Australian Journal of Basic and Applied Sciences, 5(11): 126-132, 2011 ISSN 1991-8178 Corresponding Author: Karima H. A. Salama, Department of Biology, Faculty of Science, Taif University, Taif, Saudi Arabia. 126 Choline Priming Improves Salt Tolerance in Wheat (Triticum aestivum L.) Karima H. A. Salama, Mohamed M. F. Mansour, Noaman S. Hassan Department of Biology, Faculty of Science, Taif University, Taif, Saudi Arabia. Abstract: Seed priming approach was adopted to modulate salt tolerance of wheat sensitive cultivar under saline environment. Caryopses of wheat salt sensitive cultivar (Triticum aestivum L.) were primed in different concentrations of choline chloride (CC, 0, 5, 10 mM) for 24 h at room temperature. The caryopses were then germinated in sand culture for 10 d, watered with 1/4-strength modified Hoagland solution (MHS). Next, 10-day-old seedlings grown in the sand culture were supplemented with 150 mM NaCl for three weeks. Changes in the fresh mass (FM), dry mass (DM), relative growth rates (RGR), mineral content of root and shoot, proline (Pro), glycinebetaine (GB), glutathione, lipid peroxidation and plasma membrane (PM) permeability were determined in presence and absence of choline and NaCl. Choline priming significantly alleviated the NaCl-induced growth reduction, the effect was more pronounced with 5 mM choline. Choline priming decreased Na + and Cl - and increased K + and Ca 2+ in the shoot and root of the stressed plants, more so with 5 mM choline. Pro level was reduced by choline pretreatment. GB was increased in primed seedlings relative to non-primed ones. Choline priming remarkably decreased leaf lipid peroxidation compared with non- primed plants. Salt imposition increased the PM permeability: an effect was mitigated by 5 mM choline priming. The results suggested that improvement of salt tolerance in wheat might be achieved through choline priming of caryopses. This might occur through increased GB accumulation, maintained ion homeostasis, and reduced lipid peroxidation. Key words: Choline, glycinebetaine, lipid peroxidation, priming, proline, salinity stress, wheat INTRODUCTION Salinity is one of the major environmental factors that adversely affect crop growth and productivity. About one-fifth of irrigated agricultural land is adversely affected by salinity (Munns and Tester, 2008). Most grain crops and vegetables are glycophytes and highly sensitive to soil salinity. Salt stress inhibits plant growth through two major effects. First, osmotic or water-deficit effect, that is, salt in soil water reduces the plant ability to take up water, and this leads to reduced growth. Second is: salt-specific or ion-excess effect: that is, accumulation of high level of toxic ions (e.g. Na + , Cl - ) in the cytoplasm with a reduction in beneficial ions (e.g. K + , Ca 2+ ), further reducing growth. In addition, salt stress leads to oxidative stress, which results from induced active oxygen species formation (Munns and Tester, 2008; Heidari, 2009). Cellular metabolism is disrupted by active oxygen species through oxidative damage to membrane lipid, proteins and nucleic acids (Mittler, 2002). Reduced growth and productivity induced by salinity is not parallel to increased food demands all over the world. Therefore, the need to develop salt tolerant crops is crucial. Considerable efforts have been devoted to develop salt tolerant lines or cultivars of various crop species. Conventional breeding has been employed to improve crop salt tolerance, but commercial success has been very limited because of various difficulties (Ashraf, 1994; Flowers and Yeo, 1995; Flowers, 2004; Ashraf and Foolad, 2005). Several attempts for induction of crop salt tolerance have been adopted through genetic transformation. However, limited progress has been made in developing transgenic plants with improved salt tolerance (Flowers, 2004; Ashraf and Foolad, 2005). Furthermore, testing the salt tolerance of transgenic plants under field conditions of salinity is lacking and argued (Flowers, 2004). Seed priming is one of the useful physiological approaches that could be used to adapt glycophyte species to saline conditions (Sivritepe et al., 2005; Ashraf and Foolad, 2005; Iqbal and Ashraf, 2005; Sargent et al., 2006). Therefore, seed priming in a precursor (i.e., choline) that might be synthesized to an osmoprotectant (i.e., glycinebetaine) and/or a membrane phospholipids constituent (i.e., phosphatidylcholine), that may have significance in regulating ion absorption under salt conditions, would be of great interest. A correlation between organic osmolytes (known as compatible solutes) accumulation and plant salt tolerance has been reported (Mansour, 2000; Rhodes et al., 2002; Chinnusamy et al., 2005). Compatible solutes