Influence of novel CU(II) complex on the photosystem II photochemical activity of spinach

The mechanism of action of a large group of modern agents used for weed control inhibits electron transfer in the light stage of photosynthesis at one or another site of the electron-transport chain. Impact of the novel [CuL2]Br2 complex (L = bis4H-1,3,5-triazino [2,1-b] benzothiazole-2-amine, 4-(2-imidazole)copper(II) bromide complex) on the activity of PSII membranes isolated from spinach were studied by of photosynthetic oxygen evolution as well as changes in the PSII chlorophyll fluorescence yield (FV) related to photoreduction of the QA plastoquinone, the PSII primary quinone electron acceptor. We show that [CuL2]Br2 effectively inhibits PSII photochemical activity as revealed by suppression of both the characteristic PSII photoreactions with the same similar effectiveness. [CuL2]Br2 decreases FM level exclusively at the expense of FV; causes neither changes in the F0 level nor the retardation of the photoinduced rise in FM. Artificial electron donors do not cancel the inhibitory effect of [CuL2]Br2. It is likely that [CuL2]Br2, which is included somewhere on the donor side or between its components, inhibits and/or slows down natural electron donation and/or serves as an exogenous electron donor for RC. Thus, the PSII reaction center's components are most likely the major target of [CuL2]Br2 inhibitory activity. The data obtained are compared to the literature information concerning the inhibitory effects of Cu(II) aqua ions and Cu(II)-organic complexes on PSII