Fe isotope fractionation caused by translocation of iron during growth of bean and oat as models of strategy I and II plants

Abstract

Background: The determination of the plant-induced Fe-isotopic fractionation is a promising tool to better quantify their role in the geochemical Fe cycle and possibly to identify the physiological mechanisms of Fe uptake and translocation in plants. Here we explore the isotope fractionation caused by translocation of Fe during growth of bean and oat as representatives of strategy I and II plants. Methods: Plants were grown on a nutrient solution supplemented with Fe(III)-EDTA and harvested at three different ages. We used the technique of multi-collector ICP-MS to resolve the small differences in the stable iron isotope compositions of plants. Results: Total bean plants, regardless of their age, were found to be enriched in the light iron isotopes by -1.2‰ relative to the growth solution throughout. During growth plants internally redistributed isotopes where young leaves increasingly accumulated the lighter isotopes whereas older leaves and the total roots were simultaneously depleted in light iron isotopes. Oat plants were also enriched in the light iron isotopes but during growth the initial isotope ratio maintained in all organs at all growth stages. Conclusions: We conclude that isotope fractionation in bean as a representative of strategy I plants is a result of translocation or re-translocation processes. Furthermore we assume that both uptake and translocation of Fe in oat maintains the irons' ferric state, or that Fe is always bound to high-mass ligands, so that isotope fractionation is virtually absent in these plants. However, in contrast to our previous study in which strategy II plants were grown on soil substrate, oat plants grown on Fe(III)-EDTA contain iron that enriches

The Iron Stable Isotope Fingerprint of the Human Diet

“…The analysed strategy II plants yield the highest δ 56 Fe, between -0.56 ‰ and 0.39 ‰, and lower concentrations ranging from 5 µg/g to 56 µg/g. These ranges are similar to those found in growth experiments 11,13 . The analysed strategy I plants contain mostly a lighter iron isotope composition than strategy II plants (-1.4 ‰ to -0.1 ‰) and iron concentrations mostly between 38 µg/g and 200 µg/g (with two exceptions that are discussed below).…”

“…Mapping-out the iron stable isotope composition of the human diet is so difficult as all forms of food differ widely in their composition: plant food of "strategy I" plant origin (most non-graminaceous plants) encompasses a range of 0 ‰ to -3 ‰ in 56 Fe/ 54 Fe, given that these plants use a reductive uptake strategy [11][12][13][14] . These plants also differ in the composition of their different parts, with fruits and highest leaves typically contain the strongest enrichment of the light iron isotope, 54 Fe 11,13,14 .…”

“…These plants also differ in the composition of their different parts, with fruits and highest leaves typically contain the strongest enrichment of the light iron isotope, 54 Fe 11,13,14 . In contrast, "strategy II" plants (graminaceous plants) feature a narrower range (-0.5 ‰ to +0.2 ‰) in 56 Fe/ 54 Fe, and do not differ between their parts 11,13,14 .…”

“…These plants also differ in the composition of their different parts, with fruits and highest leaves typically contain the strongest enrichment of the light iron isotope, 54 Fe 11,13,14 . In contrast, "strategy II" plants (graminaceous plants) feature a narrower range (-0.5 ‰ to +0.2 ‰) in 56 Fe/ 54 Fe, and do not differ between their parts 11,13,14 . Initial surveys of animal food show that most meat sources, except liver, are enriched in the light iron isotope to a degree similar to human blood (-2 ‰ to -2.7 ‰ in 56 Fe/ 54 Fe) 2,5,7 .…”

A preliminary study of iron isotope fractionation in marine invertebrates (chitons, Mollusca) in near-shore environments

“…Amin et al, 2009). Uptake mechanisms produce strong fractionations in terrestrial plants (von Blanckenburg et al, 2009;Guelke-Stelling and von Blanckenburg, 2012), and if enough Fe(II) is available, the light isotope may be preferentially absorbed, producing a light δ 56 Fe signal which could depend on algal type.…”