Changes in needle nitrogen partitioning and photosynthesis during 80 years of tree ontogeny in Picea abies

Needle nitrogen partitioning and photosynthesis of Norway spruce were studied in a forest chronosequence in Järvselja Experimental Forest, Estonia. Current- and previous-year shoots were sampled from upper and lower canopy positions in four stands, ranging in age from 13 to 82 years. A/c _i curves were determined to obtain maximum carboxylation rate (V _cmax) and maximum rate of electron transport (J _max), whereas needle nitrogen partitioning into carboxylation (P _R), bioenergetics associated with electron transport (P _B) and thylakoid light harvesting components (P _L) was calculated from the values of V _cmax, J _max and leaf chlorophyll concentration. The greatest changes in studied needle characteristics took place between tree ages of 13 and 26 years, and this pattern was independent of needle age and canopy position. Needle mass per projected area (LMA) was lowest in the 13-year-old stand and mass-based nitrogen concentration (N^M) was generally highest in that stand. The values of LMA were significantly higher and those of N^M lower in the 26-year-old stand. Mass-based V _cmax and J _max were highest in the 13-year-old stand. Area-based photosynthetic capacity was independent of tree age. The proportion of photosynthetic nitrogen (P _R, P _B and P _L) was highest and that of non-photosynthetic nitrogen lowest in the 13-year-old stand. Current-year needles had lower LMA and P _L, but higher photosynthetic capacity compared to 1-year-old foliage. Needles from lower canopy positions exhibited lower LMA, area-based nitrogen concentration and photosynthetic capacity than needles from upper canopy. The period of substantial reductions in needle photosynthetic capacity and changes in nitrogen partitioning coincides with the onset of reproductive phase during tree ontogeny.     

The shapes of the motor domains of two oppositely directed microtubule motors, ncd and kinesin: a neutron scattering study.

The shapes of the motor domains of kinesin and ncd, which move in opposite directions along microtubules, have been investigated. Using proteins expressed in Escherichia coli, it was found that at high salt (> 200 mM) Drosophila ncd motor domain (R335-K700) and human kinesin motor domain (M1-E349) were both sufficiently monomeric to allow an accurate determination of their radii of gyration (Rg) and their molecular weights. The measured Rg values of the ncd and kinesin motor domains in D2O were 2.06 +/- 0.06 and 2.05 +/- 0.04 nm, respectively, and the molecular weights were consistent with those computed from the amino acid compositions. Fitting of the scattering curves to approximately 3.5 nm resolution showed that the ncd and kinesin motor domains can be described adequately by triaxial ellipsoids having half-axes of 1.42 +/- 0.38, 2.24 +/- 0.44, and 3.65 +/- 0.22 nm, and half-axes of 1.52 +/- 0.23, 2.00 +/- 0.25, and 3.73 +/- 0.10 nm, respectively. Both motor domains are described adequately as somewhat flattened prolate ellipsoids with a maximum dimension of approximately 7.5 nm. Thus, it appears that the overall shapes of these motor domains are not the major determinants of the directionality of their movement along microtubules.     

The role of landscape structure in determining palynological and floristic richness

The associations between floristic and palynological richness and landscape structure were studied based on modern pollen?Cvegetation data from a patchy cultural landscape in southern Estonia (northern temperate vegetation zone). Nine study sites (small lakes and their surrounding vegetation) represent land cover gradient from closed forest to semi-open vegetation. Floristic richness (number of species) and floristic richness of pollen types (number of pollen-equivalent taxa) were used to describe the vegetation within the radius of 250?m from the pollen sampling sites. Palynological richness was calculated to describe the modern pollen samples diversity. Landscape structure was estimated on the basis of landscape openness and three landscape diversity measures: richness of community patches, Simpson evenness of community patches and Simpson diversity of community patches. To study the effect of the spatial scale of landscapes on the vegetation?Clandscape and pollen?Clandscape associations, landscape structure was estimated within eight radii (250?C2,000?m) around each lake. The results showed that landscape openness was the most important determinant of both floristic richness and palynological richness in southern Estonia and that landscape diversity estimated by Simpson diversity index was also significantly associated with the richness estimates. Floristic and palynological richness were significantly positively correlated with landscape structure within the radii greater than 1,000?m from the pollen sampling sites, which is similar to the estimated Relevant Source Area of Pollen in southern Estonia. We conclude that within one floristic or climatic region, palynological richness gives reliable estimates about the variation in floristic richness and landscape structure; however, caution must be taken when comparing pollen-inferred vegetation diversities from different regions or when interpreting fossil pollen records from times with highly different vegetation associations.     

Discovery of novel class 1 phosphatidylinositide 3-kinases (PI3K) fragment inhibitors through structure-based virtual screening

The discovery of ligand efficient and lipophilicity efficient fragment inhibitors of class 1 phosphatidylinositide 3-kinases (PI3K) is reported. A fragment version of the AstraZeneca compound bank was docked to a homology model of the PI3K p110β isoform. Interaction-based scoring of the predicted binding poses served to further prioritise the virtual fragment hits. Experimental screening confirmed potency for a total of 18 fragment inhibitors, belonging to five different structural classes.     

