Effects of prolonged darkness and temperature on the lipid metabolism in the benthic diatom Navicula perminuta from the Arctic Adventfjorden, Svalbard

Abstract

which could consequently lead to a depletion of this energy reserves before the end of the polar night. On the other hand, the membrane building phospho-and glycolipids remained unchanged during the 8 weeks darkness, indicating still intact thylakoid membranes. These results explain the shorter survival times of polar diatoms with increasing water temperatures during prolonged dark periods. Abstract The Arctic represents an extreme habitat for phototrophic algae due to long periods of darkness caused by the polar night (~4 months darkness). Benthic diatoms, which dominate microphytobenthic communities in shallow water regions, can survive this dark period, but the underlying physiological and biochemical mechanisms are not well understood. One of the potential mechanisms for long-term dark survival is the utilisation of stored energy products in combination with a reduced basic metabolism. In recent years, water temperatures in the Arctic increased due to an ongoing global warming. Higher temperatures could enhance the cellular energy requirements for the maintenance metabolism during darkness and, therefore, accelerate the consumption of lipid reserves. In this study, we investigated the macromolecular ratios and the lipid content and composition of Navicula cf. perminuta Grunow, an Arctic benthic diatom isolated from the microphytobenthos of Adventfjorden (Svalbard, Norway), over a dark period of 8 weeks at two different temperatures (0 and 7 °C). The results demonstrate that N. perminuta uses the stored lipid compound triacylglycerol (TAG) during prolonged dark periods, but also the pool of free fatty acids (FFA). Under the enhanced temperature of 7 °C, the lipid resources were used significantly faster than at 0 °C, Keywords

Dark metabolism: a molecular insight into how the Antarctic sea‐ice diatom Fragilariopsis cylindrus survives long‐term darkness

“…Any depletion in macromolecule transporters in thylakoid membranes would result in the degradation of the LHC. Diatom thylakoids are enriched with the anionic lipid SQDG, which accounts for over 40% of the total lipid content (Schaub et al., ). In this study, while speculative, the increased expression of plastid UDP‐sulfoquinovose synthase, which is essential for the production of SQDG, was observed in the dark.…”

“…() and this may illustrate that the photosynthetic apparatus of F. cylindrus was not degraded during extended darkness. This adaptive response has been noted in previous studies with polar diatoms, in which the photosynthetic apparatus is maintained so that photosynthesis can resume rapidly upon return to favourable light conditions (Bunt & Lee, ; Palmisano & Sullivan, ; Peters & Thomas, ; McMinn & Martin, ; Schaub et al., ). Furthermore, if degradation of light‐harvesting antenna complexes was occurring, a gradual reduction in the photosynthetic parameter α would be apparent, as resonance energy transfer between the antenna and photosystem II would become inefficient due to physical breakdown (Falkowski & LaRoche, ; Vernotte et al ., ; Nymark et al ., ).…”

Fast reactivation of photosynthesis in arctic phytoplankton during the polar night1

“…Overwintering strategies such as utilization of stored energy products (Schaub et al. ), formation of resting stages (Figueroa et al. ), reduction of metabolic rate (Jochem ), and a facultative heterotrophic lifestyle (Tuchman et al.…”

“…Other organisms produce spores and cysts to survive the winter (Figueroa et al 2011). However, recent studies also indicate the presence of vegetative cells of photoautotrophic species in water and sea ice during the polar night, confirming that many species are able to survive long periods of darkness in that state, probably by utilization of stored energy products in combination with reduced metabolic activity (Zhang et al 1998, McMinn et al 2010, Vader et al 2015, Schaub et al 2017. Generally, the photosynthetic apparatus of photoautotrophic organisms rapidly responds to fluctuations in light through photo-regulation and acclimation.…”

“…, Schaub et al. ). Generally, the photosynthetic apparatus of photoautotrophic organisms rapidly responds to fluctuations in light through photo‐regulation and acclimation.…”