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

Abstract

The ultrastructure of soredia of the foliose epiphytic lichen Hypogymnia physodes cultivated on agar plates for 11 days with three different concentrations of MnCl 2 (7 μM [control], 500 μM, 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 μM, 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 μM and 7 mM. At 500 μM, 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 forming 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.