THE LOCALIZATION OF LEAD IN THE LICHEN RAMALINA-DURIAEI (DENOT) BAGL

In an attempt to ascertain whether the lichen Ramalina duriaei could be employed to biomonitor atmospheric lead pollution, specimens of this lichen were exposed to Pb (NO3)2 solutions and a buffered solution (tartaric acid/sodium bitartrate, pH 2.8) of sodium rhodizonate (C6O6Na2) was used to locate lead in their thalli. The procedure entailed exposure of the lichen to 0, 5, 50 and 100 ppm Pb for 5 min and 1 h and the subsequent determination of the lead contents from photographs of the thalli. Distribution of lead in different parts of the thallus was assessed after exposure of the lichens to 2 ppm Pb (9 h or three d), 50 ppm (45 min) or 200 ppm (4d). Cross sections of vegetative parts of the thallus and of the apothecia revealed that lead penetrated into the cortical cells of the thallus but not into the algal cells of the phycobiont nor the ascospores or medullary cells. The observed massive penetration of lead into cortical cells supports the notion that Ramalina duriaei is sensitive to atmospheric lead pollution. 1990 Deutsche Botanische Gesellschaft/German Botanical Society