Induction of phenolic compounds in two dark-grown lentil cultivars with different tolerance to copper ions

The influence of a high copper sulphate concentration on growth, Cu accumulation, lipid peroxidation as well as on the contents of total phenolic compounds (PhC) and UV-absorbing compounds (UVAC) in roots of lentil (Lens culinars Medic.) cvs. Krak and Tina was investigated. The plants were subjected to 0.5 mM Cu²⁺ for 3 and 5 days in darkness. Growth inhibition and increased lipid peroxidation in the roots of both cultivars, especially in cv. Tina which accumulated more Cu, were observed. Cu²⁺ treatment caused greater PhC and UVAC accumulation in cv. Krak; however, constitutive levels of these compounds were higher in cv. Tina. The maximum absorption peak of UVAC was determined at 270 nm. HPLC analyses of these compounds revealed the presence of two main derivatives of the soluble (aglycone and ester-bound) fraction of the hydroxycinnamic acids, ferulic (FA) and p-coumaric (p-CA) acids and the flavonol, kaempferol (Kam). Greater changes in the content of phenolic acids than of Kam may suggest that the former play a more important role in protecting lentil roots against high Cu²⁺ concentration. Thus, while the lower PhC levels at a higher Cu content in the roots of cv. Tina were probably due to stress, their higher levels in cv. Krak could have been a response to ROS signaling. However, though the high concentration of Cu²⁺ stimulated PhC in cv. Krak, it was not sufficient to counteract the amount of ROS generated by metal presence. These observations may suggest that ROS can serve as a common signal for acclimation to Cu²⁺ stress and cause PhC accumulation in dark-grown roots. The role of PhC in lentil tolerance to Cu²⁺ stress is discussed.