Effects of Arginine Pretreatments on Oxidative Stress Damages and Alkaloid Content in Roots of Hyoscyamus niger under Nickel Stress

Heavy metal pollution is a worldwide problem with serious environmental consequences. The objective of the present experiment was to investigate whether arginine as nitric oxide precursor and or polyamines substrate can decrease the destructive effects of oxidative stress induced by nickel contamination in Hyoscyamus niger plant. In this study the effects of arginine pretreatment on alkaloid content of Hyoscyamus plant under heavy metal stress were investigated. In this research, four weeks seedlings were pretreated with 10 or 20 µmol arginine and then subjected to 50 or 100 µmol Ni solutions. Results showed that hydrogen peroxide content, lipoxigenase, catalase and guaiacol peroxidase activity increased in those plants which were under Ni stress, while ascorbate peroxidase activity did not change. Alkaloids content decreased in Ni stressed plants. Arginine pretreatment decreased the amounts of hydrogen peroxide and activity of these enzymes in stressed plants when compared with non-pretreated plants. Proline content also increased in Ni-stressed plants while arginine pretreatment decreased the proline content. Pretreatment of plants with arginine increased the amounts of total alkaloids in plants which were under Ni stress. In this study, it seems that protective effects of arginine were related to either polyamines or indirect synthesis of NO from polyamines.