Low reaction temperature increases the selectivity in an enzymatic reaction due to substrate solvation effects

Immobilized a-chymotrypsin was used as catalyst for studying temperature effects on acyl transfer reactions (acyl-donor: Bz-TyrOEt) in a water-immiscible organic solvent. The solubility of the two nucleophiles, Phe-NH and water, decreased with decreasing temperature. The relative decrease for the amide was larger (2.4-fold) than for water. Therefore the thermodynamic activity (estimated by the relative saturation) increased more for this substrate and hence the selectivity in the reaction was increased.     

Spatial and temporal variation in distribution of Gelidium canariensis (Rhodophyta) from natural populations of the Canary Islands

This study was designed to investigate spatial and temporal variation in Gelidium canariensis populations at two shores in northern Gran Canaria during two years. Spatial scales ranged from some hundred meters (distance between shores), 10 to 30 m (distance between plots) to less than 3 m (distance between quadrats). Gelidium individuals were defined as distinct Gelidium clumps. The results show a significant difference in size of clumps between shores, but not on the smaller spatial scales. No significant temporal variation was found. There was no significant temporal or spatial variation in standing crop or density (counts made in quadrats where Gelidium was present, rather than counts for the total shore). Sporophytic and gametophytic clumps were also distinguished by identifying reproductive structures in the field. The total proportion of sporophytes was larger than the proportion of gametophytes, but at a smaller scale there could be a shift in dominance. The survival rate of clumps was similar between shores with a mean survival rate of 85%, but there was a significant difference in recruitment between shores. The results indicate a stable population structure. This revised version was published online in June 2006 with corrections to the Cover Date.     

In vitro pollen competitive ability in Viola tricolor: temperature and pollen donor effects

In this study on Viola tricolor pollen, the competitive ability of 16 pollen donors originating from a wild population was analysed in a set of greenhouse and germination temperatures. The aim was to examine the consistency in donor pollen performance across temperatures and to see whether variation in performance was random or due to individual differences in the plastic response to temperature. Pollen tube growth rate in vitro was investigated in two greenhouse temperatures (on the day pollen was collected) and in four germination temperatures. In addition, pollen tube growth rate was assessed in vivo (in one temperature) to examine the relationship between in vivo and in vitro growth. A temperature difference of 5 K - corresponding to natural variation in time and space detected in the field - affected pollen tube growth rate. For both temperature components, significant pollen donor by temperature interactions were found and rank order of pollen donors changed across treatments. Although pollen competitive ability in violets was strongly influenced by both temperature components, the occurrence of pollen donor by temperature interactions indicates that donor siring ability varies with temperature. This, in turn, may suggest a means to maintain pollen competitive ability despite selection for this trait.     

Formation and characterisitcs of hepatic dexamethasone-receptor complexes of different molecular weight

The dexamethasone-binding receptor protein in rat liver cytosol has a Stokes radius of 61 Å and a sedimentation coefficient of 4.0 S. In contrast, cell nuclei labelled with [³H]dexamethasone in vivo or in vitro (reconstitution experiments with [³H]dexamethasone-labelled cytosol and isolated unlabelled nuclei) contain a high-salt-extractable dexamethasone-receptor complex with a Stokes radius of 30–36 Å and a sedimentation coefficient of 3.2 S. Exposure of liver homogenate or 1000 × g homogenate supernatant to low ionic strenght during preparation of cytosol resulted in conversion of the 61 Å to a 36 Å complex very similar to the intranuclear form of dexamethasone receptor. 61 → 36 Å complex-verting activity was present in both the 100 × g ?10 000 × g sediment of liver homogenate, from which it could be extracted by hypotonic media, and in the liver cell nuclei, from which it could be extracted by hypertonic media. Mild digestion of the 61 Å dexamethasone-receptor complex with trypsin also gave rise to a complex with a Stokes radius of 36 Å. Reconstitution experiments with isolated liver cell nuclei indicated that both the 61 Å and 36 Å dexamethasone-receptor complexes were taken up by the nuclei; reextraction of the nuclei incubated with the 61 Å complex revealed that this form had been converted to the 30–36 Å complex.Further digestion of teh 61 and 36 Å [³H]dexamethasone-receptor complexes with hypotonic extract of the 1000 × g ?10 000 × g sediment of liver homogenate or with trypsin resulted in formation of a third complex with a Stokes radius of 19 Å and a sedimentation coefficient of 2.5 S. The approximate molecular weights of the 61, 36 and 19 Å dexamethasone-receptor complexes were calculated as 102 000, 46 00 and 19 000, respectively, and the frictional ratios of the molecules as 1. 84, 1. 38 amd 1.00, respectively.It is concluded that the nuclear 30–36 Å dexamethasone-receptor complex is formed from the cytosol 61 Å complex by proteolytic digestion and that this latter protein contains at least two sites with a relatively high sensitivity to protelytic cleavage.     

