The oxidation/reduction kinetics of the plastoquinone pool controls the appearance of the I-peak in the O–J–I–P chlorophyll fluorescence rise: Effects of various electron acceptors

Quantitative analysis of the fluorescence induction (FI) rise was used in this study to elucidate the complex effects of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) on thylakoids. Reduced TMPD molecules, responsible for the ADRY agent effect, caused an increase in the amplitude of the O–J rise. Also, only oxidized TMPD molecules were shown to have the ability to bind the QB pocket of photosystem II (PSII). On the other hand, the I–P rise was slowed in proportion with the oxidized TMPD concentration, inducing the clear appearance of the I-peak. While this property was previously thought to be unique to TMPD, this study shows that some artificial electron acceptors of PSII, silicomolybdate, 2,5-dichloro-p-benzoquinone, and phenyl-p-benzoquinone, have a similar effect. These results demonstrated a major role of the oxido-reduction kinetics of the PQ-pool in the resolution of J–I and I–P phases in the FI of isolated thylakoids.