Maize Genotypes Differing in Salt Resistance Vary in Jasmonic Acid Accumulation During the First Phase of SaltStress

Plant hormones are considered to play an important role in plant adaptation to drought and salt stress. The objective of the study was to investigate the changes in endogenous jasmonic acid (JA) in relation to differences in the salt resistance of maize genotypes. Two maize genotypes (SR 03 and Across 8023) were compared for changes in water relations, growth and tissue JA levels in response to 100mm NaCl. Salt stress significantly reduced the shoot growth of both genotypes; however, SR 03 exhibited significantly less reduction in relative shoot fresh weight than Across 8023. Both genotypes showed an identical response to salt stress regarding plant water relations; therefore, genotypic differences in the salt resistance could not be attributed to changes in shoot turgor and these results were further confirmed by the response of both genotypes under equiosmotic stress (-0.49MPa) of either 100mm NaCl or PEG-6000. GC-MS/MS analysis showed that salt stress did not alter shoot JA levels of both genotypes, however significantly increased the root JA levels of Across 8023. In contrast, root JA levels of salt-resistant SR 03 did not change by salt stress. Increase in root JA levels in response to stress treatments does not coincide with the growth inhibition of shoot in Across 8023. In contrast, both PEG and NaCl did not change the JA concentrations in both root and shoot tissues of SR 03. Growth assays with maize seedlings showed that JA supply in root medium inhibits shoot extension growth and both maize genotypes were sensitive to the inhibitory effects of JA. These results suggest that maize genotypes differ in JA accumulation during the first phase of salt stress and JA may indirectly be involved in leaf growth inhibition of the salt-sensitive genotype. In addition, our results also showed that treatment of salt-stressed plants with exogenous JA improved the Na+ exclusion by decreasing the Na+ uptake at the root surface.