Lead (Pb) uptake and its effects on membrane integrity and chlorophyll fluorescence in different lichen species

Abstract

We report an investigation into the effect on membrane integrity and chlorophyll fluorescence of extra- and intracellular lead (Pb) concentrations in lichens possessing different photosynthetic symbionts and thallus growth forms ( Lobaria pulmonaria, Ramalina farinacea, Parmelia caperata and Peltigera canina). Pb uptake, particularly in cyanobiont lichens, caused a decrease in photosystem II (PSII) photochemical reactions, measured as a change in the ratio variable fluorescence:maximal fluorescence ( F v F m ). In the lichens L. pulmonaria and Parmelia caperata, the effect on PSII photochemical reactions could only be observed 48 h after Pb uptake, confirming that prolonged exposure to Pb caused an additional decrease in F v F m . We confirmed that Pb enters the cells of the lichens. We found identical maximal extracellular Pb concentrations among the different lichens; however, the maximal intracellular Pb concentrations were not identical in range. Lichen PSII photochemical reactions were more sensitive to Pb than cell membrane damage since, with increasing Pb concentrations, no clear alterations in lichen membrane permeability, as measured by the loss of intracellular K and Mg, were observed. The effects of Pb in lichens were shown to be dependent only on the nature of the photobiont. We confirmed that Pb displaced extracellular exchangeable Ca and Mg.