A naturally occurring chelate of iron in xylem exudate

Abstract

Com-parisons of the behavior of Fe in tobacco plant exudate and in a synthetic mixture of Fe and phosphate indicated the existence of a naturally occurring chelate of Fe in plant exudate which might serve as a transport form of Fe in plants. In contrast with Fe in synthetic mixtures, Fe in exudate was not removed by Millipore filtration; it moved on paper chromatograms; it was adsorbed by anion exchange resin, and it moved directly through a Sephadex gel filter column. These results indicate the exudate Fe is associated with a large anion. While the identity of the chelating agent has not been established as yet, the results indicate it is not an amino acid, ascorbic acid, nor an organic acid. The stability constant of the natural Fe complex appears to be between 17 and 20.7.