Differential uptake and toxicity of ionic and chelated copper in Triticum aestivum

Plants of Triticum aestivum L. cv. Atlas-66 were grown in nutrient solutions containing 0–50 μM Cu as CuSO4 or 0–800 μM Cu as Cu-EDTA to compare the toxic effects of ionic and chelated Cu when yield reductions were similar in magnitude. Plants exposed to 50 μM CuSO4 accumulated 43 ± 6 μg g−1 Cu in leaf tissues and 2300 ± 130 μg g−1 in root tissues. Plants injured by CuSO4 showed acute signs of Cu toxicity; leaves showed mild necrosis and symptoms of induced Fe deficiency and root growth and lateral root initiation were inhibited. Concentrations of Fe, Mn, and Mg in leaves of plants injured by CuSO4 were low, possibly leading to nutrient deficiencies. Concentrations of Ca in leaves were also low, but were above levels considered to be deficient. Plants exposed to 800 μM Cu-EDTA accumulated 260 ± 7 μg g−1 Cu in leaf tissues and 6600 ± 1200 μg g−1 Cu in root tissues. Despite higher tissue concentrations of Cu, plants injured by Cu-EDTA showed systemic toxicity symptoms, possibly reflecting induced Fe deficiency as the primary toxic effect. Leaves of plants injured by Cu-EDTA showed mild necrosis and symptoms of induced Fe deficiency, root growth was depressed (but to a lesser extent than with CuSO4), and lateral root initiation was unaffected. Concentrations of Fe in leaves of plants injured by Cu-EDTA were lower than plants grown with micronutrient levels of Cu, while concentrations of Mn, Ca, and Mg in leaves of Cu-EDTA injured plants were higher. Differential toxicity of CuSO4 and Cu-EDTA could occur if Cu-EDTA were absorbed across the plasma membrane as an intact complex or if the primary toxic effect of CuSO4 and Cu-EDTA were on membrane structure and (or) function.