Abstract
The absorption, translocation and metabolism of [O-ethyl-1-14C] isofenphos were examined in Japanese cypress seedlings, Endlicher Cupressus obtusa K. KOCH. The recovery of radiocarbon applied was different according to the application site and absorption reached the maximum 30, 10 and 4 days after the application by the stem top, stem base and root application, respectively. Radiocarbon absorbed in the plant tissues was the highest when it was applied to the root. The application sites made a big difference in translocation of radiocarbon in the seedlings. When it was applied to the stem top, a greater part of radiocarbon remained at the application site and a slightly lower portion of the applied region, and the translocation to the root rarely occurred. In the stem base application, upward and downward translocations of radiocarbon were scarcely observed either. In the root application, the absorption and translocation were considerably high compared with the other applications. Fractionation of radiocarbon in the plant tissues showed that a major portion of radiocarbon was partitioned in the benzene layer, and the radiocarbon in the aqueous layer and unextractable residues was very small. The examination of radiocarbon in the benzene layer by thin-layer chromatography (TLC) disclosed that isofenphos-oxon was a main metabolite and O-ethyl O-2-isopropoxycarbonylphenyl phosphoramidothioate (aminoisofenphos) and two unknown substances were minor metabolites. The transformation of isofenphos to isofenphos-oxon took place easily in the seedlings, though the transformation rate depended on the application site, and isofenphos-oxon was persistent in the seedlings. In the aqueous layer, two metabolites, O-ethyl hydrogen N-isopropylphosphoramidothioate (desphenylisofenphos) and O-ethyl hydrogen N-isopropylphosphoramidate (desphenylisofenphos-oxon) were identified.
