Responses of the model crop plant Ocimum basilicum L. grown hydroponically to combined hypoxia and salinity

Basil (Ocimum basilicum L., cv Genovese) cultivated under hydroponic conditions was subjected to salinity, hypoxia, and combined stress for varying lengths of time to assess growth, metabolic, and antioxidant responses. Analyses demonstrated that stress type was the primary factor influencing plant responses, with treatment duration playing a secondary modulatory role. Growth parameters revealed organ-specific adaptations, with hypoxia increasing water content mainly in roots and salinity enhancing water retention in aerial organs. The combined stress contributed to the maintenance of tissue hydration. Photosynthetic pigments, soluble sugars, and proteins were found to be significantly affected, with protein accumulation being higher in aerial organs under combined stress and in roots under hypoxia. Growth and photosynthetic responses differed markedly among stress conditions. At T4, shoot dry biomass under hypoxia was approximately 1.5-fold higher than under control conditions and 8-fold higher than under salinity, while chlorophyll a increased approximately 5-fold compared with T1. Conversely, under combined hypoxia and salinity, chlorophyll a decreased by approximately 95% from T1 to T4. Antioxidant enzyme activities were also strongly modulated by treatment and exposure duration; notably, root CAT activity under the combined treatment at T4 was approximately 10-fold higher than under control conditions. Phenolic compounds accumulated predominantly under hypoxia and were associated with increased antioxidant capacity. Overall, these findings indicate distinct and time-dependent physiological and biochemical responses of basil to salinity, hypoxia, and their combination.