1. Trichomes are growing long but have no sheaths, accumulate cyanophycin and liquid oil-like inclusions Filaments are long and enclosed into thin sheaths, with or without inclusions Short fragments of trichomes (hormogonia) are released into the environment Hormogonia actively escape from sheaths through polar ends, as well as by cracking and dissolving sheaths live necridic cell Long filaments, enclosed into thick multilayered sheaths Daria Tashyreva 1 and Josef Elster 1,2 1 University of South Bohemia, Faculty of Science, České Budějovice, Czech Republic & 2 Institute of Botany, Academy of Science of the Czech Republic, Třeboň, Czech Republic, E-mail: tashyreva@butbn.cas.cz * Trichomes are fragmented into hormogonia within thick sheaths No special resting cells sheaths are sealed Win ter Spr ing Autu mn Summ er Seasonal Development of Cyanobacterial Populations (Phormidium and /or Microcoleus) in the High Arctic, Svalbard Dead cells between hormogonia decay empty sheaths form pale-pink biomass spring melt Salinity increases into 3 times triggers production of sheaths? Dehydration and mechanical damage by ice crystals Adaptation –thick sealed sheaths Cells are still metabolically active Increase of temperature triggers release of hormogonia? sheathless trichomes are non-viable Hormogonia Short fragments of cyanobacterial filaments Due to the tight cell-to-cell connections, breaks of filaments occur with the help of necridic (dead) cells Serve for dissemination and asexual reproduction Light, nutrients, chemical stimuli and temperature may initiate differentiation of hormogonia Hormogonia Short fragments of cyanobacterial filaments Due to the tight cell-to-cell connections, breaks of filaments occur with the help of necridic (dead) cells Serve for dissemination and asexual reproduction Light, nutrients, chemical stimuli and temperature may initiate differentiation of hormogonia Metabolic activity during the seasonal cycle Cell respiration was detected by staining with fluorescent dye (CTC) Respiration leads to reduction of dye, which accumulates in cells as red fluorescent crystals Non-condensed nucleoids (stained with DAPI) also indicate metabolic activity Cells show constant metabolic activity during the whole season and start respiration immediately after melting Metabolic activity during the seasonal cycle Cell respiration was detected by staining with fluorescent dye (CTC) Respiration leads to reduction of dye, which accumulates in cells as red fluorescent crystals Non-condensed nucleoids (stained with DAPI) also indicate metabolic activity Cells show constant metabolic activity during the whole season and start respiration immediately after melting Viability of cells Determined according to plasma membrane integrity Dead and injured cells have disrupted membranes, which are permeable for SYTOX Green dye During the whole season there were very few dead cells Samples contained 10 to 20% of dead cells after melting Viability of cells Determined according to plasma membrane integrity Dead and injured cells have disrupted membranes, which are permeable for SYTOX Green dye During the whole season there were very few dead cells Samples contained 10 to 20% of dead cells after melting 40 min after melting CTC staining SYTOX Green staining We consider that hormogonia are normally produced during snowmelt, however, in that winter temperature was above zero for 2 weeks in January Phormidium and/or Microcoleus are among the most common terrestrial cyanobacteria in the Polar Regions. In these harsh environments, cyanobacteria are stressed with desiccation, freezing and severe fluctuations of temperature and light intensity. The seasonal development of their populations, however, have never been investigated. In this study we aimed to answer the following questions based on observation of 2 populations: How long are the populations active during the year/vegetative season? Do they produce any specialized resting cells (spores) to survive winter and/or seasonal desiccation? How much do morphology of cells and structure of populations change during the year? How many cells survive winter, and what are the possible adaptations for winter stresses? In which physiological state are cells during vegetative season? Phormidium and/or Microcoleus are among the most common terrestrial cyanobacteria in the Polar Regions. In these harsh environments, cyanobacteria are stressed with desiccation, freezing and severe fluctuations of temperature and light intensity. The seasonal development of their populations, however, have never been investigated. In this study we aimed to answer the following questions based on observation of 2 populations: How long are the populations active during the year/vegetative season? Do they produce any specialized resting cells (spores) to survive winter and/or seasonal desiccation? How much do morphology of cells and structure of populations change during the year? How many cells survive winter, and what are the possible adaptations for winter stresses? In which physiological state are cells during vegetative season? trichomes form red biomass Conclusion Our observations suggest that terrestrial species of Phormidium belong to perennial organisms. The populations were constantly metabolically active during the whole vegetative season, and quickly resumed respiration after melting. Populations are well adapted to seasonal fluctuations, and have dormant periods only when they are frozen during winter. Unlike akinete-forming cyanobacteria, they do not produce any morphologically distinct spore-like resting stages at the end of vegetative season for survival of winter period, and cell morphology does not notably change during the vegetative season. Instead, a high proportion of cells from frozen samples remained viable, indicating that vegetative cells acquired resistance to stresses related to freezing. Apparently, polysaccharide sheaths play a key role in protection of cells from damages imposed by ice crystals, since only a small number of cells in filaments without sheaths survived freezing, and freezing-associated dehydration is compensated with biochemical mechanisms. Conclusion Our observations suggest that terrestrial species of Phormidium belong to perennial organisms. The populations were constantly metabolically active during the whole vegetative season, and quickly resumed respiration after melting. Populations are well adapted to seasonal fluctuations, and have dormant periods only when they are frozen during winter. Unlike akinete-forming cyanobacteria, they do not produce any morphologically distinct spore-like resting stages at the end of vegetative season for survival of winter period, and cell morphology does not notably change during the vegetative season. Instead, a high proportion of cells from frozen samples remained viable, indicating that vegetative cells acquired resistance to stresses related to freezing. Apparently, polysaccharide sheaths play a key role in protection of cells from damages imposed by ice crystals, since only a small number of cells in filaments without sheaths survived freezing, and freezing-associated dehydration is compensated with biochemical mechanisms. spring, red soft biomass – sheathless trichomes, pale-pink is empty sheaths continuous crust with red and pink parts in autumn The study was realised within the project Creating of Working Team and Pedagogical Conditions for Teaching and Education in the Field of Polar Ecology and Life in Extreme Environment, reg. No. CZ.1.07/2.2.00/28.0190 co-financed by the European Social Fund and the state budget of the Czech Republic.