Exogenous Gallic Acid Confers Salt Tolerance in Rice Seedlings: Modulation of Ion Homeostasis, Osmoregulation, Antioxidant Defense, and Methylglyoxal Detoxification Systems

The worldwide saline-affected area is expanding day by day, and soil salinity restricts crop development and productivity, including rice. Considering this, the current study explored the response of gallic acid (GA) in conferring salinity tolerance in rice seedlings. Fourteen-day-old rice (<i>Oryza sativa</i> L. cv. BRRI dhan52) seedlings were treated with 200 mM NaCl alone or combined with 1 mM GA. Salt stress resulted in osmotic, ionic, and oxidative stress in rice seedlings. Osmotic stress increased proline accumulation and osmotic potential, which decreased the relative water content, chlorophyll contents, and dry weight. Ionic stress interrupted ion homeostasis by Na⁺ accumulation and K⁺ leakage. Osmotic and ionic stress, concomitantly, disrupted antioxidant defense and glyoxalase systems by higher production of reactive oxygen species (ROS) and methylglyoxal (MG), respectively. It resulted in oxidative damage indicated by the high amount of malondialdehyde (MDA). The supplementation of GA in salt-treated rice seedlings partially recovered salt-induced damages by improving osmotic and ionic homeostasis by increasing water balance and decreasing Na⁺ content and Na⁺/K⁺ ratio. Supplemental GA enhanced the antioxidant defense system in salt-treated rice seedlings by increasing ascorbate (AsA), glutathione (GSH), and phenolic compounds and the activities of AsA-GSH cycle enzymes, including monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) enzymes that accelerated ROS detoxification and decreased oxidative damage. Gallic acid also enhanced the detoxification of MG by triggering glyoxalase enzyme activities in salt-treated rice seedlings. The present findings elucidated that supplemental GA reversed salt-induced damage in rice seedlings through improving osmotic and ionic homeostasis and upregulating the ROS and MG detoxification system.