Movement and metabolic fate of [ 14C]ethephon in flue-cured tobacco

Abstract

The absorption, distribution, and metabolic fate of [ 14C]ethephon in flue-cured tobacco ( Nicotiana tabacum L.) was studied using autoradiography, thin-layer chromatography, high-voltage paper electrophoresis, and liquid scintillation spectrometry. Labeled ethephon penetrated mature leaf tissue easily and was translocated primarily in an acropetal direction. No 14C activity was detected in any other plant part except the treated leaf. The first day after treatment, most of the translocated 14C was detected in the midrib, and after 2 days radioactivity was noticed in veinal areas distal to the point of application. Four days later, however, 14C was detected in slight amounts only in the midrib, indicating that [ 14C]ethephon was rapidly degraded by the leaf tissue. Depending on leaf position on the stalk, as much as 92% of the radioactivity had disappeared from the leaf tissue during the first day after treatment, and as little as 5% of the applied radioactivity was recovered 4 days later. Methanol-extracted plant residues contained insignificant amounts of 14C. All of the 14C in methanol extracts was present in the form of a labeled compound with an R f value corresponding to that of ethephon, indicating the absence of any detectable metabolites of the parent compound. Smoke analysis of cigarettes showed that more [ 14C]ethylene than 14CO 2 was recovered in the main stream, whereas the trend was reversed in the case of side stream smoke.