Abstract
Adequate micronutrient concentrations in crops are essential for human health and agricultural productivity. However, 30% of cultivated soils worldwide are deficient in iron. Because of low micronutrient bioavailability, graminaceous plants have evolved to exude small molecules, called phytosiderophores, into their environment, which strongly complex and promote uptake of trace elements. The introduction of a synthetic phytosiderophore, proline-2’-deoxymugeneic acid (PDMA), has been shown to promote Fe uptake in rice plants; however, its binding capabilities with other metals, which may impact the ability promote the uptake of Fe and other trace nutrient metals commonly found in soils, remain unknown. We conducted spectrophotometric titrations to determine the stability constants (logβ) of PDMA complexes with Mn(II), Co(II), Cu(II), Ni(II), and Zn(II). We determined that PDMA complex stability constants correlated with: (1) the hydrolysis constants of metal ions (logβOH) in complexes; (2) the ionic potential of complexed metals; and (3) the corresponding complex stability constants of other mugineic acid type phytosiderophores, as well as the trishydroxamate microbial siderophore DFOB. These correlations demonstrate the potential, and limitations, on our ability to predict the stability of phytosiderophore complexes with metal ions with different properties and with potentially different coordination structures.