Effects of Antioxidant Enzymes Activities in Hordeum Vulgare Seedling Under Cd~(2+),Pb~(2+),Hg~(2+),Ni~(2+)Stresses

Trace heavy metal ions of Cd2+, Pb2+, Hg2+, and Ni2+may bepresent in soil as contaminants due to industrial activities. A wide array of toxic effects have been documented in plants including genotoxicity, inhabiting seed germination inhibition, retarding root growth, decreasing mitotic index in root cells, inducing chromosomal aberrations, forming micronucleus, and altering nucleolar structure. This study examined the individual effects of these four metal ions on enzymatic activities of superoxide (SOD), peroxidase (POD) and catelase (CAT) in Hordeum vulgare. The seedlings were exposed to each of the metal ions at the concentrations from 1 to 100 mg·L-1 for 4 to 6 days. The followingenzyme kinetic analysis showed either enhanced or inhibited catalytic activities depending on ion species and enzymes used. Pb2+and Ni2+showed enhancing effects on SOD and CAT, whose activities gradually increased along with the increase in metal concentrations and exposure duration; while POD's activity increased at and but later decreased. In contrast, Cd2+was found enhancing POD and SOD activities at low concentrations but inhibiting them at higher concentrations, whereas Cd2+also consistently inhibited CAT at all the concentrations used in this study. Such steady inhibiting effects were also observed in Hg2+to SOD, POD and CAT. A further observation about these antioxidant enzymes of SOD, POD and CAT demonstrated that they are more resistant to Cd2+and Hg2+in leaves than in roots.