Salinity effect induced by NaCl on ABA and IAA concentrations and distributions in seedlings of two rice (Oryza sativa L.) genotypes

Rice (Oryza sativa L.), a salt-sensitive species, has considerable genetic variation for salt tolerance within the cultivated gene pool. To evaluate salinity effect on ABA and IAA concentrations and distributions in different parts of two rice genotypes (IR29 and IR651, sensitive and tolerant, respectively) a green house experiment were grown in normal condition till 6th leaf was fully expanded. Seedlings were exposed to salinity, EC =12 dS m-1 and normal conditions (EC = 1.65 dS m-1, Ushida solution base EC) for one week. Samples were taken 0, 4, 12, 24, 48, 96, 168 hours after application of treatments. Amount of ABA and IAA in different leaves, leafsheaths and roots were measured by HPLC. Results showed that ABA concentration in sensitive genotype was much higher than tolerant genotype. However, salinity stress had no significant effects on ABA concentration while rate of ABA transport from root to shoot significantly changed in IR651. IAA concentration was higher in tolerant genotype and its distribution change by duration of exposure. At the beginning in salinity treatment, IAA concentration of root and leaf sheaths of both genotypes had no significant difference, however as salinity stress increased, distribution of IAA in tolerant cultivar gradually changed and concentrated from roots and leaf sheaths to leaves, especially in older leaves.