Presence of nicotianamine synthase isozymes and their homologues in the root of graminaceous plants

Nicotianamine synthase (NAS) catalyzes the synthesis of nicotianamine, which is an intermediate in the biosynthetic pathway of mugineic acid family phytosiderophores (MAs). Using polyclonal anti-NAS antibodies and recombinant NAS proteins, we identified five NAS isozymes and one NAS homologue in Fe-deficient barley roots using two-dimensional electrophoresis followed by Western blot analysis. Other unidentified NAS homologues that were induced by Fe-deficiency were also detected in barley roots. Western analysis enabled to detect NAS homologues in wheat, oats, rice, maize, and sorghum roots. In graminaceous species, both the amount and number of NAS homologues were correlated with the total NAS activity and Fe-deficiency tolerance. The NAS isoform patterns differed among the graminaceous plants.