How can we protect rare hemiparasitic plants? Early-flowering taxa ofEuphrasia andRhinanthus on the Baltic island of Gotland

Euphrasia stricta var.suecica, E. stricta var.tenuis, andRhinanthus serotinus subsp.vernalis are three endangered, hemiparasitic annual herbs found in traditionally managed hay meadows on Gotland, Sweden. We have studied — experimentally and in the field — how some features in the present and traditional management cycle affect their fitness. We set up permanent 50 × 50-cm plots in a coastal hay meadow where bothE. stricta var.suecica andRhinanthus are still quite common. The survival, growth and fecundity of cohorts ofEuphrasia andRhinanthus were followed throughout the growing season for three years. The length of the growing season was vital forEuphrasia andRhinanthus performance. In cooler summers, the percentage ofEuphrasia individuals that produced mature seeds was decreased by 20% at the time of mowing. This indicates the need to individually adjust the time of mowing, as was formerly done, to the actual phenological development in order to maintain healthy populations. It is also important to consider the effect of time of mowing on total species richness, asEuphrasia more successfully established in 10 × 10-cm squares with high species richness. Also, the time in spring when hemiparasite growth started was crucial. Cohorts of bothEuphrasia stricta var.suecica andRhinanthus that connected to hosts and started growing early in the season had a strong advantage over later cohorts by having fitness values four to eight times higher. From this we conclude that the traditional practice of spring raking is important for the long-term persistence of these hemiparasites, since raking promotes an earlier onset of both host and hemiparasite growth. Another important issue is the traditional, but nowadays often neglected practice of letting the hay dry in the meadow after mowing. Hay that was left to dry in the meadow contributed significantly moreRhinanthus seed to the meadow than hay that was taken away immediately after mowing. We also found that seedling emergence and subsequent growth ofEuphrasia stricta var.suecica was greatly enhanced by a second hay cut in September. A second cutting mimics some of the positive effects of the traditional practice of aftermath grazing, which is nowadays often abandoned.     

Composition and diversity of bird communities in Swedish farmland–forest mosaic landscapes

CapsuleThe amount of forest (at local and landscape scales) and occurrence of residual habitats at the local scale are shown to be the major factors influencing bird community composition in farmland–forest landscapes in central Sweden.

Aims To investigate the importance of local habitat and landscape structure for breeding birds in farmland–forest landscapes in central Sweden.

Methods Breeding birds were censused at 292 points. A detailed habitat mapping was made within 300 m of the points. Within a 300–600 m radius only two major habitats (forests and arable fields) were identified.

Results Cluster analyses of bird communities identified three site types that also differed in habitat composition: (i) partially forested sites in forested landscapes; (ii) heterogeneous sites with residual habitats in mosaic landscapes; and (iii) field-dominated farmland sites in open landscapes. A total of 19 of 25 farmland bird species (restricted to farmland or using both farmland and forest) had the highest abundance in farmland sites with mosaics of forest and farmland, while only six farmland species had the highest abundance in field-dominated sites. The bird community changed from being dominated by farmland species to being dominated by forest species (common in forest landscapes without farmland) at small proportions (10–20%) of forest at the local scale. A major difference in habitat composition between heterogeneous and field-dominated sites was the occurrence of different residual habitats (e.g. shrubby areas and seminatural grasslands). These habitats seemed to influence bird community composition more than land-use, despite covering <10% of the area. Seminatural grasslands were important for bird community composition and species-richness, but grazing seemed to be less important. Among different land-use types, cereal crops were the least preferred fields. Set-asides with tall vegetation and short rotation coppices were positively associated with species-richness of farmland birds.

Conclusion In general, the composition of the landscape was important for bird community composition, although amount and distribution of forests, occurrence of residual habitats and land-use of fields at the local scale had the strongest influence on bird community composition. The possible implications of these patterns for managing farmland–forest landscapes are discussed.     

Collagen binding toEscherichia coli strain NG7C

Escherichia coli strain NG7C was shown to bind iodine-labeled human type IV collagen (Cn). The binding was rapid and saturable. The number of binding sites was estimated to be 1.5×10⁴ sites/cell and the dissociation constant 85 nM. The binding was inhibited by unlabeled type I, type IV, and type X Cn, gelatin and, at high doses by vitronectin and fibrinogen. Heat treatment of bacteria abolished the binding. A cell sonicate of strain NG7C inhibited the binding. Heat or protease treatment of the sonicate reduced its inhibitory activity by more than 50% Cell surface extracts of strain NG7C likewise inhibited Cn binding. Cells ofE. coli NG7C also bound to type IV Cn immobilized on microtiter plates. The Cn binding appears to be mediated by cell surface protein(s). Type IV Cn binding toE. coli NG7C differed from the earlier reported Cn binding mechanisms toE. coli, i.e., binding of soluble type II Cn, and from binding of immobilized type V Cn by enterobacteria.E. coli strains can thus produce different surface proteins which mediate binding to collagens. Expression of Cn binding byE. coli may enhance colonization of subepithelial tissues.     

Separation of rat leukocytes by countercurrent distribution in aqueous two-phase systems. I. Characterization of subpopulations of cells.

