Concentrations of iron and phytosiderophores in xylem sap of iron-deficient barley plants

Abstract

Barley (Hordeum vulgare L. cv. Minorimugi) plants were grown hydroponically in a greenhouse under natural sunlight. The xylem sap was collected from the barley plants showing iron (Fe) deficiency symptoms in order to determine the concentrations of the mugineic acid family of phytosiderophores (PS) and Fe. The compounds of PS in the xylem sap were identified, using TLC and HPLC, as mugineic acid (MA) and 2′-deoxymugineic acid (DMA). Feeding experiments were conducted to study the effects of PS on the concentrations of Fe and PS in the xylem sap of barley plants grown under Fe-deficient conditions. The concentration of Fe in the xylem sap of the Fe-deficient plants supplied with Fe3+ (30 αM) together with varying concentrations of PS (0 to 30 αM) increased with the increase in the PS concentration in the nutrient solution, indicating the specific role of PS in the acquisition of Fe3+ by the roots. On the other hand, PS concentration in the xylem sap increased at the highest external PS concentration (30 αM). The PS : Fe ratio in the xylem sap decreased with the increase in the concentration of PS supplied to the roots. The effects of the addition of 30 αM Fe3+ and equimolar concentration of PS or ethylene diamine tetraacetic acid (EDTA) to the Fe-deficient plants were compared. Plants supplied with PS showed a higher Fe concentration in the xylem sap than those which received EDTA, suggesting that PS were more effective than EDTA in the absorption and translocation of Fe3+.