Sixty years of vegetation dynamics in a south boreal coniferous forest in southern Norway

Abstract. Vegetation data from permanent plots were collected in 1931, 1961 and 1991 in a south boreal forest 20 km north of Oslo in southern Norway. Major changes were found in the vegetation composition during those 60 years. The main changes were a reduction in the frequency of species and the frequency of joint occurrences of vascular species such as Andromeda polifolia, Calluna vulgaris, Cornus suecica, Eriophorum vaginatum, Maianthemum bifolium, Melampyrum pratense, Trientalis europaea, Vaccinium uliginosum and V. oxycoccus, and mosses, e.g. Dicranum fuscescens, Hylocomium splendens, Pleurozium schreberi, Ptilidium ciliare and Ptilium crista-castrensis. The observed changes were interpreted as being induced by internal processes e.g. notably a long-term change from paludified forest to mesic forest. In particular the growth of Picea abies seems to be a main driving force. The dominance of Picea abies and Vaccinium myrtillus appears to have rendered the conditions more unfavourable for other species. A doubling of the living stem biomass of P. abies during the last 67 yr shows that this old-growth forest has not yet reached a steady state. It was demonstrated that species such as Deschampsia flexuosa and Molinia caerulea did not increase in frequency in response to nitrogen deposition, as has occurred elsewhere in northern Europe. pH in the humus layer increased with 0.2 unit from 1961 to 1991. The results of this study indicate that protection from logging has initiated the reduction of species in the field layer and bottom layer. This study questions if monitoring of forest vegetation should be restricted to protected forests as is the practice in Scandinavia today. We recommend that also areas with some kind of selective cutting will be used for monitoring of forest vegetation.     

Can sites prone to flow induced vascular complications in a-v fistulas be assessed using computational fluid dynamics?

Arterio-venous fistulas (shunts between arteries and veins) are the preferred vascular access for hemodialysis. Despite their superior patency, compared with synthetic tubes and grafts, functional problems and inadequate flow rates are the common complications. Local flow conditions, in particular low and oscillating wall shear stresses (WSS), are central to vascular problems and a robust framework for analyzing flow conditions in vascular structures could provide an understanding of the mechanisms leading to vascular complications, such as stenoses, aneurisms, and thromboses.We hypothesize that a validated computational fluid dynamics (CFD) framework can be used to identify critical fistula configurations with elevated risk of complications. Therefore, the aim of the present study was to develop a CFD framework for analyzing fluid flow in complex vascular structures, such as arterio-venous fistulas validated by comparisons of in vitro volume flows with CFD results and flow fields from ultrasound scans with CFD simulations.Volume flows measured in vitro and CFD data differed quantitatively. However, good relative correlations exist between the data using logarithmic scales. Qualitatively, visual comparisons between ultrasound and CFD images showed good agreement between the two methods. In addition, WSS levels and the oscillatory shear index (OSI) were calculated and visualized on the model surface. The method was successfully validated and the method is deemed suitable for more thorough investigations into the field of vascular complications in a-v fistulas.     

Studies on the Germination of Pine Pollen (Pinus mugo) in vitro. I. Growth Conditions and Effects of pH and Temperature on Germination, Tube Growth and Respiration

The ability of pine pollen to grow in vitro is discussed in relation to its in situ. Optimal conditions of growth in vitro were investigated. All the experiments were made with pollen of Pinus mugo Turra. A satisfactory medium is described as that which at pH 5.2 and at 29 °C can lead to a tube growth bigger than in vivo. The initial growth (0–30) hours) in terms of tube growth and respiration is described in detail. It is shown that a correlation exists between tube growth and respiration. A method for estimating the metabolism and growth of the pollen tube, based on the uptake of ³²p-labelled phosphate, is described. Addition of known stimulators of plant growth and extension does not stimulate tube growth. Temperature studies show that under 20°C germination does not take place.     

Anti-microbial and cytotoxic 1,6-dihydroxyphenazine-5,10-dioxide (iodinin) produced by Streptosporangium sp. DSM 45942 isolated from the fjord sediment

Phenazine natural products/compounds possess a range of biological activities, including anti-microbial and cytotoxic, making them valuable starting materials for drug development in several therapeutic areas. These compounds are biosynthesized almost exclusively by eubacteria of both terrestrial and marine origins from erythrose 4-phosphate and phosphoenol pyruvate via the shikimate pathway. In this paper, we report isolation of actinomycete bacteria from marine sediment collected in the Trondheimfjord, Norway. Screening of the isolates for biological activity produced several “hits”, one of which was followed up by identification and purification of the active compound from the actinomycete bacterium Streptosporangium sp. The purified compound, identified as 1,6-dihydroxyphenazine-5,10-dioxide (iodinin), was subjected to extended tests for biological activity against bacteria, fungi and mammalian cells. In these tests, the iodinin demonstrated high anti-microbial and cytotoxic activity, and was particularly potent against leukaemia cell lines. This is the first report on the isolation of iodinin from a marine-derived Streptosporangium.     

