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 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. 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 nCeO 2 (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. 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. (Abstract shortened by UMI.)
Plant sciences|Analytical chemistry|Environmental science
Rico, Cyren M, "Effects of cerium oxide nanoparticles in cereals: Insights into the toxicity mechanisms and macromolecular modifications" (2014). ETD Collection for University of Texas, El Paso. AAI3682483.