Carboxymethyl cellulose-ferulic acid nanocomposite enhances salinity tolerance and phytochemical accumulation in Dracocephalum moldavica via coordinated redox and osmotic regulation

Salinity is a significant constraint on medicinal and aromatic plants that limits their growth and photosynthetic activity, increases oxidative stress, and disrupts water balance. The present paper prepared a carboxymethyl cellulose-ferulic acid nanocomposite (FA-NC), which is a bio-based nano-formulation to enhance the performance of Dracocephalum moldavica in the presence of salinity stress, and the effect was directly compared to free FA. Carboxymethyl cellulose was successfully used to prepare the FA-NC, which was verified by conventional physicochemical characterization. Salinity stress significantly reduced growth, fresh and dry biomass, stomatal conductance, chlorophyll pigments, and photochemical efficiency, and enhanced membrane damage and oxidative stress indicators. Both FA and FA-NC reduced these negative effects, but FA-NC was always stronger in protection compared to free FA. FA-NC was more effective in enhancing leaf hydration and membrane stability, and more powerful in minimizing oxidative damage (reducing H 2 O 2 and MDA). This increased stress alleviation was accompanied by an improved antioxidant capacity (increased CAT, APX, and GPO activities and low protease activity). FA-NC also enhanced the accumulation of proline, glycine betaine, soluble sugars, and free amino acids that assist in the enhancement of osmotic adjustment in exposure to salt. Notably, FA-NC had a greater effect on the accumulation of major secondary metabolites, such as phenolics, flavonoids, anthocyanins, and tannins, than free FA, which is beneficial in maintaining medicinal quality during stress. PCA combined responses and emphasized the greater change in the FA-NC-treated plants towards desirable associations of traits when compared to free FA. In general, FA-NC nano-formulation is a sustainable and more efficient substitute for free FA to improve salinity tolerance and phytochemical potential in D. moldavica .