title: Metabolic adaptations to mercury-induced oxidative stress in roots of Medicago sativa L.
abstract: Alfalfa (Medicago sativa) roots were treated with mercuric ions in a concentration- and time-dependent manner, and lipid peroxidation was studied biochemically as well as histochemically along with other physiological responses. Histochemical staining with Schiff's reagent and Evans blue revealed that the peroxidation of membrane lipids and loss of plasma membrane integrity in Hg-treated roots occurred in the meristem and the elongation zone. The histochemical observations were supported by the quantitative determinations of thiobarbituric acid reactive substances (TBARS). However, under the mercuric ions stress, the alfalfa plants showed no significant alteration of hydrogen peroxide in roots. Analysis of lipoxygenase activity by non-denaturing polyacrylamide gel electrophoresis (PAGE) showed that there were two isoforms in the root of alfalfa plants, but they showed quite different patterns under the Hg exposure. Also, using non-denaturing PAGE, activities of superoxide dismutase (SOD) and peroxidase (POD) were determined in roots after treatment with Hg ions. The total activities of SOD and POD increased in roots after Hg treatment of roots. Activity of ascorbate peroxides (APX) was stimulated at relatively high concentration of Hg (40microM), and after prolonged Hg exposure (20microM, 24h). In contrast, glutathione reductase activity was depressed at higher concentrations of Hg (10-20microM). Treatments of seedlings with 10-40microM Hg decreased the ascorbate and glutathione amounts but increased total non-protein thiols. The above results indicated that Hg exerted its toxic effect on the root growth of alfalfa by induction of oxidative stress.
authors.affiliation: Department of Biochemistry and Molecular Biology, College of Life Science, No. 1 Weigang, Outside the Zhoungshan Men, Building of Life Science, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Zhao Sheng
authors.initials: ZS
authors.lastname: Zhou
authors.forename: Si Qi
authors.initials: SQ
authors.lastname: Huang
authors.forename: Kai
authors.initials: K
authors.lastname: Guo
authors.forename: Surya Kant
authors.initials: SK
authors.lastname: Mehta
authors.forename: Peng Chao
authors.initials: PC
authors.lastname: Zhang
authors.forename: Zhi Min
authors.initials: ZM
authors.lastname: Yang
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D015227:Lipid Peroxidation; D000455:Medicago sativa / Q000187:drug effects* / Q000254:growth & development; D008628:Mercury / Q000494:pharmacology*; D018384:Oxidative Stress; D018517:Plant Roots / Q000187:drug effects* / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D017392:Thiobarbituric Acid Reactive Substances / Q000378:metabolism
chemical_list: D017392:Thiobarbituric Acid Reactive Substances; D013482:Superoxide Dismutase; D008628:Mercury