: Reports about the influence of cerium-oxide nanoparticles (nCeO₂) on plants are contradictory due to their positive and negative effects on plants. Surface modification may affect the interaction of nCeO₂ with the environment, and hence its availability to plants. In this study, the uncoated and glucose-, levan-, and pullulan-coated nCeO₂ were synthesized and characterized. The aim was to determine whether nontoxic carbohydrates alter the effect of nCeO₂ on the seed germination, plant growth, and metabolism of wheat and pea. We applied 200 mgL^-1 of nCeO₂ on plants during germination (Ger treatment) or three week-growth (Gro treatment) in hydroponics. The plant response to nCeO₂ was studied by measuring changes in Ce concentration, total antioxidative activity (TAA), total phenolic content (TPC), and phenolic profile. Our results generally revealed higher Ce concentration in plants after the treatment with coated nanoparticles compared to uncoated ones. Considering all obtained results, Ger treatment had a stronger impact on the later stages of plant development than Gro treatment. The Ger treatment had a stronger impact on TPC and plant elongation, whereas Gro treatment affected more TAA and phenolic profile. Among nanoparticles, levan-coated nCeO₂ had the strongest and positive impact on tested plants. Wheat showed higher sensitivity to all treatments.

Continuous increasing leaf photosynthesis may enhance plant yield. As an evolutionary property, plants use less photosynthetic capacity than is theoretically possible. Plant nanobionics is a bioengineering field that improves plant functions using nanoparticles. We applied orange carbon dots (o-CDs) onto the foliage of green beans (Phaseolus vulgaris) grown in hydroponics to improve their photosynthetic performance and CO2 assimilation. Photosynthesis parameters, photosynthetic pigments content, total phenolic content (TPC) and antioxidative activity (TAA) were measured. Results show that photosynthetic pigments remained unchanged, while photosynthesis was improved. Both o-CDs concentrations decreased TPC and TAA. The light response curve showed higher CO2 assimilation at both o-CDs concentrations, particularly at lower light intensity. Correlation analysis confirmed increased CO2 binding and assimilation at 1 mg L−1. This study demonstrated the potential of using o-CDs as a safe biostimulator through photosynthesis increase and CO2 assimilation without toxic effects on plants. This may stimulate yield increase that paves the way for their agricultural application.