DCMU

DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a herbicide that inhibits photosynthesis. It was released by Bayer in 1954 under the name of Diuron.

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Mechanism of action

DCMU is a very specific and sensitive inhibitor of photosynthesis. It blocks the plastoquinone binding site of photosystem II, disallowing the electron flow from where it is generated, in photosystem II, to plastoquinone. This interrupts the photosynthetic electron transport chain in photosynthesis and thus blocks the ability of the plant to turn light energy into chemical energy (ATP and reductant potential).

DCMU only blocks electron flow from photosystem II, it has no effect on photosystem I or other reactions in photosynthesis, such as light absorption or carbon fixation in the Calvin cycle.

However, because it absorbs electrons oxidized from water in PS II, the electron "hole" of PS I cannot be satisfied, effectively shutting down photosynthesis by blocking the reduction of NADP⁺ to NADPH, and the cyclic photosynthetic pathway since electron shuttling is associated with proton pumping across the membrane into the lumen.

Applications

Besides its use a herbicide, DCMU is often used to research energy flow in photosynthesis.

References