Nicotianamine is a metal-chelating molecule ubiquitous in higher plants. It is also used as a precursor for the synthesis of phytosiderophores which play a key role in iron uptake from the soil in graminaceous plants. Biochemically, it is synthesized by the enzyme nicotianamine synthase, which uses three molecules of S-adenosylmethionine.
The enzyme nicotianamine synthase converts three units of its substrate, S-adenosyl methionine, into nicotianamine and three units of 5â²-methylthioadenosine as a by-product.
Nicotianamine binds efficiently to iron II but much less well to the iron III mainly found in soil. Plants convert it into other phytosiderophores which are more efficient in scavenging iron III and other ions. For example, the enzymes nicotianamine aminotransferase (NAAT) and 3-deamino-3-oxonicotianamine reductase (DOR) give two additional compounds:
Further additions of hydroxyl groups, catalysed by alpha-ketoglutarate-dependent hydroxylases, convert 2'-deoxymugineic acid to mugineic acid and related phytosiderophores.