This course of, occurring throughout the thylakoid membranes of chloroplasts, represents another electron pathway throughout the light-dependent reactions. As a substitute of electrons transferring linearly from water to NADPH, they cycle from photosystem I (PSI) again to the cytochrome b6f advanced. This, in flip, contributes to the proton gradient throughout the thylakoid membrane, driving ATP synthesis by way of chemiosmosis. The first output of this pathway is ATP; importantly, no NADPH or oxygen is produced on this remoted circuit.
A essential perform is to steadiness the ATP to NADPH ratio throughout the chloroplast. When NADPH ranges are excessive and the Calvin cycle’s demand for ATP will increase, this pathway turns into extra prevalent. This ensures adequate ATP manufacturing for carbon fixation. Moreover, it might supply photoprotective advantages beneath situations of excessive mild depth, stopping photoinhibition by diverting electron move away from NADPH manufacturing. Analysis suggests its evolutionary significance might lie in its presence in early photosynthetic organisms going through totally different environmental stressors.