Many herbicides act by interfering with photosynthesis. Two herbicides, atrazine

Question

Many herbicides act by interfering with photosynthesis. Two herbicides, atrazine and diuron, work by preventing electrons from being transferred from the excited chlorophyll molecules in photosystem II to the first electron carrier in the electron transport chain. (Note: photosystem II occurs before photosystem I in the thylakoid membrane.) Provide an object to represent one of these herbicide molecules and demonstrate what happens. Describe, specifically, what happens to photosynthesis when one of these herbicides is present.

Explanation / Answer

The key step in ETC is reduction of plastoquinone by D1 protein in thylakoid membrane. Herbicides act as inhibitors of plastoquinone binding. These herbicides bind to D1 protein and inhibit the binding of PQ hence, the process of photosynthetic electron transfer is interrupted, and also the synthesis of ATP and NADPH in the chloroplast is not accomplished. Which, results in inability to fix CO2. It also causes oxidative stress, and the free radicals generated cause rapid cellular damage.

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