Figure 1.

Iron uptake and intracellular trafficking in an Arabidopsis cell. The ferric iron (Fe³⁺) is primarily reduced to ferrous iron (Fe²⁺) by surface reductase FRO2. Iron uptake is carried out at the plasma membrane by iron transporter IRT1. When iron enters the cytosol, it can be delivered into the chloroplast, vacuole, and mitochondria by iron transporters. In the chloroplast, FRO7 is the main iron transporter. Moreover, PIC1 can mediate iron transport across the inner envelope of chloroplasts. The import iron is mainly stored in ferritin proteins (AtFER1-AtFER4). In the vacuole, iron accumulation and storage are controlled by the VIT1, AtNRAMP3, and AtNRAMP4 proteins. In the mitochondria, FRO3 and FRO8 are proposed to be required for iron transport. The ABC transporter protein AtABCB25 functions in iron efflux to the cytosol