Metal binding with root exudates of low molecular weight

SUMMARY Root exudates were collected from maize plants ( Zea mays L .), grown under sterile and hydroponic conditions. Exudates of low molecular weight were isolated by filtration and dialysis (MW 1000) of the nutrient solution and analysed. Metal binding properties of the exudates were investigated at 25°C in 0.1 m NaCIO 4 ionic medium, using a potentiometric method. The total acidity of the exudates and the successive stability constants of complexes formed with Cu 2+ , Pb 2+ and Zn 2+ were determined. Sugars and organic acids were the major components of the exudates. Measured total acidity was resolved into strong (5.85meq g −1 C), weak (2.10meq g −1 C) and very weak (2.20 meq g −1 C) acidities. Mono‐complexes were formed with Cu, Pb and Zn and bis‐complexes with Cu. At pH 5, stability constants followed the order Cu>Pb>Zn.