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.     

Effects of Cadmium on Antioxidant Enzyme Activities in Sugar Cane

Sugar cane (Saccharum officinarum L. cv. Copersucar SP80-3280) seedlings were grown in nutrient solution with varying concentrations (0, 2 and 5 mM) of cadmium chloride for 96 h. Leaves were analysed for catalase (CAT), glutathione reductase (GR) and superoxide dismutase (SOD) activities. Although a clear effect of CdCl₂ on plant growth was observed, the activity of SOD was not altered significantly. However, the CAT activity decreased as the concentration of CdCl₂ increased. GR exhibits a significant increase in activity at 2 and 5 mM CdCl₂. CAT and SOD isoenzymes were further characterised by analysis in non-denaturing PAGE. Activity staining for SOD revealed up to seven isoenzymes in untreated control and 2 mM CdCl₂ treated plants, corresponding to Cu/Zn-SOD isoenzymes. At 5 mM CdCl₂, only six Cu/Zn-SOD isoenzymes were observed. No Fe-SOD and Mn-SOD isoenzymes were detected. For CAT, one band of activity was observed.