title: Branched-chain amino acid biosynthesis inhibitors: herbicide efficacy is associated with an induced carbon-nitrogen imbalance.
abstract: Acetolactate synthase (ALS; EC 4.1.3.18) and ketol-acid reductoisomerase (KARI; EC 1.1.1.86) are two consecutive enzymes in the biosynthesis of branched-chain amino acids. Several commercial herbicides inhibit ALS as their primary site of action. KARI has also attracted attention as a potential target for herbicides. Although potent and selective inhibitors of KARI have been discovered, these inhibitors display less herbicidal activity than ALS-inhibiting herbicides. To obtain a better understanding of these findings, we have compared the physiological effects induced in pea plants after KARI or ALS inhibition. Although, both types of inhibitors induce growth arrest and photosynthesis inhibition, plant death occurs more rapidly under ALS inhibition than KARI inhibition. Carbohydrates accumulated in the leaves and roots following treatments with both inhibitors. The carbohydrate accumulation in the leaves occurred as a consequence of a decrease in sink strength. In contrast, the free amino acid content was only affected through ALS inhibition. These results indicate that although KARI and ALS inhibition block the same biosynthetic pathway and exert common effects on carbon metabolism, nitrogen metabolism is more affected via ALS than KARI inhibition. Thus, metabolic alterations in nitrogen metabolism induced through ALS inhibitors might contribute to the increased efficacy of these chemicals as herbicides.
authors: Departamento de Ciencias del Medio Natural, Universidad Pública de Navarra, Campus de Arrosadia, E-31006, Pamplona, Spain.
authors: Ana
authors: A
authors: Zabalza
authors: Amaia
authors: A
authors: Zulet
authors: Miriam
authors: M
authors: Gil-Monreal
authors: Maria
authors: M
authors: Igal
authors: Mercedes
authors: M
authors: Royuela
mesh_terms: D000095:Acetolactate Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D006540:Herbicides / Q000494:pharmacology*; D050540:Ketol-Acid Reductoisomerase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007773:Lactates / Q000032:analysis / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D018532:Pisum sativum / Q000201:enzymology* / Q000254:growth & development / Q000502:physiology; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology; D018515:Plant Leaves / Q000201:enzymology / Q000254:growth & development / Q000502:physiology; D018517:Plant Roots / Q000201:enzymology / Q000254:growth & development / Q000502:physiology; D018520:Plant Shoots / Q000201:enzymology / Q000254:growth & development / Q000502:physiology; D018526:Plant Transpiration / Q000187:drug effects / Q000502:physiology; D011801:Quinic Acid / Q000378:metabolism
chemical_list: D000597:Amino Acids, Branched-Chain; D006540:Herbicides; D007773:Lactates; D011801:Quinic Acid; C024311:N-cyclopropyl adenosine-5'-carboxamide; C006359:alpha-acetolactate; D002244:Carbon; D050540:Ketol-Acid Reductoisomerase; D000095:Acetolactate Synthase; D000241:Adenosine; D009584:Nitrogen