Nanopriming is a unique way to change the metabolism and stress tolerance of plants. In this study, the effects of seed priming with gold nanoparticles (Au-NPs, 15 nm) on the photosynthetic apparatus, pro-/antioxidant balance, and cold tolerance of tomato (Solanum lycopersicum L.) were examined for the first time. The study revealed that nanopriming with Au-NPs (20 µg mL⁻¹ for 24 h) causes an increase in cold tolerance both under control conditions and after cold adaptation at 9 °C for 5 d. In additional, nanopriming leads to the formation of tomato plants with altered photosynthetic apparatus and pro-/antioxidant status. At the same time, nanoparticles do not accumulate in the aboveground parts of the plants. Under control conditions, nanopriming enhances photosynthesis rate, the relative expression of rbcS gene, the number of grana in chloroplast, and the content of photosynthetic pigments in leaves. Regardless of the temperature (in control conditions and during cold adaptation), nanopriming increases the size of chloroplast, the relative expression of rbcL gene, the content of malonic dialdehyde and H₂O₂, and the activity of catalase and superoxide dismutase in leaves. Nanopriming decreases the activity of ascorbate peroxidase and sugar content in tomato leaves and leads to a number of structural changes in chloroplasts. This study highlights the potential of the use of Au-NPs as a promising strategy to mitigate cold stress in tomato plants by affecting photosynthesis and the antioxidant system.

It is of utmost importance to investigate the effect of carbon-based nanostructures on plants in order to fully unlock their potential for enhancing productivity and stress tolerance. In this study, a comprehensive assessment of the effect of pre-sowing treatment of wheat seeds with fullerenol (PHF [C₆₀(OH)₂₄], 0.1 mg/L) solution on a number of physiological and biochemical parameters in seedlings under optimal and low temperature (LT, 4 °C, 5 days) conditions was carried out. Seedlings primed with PHF differed from control variant in accelerated growth (by 27–34%), increased biomass (by 10%), larger area of chloroplasts and mesophyll cells (by 40%), more intensive photosynthesis (1.5-fold higher), increased content of chlorophyll a (by 11%), proteins (by 28%) and ascorbic acid, reduced level of MDA and H₂O₂, decreased SOD activity (by 45%) and a higher level of COR-genes (WCOR15, WCOR726) transcription (p < 0.05). Under LT conditions, PHF nanopriming enhanced photosynthesis intensity by increasing chloroplast area, content of chlorophyll b (by 22%) and proportion of chlorophyll in LHC (by 11%), as well as increasing the expression of RBCS (fourfold higher), content of proline, and COR-gene expression (p < 0.05). All these changes are adaptive and expand the adaptive potential of plants. It is concluded that nanopriming with PHF is an active metabolic modulator that reduces ROS generation and enhances cold acclimation of wheat.