An average of 9 μg g−1 of copper is present in the soil. Cu deficiency is rarely observed in plants since its requirement is low. A wide range of gene families and proteins have been identified, which are involved in Cu transport and Cu homeostasis, such as COPT1, AtHMA6/PAA1, AtHMA8/PAA2, AtHMA7/RAN1, AtHMA5 and possibly YSL1 and YSL3. To protect Cu from improper interactions with other cellular constituents, Cu is chelated with nicotianamine (CuNA) and transported within the xylem sap from root to shoot. CuCCH (copper chaperone) complex is involved in inserting Cu into the active sites of Cu-dependent enzymes.