Metallothioneins have a high content of cysteine residues that bind various heavy metals (Probable). Functions as metal chelator of copper (Cu) and zinc (Zn). Functions cooperatively with the phytochelatin synthase PCS1 to protect plants from Cu and cadmium toxicity (PubMed:18287486). 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 (PubMed:24635746). Expressed in vascular tissues of all organs. Expressed in root and leaf phloem, pollen and root hairs. Belongs to the metallothionein superfamily. Type 15 family.