Stable Isotopes of Cu and Zn in Higher Plants: Evidence for Cu Reduction at the Root Surface and Two Conceptual Models for Isotopic Fractionation Processes

• Published in: Environmental science & technology 2012-03, Vol.46 (5), p.2652-2660
• Main Authors: Jouvin, D, Weiss, D. J, Mason, T. F. M, Bravin, M. N, Louvat, P, Zhao, F, Ferec, F, Hinsinger, P, Benedetti, M. F
• Format: Article
• Language: English
• Subjects: Adsorption; Animal, plant and microbial ecology; Applied ecology; Biodegradation, Environmental; Biological and medical sciences; Biological Transport; Biomass; Cell Membrane - metabolism; Chemical Fractionation; Copper; Copper - metabolism; Diffusion; Earth Sciences; Ecotoxicology, biological effects of pollution; Flowers & plants; Fundamental and applied biological sciences. Psychology; General aspects; Ions; Iron; Iron - metabolism; Isotopes; Life Sciences; Membranes; Models, Biological; Oxidation-Reduction; Plant Development; Plant Roots - metabolism; Plant Shoots - metabolism; Plants - metabolism; Sciences of the Universe; Solutions; Surface Properties; Zinc; Zinc - metabolism; Zinc Isotopes - metabolism
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es202587m

Recent reports suggest that significant fractionation of stable metal isotopes occurs during biogeochemical cycling and that the uptake into higher plants is an important process. To test isotopic fractionation of copper (Cu) and zinc (Zn) during plant uptake and constrain its controls, we grew lettuce, tomato, rice and durum wheat under controlled conditions in nutrient solutions with variable metal speciation and iron (Fe) supply. The results show that the fractionation patterns of these two micronutrients are decoupled during the transport from nutrient solution to root. In roots, we found an enrichment of the heavier isotopes for Zn, in agreement with previous studies, but an enrichment of isotopically light Cu, suggesting a reduction of Cu(II) possibly at the surfaces of the root cell plasma membranes. This observation holds for both graminaceous and nongraminaceaous species and confirms that reduction is a predominant and ubiquitous mechanism for the acquisition of Cu into plants similar to the mechanism for the acquisition of iron (Fe) by the strategy I plant species. We propose two preliminary models of isotope fractionation processes of Cu and Zn in plants with different uptake strategies.