Biologia 66/5: 813—820, 2011 Section Cellular and Molecular Biology DOI: 10.2478/s11756-011-0102-6 Phenolic content and antioxidant activity in two contrasting Medicago ciliaris lines cultivated under salt stress Im` ene Ben Salah 1 *, Héla Mahmoudi 2 *, Margaret Gruber 3 , Tarek Slatni 1 , Mondher Boulaaba 1 , Mhemmed Gandour 1 , Dorsaf Messedi 1 , Karim Ben Hamed 1 , Riadh Ksouri 1 , Abdelali Hannoufa 4 & Chedly Abdelly 1 1 Laboratoire des Plantes Extr˛ emophiles, CBBC, BP 901, 2050 Hammam-Lif, Tunisia; e-mail: imen ben salah@yahoo.fr 2 Physiologie et Biochimie de la Tolérance au Sel des Plantes, Faculté des Sciences de Tunis, Campus Universitaire, 2092 Tunis El Manar, Tunisia 3 Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK, S7N0X2, Canada 4 Southern Crop Protection and Food Research Centre, Agriculture and Agri-Food Canada, 1391 Sandford Street, London, ON, N5V 4T3, Canada Abstract: The objective of this study was to determine more indepth physiological and antioxidant responses in two Medicago ciliaris lines (a salt-tolerant line TNC 1.8 and a salt-sensitive line TNC 11.9) with contrasting responses to 100 mM NaCl. Under salt stress, both lines showed a decrease in total biomass and in the growth rate for roots, but TNC 1.8 was less affected by salt than TNC 11.9 in that it maintained leaf growth even in the presence of added salt. In both lines, salt stress mainly affected micronutrient status (Fe, Mn, Cu and Zn) rather than K nutrition, but the tolerant line TNC 1.8 accumulated more Na in leaves and less in roots compared with TNC 11.9. Salt stress decreased total soluble sugars (TSS) in all organs of the sensitive line TNC 11.9, whereas TSS was only reduced in roots of the tolerant line. The salt-induced drop in growth was linked to an increase in lipid peroxidation in roots of both lines and in leaves of the sensitive line. The salt-tolerant line TNC 1.8 was more efficient at managing salt-induced oxidative damage in leaves and to a lesser extent in roots than the salt-sensitive line TNC 11.9, by preserving higher phenolic compound and superoxide dismutase levels in both organs. Key words: oxidative stress; peroxidase; phenolics compounds; salt stress; superoxide dismutase. Abbreviations: CE, catechin equivalent; DM, dry matter; GAE, gallic acid equivalents; MDA, malondialdehyde; RGR, rel- ative growth rate; ROS, reactive oxygen species; SOD, superoxide dismutase; TBA, thiobarbituric acid; TCA, trichloroacetic acid; TSS, total soluble sugars. Introduction Salinity is becoming an increasing problem, especially in arid and semi-arid regions where irrigation is prac- ticed. In such areas, limited rainfall, high evapo- transpiration, high temperature and inadequate water management each contribute to increased soil salin- ity. Salinity is considered one of the most threatening factors to the natural environment and is responsible for widespread limitations to crop production, espe- cially sensitive crops such as legumes (Munns & Tester 2008). The depressive effect of salinity on plants has been attributed to osmotic effect, ion toxicity and nu- tritional imbalance (Munns & Tester 2008). In the past few years, however, an increasing body of evidence has suggested that sensitivity to salt stress is associated with oxidative stress (Cavalcanti et al. 2007; Ksouri et al. 2007; T¨ urkan & Demiral 2009; Tounekti et al. 2011). This stress presumably is due to a disturbance in the balance between the rates of reactive oxygen species (ROS) production and elimination. Such accu- mulation is extremely dangerous and is able to induce or accelerate ageing and senescence (Polle & Rennen- berg 1993) probably by disturbing normal metabolism through damage to lipids, nucleic acids and proteins (T¨ urkan & Demiral 2009). In order to avoid damage from salinity, plants have evolved a defence system which limits ROS formation and includes antioxidant enzymes and chemicals act- ing in concert. Among the antioxidant enzymes, su- peroxide dismutase (SOD) is considered to be the first line of defence. This enzyme scavenges superoxide in various cell compartments (chloroplasts, mitochondria, peroxisomes, the cytosol and the apoplast) leading to the formation of H 2 O 2 and O 2 .H 2 O 2 is then decom- posed by catalase and peroxidase (Cavalcanti et al. * These authors contributed equally to this work c 2011 Institute of Molecular Biology, Slovak Academy of Sciences Unauthenticated Download Date | 7/21/18 11:36 PM