Measurement of Pb2+, Cu2+ and Cd2+ binding with mucilage exudates from maize (Zea mays L.) roots

Summary The pectic nature of root mucilages suggests a hypothetical action of these substances on heavy metal flux into the root. In this study the existence of relations between heavy metals and root mucilages were verified and quantified. In order to obtain substantial amounts of pure root mucilages, two methods of collection were developed, using: (1) maize plants grown in the field and (2) hydroponic axenic cultures. The study of mucilage-metal binding was conducted using the dialysis method, which was developed in a previous work. Results show that root mucilages are able to bind metals. The importance of the binding depends on the nature of the cation, following the order Pb > Cu > Cd. These reactions could be due to exchange processes involving mucilage cations (Ca²⁺, Mg²⁺) and heavy metals. The role of mucilages on the retention of heavy metals in the rhizosphere is also discussed.