Resistance of Antarctic lichens and freshwater algae from James Ross Island to radiation, temperature, dehydration, UV-B and salt stress assessed by photosynthetic parameters
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|Lichen species Usnea antarctica, Usnea aurantiaco-atra, Xanthoria elegans, and algae Klebsormidium sp. and Zygnema sp. were investigated in our study by various biochemical and biophysical approaches in order to evaluate their resistance to particular environmental factors. The methods comprised oxymetric, fluorometric (fast (OJIP), and slow Chl fluorescence curves with quenching analysis), spectrophotometric methods (UV screens, photosynthetic pigments, glutathione). In lichens, short-term photoinhibition using (i) high, (ii) medium light doses were used. Involvement of photoprotective mechanisms was investigated. Chl fluorescence parameters, such FV/FM, yield of PSII, fast transient (OJIP) revealed that Usnea antarctica was less susceptible to photoinhibition than U. aurantiaco-atra. More pronounced reduction in Chla,b contents was found in U. aurantiaco-atra than U. antarctica. Total GSH showed an initial increase (first 30-40 min) followed by a decrease (60 min) and an increase during dark recovery. Full GSH recovery was not finished in U. aurantiaco-atra even after 5 h indicating lower capacity of photoprotective mechanisms. OJIPs decreased in both species, however, the recovery of their shape was faster and more apparent in U. antarctica than in U. aurantiaco-atra. For two algal species, simultaneous measurements of oxygen evolution rate (OER) and effective quantum (PSII yield) were done at different temperatures to gain photosynthetic light-response curves. In both species, OER and yield PSII were well related throughout a range of light (0-500 micromols m-2 s-1 of PAR. In a photobioreactor (PSI), repetitive photoinhibition (high light doses) was applied Klebsormidium sp. culture by simultaneous measurements of OER and PSII yield. The data revealed large resistance against photoinhibition, however, the courses of respiratory OER and potential PSII yield measured at dark changed with increasing number of photoinhibitory treatments. The effects of NaCl treatment on excitation energy transfer from LHCs to PSIIs in two Antarctic algae: Klebsormidium sp. and Zygnema sp. were investigated using Chl fluorescence transients (OJIPs). Short-term salt stress led to significant changes in the shape of OJIPs indicating altered functioning of PSII. With time of exposition to NaCl treatment, the fluorescence yield at the phases J, I and P declined considerably in both species. Acknowledgements: The authors thank CzechPolar infrastructure of laboratory facilities.