Effect of Salt and Drought Stresses on Some Physiological Traits of Three Rice Genotypes Differing in Salt Tolerance

Salt and drought stresses are among major constraints to rice (oryza sativa l.) production. in order to find some keysfor better understanding of the mechanism of salt tolerance in rice, we compared the impact of salinity and drought onseedlings of three rice cultivars including ir29, fl478 and gharib, which are salt sensitive, tolerant and moderatelytolerant respectively . the two days seedlings were transferred to ms media complemented with iso-osmoticconcentrations of nacl (0, 50, 100 and 150 mm) or mannitol (0, 100, 180 and 275 mm) for 10 days. both salt anddrought stresses resulted in reduction of shoot biomass, alteration of protein content and antioxidant activities in allstudied cultivars. however, some isoforms of antioxidant enzymes were induced by drought and suppressed bysalinity. moreover, proline content was considerably increased only under salt treatments . also, there were somevariations regarding response to each stress in different cultivars such as induction of some protein and peroxidasebands by salt stress as well as proline accumulation by drought which were exclusively observed in fl478. theseresponses together with higher superoxide dismutase activity of fl478 under salinity probably play some roles inhigher osmotic tolerance of this recombinant cultivar. comparative analysis of the studied rice genotypes confirmedthe importance of the osmotic component of salt stress in rice, since the salt tolerant cultivar fl478 displayed lessinjuries caused by drought compared to gharib and ir29 respectively