Nano-enabled enhancement of salt stress tolerance in barley using chitosan-selenium nanoparticles: physiological and molecular insights

Salinity stress severely limits barley (Hordeum vulgare L.) growth and productivity. This study examined the effects of chitosan (Cs), selenium (Se), and chitosan-selenium nanoparticles (Cs-Se NPs) on salt tolerance of two barley cultivars, Mv Initium and Tectus, exposed to 0, 100, and 200 mM NaCl. Salinity reduced plant height, biomass, and chlorophyll content. Foliar application of Cs and especially Cs-Se NPs significantly improved these traits. Cs-Se NPs enhanced proline (PRO) accumulation and activities of ascorbate peroxidase (APX) and catalase (CAT) under salt stress in both cultivars, which supports improved ROS scavenging capacity. The significant upregulation of antioxidant enzyme genes (HvAPX, HvSOD, HvCAT) following Cs-Se NPs treatment under salinity strongly indicates enhanced reactive oxygen species (ROS) detoxification. Key ion homeostasis genes (HvSOS1, HvSOS3, HvNHX1 and HvHKT2) were also upregulated, supporting improved salt stress tolerance. Strong correlations were found between antioxidant activity, chlorophyll content, and growth. These findings suggest that Cs-Se NPs effectively boost barley's physiological and molecular defenses against salinity.