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Effect of various NaCI treatments (0, 50, 100, 200 and 300m M) at different growth and development stages (tillering, boot swollen, flowering and anthesis) of two wheat cultivars (Ghods: salt- sensitive, Boolani : salt-tolerant) on the kinetic activity of leaf nitrate reductase (NR) was studied under greenhouse conditions. In general, in response to salinity treatments: the decrease of NR activity was more in root and leaf in cultivar Ghods than cultivar Boolani. It seems, differential compartmentation of ions and NR and less accumulation of Na+ in more salt-resistant cultivar, protect NR from NaCl. We have also found that in response to salinity, more Na+ was accumulated in cultivar Ghods. Thus, in biochemical point of veiw, more resistance to salinity in cultivar Boolani, in comparison to cultivar Ghods, is higher activity of NR activity in Boolani.