This is done through a process called ‘redox regulation'—the activation and deactivation of proteins via changes in their redox states. What happens in the presence of light is well understood: the ferredoxin-thioredoxin reductase (FTR)/thioredoxin (Trx) pathway is responsible for the reduction process, which activates the photosynthetic pathway. However, scientists have long been in the dark about what happens in the absence of light, and how plants reset photosynthetic proteins to be ready to function when light is resumed.
Keisuke Yoshida, Toru Hisabori, and colleagues identified two proteins, constituting the thioredoxin-like2 (TrxL2)/2-Cys peroxiredoxin (2CP) redox cascade, that help control the reoxidation of these photosynthetic proteins by modifying key parts of the molecular players.
These two proteins appear to function as part of a cascade that draws energy from the photosynthetic proteins to the always energy-hungry hydrogen peroxide. TrxL2 seems to be specialized for the ‘switching off' process. TrxL2 is an efficient oxidizer of many proteins, but only reduces 2CP, allowing the energy drained by TrxL2 from several upstream reactions to pass to 2CP and thence hydrogen peroxide. This cascade thus keeps photosynthesis on standby until light is available again.
For more details, read the Tokyo Tech News.