Cellular acclimation of snow and ice algae

Snow fields, glacier ice and temporarily open permafrost areas dominate the landscape in polar and high mountain regions. Growth of photosynthetic organisms is restricted to a low species number of adapted higher plants, ferns and mosses. A comparable richer vegetation has been developed in the lichens and algae, including cyanobacteria. Macroscopic visible mass accumulations of certain algae frequently cause the phenomena of Red or Green Snow during summer in alpine and polar regions. Most of these organisms belong to the genera Chlamydomonas and Chloromonas (Chlorophyta, Volvocales), but the exact taxonomic identification is in many cases not finished. Those species which cause Red Snow, like Chlamydomonas nivalis, live in their habitat most of the time as cysts stages. The development of such cysts is characterized by cell wall thickening and a massive production of reserve material, earlier called "haematochrom". We have shown that the coloration is caused mainly by extraplastidal secondary carotenoids, which are esterified with fatty acids. Green Snow is caused by different species, like Ko- liella and some green Chlamydomonas. Our previous studies focused on ecophysiology of Red Snow algae. While those still arise some open questions like molecular species identification and carbohydrate metabolism in the course of this application, we will mainly move to other snow and also ice algae which have no protection by thick cell walls or masses of secondary carotenoids. They must have developed different stress resistance mechanisms. We have recently started promising research with Klebsormidium sp., collected in the maritime Antarctic, and with Mesotaenium berggrenii, growing on bare glacier surfaces in the Alps. Further, other species from Green Snow shall be included. The general objective of the study is to find a deeper understanding of stress adaptation / avoid- ance mechanisms, finally resulting in a more complete view of the cellular stress resistance of snow algae. This includes the following important aspects of: temperature adaptation: what kind of substances cause the cellular cryotolerance (anti freezing components like sugars, polyols) and to what extent is photosynthesis maintained at levels of about 0 or even slightly below? How does the enzymatic apparatus of these algae react under exposure to higher temperatures? light stress adaptation: snow algae have to cope with a wide range of irradiance. Some of them are low light spe- cialists growing deeper in the snow, others have to cope with high irradiation on the top of a snow field To with extend are chloroplasts modified between these two extremes in morphology way as well as in their physiology? secondary metabolites: many snow algae produce high amounts of secondary metabolites. Do some not yet de- scribed ones have also UV-absorbing capacities like 13Z cis-astaxanthin (cryoxanthin, detected by us) in Chlamydomonas nivalis? Alpine/Arctic/Antarctic comparison: are adaptation strategies in algae from the high arctic or from Antarctica com- parable to alpine species despite different solar light exposure and different nutrient supply by the snow? species identification we continue the cooperation with Dr. T. Leya for molecular strain classification, because the taxonomy of snow algae is still poorly resolved. Understanding the ecophysiology of snow algae is of great interest, since these species have to be adapted to an harsh environment with cold temperatures, frequent freeze thaw cycles and poor nutrition levels. Especially the question how to protect against occasionally very high (short-wave-) irradiation is important, in par- ticular that some species stay green and do not form protective secondary carotenoids or cyst stages.

Snow fields, glacier ice and permafrost areas dominate the landscape in polar and high mountain regions. Growth of photosynthetic organisms is restricted to a low species number of adapted higher plants, ferns and mosses. A comparable richer vegetation has been developed in algae, living on snow and ice. Macroscopic visible mass accumulations of certain algae cause the phenomena of Red or Green Snow in alpine and polar regions. Most of these organisms belong to the genera Chlamydomonas and Chloromonas (Chlorophyta, Volvocales), Those species which cause Red Snow, like Chlam. nivalis, live in their habitat mostly as cysts stages with thick cell walls and a massive production of secondary carotenoids. The pigments block against high solar irradiation, even in the UV - region, as we could prove in UV-simulation studies. Another topic of our work was to understand the cold- and frost resistance of cryophilic algae better. We improved separation methods for seldom occurring soluble carbohydrates. Thus it was possible to identify carbohydrate composition in several algal species. Together with common sugars like glucose, sugar alcohols were frequently measured, but the main component was glycerol. Equipped with these sugars, the cells should manage good freezing depressions and frost resistance; in addition, the chemical nature of these sugars as polyols also stabilizes proteins. A third topic in our research activities took up the stress physiology of typical ice algae. Selected members were Ancylonema sp. from the High Arctic, Klebsormidium sp., collected in the maritime Antarctic, and Mesotaenium berggrenii, growing on glacier surfaces in the Alps. Similar to the snow algae the ice algae could easily manage photosynthesis between 0C and +15 C. They also resist high light intensities, which was not expected in polar algae because of the low solar angle (lower intensity) in their habitats. Cells of ice algae contain always a large vacuole, which is filled with a brownish-purple sap. We tried to identify composition and chemical structure of the compounds from this sap. Finally, and with good cooperation, we were successful: Main components in Mesotaenium and in Ancylonema are purpuro (=purple) gallotannins, substituted with different sugars. This is surprising, because the class of gallotannins have never been described in algae. Comparable compounds are also rare in higher plants, similar gallotannins develop in tea plants, when the leaves undergo fermentation, by oxidation processes. These new gallotannins protect the algal cells against visible and against UV irradiation, which can be tremendous in high altitudes. Further, they show antioxidative and antimicrobial activities, when isolated. These properties should protect again snow algae in their habitat. In case of Klebsormidium we have not yet finished all studies. The research activities on stress physiology of cryophilic algae included two expeditions to the High Arctic (Spitsbergen) and one expedition to the maritime Antarctic. Funding by the FWF and good international cooperation guaranteed also these research activities.