Osmotic stress and ion-toxicity effects of salt stress using immediate photosynthetic responses of durum wheat

Salinity affects plant growth by the osmotic stress of salt around the roots as well as by toxicity caused by excessive accumulation of salt in leaves. The study of photosynthetic traits as a rapid and non-destructive tool demonstrates the great potential for improving plant productivity and stress tolerance. A pot experiment was carried out to investigate short-term effects of osmotic stress (45 min) on photosynthetic traits of four durum wheat genotypes (namely Coulter and Seklavi, Candicans and Brkulja) differing in salt tolerance under low concentrations of 50 mM KCl and NaCl. Gas exchange and photosynthesis were reduced immediately after the onset of osmotic stress caused by both treatment (10-15% and 5-10%, respectively), but were recovered immediately over the time. Photosynthetic traits responded similarly to iso-osmotic concentrations of KCl and NaCl. The relationship between Na+ concentration in the leaf and stomatal conductance response in all four genotypes exposed to both salt treatments for 45 min showed no effect of Na+ toxicity within the plant. Stomatal factors limit photosynthesis of salt-stressed plants more than non-stomatal components of photosynthesis. In general, it seems that the main factor affecting of photosynthetic responses using diferrent osmotic was osmotic pressure of the salt outside the roots not the Na+ toxicity.