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Keywords: Carob tree (Ceratonia siliqua), Salt stress, Water stress, In vitro germination, Morpho-physiological characteristics, Biochemical properties
Understanding the mechanisms of abiotic stress tolerance in carob (Ceratonia siliqua L.) is essential to mitigate the adverse effects of stress and uncover the adaptive strategies employed by this species. The present study aimed to evaluate the effects of salt and water stresses induced by sodium chloride (NaCl) and polyethylene glycol 6000 (PEG-6000) at different concentrations on morpho-physiological and biochemical traits of carob in vitro seedlings. Seed germination was conducted under salt (0, 30 mM, 60 mM, and 120 mM) and water (0, 5, 10, and 20 g/l) stresses to assess the species responses at this stage. Subsequently, seedlings growth and development were evaluated under in vitro conditions. The results showed that NaCl and PEG-6000 did not have a pronounced effect on germination rates but significantly impacted the growth of plantlets, especially under intense stress conditions. In vitro exposure of carob plantlets to salinity and drought induced significant physiological and biochemical responses, particularly in the accumulation of osmoprotectants and phenolic compounds. Under severe salt stress, plantlets exhibited marked increases in soluble sugars (30%), proline (26%), glycine betaine (21%), polyphenols (36%), flavonoids (31%), and tannins (78%). Drought stress elicited comparatively milder responses, with increases in soluble sugars (9%), proline (20%), glycine betaine (5%), and polyphenols (9%). Antioxidant activity rose by 9% under drought stress but declined by 25% under salt stress. These findings underscore the importance of osmoprotective metabolites and phenolic antioxidants in the stress resilience of carob, and lay the groundwork for further investigation into the molecular and physiological mechanisms underlying its tolerance to abiotic stress. Understanding these stress responses holds significant potential for improving crop resilience and promoting sustainable agriculture under climate change conditions.
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Natural Resources and Local Products Research Unit, Regional Center of Agricultural Research of Agadir, National Institute of Agricultural Research, Rabat, Morocco