Cadmium signalling in sunflower. The involvement of superoxide anion and H2O2

IANUZZO MP; GROPPA MD; GALLEGO SM; BENAVIDES MP; TOMARO ML

Viena-Austria

Congreso; 9th International Congress on Amino Acids and Proteins; 2005

Reactive oxygen species (ROS), such as superoxide anion (O2.-) and H2O2, could function as intracellular second messengers. In the present work, we studied the participation of O2.- and H2O2 in the signal transduction pathway that mediates Cd2+ toxicity symptoms in sunflower leaf discs, by using several inhibitors (LaCl3, ODQ, DPI, EGTA, Zn2+) or inducers (Ca2+). H2O2 and O2.- were evidenced by nitroblue tetrazolium (NBT) and diaminobenzidine assays. Total GSH decreased significantly after 14h of 0.5 mM Cd2+ treatment and the effect was partially reversed by a Ca2+ channel blocker, LaCl3, and by ODQ, an inhibitor of cGMP. TBARS content increased an average of 30% under Cd2+ stress and this increase was not reversed by any of the inhibitors tested. Catalase activity was reduced by Cd2+ and this decay was partially reversed by LaCl3, Ca2+ and Zn2+. The production of O2.-was completely inhibited by 0.5 mM Cd2+ after 14 h of treatment. Again, LaCl3 abolished the effect of Cd2+. However, when Cd2+ was used at 0.01, 0.1 or 0.5 mM for 1 h, O2.- formation in treated discs occurred as in controls. The inhibition of the O2.- formation started after 3 h of treatment with 0.5 mM Cd2+ or later with the lower Cd2+ concentrations. The results obtained in relation to SOD activity or H2O2 formation were not clear enough to definitively clarify their roles in Cd2+ toxicity. The role of NADPH oxidase-like enzyme as the target of Cd2+ and the involvement of Ca2+ as mediator of Cd2+ effect is discussed.