RESUMO
Lichens produce a great number of secondary metabolites that participate in ecological interactions and respond to environmental changes. We examined the influence of heavy metal accumulations on lichen secondary metabolism. Thalli of Hypogymnia physodes were transplanted for 6 months to the Cracow-Silesia industrial region. Based on heavy metal accumulations in lichen, two of the investigated sites were classified as highly polluted. The highest concentrations of Cd, Pb, and Zn were found in lichens transplanted in the vicinity of a Zn-Pb smelter. Significant accumulations of Cr and Ni were detected in Hypogymnia transplanted near a chemical industry. Physodic, physodalic, hydroxyphysodic acids, and atranorin were identified and analyzed in extracts obtained from specimen samples. The most detrimental changes were observed in lichen transplanted into the vicinity of a chemical industry producing chromium, phosphor, and sulfur compounds that contained 340-fold higher Cr levels than control thalli. Decreases in the levels of physodic acid, hydroxyphysodic acid, and atranorin were detected, and one additional polar compound (probably product of degradation of lichen acids) appeared in the extract. The content of physodalic acid increased in every thalli sample transplanted, suggesting a possible role of this compound in defense against stress caused by accumulated pollutants. The levels of physodic acid decreased in thalli from both of the most polluted sites compared to those of the controls--but were not changed in thalli transplanted to less polluted sites. Our results illustrate that lichen compounds are sensitive to heavy metal accumulation and could be used as biomarkers in environmental studies.
