BIOLOGIA PLANTARUM 53 (2): 334-338, 2009 334 BRIEF COMMUNICATION Effects of salicylic acid and salinity on apoplastic antioxidant enzymes in two wheat cultivars differing in salt tolerance S. MUTLU 1 , Ö. ATICI 1 * and B. NALBANTOGLU 2 Department of Biology, Science Faculty, Atatürk University, 25240 Erzurum, Turkey 1 Department of Chemistry, Science Faculty, Atatürk University, 25240 Erzurum, Turkey 2 Abstract The effects of salicylic acid (SA) and salinity on the activity of apoplastic antioxidant enzymes were studied in the leaves of two wheat (Triticum aestivam L.) cultivars: salt-tolerant (Gerek-79) and salt-sensitive (Bezostaya). The leaves of 10-d-old seedlings grown at nutrient solution with 0 (control), 250 or 500 mM NaCl were sprayed with 0.01 or 0.1 mM SA. Then, the activities of catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) were determined in the fresh leaves obtained from 15-d-old seedlings. The NaCl applications increased CAT and SOD activities in both cultivars, compared to those of untreated control plants. In addition, the NaCl increased POX activity in the salt-tolerant while decreased in the salt-sensitive cultivar. In control plants of the both cultivars, 0.1 mM SA increased CAT activity, while 0.01 mM SA slightly decreased it. SA treatments also stimulated SOD and POX activity in the salt-tolerant cultivar but significantly decreased POX activity and had no effect on SOD activity in the salt- sensitive cultivar. Under salinity, the SA treatments significantly inhibited CAT activity, whereas increased POX activity. The increases in POX activity caused by SA were more pronounced in the salt-tolerant than in the salt-sensitive cultivar. SOD activity was increased by 0.01 mM SA in the salt-tolerant while increased by 0.1 mM SA treatment in the salt-sensitive cultivar. Additional key words: catalase, NaCl stress, peroxidase, superoxide dismutase, Triticum aestivum. ⎯⎯⎯⎯ Salt stress belongs to factors limiting the plant productivity. Similarly to other stresses, reactive oxygen species (ROS) such as superoxide, hydrogen peroxide and hydroxyl radicals are also produced during salinity (Bartosz 1997, Meloni et al. 2003). ROS can seriously disrupt normal metabolism through oxidative damage to lipids, protein and nucleic acids (Rout and Shaw 2001). Antioxidative enzymes are the most important compo- nents in the scavenging system of ROS. Superoxide dismutase (SOD) is a major scavenger of superoxide, and its enzymatic action results in the formation of H 2 O 2 which is then scavenged by catalase (CAT) and a variety of peroxidases (POX) (Noctor and Foyer 1998). A correlation between the intracellular antioxidant capacity and NaCl tolerance has been demonstrated in some plant species including wheat (Dionisio-Sese and Tobita 1998, Sairam and Srivastava 2002, Agarwal and Pandey 2004, Mandhania et al. 2006). The effects of environmental stresses on the antioxidant system in the apoplastic space have been studied by some researchers, and it has been suggested that this compartment is important in plant response to abiotic stresses (Luwe 1996, Vanacker et al. 1998, Atici and Nalbantoglu 2003). In plant cells subjected to stresses, initial events occur mostly in apoplastic space (Vanacker et al. 1998, Atici and Nalbantoglu 2003, Taşkın et al. 2003, 2006). On the other hand, some researches have showed that adverse environmental factors are capable of inducing the synthesis of ROS in apoplastic space of plants (Luwe 1996, Ranieri et al. 1996, Vanacker et al. 1998, Hernandez et al. 2001, Taşgın et al. 2006). Hernandez et al. (2001) showed different sensitivity of leaf apoplastic antioxidant enzymes to NaCl in two pea cultivars. Salicylic acid (SA) is a natural and hormone-like signal molecule for the activation of plant defenses, and ⎯⎯⎯⎯ Received 13 June 2007, accepted 10 January 2008. Abbreviations: CAT - catalase; POX - peroxidase; SOD - superoxide dismutase; SA - salicylic acid. Acknowledgements: This work was supported by the Research Fund of Atatürk University, grant No: BAP-2003/267. * Corresponding author; fax: (+90) 442 2360948, e-mail: oatici@atauni.edu.tr