Environmental and Experimental Botany 82 (2012) 74–79 Contents lists available at SciVerse ScienceDirect Environmental and Experimental Botany journa l h o me pa g e: www.elsevier.com/locate/envexpbot Does salt stress increase the ability of the exotic legume Acacia longifolia to compete with native legumes in sand dune ecosystems? Maria Cristina Morais a,∗ , Maria Rosaria Panuccio b , Adele Muscolo c , Helena Freitas a a Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3001-401 Coimbra, Portugal b Department BIOMA, Agriculture Faculty, Mediterranea University of Reggio Calabria, Feo di Vito 89122 Reggio Calabria, Italy c Department GESAF, Agriculture Faculty, Mediterranea University of Reggio Calabria, Feo di Vito 89122 Reggio Calabria, Italy a r t i c l e i n f o Article history: Received 29 September 2011 Received in revised form 29 February 2012 Accepted 30 March 2012 Keywords: Acacia longifolia Antioxidant enzymes Germination Invasion ability NaCl Ulex europaeus a b s t r a c t Sand dune ecosystems are one of the areas most affected by the introduction of invasive species which represents a threat for biodiversity conservation. Their invasion patterns and spread may depend on their salinity tolerance, besides other factors. To test this hypothesis, we investigated the effects of salt stress on seed germination and on the activity of antioxidant enzymes (catalase, CAT; ascorbate peroxidase, APX; peroxidase, POX; and glutathione reductase, GR) in two legume species, an invasive, Acacia longifolia (Andrews.) Willd., and a native, Ulex europaeus (L.), very common in the sand dunes of the coast of Portugal. Salt stress was induced by adding NaCl at different concentrations, 0, 50, 100 and 200 mM, for 15 days. Results showed that the highest germination percentages were obtained in distilled water (control) and that, with increasing salt concentration, seed germination was delayed and decreased in both species. Inhibition of germination was higher in the native species, only 3% of seeds germinated at 100 mM and no seeds germinated at 200 mM NaCl. In the invasive species, the reduction was higher at 200 mM NaCl (16%). Considering the coefficient of germination velocity, a decrease in both species with increasing NaCl concentration was observed. The CAT and GR activities decreased in A. longifolia with increasing salinity. In turn, APX activity significantly increased as NaCl concentration increased while the POX activities declined at the highest NaCl concentration. On the other hand, at 50 mM NaCl lower activity of CAT and APX and higher GR and POX were found in U. europaeus. In both species, protein content increased as NaCl concentration increased. In addition, it seems that APX activities play an essential role in the scavenging reactive oxygen species (ROS). These results suggest that the seeds of the invasive legume A. longifolia are more tolerant to salinity than the native legume U. europaeus, and seem better equipped to handle the physiological stress of high salinity, which may contribute to its invasive ability in sand dunes. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Salinity is one of the environmental factors that have a critical influence on the germination of halophyte seeds and plant estab- lishment (Katembe et al., 1998). Increasing salt concentration often causes osmotic/or specific ionic toxicity, which may reduce, retard (Khan and Gulzar, 2003; Abari et al., 2011) or completely inhibit seed germination (Benabderrahim et al., 2011). High levels of salt also promote alterations in the integrity of cell membranes, inhi- bition of different enzymatic activities and photosynthesis (Sairam and Tyagi, 2004). However, low salt concentration can stimulate germination in some species (Croser et al., 2001). Abbreviations: APX, ascorbate peroxidase; CAT, catalase; CVG, coefficient of ger- mination velocity; GR, glutathione reductase; POX, peroxidase; ROS, reactive oxygen species. ∗ Corresponding author. Tel.: +351 239 855210; fax: +351 239 855211. E-mail address: maria.morais@ci.uc.pt (M.C. Morais). The effects on germination depend on the concentration of NaCl and on the species examined (Croser et al., 2001). It is well recog- nized that plant species differ in their sensitivity or tolerance to salts (Ashraf and Harris, 2004). There are also evidences that the organs, tissues and cells of plants exhibit varying degrees of tol- erance to salinity at different developmental stages (Abari et al., 2011). One of the biochemical changes occurring when plants are sub- jected to biotic or abiotic stresses such as salinity, drought or extreme temperatures is the formation of reactive oxygen species (ROS) (Dionisio-Sese and Tobita, 1998; Eyidogan and Oz, 2007). ROS are a product of altered chloroplast and mitochondrial metabolism during stress (Manchanda and Garg, 2008). The major sources of ROS are the superoxide radical (O 2 - ), hydrogen peroxidase (H 2 O 2 ), single oxygen (O 2 ) and the hydroxyl radical (OH) which are pro- duced in all cellular compartments within a variety of processes. In general, they are produced during normal aerobic metabolism in plants (Noctor and Foyer, 1998; Kim et al., 2004; Ashraf and Harris, 2004; Sohn et al., 2005) and maintained at constant basal 0098-8472/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.envexpbot.2012.03.012