Integrative physiological and metabolomic study of Hirschfeldia incana under short- and medium-term lead (Pb) stress

Physiological and metabolic responses of the Pb-tolerant Brassicaceae Hirschfeldia incana to short-term (3 days) and medium-term (15 days) Pb exposure were evaluated. Physiological traits revealed an early and sustained control of oxidative stress. By day 3, non-enzymatic antioxidants and soluble sugars increased to support ROS quenching and promote osmotic adjustment. By day 15, POD activity further increased, while phenolic and soluble sugar contents remained elevated and chl b decreased selectively. Non-targeted metabolomics revealed a stronger response in roots than in shoots, highlighting the organ-specific nature of Pb tolerance in H. incana. Constitutive metabolic features were distinguished from time-dependent induced ones. Roots displayed a constitutive antioxidant defense driven by metabolic diversion from tryptophan and glucosinolates. Over time, this constitutive strategy was strengthened by an expansion of phenolics, particularly ferulic acid and sinapic acid to enhanced cell wall lignification. By day 15, the marked depletion of soluble non-enzymatic antioxidants (ascorbate and glutathione) likely reflected the sustained ROS turnover under elevated H₂O₂ levels. Although shoots accumulated less Pb, they still mounted an antioxidant response centered on anthocyanins and phenolics, along with an increase in small dipeptides, consistent with peptide-mediated nitrogen shuttling and repair. These data provide a comprehensive insight into the overall Pb stress response mechanisms in H. incana. These findings also support the potential use of this species as a model for understanding Pb tolerance and for developing phytoremediation-oriented strategies in contaminated environments.