Re-evaluation of the side effects of cytochrome b(6)f inhibitor dibromothymoquinone on photosystem II excitation and electron transfer.

Photosynthesis research

PubMedID: 23377902

Belatik A, Joly D, Hotchandani S, Carpentier R. Re-evaluation of the side effects of cytochrome b(6)f inhibitor dibromothymoquinone on photosystem II excitation and electron transfer. Photosyn Res. 2013;.
Dibromothymoquinone (DBMIB) has been used as a specific inhibitor of plastoquinol oxidation at the Q(0) binding site of the cytochrome b(6)f complex for 40 years. It is thought to suppress electron transfer between photosystem (PS) II and I, as well as cyclic electron transfer around PSI. However, DBMIB has also been reported to act as a quencher of chlorophyll excited states. In this study, we have re-evaluated the effects of DBMIB on chlorophyll excited states and PSII photochemistry. The results show that DBMIB significantly quenches the chlorophyll excited states of PSII antenna even at low concentration (from 0.1 µM), lowering the effective excitation rate of the actinic light. It also acts as a potent PSII electron acceptor retarding the reduction of the plastoquinone pool with almost maximal potency at 2 µM. Altogether, these results suggest that experiments using DBMIB can easily be misinterpreted and stress on the importance of taking into account all these side effects that occur in the same range of DBMIB concentration used for inhibition of plastoquinol oxidation (1 µM).