Cadmium stress in sugar cane callus cultures: Effect on antioxidant enzymes

Catalase (CAT) and superoxide dismutase (SOD) are antioxidant enzymes which are important in the metabolism of reactive oxygen species (ROS), and can be induced by environmental stresses including cadmium (Cd), a heavy metal toxic to living organisms. Sugar cane (Saccharum officinarumL.) in vitro callus cultures were exposed to CdCl2 and the activities of CAT and SOD were analysed. Lower concentrations of CdCl2, such as 0.01 and 0.1 mM caused a significant increase in callus growth, whereas 0.5 and 1 mM CdCl2 strongly inhibited growth of the callus cultures, but only after 9 days of CdCl2 treatment. Red-brown patches were also observed in calluses exposed to 0.5 and 1 mM CdCl2. Calluses grown in 0.01 and 0.1 mM CdCl2 did not exhibit any changes in CAT activity even after 15 days of growth in the presence of CdCl2. However, for calluses grown in higher concentrations of CdCl2 (0.5 and 1 mM), a rapid increase in CAT activity was detected, which was 14-fold after 15 days. Furthermore, up to five CAT isoforms were observed in callus tissue. Total SOD activity did not exhibit any major variation. One Mn-SOD and two Cu/Zn-SOD isoenzymes were observed in callus cultures and none exhibited any variation in response to the CdCl2 treatments. The results suggested that in sugar cane callus cultures, CAT may be the main antioxidant enzyme metabolizing H2O2.