EFFECTS OF IRON NUTRITIONAL-STATUS AND TIME OF DAY ON CONCENTRATIONS OF PHYTOSIDEROPHORES AND NICOTIANAMINE IN DIFFERENT ROOT AND SHOOT ZONES OF BARLEY

The diurnal pattern in concentrations of phytosiderophores (PS) and its precursor nicotianamine (NA) was studied in different root and shoot zones of iron (Fe)-sufficient and Fe-deficient barley (Hordeum vulgare L. cv. Europa) grown in nutrient solution. Roots were separated into apical (0-3 cm) and basal zones (>3 cm) and shoots into young (3 cm basal. zones of youngest two leaves) and old (remaining zones of youngest two leaves and oldest leaf) parts. The main PS in barley was identified as epi-hydroxymugineic acid (epi-HMA). Regardless of the sampling zone and time of day, epi-HMA concentrations were several times higher in Fe-deficient than in Fe-sufficient plants and several times higher in the roots than in the shoots. In roots and shoots, epi-HMA concentrations were always higher in the younger compared with the older zones. In both root zones of Fe-deficient plants, an inverse diurnal rhythm occurred in epi-HMA concentrations and in its release by the roots. In contrast, such a rhythm was absent in roots of Fe-sufficient plants and in the shoots regardless of the Fe nutritional status. Nicotianamine concentrations in roots were not affected by the Fe nutritional status in apical zones but slightly enhanced under Fe deficiency in basal zones. In contrast to roots, NA concentrations in both shoot parts were lower in Fe-deficient than in Fe-sufficient plants. Regardless of the Fe nutritional status in roots and shoots, NA concentrations were higher in young than in old parts and no consistent diurnal variations were observed. The results suggest that PS are also synthesized in the shoot, although at much lower rates than in roots. As with roots, PS synthesis in the shoot is enhanced under Fe deficiency and is mainly localized in young growing tissue. The distinct diurnal rhythm in PS release in roots is apparently not regulated by variation in the rate of PS synthesis during the day.