Abstract
Iron is an essential element for organisms, but its solubility in soil is often extremely low. Previously, plants were considered to take up iron only after its reduction to ferrous ions. Takagi reported that oat and rice secrete chelating substances that solubilize ferric iron in the rhizosphere for efficient iron uptake. In 1978, Takemoto et al. reported the chemical structure of an iron-chelating compound secreted from barley roots, designated as mugineic acid. Mugineic acid and its derivatives, collectively known as mugineic acid family phytosiderophores (MAs), chelate ferric iron using octahedral hexacoordination. The specific iron uptake system by MAs in graminaceous plants was later classified by Römheld and Marschner as Strategy II, in contrast to Strategy I for reduction-based iron uptake by non-graminaceous plants. Further studies on MAs by Japanese researchers led to the identification of their biosynthetic pathways, corresponding enzymes and encoding genes, their regulation mechanisms, and the production of iron deficiency-tolerant and iron-rich crops.