Antioxidant enzyme activities as affected by trivalent and hexavalent chromium species in Fontinalis antipyretica Hedw Marc Dazy a, * , Eric Béraud a , Sylvie Cotelle a , Eric Meux b , Jean-François Masfaraud a , Jean-François Férard a a Université Paul Verlaine-Metz, Laboratoire ‘‘Interactions Ecotoxicologie, Biodiversité, Ecosystèmes”, CNRS UMR 7146, Campus Bridoux, Rue du Général Delestraint, 57070 Metz, France b Université Paul Verlaine-Metz, Laboratoire ‘‘Electrochimie des Matériaux”, CNRS UMR 7555, ICPM, 1 bd Arago, CP 87811, 57078 Metz Cedex 3, France article info Article history: Received 6 March 2008 Received in revised form 3 June 2008 Accepted 13 June 2008 Available online 8 August 2008 Keywords: Heavy metals Oxidative stress Antioxidant enzymes Glutathione Chlorophyll Aquatic moss abstract The detoxification mechanisms of the aquatic moss, Fontinalis antipyretica Hedw., exposed to Cr was ana- lyzed. In addition, the influence of Cr salts (as Cr nitrate, chloride and potassium bichromate) on these mechanisms has also been studied. The activity of antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1.), catalase (EC 1.11.1.6.), ascorbate peroxidase (APX, EC 1.11.1.11.), guaiacol peroxidase (GPX, EC 1.11.1.7.) and glutathione reductase (GR, EC 1.6.4.2.) increased in plants treated with Cr concen- trations ranging from 6.25  10 5 to 6.25 mM when given as Cr(NO 3 ) 3 . Antioxidant enzymes responded to the other two salts CrCl 3 and K 2 Cr 2 O 7 only with Cr concentrations higher than 6.25  10 2 mM. Glu- tathione level and GSSG/GSH ratio also responded to Cr exposure but no dose–effect relationship could be observed. Moreover, two unknown thiol compounds were observed in mosses exposed to the highest Cr concentrations. Effects on chlorophyll contents and chlorophyll a/b ratios were also shown even at low Cr concentrations. Our results indicated that environmentally realistic concentrations of Cr could lead to impairment of the cellular activity towards F. antipyretica and that Cr(III), when present as a nitrate salt, was as harmful as Cr(VI). Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Due to its widespread use in leather tanning, textile, and pig- ment electroplating industries, Cr has become one of the most abundant pollutants in aquatic and terrestrial ecosystems (Rai et al., 2004). It can be found in several oxidation states even if the most common and stable forms are the trivalent and the hexa- valent species, which respectively occur as free Cr 3+ or associated with oxygen as chromate (CrO 2 4 ) or dichromate (Cr 2 O 2 7 ) oxya- nions (Shanker et al., 2005; Sinha et al., 2005). The bioavailability and toxicity of Cr depends on its speciation. In plants, Cr(III) and Cr(VI) are both able to cross biological mem- branes (Gorbi et al., 2001). Cr was shown to be accumulated by plants and notably by the moss Fontinalis antipyretica up to 40– 60 mg/kg dry weight (Samecka-Cymerman et al., 2005; Vardanyan and Ingole, 2006) and biomagnified at different trophic levels through the food chains (Gorbi et al., 2004; Rai et al., 2004). Inside the cells, Cr interferes with several metabolic processes like photosynthesis, causing phytotoxicity as exhibited by reduced growth and biomass, chlorosis, ultrastructural effects on organ- elles, chromatin condensation, swelling of mitochondria, mem- brane damages, development stunting and finally plant death (Vazquez et al., 1987; Kimbrough et al., 1999; Ali et al., 2004; Sper- anza et al., 2007). Cr has also been demonstrated to stimulate the formation of reactive oxygen species (ROS) in a wide range of species and cultured cells, either by direct electron transfer involving metal cations or as a consequence of metal-mediated inhibition of meta- bolic reactions (review by Stohs and Bagchi, 1995). Oxidative dam- ages resulting from ROS towards biomolecules such as lipids, proteins and nucleic acids is well documented for plant species (Kanazawa et al., 2000; Singh et al., 2006). However, plants possess defence mechanisms in order to limit oxidative damages. Antioxidants such as ascorbate, carotenoids and thiols, act as free radicals scavengers while antioxidant en- zymes, like catalase (CAT), superoxide dismutase (SOD) and perox- idases play an important role in ROS reduction and cell injury protection (Harris, 1992). If the hyperactivity of antioxidant en- zymes and accumulation of cellular antioxidants in aquatic and terrestrial plants under cadmium, copper or zinc exposure have been reported (Chaoui et al., 1997; Laspina et al., 2005; Lombardi and Sebastiani, 2005), no study has been published about effects of Cr(III) and Cr(VI) on antioxidant defence system in aquatic plants. Among aquatic plants, bryophytes are often used for freshwater biomonitoring purposes especially by the extend use of moss bags (Empain, 1977; Figueira and Ribeiro, 2005). These plants lack 0045-6535/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2008.06.044 * Corresponding author. Tel.: +33 03 87 37 85 00; fax: +33 03 87 37 85 12. E-mail address: dazy@univ-metz.fr (M. Dazy). Chemosphere 73 (2008) 281–290 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere