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Highlights • Heat stress damage the cell membrane integrity. • High temperature reduces chlorophyll content and leaf water potential. • SA elevated antioxidant enzymes activities that decreases oxidative damage. • SA increases photosynthetic efficiency. Abstract Heat stress seriously inhibits plant growth and development through damage the photosynthetic components and antioxidant enzymes functions. Salicylic acid (SA) is an important growth hormone regulator for combating heat stress, but its roles in response to high temperature in tomato are largely unknown. The present study was undertaken with a view to investigate the functional along with the potentiality of SA and how to nullify the adverse effects of heat stress (42 °C) in tomato seedlings. Our findings revealed that supplementation of 1 mM SA enhanced the gas exchange parameters (Pn, Gs, Ci, Tr, Ls), maximum quantum yield of photosystem II (Fv/Fm), water use efficiency, reduced electrolyte leakage and increased the antioxidant enzymes (SOD, POD, CAT, and APX) activity that helps to reduce oxidative damage through scavenging more reactive oxygen species (ROS) which directly impacts on plants by protecting cell membrane from damage, higher chlorophyll content, lower accumulation of lipid peroxidation, and H 2 O 2. Additionally, exogenous application of SA increased the proline content thus added on osmotic potential which influencing plants for better uptake of water that caused to beneficial effects on stomatal aperture together with photosynthetic apparatus, whereas, high temperature reduced leaf chlorophyll pigment, carotenoid content, leaf water potential, and osmotic potential. Taken together, we concluded that the adverse effects of heat stress could be suppressed by pretreated SA through both in increased photosynthesis activity and antioxidant enzymes functions. [ABSTRACT FROM AUTHOR]