A nonlinear dynamic simulation model for xenobiotic transport and whole plant allocation following foliar application - I. Conceptual foundation for model development

A dynamic, nonlinear simulation model(ERMESSE) was developed for whole plan t transport and allocation of foliar-applied xenobiotics. This model integr ates xenobiotic physicochemical parameters (octanol/water partition coeffic ient, molar volume, and acid dissociation constant) with plant anatomical, physiological, and biochemical characteristics (e.g., xylem/phloem connecti ons; membrane permeability; apoplast, symplast, and vascular sap pH). The p rocesses governing foliar-applied xenobiotic transport and allocation are d iscussed and mathematical relationships are developed to describe these pro cesses. Xenobiotic movement from the leaf surface involves transfer through the cuticle, movement into the leaf mesophyll symplast, phloem loading, lo ng-distance transport in the phloem, phloem unloading to sink regions, and potential xylem/phloem exchange. Because of the xylem/phloem exchange both basipetal and acropetal movement can occur Moreover, xenobiotic metabolism and water translocation through the sail-plant-atmosphere continuum are als o considered. The model assumes that metabolism leads to inactivation. The mathematical relationships developed in this paper form the physiological b asis to develop the computer simulation model for prediction of xenobiotic allocation patterns in plants. (C) 2000 Academic Press.