What is the primary function of plastoquinone during the light reactions of photosynthesis?

The primary function of plastoquinone during the light reactions of photosynthesis is to move H+ ions from the stroma to the lumen of the thylakoid. This process is essential for establishing a proton gradient across the thylakoid membrane, which ultimately drives ATP synthesis through chemiosmosis. As light energy is absorbed by chlorophyll and used to excite electrons, these high-energy electrons travel through the electron transport chain. Plastoquinone acts as a mobile electron carrier, accepting electrons from photosystem II and transferring them further along the chain, while simultaneously transporting protons into the thylakoid lumen. This creates a higher concentration of H+ ions inside the lumen as compared to the stroma, leading to a potential energy difference that is utilized by ATP synthase to generate ATP from ADP and inorganic phosphate. Understanding this role of plastoquinone highlights its importance in the overall process of photosynthesis, particularly in the context of energy conversion.