Biosynthesis of phytosiderophores. In vitro biosynthesis of 2'-deoxymugineic acid from L-methionine and nicotianamine

2'-Deoxymugineic acid (DMA), one of mugineic acid-family phytosiderophores (MAs), was synthesized in vitro both from L-methionine and from nicotianamine (NA) with a cell-free system derived from root tips of iron-deficient barley (Hordeum vulgare L.). The reactions producing DMA from NA needed an amino group acceptor (i.e. 2-oxoglutarate, pyruvate, or oxalacetic acid) and a reductant (i.e. NADH or NADPH). The activity of the enzymes to produce NA from L-methionine was the highest at about pH 9. This biosynthetic activity was markedly induced by iron-deficiency stress. The synthesis of NA from S-adenosyl-L-methionine was more efficient than from L-methionine. From the results with the cell-free system reported here, we propose a revised biosynthetic pathway of MAs