Investigation on Changes in Single Stranded DNA Preferring Nuclease Activity, Protein and Chlorophyll Contents During Salt Stress in Two Sensitive and Tolerant Barley Cultivars (Hordeum vulgare L.)

This research was conducted to investigate changes in single starnded DNA preferring nuclease (SSPN) activity، protein and chlorophyll contents in barley، under salt stress. Tolerant (Sahra) and sensitive (Rayhan) barley cultivars were used in a complete random plot with a factorial design، using 3 replicates at 0 and 120 mM NaCl concentrations. Nuclease activity on ssDNA was measured at pH 5. 6 and 7. 0 in the presence of 1 mM of one of the following divalent cations: Cu2+، Zn2+، Mg2+، Ca2+ and EDTA، by spectrophotometry and native-PAGE assays. The highest enzyme activity was observed in the presence of Ca2+ at 120 mM NaCl and pH 7. 0 and the lowest enzyme activity was observed in the presence of Cu2+ at 0 mM NaCl and pH 5. 6. EDTA inhibited SSPN activity. In the gel assay، 5 enzymes were revealed، amongst which 59، 47 and 43 kD enzyme at both pHs and 34 and 41 kD enzymes were revealed only at pH 7. 0. Na+ content، K+/Na+ ratio and chlorophyll and protein contents decreased significantly upon salt stress in both cultivars. Salt stress caused an increase in the nuclease activity and a decrease in protein and chlorophyll contents in both cultivars. However، these changes were significantly lower in the tolerant cultivar، compared to the sensitive one