The Arginine of the DRY Motif in Transmembrane Segment III Functions as a Balancing Micro-switch in the Activation of the β2-Adrenergic Receptor

Recent high resolution x-ray structures of the β2-adrenergic receptor confirmed a close salt-bridge interaction between the suspected micro-switch residue ArgIII:26 (Arg3.50) and the neighboring AspIII:25 (Asp3.49). However, neither the expected "ionic lock" interactions between ArgIII:26 and GluVI:-06 (Glu6.30) in the inactive conformation nor the interaction with TyrV:24 (Tyr5.58) in the active conformation were observed in the x-ray structures. Here we find through molecular dynamics simulations, after removal of the stabilizing T4 lysozyme, that the expected salt bridge between ArgIII:26 and GluVI:-06 does form relatively easily in the inactive receptor conformation. Moreover, mutational analysis of GluVI:-06 in TM-VI and the neighboring AspIII:25 in TM-III demonstrated that these two residues do function as locks for the inactive receptor conformation as we observed increased G(s) signaling, arrestin mobilization, and internalization upon alanine substitutions. Conversely, TyrV:24 appears to play a role in stabilizing the active receptor conformation as loss of function of G(s) signaling, arrestin mobilization, and receptor internalization was observed upon alanine substitution of TyrV:24. The loss of function of the TyrV:24 mutant could partly be rescued by alanine substitution of either AspIII:25 or GluVI:-06 in the double mutants. Surprisingly, removal of the side chain of the ArgIII:26 micro-switch itself had no effect on G(s) signaling and internalization and only reduced arrestin mobilization slightly. It is suggested that ArgIII:26 is equally important for stabilizing the inactive and the active conformation through interaction with key residues in TM-III, -V, and -VI, but that the ArgIII:26 micro-switch residue itself apparently is not essential for the actual G protein activation.     

Conserved Water-mediated Hydrogen Bond Network between TM-I, -II, -VI,and -VII in 7TM Receptor Activation

Five highly conserved polar residues connected by a number of structural water molecules together with two rotamer micro-switches, TrpVI:13 and TyrVII:20, constitute an extended hydrogen bond network between the intracellular segments of TM-I, -II, -VI, and -VII of 7TM receptors. Molecular dynamics simulations showed that, although the fewer water molecules in rhodopsin were relatively movable, the hydrogen bond network of the β2-adrenergic receptor was fully loaded with water molecules that were surprisingly immobilized between the two rotamer switches, both apparently being in their closed conformation. Manipulations of the rotamer state of TyrVII:20 and TrpVI:13 demonstrated that these residues served as gates for the water molecules at the intracellular and extracellular ends of the hydrogen bond network, respectively. TrpVI:13 at the bottom of the main ligand-binding pocket was shown to apparently function as a catching trap for water molecules. Mutational analysis of the β2-adrenergic receptor demonstrated that the highly conserved polar residues of the hydrogen bond network were all important for receptor signaling but served different functions, some dampening constitutive activity (AsnI:18, AspII:10, and AsnVII:13), whereas others (AsnVII:12 and AsnVII:16) located one helical turn apart and sharing a water molecule were shown to be essential for agonist-induced signaling. It is concluded that the conserved water hydrogen bond network of 7TM receptors constitutes an extended allosteric interface between the transmembrane segments being of crucial importance for receptor signaling and that part of the function of the rotamer micro-switches, TyrVII:20 and TrpVI:13, is to gate or trap the water molecules.     

Trait Associations across Evolutionary Time within a Drosophila Phylogeny: Correlated Selection or Genetic Constraint?

Traits do not evolve independently. To understand how trait changes under selection might constrain adaptive changes, phenotypic and genetic correlations are typically considered within species, but these capture constraints across a few generations rather than evolutionary time. For longer-term constraints, comparisons are needed across species but associations may arise because of correlated selection pressures rather than genetic interactions. Implementing a unique approach, we use known patterns of selection to separate likely trait correlations arising due to correlated selection from those reflecting genetic constraints. We examined the evolution of stress resistance in >90 Drosophila species adapted to a range of environments, while controlling for phylogeny. Initially we examined the role of climate and phylogeny in shaping the evolution of starvation and body size, two traits previously not examined in this context. Following correction for phylogeny only a weak relationship between climate and starvation resistance was detected, while all of the variation in the relationship between body size and climate could be attributed to phylogeny. Species were divided into three environmental groups (hot and dry, hot and wet, cold) with the expectation that, if genetic correlations underpin trait correlations, these would persist irrespective of the environment, whereas selection-driven evolution should produce correlations dependent on the environment. We found positive associations between most traits in hot and dry environments coupled with high trait means. In contrast few trait correlations were observed in hot/wet and cold environments. These results suggest trait associations are primarily driven by correlated selection rather than genetic interactions, highlighting that such interactions are unlikely to limit evolution of stress resistance.