Effects of salinity and deficit irrigation on ion distribution in different tissues of bread wheat (Triticum aestivum L.)

Background and Objectives Plants are often subjected to water deficit and soil salinity in arid and semiarid regins. Water deficit and salinity threaten crop productivity as both stresses reduced the soil water potential. In the natural invironment drought and salinity frequently combined. Understanding how plants responds to water deficit, salt and co-occurring stresses can play a major role to improving the toleranc of crops to both water deficit and salinity. Salinity may cause ions imbalances, due to the competition of Na+ with nutritons such as K+. Reduced transpiration rates due to water deficit reduces the nutrient uptake and transport. Deficit irrigation with fresh water can increase water use efficiency without significantly decreasing yield. Several studies have focused on effect of water deficit and salinity on nutrients uptake but there is still no information on the effect of these conditions on ions relations and water use efficiency. The aim of this study was to investigate the effects of salinity and water deficit on ion distribution in different tissues and water use efficiency of bread wheat cultivars with contrasting of sodium concentration.   Materials and methods In this study, ions distribution and grain water use efficiency (WUE) of two bread wheat cultivars (Arg and Tajan) with contrasting of sodium concentration to different irrigation regimes (full irrigation, 80 and 70 percent of water requirement) and different salinity levels (0 and 150 mM NaCl) in a greenhouse experiment with three replications were evaluated. Treatments were imposed when the leaf 4 was fully expanded. For sodium and potassium analysis, at 7 weeks after treatments, plants were completely harvested from pots, washed and divided into required parts. Roots, flag leaf sheath, flag leaf blade and leaf 3 blade used for determining Na+ and K+ concentrations. The remaining plants were left to grow until physiological maturity. Plants were harvested after 16 weeks to measure yield and root biomass. Results and discussion Whole plant sodium concentration of cultivars was significantly increased under salt stress. In salt treatment, the tissues Na+ and K+ concentration was significantly higher in Arg than Tajan. Under salt stress, water deficit caused a reduction in Na+ concentration in all tissues. Sodium uptake by root was similar in cultivars but Tajan maintained lower Na+ concentration in shoot tissues under salinity. Differences in sodium concentration were found in flag leaf blade in cultivars. Genotypic differences in the rate of sodium transfer from the root to shoot are caused to occure genotypic differences in leaves Na+ concentration. Tajan had more control of ion transport from root to shoot. Under salt stress, K+ concentration was not affected by water deficit in tissues. Arg maintained higher K+ concentration with K+/Na+ ratios in flag leaf blade than Tajan cultivare. Root biomass decreased in cultivars at 150 mM NaCl whereas don’t affected by deficit irrigation. An NaCl concentration of 150 mM was found suitable to identify genetic variation in root wheat genotypes. NaCl decreased grain yield and grain WUE in salt stress conditions and Tajan showed more decreases from this aspect. It seems that, a lower decrease in grain WUE in Arg, is due to greater tissue tolerance. Conclusions: Differences in Na+ concentration under salinity and drought, mainly occur in the youngest leaf blade between cultivars and lower sodium transfer from the root to shoot, lower sodium accumulation in younger leaves and higher K+/Na+ ratios can be important in stabilizing wheat yield and grain water productivity. Tajan have a more resistance to osmotic stress than Arg and tissue tolerance in Arg was greater than Tajan cultivare. Cultivars that maintained low concentration of Na+ in shoots and have a greater degree of tissue tolerance, in regions with poorer quality irrigation water, have more water productivity and thus this is an imperative to develop cultivars with above mentioned characteristics in soils with higher salt and limited water.