Salinity is one of the major factors that affect plant growth in Tunisia, where there is a wide variety of salinesodic soils in depression and in the main sebkhas and chotts (Mtimet, 2001; Mezni et al., 2002). Moreover, in irrigated areas, the
low quality of irrigation water charged with dissolved salts has resulted unfortunately in soil secondary salinization responsible for decline in productivity (Mtimet, 2001). Increased tolerance to salinity stress in crop plants, such as lettuce, is necessary in order to increase productivity in conditions of limited water supply and high salinity.