Photoprotection and high-light acclimation in semi-arid grassland lichens – a cooperation between algal and fungal partners

Antarctic lichens exhibit diverse photobiont distributions and a complex regulation of non-photochemical quenching

The structure, function, and molecular mechanisms of lichen survival in harsh habitats like Antarctica and Alpine localities, where environmental extremes change frequently, are highly interesting yet largely underexplored. We used high resolution microscopy, Raman spectroscopy, and chlorophyll a fluorescence to investigate the basic structure and function, i.e., intrathalline distribution and allocation of photobionts, as well as the heat dissipation process in three Antarctic lichens: Dermatocarpon polyphyllizum (DP), Umbilicaria antarctica (UA), and Leptogium puberulum (LP). Microscopic images of their transverse slices revealed visual insights into the heterogeneous distribution of photobionts within their structurally distinct thalli. Raman spectra showed shifts in the carotenoid Raman ν1(CC) band between lichens with algal (DP and UA) and cyanobacterial (LP) photobionts, and interestingly, they revealed biosynthesis of scytonemin, a UV-screening pigment, in cyanolichen LP. We found that increasing actinic irradiance has a nearly equal effect on the shape of chlorophyll fluorescence transients also during dark relaxation in lichens with algal photobionts, but it differed greatly for cyanolichen LP. The dark relaxation kinetics of non-photochemical quenching (NPQ) in experimental lichens differed significantly between lichens with algal photobionts DP and UA; however, this parameter could not be calculated in cyanolichen LP. The components of NPQ revealed that rapidly relaxing energy dependent quenching, ΦqE, is active and protects the thallus of DP predominantly; however, in UA state transition quenching, ΦqT, predominates. The diversity in NPQ across the three examined lichens revealed intriguing aspects of heat dissipation in their photobionts as a mechanism for survival under Antarctica conditions.

Does the Symbiotic Relationship Between Hydra Viridissima and Photoautotrophic Alga Provide an Evolutionary Advantage in Protecting DNA against Damage by the Cytotoxic or Genotoxic Mode of Action of Environmental Stressors?

The aim of this paper was to evaluate whether symbiotic cooperation between green hydra (Hydra viridissima) and photoautotrophic alga gives higher resistance of the preservation of DNA integrity compared to brown hydra (Hydra oligactis). Norflurazon concentrations were 0.061 or 0.61 mg/L and UV-B light 254 nm, 0.023mWcm- 2 applied separately or simultaneously. By alkaline comet assay primary DNA damage was assessed and cytotoxicity by fluorescent staining. Norflurazon at 0.61 mg L- 1 significantly increased DNA damage in brown hydras compared to the control (6.17 ± 0.6 μm, 5.2 ± 1.7% vs. 2.9 ± 0.2 μm, 1.2 ± 0.2%). Cytotoxicity was significantly elevated, being higher in brown hydras (25.7 ± 3.5% vs. 8.2 ± 0.2%). UV-B irradiation induced significant DNA damage in brown hydras (13.5 ± 1.0 μm, 4.1 ± 1.0%). Simultaneous exposure to UV-B and norflurazon led to a synergistic DNA damaging. The frequency of cytotoxicity and hedgehog nucleoids was more pronounced in brown (78.3 ± 9.4%; 56.4 ± 6.0%) than in green hydras (34.7 ± 2.5%; 24.2 ± 0.6%). Evolutionary established symbiotic cooperation proved to provide resistance against cyto/genotoxicity.

Cryptogamic Biomass in Pannonic Acidic Sand Steppes Subject to Changing Land-Use

Cryptogams, often neglected in vegetation dynamics studies, compose a large part of biomass and contribute to the biodiversity of sandy grasslands. Since the work of Verseghy (1970s), their productivity has not been analyzed in Hungary. We studied the lichen and bryophyte dynamics (hereinafter called cryptogams) at two Eastern Hungarian dry sandy grassland sites. The sites of Corynephorus canescens and of Festuca vaginata dominance, respectively, belonging to the community Festuco vaginatae-Corynephoretum have been monitored. We aimed at (1) quantifying the diversity and biomass of the cryptogamic communities; (2) exploring the cryptogamic response to management changes; and (3) studying the effect of experimental management (fencing) on the cryptogamic assemblages. The sites have been compared in 2013 and 2018, respectively. Forty microplots per site per management have been analyzed in both years. Samples of lichens and bryophytes were hand-sorted, dried and then measured. Fencing has led to increased biomass of cryptogams within a few years. Lichens in general benefited comparatively more from exclosure than bryophytes. The increase in lichen biomass (especially that of Cladonia rangiformis) is clearly due to the over 10-year absence of grazing. The only lichen favored by moderate grazing is the legally protected C. magyarica. Short spells of low-intensity grazing can promote the species richness of cryptogams in the community.

The long-term effect of removing the UV-protectant usnic acid from the thalli of the lichen Cladonia foliacea

Terricolous lichens are abundant in semi-arid areas, where they are exposed to high irradiation. Photoprotection is essential for the algae as the photobiont provides the primer carbon source for both symbionts. The UV-protectant lichen metabolites and different quenching procedures of the alga ensure adequate photoprotection. Since the long-term effect of diminishing UV-protectant lichen metabolites is unknown, a major part of lichen secondary metabolites was removed from Cladonia foliacea thalli by acetone rinsing, and the lichens were then maintained under field conditions to investigate the effect on both symbionts for 3 years. Our aim was to determine if the decreased level of UV-protectant metabolites caused an elevated photoprotection in the algae and to reveal the dynamics of production of the metabolites. Photosynthetic activity and light protection were checked by chlorophyll a fluorescence kinetics measurements every 6 months. The concentrations of fumarprotocetraric and usnic acids were monitored by chromatographic methods. Our results proved that seasonality had a more pronounced effect than that of acetone treatment on the function of lichens over a long-term scale. Even after 3 years, the acetone-treated thalli contained half as much usnic acid as the control thalli, and the level of photoprotection remained unchanged in the algae. However, the amount of available humidity was a more critical limiting environmental factor than the amount of incoming irradiation affecting usnic acid production. The lichenicolous fungus Didymocyrtis cladoniicola became relatively more abundant in the acetone-treated samples than in the control samples, indicating a slight change caused by the treatment.