Effects of Copper on Wild and Tolerant Strains of the Lichen Photobiont Trebouxia erici (Chlorophyta) and Possible Tolerance Mechanisms

Abstract

The influence of copper was assessed on wild and tolerant strains of the lichen photobiont Trebouxia erici and shown to have multiple toxic effects. Addition of 4 mM copper chloride into Trebouxia media reduced growth rates of the wild type to less than 1% of control levels. It also injured cell membranes, inhibited dehydrogenase activity, altered pigment composition, and reduced activity of photosystem II. Membrane damage was assessed through measuring electrical conductivity and potassium content, dehydrogenase activity by degree of conversion of 2,3,5-triphenyl tetrazolium chloride to red triphenylformazan, and functioning of PS II by chlorophyll a fluorescence. In respect to most parameters the tolerant strain was usually less affected by copper than the wild strain and, in some cases, not at all. We demonstrated by inductively coupled plasma atomic emission spectrometry and energy-dispersive X-ray microanalysis that enriched copper in the medium resulted in increased uptake by both wild and tolerant photobiont cells, but extracellular concentrations were significantly higher in the tolerant strain. This suggested that, at least in vitro, extracellular deposition was a mechanism of copper tolerance.

Cadmium distribution and effects on ultrastructureand chlorophyll status in photobionts and mycobionts of Xanthoria parietina

“…Treated and control thalli of X. parietina showed similar PhQ values among each other (Fig. 4), being in turn comparable to those measured in the epiphytic fruticose lichen Ramalina lacera growing in non-polluted or slightly HM-polluted areas (Garty et al, 2001) and in the aposymbiotically grown photobiont alga Trebouxia erici, exposed to low Cu concentrations (Bačkor et al, 2003). Thus, mechanisms other than substitution of Mg have to be envisaged to explain the considerable loss of Chl noticed in X. parietina thalli exposed to Cd.…”

“…Studies on HM toxicity towards lichens mainly concern copper (Cu), zinc (Zn), lead (Pb), manganese (Mn), and chromium (Cr) (Bačkor et al, 2003;Branquinho, 2001;Chettri et al, 1998;Garty, 2000a,b;Hauck et al, 2003;Sanità di Toppi et al, 2004). By contrast, a substantial lack of information as regards the impact of Cd on lichen structure and functions has to be emphasized.…”

Dehydration rate and time of desiccation affect recovery of the lichenic algae Trebouxia erici: alternative and classical protective mechanisms

“…Superoxide dismutase (SOD) activity was measured spectrophotometrically as described by Beyer and Fridovich (1987). In this assay, 1 U of SOD is defined as the amount required to inhibit the photoreduction of nitroblue tetrazolium by 10% (Bačkor et al 2003). Viability of algal cells was assessed via the oxidation of triphenyl-tetrazolium chloride according to Bačkor and Fahselt (2005).…”

Response to cobalt toxicity in lichen Pseudevernia furfuracea; uptake, photosynthetic quantum yield, membrane integrity and deoxyribonucleic acid fragmentation

“…Electrical conductivity is considered to indicate injury to cell membranes and has been previously used for the assessment of electrolyte leakage in lichen. [17,18] [21][22][23] Photosynthetic efficiency data in our study has shown that thallus of P. furfuracea can tolerate concentrations of H 2 O 2 at an approximate range of 6-52 µM (see Table 1). de Pinto et al [24] showed that only simultaneous increase of H 2 O 2 in tobacco cells induced cell death that had typical cytological and biochemical features of DNA fragmentation.…”