LEAD (PB) UPTAKE AND ITS EFFECTS ON MEMBRANE INTEGRITY AND CHLOROPHYLL FLUORESCENCE IN DIFFERENT LICHEN SPECIES

We report an investigation into the effect on membrane integrity and c hlorophyll fluorescence of extra-and intracellular lead (Pb) concentra tions in lichens possessing different photosynthetic symbionts and tha llus growth forms (Lobaria pulmonaria, Ramalina farinacea, Parmelia ca perata and Peltigera canina). Pb uptake, particularly in cyanobiont li chens, caused a decrease in photosystem II (PSII) photochemical reacti ons, measured as a change in the ratio variable fluorescence:maximal f luorescence (F-v/F-m). In the lichens L. pulmonaria and Parmelia caper ata, 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 ce lls of the lichens. We found identical maximal extracellular Pb concen trations among the different lichens; however, the maximal intracellul ar Pb concentrations were not identical in range. Lichen PSII photoche mical reactions were more sensitive to Pb than cell membrane damage si nce, 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 depe ndent only on the nature of the photobiont. We confirmed that Pb displ aced extracellular exchangeable Ca and Mg. (C) 1997 Elsevier Science B .V.