Inhibitor Binding and Displacement in Plastoquinone Depleted Chloroplasts

Abstract

Photosystem II inhibiting chemicals are useful tools for partial evaluation of photosynthetic electron transport pathways and as agrochemicals as well. As to their mechanism of action, evidence most recently is accumulating that they directly interfere with plastoquinone binding at the reducing side of photosystem II. We have recently demonstrated that indeed DCMU can be competitively displaced from the thylakoid membrane by the short chain plastoquinone analogue plastoquinone-1. Due to the high endogeneous plastoquinone content of the thylakoid membrane, however, this displacement can only be observed in thylakoid preparations which are depleted of plastoquinone by means of n-hexane extraction (Soll, Oettmeier, 1983). Here we report on binding of different kinds of photosystem II inhibitors to plastoquinone-depleted thylakoids, the displacement of DCMU by various 1,4-benzoquinones and a quantitative structure activity relationship (QASAR) thereof.