Plastocyanin affects photosynthesis and high light acclimation by modulating redox states of electron transport chain in Chlamydomonas reinhardtii.

The role of plastocyanin in regulating photosynthetic and high light response remains unclear. Here we found that a larger PC pool effectively increased the linear electron flow while lowering the reduction state of plastoquinone (PQ) and ferredoxin (Fd), subsequently decreasing ROS formation. The biomass yield was increased in PC-rich cells, which, along with a decrease in intracellular starch content, up-regulated the RuBisCO activity, thereby enhancing carbon fixation. Meanwhile, we observed that ADP-glucose pyrophosphorylase activity was down-regulated, probably due to a lower Fd reduction state leading to reduced starch synthesis. During the transition from low to high light, PC accumulates to a substantial level, effectively reducing the reduction state of PQ and restoring Fv/Fm. These findings highlight the critical function of PC as a redox capacitor in affecting PET, CO fixation, and high light acclimation by modulating the redox states of the electron transport chain (ETC) and its potential for optimizing photosynthetic processes.