Question

If anyone is good at photosynthesis i have a question on DCMU.

1a) if DCMU blocks plastoquinoe from binding to photosystem 2 then in what state (oxidized or reduced) will the chlorophyll of a photosystem 2 be stuck?

- oxidized ???,

b) based on the answer above, in what state would plastoquinoe be stuck and why?

- would it be oxidized because DCMU kills plants so youre losing electrons ?

Answer 1

DCMU : (3-(3,4- dicholorophenyl)-1- dimethylurea is an algicide, herbicide which inhibits photosynthesis.

role of DCMU:

• very specific and sensitive inhibition of photosynthesis.
• blocks plastoquinone binding site of photosystem II.
• disallow the electron flow from photosystem II to plastoquinone.
• causing interruption in the photosynthetic ETC in photosynthesis.
• reducing the ability of the plant to turn light energy into chemical energy.
• primary symptom of DCMU phytotoxicants in plants is the destruction of chlorophyll.

a) if DCMU blocks plastoquinone from binding to photosystem II, the cholorophyll will be stucked in oxidized state because water oxidation generating atmospheric oxygen occurs in PS II - large protein pigment complex located in the thylakoid membrane. there if DCMU acts on inhibition, the chlorophyll is stucked in oxidizing stage.

b) DCMU blocks plastoquinone binding site of photosystem II, disallowing the electron flow from photosystem II to plastoquinone. the flow of electron from PS II to PS I, supressing the linear photosynthesis and blocking the reduction of NADP+ to NADPH. They prevent the formation of O2 from H2O. Due to absence of potential gradient there is no translocation of the proteins across the membrane. Therefore blocking the ability of the plant to convert light energy into Chemical energy.