Ultrastructural changes in soredia of the epiphytic lichen Hypogymnia physodes cultivated with manganese

The ultrastructure of soredia of the foliose epiphytic lichen Hypogymnia physodes cultivated on agar plates for I I days with three different concentrations of MnCl2 (7 muM [control], 500 muM, 7 mM) was compared by means of transmission electron microscopy. Photobiont cells (Trebouxia jamesii) of Mn-exposed soredia had swollen and contracted thylakoids. The chloroplasts were reduced in size, and numerous lysosome-like vesicles occurred in cells with degenerated chloroplast. At 500 muM, autospores of T jamesii were more severely damaged than vegetative cells. At 7 mM, autospore formation was strongly reduced. Concentric bodies and mesosome-like structures were nearly completely absent from mycobiont cells of Mn-treated soredia at both 500 muM and 7 mM. At 500 muM, the photobiont of not grown soredia was more severely damaged compared to grown soredia (defined as soredia where division of algal cells had taken place). At 7 mM, ultrastructural damage was observed in both grown and not grown soredia. This suggests that even soredia that survived the first days of cultivation are probably not capable of fort-ning thalli on Mn-rich substrates. The ultrastructural changes in Mn-exposed soredia support the hypothesis that high Mn concentrations in bark or stemflow are a limiting factor for the abundance of H. physodes and other epiphytic lichens in coniferous forests of Europe and North America. (C) 2004 Elsevier B.V. All rights reserved.