*2.5. E*ff*ects of GABA Priming on Ion Accumulation under Salinity, Osmotic Stress and OS*+*S*

The obtained results showed that salinity and OS+S stresses significantly increased the Na<sup>+</sup> concentration in the leaf and root tissues as compared to the control condition, and a higher concentration of Na<sup>+</sup> was observed in the root as compared to the leaf (Figure 2). Interestingly, the Na<sup>+</sup> concentration was not significantly reduced by GABA priming in the leaf and root under the unstressed condition. However, under the salinity and OS+S stresses, the GABA priming resulted in a significant reduction of the Na<sup>+</sup> concentrations in the leaf and root as compared with unprimed seeds. Priming decreased Na<sup>+</sup> concentrations under osmotic stress, salinity and OS+S stresses by 2.20%, 23.72% and 48.87% in the leaf, and in the root by 0.64%, 36.39% and 31.00%, respectively. Irrespective of the salinity, osmotic stress and their combination, priming with 0.5 mM GABA significantly improved the K<sup>+</sup> concentration in the leaf and root tissues (Figure 2). It could be concluded that priming seeds with GABA significantly improved the K<sup>+</sup> concentration in the leaf by 23.84%, 43.89%, and 30.65%, and in the root by 25.96%, 31.68%, and 37.50% under the osmotic stress, salinity and OS+S stresses, respectively (Figure 2). The present study suggested that priming with 0.5 mM GABA has the potential to maintain the balance between the accumulation of Na<sup>+</sup> in the plant cell and the loss of K<sup>+</sup> under salinity, osmotic stress and their combination.

**Figure 2.** Effects of GABA treatment on the concentration of Na<sup>+</sup> in the leaf (**A**), Na<sup>+</sup> in the root (**B**), K<sup>+</sup> in the leaf (**C**), K<sup>+</sup> in the root (**D**), Na+/K<sup>+</sup> ratio in the leaf (**E**) and Na+/K<sup>+</sup> ratio in the roots (**F**) of rice seedlings exposed to salinity, osmotic stress, and their combined stress (OS+S). OS (Osmotic stress); S (Salinity).

#### *2.6. E*ff*ects of GABA Priming on Enzyme Activities under Salinity, Osmotic Stress and OS*+*S*

As shown in Figure 3A–C, the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and ascorbic peroxidase (APX) increased in the seedlings exposed to osmotic stress, salinity and OS+S stresses as compared with their respective controls. Priming seeds with 0.5 mM GABA significantly improved the activities of these enzymes under the salinity, osmotic stress and their combination, but the impact was more obvious under the salinity stress as compared with osmotic stress and the combined stress (Figure 3A–C). Compared to the unprimed seeds, SOD activity was improved in the GABA-primed seeds under osmotic stress, salinity and OS+S stresses by 36.46%, 40.64% and 28.29%; CAT activity by 36.92%, 49.06% and 30.17%, and APX activity by 39.64%, 32.89% and 27.65%, respectively (Figure 3A–C). It seems that the application of 0.5 mM GABA can regulate the antioxidant enzymes activity which played a crucial role in scavenging H2O2 helping to minimize excessive ROS in the stressed plants under salinity, osmotic stress and their combination.

**Figure 3.** Effects of GABA treatment on SOD (**A**), CAT (**B**), APX (**C**) activities; *SOD1* (**D**); *CATa* (**E**); *APXa* (**F**); PAL (**G**); PPO (**H**); SKDH (**I**); *PAL1* (**J**); *PPO* (**K**) and *SKDH* (**L**) of rice seedlings exposed to salinity, osmotic stress, and their combined stress (OS+S). OS (Osmotic stress); S (Salinity).
