Nanopriming with Au-NPs Enhances Tomato Metabolism and Cold Tolerance

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.