Biological soil crusts of Arctic Svalbard and of Livingston Island, Antarctica

Biological soil crusts (BSCs) occur in arid and semi-arid regions worldwide including the Polar Regions. They are important ecosystem engineers, and their composition and areal coverage should be understood before assessing key current functional questions such as their role in biogeochemical nutrient cycles and possible climate change scenarios. Our aim was to investigate the variability of BSCs from Arctic Svalbard and the Antarctic Island, Livingston, using vegetation surveys based on classification by functional group. An additional aim was to describe the structure of BSCs and represent a classification system that can be used in future studies to provide a fast and efficient way to define vegetation type and areal coverage. Firstly, this study demonstrates huge areas occupied by BSCs in Arctic Svalbard, with up to 90 % of soil surface covered, dominated by bryophytes and cyanobacteria, and showing an unexpectedly high variability in many areas. Livingston Island has lower percentage coverage, up to 55 %, but is dominated by lichens. Our findings show that both Polar Regions have varied BSC coverage, within the sites and between them, especially considering their harsh climates and latitudinal positions. Secondly, we have classified the BSCs of both areas into a system that describes the dominant functional groups and local geography, creating a simple scheme that allows easy identification of the prevailing vegetation type. Our results represent the first contribution to the description of BSCs based on their functional group composition in Polar Regions

The Contractile Vacuole as a Key Regulator of Cellular Water Flow in Chlamydomonas reinhardtii

Most freshwater flagellates use contractile vacuoles (CVs) to expel excess water. We have used Chlamydomonas reinhardtii as a green model system to investigate CV function during adaptation to osmotic changes in culture medium. We show that the contractile vacuole in Chlamydomonas is regulated in two different ways. The size of the contractile vacuoles increases during cell growth, with the contraction interval strongly depending on the osmotic strength of the medium. In contrast, there are only small fluctuations in cytosolic osmolarity and plasma membrane permeability. Modeling of the CV membrane permeability indicates that only a small osmotic gradient is necessary for water flux into the CV, which most likely is facilitated by the aquaporin major intrinsic protein 1 (MIP1). We show that MIP1 is localized to the contractile vacuole, and that the expression rate and protein level of MIP1 exhibit only minor fluctuations under different osmotic conditions. In contrast, SEC6, a protein of the exocyst complex that is required for the water expulsion step, and a dynamin-like protein are upregulated under strong hypotonic conditions. The overexpression of a CreMIP1-GFP construct did not change the physiology of the CV. The functional implications of these results are discussed

Transcriptomics of Desiccation Tolerance in the Streptophyte Green Alga <i>Klebsormidium</i> Reveal a Land Plant-Like Defense Reaction

<div><p>Background</p><p>Water loss has significant effects on physiological performance and survival rates of algae. However, despite the prominent presence of aeroterrestrial algae in terrestrial habitats, hardly anything is known about the molecular events that allow aeroterrestrial algae to survive harsh environmental conditions. We analyzed the transcriptome and physiology of a strain of the alpine aeroterrestrial alga <i>Klebsormidium crenulatum</i> under control and strong desiccation-stress conditions.</p><p>Principal Findings</p><p>For comparison we first established a reference transcriptome. The high-coverage reference transcriptome includes about 24,183 sequences (1.5 million reads, 636 million bases). The reference transcriptome encodes for all major pathways (energy, carbohydrates, lipids, amino acids, sugars), nearly all deduced pathways are complete or missing only a few transcripts. Upon strong desiccation, more than 7000 transcripts showed changes in their expression levels. Most of the highest up-regulated transcripts do not show similarity to known viridiplant proteins, suggesting the existence of some genus- or species-specific responses to desiccation. In addition, we observed the up-regulation of many transcripts involved in desiccation tolerance in plants (e.g. proteins similar to those that are abundant in late embryogenesis (LEA), or proteins involved in early response to desiccation ERD), and enzymes involved in the biosynthesis of the raffinose family of oligosaccharides (RFO) known to act as osmolytes). Major physiological shifts are the up-regulation of transcripts for photosynthesis, energy production, and reactive oxygen species (ROS) metabolism, which is supported by elevated cellular glutathione content as revealed by immunoelectron microscopy as well as an increase in total antiradical power. However, the effective quantum yield of Photosystem II and CO₂ fixation decreased sharply under the applied desiccation stress. In contrast, transcripts for cell integrative functions such as cell division, DNA replication, cofactor biosynthesis, and amino acid biosynthesis were down-regulated.</p><p>Significance</p><p>This is the first study investigating the desiccation transcriptome of a streptophyte green alga. Our results indicate that the cellular response is similar to embryophytes, suggesting that embryophytes inherited a basic cellular desiccation tolerance from their streptophyte predecessors.</p></div

Glutathione content of <i>Klebsormidium crenulatum</i> cells.

<p>Values are means with standard errors, and document the total amount of gold particles bound to glutathione per μm² in different cell compartments and whole cells of <i>Klebsormidium crenulatum</i> grown under control and desiccation conditions. n = 40 for the individual cell structures and n = 25 for the whole cell. Different lowercase letters indicate significant differences (P<0.05) analyzed with the Kruskal-Wallis test followed by post-hoc comparison according to Conover. n.d. = not determined.</p><p>Glutathione content of <i>Klebsormidium crenulatum</i> cells.</p

Biosynthesis of carotenoids in <i>Klebsormidium crenulatum</i>.

<p>(A) Terpenoid backbone synthesis, the cytosolic mevalonate pathway is inhibited. (B) Carotenoid biosynthesis is up-regulated.</p

Similarity of <i>Klebsormidium crenulatum</i> contigs to other organisms.

<p>24,183 contigs were blasted against the protein database of the selected organisms listed (obtained from Phytozome). The number of BLASTX hits (e-value </p><p>Similarity of <i>Klebsormidium crenulatum</i> contigs to other organisms.</p