SALINITY STRESS Growth Properties and Ion Distribution in Different Tissues of Bread Wheat Genotypes (Triticum aestivum L.) Differing in Salt Tolerance A. Rahnama 1 , K. Poustini 2 , R. Tavakkol-Afshari 2 , A. Ahmadi 2 & H. Alizadeh 2 1 Department of Agronomy and Plant Breeding, College of Agriculture, Shahid Chamran University, Ahvaz, Iran 2 Department of Agronomy and Plant Breeding, Faculty of Agriculture and Natural Resources, University of Tehran, Karaj, Iran Introduction Salinity is a major abiotic stress that adversely affects crop productivity and quality (Boyer 1982). Plant responses to salinity occur in two phases through time: Osmotic and ion-specific phases. Osmotic phase is a rapid response to the increase in external osmotic pressure and occur due to the osmotic effect of the salt outside the roots. This phase immediately reduces shoot growth. Ion-specific phase is a slow response and starts when salt accumulates to toxic concentrations in the old leaves. The osmotic stress has a greater effect on growth rates than the ionic stress. Ionic stress impacts on growth much later and with less effect than the osmotic stress, especially at low to moderate salinity levels (Munns and Tester 2008). Bread wheat and other hexaploide wheats are rela- tively more salt-tolerant than durum wheat (Munns et al. 2000, Munns et al. 2003). Low accumulation of Na + in the leaves of genus Triticum is associated with salt tolerance (Munns et al. 2003). Salt tolerance in wheat (Triticum aestivum L.) and many other species is associated with the ability to exclude Na + , so that high Na + concentrations do not occur in leaves, particularly in the leaf blade (Tester and Davenport 2003, Munns 2005). High leaf Na + concentrations can cause prema- ture leaf senescence and loss of photosynthetic activity by which it reduces the rate of carbon assimilation and ultimately grain yield (James et al. 2002, Husain et al. 2003). Low rates of salt transport to shoots and tolerance of high leaf salt concentrations by efficient sequestration within cell vacuoles are two main mechanisms for salt tolerance in plants (Schachtman and Munns 1992, Ashraf et al. 2001). Keywords grain yield; ion distribution; Na + sequestration; salt stress; wheat Correspondence A. Rahnama Department of Agronomy and Plant Breeding, College of Agriculture, Shahid Chamran University, Ahvaz, Iran Tel.: +986113364056 Fax: +986113330079 Email: a.rahnama@scu.ac.ir Accepted June 7, 2010 doi:10.1111/j.1439-037X.2010.00437.x Abstract Four bread wheat genotypes differing in salt tolerance were selected to evaluate ion distribution and growth responses with increasing salinity. Salinity was applied when the leaf 4 was fully expanded. Sodium (Na + ), potassium (K + ) concentrations and K + /Na + ratio in different tissues including root, leaf-3 blade, flag leaf sheath and flag leaf blade at three salinity levels (0, 100 and 200 mm NaCl), and also the effects of salinity on growth rate, shoot biomass and grain yield were evaluated. Salt-tolerant genotypes (Karchia-65 and Roshan) showed higher growth rate, grain yield and shoot biomass than salt- sensitive ones (Qods and Shiraz). Growth rate was reduced severely in the first period (1–10 days) after salt commencements. It seems after 20 days, the major effect of salinity on shoot biomass and grain yield was due to the osmotic effect of salt, not due to Na + -specific effects within the plant. Grain yield loss in salt-tolerant genotypes was due to the decline in grain size, but the grain yield loss in salt-sensitive ones was due to decline in grain number. Salt-toler- ant genotypes sequestered higher amounts of Na + concentration in root and flag leaf sheath and maintained lower Na + concentration with higher K + /Na + ratios in flag leaf blade. This ion partitioning may be contributing to the improved salt tolerance of genotypes. J. Agronomy & Crop Science (2011) ISSN 0931-2250 ª 2010 Blackwell Verlag GmbH, 197 (2011) 21–30 21