Photosynthetic carbon acquisition in the lichen photobionts Coccomyxa and Trebouxia (Chlorophyta)

Processes involved in photosynthetic CO₂ acquisition were characterised for the isolated lichen photobiont Trebouxia erici (Chlorophyta, Trebouxiophyceae) and compared with Coccomyxa (Chlorophyta), a lichen photobiont without a photosynthetic CO₂-concentrating mechanism. Comparisons of ultrastructure and immuno-gold labelling of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) showed that the chloroplast was larger in T. erici and that the majority of Rubisco was located in its centrally located pyrenoid. Coccomyxa had no pyrenoid and Rubisco was evenly distributed in its chloroplast. Both species preferred CO₂ rather than HCO₃^? as an external substrate for photosynthesis, but T. erici was able to use CO₂ concentrations below 10–12 μM more efficiently than Coccomyxa. In T. erici, the lipid-insoluble carbonic anhydrase (CA; EC 4.2.1.1) inhibitor acetazolamide (AZA) inhibited photosynthesis at CO₂ concentrations below 1 μM, while the lipid-soluble CA inhibitor ethoxyzolamide (EZA) inhibited CO₂-dependent O₂ evolution over the whole CO₂ range. EZA inhibited photosynthesis also in Coccomyxa, but to a much lesser extent below 10–12 μM CO₂. The internal CA activity of Trebouxia, per unit chlorophyll (Chl), was ca 10% of that of Coccomyxa. Internal CA activity was also detected in homogenates from T. erici and two Trebouxia-lichens (Lasallia hispanica and Cladina rangiferina). In all three, the predominating CA had α-type characteristics and was significantly inhibited by low concentrations of AZA, having an I₅₀ below 10–20 nM. In Coccomyxa a β-type CA predominates, which is much less sensitive to AZA. Thus, the two photobionts differed in three major characteristics with respect to CO₂ acquisition, the subcellular location of Rubisco, the relative requirement of CA and the biochemical characteristics of their predominating internal CA. These differences may be linked to the ability of Trebouxia to accumulate dissolved inorganic carbon internally, enhancing their CO₂ use efficiency at and below air-equilibrium concentrations (10–12 μM CO₂) in comparison with Coccomyxa.     

Structural elucidation of 13-acetoxylichesterinic and 13-acetoxyprotolichesterinic acids,two aliphatic lichen metabolites from Neuropogon trachycarpus

From the lichen Neuropogon trachycarpus, six aliphatic acids related to lichesterinic acid have been isolated: neuropogolic, murolic, isomuronic an     

Isolation by distance in the crustose lichens Candelariella vitellina and Placynthium nigrum colonising gravestones in northeast Scotland

The majority of estimates of isolation by distance are produced byindirect molecular methods rather than direct observation of dispersal events orcolonisation rates. This is in part due to technical difficulties in recordingrare dispersal events in the field, and may be limiting the testing ofmetapopulation models. The fact that tombstones are dated on erection was usedto perform direct measurements of rates of colonisation for two contrasting speciesof crustose lichen, Candelariella vitellina andPlacynthium nigrum, which occur commonly on sandstone andgranite headstones, respectively. The effects of isolation by distancewere observed in the colonisation of sandstone by C. vitellina within the first 50 years of the erection of headstones in thesmallest of three burial grounds investigated in northeast Scotland. When therate of colonisation was estimated over different periods of time the effect ofisolation by distance was seen to decline as the stones aged. There was noapparent effect of isolation by distance on the rate of colonisation of graniteheadstones by P. nigrum at any of the three study sites atany period of colonisation. This study suggests that effects of isolation by distance are likely to behighly case specific, varying between species, between sites and over time. Thisimplies that great care should be taken when producing parameter estimates formetapopulation models.     

Climate warming causes photobiont degradation and carbon starvation in a boreal climate sentinel lichen

Premise

The long-term potential for acclimation by lichens to changing climates is poorly known, despite their prominent roles in forested ecosystems. Although often considered “extremophiles,” lichens may not readily acclimate to novel climates well beyond historical norms. In a previous study (Smith et al., 2018), Evernia mesomorpha transplants in a whole-ecosystem climate change experiment showed drastic mass loss after 1 yr of warming and drying; however, the causes of this mass loss were not addressed.

