The proton gradient is formed due to accumulation of protons on the lumen side of the thylakoid. Also, the transport of electrons through the photosystem moves protons from the stroma to the lumen side, decreasing the proton concentration in the stroma and increasing it on the lumen side. This results in the generation of a proton gradient across the thylakoid membrane. The ATPase enzyme breaks down this proton gradient and uses its energy for the synthesis of ATP molecules.
