Phloem Mobility of Xenobiotics

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Abstract
Two bioassays were used to test phloem mobility of selected xenobiotic compounds: (a) excised bean leaf assay; (b) rooted bean leaf assay. Compounds asssayed were N-alkylpyridiniums with systematic variation in octanol-water partition coefficients (log Kow) substituted benzoic acids with about the same log Kow value but variable acidities. Results of the assays strongly conform, quantitatively, to the predictions of the unified mathematical model. Results also indicate that the membrane permeability value of a compound, which depends directly on log Kow, value, is the overriding factor in determining phloem mobility. When the weak acid functionality of a compound confers increased phloem mobility, it does so principally by making the log Kow value, and consequently the membrane permeability of the compound more optimal.