The enhancement of the oxidative pentose phosphate pathway maybe involved in resolving imbalance between photosystem I and II in Dunaliella salina

Dunaliella salina is a unicellular green alga extensively studied due to its capability of salt stress tolerance and high economic value for β-carotene production. Glycerol is synthesized to regulate intracellular osmotic pressure during salt stress in D. salina. In order to demonstrate the electron and reducing power distribution pattern in this process, photosynthetic performance and oxidative pentose phosphate pathway (OPPP) operation during salt stress were investigated. Glycerol was accumulated massively when D. salina was subjected to salt stress. Meanwhile, photosystem II (PSII) activity was increased while photosystem I (PSI) activity was decreased. This suggests that a small portion of the electrons generated in PSII were leaked and were transferred to generate reactive oxygen species (ROS), while most electrons subsequently used to PSI to generate ATP and NADPH. Furthermore, the OPPP was enhanced in order to provide reducing power and carbon skeleton for glycerol synthesis. In conclusion, during salt stress, the imbalance of photosynthetic electron distribution between PSII and PSI in D. salina resulted in a shortage of NADPH and ATP for glycerol biosynthesis, which also led the enhancement of the OPPP and ROS generation.