Physiological responses of Xanthoria parietina to longterm copper excess: role of the extracellular secondary metabolite parietin

Abstract

Xanthoria parietina is a common lichen that is widespread around the world. Tolerance of heavy metal pollution in this lichen is well known. Xanthoria parietina contains the secondary metabolite parietin, which protects the photobiont from high UV- radiation. Secondary metabolites of lichens have been found to form complexes with metal cations. In a long-term experiment (lasting 8 weeks), we tested the resistance of X. parietina with and without the secondary metabolite parietin against two concentrations of Cu (50 μM and 500 μM). Removal of parietin did not affect the measured physiological parameters. However, it caused higher accumulation of intracellular Cu. De novo synthesis of parietin in the lichen thallus after removal of the metabolite was not observed. Physiological parameters (chlorophyll a fluorescence, chlorophyll a integrity, content of soluble proteins, ergosterol levels, TBARS production) were affected by the higher dose of Cu during the long-term experiment. It seems that the secondary metabolite parietin does not protect the lichen against Cu excess.

Keywords

• parietin
• lichens
• heavy metals
• accumulation
• tolerance