ORIGINAL ARTICLE Physiological and antioxidant responses of Mentha pulegium (Pennyroyal) to salt stress Samia Oueslati • Najoua Karray-Bouraoui • Houneı ¨da Attia • Mokded Rabhi • Riadh Ksouri • Mokhtar Lachaal Received: 5 June 2009 / Revised: 19 August 2009 / Accepted: 28 September 2009 / Published online: 14 October 2009 Ó Franciszek Go ´rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´w 2009 Abstract Mentha pulegium L. is a medicinal and aro- matic plant belonging to the Labiatae family present in the humid to the arid bioclimatic regions of Tunisia. We studied the effect of different salt concentrations on plant growth, mineral composition and antioxidant responses. Physiological and biochemical parameters were assessed in the plant organs after 2 weeks of salt treatment with 25, 50, 75 and 100 mM NaCl. Results showed that, growth was reduced even by 25 mM, and salt effect was more pro- nounced in shoots (leaves and stems) than in roots. This growth decrease was accompanied by a restriction in tissue hydration and K ? uptake, as well as an increase in Na ? levels in all organs. Considering the response of antioxi- dant enzymes to salt, leaves and roots reacted differently to saline conditions. Leaf and root guaiacol peroxidase activity showed an increase by different concentration of NaCl, but superoxide dismutase activity in the same organs showed a slight modification in NaCl-treated leaves and roots. Moreover, polyphenol contents and antioxidant activity were analysed in M. pulegium leaves and roots under salt constraint. The analysis showed an increase of total polyphenol content (2.41–8.17 mg gallic acid equiv- alent g -1 dry weight) in leaves. However, methanol extract of leaves at 100 mM NaCl displayed the highest DPPH scavenging ability with the lowest IC 50 value (0.27 lg ml -1 ) in comparison with control which exhibited IC 50 equal to 0.79 lg ml -1 . Keywords Antioxidant enzymes  DPPH test  Growth  Mentha pulegium L.  Polyphenol contents  Salinity Abbreviations POD Guaiacol peroxidase SOD Superoxide dismutase AMP Aromatic and medicinal plants ROS Reactive oxygen species DW Dry weight FW Fresh weight RGR Relative growth rate PAR Photosynthetic active radiations DPPH 2,2 0 -Diphenyl-1-picrylhydrazyl GAE Gallic acid equivalent Introduction The Tunisian flora is characterised by a large diversity of aromatic and medicinal plants (AMP). There is an increasing demand for the latter in several fields such as agroalimentary, perfumes, pharmaceutical industry, and natural cosmetic products. However, like most of the cul- tivated plants, growth and yield of these plants can be affected by environmental constraints such as soil and water salinity. It is assumed that salt stress would cause an imbalance of the cellular ions resulting ion toxicity and Communicated by G. Bartosz. S. Oueslati (&)  N. Karray-Bouraoui  H. Attia  M. Lachaal Unite ´ de Physiologie et Biochimie de la Tole ´rance au sel des Plantes, De ´partement de Sciences Biologiques, Faculte ´ des Sciences de Tunis, Campus Universitaire, 1060 Tunis, Tunisia e-mail: oueslati_samia@yahoo.fr M. Rabhi  R. Ksouri Laboratoire d’Adaptation des Plantes aux Stress Abiotiques, Centre de Biotechnologie de Borj-Ce ´dria, Technopole de Borj-Ce ´dria, BP 901, 2050 Hammam-Lif, Tunisia 123 Acta Physiol Plant (2010) 32:289–296 DOI 10.1007/s11738-009-0406-0