Iranian Int. J. Sci. 5(2), 2004, p.145-150 Selection of Salt Tolerant Cell Lines From Cell Suspension Cultures of alfalfa (Medicago sativa) Amini, F., and Ehsanpour, A.A. Dept. of Biology, Esfahan University, Esfahan, Iran E-mail: ehsanpou@yahoo.com Fax: 311-7932456 (received: 1/3/2003 ; accepted: 3/3/2004) Abstract Plant breeding improvement and using conventional methods is difficult and relatively time consuming. Biotechnological methods, especially tissue culture and cell suspension culture can be used to transfer desirable traits such as salt resistance to forage plants such as Medicago. Stem, leaf and root explants belonging to three Medicago species: rigidula, scutellata and sativa, were initially cultured on MS (Murashige and Skoog, 1962) medium containing 2 mg/L yeast extract, 2mg/L 2,4-dichlorophenoxyacetic acid (2,4-D), 2 mg/L a- naphthaleneacetic acid (NAA), 1.5 mg/L benzyladenine (BA), 0.5 mg/L Thiodizuron (TDZ) and 2 mg/L Kinetin. Only M. sativa produced callus and was able to produce cell suspension in liquid medium. Viable cells were then transferred to the same liquid medium with 0, 30, 60, 90, 120 mM NaCl and finally, tolerant cell lines were selected at 90 mM NaCl according to packed cell volume (PCV). Keywords: cell suspension, in vitro, Medicago sativa, Medicago rigidula, Medicago scutellata, salt tolerance. Introduction Abiotic stresses which plants are subjected to are salt and heavy iones in the soil and water, oxidative, UV, and temperature (cold and heat) stresses. For plants, any level of these factors that differ significantly (more or less) from levels to which they are usually adapted to can be considered as a stressful factor. The loss of yield due to such stresses can be tremendous. Thus, it would be desirable to obtain crop plants that can tolerate specific stresses, and yet maintain high yield. Since the conventional plant breeding methods are in some cases difficult or