Interference of ruthenium red analogues at photosystem II of spinach thylakoids

The effect of ruthenium red analogues on several thylakoid photosynthetic activities has been investigated. RR, RV, RRPh1, RRPh2 and Ph inhibit ATP synthesis and electron flow from water to MV (basal, phosphorylating and uncoupled) as their concentration increases, thus, they act as a Hill reaction inhibitor. They inhibit uncoupled electron transport through PSII from water to DCPIP and partially from DPC to DCPIP. However, these compounds do not affect uncoupled PSI electron transport from DCPIP to MV. Therefore, the target of interaction is at the level of OEC and the span P(680) to Q(A) for RR, RRPh1 and RRPh2. Chlorophyll a fluorescence studies corroborate the already found interference sites and may affect the disconnection between chlorophyll molecules within the LHCII and/or between antennae and RCs, or decreases the exciton to reach the RC and inhibition of PSII occurs. RRPh2 is six times more active than RR. Finally, Ph inhibits electron flow interacting at the level of Q(B).