Metabolization of iron by plant cells using O-Trensox, a high-affinity abiotic iron-chelating agent

Abstract

A synthetic siderophore, O-Trensox (L), has been designed and synthesized to improve iron nutrition of plants. The affinity for iron of this ligand [pFe(III) = 29.5 and pFe(II) = 17.9] is very high compared with EDTA. In spite of its high and specific affinity for iron, O-Trensox was found to be able to prevent, and to reverse, iron chlorosis in several plant species grown in axenic conditions. It also allows the iron nutrition and growth of Acer pseudoplatanus L. cell suspensions. The rate of iron metabolization was monitored by 59Fe radioiron. Ferritins, the iron storage proteins, are shown to be the first iron-labelled proteins during iron metabolization and to be able to further dispatch the metal. Using Fe(III)-Trensox, the rate of iron incorporation into ferritin was found to be higher than when using Fe-EDTA, but slower than with Fe-citrate, the natural iron carrier in xylem. During a plant cell culture, the extracellular concentrations of iron complex and free ligand were measured; changes in their relative amounts showed that the iron complex is dissociated extracellularly and that only iron is internalized. This suggests a high affinity for iron of a putative carrier on the plasmalemma. In contrast with Fe-citrate and Fe-EDTA complexes, Fe(III)-Trensox is not photoreducible. Its ability to induce radical damage as a Fenton reagent was tested using supercoiled DNA as target molecule. Unlike Fe-citrate and Fe-EDTA, Fe(II)-Trensox and Fe(III)-Trensox were proven to be harmless even during ascorbate-driven reduction, while Fe-EDTA and Fe-citrate generate heavy damage to DNA.