Figure 1.

A hypothetical scheme showing the co-existence of strategy I and strategy II Fe uptake system in maize. In strategy II, MAs are synthesized in root cells by NAS, NAAT and DMAS, and MAs are secreted into rhizosphere by TOM1. Then, Fe(III)-MAs are transported in to cells by YSLs. Strategy I may serve as a complementary mechanism in maize, which involves the direct acquisition of Fe(II) by ZmIRT1 on root surface. The genes corresponding for acidification and ferric reduction are still uncovered in maize. MAs, mugineic acids; NAS, nicotianamine synthase; NAAT, nicotianamine aminotransferase; DMAS, deoxymugineic acid synthase; YSL, yellow strip like; TOM1, transporter of mugineic acid family phytosiderophores 1; IRT1, iron regulated transporter 1.