The adaptive response of lichens to mercury Exposure involves changes in the photosynthetic machinery

Lichens are an excellent model to study the bioaccumulation of heavy metals but limited information isavailable on the molecular mechanisms occurring during bioaccumulation. We investigated the changesof the lichen proteome during exposure to constant concentrations of mercury. We found that most ofchanges involves proteins of the photosynthetic pathway, such as the chloroplastic photosystem Ireaction center subunit II, the oxygen-evolving protein and the chloroplastic ATP synthase b-subunit.This suggests that photosynthesis is a target of the toxic effects of mercury. These findings are alsosupported by changes in the content of photosynthetic pigments (chlorophyll a and b, and b-carotene).Alterations to the photosynthetic machinery also reflect on the structure of thylakoid membranes of algalcells. Response of lichens to mercury also involves stress-related proteins (such as Hsp70) but notcytoskeletal proteins. Results suggest that lichens adapt to mercury exposure by changing the metabolicproduction of energy