Ferric chelate reductase involved in iron reduction in roots. May participate in the transport of electrons to a Fe(3+) ion via FAD and heme intermediates. 2 a Fe(II)-siderophore + H(+) + NAD(+) = 2 a Fe(III)-siderophore + NADH Expressed in root steele. Detected in shoots, leaves, stems, siliques, flowers and cotyledons. Up-regulated in roots and shoots by iron deficiency and copper deficiency. It is not clear whether or not FRO3 functions in iron import to mitochondria or is involved in iron efflux to the cytosol. May be due to intron retention. Belongs to the ferric reductase (FRE) family.