The presence of usnic acid does not protect the lichen Cladina arbuscula subsp. mitis against the long-term copper excess

Abstract

a b s t r a c tCladina arbuscula subsp. mitis grows on the surfaces of historical Cu-mine spoil heaps rich in Cu, as well as on the surfaces of substrata that are not metal contaminated. This lichen contains the extracellular secondary metabolite, usnic acid (UA), which was previously found to form complexes with metal cations, including Cu. As UA can be experimentally removed from dry lichen thalli using acetone and without the loss of lichen viability, this study attempted to evaluate its role in long-term (8 wks) Cu tolerance in C. arbuscula subsp. mitis. Removal of UA by acetone did not affect the viability of the lichen, however it caused lower intracellular Cu accumulation after 8 wks of experiment at the highest 500 μM Cu doses tested. Thus far, we did not observe de novo synthesis of UA in the UA− variant of the study during the 8 wks of the experiment. Based on the measurements of the selected metabolic processes in the lichen (chlorophyll a fluorescence, chlorophyll a integrity, TBARS production, content of ergosterol and content of soluble proteins) it would seem that presence of UA in C. arbuscula subsp. mitis did not protect this lichen against Cu excess.

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

“…mitis and P. rufescens (Bačkor et al 2009(Bačkor et al , 2011. A time-and dose-dependent decrease in the content of soluble proteins was demonstrated in an experiment with Cu excess lasting 8 weeks (Bačkorová et al 2015). In our experiment, we obtained similar results: the content of soluble proteins decreased during 2-8 weeks of exposure to conditions of excessive Cu.…”

“…High content of Cu can cause a decrease of chlorophyll a in lichens (Puckett 1976;Bačkor et al 2003), which leads to disturbed integrity of the photosynthetic apparatus. Bačkorová et al (2015) tested the effect of Cu excess in a long-term experiment and, as in the present study, observed a decrease of chlorophyll a integrity and other photosynthetic parameters during the 8 weeks of their experiment. Values between 1.2 and 1.4 are typical for healthy lichen thalli, and a gradual decrease was observed in our experiment after exposure to the higher tested Cu dose in both thallus variants over the course of 8 weeks.…”

“…A decrease of ergosterol was also confirmed in a longterm experiment with Cu excess on C. arbuscula subsp. mitis (Bačkorová et al 2015). We observed continuous decreases in the level of ergosterol as a function of the time of exposure to excessive Cu doses.…”

“…Photosynthetic efficiency is defined as the potential quantum yield of electron transfer through photosystem II (Bačkorová et al 2015). This parameter is expressed as the F V /F M ratio, which in healthy lichen thalli is in the range of 0.6-0.7 (Kappen et al 1998).…”

The Effects of Edaphic and Climatic Factors on Secondary Lichen Chemistry: A Case Study Using Saxicolous Lichens

“…Moreover, lichen communities growing in metal-rich ultramafic alpine areas may exhibit differences in terms of secondary metabolite production compared to those of adjacent non-ultramafic areas (e.g., lower frequency of species with depsidones) [45]. However, in other cases, lichen acids play no role in protection of thalli against airborne heavy metal pollutants [46] or against metals taken from a substrate [47]. Factors other than secondary metabolites may also affect metal accumulation as shown by two closely-related species containing the same lichen acid and growing in the same habitat but having dramatically different heavy metal concentrations [32].…”