Environmental and Experimental Botany 69 (2010) 9–16 Contents lists available at ScienceDirect Environmental and Experimental Botany journal homepage: www.elsevier.com/locate/envexpbot Antioxidative response of Atriplex codonocarpa to mercury Cristina Lomonte a,b,c,∗ , Cristina Sgherri c , Alan J.M. Baker b , Spas D. Kolev a , Flavia Navari-Izzo c a School of Chemistry, The University of Melbourne, Victoria 3010, Australia b School of Botany, The University of Melbourne, Victoria 3010, Australia c Dipartimento di Chimica e Biotecnologie Agrarie, Universita’ di Pisa, Pisa, Italy article info Article history: Received 5 June 2009 Received in revised form 18 February 2010 Accepted 22 February 2010 Keywords: Ascorbate Ascorbate peroxidase Atriplex codonocarpa Glutathione Glutathione reductase Mercury Superoxide dismutase 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Among the heavy metals frequently present in contaminated soils, mercury is arguably of the greatest environmental and public health concern (Lomonte et al., 2010). This is due to its extremely high toxicity in both its organic and inorganic compounds and its ability to bioaccumulate, thus further increasing the risks to expo- sure even at trace levels (Kelly et al., 2006). As heavy metals such as mercury do not decompose in the environment, effective strategies are needed to remove these compounds from contaminated soils. Environmental restoration of contaminated soils with traditional physical and chemical methods is expensive and environmen- tally invasive, and demands extreme investments of economic and technological resources (Quartacci et al., 2003). Phytoreme- diation is a developing technology which utilizes plants to remove or make innocuous pollutants and it is the most innovative and environment-friendly technique (Chaney et al., 1997). Mercury is a phytotoxic metal: it has been stated that formation of toxic free radicals due to excess accumulation of Hg disrupts ∗ Corresponding author at: School of Chemistry, The University of Melbourne, Victoria 3010, Australia. Tel.: +61 3 83447093. E-mail address: c.lomonte@pgrad.unimelb.edu.au (C. Lomonte). normal functioning of plants and brings about metabolic changes (Patra et al., 2004; Moreno et al., 2008; Zhou et al., 2009). For exam- ple, Hg inhibits photosynthesis and is also able to bind with water channel proteins of root cells inducing leaf stomata to close and thus causing a physical obstruction to water flow, which affects transpiration (Zhang and Tyerman, 1999). Additionally, interfer- ence of mitochondrial activity has been reported (Messer et al., 2005). There are also reports indicating that Hg accumulation in roots blocks the uptake and transport of nutrient elements, like nitrogen and phosphorus (Boening, 2000) and induces excess ethy- lene production (Goren and Siegel, 1976). The biochemical toxicity of Hg is conditioned by its reaction with sulphydryl groups of proteins and induction of the Fenton reaction, thus inducing oxidative stress in plants and resulting in lipid peroxidation, K + leakage and overproduction of reactive oxygen species (ROS) as the superoxide radical (O 2 •- ), singlet oxy- gen ( 1 O 2 ), hydroxyl radical (OH • ) and hydrogen peroxide (H 2 O 2 ) (Han et al., 2007). As a consequence of enhanced production of ROS, chlorophyll levels and biomass production are reduced (Patra et al., 2004). The plant capability to activate the defence system against oxidative destruction may be a key link in the mecha- nism of plant tolerance to unfavourable conditions. To combat Hg toxicity for the removal of ROS and subsequent protection of cellular membranes and organelles from oxidative damage, plant 0098-8472/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2010.02.012