Role of uronic acid polymers on the availability of iron to plants

The interaction between polygalacturonic acid and Fe(III) was studied in the presence and in the absence of pyruvic, malic, and citric acids. Kinetical data and FT-IR analyses show that the polysaccharidic matrix acts as an accumulator of Fe(III) and that the metal ion interacts electrostatically with both the carboxylic and other functional groups of the polysaccharidic matrix. Copper(II) ions, which have a high affinity towards the carboxylic groups of the polysaccharide, do not influence markedly the Fe(III) absorption indicating that the carboxylic groups are not determining in the Fe(III) accumulation process. Furthermore, the results suggest that iron inside the fibrils is under an hydrolyzed form or as Fe(III) hydroxy polymer. In the presence of malic and citric acids the amount of Fe(III) accumulated at pH 4.7 and 6.0 is markedly lower than that found in the presence of pyruvic acid what was attributed to the higher affinity of citric and malic acid towards the metal ion.