Salinity-induced phytohormonal changes in leaves and roots ofP. pinnata under progressive salt stress
Upon salt stress, Pongamia accumulated various hormones tissue specifically and time dependently. Accordingly, we quantified phytohormones by using LC-MS analysis. All seven hormones zeatin, IAA, IBA, MeJA, SA, ABA, and JA were showed a significant increase in leaves of 300 and 500 mM NaCl treated plants at 1, 4 and 8DAS (Figure 1B-D). As shown in the Figure 1B-D, the hormone accumulation pattern was changed with the treatment time in leaves of 300 mM NaCl plants. At 1DAS, six hormones zeatin, IAA, IBA, MeJA, ABA, and JA were showed significant increase in leaves of 300 mM NaCl treated plants, while SA levels did not change significantly. Hormones such as zeatin, IAA, MeJA and JA showed significant up-regulation at 4DAS. IAA, ABA and JA levels were significantly enhanced in leaves of 300 mM NaCl treated plants at 8DAS. Moreover, in roots, the phytohormone levels varied with salt concentration and treatment time. Zeatin, IBA and MeJA levels increased significantly in roots of 300 mM NaCl treated plants at 1DAS. Similarly, zeatin and ABA levels showed significant up-regulation in 500 mM NaCl treated plants at 1DAS (Figure 1E). At 4DAS, only zeatin showed significant increase by ~3.7-fold in roots of 300 mM NaCl treated plants. In response to 500 mM NaCl treatment, MeJA and JA levels showed ~3.3 and 2.0-fold up-regulation in roots at 4DAS respectively (Figure 1F). At 8DAS, zeatin and IAA levels were increased by ~2.2 and 2.3-fold in roots of 300 mM NaCl treated plants respectively (Figure 1G). In response to 500 mM NaCl stress, only IBA levels showed significant increase by ~3.0-fold at 8DAS.
Correlation studies among hormones are essential to explore hormonal interactions under salt stress. Accordingly, correlation studies were performed based on stress treatment time. Each stress time point was grouped individually in the form of a correlation cluster matrix to show the interactive responses of each individual hormone under salt stress. We observed significant correlation between JAs and IAA over time in leaves of 300 mM NaCl treated plants (Figure 2A-C). Similarly, JA showed significant correlation with MeJA in leaves of 500 mM NaCl treated plants across all-time points (Figure 2D-F). Jasmonates (JA and MeJA) and SA showed significant interaction with other hormones in roots of 300 and 500 mM NaCl at all-time points (Figure 2G-L).