Salinity induces dose-dependent metabolic reprogramming while maintaining apparent growth stability in Limonium irtaense

MAIN CONCLUSION: Limonium irtaense maintains an apparently stable growth phenotype under salt stress through selective regulation of ion transport and extensive biochemical and metabolic reprogramming, revealing substantial stress adjustment costs. Although previous studies have examined some aspects of Limonium irtaense's salt tolerance mechanisms, the metabolomic basis underlying its response to salinity remains unknown. Here, we provide the first comprehensive metabolomic characterization of salt stress responses in this species. Plants were exposed to increasing NaCl concentrations (0-0.3 M), and their responses were assessed through an integrated physiological, biochemical, and metabolomic approach, offering new insights into the mechanisms supporting adaptation to saline environments. Growth variables were not significantly affected by the salt treatments although the consistent downward trend in the mean values suggest a potential cost of salinity that may not be detectable at the salt concentrations applied. In contrast, biochemical and metabolomic analyses revealed pronounced internal adjustments, particularly at higher salinity. Proline, flavonoids, and polyols (xylitol, erythritol) accumulated progressively, whereas soluble sugars declined and lipid peroxidation increased, indicating enhanced oxidative stress. Untargeted metabolomics further revealed dose-dependent modulation of amino acid and carbohydrate pathways, alongside the novel induction of catecholamines, suggesting additional roles in antioxidant defense and ion regulation. These results highlight the tolerance of L. irtaense, supported by extensive biochemical and metabolic reprogramming. Beyond its conservation relevance, this study provides new insights into the adaptive strategies of halophytes and identifies metabolites that may represent candidate biochemical markers of salt tolerance. By integrating physiological and metabolomic evidence, this work advances understanding of how halophytes maintain growth under salinity while revealing the hidden physiological costs associated with stress tolerance.