6 DCMU effects the photosynthesis by attacking at
(1) Ps I         (2) PS II
(3) PC          (4) Cyt b-f₆

DCMU Effects on Photosynthesis: Target Site

Introduction

Key phrase: DCMU inhibits photosynthesis at photosystem II

DCMU is a widely studied herbicide because of its precise inhibition point in the light-dependent reactions of photosynthesis. Understanding how DCMU works, which molecular target it blocks, and the consequences for plant metabolism is critical for biology students, researchers, and agronomists.

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Detailed Explanation of Each Option

• (1) Ps I (Photosystem I):

  • Incorrect. DCMU does not inhibit PSI. PSI functions downstream in the electron transport chain and is not directly affected by DCMU’s action.

• (2) PS II (Photosystem II):

  • Correct. DCMU specifically blocks the electron flow in PSII by inhibiting the binding site for plastoquinone (QB). This prevents electron transfer from PSII to plastoquinone, effectively halting oxygen production, ATP, and NADPH formation. This makes it a classic “photosynthetic electron transport inhibitor”.

• (3) PC (Plastocyanin):

  • Incorrect. PC is a mobile electron carrier between cytochrome b6f and PSI, not the target of DCMU. DCMU acts before electrons reach PC in the electron flow pathway.

• (4) Cyt b-f6 (Cytochrome b6f):

  • Incorrect. Cytochrome b6f is a protein complex downstream of PSII and plastoquinone in the electron transport chain. DCMU blocks electron transfer before this stage, preventing electrons from even reaching this complex.

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Quick Facts About DCMU Action

• Target: Photosystem II, plastoquinone (QB) binding site.

• Consequence: Stops electron flow from water via PSII, halts ATP/NADPH production, and inhibits oxygen evolution.

• Use: DCMU is used as a herbicide and a tool in photosynthesis research to study electron transport.