Cells from rat spleen, lymph nodes, and thoracic duct were separated by countercurrent distribution in aqueous two-polymer phase systems containing dextran and polyethylene glycol. Lymphoid cells from the different organs gave distinct, highly reproducible distribution patterns. The yield of separated cells and their viability compared well with other methods of physical separation. The majority of the leukocytes was separated from erythrocytes. Cells with surface immunoglobulin were recovered in one side of the distribution, while thymus-derived lymphocytes as determined by indirect immunofluorescence and histochemical staining were found in all fractions. However, cells responding to PHA and Con A were concentrated in a small area of the distribution, indicating a separation of subpopulations of thymus-derived lymphocytes.     

Differential expression of VRN1 and other MADS-box genes in Festuca pratensis selections with different vernalization requirements

Most perennial and winter annual temperate grasses have a vernalization requirement (VR) for flowering, that is, they require a cold period before they can flower in response to long days. From a F1 mapping population of the outbreeding perennial forage grass Festuca pratensis Huds. (meadow fescue) previously used to map several quantitative trait loci (QTLs) for VR, we produced two F2 populations divergently selected for high or low VR. The two populations were characterised for flowering behaviour and gene expression of VRN1 as well as other MADS-box genes with a putative function in the induction of flowering. Expression of FpVRN1 and the VRN1-like genes FpMADS2 and FpMADS3 was associated with flowering but the response of gene expression to vernalization differed between genes and populations. The expression of the SVP-like genes FpMADS10 and FpMADS16 was not affected by vernalization and did not differ between the two F2 populations.     

An efficient assay for dolichyl phosphate-mannose: protein O-mannosyltransferase

A novel method for quantifying the reaction product from dolichyl phosphoryl mannose:polypeptide mannosyltransferase (protein mannosyl transferase; PMT), was developed. The assay quantifies the amount of radioactivity incorporated into the acceptor peptide YNPTSV from dolichyl phosphoryl [3H]mannose (Dol-P-Man). A novel delivery system, large unilamellar vesicles (LUV), composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), is used to keep the poorly soluble donor substrate, Dol-P-Man, in solution. The use of LUV allows generation of truly reproducible data and, as an additional benefit, also results in a more than 10 times increase in transfer efficiency. In contrast to the solvent extraction procedures commonly used in previously described PMT assays, the assay reaction product is separated from the radioactive donor substrate on C(18) cartridges. The use of C(18) cartridges allows generation of reproducible data with a low, consistent background and also produces a significant reduction in the time and labor needed for the product workup. In a reaction mixture consisting of 100 microg POPC LUV, 9 x 10(5)cpm (approximately 15 pmol) Dol-P-Man, 100 nmol YNPTSV, and aproximately 4 microg of crude yeast microsomal extract, time-dependent formation of glycosylated product obeys Michaelis-Menten-type kinetics throughout the course of the reaction-until exhaustion of the donor substrate. The linear initial rates of the reaction allowed calculation of an apparent K(m) of 1mM, for the acceptor peptide YNPTSV. Variations in detergent concentration in the assay influence transfer efficiency, possibly through interference with the LUV-based donor substrate delivery system. Hence detergent concentrations should be kept constant.     

Function of the lectin domain of polypeptide N-acetylgalactosaminyltransferase 1

All UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases cloned to date contain a lectin domain at the C-terminus, consisting of three tandem repeat sequences (alpha,beta, and gamma). We previously reported that the alpha repeat of one of the most ubiquitous isozymes, GalNAc-T1, is a functional lectin that recognizes O-linked GalNAc residues on the acceptor polypeptides with multiple acceptor sites; the domain appears not to be involved in the glycosylation of acceptors with a single acceptor site. In this report, we studied the function of the beta and gamma repeats in the GalNAc-T1 lectin domain, by site-directed mutagenesis and analysis of the catalytic properties of mutant enzymes. We found that the beta repeat recognizes GalNAc and is involved in glycosylation of acceptors with multiple glycosylation sites. The gamma repeat, on the other hand, showed no significant GalNAc-binding activity. These results indicate that the lectin domain of GalNAc-T1 has at least two functional repeats, allowing the possibility of multivalent interactions with GalNAc residues on the acceptor polypeptide during glycosylation.     

The acceptor specificity of UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases

The in vitro and in vivo specificity of the family of peptide:N-acetylgalactosaminyltransferases (GalNAcT) is analyzed on the basis of the reactivity and/or inhibitory activity of peptides and protein segments. The transferases appear to be multi-substrate enzymes with extended active sites containing a least nine subsites that interact cooperatively with a linear segment of at least nine amino acid residues on the acceptor polypeptide. Functional acceptor sites are located on the surface of the protein and extended conformations (-strand conformation) are preferred. The acceptor specificity of GalNAc-T can be predicted from the primary structure of the acceptor peptide with an accuracy of 70 to 80%. The same GalNAc-T enzymes catalyze the glycosylation of both serine and threonine residues. The higher in vitro catalytic efficiency toward threonine versus serine is the result of enhanced binding as well as increased reaction velocity, both effects being the result of steric interactions between the active site of the enzyme and the methyl group of threonine. Results from substrate binding studies suggest that GalNAc-T catalyzed transfer proceeds via an ordered sequential mechanism.