Enhancing ZincBioavailability in Rice Using the NovelSynthetic Siderophore Ligand Proline-2′-Deoxymugineic Acid(PDMA): Critical Insights from Metal Binding Studies and GeochemicalSpeciation Modeling

Bioavailable ligands that bind metals mediate their uptake in plants, leading to the study of artificial ligands as potential fertilizers. Proline-2′-deoxymugineic acid (PDMA) has shown a high affinity for Fe^III, enhancing iron uptake in rice and suggesting that it could be used for improving zinc uptake. This work studied chemical solution parameters, i.e., redox potential, ion strength, pH, and ligand/metal concentrations controlling Zn^II–PDMA complex formation in rice-producing soils using geochemical speciation modeling. We show that PDMA is generally selective for Zn^II in reducing, saline, and alkaline soil solutions. Comparison with a recent micronutrient uptake study in rice suggests that free PDMA should be added in reducing conditions to avoid competition with Cu^II and Fe^III or as the Zn^II–PDMA complex at pH below 9. The Zn/M ratios (M = Cu^II, Fe^III) needed to form stable Zn^II–PDMA complexes were also identified. This study shows the promise of PDMA as a fertilizer to overcome zinc deficiencies in alkaline and flooded soils.