Hydrogen sulfide signaling fortifies lavender: Antioxidant defense, phytochemical modulation, and genetic responses under salt and drought stress

Abiotic stresses, particularly salinity and drought, severely constrain plant growth and productivity by disrupting key physiological and biochemical processes. In recent years, hydrogen sulfide (H₂S) has emerged as a signaling molecule with promising roles in mitigating environmental challenges. This study investigated the effects of exogenous H₂S, applied as sodium hydrosulfide (NaHS) at 100 and 200 μM, on antioxidant defenses, phytochemical traits, essential oil composition, and gene expression in Lavandula angustifolia . Plants were subjected to salt stress (0, 150, and 300 mM NaCl) and drought stress (100, 50, and 25% field capacity, FC) for 7 and 14 days. Results demonstrated that NaCl (300 mM) combined with NaHS (200 μM) significantly enhanced phytochemical accumulation, with chlorogenic acid, rutin, and cinnamic acid increasing by 86%, 11%, and 33%, respectively. Essential oil constituents, such as alpha-pinene, 1,8-cineole, and camphor, also increased by 11–25% compared to untreated controls. Gene expression analysis revealed that CINs and LIMs were upregulated by 78% and 110% under NaCl (150 mM) + NaHS (200 μM), whereas LINs expression declined by 33%. Under drought stress, NaHS application at 25% FC reduced the expression of phenolics, flavonoids, FRAP, rutin, coumaric acid, and LINs by 12–67%. Conversely, notable increases were observed in secondary metabolites, including gallic acid (444%), chlorogenic acid (603%), and rosmarinic acid (205%), alongside elevated CINs (73%) and LIMs expression (55%). Overall, these findings highlight the dual role of H₂S in enhancing stress tolerance and stimulating secondary metabolite production in lavender, offering new insights into its potential as a stress-mitigating agent.