Photosynthetic processes in two algal species from Antarcticlakes in response to stress factors

Klebsormidium sp. and Zygnema sp. are typical algal species forming microbiological mats in Antarctic lakes, streams and seepages of the James Ross Island (Antarctica). For physiological study focused on their photosynthesis, two strains collected at the island (Klebsormidium sp. SNOKHOUSOVA et ELSTER 2008/8, and Zygnema sp. SNOKHOUSOVA et ELSTER 2009/8) were obtained from Culture Collection of Autotrophic Organisms, Institute of Botany, Třeboň. Cultivation was carried out in liquid 3N BBM solution under constant temperature and a 12/12 h light/dark period in a FS130 phytoscope (PSI). In this study, we present the results of experiments focused on interspecific differences in photosynthesis as dependent on light, temperature, repetitive photoinhibition and osmotic stress. Light-response curves of photosynthesis: Simultaneous measurements of oxygen evolution rate (OER) and effective quantum yield of PSII (PSII yield) by an inbuilt Theta 90 (ldv) oxygen electrode and a FL-400 (PSI), fluorometer, respectively, were done at fixed above-zero temperatures. In both species, OER and yield PSII were well related throughout a range of light (0-500 micromols m-2 s-1 of photosynthetically active radiation (PAR). Photoinhibitory treatment: Using a FMT 400 photobioreactor (PSI), repetitive photoinhibition and dark recovery was studies in Klebsormidium sp. by simultaneous measurements of OER and PSII yield. The data revealed large resistance of the two species against photoinhibition, however, the courses of respiratory OER and potential PSII yield measured at dark changed with increasing number of photoinhibitory treatment. Osmotic stress: The effects of salt (NaCl) treatment on excitation energy transfer from light harvesting complexes to photosystem II (PSII) in two Antarctic algae: Klebsormidium sp. and Zygnema sp. were investigated using chlorophyll 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.