Abstract
Graminacious plants secrete mugineic acid family phytosiderophores (MAs) from their roots to solubilize the external insoluble iron and absorb the chelated iron. The MAs secretion from root increases under Fe-deficient condition and followed the circadian rhythm. The particular vesicles derived from rER were observed to accumulate at the cell periphery near the cell membrane in Fe-deficient barley roots before sunrise. Immunocytochemical analysis on nicotianamine synthase (NAS), nicotianamine aminotransferase (NAAT), and IDS3, enzymes in MAs biosynthesis pathway, revealed that these enzymes were increased in Fe-deficient root epidermis. The subcellular localization of NAS, NAAT, and IDS3 were determined to be on the membrane, inside, and in the vicinity of the vesicle, respectively. It is suggested that deoxymugineic acid could be synthesized in the vesicle, and then DMA could be transported to the cytoplasm to convert to MAs. The polar vesicle transport may regulate the diurnal rhythm of MAs secretion from barley root.
