Abstract
The free-ion model (FIM) describes iron (Fe) uptake by barley [Hordeum vulgare(L.) ‘Grammett’] as being controlled by the activity of the buffered, free, uncomplexed Fe3 + in solution. Chelators' effect on Fe uptake by barley was evaluated and the rate of exchange of Fe between chelators was examined. Barley was grown for two weeks in a low-Fe nutrient solution and transferred to solutions varying in Fe and chelators for 6 h assays. Shoot 59Fe was higher in barley grown in citrate (7743 and 1928 59Fe Bq g− 1) than in NTA (3220 and 1113 59Fe Bq g− 1; P = 0.045) despite similar free-Fe3 + activities. A comparison of Fe uptake by barley from solutions with pFe3 + activities of 17.1 and 24.6 showed < 5% was from indiscriminate apoplastic-flow uptake (3250 59Fe Bq g− 1 vs. 160 59Fe Bq g− 1). Using nutrient solutions from the barley studies but without plants, Fe exchange between chelators and a simulant for the barley phytosiderophore occurred within hours (for NTA and citrate), or days (EDTA and HEDTA). Results were similar between the barley and Fe-exchange experiments for the two nutrient-solution treatments where the same Fe3 + activities but different total-Fe concentrations were used: the higher total-Fe treatment resulted in six-fold higher shoot 59 Fe, while in the Fe-exchange study that treatment had six-fold more Fe bound to the phytosiderophore simulant after 2 d. Results indicated deviations from the FIM were not explained by indiscriminate-flow uptake, and that sluggish Fe-exchange reactions between chelate and phytosiderophore-simulant, not FIM guidelines, may be more important in explaining Fe uptake from synthetic chelates by Fe-deficient barley.
Published Version
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