Over-expression of Cu/ZnSOD Increases Cadmium Tolerance in Arabidopsis thaliana

Over-expression of a copper/zinc superoxide dismutase (Cu/ZnSOD) resulted in substantiallyincreased tolerance to cadmium exposure in Arabidopsis thaliana. Lower lipid peroxidation and H2O2 accumulationand the higher activities of H2O2 scavenging enzymes, including catalase (CAT) and ascorbateperoxidase (APX) in transformants (CuZnSOD-tr) compared to untransformed controls (wt) indicated thatoxidative stress was the key factor in cadmium tolerance. Although progressive reductions in the dark-adaptedphotochemical efficiency (Fv/Fm) and quantum efficiency yield were observed with increasing cadmium levels,the chlorophyll fluorescence parameters were less marked in CuZnSOD-tr than in wt. These observationsindicate that oxidative stress in the photosynthetic apparatus is a principal cause of Cd-induced phytotoxicity,and that Cu/ZnSOD plays a critical role in protection against Cd-induced oxidative stress.