Mechanism of Hormonal Actions Induced by Root-Applied Clomeprop in Radish Seedlings

Morphological changes, ethylene production, activation of ACC (1-aminocyclo-propane-1-carboxylic acid) synthase and ACC oxidase in leaves of radish (Raphanus sativus L. var. hortensis cv. Shogoin) seedlings by root applied clomeprop [2-(2, 4-dichloro-m-tolyloxy) propionanilide] and its acid metabolite 2-(2, 4-dichloro-m-tolyloxy)-propionic acid (DMPA) were investigated. The results were compared with our previous data in shoot application. In root application, clomeprop induced less leaf angle increase than in shoot application. Root-applied clomeprop stimulated ACC synthase activity and ethylene production, however, they were much less than that in shoot application. In contrast, root-applied DMPA, which is assumed as an active compound for auxinic activity, induced marked leaf curling and leaf angle increase. Furthermore, root-applied DMPA rapidly activated ACC synthase and ethylene production. The amount of ethylene production was closely related to the degree of morphological change. Therefore, the morphological changes of root-applied clomeprop or DMPA are believed to be caused by ethylene which is increased by DMPA-induced ACC synthase in shoots.