Evaluation of Sodium Accumulation in Leaves of Wheat (Triticum Aestivum L.) Cultivars Differing in Salt Tolerance

Background and Objectives Two main mechanisms for salt tolerance in plants are low rate of salt transport to shoots and tolerance of high leaf salt concentrations by sequestration of Na within cells vacuoles. Recently research for genetic variation in Na accumulation within bread wheat has revealed large variation in leaf Na concentration. The control of Na accumulation in leaf is an important physiological process conferring salt tolerance to wheat. Many studies have shown that low sodium concentration in leaves correlate with salt tolerance. Sodium concentration in leaves may be influenced by sodium uptake by roots and transport from root to shoot.
Materials and Methods In order to understand the salt tolerance mechanisms and the pattern of Na accumulation, 3 bread wheat cultivars differing in salt tolerance (Kavir, Mahdavi and Jajan), were evaluated through two factorial experiments based on completely randomized design in three replications. Experiment 1 used 3 cultivars (Kavir, Mahdavi and Jajan) with four salt treatments (0, 50, 100 and 150 mM NaCl) and experiment 2 used three cultivars (Kavir, Mahdavi and Jajan) with two salt treatments (0 and 150 mM NaCl).
Results Leaf Na concentration of genotypes was increased in response to increasing salinity after 14 days but Na concentration was greater in sensitive genotype (Tajan) than tolerant genotypes (Kavir and Mahdavi). There were no significant differences between genotypes in RGR and shoot: root ratio. Results showed that the differences between genotypes in Na transport were responsible for differences in shoot Na concentrations. Na concentration in the root of all genotypes was the same but salt tolerant genotypes maintained higher K: Na ratio in shoot. Shoot biomass was significantly reduced at 150 mM NaCl, whereas this reduction was almost the same for all genotypes. Kavir had the highest ability to tolerate high leaf tissue concentrations of Na and leaf Na concentrations were much lower in Mahdavi than two other cultivars.
Discussion It seems that the major effect of salinity on shoot biomass was due to the osmotic effect of salt, not due to Na+specific effects within the plant. Differences in Na transport rates from roots to shoots may cause different patterns of sodium accumulation through time. The comparison of genotypes suggests that at least there are two main mechanisms for salt tolerance in hexaploid wheat. One is a lower rate of Na accumulation in shoot and the other is tolerance of tissue to high concentrations of Na.