Towards to hENT1-nucleoside transporter selective imaging agents. Synthesis and in vitro evaluation of the radiolabeled SAENTA analogues

Three new potential hENT₁ inhibitors suitable for labeling with PET/SPECT radioisotopes were prepared from an advanced intermediate 4. They were tested for their capability to inhibit binding of SAENTA-fluorescein to HL60 leukemia cells in flow cytometry assay and SAENTA-I (5) was determined to be the most active compound. ¹³¹I-5 showed high hENT₁-specific binding (up to 54% ID) to 6 from 7 tested tumor cell lines and was chosen for further in vivo study.     

Habitat preferences and distribution characteristics are indicative of species long-term persistence in the Estonian flora

Large-scale changes in regional floras provide direct information about changes in biodiversity through time and enable the evaluation of conservation targets. We compared the distribution ranges in 2004 of Estonian native terrestrial flora with the distribution ranges before 1970, using the Atlas of Estonian Flora. Relative persistence was related to species endemism, commonness, occurrence at its border of the global distribution range, main habitat type, sensitivity to human impact, life-form, conservation category, and Red List category. A literature-based database of the flora of Estonian habitat types was used to evaluate relative persistence of the flora of different habitats. Changes in the flora are largely dependent on human activities. The decrease in mire and grassland habitats and the increase in forests are reflected in the persistences of related species. Flora of mire habitats decreased the most. The fact that an almost ten-fold decrease of grasslands has not resulted in as large a decrease in the ranges of grassland species could serve as evidence of the extinction debt of these habitats. We also found a greater decrease among habitat specialists than habitat generalists and lower average persistence of the species of species-rich habitats. Our data show that current prioritization of species for conservation is in concordance with needs, as reflected in the changes in the range of species. However, conservation has not been entirely successful: the decrease of protected species continues. Our simple method for summarizing large databases was effective for the evaluation of large scale effects of conservation actions.     

From bog to fen: palaeoecological reconstruction of the development of a calcareous spring fen on Saaremaa,Estonia

Vegetation History and Archaeobotany - This study of the Kanna calcareous spring fen on Saaremaa, the largest island of Estonia, elucidates its history of fen development and vegetation diversity...     

Selenium toxicity: aminoacylation and Peptide bond formation with selenomethionine

Selenomethionine and methionine were compared as substrates for in vitro aminoacylation, ribosome binding, and peptide bond formation with preparations from wheat germ. Selenomethionine paralleled methionine in all steps of the translation process except peptide bond formation. Peptide bond formation with the initiating species of tRNA^Met demonstrated that selenomethionyl-tRNA^Met was less effective as a substrate than was methionyl-tRNA_f^Met. Participation of selenomethionine in the initiation process of translation could be expected to reduce the overall rate of protein synthesis and might aid in explaining selenium toxicity in selenium-sensitive plants.     

Kinesin motors: no strain, no gain

The processive movement of the dimeric motor protein kinesin 1 along microtubules requires communication between the two motor domains. Yildiz et al. (2008) now show that tension between the motor domains not only is necessary for normal processivity but also may be sufficient for motor motility under some conditions.     

The relative share of graminoid and forb life-forms in a natural gradient of herb layer productivity

The proportional share of graminoid and forb life-form in the herbaceous layer was investigated along a productivity gradient at Laelatu, western Estonia With an increase in the herbaceous layer standing crop from 43 5 to 723 7 g m⁻² the graminoid life-form became dominant in total above-ground mass and in species number Three hypotheses to better explain competitive ability of graminoids were tested 1) graminoids are able to form higher foliage, 2) they are able to distribute foliage nitrogen in a more beneficial way, 3) they have better nitrogen use efficiency 21 sample plots 50 × 50 cm were harvested All above-ground parts of vascular plants were removed by two canopy layers Vertical separation of layers were made according to the height of half light interception A species list was compiled, total and leaf masses and leaf nitrogen content of both life-forms were measured by layer ANOVA showed that there were no significant differences in vertical distribution of foliage or foliage nitrogen between life-forms in the productivity gradient, and hypotheses 1) and 2) are not supported by our data-set Hypothesis 3) is approved partly as the nitrogen concentration in graminoid foliage was 20% less than in forbs If one supposes that nitrogen retention time is equal in both life-forms then graminoids must have higher nitrogen use efficiency when compared to forbs Although the influence of life-form x productivity interaction on leaf nitrogen concentration was not significant, there was a tendency that difference in leaf mass to nitrogen ratio of the two life-forms increased with increasing incident light Thus, we can hypothesize that graminoid species dominate in high productive plots where the incident light intensity is also higher due to their better nitrogen use efficiency when compared to forb species