Mechanism of Action of the Herbicide 4,6-Dinitro-o-cresol in Photosynthesis

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Abstract
The herbicide 4,6-dinitro-o-cresol inhibits electron transport to ferricyanide and non-cyclic photophosphorylation for 50% at about 15 μm. At higher concentrations the photosystem I depen­dent Mehler reaction ascorbate/dichlorophenolindophenol to methyl viologen is stimulated, while cyclic photophosphorylation is inhibited. The herbicide thus is an inhibitory uncoupler. Although the chemical structure of 4,6-dinitro-o-cresol is different from that of the diuron-type herbicides, its site and mechanism of action is similar. Both 4,6-dinitro-o-cresol and diuron inhibit electron transport between the primary electron acceptor of Photosystem II and the plastoquinone pool. This causes a closing of the reaction centers of Photosystem II. The interaction with the inhibited molecule however is different for the two herbicides.

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