Cystoseira tamariscifolia Aqueous Extract Mitigates Salinity Stress in Tomato Plants by Mediating Their Physiology and Biochemistry

Salinity is one of the major factors that limit tomato growth and productivity, causing morphological and physiological changes and impacting plant metabolism. Seaweed extracts can reduce these harmful effects. Therefore, in this study we examined the effect of Cystoseira tamariscifolia extract (CTE) on NaCl stress tolerance in tomato plants. We assessed the effect of different concentrations of CTE on germination parameters of tomato seeds to determine the most effective concentrations. Then, we applied the chosen concentrations (2%, 5%, and 10%) of CTE as soil drench to tomato seedlings (Solanum lycopersicum L.) grown under salinity. Our findings revealed a decrease in the growth of tomato plants exposed to 50 mM of NaCl compared to unstressed ones. However, CTE supplementation, especially at 2%, to the stressed plants increased the plant height by 32.24% compared to stressed control without treatment and elevated biomass and chlorophyll content. Additionally, CTE decreased hydrogen peroxide and malondialdehyde accumulation and increased the activities of antioxidant enzymes: superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione S-transferase (GST). Moreover, CTE supplementation regulated the alterations in carbon and nitrogen metabolism by increasing the activity of carbon–nitrogen enzymes: phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (NAD-MDH), glutamine synthase (GS), glutamate dehydrogenase (GDH), and aspartate aminotransferase (AAT). Furthermore, CTE application increased notably the content of indole acetic acid, soluble sugars, and amino acids and improved the expression of antioxidant metabolites like flavonoids and polyphenols. Overall, our investigations demonstrate that CTE can be used as biostimulant to enhance the salt stress tolerance of tomato plants.