Using a dual-stable isotope tracer method to study the uptake, xylem transport and distribution of Fe and its chelating agent from stereoisomers of an Fe(III)-chelate used as fertilizer in Fe-deficient Strategy I plants
12 Pags., 1 Tabl., 8 Figs. ; A dual-stable isotope tracer experiment was carried out with Fe-deficient sugar beet plants grown hydroponically and resupplied with differentially Fe labeled racemic and meso Fe(III)-chelates of the ethylendiamine di(o-hydroxyphenylacetic) acid (o,oEDDHA). No short-term Fe isotope exchange reactions occurred in the nutrient solution and plants did not discriminate between 54Fe and 57Fe. After 3–6 h, stable Fe isotopes, chelating agents and chelates were analyzed in roots, xylem sap and leaves by ICP-MS and HPLC-ESI/TOFMS. Ferric chelate reductase rates, xylem transport and total uptake were 2-fold higher with the meso isomer than with the racemic one. Both chelating agent isomers were incorporated and distributed by plants at similar rates, in amounts one order of magnitude lower than those of Fe. After 6 h of Fe resupply, most of the Fe acquired was localized in roots, whereas most of the chelating agent was in leaves. In a separate experiment, Fe-deficient sugar beet and tomato plants were treated with different concentrations of Fe(III)-o,oEDDHA (with a meso/racemic ratio of 1). The xylem sap Fe concentration at 24 h was unaffected by the chelate concentration, with xylem Fe(III)-o,oEDDHA accounting for 1–18% of total Fe and xylem meso/racemic ratio close to 1. Although most of the Fe coming from Fe(III)-o,oEDDHA was taken up through a reductive dissociative mechanism, a small part of the Fe may be taken up via non-dissociative mechanisms. ; This work was supported by the Spanish Ministry of Science and Innovation (MICINN) (projects AGL2007-61948 and AGL2009-09018, co-financed with FEDER), the Commission of European Communities (ISAFRUIT Project, Thematic Priority 5-Food Quality and Safety, of the 6th Framework Programme of RTD; Contract No. FP6-FOOD-CT-2006- 016279), the trilateral Project Hot Iron (ERA-NET Plant Genome Research KKBE; MICINN EUI2008-03618) and the Arago´ n Government (Group A03). IO was supported by a CONAID-DGA predoctoral fellowship and a CAI-Europa grant. ; Peer reviewed