Assessment of the effect of sodium accumulation on chlorophyll content and some of physiological traits under salt conditions in wheat and barley

Salinity impacts on crop production is further increasing as the global demand for food means agriculture extends into naturally salt-affected lands. Chlorophyll retention and the low sodium traits were associated with salt tolerance in wheat and barley under salinity conditions. Saline soils limit plant growth due to osmotic stress, ionic toxicity, and a reduced ability to take up essential minerals. Barley and wheat have different salt tolerances capacities and are grown as major grain crops in both saline and non-saline soils. The net sodium uptake for a plant growing in 150mM NaCl with perfect osmotic adjustment is similar to actual rates measured for wheat and barley. Our hypothesis is that salinity reduces the growth of wheat more than barley by reducing chlorophyll content. The aims of this study were to analyse the effects of salinity on the growth and yield of barley and wheat cultivars to explore the links between the sodium accumulation and chlorophyll content.

Tow bread wheat cultivars differing in salt tolerance (Arg and Tajan) and a barley cultivar (Nik) were used to assess the change in the chlorophyll content and sodium accumulation over time under saline conditions. Two levels of NaCl (0 and 150 mM NaCl) were imposed as the salinity treatments when the leaf 4 was fully expanded. At 21 days after salt treatment plants were harvested and shoot and root dry weight, root length and sodium root were measured. Sodium accumulation rates and chlorophyll content examined between days 14 and 42 after salt added. Na+ and K+ flag leaf were measured in days 49 after salt treatment started.

Results showed that the rate of sodium accumulation initially was the same for both wheat cultivars in leaf. After 30 days of salinity, the rate of sodium accumulation rose in Arg compared with Tajan. In Nik barley cultivar, shoot sodium concentration was higher than bread whit cultivars. Salinity caused degradation in chlorophyll content in both bread wheat cultivars and at the determination of this experiment Tajan had lower chlorophyll content than Arg cultivar. Nik barley cultivar showed much longer chlorophyll retention than tow bread wheat cultivars. Salinity decrease K+ flag leaf, K+/Na+ flag leaf, shoot and root dry weight, seminal root length, yield and increase Na+ flag leaf and Na+ roots compared to control. Flag leaf K+/Na+ ratio was higher in salt tolerance cultivar (Arg) compared to Tajan and Nik, despite the similar roots sodium concentration. Flag leaf Na+ concentration was the same in tow wheat cultivars and barley under salinity stress and there was no relationship between Na+ exclusion and salt tolerance in cultivars in our experiment. Yield loss of 35 percentages was found in wheat cultivars on average and in barley did not observed remarkable decrease in seed yield. There was may be no beneficial effect of the low Na+ trait at 150 mM NaCl (high salinity level) in all cultivars. Root length reduction in cultivars was due to osmotic stress of salt solution out of the roots. A significant correlation between shoot dry weight and sodium flag leaf showed that sodium concentration in leaf can be used as an index for evaluating salt tolerance.

Given the effect of salinity on shoot growth, it seems that other factors may have influenced net carbon gain before any reduction in the concentration of chlorophyll. It implies that osmotic and tissue tolerance in bread wheat and barley contributed to the salt tolerance in tolerant cultivars and preferential sodium accumulation and maintains in roots and old leave relative to young leaves can caused an increase in salt tolerant. The low shoot sodium concentration was not associated with chlorophyll content in wheat cultivars.