Effect of Metal Cations Pb2+, Cu2+, Zn2+, Mg2+ and Fe2+ on Some Physiological Parameters of Lichen Parmotrema dilatatum

Abstract

Lichens are used in air quality biomonitoring. They accumulate the air pollutants including trace metal elements. However, the bioaccumulation of trace metal elements in the thalli of lichens has considerable consequences on their physiology. Indeed, trace metal elements have the ability to induce the production of reactive oxygen species (ROS) which react with several vital biomolecules of the species. This causes serious morphological, metabolic and physiological abnormalities depending on the lichen species. In this study, fresh thalli of Parmotrema dilatatum lichen are in contact with a metal salt solution at different concentrations. The content of chlorophyll a, phospholipids, total polyphenols and total proteins were determined before and after treatment with the different metal salt solutions. The chlorophyll a content decreases significantly in the presence of copper and zinc ions while carotenoids degrade significantly in the presence of zinc. Significant degradation of the species' membrane in the presence of Iron and Copper was also observed. These observations suggest the possibility of electrolyte leakage in case of a biomonitoring situation on fixed sites, which are potentially rich in copper and iron. Also lichen Parmotrema dilatatum present a great capacity of metal cations detoxification by using proteins in particular in case of lead and copper. A non-protein detoxification response was observed with the carotenoids in presence of zinc.