Branched-chain amino acid biosynthesis inhibitors: Herbicide efficacy is associated with an induced carbon–nitrogen imbalance

• Published in: Journal of plant physiology Vol. 170; no. 9; pp. 814 - 821
• Main Authors: Zabalza, Ana, Zulet, Amaia, Gil-Monreal, Miriam, Igal, Maria, Royuela, Mercedes
• Format: Journal Article
• Language: English
• Published: Germany Elsevier GmbH 15.06.2013
• Subjects: Acetolactate synthase; Acetolactate Synthase - antagonists & inhibitors; Acetolactate Synthase - metabolism; Adenosine - analogs & derivatives; Adenosine - pharmacology; amino acid composition; Amino acids; Amino Acids, Branched-Chain - metabolism; Biosynthesis; Branched-chain amino acid; Carbohydrate Metabolism; carbohydrates; carbon; Carbon - metabolism; death; Dose-Response Relationship, Drug; Effectiveness; growth arrest; herbicidal properties; Herbicide; Herbicides; Herbicides - pharmacology; Inhibition; Inhibitors; Ketol-acid reductoisomerase; Ketol-Acid Reductoisomerase - antagonists & inhibitors; Ketol-Acid Reductoisomerase - metabolism; Lactates - analysis; Lactates - metabolism; Leaves; Mode of action; Nitrogen - metabolism; peas; photosynthesis; Photosynthesis - drug effects; Photosynthesis - physiology; Pisum sativum - enzymology; Pisum sativum - growth & development; Pisum sativum - physiology; Plant Leaves - enzymology; Plant Leaves - growth & development; Plant Leaves - physiology; Plant Roots - enzymology; Plant Roots - growth & development; Plant Roots - physiology; Plant Shoots - enzymology; Plant Shoots - growth & development; Plant Shoots - physiology; Plant Transpiration - drug effects; Plant Transpiration - physiology; Plants (organisms); Quinic Acid - metabolism; roots; CPCA; IM; ALS; Acetolactate synthase; Ketol-acid reductoisomerase; Branched-chain amino acid; BCAA; KARI; Herbicide; Mode of action
• ISSN: 0176-1617; 1618-1328
• DOI: 10.1016/j.jplph.2013.01.003

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.