Catalyzes the reduction of a 3''-keto intermediate during the biosynthesis of 2'-deoxymugineic acid (DMA) from L-Met. Involved in the formation of phytosiderophores (MAs) belonging to the mugineic acid family and required to acquire iron. 2'-deoxymugineate + NAD(+) = 3''-deamino-3''-oxonicotianamine + H(+) + NADH 2'-deoxymugineate + NADP(+) = 3''-deamino-3''-oxonicotianamine + H(+) + NADPH Optimum pH is 8-9. Siderophore biosynthesis. Confined to cells participating in long distance transport (e.g. in the parts of pericycle cells adjacent to the protoxylem and metaxylem) in roots and to vascular bundles in shoots. Expressed in germinating seeds prior to protrusion of the radicle, especially in the vascular bundle of the seminal root 3 days after sowing. Up-regulated under iron-deficient conditions in root and shoot tissues (PubMed:16926158, PubMed:18224446, PubMed:24887487). Slightly induced in shoots by zinc deficiency (PubMed:18224446). Belongs to the aldo/keto reductase family.