Regulatory role of methylglyoxal in osmotic stress adaptation: Insights into the antioxidant defense, glyoxalase system, and osmoprotectant metabolism in maize seedlings

Methylglyoxal (MG) functions in plants as both a cytotoxic byproduct and a signaling molecule that regulates responses to abiotic stress. To investigate its dose-dependent effects, maize seedlings were subjected to polyethylene glycol (PEG)-induced osmotic stress combined with different MG concentrations (5, 10, 25, and 35 mM). Measurements included relative water content, oxidative stress markers, proline, polyamines, and antioxidant enzyme activities (SOD, CAT, APX, GPX), as well as glyoxalase (Gly I, Gly II) enzyme activities, along with the expression of related genes. Results showed that low MG levels, particularly 10 mM, significantly improved RWC, enhanced antioxidant and glyoxalase activities, upregulated genes involved in antioxidant defense and osmoprotectant biosynthesis, while downregulating genes related to proline and polyamine catabolism. These changes reduced oxidative damage and promoted the accumulation of osmoprotectants. By contrast, higher MG doses increased oxidative stress, MG accumulation, and reduced stress tolerance. Overall, MG exhibited a concentration-dependent dual role in osmotic stress tolerance: acting as a beneficial signaling molecule at low levels but exerting toxicity at higher concentrations. This study highlights MG’s regulatory role in stress adaptation and provides a theoretical basis for its potential application in improving drought resilience in crops.