Modeling Response of N Addition on C and N Allocation in Scandinavian Norway Spruce Stands

Because nitrogen is considered to be the major growth-limiting element in boreal forests, the increasing nitrogen availability from deposition should lead to increasing growth. We have tested this assumption by simulating, with a simple model, carbon and nitrogen development in seven long-term fertilization experiments in three Nordic countries. The only differences between sites in the model are climate, the ambient nitrogen deposition, nitrogen fertilization regimes, and the initial conditions at the start of the experiment. The model simulates the observed stand development well as long as nitrogen remains the limiting factor. The simulated retention of deposited nitrogen is in general low (less than 50%), whereas retention of fertilizer nitrogen is higher. This seems to imply that the higher production in the fertilized stands will not be maintained once the fertilization is stopped. The model results also indicate that the major effect of climate on site productivity is through soil processes, not tree physiology.     

Phylogenetic relationships of Microdontinae (Diptera: Syrphidae) based on molecular and morphological characters

The intrasubfamilial classification of Microdontinae Rondani (Diptera: Syrphidae) has been a challenge: until recently more than 300 out of more than 400 valid species names were classified in Microdon Meigen. We present phylogenetic analyses of molecular and morphological characters (both separate and combined) of Microdontinae. The morphological dataset contains 174 characters, scored for 189 taxa (9 outgroup), representing all 43 presently recognized genera and several subgenera and species groups. The molecular dataset, representing 90 ingroup species of 28 genera, comprises sequences of five partitions in total from the mitochondrial gene COI and the nuclear ribosomal genes 18S and 28S. We test the sister‐group relationship of Spheginobaccha with the other Microdontinae, attempt to elucidate phylogenetic relationships within the Microdontinae and discuss uncertainties in the classification of Microdontinae. Trees based on molecular characters alone are poorly resolved, but combined data are better resolved. Support for many deeper nodes is low, and placement of such nodes differs between parsimony and Bayesian analyses. However, Spheginobaccha is recovered as highly supported sister group in both. Both analyses agree on the early branching of Mixogaster, Schizoceratomyia, Afromicrodon and Paramicrodon. The taxonomical rank in relation to the other Syrphidae is discussed briefly. An additional analysis based on morphological characters only, including all 189 taxa, used implied weighting. A range of weighting strengths (k‐values) is applied, chosen such that values of character fit of the resulting trees are divided into regular intervals. Results of this analysis are used for discussing the phylogenetic relationships of genera unrepresented in the molecular dataset.     

Anther extrusion and plant height are associated with Type I resistance to Fusarium head blight in bread wheat line ‘Shanghai-3/Catbird’

Fusarium head blight (FHB) is a destructive wheat disease of global importance. Resistance breeding depends heavily on the Fhb1 gene. The CIMMYT line Shanghai-3/Catbird (SHA3/CBRD) is a promising source without this gene. A recombinant inbred line (RIL) population from the cross of SHA3/CBRD with the German spring wheat cv. Naxos was evaluated for FHB resistance and related traits in field trials using spray and spawn inoculation in Norway and point inoculation in China. After spray and spawn inoculation, FHB severities were negatively correlated with both anther extrusion (AE) and plant height (PH). The QTL analysis showed that the Rht-B1b dwarfing allele co-localized with a QTL for low AE and increased susceptibility after spawn and spray inoculation. In general, SHA3/CBRD contributed most of the favorable alleles for resistance to severity after spray and spawn inoculation, while Naxos contributed more favorable alleles for reduction in FDK and DON content and resistance to severity after point inoculation. SHA3/CBRD contributed a major resistance QTL close to the centromere on 2DLc affecting FHB severity and DON after all inoculation methods. This QTL was also associated with AE and PH, with high AE and tall alleles contributed by SHA3/CBRD. Several QTL for AE and PH were detected, and low AE or reduced PH was always associated with increased susceptibility after spawn and spray inoculation. Most of the other minor FHB resistance QTL from SHA3/CBRD were associated with AE or PH, while the QTL from Naxos were mostly not. After point inoculation, no other QTL for FHB traits was associated with AE or PH, except the 2DLc QTL which was common across all inoculation methods. Marker-assisted selection based on the 2DLc QTL from SHA3/CBRD combined with phenotypic selection for AE is recommended for resistance breeding based on this valuable source of resistance.