LAUSR

The present study was performed to investigate the regulatory role of selenium (Se) in the antioxidant defense system, Na+ uptake, and essential oil (EO) production of Stachys byzantine (S. byzantine) under salt stress. For this purpose, a greenhouse study was conducted in a factorial experiment based on a randomized complete design with three replications. The studied factors included foliar-applied Se (0, 4, 8, and 16 mg L−1) and salinity (0, 30, 60, and 90 mM NaCl). Malondialdehyde, H2O2, electrolyte leakage, oxidized glutathione (GSSG), ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD) significantly decreased by increasing salinity. Conversely, the chlorophyll content and glutathione (GSH), as well as monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) activities, represented noticeable decreases. However, Se supplementation alleviated the oxidative stress by activating some enzymes involved in the ascorbate–glutathione (AsA-GSH) cycle, including APX, DHAR, MDHAR, and GR activities, which further enhanced the activities of CAT and SOD. Exposition to Se also modulated the redox state by reducing GSSG while enhancing AsA and GSH contents when compared to non-Se supplemented salt-stressed S. byzantine plants. Mild salinity stress (30 mM NaCl), especially when combined with Se treatments, resulted in the highest production of the EO of S. byzantine. The findings of this study suggest the use of Se treatment as an efficient method for increasing the resistance of S. byzantine to salinity by reducing the damage to oxidative stress, activating antioxidant enzymes, modulating the redox state, and finally, improving the production of EOs.