Mitigation Of Oxidative Response Triggered By HG Via Exogenous CO In Roots Of Brasica Juncea

Mercury (Hg), one of the non-essential elements of plants, has become one of the primary sources of heavy metal pollution. To dissect the mechanisms of detoxication of oxidative stress in plants, we treated the seedlings of indian mustard with specific concentrations of Hg2+(5-20μM HgCl2) in consecutive 24 h. The increasing content of TBARS represented a high level of oxidative stress in the root cells, which also showed the increase in content of NPT and proline. Histochemical staining with Schiff’s reagent and Evans blue revealed the peroxidation of membrane lipids and loss of plasma membrane integrity in the Hg-treated roots. Non-denaturing polyacrylamide gel electrophoresis (PAGE) indicated that there were four isoenzymes of POD and they showed similar patterns under Hg stress in root seedling of indian mustard. In addition, the analysis of SOD and APX activity seemed to be of the same pattern. The expression of mRNAs of antioxidant enzymes were down-regulated by various concentration of Hg and DNA laddering agarose gel electrophoresis showed a apoptosis happened after treatment of consecutive 24 hours.Carbon monoxide (CO) is a signal molecule mediating many biotic and environmental stress-induced physiological responses in plants. We investigated the role of CO in regulating Hg-induced oxidative stress in the roots of indian mustard. Plants pretreated with 0.2 mM CO for 6 h and subsequently exposed to 10μM Hg2+ for 24 h displayed attenuated toxicity to the roots. The CO-promoted root elongation was correlated with decreased lipid peroxidation in root cells. The ameliorating effect of CO was confirmed by the histochemical staining for the detection of loss of membrane integrity in Hg-treated roots. We show that treatment with 0.2 mM CO increased the activity of CAT, APX and POD in the roots exposed to Hg. However, a slightly decreased SOD activity was observed in CO+Hg-treated roots when compared to those of Hg treatment alone. We found that roots treated with CO in the presence of Hg accumulated less NPT and more proline than those treated with Hg alone. RT-PCR analysis showed that CO can increase the transcripts of antioxidant enzymes.