Effect of exogenously applied amino acids on photosynthetic pigments, metabolites and enzymatic antioxidants in Zea mays L. subjected to salt stress.

Abiotic stresses are major constraints to sustainable agriculture. Among this salinity is a critical abiotic stress that severely affects crop productivity in arid and semi-arid regions. It impaired physiological and biochemical functions of plants. It also affects nutrient uptake and causes ionic disbalance. The main aim of this study was to evaluate the effectiveness of four selected exogenously applied amino acids (methionine, tryptophan, glycine betaine, and lysine) in mitigating salt stress and improving physiological performance of maize. Although amino acids are widely used as bio-stimulants but comparative evidence on their parameter specific effects under salinity is limited. The current study has been designed to investigate the effect of different concentrations (0, 25, 75, 100 ppm) of each amino acid in alleviating the effect of salt stress (120 mM NaCl) in Zea mays L. plants. Two factorial (amino acid treatments & salt stress) completely randomized design pot experiment with three replicates was conducted in control conditions. Salt stress reduced the morpho-physiological parameters along with antioxidant activities in Z. mays plants. Conversely, the applications of amino acids increased the growth parameters. Maximum shoot length and biomass were noted under the application of lysine. While maximum increase in root length, number of leaves and biomass of roots was observed under the application of glycine betaine, methionine, and tryptophan, respectively. Photosynthetic pigments were maximized under the influence of glycine betaine. Amino acids also triggered antioxidant activity and increased the production of metabolites. Like, total phenolics, total soluble proteins (TSP) and superoxide dismutase (SOD) were maximized by the application of glycine betaine. Similarly, catalase (CAT), peroxidase (POD) and flavonoids were maximized by the application of tryptophan, and total free amino acids (TFA) were maximized under the effect of methionine application. With increase in concentration of amino acids the studied parameters were also increased gradually. It is concluded that specific amino acids target distinct biochemical pathways to exhibit potential to induce tolerance against saline stress. These findings highlight the potential of amino acids, as bio-stimulants to enhance salt stress tolerance in maize. This indicates a role in boosting the plant's antioxidant defense system under salt stress. However, validation under field conditions will be crucial to clarify molecular mechanisms to optimize the role of amino acids in sustainable crop production.