Molecular characterization of the chalcone isomerase gene family in Deschampsia antarctica

Deschampsia antarctica (Poaceae) is one of the two vascular plants known to have colonized the Antarctic region. Studies examining the biosynthesis of flavonoids, compounds which plants use, for example, for protection against overexposure to UV light or as antioxidants that scavenge free radicals and other oxidative species, in D. antarctica may provide clues to its success in that extreme environment. We characterized the family of genes encoding chalcone isomerase (CHI EC 5.5.1.6), an important enzyme involved in flavonoid biosynthesis, in D. antarctica. Sequence analysis of the three family members revealed differences in numbers of introns and lengths of coding regions among the three and suggest that DaCHI3 is likely a pseudogene (ψDaChi2). Salinity stress resulted in differential mRNA expression of the DaCHI genes with ψDaCHI2 exhibiting the earliest response (3-h post-treatment), induced by as much as sevenfold, while DaCHI1 and DaCHI2 mRNAs accumulated later (3d and 5d post-treatment, respectively) and, in the case of DaCHI2, with a response of nearly sixfold. We discuss how differences in the proposed gene structures, deduced protein characteristics, and mRNA expression patterns suggest that the members of this gene family may have unique functions in the phenylpropanoid pathway in D. antarctica.     

Taxonomic affinities of dark septate root endophytes of Colobanthus quitensis and Deschampsia antarctica,the two native Antarctic vascular plant species

Although dark septate fungal endophytes (DSE) occur widely in association with plant roots in cold-stressed habitats, little is known of the taxonomic status of DSE in Antarctica. Here we investigate the phylogenetic affinities of DSE colonising the roots of Colobanthus quitensis and Deschampsia antarctica, the two maritime Antarctic vascular plant species. Two hundred and forty-three DSE were isolated from roots collected from 17 sites across a 1 470 km transect through maritime and sub-Antarctica. The ITS1-5.8S-ITS2 nuclear ribosomal gene cluster of representative isolates was sequenced, and the sequences were recovered in 10 sequence groups and sub-groups. Nine of the sequence groupings could be placed in the Helotiales and the remaining one showed high homology to a large number of currently unassigned anamorphic ascomycete sequences. Of the Helotiales, Leptodontidium orchidicola, Rhizoscyphus ericae and species of Tapesia and Mollisia could be confidently identified. This study demonstrates that members of the Helotiales, including several widely-recognised DSE genera, commonly colonise the roots of C. quitensis and D. antarctica in the Antarctic.     

Characterization of a novel antarctic plant growth-promoting bacterial strain and its interaction with antarctic hair grass (Deschampsia antarctica Desv)

Deschampsia antarctica is the only hair grass that has been able to successfully colonize the Antarctic continent. However, there is little research on the role of microorganisms associated with the rhizosphere that may participate in its growth and development. The objective of this research was to characterize a psychrotolerant bacterial strain isolated from the rhizosphere of D. antarctica. Biochemical and molecular studies were performed to characterize this bacterium. It was determined that this strain secretes a neutral polysaccharide that presents different compositions at different temperatures (4 and 20 °C). Based on biochemical and phylogenetic analyses, the Antarctic rhizobacterium could be a new species of Pseudomonas. To determine their ability to solubilize different sources of inorganic phosphate, qualitative and quantitative analyses were conducted to determine P released at 4 °C. The Antarctic strain of Pseudomonas sp. was able to solubilize all sources of phosphates, and 34.2 mg P/L was released from rock phosphate. Growth physiological parameters were evaluated for seedlings of D. antarctica inoculated with the rhizobacteria. It was found that the bacterial inoculation promoted plant root development. SEM analysis of the roots showed that the bacterium is mainly located in the root hairs of D. antarctica.     

Antarctic moss carpets facilitate growth of Deschampsia antarctica but not its survival

The vegetation of the Antarctic tundra is dominated by mosses and lichens. Deschampsia antarctica, the Antarctic hairgrass, is one of two vascular plant species which grow along the west coast of the Antarctic Peninsula. However, little is known about its recruitment and interaction with non-vascular tundra plants. Although several authors propose that tolerance and/or competition should be the main forms of interaction between moss carpets and D. antarctica, no relevant studies exist so far. We investigated whether positive interactions are predominant at the Shetland Islands and the west coast of the Antarctic Peninsula and focussed on the role that moss carpets play in the recruitment of D. antarctica. Across the studied zone, D. antarctica showed a significant association with moss carpets, with higher frequencies as well as more and larger individuals than on bare ground. At one site, we conducted moss removal and seedlings transplant experiments to assess the relevance of the moss carpets for different life stages of hairgrass. All experimental individuals survived until the following summer whether the moss carpet was removed or not, but growth rate was significantly lower in tussocks with moss carpets removed. Likewise, tiller size was higher in plants growing in moss carpets than on bare ground. The detected positive interactions with mosses seem to be important for the expansion of D. antarctica, raising the question about their importance under future climate change scenarios.     

Influence of soil properties on the distribution of Deschampsia antarctica on King George Island, Maritime Antarctica

The extremely cold and infertile Antarctic is one of the harshest terrestrial ecosystems for the growth of vegetation, except for the grass species Deschampsia antarctica. We examined the main soil variables that determine the distribution of D. antarctica in King George Island by using Bayesian analysis of variance and regression methods. This study compared the density of D. antarctica between 2 sites; the density remained relatively stable at site 1, whereas it severely decreased in site 2 over a period of 3?years. Although site 2 showed better soil conditions for the growth of D. antarctica such as organic matter content, available phosphorus, NO₃-N, and extractable cations, its poor drainage and low soil pH may affected the survival of D. antarctica by altering nutrition availability and inhibiting root respiration. Poisson analysis of covariance showed that the early melting of snow was also an important factor in the distribution of D. antarctica. The results also showed that seabirds and mammals might have greatly influenced the distribution of the grass species in King George Island by transferring nutrients from the sea onto land; thus, changing the chemical characteristics of the soil.     

Shell structure of two polar pelagic molluscs, Arctic Limacina helicina and Antarctic Limacina helicina antarctica forma antarctica

The purpose of this study was to investigate shell growth performance in two thin-shelled pelagic gastropods from cold seawater habitats. The shells of Arctic Limacina helicina and Antarctic Limacina helicina antarctica forma antarctica are very thin, approximately 2–9 μm for shells of 0.5–6 mm in diameter. Many axial ribbed growth lines were observed on the surface of the shell of both Limacina species. Distinct axial ribs were observed on the outermost whorl, while weak or no rib-like structures were observed on the inner whorls in the larger shell of L. helicina antarctica forma antarctica. For L. helicina, no ribs were observed on small individuals with three whorls, while larger individuals had distinct ribs on the outer whorls. Shell microstructure was examined in both species. There is an inner crossed-lamellar and extremely thin outer prismatic layer in small individuals of both species, and a distinct thick inner prismatic layer was observed beneath the crossed-lamellar layer in large Antarctic individuals. Various orientations of the crossed-lamellar structure were observed in one individual. Shell structure appeared to be different between the Antarctic and Arctic species and among shells of different size.