Involvement of Ethylene in Clomeprop-Induced Actions in Radish Seedlings

Abstract

Whether ethylene is involved in morphological changes due to clomeprop [2-(2, 4-dichloro-m-tolyloxy) propionanilide] was examined to further determine the mode of action of the herbicide in radish seedlings. Aminooxyacetic acid (AOA), an 1-aminocyclopropane-1-carboxylic acid (ACC) synthase inhibitor, arrested clomeprop- or its hydrolyzed product, 2-(2, 4-dichloro-m-tolyloxy) propionic acid (DMPA)-induced morphological changes in radish seedlings, such as leaf curling and epinasty to some extent. These morphological changes were considerably reduced when 2, 5-norbornadiene (NBD), a competitive ethylene binding inhibitor, was applied after clomeprop or DMPA treatment. Ethephon (2-chloroethyl-phosphonic acid), an ethylene releasing agent, inhibited elongation of the first leaves. The enhancement of ethylene evolution by clomeprop occurred later than DMPA. ACC synthase, which converts S-adenosylmethionine (SAM) to ehtylene precursor ACC, was activated by clomeprop and DMPA, however, ACC oxidase, the enzyme that converts ACC to ethylene, was not activated by either substance. These results suggest that clomeprop is hydrolyzed to DMPA and then promotes ethylene production by activating ACC synthase. Accumulated ethylene might be responsible for clomeprop-induced morphological changes in radish seedlings.