*2.4. E*ff*ects of GABA Priming on ROS, MDA, Proline and GR under Salinity, Osmotic Stress and OS*+*S*

The results revealed that osmotic stress, salinity and OS+S improved ROS, i.e., hydrogen peroxide (H2O2), superoxide radical (O2 −) and hydroxyl ion (OH−) accumulation in the leaf tissues as compared with the control condition (Table 3). Priming treatment significantly reduced the accumulation of the H2O2 under osmotic stress, salinity and OS+S by 43.75%, 38.01% and 28.91%; O2 − by 0.37%, 30.88%, and 26.93%; and OH− by 17.64%, 22.38% and 25.64%, respectively, as compared with unprimed seeds (Table 3), and these findings were confirmed by the confocal microscopic investigation as depicted in Figure 1. Plants exposed to osmotic stress, salinity and OS+S experienced a significant increase in proline, malonaldehyde (MDA), and glutathione reductase (GR) concentrations as compared with the unstressed condition (Table 3). Proline, MDA and GR contents were not significantly affected by 0.5 mM GABA priming irrespective of the stress effects. However, the primed seedlings exposed to osmotic stress, salinity and OS+S had the lowest contents of MDA and proline, specifically under osmotic stress. Priming with 0.5 mM GABA resulted in a significant decrease of proline under osmotic stress, salinity, and OS+S, by 28.81%, 43.05% and 35.66%, respectively, relative to unprimed seeds (Table 3). By contrast, priming with 0.5 mM GABA resulted in a significant increase in the GR activity under the stress condition. It could be concluded that priming with 0.5 mM GABA improved GR activity under osmotic stress, salinity and OS+S stresses by 43.41%, 27.8% and 37.46%, respectively, relative to unprimed seeds. It could be stated that 0.5 mM GABA inhibited the release of free radicals by reducing the ROS and MDA levels and thus reducing the cell membrane damage under salinity, osmotic stress and their combination.

**Figure 1.** Effects of priming treatment on H2O2 accumulation in the root cells of rice seedlings exposed to salinity, osmotic stress, and their combined stress (OS+S). P (Priming) OS (Osmotic stress); S (Salinity).
