The Behavior of Systox-isomers in Bean and Citrus Plants1

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Abstract
The comparative behavior of radiotracer preparations of the thiono- and thiol-isomers of Systox was investigated in bean and lemon plants. The isomers are readily absorbed by the roots and stems of lemon seedlings and translocated to the leaves in amounts toxic to the citrus red mite and greenhouse thrips. The translocated materials concentrate most strongly in the peripheral growing areas of the upper leaves, and the systemic behavior closely resembles that of schradan. Following topical application of the thiol-isomer to the stems of bean and lemon plants, radio-activity accumulated in the upper leaves from 5 to 10 times as fast as it did following the application of the thiono-isomer. Studies of the quantitative metabolism of the Systox-isomers in bean and lemon leaves by paper chromatography indicated a rapid metabolism of both isomers. In the bean plants 80 to 90% of the total radioactivity in the leaves was in metabolized forms within 24 hrs. Metabolism was slightly slower in lemon plants, but 97 to 100% of the total radioactivity was in metabolized forms within 4 days. From the results of 2 independent sets of paper chromatographic studies with entirely different solvents and stationary phases, it appears that a single toxic metabolite comprises about 90% or more of the initial metabolic products for each of the isomers. Contact toxicity studies showed that the thiol-isomer is from 3 to 5 times as toxic as the thiono-isomer to the greenhouse thrips and citrus red mite. The LD100 of the thiono-isomer metabolite to these pests was estimated at about 300 [mu]g/g of leaf, while that of the thiol-isomer metabolite was less than 40 [mu]g/g of leaf. The pure thiono-isomer is of low activity as an inhibitor of fly-brain cholinesterase, but the thiol-isomer is highly active, as are the principal metabolites of both isomers. Radioactive vapors could not be isolated from the leaves of bean or lemon plants topically treated on the stem by the tracer isomers of Systox.