Photosynthetic Electron Transport Inhibitors: Some Problems Related to an Accurate Determination of the Molecular Site of Action

When DCM U and D C M U -type in h ib ito r concentrations vary over a large range, different effects may be observed on chlorophyll fluorescence param eters such as fluorescence transients, areas over fluorescence induction curves as well as kinetics o f area accum ulation . These results would indicate a heterogeneity o f PS II electron acceptors, or an in h ib ito r p a rtition ing behavior dependent on the concentration. Also, a threshold value can be reached at supra-op tim al con­ centrations, beyond which the back reaction is alm ost com pletely blocked. Such an approach makes it possible to find out inconsistencies in the results, b ro u g h t a b o u t by dual effects o f some inhibitors such as phenol-type herbicides, as previously proposed.