Supplemental monochromatic red light mitigates salt-induced stress in pepper (Capsicum annuum L.) plants

The use of supplemental light spectra is emerging as a promising strategy to enhance plant tolerance to abiotic stress. This study examines the role of red (R) LED light in modulating the response of pepper (Capsicum annuum L.) plants to salinity stress. Plants were exposed to 50 mM NaCl for two weeks, with or without prior R LED (GH CSSRM5.24 OSLON® Square model) exposure, resulting in four treatments: control (CON), R LED alone (R LED), NaCl alone (NaCl), and R LED pre-treatment combined with NaCl (LED+NaCl). The LED+NaCl treatment significantly improved shoot biomass, stomatal conductance, transpiration, and photosynthetic rates compared to NaCl alone, alleviating salinity-induced damage. These benefits were associated to enhanced stomatal aperture and upregulated expression of PIP1;2 and PIP1;5, key aquaporin isoforms for water and CO₂ transport. In contrast, the downregulation of PIP2;7 in root tissues under LED+NaCl suggests its role in reducing water loss and generating hydraulic signals for stomatal regulation. Additionally, LED+NaCl-treated plants exhibited higher antioxidant capacity and increased flavonoid and phenolic accumulation, reinforcing oxidative stress tolerance. These findings suggest that R LED pre-treatment is a viable strategy to enhance salt tolerance in pepper by optimizing water and CO₂ transport, preserving stomatal function, and strengthening antioxidant defenses, offering insights for sustainable crop management.