Integrated morpho-physiological and metabolic responses of tomato seed germination to hydrazine hydrate stress: The protective role of Se and Zn.

Hydrazine hydrate, a genotoxic alkylating agent, poses severe environmental and health risks due to its widespread industrial applications. Although seed germination is a critical early life-stage highly sensitive to abiotic stress, the specific phytotoxic mechanisms of hydrazine hydrate during this stage remain poorly understood. This study evaluated the morpho-physiological and metabolic responses of tomato (Lycopersicum esculentum var. Rio Grande) seeds exposed to hydrazine hydrate (0, 10, 30, 60 and 70 mM). Hydrazine hydrate dose-dependently reduced seed germination, germination index, coefficient of velocity, and seedling vigor index, while inducing severe root morphological alterations. These alterations were associated with enhanced oxidative stress, increased activity of antioxidant enzymes (SOD, CAT, and GPX), and disruption of the IAA/GA3 balance. Untargeted analysis of hydrazine hydrate-responsive metabolites, performed at the half-maximal inhibitory dose (IC50, 70 mM) revealed a preferential metabolic shift toward reactive defense compounds, activating of some branches of the phenylpropanoid, steroid glycoalkaloid, steroid saponin, phenolamide, and oxylipin pathways. Notably, exogenous selenium (Se) and Zinc (Zn) supplementation mitigated hydrazine hydrate toxicity, restoring seed germination and physiological and metabolic homeostasis by modulating ROS dynamics. These results provide novel insights into hydrazine hydrate phytotoxicity and deliver potential corrective solutions.