Unveiling the mechanisms of silicon-induced salinity stress tolerance in Panicum turgidum: Insights from antioxidant defense system and comprehensive metabolic and nutritional profiling

Salinity is a global challenge to sustainable agriculture, impacting plant growth at cellular and functional levels. Nevertheless, silicon (Si), a multifunctional micro-element, plays a vital role in restoring and maintaining growth and development during unfavourable abiotic conditions such as high salinity exposure. Therefore, in the current research, two salinity levels [S1; 1 M (1000 mM) NaCl and S2; 2 M (2000 mM) NaCl] were used to assess the effects of exogenous Si (Si-1; 150 mg/L and Si-2; 250 mg/L) on key biological characteristics and especially the metabolite profiles of Panicum turgidum plants. Our findings revealed that the salt stress negatively affected the plants through high salt content (Na⁺ and Cl⁻) that further antagonized the essential nutrient balance in tissues; increased NH₄⁺, but lowered NO₃⁻ and K⁺ in both roots and leaves. The excessive production of NH₄⁺ led to over-accumulation of methylglyoxal (MG), resulting in the hyper-accumulation of sugars and altering the concentrations of amino acids, thereby inducing diabetes-like symptoms in P. turgidum plants. Interestingly, Si application restored the growth of P. turgidum plants by reducing oxidative damage thereby modifying the nutritional status, metabolic and biochemical characteristics of the plants. Specifically, the application of Si-2 showed improvement of key biological indictors in leaves and roots under both salinity levels. The current study also demonstrated that Si substantially reduced the NH₄⁺-mediated MG-induced stress by lowering the concentration of MG, up-regulating the antioxidant capacity of various enzymes glyoxalase I (Gly-I), glyoxalase II (Gly-II), glutathione (GSH), glutamine: 2-oxoglutarate aminotransferase (GOGAT), nitrate reductase (NR), glutamine synthetase (GS), glutamate dehydrogenase (GDH); with concomitant changes in the levels of sugar/carbohydrates in roots and leaves of P. turgidum.