Dandelion is more tolerant to cadmium than to nickel excess

Comparative accumulation of cadmium (Cd) and nickel (Ni) and the consequences for the metabolism of common weed dandelion (triploid ones of Taraxacum sect. Taraxacum) were studied here for the first time. Cd accumulated more in both shoots and roots (489 and 2486 μg/g DW) than Ni (165 and 858 μg/g DW) after 14 days of exposure and only root Ni content did not increase between 7 and 14 days of exposure. Surprisingly, though Ni was less accumulated than Cd, it had more negative impact on basic physiology (root dry biomass, shoot water content and chlorophyll amount). Ni also evoked more extensive depression of mineral nutrients (K, Ca, Mg, and Mn) in the shoots than Cd while root potassium content was elevated by both metals. Ni suppressed accumulation of total thiols but anatomical changes and ROS formation (detected by fluorescence microscopy of total ROS and lipid peroxidation) were induced more by Cd. Total soluble phenols, major (caftaric and cichoric) and minor (chlorogenic and caffeic) phenolic acids were elevated by both metals and rather increased with prolonged exposure in the shoots (14 versus 7 days). On the contrary, typically depletion of these metabolites was found in the roots after prolonged exposure to Ni, but not to Cd. Data showed distinct toxicity of Cd and Ni in dandelion. More expressive tolerance of dandelion to Cd than to Ni indicates its potential use for the remediation of Cd-contaminated environment.