Integrated physiological and transcriptomic analyses reveal the mechanisms of exogenous selenium-mediated alleviation of saline-alkali stress in tomato seedlings

Abstract Background Tomato growth is severely constrained by saline-alkali stress. Although the mitigating effects of exogenous selenium on various abiotic stresses have been documented, its physiological and molecular regulatory mechanisms in tomato seedlings under saline-alkali stress remain insufficiently understood. Results In this study, the tomato inbred line Solanum lycopersicum cv. Ailsa Craig was selected as the experimental material. Saline-alkali conditions were established by supplementing 1/4 Hoagland nutrient solution with a complex saline-alkali mixture, and sodium selenite was used for exogenous selenium application. Growth phenotypes and physiological parameters were evaluated, and transcriptome sequencing was conducted to examine the associated molecular regulatory mechanisms. This treatment reduced chlorophyll degradation, increased the activities of superoxide dismutase (SOD by 377.37%), catalase (CAT by 145.67%), peroxidase (POD by 3.39%), and phenylalanine ammonia-lyase (PAL by 340.30%), and promoted the accumulation of salicylic acid and jasmonic acid. Concurrently, malondialdehyde content and reactive oxygen species accumulation were reduced. Transcriptomic profiling indicated that phenylalanine metabolism, carotenoid biosynthesis, galactose metabolism, and related pathways were activated, which supported the improved saline-alkali tolerance of tomato seedlings. Conclusions In summary, exogenous Se synergistically enhances saline-alkali tolerance in tomato seedlings through multiple pathways, including the enhancement of antioxidant system activity, protection of photosynthetic function, maintenance of cell membrane homeostasis, and modulation of metabolic pathways such as phenylalanine and galactose metabolism. This study provides a theoretical basis and genetic resource support for the stress-tolerant cultivation of tomato and the genetic improvement of elite saline-alkali-tolerant germplasm under saline-alkali stress.