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.

Despite the remarkable number of publications on the interaction of engineered nanoparticles (ENPs) with plants, knowledge of the implications of ENPs in the nutritional value of food crops is still limited. This research was performed to study the quality of rice grains harvested from plants grown in soil treated with cerium oxide nanoparticles (nCeO2). Three rice varieties (high, medium, and low amylose) were cultivated to full maturity in soil amended with nCeO2 at 0 and 500 mg kg(-1) soil. Ce accumulation, nutrient content, antioxidant property, and nutritional quality of the rice grains were evaluated. Results showed that rice grains from nCeO2-treated plants had less Fe, S, prolamin, glutelin, lauric and valeric acids, and starch. Moreover, the nCeO2 reduced in grains all antioxidant values, except flavonoids. Medium- and low-amylose varieties accumulated more Ce in grains than the high-amylose variety, but the grain quality of the medium-amylose variety showed higher sensitivity to the nCeO2 treatment. These results indicate that nCeO2 could compromise the quality of rice. To the authors' knowledge, this is the first report on the effects nCeO2 on rice grain quality.

Little is known about the physiological and biochemical responses of plants exposed to surface modified nanomaterials. In this study, tomato (Solanum lycopersicum L.) plants were cultivated for 210days in potting soil amended with uncoated and citric acid coated cerium oxide nanoparticles (nCeO2, CA+nCeO2) bulk cerium oxide (bCeO2), and cerium acetate (CeAc). Millipore water (MPW), and citric acid (CA) were used as controls. Physiological and biochemical parameters were measured. At 500mg/kg, both the uncoated and CA+nCeO2 increased shoot length by ~9 and ~13%, respectively, while bCeO2 and CeAc decreased shoot length by ~48 and ~26%, respectively, compared with MPW (p≤0.05). Total chlorophyll, chlo-a, and chlo-b were significantly increased by CA+nCeO2 at 250mg/kg, but reduced by bCeO2 at 62.5mg/kg, compared with MPW. At 250 and 500mg/kg, nCeO2 increased Ce in roots by 10 and 7 times, compared to CA+nCeO2, but none of the treatments affected the Ce concentration in above ground tissues. Neither nCeO2 nor CA+nCeO2 affected the homeostasis of nutrient elements in roots, stems, and leaves or catalase and ascorbate peroxidase in leaves. CeAc at 62.5 and 125mg/kg increased B (81%) and Fe (174%) in roots, while at 250 and 500mg/kg, increased Ca in stems (84% and 86%, respectively). On the other hand, bCeO2 at 62.5 increased Zn (152%) but reduced P (80%) in stems. Only nCeO2 at 62.5mg/kg produced higher total number of tomatoes, compared with control and the rest of the treatments. The surface coating reduced Ce uptake by roots but did not affect its translocation to the aboveground organs. In addition, there was no clear effect of surface coating on fruit production. To our knowledge, this is the first study comparing the effects of coated and uncoated nCeO2 on tomato plants.

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.

A soil microcosm study was performed to examine the impacts of cerium oxide nanoparticles (nCeO2) on the physiology, productivity, and macromolecular composition of barley (Hordeum vulgare L.). The plants were cultivated in soil treated with nCeO2 at 0, 125, 250, and 500 mg kg(-1) (control, nCeO2-L, nCeO2-M, and nCeO2-H, respectively). Accumulation of Ce in leaves/grains and its effects on plant stress and nutrient loading were analyzed. The data revealed that nCeO2-H promoted plant development resulting in 331 % increase in shoot biomass compared with the control. nCeO2 treatment modified the stress levels in leaves without apparent signs of toxicity. However, plants exposed to nCeO2-H treatment did not form grains. Compared with control, nCeO2-M enhanced grain Ce accumulation by as much as 294 % which was accompanied by remarkable increases in P, K, Ca, Mg, S, Fe, Zn, Cu, and Al. Likewise, nCeO2-M enhanced the methionine, aspartic acid, threonine, tyrosine, arginine, and linolenic acid contents in the grains by up to 617, 31, 58, 141, 378, and 2.47 % respectively, compared with the rest of the treatments. The findings illustrate the beneficial and harmful effects of nanoceria in barley.