ALBERT

Description: The German research icebreaker RV Polarstern drifted within the western Weddell Sea pack from 27 November, 2004 until 2 January, 2005, initially anchored to a 10 km x 10 km sized floe. This was composed of 2-m thick second-year ice with 0.8 m snow on top, interspersed by first-year ice with modal thicknesses of 0.9 m and 1.8 m, covered with 0.3 m of snow. ISPOL traveled over a distance of 290 km with a net south-north displacement of 98 km due to various loops in the ice floe trajectory. These loops seem common since ISW-1 and tagged ice floes and icebergs followed similar deflections during their course. For 36 days Polarstern served an interdisciplinary scientific team from eight countries (Australia, Belgium, Finland, Netherlands, Russia, United Kingdom, U.S.A., and Germany) as accommodation and laboratory as well as platform for field and water column studies. The local view was extended to both sides of the floe trajectory using helicopters with an operational range of 120 km to conduct sea ice thickness and ice dynamics measurements, iceberg marking, and water column sampling. On 2 December, 2004 the floe cracked into several pieces, reducing the main station floe to a size of 1.5 km x 1.5 km. On 24 December the ice floe again fractured, leaving a piece of 0.7 km x 0.8 km for the remaining experiment.

Description: One of the most extreme environments in the polar regions is sea ice. Low temperatures, high salinities and high pH values together with extreme fluctuations in irradiance have lead to the development of a unique community in sea ice brine channels, which is dominated by diatoms. One of the best studied and most successful members of this community is the diatom Fragilariopsis cylindrus which is physiologically active at temperatures as low as 20°C and salinities of up to 100 PSU.To study molecular adaptations to this extreme habitat an expressed sequence tag (EST) approach was used, based on cultures subjected to elevated external salt concentrations (70 PSU). To 44 % of the sequences (1692 unigenes) a putative function could be assigned and a large number of genes involved in transport processes, oxidative stress defence, osmolyte synthesis and protein turnover as well as chaperones could be successfully identified, stressing the importance of these mechanisms in salt stress acclimatisation.Furthermore, four different full length sequences encoding a new class of ice-binding proteins yet unknown in animals and plants were found and further studies proved its occurrence in a number of polar diatom species, but not in mesophilic ones. These proteins are most probably exuded into the extracellular space and hence might be of fundamental importance in enabling survival in the brine channel system.The accumulation of the organic osmolyte proline synthesized upon osmotic stress was investigated. Measurements of transcript levels of four genes (P5CS, P5CR, OAT and ProDH) revealed an as yet unobserved regulation of the proline synthesis pathway in comparison to higher plants. A strong down regulation of P5CS and a simultaneously upregulated OAT suggested that ornithine rather than glutamate serves as a substrate for proline synthesis. The catabolic pathway via ProDH was also 3 fold up regulated after the salt shock indicating a high turnover of proline, but still enabling a net build up of proline 6 times higher than in control cultures. Photophysiological measurements demonstrated a more severe impact of a twofold increase in salinity, compared to a reduction in temperature by 7°C. Damage of PSII in the salinity treated cultures was five times increased as opposed to the cold shock and the regeneration of PSII was retarded.

Description: Saisonal auftretendes Meereis stellt zeitweise eines der größten Ökosysteme, mit einer Fläche von 20x106 km2 und 16x106 km2 in der Antarktis bzw. Arktis, weltweit dar. Charakterisiert ist dieses Habitat durch starke Gradienten in den wichtigen abiotischen Faktoren Licht, Nährstoffverfügbarkeit, Temperatur und Salinität, die gegenüber Meerwasser in Abhängigkeit von der Temperatur um den Faktor 5 erhöht sein kann. Untersucht wurde welche Mechanismen es der psychrophilen Diatomee Fragilariopsis cylindrus ermöglichen diesen Salzstress zu tolerieren. Als Grundlage für diese Arbeiten wurde eine Salzstress induzierte cDNA Bank erstellt und ca. 2900 Klone aus dieser Bank sequenziert und analysiert. Aus dieser Bank konnten 8.6% der funktionell charakterisierbaren Gene mit Stressaklimation in Bezug gesetzt werden. Dies beinhaltet Gene der Synthese von organischen Osmolyten, Chaperone, Ionen Anti- und Symporter und Gene verantwortlich für die detoxifizierung von reaktiven Sauerstoff Spezies. Überraschenderweise wurde ebenfalls eine neue Klasse von Ice-binding Proteinen gefunden die noch nicht aus höheren Pflanzen und Tieren bekannt ist. Diese Proteine beeinflussen das Wachstum und die Rekristallisation von Eiskristallen und sind somit für das Überleben im Solekanalsystem von außerordentlicher Bedeutung.Im Anschluss wurde die Regulation der Synthese des organischen Osmolyts Prolin mit Hilfe der quantitativen PCR untersucht. Dabei zeigte sich das im Gegensatz zur Synthese bei höheren Pflanzen, diese unter Salzstress verstärkt über Ornithin und nicht Glutamat als Ausgangssubstrat erfolgt.