Is salinity tolerance of rice lines concerned to endogenous ABA content or to the cellular ability for ABA synthesis under stress?
In this work we tested its putative relationship of Abscisic acid with the degree of tolerance to this abiotic stress. For this purpose, we have examined the responses of sensitive (IR29) and tolerant (IR651) varieties of indica rice (Oryza sativa L.) to a range of salinity (0 (control) and 90 mM NaCl. Shoot and root dry weight reduced and leaf Na concentration increased in response to salinity for both cultivars with a higher extent of sensitivity. Tolerance of IR29 to saline stress was generally improved by ABA treatment and leaves Na content reduced to the level of their respective control treatment. This ABA effect was evident in IR29 with low tolerance, as their ability to recover from stress increased up to seven fold. Independence of the saline treatment and the absolute endogenous leaf ABA content in sensitive variety was significantly more than that of the tolerant one. However, with stress, the increase in endogenous ABA synthesis was higher in tolerant than in sensitive varieties. These data together with those obtained by using fluridone, an inhibitor of ABA synthesis, suggest first of all, that there was differential sensitivity to ABA in the tolerant and sensitive leaves cultivars and enhanced concentrations at tolerant levels acted primarily to maintain root and shoot growth and secondly, the differences in the level of tolerance to saline stress is related to their different capacity of ABA synthesis under stress conditions.
Key words: Abscisic acid, fluridone, Oryza sativa L., salinity.