RESEARCH PAPER Root antioxidant responses of two Pisum sativum cultivars to direct and induced Fe deficiency N. Jelali 1 , S. Donnini 2 , M. Dell’Orto 2 , C. Abdelly 1 , M. Gharsalli 1 & G. Zocchi 2 1 Laboratory of Extremophile Plants (LPE), Biotechnology Centre of Borj Cedria, (CBBC), Hammam-Lif, Tunisia 2 Dipartimento di Scienze Agrarie e Ambientali – Produzione, Territorio, Agroenergia, Universit a degli Studi di Milano, Milano, Italy Keywords Iron deficiency; lipid peroxidation; pea; peroxidase isoforms; root antioxidant enzymes. Correspondence N. Jelali, Laboratoire d’Adaptation des Plantes aux Stress Abiotiques, Centre de Biotechnologie, Technopole de Borj-Cedria (CBBC), B.P. 901, 2050 Hammam-Lif, Tunisia. E-mail: nahidajelali@yahoo.fr Editor M. Hawkesford Received: 5 November 2012; Accepted: 12 July 2013 doi:10.1111/plb.12093 ABSTRACT The contribution of antioxidant defence systems in different tolerance to direct and bicarbonate-induced Fe deficiency was evaluated in two pea cultivars (Kelvedon, toler- ant and Lincoln, susceptible). Fe deficiency enhanced lipid peroxidation and H 2 O 2 concentration in roots of both cultivars, particularly in the sensitive one grown under bicarbonate supply. The results obtained on antioxidant activities (SOD, CAT, POD) suggest that H 2 O 2 accumulation could be due to an overproduction of this ROS and, at the same time, to a poor capacity to detoxify it. Moreover, under bicarbonate supply the activity of POD isoforms was reduced only in the sensitive cultivar, while in the tolerant one a new isoform was detected, suggesting that POD activity might be an important contributor to pea tolerance to Fe deficiency. The presence of bicarbonate also resulted in stimulation of GR, MDHAR and DHAR activities, part of the ASC- GSH pathway, which was higher in the tolerant cultivar than in the sensitive one. Overall, while in the absence of Fe only slight differences were reported between the two cultivars, the adaptation of Kelvedon to the presence of bicarbonate seems to be related to its greater ability to enhance the antioxidant response at the root level. INTRODUCTION Iron (Fe) deficiency is a common abiotic stress affecting plant productivity in many areas of the world, particularly in calcare- ous soils. The high pH in such soils causes low Fe availability, thus exposing the plant to severe deficiency of this nutrient (Bavaresco & Poni 2003; Abad  ıa et al. 2011). In the Mediterra- nean area, including Tunisia, calcareous soils are frequent (Jelali et al. 2010a). This can be a matter of concern for the development of several leguminous species, which commonly face Fe deficiency-induced chlorosis. Reports have shown the presence of genotypic-dependent variability in plant responses to low soil Fe availability, both among legume species and among other species (Jim enez et al. 2009). Several environmental conditions are reported to induce oxidative stress in plants (Foyer et al. 1997). Mineral deficien- cies are among the main stress factors affecting the activity of antioxidant enzymes (Chou et al. 2011). In particular, iron (Fe) can lead to oxidative stress both when scarce and when present at toxic levels. Indeed, Fe is a cofactor of many antioxi- dant enzymes and, at the same time, it can generate reactive oxygen species (ROS) through the Fenton reaction (Dasgan et al. 2003). Plants have developed different adaptive mecha- nisms to reduce oxidative damage resulting from altered Fe homeostasis through a cascade of antioxidative responses that stop the propagation of ROS-generating chain reactions. In this case, superoxide dismutase (SOD), converting O 2 À to H 2 O 2 , constitutes the first line of defence against ROS (Mittler 2002). This antioxidant response is considered to be critical for protecting plants against oxidative damage under several envi- ronmental stresses, including excess UV light, salinity, drought, heavy metals and nutritional deprivation (Molassiotis et al. 2006). At the same time, the H 2 O 2 detoxification is controlled by several enzymes, the most important being non-specific per- oxidase (POD) and catalase (CAT) (Corpas et al. 1999). More- over, ascorbate peroxidases (APX), i.e. monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), are part of an effective enzy- matic ROS scavenging system, called the ascorbate–glutathione (ASC–GSH) or Foyer–Halliwell–Asada pathway that catalyses H 2 O 2 conversion into water (Cervilla et al. 2007; Hafsi et al. 2010; Foyer & Noctor 2011). In the literature, there are few previous studies describing the effect of Fe deficiency on the ASC–GSH cycle enzymes. Peroxidases, by means of their hydroxylic or peroxidative activity, can regulate both production and scavenging of ROS in cell compartments (Romero-Puertas et al. 2007). Addition- ally, they are directly involved in lignin biosynthesis (Ranieri et al. 2001). The H 2 O 2 scavenging activity of the soluble PODs mainly plays a detoxification role in the cell wall, while both covalently and ionically bound PODs catalyse the polymerisa- tion of lignin precursors and cross-links between extensins and feruloylated polysaccharides (Ranieri et al. 2003). Several works have well documented that some growth conditions are responsible for an increase in cell wall lignification, which, by reducing cell growth, may represent plant adaptation to adverse conditions (Jbir et al. 2001; Lequeux et al. 2010; Donnini et al. 2011). With regard to plants grown under Fe Plant Biology © 2013 German Botanical Society and The Royal Botanical Society of the Netherlands 1 Plant Biology ISSN 1435-8603