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 plant transport and allocation of foliar-applied xenobiotics. This model integrates xenobiotic physicochemical parameters (octanol/water partition coefficient, molar volume, and acid dissociation constant) with plant anatomical, physiological, and biochemical characteristics (e.g., xylem/phloem connections; membrane permeability; apoplast, symplast, and vascular sap pH). The processes governing foliar-applied xenobiotic transport and allocation are discussed and mathematical relationships are developed to describe these processes. Xenobiotic movement from the leaf surface involves transfer through the cuticle, movement into the leaf mesophyll symplast, phloem loading, long-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 soil-plant-atmosphere continuum are also considered. The model assumes that metabolism leads to inactivation. The mathematical relationships developed in this paper form the physiological basis to develop the computer simulation model for prediction of xenobiotic allocation patterns in plants.