... FEBS 4773 of QA– in PSII centers that are affected by the nonsatu-rating concentration of inhibitor [7,8]. The Em of QAisraised in the presence of DCMU in the QBpocket,making it energetically ... N,N,N¢,N¢-tetramethyl-p-phenylenediamine [23,24]. The use of a nonsaturating concentration of DCMU,an inhibitor known to close the PSII reaction center bybinding in the QBpocket and blocking electron transfer from QAto ... to the reduction of the PQ pool.ResultsAs reported in the literature, the I step of the O–J–I–Pfluorescence transient cannot be clearly distinguishedby visual analysis of the FI traces obtained...