Mechanical Disturbance of Trichomes Enhances Cd ²⁺ Uptake via Malate-Mediated Stomatal Opening in Arabidopsis

Phytoremediation of cadmium-contaminated soils relies on efficient metal uptake and translocation in plants. We previously found that gentle mechanical stimulation of non-glandular trichomes by brushing significantly enhances shoot Cd²⁺ accumulation in Arabidopsis thaliana , although the underlying physiological mechanism remained unclear. Here, we demonstrate that trichome brushing specifically induces stomatal opening, elevates transpiration, and promotes Cd²⁺ uptake, as evidenced by measurements of stomatal aperture, stomatal conductance, transpiration rate, and Cd²⁺ concentration in wild-type and mutant leaves. These responses are absent in the glabrous gl1-1 mutant and are not elicited by brushing epidermal pavement cells, indicating a trichome-specific mechanosensory pathway. Mechanistically, this pathway requires MPK3/MPK6 activity and employs malic acid as a key regulator of stomatal aperture, functioning independently of canonical ABA signaling. Our findings uncover a previously unrecognized trichome-to-stomatal signaling cascade that links trichome mechanostimulation to enhanced heavy metal accumulation.