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 and heavy metals. Supplied Cu replaced the naturally acquired extracellular Mg and Ca and induced alterations in the passage of K across the cell membrane. For Usnea spp. intracellular uptake saturated at low supplied Cu concentrations (0.0157 mM) and was toxic, as indicated by chlorophyll fluorescence measurements. In Ramalina fastigiata intracellular Cu concentrations above ca. 4.0 mu mol g(-1) were linked to a decline in chlorophyll fluorescence. The fluorescence parameter F-v/F-m was shown to be useful in determining the sensitivity of the lichens to Cu uptake. Usnea spp. were the lichens most sensitive to Cu uptake, since 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 species to Cu uptake. (C) 1997 Elsevier Science B.V.