A Comparison of Theoretical and Actual Coumarin Exudation Under Iron Limitation to Understand Root Exudation Mechanics

Abstract

Nutrient cycling is an important component of plants’ immune systems, largely driven by the act of exuding environmentally influential metabolites from roots. Root exudation may be driven by multiple unique mass-transport mechanisms, including active and passive transport types, though the latter is not well-studied despite being labelled a significant driver of low molecular weight metabolite exudation. This research investigates the generally accepted assumption that low molecular weight metabolites, including iron-fixing coumarins (scopoletin, fraxetin, etc.) are primarily exuded passively, and high molecular weight metabolites follow an active exudation approach. Scopoletin and scopolin exudation from Arabidopsis thaliana in low-iron and replete conditions is quantified to determine if the hypothesized passive diffusion mechanism is a significant contributor to coumarin exudation. LC-MS analysis suggests that passive diffusion of scopoletin and scopolin from roots plays a significant role in total coumarin exudation values. Further research should include investigating the implications of passive coumarin exudation on long-term iron storage and soil health in addition to the relationship between coumarin production and exudation.