The possible role of quinate in the mode of action of glyphosate and acetolactate synthase inhibitors.
BACKGROUND
The herbicide glyphosate inhibits the biosynthesis of aromatic amino acids by blocking the shikimate pathway. Imazethapyr and chlorsulfuron are two herbicides that act by inhibiting branched-chain amino acid biosynthesis. These herbicides stimulate secondary metabolism derived from the aromatic amino acids. The aim of this study was to test if they cause any cross-effect in the amino acid content and if they have similar effects on the shikimate pathway.


RESULTS
The herbicides inhibiting two different amino acid biosynthesis pathways showed a common pattern in general content of free amino acids. There was a general increase in total free amino acid content, with a transient decrease in the proportion of amino acids whose pathways were specifically inhibited. Afterwards, an increase in these inhibited amino acids was detected; this was probably related to proteolysis. All herbicides caused quinate accumulation. Exogenous application of quinate arrested growth, decreased net photosynthesis and stomatal conductance and was ultimately lethal, similarly to glyphosate and imazethapyr.


CONCLUSIONS
Quinate accumulation was a common effect of the two different classes of herbicide. Moreover, exogenous quinate application had phytotoxic effects, showing that this plant metabolite can trigger the toxic effects of the herbicides. This ability to mimic the herbicide effects suggests a possible link between the mode of action of these herbicides and the potential role of quinate as a natural herbicide.
Orcaray
Luis
L
Departamento de Ciencias del Medio Natural, Universidad Pública de Navarra, Campus Arrosadia, E-31006 Pamplona, Spain.
Igal
María
M
Marino
Daniel
D
Zabalza
Ana
A
Royuela
Mercedes
M
D000095:Acetolactate Synthase / Q000037:antagonists & inhibitors*; D000596:Amino Acids / Q000096:biosynthesis / Q000378:metabolism; D002264:Carboxylic Acids / Q000378:metabolism; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006540:Herbicides / Q000494:pharmacology*; D018532:Pisum sativum / Q000187:drug effects / Q000378:metabolism; D011801:Quinic Acid / Q000378:metabolism* / Q000494:pharmacology; D000097797:Glyphosate
D000095:Acetolactate Synthase; D000596:Amino Acids; D002264:Carboxylic Acids; D004791:Enzyme Inhibitors; D005998:Glycine; D006540:Herbicides; D011801:Quinic Acid; D000097797:Glyphosate