Research article Nickel elicits a fast antioxidant response in Coffea arabica cells R.A. Gomes-Junior a , C.A. Moldes a , F.S. Delite a , P.L. Gratão a , P. Mazzafera b P.J. Lea c , R.A. Azevedo a, * a Departamento de Genética, Escola Superior de Agricultura Luiz de Queiroz, Universidade de São Paulo, Piracicaba 13418-900, SP, Brazil b Departamento de Fisiologia Vegetal, Instituto de Biologia, CP 6109, Universidade de Campinas, Campinas 13083-970, SP, Brazil c Department of Biological Sciences, University of Lancaster, Lancaster LA1 4YQ, UK Received 1 December 2005 Available online 13 June 2006 Abstract The antioxidant responses of coffee (Coffea arabica L.) cell suspension cultures to nickel (Ni) were investigated. Ni was very rapidly accu- mulated in the cells and the accumulation could be directly correlated with the increase of NiCl 2 concentration in the medium. At 0.05 mM NiCl 2 growth was stimulated, but at 0.5 mM NiCl 2 , the growth rate was reduced. An indication of alterations in the presence of reactive oxygen species was detected by an increase in lipid peroxidation at 0.5 mM NiCl 2 . Catalase (CAT; EC 1.11.1.6), glutathione reductase (GR; EC 1.6.4.2), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GOPX; EC 1.11.1.7) and superoxide dismutase (SOD; EC 1.15.1.1) activities were increased, particularly at earlier NiCl 2 exposure times and the activities were higher at 0.5 mM NiCl 2 for most of exposure times tested. Non-denaturing PAGE revealed one CAT isoenzyme, nine SOD isoenzymes and four GR isoenzymes. The SOD isoenzymes were differentially affected by NiCl 2 treatment and one GR isoenzyme was increased by NiCl 2 . NiCl 2 at 0.05 mM did not induce lipid peroxidation and the main response appeared to be via the induction of SOD, CAT, GOPX and APX activities for the removal of the reactive oxygen species and through the induction of GR to ensure the availability of reduced glutathione. © 2006 Elsevier SAS. All rights reserved. Keywords: Coffea arabica; Oxidative stress; Lipid peroxidation; Nickel; Catalase; Glutathione reductase; Superoxide dismutase 1. Introduction Heavy metals can be included in the main category of pol- lutants. Ni is a heavy metal used extensively in electroplating, in the manufacture of steel and other alloys, in the manufacture of batteries and electronic devices [15], oil products and the products of fossil fuel combustion (ash, slag, clinker) [47]. Ni can contaminate the soil mainly through sewage sludge, indus- trial compost and atmospheric fallout, especially near proces- sing plants [47]. In trace amounts, Ni is a necessary element for living organisms because it functions as an irreplaceable com- ponent of urease, which is responsible for the hydrolysis of urea [63]. More recently, Ni and other metals were shown to be a cofactor of enzymatic cupin class of plant proteins, although the majority contain iron as an active site metal [18]. However, in higher concentrations Ni is a toxic pollutant for humans, animals and plants [47]. Ni also induces lipid per- oxidation and oxidative stress, that is involved in the molecular mechanisms of Ni toxicity and carcinogenicity [15]. Ni has been shown to be accumulated in distinct tissues of Ni hyper- accumulating plant species [8,11,60], which can be used for phytoremediation of Ni contaminated areas. Ni phytotoxicity results in leaf chlorosis and reduction of green biomass [31], reduced rates of photosynthesis and respiration [56], low seed germination [48], weak plant growth, yield depression and may even be accompanied by reduced nutrient uptake, disorders in plant metabolism and, in legumi- nous plants, a reduced capacity of nitrogen fixation [47]. Recent research revealed that transgenic canola plants expres- sing 1-aminocyclopropane-1-carboxylic acid deaminase from bacteria exhibited a significant increase in tolerance to Ni when compared to the non-transformed control plants when www.elsevier.com/locate/plaphy Plant Physiology and Biochemistry 44 (2006) 420–429 * Corresponding author. Fax: +55 19 3433 6706. E-mail address: raazeved@esalq.usp.br (R.A. Azevedo). 0981-9428/$ - see front matter © 2006 Elsevier SAS. All rights reserved. doi:10.1016/j.plaphy.2006.06.002