Substituted p-Benzoquinones Having High Electron Affinity as Photosystem II Electron Acceptors

Abstract Substituted Benzoquinones, Photosystem II Acceptors Benzoquinones (BQ) substituted with alkyl or alkoxy groups 2,5-dimethoxy-3,6-dichloro-p-benzoquinone (DCDMQ), 2,3,5,6-tetramethoxy-p-benzoquinone (TMQ) have been tested for their electron affinity and site of action in the photosynthetic electron transport chain in whole cells and chloroplasts. Both the substituted compounds were found to be good electron acceptors of photosystem II. DCDMQ showed higher electron affinity than BQ as demonstrated by its two fold stimulation of O2 evolution in chloroplasts and efficiency in quenching DCMU fluorescence. TMQ on the other hand showed low electron affinity.