Question

DCMU is a herbicide, which kills the plant by

• A. Inhibiting photolysis of water as it is a strong inhibitor of pigment system II.
• B. Inhibiting $C{O}_2$ function as it is a strong inhibitor of pigment system II.
• C. Checking respiration.
• D. Destroying chloroplast.

Answer 1

Answer: (A)

Inhibiting photolysis of water as it is a strong inhibitor of pigment system II.

DCMU is 3-(3,4-dichlorophenyl)-1,1-dimethyl urea. When chloroplasts are treated with DCMU, or diuron, a potent herbicide, $O_2$ evolution and photophosphorylation cease. Oxygen evolution, but not photophosphorylation, can be restored by addition of an external electron acceptor, or Hill reagent. DCMU competes with plastoquinone for binding site in PSII. Thus, it inhibits photolysis.