Involvement of an antioxidant defence system in the adaptive response to heavy metal ions in Helianthus annuus L. cells

A relationship between the antioxidant defence system and metal ion tolerance in two types of sunflower callus differing in metal ion sensitivity was studied. The antioxidant defence system of callus subjected to an adaptation treatment of Cd(II), Al(III) and Cr(III) responded differently to 150 muM of each metal compared with the corresponding controls under shock treatment. The GSH/GSSG ratio remained similar to control values for the three metal-acclimated calli and in the chromium shock treatment, decreasing moderately in the acute treatment with cadmium and aluminum. In contrast, the As/DAs ratio was decreased in the two different treatments for the three metals ions, but the decrease was greater with acute stress. The antioxidant enzymes responded differently according to the metal and treatment used. In chromium adapted callus, all antioxidant enzymes increased except for glutathione reductase. However, in the shock treatment ascorbate peroxidase activity was diminished with each metal ion assayed. Guaiacol peroxidase was decreased by cadmium and chromium and remained similar to control values with aluminum. Glutathione reductase was only decreased by cadmium, and superoxide dismutase and catalase activities were less increased than in tolerant cells. These results suggest the involvement of an antioxidant defence system in the adaptive response to heavy metal ions in Helianthus annuus L. cells.