Physiological responses of Xanthoria parietina to longterm copper excess: Role of the extracellular secondary metabolite parietin

Ivana Biľová,Michal Goga,Martin Backor

doi:10.2298/botserb1902133b

Ivana Biľová, Michal Goga + Show 1 more

Open Access

https://doi.org/10.2298/botserb1902133b

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Abstract

Xanthoria parietina is a common lichen that is widespread around the world. Tolerance of heavy metal pollution in this lichen is well known. Xanthoria parietina contains the secondary metabolite parietin, which protects the photobiont from high UV- radiation. Secondary metabolites of lichens have been found to form complexes with metal cations. In a long-term experiment (lasting 8 weeks), we tested the resistance of X. parietina with and without the secondary metabolite parietin against two concentrations of Cu (50 ?M and 500 ?M). Removal of parietin did not affect the measured physiological parameters. However, it caused higher accumulation of intracellular Cu. De novo synthesis of parietin in the lichen thallus after removal of the metabolite was not observed. Physiological parameters (chlorophyll a fluorescence, chlorophyll a integrity, content of soluble proteins, ergosterol levels, TBARS production) were affected by the higher dose of Cu during the long-term experiment. It seems that the secondary metabolite parietin does not protect the lichen against Cu excess.

Highlights

Lichens represent a typical example of mutualistic symbiosis, where symbionts need each other in order to benefit
While total Cu content was comparable in both variants of the experiment, after 8 weeks of prolonged exposure we observed increased accumulation of intracellular Cu in the P+ variant of the experiment when compared to the P- variant (Fig. 2AD)
We studied physiological adaptations of both P+ and Pthalli of X. parietina to excessive (50 μM and 500 μM) doses of Cu tested over 8 weeks of experimentation

Summary

Introduction

Lichens represent a typical example of mutualistic symbiosis, where symbionts need each other in order to benefit. It has been known for almost 150 years that lichens consist of a photobiont (green algae and/or cyanobacteria) and a mycobiont (lichenised fungi). Lichens are dominant vegetation of approximately 8% of terrestrial ecosystems, including habitats with extreme environmental conditions of temperature, desiccation or nutrient levels (Larson 1987; Ahmadjian 1993). Lichens are frequently exposed to excesses of metals in their natural habitats. Zinc, cadmium, lead, chromium or mercury are major environmental pollutants that accumulate in areas under anthropogenic pressure of industries and agriculture.

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