Salt-Induced Metabolic Changes in Dunaliella salina

An increase of medium NaCl concentration induces Dunaliella cells to evolve O₂ photosynthetically even in the absence of CO₂. This NaCl-induced O₂ evolution may reflect the induced conversion of reserve carbohydrate to glycerol. The quantum yield for the NaCl-induced O₂ evolution, in the absence of CO₂, is 1.5-fold higher than that obtained for CO₂ fixation. Since the synthesis of glycerol from reserve carbohydrate in the absence of CO₂ requires only 0.5 ATP/NADPH, whereas photosynthesis requires at least 1.3 ATP/NADPH, it is concluded that the ATP/2e⁻ ratio coupled to NADP reduction in Dunaliella is lower than required for CO₂ fixation.