Plant Science 179 (2010) 423–436 Contents lists available at ScienceDirect Plant Science journal homepage: www.elsevier.com/locate/plantsci Redox regulation of the glutathione reductase/iso-glutaredoxin system in germinating pea seed exposed to cadmium Moêz Smiri a,b,∗ , Abdelilah Chaoui a , Nicolas Rouhier b , Eric Gelhaye b , Jean-Pierre Jacquot b , Ezzedine El Ferjani a a Bio-Physiologie Cellulaires, Faculté des Sciences de Bizerte, 7021 Zarzouna, Tunisia b Unité Mixte de Recherches, 1136 Interaction arbres-microorganismes INRA-Université Henri-Poincaré, IFR110, Faculté des Sciences, BP 239, 54506 Vandoeuvre cedex, France article info Article history: Received 29 January 2010 Received in revised form 28 June 2010 Accepted 29 June 2010 Available online 6 July 2010 Keywords: Cadmium Germination Glutaredoxin Pisum sativum abstract The present work aims at understanding the regulation of the glutathione/glutathione reduc- tase/glutaredoxin system (GSH/GR/GRX) in plant, namely the transition from heterotrophic growth to photoautotrophic metabolism in seedlings. Pea seeds were analyzed between 0 and 5 days. This study compares seedlings grown in the presence or absence of external cadmium. GSH/GR/GRX system was studied separately in cotyledons that mainly serve to reserve breakdown and in embryonic axes that prepare for cell elongation and cell division associated with radicle emergence. We made extracts of the proteins at various stages of the development, quantify their protein content and use them for activ- ity measurements and estimation of specific protein levels. Cadmium caused a reduction of the total glutathione content. The levels of glutaredoxin C4 (GRX C4) and glutaredoxin S12 (GRX S12) showed a Cd-dependent increase, although GRX activity was depressed. Glutathione reductase activity was signif- icantly reduced by cadmium. However, Cd treatment provoked a strong induction in protein level and activity of glutathione peroxidase (GPX). The disturbances in the resumption of redox metabolism may be a contributory cause of deleterious effect of cadmium on pea seed germination. © 2010 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Metals interact with thiols, and thiols are central components of redox-sensitive proteins in redox state and control pathways [1]. Although cadmium (Cd) has been implicated as a pro-oxidant, it differs from other pro-oxidant metal ions like copper (Cu) and iron (Fe), because it does not participate in redox cycling [2]. Cadmium, being a highly toxic metal pollutant of soils, inhibits root and shoot growth and yield production, affects nutrient uptake and home- ostasis, and is frequently accumulated by agriculturally important crops including pea with a significant potential to impair animal and human health [3]. In pea, a number of toxic effects of Cd on metabolism have been reported, such as decreased uptake of nutri- ent elements [4], inhibition of various enzyme activities [5], and induction of oxidative stress [6] including alterations in enzymes of the antioxidant defence system. Cd can cause oxidative stress by inducing the generation of reactive oxygen species (ROS), such as hydrogen peroxide (H 2 O 2 ), O 2 •- radicals, and • OH radicals, as well ∗ Corresponding author at: Unité Mixte de Recherches, 1136 Interaction arbres- microorganismes INRA-Université Henri-Poincaré, IFR110, Faculté des Sciences, BP 239, 54506 Vandoeuvre cedex, France. Tel.: +216 72 591906; fax: +216 72 590566. E-mail addresses: moez.smiri@scbiol.uhp-nancy.fr, smirimoez@yahoo.fr (M. Smiri). as disturbances in the antioxidative systems for the detoxification of ROS [6]. Binding of Cd to critical cellular components as the mech- anism of toxicity, and proteins with vicinal disulfides are expected to be particularly sensitive to inactivation by cadmium [7]. Two major redox systems are involved in maintaining of the reduced state in the plant: GSH/GR/GRX system and the thiore- doxin [8]. GRX is a 12-kDa protein that has been characterized in vitro as a specific catalyst for the reduction of protein-glutathionyl- mixed disulfides (protein-SSG) [1]. Arabidopsis thaliana contains three classes of GRX encoded by at least 31 genes. There are 14 bicysteinic (9 localized in cytosol, 3 secreted and 2 localized in the chloroplasts) and 17 monocysteinic (12 localized in cytosol, 4 local- ized in chloroplasts and 1 in mitochondria) [9]. GRX contain the conserved motif Cxx[C/S], CGFS or CCx[C/S/G] in their active sites and composed of a central  sheet surrounded by  helices. On the other hand, GSH is the major non-protein sulfhydryl compound in all living organisms, including plants [1]. GSH functions to reduce cellular disulfide bonds, often in conjunction with GRX. Under nor- mal conditions, the intracellular milieu is predominately reducing, but stress conditions can shift the redox balance toward an oxidiz- ing milieu. The reaction catalyzed by GRX is selective for GSH as the reducing substrate. This thiol–disulfide interchange reaction is likely crucial for maintaining intracellular thiol status. Accumula- tion of protein-SSG has been reported in different cell types under a variety of oxidative conditions [1]. GSH has been implicated in 0168-9452/$ – see front matter © 2010 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.plantsci.2010.06.015 RETRACTED