Chitosan nanoparticles enhance salinity tolerance in Lallemantia iberica by modulating physiological and biochemical responses

Soil salinity severely restricts the growth of Lallemantia iberica , a salt-sensitive medicinal plant. This study evaluated whether chitosan nanoparticles (CNs) enhance salinity tolerance by modulating physiological and biochemical responses. Plants subjected to 0, 30, and 60 mM NaCl were sprayed with 0, 75 mg L -1 (CN75) or 150 mg L -1 (CN150). Severe salinity reduced biomass and chlorophylls by ~40–65%, caused a sevenfold decline in carotenoids, doubled malondialdehyde (MDA), increased hydrogen peroxide (H 2 O 2 ) by ~65%, and lowered the K + /Na + ratio from 8.49 to 0.72. CNs alleviated these impairments in a dose- and stress-dependent manner: CN75 was most effective under severe stress, reducing MDA by 36%, lowering H 2 O 2 to ~65% of untreated plants, and increasing total soluble protein by ~25%, while CN150 supported higher pigment retention and partially restored ionic homeostasis under moderate salinity. The CN application also enhanced antioxidant enzyme activities (SOD, CAT, POD), stabilised proteins, and stimulated phenolic metabolism by increasing phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activities, consistent with elevated levels of gallic and rosmarinic acids detected by HPLC. Multivariate analyses confirmed coordinated improvements in redox balance, osmotic regulation, ion homeostasis, and secondary metabolism. By strengthening antioxidant capacity and metabolic integration, CNs enabled L. iberica to maintain functional stability and growth under salinity stress. Totally, these findings highlight CNs as effective nanobiostimulants that enhance resilience through integrated physiological and metabolic adjustments. • Salinity stress markedly reduced growth, pigments, and ion balance in Lallemantia iberica . • Chitosan nanoparticles (CNs) efficiently mitigated these salinity-induced damages. • CNs enhanced antioxidant defense and phenylpropanoid metabolism. • HPLC profiling revealed elevated gallic and rosmarinic acids under CN treatments. • CNs act as eco-friendly nanobiostimulants, improving plant resilience to salt stress.