Exogenous application of plant growth regulators is one the important strategies that is being employed to improve tolerance to salinity. The comparative protective potentiality of exogenously applied plant growth regulators (PGRs) abscisic acid (ABA), gibberellic acid (GA3), indole-3-acetic acid (IAA) and cytokinin (CK), in mitigating NaCl toxicity and inducing short-term salinity tolerance in two indica rice varieties, namely IR29 (salt-sensitive) and FL485 (salt-tolerant) have been presented. The reduction in photosynthetic pigments, grain soluble sugars and grain starch, the slight increment in leaf soluble proteins and considerable elevation in leaf starch, all of which were particularly noteworthy in IR29 and FL485 during salinity stress, was appreciably changed by co-treatment with PGRs. CK application followed by ABA showed higher effect in elevating grain proteins level than GA and IAA treatments. IAA and CK proved to be the most effective way in enhancing grain yield under salinity stress among four PGRs tested. Regardless to salinity there was a drastic fall in grain starch level result in GA application in both cultivars. Seemingly, GA treatment exacerbate the adverse effect of salinity and cause the reduction of grain yield of both cultivars as compared to plants receiving no external treatment. It can be concluded that the effect of exogenous hormones were predominantly mediated by changes in endogenous hormone contents, which affected grain filling process. This work indicated that an increase in the rice grain yield, 1,000-grain weight and filled-grain percentage are associated with an increase in the contents of starch in grains caused by the application of CK and IAA. © 2014 The National Academy of Sciences, India.
