Singlet oxygen scavenging activity of plastoquinol in photosystem II of higher plants: Electron paramagnetic resonance spin-trapping study

Abstract Singlet oxygen ( 1 O 2 ) scavenging activity of plastoquinol in photosystem II (PSII) of higher plants was studied by electron paramagnetic resonance (EPR) spin-trapping technique. It is demonstrated here that illumination of spinach PSII membranes deprived of intrinsic plastoquinone results in 1 O 2 formation, as monitored by TEMPONE EPR signal. Interestingly, the addition of exogenous plastoquinol (PQH 2 -1) to PQ-depleted PSII membranes significantly suppressed TEMPONE EPR signal. The presence of exogenous plastoquinols with a different side-chain length (PQH 2 -n, n isoprenoid units in the side chain) caused a similar extent of 1 O 2 scavenging activity. These observations reveal that plastoquinol exogenously added to PQ-depleted PSII membranes serves as efficient scavenger of 1 O 2 .