Ca-polygalacturonate as a useful model to study the interaction of ions at the soil-root interface: aluminium as a case study.

This chapter presents results of the adsorption of aluminium and its influence on the mobility of nutrients, in particular phosphate at the soil-root interface. Ca-polygalacturonate (Ca-PG) is the major constituent of the root mucilage and thus the soil-root interface. A Ca-PG network, which resembles the natural root mucilages and thus constitutes a good system model of natural systems, was used to study the interaction with aluminium. The first part of the chapter discusses the effect of aluminium adsorption on the structure of a Ca-membrane. The Ca-PG membrane is organised in a fibrillar and porous network acting as a bio-filter for ions and water and playing thereby a fundamental role in plant nutrition. Metal sorption alters this fibrillar structure and consequently its functionality. Structural modifications determined by FT-IR spectroscopy, Thermogravimetric (TG), Differential Thermal Analysis (DTA) and Scanning electron microscopy (SEM) are described. The final part of the chapter examines alterations induced by aluminium of the functionality of the root mucilage.