Ce was largely localized in soil and at the root surface in nanoparticulate form (84-89%). However, a few hot spots on root surfaces revealed highly significant reduction (55-98%) of CeO2-NPs [Ce(IV)] to Ce(III) species. Interestingly, only roots in close proximity to hot spots showed Ce uptake which was largely CeO2 (89-91%) with very little amount Ce(III) (9-10%). These results suggest that the reduction of CeO2-NPs to Ce(III) is needed to facilitate uptake of Ce

Shifts in N and δ15N in wheat and barley exposed to cerium oxide nanoparticles

The effects of cerium oxide nanoparticles (CeO2-NPs) on 15N/14N ratio (δ15N) in wheat and barley were investigated. Seedlings were exposed to 0 and 500 mg CeO2-NPs/L (Ce-0 and Ce-500, respectively) in hydroponic suspension supplied with NH4NO3, NH4 +, or NO3 -. N uptake and δ15N discrimination (i.e. differences in δ15N of plant and δ15N of N source) were measured. Results showed that N content and 15N abundance decreased in wheat but increased in barley. Ce-500 only induced whole-plant δ15N discrimination (-1.48‰, P ≤ 0.10) with a simultaneous decrease (P ≤ 0.05) in whole-plant δ15N (-3.24‰) compared to Ce-0 (-2.74‰) in wheat in NH4 +. Ce-500 decreased (P ≤ 0.01) root δ15N of wheat in NH4NO3 and NH4 + (3.23 and -2.25‰, respectively) compared to Ce-0 (4.96 and -1.27‰, respectively), but increased (P ≤ 0.05) root δ15N of wheat in NO3 - (3.27‰) compared to Ce-0 (2.60‰). Synchrotron micro-XRF revealed the presence of CeO2-NPs in shoots of wheat and barley regardless of N source. Although the longer-term consequences of CeO2-NP exposure on N uptake and metabolism are unknown, the results clearly show the potential for ENMs to interfere with plant metabolism of critical plant nutrients such as N even when toxicity is not observed

Intergenerational responses of wheat (Triticum aestivum L.) to cerium oxide nanoparticles exposure.

The intergenerational impact of engineered nanomaterials in plants is a key knowledge gap in the literature. A soil microcosm study was performed to assess the effects of multi-generational exposure of wheat (Triticum aestivum L.) to cerium oxide nanoparticles (CeO2-NPs). Seeds from plants that were exposed to 0, 125, and 500 mg CeO2-NPs/kg soil (Ce-0, Ce-125 or Ce-500, respectively) in first generation (S1) were cultivated in factorial combinations of Ce-0, Ce-125 or Ce-500 to produce second generation (S2) plants. The factorial combinations for first/second generation treatments in Ce-125 were S1-Ce-0/S2-Ce-0, S1-Ce-0/S2-Ce-125, S1-Ce-125/S2-Ce-0 and S1-Ce-125/S2-Ce-125, and in Ce-500 were S1-Ce-0/S2-Ce-0, S1-Ce-0/S2-Ce-500, S1-Ce-500/S2-Ce-0 and S1-Ce-500/S2-Ce-500. Agronomic, elemental, isotopic, and synchrotron X-ray fluorescence (XRF) and X-ray absorption near-edge spectroscopy (XANES) data were collected on second generation plants. Results showed that plants treated during the first generation only with either Ce-125 or Ce-500 (e.g. S1-Ce-125/S2-Ce-0 or S1-Ce-500/S2-Ce-0) had reduced accumulation of Ce (61 or 50%), Fe (49 or 58%) and Mn (34 or 41%) in roots, and δ15N (11 or 8%) in grains compared to the plants not treated in both generations (i.e. S1-Ce-0/S2-Ce-0). Plants treated in both generations with Ce-125 (i.e. S1-Ce-125/S2-Ce-125) produced grains that had lower Mn, Ca, K, Mg and P relative to plants treated in the second generation only (i.e. S1-Ce-0/S2-Ce-125). In addition, synchrotron XRF elemental chemistry maps of soil/plant thin-sections revealed limited transformation of CeO2-NPs with no evidence of plant uptake or accumulation. The findings demonstrated that first generation exposure of wheat to CeO2-NPs affects the physiology and nutrient profile of the second generation plants. However, the lack of concentration-dependent responses indicate that complex physiological processes are involved which alter uptake and metabolism of CeO2-NPs in wheat

Intergenerational responses of wheat (Triticum aestivum L.) to cerium oxide nanoparticles exposure.

The intergenerational impact of engineered nanomaterials in plants is a key knowledge gap in the literature. A soil microcosm study was performed to assess the effects of multi-generational exposure of wheat (Triticum aestivum L.) to cerium oxide nanoparticles (CeO2-NPs). Seeds from plants that were exposed to 0, 125, and 500 mg CeO2-NPs/kg soil (Ce-0, Ce-125 or Ce-500, respectively) in first generation (S1) were cultivated in factorial combinations of Ce-0, Ce-125 or Ce-500 to produce second generation (S2) plants. The factorial combinations for first/second generation treatments in Ce-125 were S1-Ce-0/S2-Ce-0, S1-Ce-0/S2-Ce-125, S1-Ce-125/S2-Ce-0 and S1-Ce-125/S2-Ce-125, and in Ce-500 were S1-Ce-0/S2-Ce-0, S1-Ce-0/S2-Ce-500, S1-Ce-500/S2-Ce-0 and S1-Ce-500/S2-Ce-500. Agronomic, elemental, isotopic, and synchrotron X-ray fluorescence (XRF) and X-ray absorption near-edge spectroscopy (XANES) data were collected on second generation plants. Results showed that plants treated during the first generation only with either Ce-125 or Ce-500 (e.g. S1-Ce-125/S2-Ce-0 or S1-Ce-500/S2-Ce-0) had reduced accumulation of Ce (61 or 50%), Fe (49 or 58%) and Mn (34 or 41%) in roots, and δ15N (11 or 8%) in grains compared to the plants not treated in both generations (i.e. S1-Ce-0/S2-Ce-0). Plants treated in both generations with Ce-125 (i.e. S1-Ce-125/S2-Ce-125) produced grains that had lower Mn, Ca, K, Mg and P relative to plants treated in the second generation only (i.e. S1-Ce-0/S2-Ce-125). In addition, synchrotron XRF elemental chemistry maps of soil/plant thin-sections revealed limited transformation of CeO2-NPs with no evidence of plant uptake or accumulation. The findings demonstrated that first generation exposure of wheat to CeO2-NPs affects the physiology and nutrient profile of the second generation plants. However, the lack of concentration-dependent responses indicate that complex physiological processes are involved which alter uptake and metabolism of CeO2-NPs in wheat

Impact of Cerium Oxide Nanoparticles on Cilantro (Coriandrum sativum)

The impact of nanoparticles (NPs) on edible plants is currently a theme of great concern. Cerium oxide NPs (CeO2 NPs) are widely used in biomedical applications, fuel additives, and other consumer products. Studies have shown that these NPs are associated with liver damage. In addition, studies from our research group have also shown that CeO2 NPs are stored in plant tissues without modification. Thus, these NPs could be distributed in the food chain through edible plants, posing a threat for human health. Cilantro (Coriandrum sativum) is a very important culinary and medicinal plant worldwide. It is consumed either as a fresh herb or as a spice. In this research we are exposing cilantro plants to different concentrations of CeO2 NPs. Several spectroscopic and microscopic techniques are being used to analyze the NP treated plants. Data about the impact of CeO2 NPs on plant growth and uptake of the CeO2 NPs by cilantro plants will be presented