Abstract
Nanoparticles have been shown to enhance salinity and drought stress tolerance in various crops, but their potential to enhance thermotolerance remains less studied. This study evaluated the effects of foliar applications of CuO, SiO
2
, and ZnO nanoparticles on the thermotolerance of tomato (
Solanum lycopersicum
) seedlings. ‘Celebrity’ tomato seedlings were treated weekly with 10 ppm CuO, 50 ppm SiO
2
, or 50 ppm ZnO nanoparticles for 4 weeks and subjected to either optimal (26/19 °C, day/night) or heat stress (38/30 °C) conditions in growth chambers. Under heat stress, all nanoparticle treatments improved chlorophyll fluorescence (Fv/Fm), and SiO
2
nanoparticles reduced reactive oxygen species (ROS) accumulation by 9.6%. However, nanoparticle treatments did not enhance shoot and root biomass, leaf pigment and proline content, and enzymatic and nonenzymatic antioxidant capacity. Additionally, CuO and SiO
2
nanoparticles reduced leaf transpiration rates by 27.7% and 30.5%, respectively, potentially limiting evaporative cooling under heat stress. In conclusion, although nanoparticles influenced specific physiological responses, they did not improve the overall thermotolerance in tomato seedlings.