Heavy-metal-binding protein. Binds cadmium. May be involved in cadmium transport and play a role in cadmium detoxification. Interacts with ZHD11/HB29. A number of isoforms are produced. According to EST sequences. Expressed at low levels in leaves and sepals. Hipp20, hipp21 and hipp22 triple mutants are cadmium sensitive. Belongs to the HIPP family.