چكيده لاتين
Environmental stresses, including low temperature, are among the most significant factors limiting the growth and physiological performance of algae and other photosynthetic organisms. Reduced temperatures can disrupt membrane structure, decrease enzyme activity, and impair photosystem efficiency, leading to reduced growth and biological yield. In recent years, melatonin has garnered considerable attention from researchers as a growth regulator and potent antioxidant. This study aimed to investigate the effect of exogenous melatonin on the growth, photosynthetic pigments, and antioxidant responses of the unicellular alga Dunaliella tertiolecta under cold stress. In this study, algae were cultured in Johnsonʹs medium with a salt concentration of 0.17 M, and melatonin treatment was applied at concentrations of 0.25 and 0.5 mM. After one day, samples were exposed to cold stress at 15 ± 1 °C. After one week, cell growth indices, chlorophyll content, beta-carotene, total antioxidant capacity, lipid peroxidation, and chlorophyll fluorescence parameters were evaluated. The results showed that low concentrations of melatonin under cold stress significantly increased cell growth, maintained photosynthetic pigments, and reduced lipid peroxidation compared to cold stress alone, but had no effect on total antioxidant capacity. Analysis of chlorophyll fluorescence curves indicated that melatonin prevented cold-induced damage by improving the efficiency of photosystem II, increasing the electron transfer rate, and maintaining the stability of thylakoid membranes. Overall, the findings of this study suggest that melatonin can be used as an effective compound to improve the cold stress tolerance of Dunaliella tertiolecta. These results could be effective in developing biotechnological strategies to increase the stability of biomass production and valuable algal compounds under adverse environmental conditions.
