Modifications in catalase activity and expression in developing sunflower seedlings under cadmium stress

Catalase (CAT) dismutates the reactive oxygen species H2O2 into water and dioxygen and in plants; it is located in peroxisomes and glyoxysomes. In the present study, we investigated the effect of cadmium (a well-known oxidative stress inducer) on catalase in roots and cotyledons of developing sunflower seedlings, at 10 mu M and 100 mu M. Although germination was unaltered after 48 h of exposure to 100 mu M Cd2+, root length was significantly reduced. CAT activity was also significantly reduced, but this activity was completely restored (10 mu M treatment) or even enhanced (100 mu M treatment) 24 h later. Although CAT protein abundance remained similar to control in roots and cotyledons of Cd-treated seedlings, cadmium produced CAT protein oxidation, indicating that the mechanism of CAT inactivation by Cd2+ involves oxidation of the protein structure. The transcripts of the four genes described for sunflower (CATA1 to CATA4) increased after cadmium treatment; CATA1 and CATA2 were the most overexpressed in cotyledon and root, respectively. The differential expression of catalase genes in sunflower seedlings under Cd stress might be related to the synthesis of CAT isoforms less sensitive to oxidation, which would prevent enzyme inactivation and H2O2 accumulation.