THE CELLULAR LOCATION OF CU IN LICHENS AND ITS EFFECTS ON MEMBRANE INTEGRITY AND CHLOROPHYLL FLUORESCENCE

The data in the present study supported the hypothesis that Na-2-EDTA at pH 4.5 is an efficient chelating agent for extracellular Cu without causing cell membrane damage, and that it can be used in a sequential elution procedure to determine the cellular location of Cu in lichens . The patterns of extracellular uptake vs. time or concentration were anticipated from conventional kinetics studies with other organisms an d heavy metals. Supplied Cu replaced the naturally acquired extracellu lar Mg and Ca and induced alterations in the passage of K across the c ell membrane. For Usnea spp. intracellular uptake saturated at low sup plied Cu concentrations (0.0157 mM) and was toxic, as indicated by chl orophyll fluorescence measurements. In Ramalina fastigiata intracellul ar Cu concentrations above ca. 4.0 mu mol g(-1) were linked to a decli ne in chlorophyll fluorescence. The fluorescence parameter F-v/F-m was shown to be useful in determining the sensitivity of the lichens to C u uptake. Usnea spp. were the lichens most sensitive to Cu uptake, sin ce physiological changes occurred for lower supplied Cu concentrations than for R. fastigiata. With this work we were able to determine and quantify the cellular location of Cu in lichens. We were also able to evaluate through membrane integrity and fluorescence measurements the physiological state and the relative sensitivity of different lichen s pecies to Cu uptake. (C) 1997 Elsevier Science B.V.