PHLOEM MOBILITY OF XENOBIOTICS - TABULAR REVIEW OF PHYSICOCHEMICAL PROPERTIES GOVERNING THE OUTPUT OF THE KLEIER MODEL

The Kleier model of phloem-mobility of xenobiotics combines the interm ediate permeability hypothesis with the acid trap mechanism for weak a cids. The output of the model is dependent on the lipophilicity of a c ompound, for which octanol/water partition coefficients (log K-OW) hav e been used as a measure. The membrane permeability of xenobiotics is predicted from these partition coefficients, and the nature of the sie ve tube membranes has been modelled using regressions derived from Nit ella or potato permeability data. A wide range of log K-OW values for herbicides, fungicides, insecticides and experimental compounds (appro ximate to 400) have been tabulated along with the model output for var ious membrane parameters. The application of the model is in broad agr eement with literature and experimental observations on many of the kn own phloem mobile herbicides and predicts low phloem mobility for the fungicides and insecticides considered here, again in agreement with t he literature. The behaviour of herbicides representative of the main chemical families and modes of action are reviewed, along with example s of the few phloem-mobile fungicides and insecticides identified.