REVIEW ARTICLE: Compartmental redistribution and long-distance transport of abscisic acid (ABA) in plants as influenced by environmental changes in the rhizosphere —a biomathematical model

Abstract

Based on experimental data obtained in earlier studies on membrane permeabilities of abscisic acid (ABA) for cortex and stele cells of roots and on measured com-partmental pH shifts after onset or release of different types of soil-borne stresses, a biomathematical model was developed which permits computer analysis of the dynamics of compartmental ABA distribution within different root tissues (cortex, stele) and their compartments (apoplast, cytosol, vacuole), and in the xylem sap of the root stele. Metabolism and conjugation of ABA and its export from roots via the xylem and its import into roots via phloem sap flow are also taken into consideration. We want to know which soil-borne stresses can biophysically provoke a root-to-shoot signal of ABA. In this communication we describe the biomathematical structure of the root model and present all necessary morphological (volumes, surfaces etc.) and physiological (pH, membrane conductances etc.) parameters of unstressed roots. This root model and an available leaf model are integrated to a plant model (rosette plant). Simulations reveal the fundamental role of the stele tissues, the rhizospheric ABA concentration and the ABA synthesis in roots (root-to-shoot communication). The shoot-to-root communication strongly depends on ABA synthesis in leaves, but hardly on ABA redistribution effects after stress-induced compartmental pH-shifts in leaves.