Q.33 Match the herbicides in Group Iwith the target enzymesin Group II.
Group I Group II
P. Glyphosate 1. Nitrilase
Q. Bromoxynil 2. Acetolactatesynthetase
R. Sulphonylureas 3. Dehalogenase
S. Dalapon 4. 5-Enolpyruvyl shikimate3-phosphate synthase
(A) P-4, Q-1, R-2, S-3 (B) P-2, Q-1, R-4, S-3
(C) P-4, Q-3, R-2, S-1 (D) P-3, Q-2, R-4, S-1
Herbicide Enzyme Targets Matching: Glyphosate, Bromoxynil, Sulfonylureas, Dalapon
Correct Answer: (A) P-4, Q-1, R-2, S-3. Glyphosate inhibits EPSPS, bromoxynil targets nitrilase, sulfonylureas block acetolactate synthase, and dalapon engages dehalogenase.
Herbicide Mechanism Overview
Herbicides disrupt plant-specific metabolic pathways absent in mammals. Amino acid biosynthesis inhibitors dominate commercial products, targeting shikimate pathway enzymes or branched-chain amino acid synthesis for selective weed control.
Correct Matching Explained
P. Glyphosate → 4. 5-Enolpyruvylshikimate-3-phosphate synthase (EPSPS). Competitive inhibitor mimics PEP substrate, binding EPSPS active site and halting aromatic amino acid (Phe, Tyr, Trp) production via shikimate pathway blockage.
Q. Bromoxynil → 1. Nitrilase. Inhibits nitrilase enzymes involved in auxin metabolism, disrupting hormone balance and causing rapid tissue necrosis in susceptible broadleaf weeds.
R. Sulphonylureas → 2. Acetolactate synthase (ALS). Competitive inhibitors of ALS (AHAS), preventing valine, leucine, isoleucine synthesis; plants starve protein production within hours.
S. Dalapon → 3. Dehalogenase. Chlorinated herbicide degraded by microbial haloacid dehalogenase; resistance involves upregulated dehalogenases hydrolyzing C-Cl bonds for detoxification.
Option Analysis
Option (B) P-2, Q-1, R-4, S-3 incorrectly assigns glyphosate to ALS (shikimate inhibitor) and sulfonylureas to EPSPS (ALS-specific).
Option (C) P-4, Q-3, R-2, S-1 mismatches bromoxynil to dehalogenase (nitrilase target) and dalapon to nitrilase (dehalogenase substrate).
Option (D) P-3, Q-2, R-4, S-1 wrongly pairs glyphosate with dehalogenase (EPSPS binder), bromoxynil to ALS (nitrilase inhibitor), sulfonylureas to EPSPS.
Agricultural Biotechnology Impact
EPSPS/ALS inhibitors revolutionized weed management; glyphosate-resistant crops (Roundup Ready) express mutant EPSPS, while ALS mutations confer sulfonylurea tolerance. Enzyme target specificity minimizes non-target effects.
