**Background:** Salinity is a major environmental stress affecting 20% of cultivated land and 33% of irrigated agricultural land globally. Lemon verbena (Aloysia citrodora) is a medicinal plant used for antispasmodic, antipyretic, anti-inflammatory, and digestive properties, but its cultivation is limited by salt sensitivity. Selenium (Se) is an essential trace element for humans with antioxidant properties, and while not essential for plants, it has been shown to alleviate various abiotic stresses. Nano-selenium (N-Se) has different physicochemical properties that may enhance its bioavailability and efficacy. This study tested the hypothesis that exogenous Se and N-Se could alleviate salinity stress in lemon verbena through antioxidant mechanisms.
**Methods:** Rooted lemon verbena cuttings were grown in 4-L pots with coco-peat and perlite in a greenhouse (25/18±2°C day/night, 60-70% relative humidity). After one month of establishment with 1/4 Hoagland solution, plants received five salinity treatments (0, 40, 80, 120, 160 mM NaCl) combined with three Se treatments (control distilled water, 10 µM N-Se, 10 µM Se as Na₂SeO₃). Se treatments were applied as foliar spray weekly after the first week of salinity treatment, continuing for two months. Measurements included growth parameters, chlorophyll a/b, relative water content (RWC), electrolyte leakage (LEL), malondialdehyde (MDA), hydrogen peroxide (H₂O₂), proline, soluble sugars, protein, antioxidant enzymes (CAT, POD, SOD), total phenols, flavonoids, total antioxidant capacity (DPPH), essential oil content/yield, and Na⁺/Cl⁻ concentrations. Data were analyzed by ANOVA with Duncan's multiple range test (p<0.05).
**Key Results:** Salinity stress significantly reduced all growth parameters, with the lowest values at 160 mM NaCl. At 160 mM NaCl without Se, plant height was 37.33 cm, shoot fresh weight 11.75 g, and shoot dry weight 4.70 g. Both Se and N-Se treatments improved growth across all salinity levels. For example, at 160 mM NaCl, N-Se increased plant height by 20.54%, shoot fresh weight by 126.29%, and shoot dry weight by 122.60% compared to untreated controls. Chlorophyll a decreased by 45.00% at 160 mM NaCl in control plants, but N-Se and Se treatments increased chlorophyll a by 18-34% under salt stress. MDA accumulation increased by up to 180% under salinity, but N-Se reduced MDA by 32.52%, 34.58%, and 37.86% at 80, 120, and 160 mM NaCl, respectively. H₂O₂ increased by up to 285% under salinity; N-Se reduced H₂O₂ by 60.56%, 37.29%, and 38.28% at these same salinity levels. Proline increased by 8-94% under salinity, and Se treatments further increased proline by 26.74% (N-Se) and 16.67% (Se). CAT activity increased by up to 104.79% under salinity alone; N-Se further increased CAT by 22-31% across salinity levels. SOD activity increased by 28.01% at 80 mM NaCl; N-Se boosted SOD by 18.90-37.64% under salinity. Total phenols increased by 9.46-17.82% under salinity alone; N-Se increased phenols by up to 10.09% under non-stress and 8.93% at 80 mM NaCl. Flavonoids increased by 18.64-110.16% under salinity; N-Se increased flavonoids by 13-44% at most salinity levels. Essential oil percentage increased by 26.53% at 40 mM NaCl but essential oil yield decreased by up to 72.72% at 160 mM NaCl due to biomass reduction. N-Se increased essential oil yield by 75.75-153.73% across salinity levels. Root Na⁺ content increased by 421-641% under salinity; N-Se reduced root Na⁺ by 32.70% at 40 mM and 25.38% at 80 mM NaCl. Shoot Cl⁻ content increased with salinity; both Se and N-Se increased shoot Cl⁻ by 9.15% and 8.45%, respectively.
**Clinical Implications:** While this is a plant science study without direct clinical implications, lemon verbena is used in folk medicine for its antispasmodic, anti-inflammatory, and digestive properties. The finding that Se and N-Se application increases phenolic compounds, flavonoids, and essential oil content under salinity stress suggests that Se fertilization could enhance the medicinal quality and consistency of lemon verbena grown in saline conditions. This may help maintain supply of this medicinal plant for traditional medicine applications. The improved antioxidant capacity (17.99% increase with N-Se) of Se-treated plants may translate to higher levels of bioactive compounds in harvested material. However, clinical studies on human health effects would be needed to determine whether these changes in secondary metabolite profiles have meaningful therapeutic impacts.