Incorporation of 15N and 14C of methionine into the mugineic acid family of phytosiderophores in iron‐deficient barley roots

The role of methionine as a precursor in mugineic acid (MA) biosynthesis was studied by feeding 15N‐ammonium sulfate, 14C‐amino acids, and [1‐14C, 15N]‐methionine to iron‐deficient barley roots (Hordeum vulgare L. cv. Minorimugi), grown hydroponically. The incorporation of isotopes into amino acids was also examined. Methionine appears to be the most efficient precursor of the mugineic acid family (MAs) of phytosiderophores; homoserine was also incorporated into the MAs, but other amino acids such as glutamate, alanine, and γ‐amino butyric acid did not act as precursors of MAs. Carbon‐14 and 15N of methionine were incorporated into MAs. This specific incorporation of 14C and 15N indicated that the nitrogen atoms of MAs were derived from two molecules of methionine. It is suggested that deoxymugineic acid (DMA) is probably the first phytosiderophore to be synthesized on the biosynthetic pathway of MAs.