Destroys radicals which are normally produced within the cells and which are toxic to biological systems. Mediates tolerance to stress, including photo-oxidative stress. 2 H(+) + 2 superoxide = H2O2 + O2 Binds 1 copper ion per subunit. Binds 1 zinc ion per subunit. Homotetramer. Expressed in leaves (at protein level). The spatial localization is regulated by miR398-mediated silencing. Mostly present in flowers, old rosette leaves and inflorescence, and, to a lower extent, in cauline leaves, stems and roots. Upon photosynthetically active radiation (PAR) (e.g. light fluence) increase and UV-B treatment. Accumulates in response to ozone fumigation, during recovery. Induced in response to oxidative stress, via a reduction of miR398-mediated silencing. Repressed by sucrose in a miR398-mediated silencing-dependent manner. Repressed by salt stress. Down-regulated by aconitase. Growth retardation (e.g. delayed flowering) and abnormal chloroplasts (e.g. less organized with fewer stacks). This phenotype is reversed under very low light conditions. Enhanced tolerance to oxidative stress. Belongs to the Cu-Zn superoxide dismutase family.