Comparative Mechanisms of Mercury and Cadmium Phytotoxicity: From Uptake and Intracellular Targets to Stress Signaling and Remediation

Mercury (Hg) and cadmium (Cd) contamination in agricultural soils severely compromises plant growth, food safety, and ecosystem stability. Although both metals inhibit plant growth and induce oxidative damage and metabolic dysfunction, their phytotoxic effects arise from distinct physicochemical and biological mechanisms. This perspective develops a comparative mechanistic framework for Hg- and Cd-induced phytotoxicity across uptake and translocation, intracellular targeting, signaling responses, and epigenetic regulation. It further delineates the overlapping toxic phenotypes and metal-specific regulatory mechanisms underlying plant stress responses.In particular, it highlights the speciation-dependent and thiophilic behaviors of Hg with the essential ion mimicry and disruption of metal homeostasis caused by Cd. This comparative framework provides a mechanistic basis for refined ecological risk evaluation and metal-specific remediation of contaminated agricultural systems.