| Abstract: | The metabolic fate of the auxin herbicide (4-chloro-2-methylphenoxy)aceticacid (MCPA) has been determined in a number of species usinga vacuum infiltration technique. In all cases MCPA became hydroxylatedto form (4-chloro-2-hydroxymethylphenoxy)acetic acid, whichaccumulated largely as a glycosidic conjugate. The nature ofthe oxidized metabolite from oat (Avena sativa L.) was verifiedby GC/MS. In all cases at least one diethyl ether-soluble conjugateof MCPA was formed; these are suggested to be amino acid conjugates.Several minor aglycones were also formed. Important speciesvariations in both the rate and quantitative nature of metabolismwere observed. Pretreatment of potato (Solarium tuberosum L.)tuber slices with unlabelled MCPA and other auxins increasedthe capacity for hydroxylation, but particularly induced theformation of an MCPA-glycoside. This was never a major metaboliteunder normal circumstances. The rate of hydroxylation was alsoenhanced by ageing in MnCl2. Although the ether-soluble conjugatesof MCPA were stable metabolites, exogenously applied conjugateisolated from carrot (Daucus carota L.) was readily cleavedin four species. Free MCPA and the products normally derivedfrom it were identified. MCPA Metabolism Hydroxylation Conjugation |
