Environmental and Experimental Botany 74 (2011) 162–170 Contents lists available at ScienceDirect Environmental and Experimental Botany j o ur nal homep age : www.elsevier.com/locate/envexpbot High temperature positively modulates oxidative protection in salt-stressed cashew plants Sérgio Luiz Ferreira-Silva a , Eduardo Luiz Voigt b , Evandro Nascimento Silva a , Josemir Moura Maia b , Adilton de Vasconcelos Fontenele a , Joaquim Albenisio Gomes Silveira a,∗ a Departamento de Bioquímica e Biologia Molecular/Instituto Nacional de Ciência e Tecnologia em Salinidade (INCTsal/CNPq), Universidade Federal do Ceará, CP 6033, CEP 60451-970 Fortaleza, Ceará, Brazil b Laboratório de Estudos em Biotecnologia Vegetal, Departamento de Biologia Celular e Genética, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Campus Universitário Lagoa Nova, Caixa Postal 1648, CEP 59078-970 Natal, RN, Brazil a r t i c l e i n f o Article history: Received 17 August 2010 Received in revised form 4 April 2011 Accepted 23 May 2011 Keywords: Heat stress Salt stress Combined stresses Antioxidant enzymes Nonenzymatic antioxidant Anacardium occidentale a b s t r a c t This work evaluated the oxidative protection mechanisms triggered by high temperatures in salt-stressed cashew (Anacardium occidentale) plants. In the first experiment, cashew plants in a greenhouse were sub- jected to a wide range of NaCl concentrations under natural conditions involving high temperatures. In the second experiment, the plants were exposed to 100 mM NaCl alone, heat alone (42 ◦ C) or a combi- nation of both heat and NaCl. Data analysis from the two experiments revealed that salt-stressed plants were favored by high temperatures in terms of oxidative protection, as indicated by a decrease in lipid peroxidation and H 2 O 2 concentration. The H 2 O 2 concentration and lipid peroxidation results were cor- roborated in long-term salt exposure in a greenhouse; however, greenhouse plants that were subjected to high salinity exhibited mild protein oxidation. High temperature positively modulated protein content and the activities of catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX) in salt- stressed plants, but salinity exerted a negative effect on APX activity. The changes in ascorbate redox state were favorable for cashew protection under high salinity combined with heat. The data demonstrate that high temperature is essential for the oxidative protection of salt-stressed cashew plants, which display an efficient protection mechanism represented by the activities of CAT, SOD and APX as well as favorable changes in the ascorbate redox state under acute salt stress. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. 1. Introduction Plant species cultivated in tropical semi-arid regions face a com- plex combination of abiotic stress factors, such as drought, salinity, high temperatures and high radiation (Cavalcanti et al., 2004; Mittler, 2006). Some species adapted for those regions, such as cashew plants (Anacardium occidentale L.), have developed genetic, molecular and physiological mechanisms to overcome adverse conditions (Silveira et al., 2003). Indeed, cashew plants display good growth performance when cultivated in dry, hot and saline sites in Brazil (Ferreira-Silva et al., 2008). Recent studies have demonstrated that plants exhibit complex responses when they are simultaneously subjected to combined abiotic stresses (Wang et al., 2003; Mittler, 2006). Abbreviations: APX, ascorbate peroxidase; AsA, ascorbic acid; CAT, catalase; DHA, dehydroascorbate acid; ROS, reactive oxygen species; SOD, superoxide dis- mutase. ∗ Corresponding author. Tel.: +55 85 3366 9821; fax: +55 85 3366 9821. E-mail address: silveira@ufc.br (J.A.G. Silveira). The molecular, biochemical and physiological mechanisms involved in plant response to combined stresses are very complex (Kreps et al., 2002; Rizhsky et al., 2002, 2004; Mittler, 2006; Kotak et al., 2007; Kant et al., 2008). Oxidative metabolism is currently the most promising area of plant biology for investigating the complex metabolic networks involved in environmental stress responses (Mittler et al., 2004; Gechev and Hille, 2005; Møller et al., 2007; ´ Slesak et al., 2007). Although oxidative metabolism represents a common route for signaling and gene expression involved in abiotic stress response and tolerance (Neill et al., 2002), the understanding of this process is incipient and fragmentary (Mittler, 2002; Mittler et al., 2004). High temperatures, whether isolated or in combination with other stresses, are capable of inducing dramatic changes in plant metabolism (Penfield, 2008; Baisakh and Subudhi, 2009; Ruelland and Zachowski, 2010; Silva et al., 2010). Heat stress is often accom- panied by water deficiency and stomatal closure (Wahid et al., 2007), which reduces CO 2 availability and may decrease the CO 2 /O 2 ratio in chloroplasts (Foyer and Noctor, 2000). These changes can strongly affect photosynthetic efficiency, a process considered to be more sensitive to heat (Wise et al., 2004). In addition, heat stress 0098-8472/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.envexpbot.2011.05.015