Methods

We examined the causes of this warming-induced mass loss by measuring physiological, functional, and reproductive attributes of lichen transplants.

Results

Severe loss of mass and physiological function occurred above +2°C of experimental warming. Loss of algal symbionts (“bleaching”) and turnover in algal community compositions increased with temperature and were the clearest impacts of experimental warming. Enhanced CO₂ had no significant physiological or symbiont composition effects. The functional loss of algal photobionts led to significant loss of mass and specific thallus mass (STM), which in turn reduced water-holding capacity (WHC). Although algal genotypes remained detectable in thalli exposed to higher stress, within-thallus photobiont communities shifted in composition toward greater diversity.

Conclusions

The strong negative impacts of warming and/or lower humidity on Evernia mesomorpha were driven by a loss of photobiont activity. Analogous to the effects of climate change on corals, the balance of symbiont carbon metabolism in lichens is central to their resilience to changing conditions.     

Antifungal activity of lichen compounds against dermatophytes: a review

The growth rate inhibition of dermatophytes by compounds extracted by acetone, ethanol, methanol and water derived from representatives of several lichen genera (e.g. Caloplaca, Everniastrum, Heterodermia, Hypotrachyna, Platismatia and Ramalina) were compared on the basis of a worldwide review of published research. The examined dermatophytes included Epidermophyton floccosum, Microsporum audouinii, M. canis, M. gypseum, M. nanum, Trichophyton longifusus, T. mentagrophytes, T. rubrum, T. tonsurans and T. violaceum. The influence of selected secondary lichen compounds, for example, usnic acid, on the growth rates of these dermatophytes was also reviewed. The measurement of inhibition by lichen compounds was performed by several methods, but mostly those employing disc diffusion, broth dilution and agar dilution. The fungicidal activity of water-extracted compounds from Heterodermia leucomela and Hypotrachyna cirrhata and of methanol-extracted compounds from Evernia divaricata and Ramalina pollinaria, as well as protolichesterinic and 2-hydroxy-4-methoxy-3,6-dimethylbenzoic acids, are distinguished.     

A biological basis for lichenometry?

Aim Develop a biologically defensible conceptual model to explain lichen population dynamics. Methods This work critically examines the biological basis for several of the key assumptions that are used to interpret lichen-size age data. It then presents a biologically defensible conceptual model that can be used to develop computer based simulations of lichen population dynamics or to design alternative approaches to lichenometry. Main conclusions Most lichenometric ages are not verifiably accurate and are generated by methodologies that do not incorporate widely accepted biological principles. Polymodality in thallus-size distributions is not always the product of discrete events. Polymodality could reflect continuous changes in the availability of inhabitable patches (gaps) in a heterogenous mosaic. Improvement in lichenometry could be realized by investigations that seek to quantify the temporal and perhaps density-dependent onset of departures from statistical normality for certain lichen cohorts or species groupings. The study of lichen communities on substrates of known age may, in the short term provide some indication of the relative timing of age-stage changes in lichen demographic structure.     

Genetic and environmental effects of growth and production of secondary compounds in Cladonia cristatella

This is the first study under controlled conditions to evaluate genetic and environmental variables acting on the whole lichen. Four cloned lines of Cladonia cristatella, derived from single spores and re-associated with teh normal algal partner (Trebouxia erici), were grown in a phytotron and chemically analysed. Growth, as measured by cover, was significantly affected by clone and consistently decreased at lower temperatures and at higher light intensities. The two biogenetically distinct pathways leading to the characteristic secondary products were affected differently by factors related to the genetic component (clone), the developmental stage (age) and the environment (temperature and light). Products fo the barbatic acid pathway, leading to depsides, were detected in the youngest lichenized hyphae, and the concentrations did not change significantly with age. products of the didymic acid pathway, leading to dibenzofurans, were incrasingly abundant in progressively older squamules. The four clones showed significantly different capacities for the production of compounds by the two pathways and significantly different responses to the environmental factors studied. The concentrations of compounds from the barbatic acid pathway increased at lower temperatures; those of compounds from the didymic acid pathway either changed little or decreased appreciably according to clone. Of the factors studied, light had the least effect on chemistry. Between-pathway variation in production of secondary products was greater than within-pathway variation.