Stable Cu Isotope Ratios Show Changes in Cu Uptake and Transport Mechanisms in Vitis vinifera Due to High Cu Exposure

Abstract

Even though copper (Cu) is an essential plant nutrient, it can become toxic under certain conditions. Toxic effects do not only depend on soil Cu content, but also on environmental and physiological factors, that are not well understood. In this study, the mechanisms of Cu bioavailability and the homeostasis of Vitis vinifera L. cv. Tannat were investigated under controlled conditions, using stable Cu isotope analysis. We measured Cu concentrations and δ65Cu isotope ratios in soils, soil solutions, roots, and leaves of grapevine plants grown on six different vineyard soils, in a 16-week greenhouse experiment. The mobility of Cu in the soil solutions was controlled by the solubility of soil organic matter. No direct relationship between Cu contents in soils or soil solutions and Cu contents in roots could be established, indicating a partly homeostatic control of Cu uptake. Isotope fractionation between soil solutions and roots shifted from light to heavy with increasing Cu exposure, in line with a shift from active to passive uptake. Passive uptake appears to exceed active uptake for soil solution concentrations higher than 270 μg L–1. Isotope fractionation between roots and leaves was increasingly negative with increasing root Cu contents, even though the leaf Cu contents did not differ significantly. Our results suggest that Cu isotope analysis is a sensitive tool to monitor differences in Cu uptake and translocation pathways even before differences in tissue contents can be observed.

Stable Isotope Fractionation of Metals and Metalloids in Plants: A Review

“…However, studies on yeast mutants showed that specific Cu membrane transporters favor light isotopes without a preceding Cu reduction indicating that the preferential uptake of light Cu isotopes is not solely controlled by Cu reduction ( Cadiou et al, 2017 ). Moreover, distinct Fe supply neither affected Δ 65 Cu plant-source nor Δ 65 Cu roots-source ( Jouvin et al, 2012 ; Ryan et al, 2013 ) while a higher Cu supply shifted Δ 65 Cu roots-source from light to heavy in grapevine plants ( Blotevogel et al, 2022 ). This shift was assigned to a switch from active toward passive uptake pathways due to increased Cu availability.…”

“…Cu isotope fractionation between the Cu source and plants (Δ 65 Cu root-source ) and the Cu source and the root can be positive, negative, or zero ( Jouvin et al, 2012 ; Ryan et al, 2013 ; Li et al, 2016 ; Blotevogel et al, 2022 ; Figure 8 ). Results on Cu isotope fractionation during plant uptake are difficult to compare as in most cases Δ 65 Cu roots-source values were reported instead of Δ 65 Cu plant-source .…”

“…Copper isotope fractionation between root and shoot (Δ 65 Cu shoot-root ) can be positive, negative or zero ( Weinstein et al, 2011 ; Jouvin et al, 2012 ; Ryan et al, 2013 ; Li et al, 2016 ; Blotevogel et al, 2022 ; Figure 8 ). Similarly, as for the Δ 65 Cu plants-source values, the comparison of Δ 65 Cu shoot-root values may be limited particularly due to different Cu root desorption strategies ( Jouvin et al, 2012 ; Ryan et al, 2013 ).…”

“…Enrichment of light isotopes in shoots compared to roots was ascribed to Cu diffusion and membrane transport that were categorized as kinetic fractionation processes ( Weinstein et al, 2011 ; Jouvin et al, 2012 ). Light isotope enrichment in leaves was accentuated in grapevine at high Cu supply ( Blotevogel et al, 2022 ). Exposed to high Cu concentrations and after root Cu desorption, Δ 65 Cu shoot-root was neutral in oat (strategy II) while tomato (strategy I) shoots were enriched in heavy isotopes compared to their roots ( Ryan et al, 2013 ).…”

“…Within plant shoots, an enrichment of light isotopes in leaves appears to increase with plant height in hairy-leaved sedge ( Weinstein et al, 2011 ) and/or with Cu concentration in grapevine leaves ( Blotevogel et al, 2019 , 2022 ; Figure 8 ). The enrichment of light Cu isotopes was ascribed to diffusion and membrane transport ( Weinstein et al, 2011 ) as well as Cu immobilization by Cu complexation to S (Cu(I)-S) that favors light isotopes ( Cadiou et al, 2017 ; Blotevogel et al, 2019 ).…”