Metallothioneins have a high content of cysteine residues that bind various heavy metals (Probable). Functions as a metal chelator of copper (Cu) and zinc (Zn). Plays a role in Cu homeostasis in the roots under elevated Cu concentration. Functions cooperatively with the phytochelatin synthase PCS1 to protect plants from Cu and cadmium (Cd) toxicity. Plays a role in Cu homeostasis, specifically in the remobilization of Cu from senescing leaves. The mobilization of Cu from internal sources is important for seed development. Confers tolerance to Cd and plays a role in Cd and Zn homeostasis