High Quality Content by WIKIPEDIA articles! Plastoquinone (PQ) is a quinone molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. Plastoquinone is reduced (accepts two protons (H+) from the stromal matrix of the chloroplast, coupled to two electrons (e-) from photosystem II), forming plastoquinol. It transports the protons to the lumen of thylakoid discs, while the electrons continue through the electron transport chain into the cytochrome b6f protein complex.