Destroys radicals which are normally produced within the cells and which are toxic to biological systems. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 copper ion per subunit. Binds 1 zinc ion per subunit. Homodimer. Expressed in leaves (at protein level). Upon photosynthetically active radiation (PAR) (e.g. light fluence) increase or after high-light pulse, and UV-B treatment. Accumulates in response to ozone fumigation, during recovery. Repressed by salt stress. Belongs to the Cu-Zn superoxide dismutase family.