Foliar treatments of salicylic acid and iron nanoparticles enhanced antioxidant potential and essential oil production of ajowan under salt stress

Foliar spray of growth regulators and nutrients is a new approach to reduce the adverse impacts of salinity on plant performance. Thus, two experiments were undertaken as factorial with randomized complete block design in three replicates, to find out the mechanisms behind individual and simultaneous application of 1 mM salicylic acid (SA) and 3 mM Fe2O3 nanoparticles (Fe2O3-NPs) on ajowan plants under different salinity levels (non-saline and low, moderate and high NaCl salinities), paying particular attention to the effects on essential oil content and antioxidant capacity. Foliar application of SA, Fe2O3-NPs and particularly SA+Fe2O3-NPs decreased Na uptake and increased nutrients and SA contents, phenylalanine ammonia lyase and tyrosine ammonia lyase activities, and phenols under different levels of salinities, especially under moderate and high salinities. The seed essential oil content was reduced with progressing seed development. Rising salinity enhanced essential oil accumulation in seeds of treated and untreated ajowan plants at all developing stages. The highest essential oil and antioxidant activity was recorded for plants treated with SA+Fe2O3-NPs under all salinity levels. Therefore, foliar spray of SA+Fe2O3-NPs is suggested as the best treatment for improving production and antioxidant potential of ajowan essential oil.