Antioxidative response of Atriplex codonocarpa to mercury

Abstract

Seedlings of Atriplex codonocarpa were grown for 4 weeks in hydroponic culture containing 0, 0.05, 0.1 and 1 mg L −1 Hg. Mercury concentrations increased in both shoots and roots with increasing Hg concentration in the medium. The greatest accumulation (6001 mg kg −1 dry weight, DW) was in roots as a result of the 1 mg L −1 Hg treatment. Mercury inhibited plant growth, mainly in roots. Membrane integrity, measured as solute leakage from roots, increased with the increase in external Hg concentration whereas total glutathione decreased in both shoots and roots. In roots of plants treated with 0.1 mg L −1 Hg, total ascorbate (AsA + DHA) was 4.5-fold higher than in the control. The AsA/DHA ratio in shoots was found to increase proportionally with the increase in the external Hg concentration while in roots this ratio was much lower than in shoots and decreased up to 0.1 mg L −1 Hg after which it slightly increased. Glutathione reductase (GR) activity was inhibited by 65% in roots and by 20–30% in shoots after 1 mg L −1 Hg treatment. However, mercury enhanced the activity of ascorbate peroxidase (APX) in both shoots and roots with the maximum activity in roots at 0.05 mg L −1 Hg treatment more than doubling. A significant Hg induced increase in the superoxide dismutase (SOD) activity in roots of A. codonocarpa seedlings was observed which peaked at 0.1 mg L −1 Hg. In shoots, SOD activity increased gradually and levelled off at 0.1 mg L −1 Hg. Two isoforms of SOD were detected in both shoots and roots of A. codonocarpa under Hg stress and they were identified as CuZn-SODs.