During formation of ATP in chloroplast by chemiosmosis the part of the thylakoid which acts as proton pump is 

Pump is protein involved in active movement of ions. In chemiosmotic theory, the pump is proton pump. In photosynthetic light reaction, Cytochrome ${\text{b}}_6/\mathrm{f}$ complex acts as pump for the active movement protons from stroma to lumen by using the energy liberated from down hill movement of electrons. Plastoquinone is a benzoquinone and not a protein. ${\mathrm{CF}}_0$ is proton channel and ${\mathrm{CF}}_1$ is catalytic site for the formation of ATP from ADP and Pi.