Abstract

Solanum lycopersicum L. (tomato) is an economically and nutritionally important crop whose germination and early seedling growth are highly sensitive to abiotic stresses that disrupt physiological processes and intensify oxidative damage. Seed priming has emerged as a low-cost physiological preconditioning strategy to enhance stress tolerance by activating repair and defense mechanisms prior to stress exposure. This study evaluated the effects of osmopriming (PEG 6000), halopriming (KNO3), and chemopriming (SNP) on germination, early seedling growth, antioxidant enzyme activity, and lipid peroxidation in S. lycopersicum under salt stress and iron toxicity. Salt stress was induced with NaCl (100 mM) and iron toxicity with Fe-EDTA (4 mM). Priming treatments included osmopriming with PEG 6000 (−0.4 and −0.8 MPa), halopriming with KNO3 (25 and 50 mM), and chemopriming with sodium nitroprusside—SNP (0.1 and 0.2 mM). Under salt stress, NaCl (100 mM) completely inhibited germination and increased CAT activity by approximately 49% and POX activity by 4%; however, this antioxidant response was insufficient to reduce MDA content, which remained approximately 58% higher than the control. Under iron toxicity, Fe-EDTA (4 mM) reduced germination to 79% and caused a 425% increase in MDA content relative to the control, indicating severe oxidative damage despite a 59% increase in CAT and 47% increase in POX activities. Among the priming treatments evaluated, halopriming with KNO3 (50 mM) was the most effective strategy under salt stress, restoring germination to 81%, increasing CAT activity by 103%, and reducing MDA by 18% relative to non-primed salt-stressed seeds. Under iron toxicity, all priming treatments consistently increased antioxidant enzyme activities; however, none were capable of reducing lipid peroxidation or restoring seedling growth to control levels, likely due to continuous ROS generation via Fenton-type reactions that overwhelmed enzymatic detoxification capacity.

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