Effects of exogenous ellagic acid on reactive oxygen species, antioxidant defense system and nitrogen metabolism in chickpea (Cicer arietinum L.) and wheat (Triticum aestivum L.) leaves subjected to salt stress

Salt stress is one of the most significant abiotic stress factors limiting agricultural production worldwide, negatively affecting plant growth and development. This stress disrupts photosynthesis, water balance, and metabolism by causing osmotic imbalance, ion toxicity, and ROS accumulation, leading to lipid peroxidation, RWC, and impaired membrane stability. Phenolic compounds can mitigate such damage by enhancing antioxidant defences. They have the potential to reduce the harmful effects of salt stress by strengthening plants' antioxidant defence mechanisms. In our thesis study, the effects of ellagic acid (EA) were evaluated by applying 12.5 µM EA to wheat and chickpea plants under 100 mM salt stress. It was determined that relative growth rates (RGR) and RWC significantly decreased in both wheat and chickpea plants under salt stress, accompanied by significantly increased electrical conductivity (EC) levels, especially in chickpea. Additionally, oxidative stress due to salt stress resulted in increased hydrogen peroxide (H₂O₂) levels in the environment and a significant rise in TBARS content, indicating enhanced lipid peroxidation. These increases were particularly pronounced in chickpea plants, likely because ion accumulation in these plants occurs more rapidly with increasing sodium (Na) concentration compared to wheat. Salt stress also disrupted nitrogen metabolism, causing toxicity through elevated ammonium (NH₄⁺) content, particularly in chickpeas. This accumulation is believed to result from decreased or unchanged activity of key enzymes, including nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH). However, with exogenous EA application, significant improvements in RGR and RWC values were observed, alongside reduced EC levels, particularly in chickpea plants. The increased superoxide dismutase (SOD) activity in the EA+Salt treatment suggests that H₂O₂ formed in the environment likely plays a role in signalling mechanisms, stimulating the antioxidant system. Consequently, excessive H₂O₂ accumulation was prevented, and lipid peroxidation levels improved due to increased peroxidase (POX) and, notably, ascorbate peroxidase (APX) activity in wheat. Furthermore, EA application under salt stress conditions reduced NH₄⁺ accumulation, which correlated with increased activities of NR, GOGAT, and GDH. In conclusion, EA was found to be an effective phenolic compound for alleviating oxidative damage caused by salt stress in both wheat and chickpea plants.