Mechanism of Action of the Herbicide 2‐Chloro‐3(4‐chlorophenyl) Propionate and its Methyl Ester: Interaction with Cell Responses Mediated by Auxin

Chlorfenprop-methyl (the herbicidal component of BIDISIN®), and to a lesser extent the free acid, chlorfenprop, inhibit auxin mediated cell responses in coleoptiles of Avena sativa L. and Zea mays L., such as cell elongation, auxin-uptake, -transport and -metabolism, acidification of growth media, and binding of naphthyl-I-acetic acid to auxin-specific binding sites in homo-genates of corn coleoptiles. Within a very narrow concentration range (1 to 2μM) chlorfenprop-methyl arrests growth from 0 to 100% in sensitive cultivars. The compound displays neither auxin-nor anti-auxin-activity, and only the l(-)-enantiomer is active. The interaction of the herbicide with auxin at the level of membranes is proposed.