The Nutrient Use Efficiency in intensive agriculture is lower than 50% for macronutrients. This feature results in unsustainable financial and environmental costs. Nanofertilizers are a promising application of nanotechnology in agriculture. The use of nanofertilizers in an efficient and safe manner calls for knowledge about the actual effects of nanoproducts on the plant metabolism and eventually on the carrier release kinetics and nutrient accumulation. Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) nanoparticles (nHA) have an interesting potential to be used as nanofertilizers. In this study, the effects of different nHA solutions stabilized with carboxymethylcellulose (CMC) were evaluated on germination, seedling growth, and metabolism of Solanum lycopersicum L., used as model species. Our observations showed that the percentage germination of S. lycopersicum is not influenced by increasing concentrations of nHa, while root elongation is strongly stimulated. Tomato plants grown in hydroponics in the presence of nHA have not suffered phytotoxic effects. We conclude that nHA had nontoxic effects on our model plant and therefore it could be used both as a P supplier and carrier of other elements and molecules.

Metallic nanoparticles (MeNPs) can be formed in living plants by reduction of the metal ions absorbed as soluble salts. It is very likely that plant metabolism has an important role in MeNP biosynthesis. The in vivo formation of silver nanoparticles (AgNPs) was observed in Brassica juncea, Festuca rubra and Medicago sativa. Plants were grown in Hoagland's solution for 30 days and then exposed for 24 h to a solution of 1,000 ppm AgNO3. In the leaf extracts of control plants, the concentrations of glucose, fructose, ascorbic acid, citric acid and total polyphenols were determined. Total Ag content in plant fractions was determined by inductively coupled plasma atomic emission spectroscopy. Despite the short exposure time, the Ag uptake and translocation to plant leaves was very high, reaching 6,156 and 2,459 mg kg−1 in B. juncea and F. rubra, respectively. Ultrastructural analysis was performed by transmission electron microscopy (TEM), and AgNPs were detected by TEM X-ray microanalysis. TEM images of plant fractions showed the in vivo formation of AgNPs in the roots, stems and leaves of the plants. In the roots, AgNPs were present in the cortical parenchymal cells, on the cell wall of the xylem vessels and in regions corresponding to the pits. In leaf tissues, AgNPs of different sizes and shapes were located close to the cell wall, as well as in the cytoplasm and within chloroplasts. AgNPs were not observed in the phloem of the three plant species. This is the first report of AgNP synthesis in living plants of F. rubra. The contents of reducing sugars and antioxidant compounds, proposed as being involved in the biosynthesis of AgNPs, were quite different between the species, thus suggesting that it is unlikely that a single substance is responsible for this process.

The aims of our experiment were to evaluate the uptake and translocation of cerium and titanium oxide nanoparticles and to verify their effects on the growth cycle of barley (Hordeum vulgare L.). Barley plants were grown to physiological maturity in soil enriched with either 0, 500 or 1000 mg·kg⁻¹ cerium oxide nanoparticles (nCeO₂) or titanium oxide nanoparticles (nTiO₂) and their combination. The growth cycle of nCeO₂ and nTiO₂ treated plants was about 10 days longer than the controls. In nCeO₂ treated plants the number of tillers, leaf area and the number of spikes per plant were reduced respectively by 35.5%, 28.3% and 30% (p ≤ 0.05). nTiO₂ stimulated plant growth and compensated for the adverse effects of nCeO₂. Concentrations of Ce and Ti in aboveground plant fractions were minute. The fate of nanomaterials within the plant tissues was different. Crystalline nTiO₂ aggregates were detected within the leaf tissues of barley, whereas nCeO₂ was not present in the form of nanoclusters.

The implications of metal nanoparticles (MeNPs) are still unknown for many food crops. The purpose of this study was to evaluate the effects of cerium oxide (nCeO₂) and titanium oxide (nTiO₂) nanoparticles in soil at 0, 500 and 1000 mg·kg⁻¹ on the nutritional parameters of barley (Hordeum vulgare L.) kernels. Mineral nutrients, amylose, β-glucans, amino acid and crude protein (CP) concentrations were measured in kernels. Whole flour samples were analyzed by ICP-AES/MS, HPLC and Elemental CHNS Analyzer. Results showed that Ce and Ti accumulation under MeNPs treatments did not differ from the control treatment. However, nCeO₂ and nTiO₂ had an impact on composition and nutritional quality of barley kernels in contrasting ways. Both MeNPs left β-glucans unaffected but reduced amylose content by approximately 21%. Most amino acids and CP increased. Among amino acids, lysine followed by proline saw the largest increase (51% and 37%, respectively). Potassium and S were both negatively impacted by MeNPs, while B was only affected by 500 mg nCeO₂·kg⁻¹. On the contrary Zn and Mn concentrations were improved by 500 mg nTiO₂·kg⁻¹, and Ca by both nTiO₂ treatments. Generally, our findings demonstrated that kernels are negatively affected by nCeO₂ while nTiO₂ can potentially have beneficial effects. However, both MeNPs have the potential to negatively impact malt and feed production.

This study aimed to provide insight regarding the influence of Ce oxide nanoparticles (nCeO₂) with different concentrations and two different particle sizes on the germination and root elongation in seedlings of spontaneous terrestrial species. In a bench-scale experiment, seeds of the monocot, Holcus lanatus and dicots Lychnis-flos-cuculi and Diplotaxis tenuifolia were treated with solutions containing nCeO₂ 25 nm and 50 nm in the range 0–2000 mg Ce L⁻¹. The results show that nCeO₂ enters within the plant tissues. Even at high concentration, nCeO₂ have positive effects on seed germination and the development of the seedling roots. This study further demonstrated that the particle size had no influence on the germination of L. flos-cuculi, while in H. lanatus and D. tenuifolia, the germination percentage was slightly higher (+10%) for seeds treated with nCeO₂ 25 nm with respect to 50 nm. In summary, the results indicated that nCeO₂ was taken up by germinating seeds, but even at the highest concentrations, they did not have negative effects on plant seedlings. The influence of the different sizes of nCeO₂ on germination and root development was not very strong. It is likely that particle agglomeration and ion dissolution influenced the observed effects.

Cerium oxide nanoparticles (nCeO₂) have a wide variety of applications in industry. Models demonstrated that nCeO₂ can reach environmental compartments. Studies regarding the relationships between plants and nCeO₂ considered only crop species, whereas a relevant knowledge gap exists regarding wild plant species. Specimens of Silene flos-cuculi (Caryophyllaceae) were grown in greenhouse conditions in a substrate amended with a single dose (D1) and two and three doses (D2 and D3) of 20 mg kg⁻¹ and 200 mg kg⁻¹nCeO₂ suspensions, respectively. sp-ICP-MS and ICP-MS data demonstrated that nCeO₂ was taken up by plant roots and translocated towards aerial plant fractions. Biometric variables showed that plants responded negatively to the treatments with a shortage in biomass of roots and stems. Although not at relevant concentrations, Ce was accumulated mainly in roots and plant leaves.