Figure 4. Iron transport in rice.

Rice takes up iron from the soil as Fe³⁺ deoxymugineic acid (DMA) by the OsYSL15 transporter. Rice also uses the OsIRT1 transporter to take up Fe²⁺, which is abundant in submerged and anaerobic conditions. DMA, which is the primary phytosiderophore that aids in iron transport, is synthesized from S-adenosyl methionine through three sequential enzymatic reactions mediated by nicotianamine synthase (NAS), nicotianamine aminotransferase (NAAT), and DMA synthase (DMAS), and then secreted by the efflux transporter TOM1 to solubilize iron in the soil. Nicotianamine, which is the biosynthetic precursor of DMA, is a chelator of divalent metals and plays a part in translocation of metals within plants. Nicotianamine is secreted into the cell wall by the nicotianamine efflux transporter ENA1. The iron–nicotianamine transporter OsYSL2 mediates iron influx into rice grains. The photograph shows iron staining (blue coloration) of a rice seed (inset shows rice seeds). Iron is mainly localized to the embryo and the outer layers of the grain.