BIOLOGIA PLANTARUM 53 (2): 214-222, 2009 214 REVIEW Interactions of lichens with heavy metals M. BAČKOR* 1 and S. LOPPI** Institute of Biology and Ecology, Department of Botany, Šafárik University, Mánesova 23, SK-04167, Košice, Slovak Republic* Department of Environmental Science, G. Sarfatti University of Siena, Via P.A. Mattioli 4, I-53100, Siena, Italy** Abstract Recent developments in knowledge about the interactions between lichens and heavy metals at different levels, from populations to cells and from ecology to molecular biology are reviewed. Sources of heavy metals, mechanisms of heavy metal accumulation and detoxification by lichens are discussed. Special emphasis is placed on ultrastructural changes as well as physiological parameters such as membrane integrity, pigment composition, chlorophyll a fluorescence, photosynthesis, respiration, contents of ATP, amino acids, ergosterol, ethylene, non-protein thiols, activity of antioxidant enzymes and expression of stress proteins. Additional key words: biomonitoring, cadmium, copper, detoxification, exclusion, lead, manganese, mercury, zinc. Introduction Lichens are the dominant organisms of ca. 8 % terrestrial ecosystems (Larson 1987) and are typically found in environments subject to extremes of temperature, desiccation and nutrient status. As lichens have no root apparatus, their mineral nutrition depends mainly on atmospheric inputs and owing to the lack of protective cuticle and stomata, thalli can accumulate mineral elements, including heavy metals, at levels exceeding their metabolic requirements. Moreover, lichens are long- living, ectohydric organisms with a limited control on water and gas exchange. These characteristics make them very good bioindicators of air pollution (Garty 2001). Lichens are widely used through the world for biomonitoring atmospheric heavy metals and progress in this field has been already reviewed (e.g. Garty 2001, Bargagli and Mikhailova 2002). However, in the last few years research has chiefly focused on the physiological and biochemical effects of heavy metal accumulation in lichens. This paper aims at reviewing recent develop- ments in the study of interactions of lichens with heavy metals at different levels, from populations to cells and from ecology to molecular biology. Lichens and excess heavy metals The effectiveness of lichens in intercepting particles not only from the atmosphere but also from substrate has been documented in many studies (Loppi et al. 1999, Pirintsos et al. 2006). These particles may be deposited onto the lichen surface or trapped in the intercellular spaces of the medulla (Garty et al. 1979) and can remain unaltered for a long time. Lichens thus accumulate and retain many heavy metals in quantities that vastly exceed their physiological requirements and tolerate these high concentrations by sequestrating metals extracellularly as ⎯⎯⎯⎯ Received 10 June 2008, accepted 2 December 2008. Abbreviations: APX - ascorbate peroxidase; CAT - catalase; d.m. - dry mass; GR - glutathione reductase; GSH - reduced glutathione; GSSG - oxidized glutathione; HPCD - hydroperoxi-conjugated dienes; HSP - heat shock protein; MDA - malodialdehyde; PCs - phytochelatins; SOD - superoxide dismutase; TPF -triphenyl formazan; TTC - triphenyl tetrazolium chloride. Acknowledgements: This work was financially supported by the Science and Technology Assistance Agency (Slovak Republic) under contract No. APVT-20-003004 and by Slovak Grant Agency (VEGA 1/4337/07) to MB. The authors are indebted to Prof. Dianne Fahselt (UWO, Canada) for useful comments and linguistic assistance. 1 Author for correspondence; fax: (+421) 556222124, e-mail: martin.backor@upjs.sk