Ecological effects of lime treatment of acidified lakes and rivers in Sweden

Effects on the aquatic biota of lime (CaCO₃) application in acidified lakes and streams were studied in a number of waters. After treatment, lime-sensitive species of mosses (Sphagnum spp.) decreased, but species such as Potamogeton natans and Myriophyllum alterniflorum seemed to be favoured. A few years after liming species composition and diversity of phytoplankton, zooplankton and benthic insect larvae were almost identical to that found in oligotrophic and non-acid lakes. Molluscs and benthic crustaceans may have difficulties recolonizing. Reproduction of remaining species of fish was successful as soon as pH increased. High survival of larvae and fry can result in some extremely rich year classes with slow individual growth. In most cases restocking of depleted fish stocks was successful.     

Differential Inhibition of Cell Division in Euglena gracilis by Cysteamine and Cystamine

Cysteamine (2-aminoethanethiol) inhibited cell division in synchronously dividing cultures of Euglena gracilis at relatively low concentrations (0.005 M), Cystamine (2,2′-dithiobis(ethylamine). however, was only partially inhibitory at high concentrations (0.1 M). This differential inhibition may reflect certain unique features of nuclear division in euglenoid flagellates.     

Influence of some aliphatic alcohols on the metabolism of rat liver slices

The influence of some aliphatic alcohols on oxygen uptake, carbon dioxide production, acid formation and lactate and pyruvate concentrations of rat liver slices was studied. At the concentrations used, none of the alcohols was found to influence oxygen uptake. Of the alcohols that are not oxidized by liver alcohol dehydrogenase, methanol increased carbon dioxide production, propan-2-ol decreased it and 2-methylpropan-2-ol was without influence. All the alcohols that are oxidized by the enzyme strongly decreased carbon dioxide production. The alcohols that are not oxidized had no marked effect on the lactate/pyruvate concentration ratio, whereas the other alcohols strongly increased the ratio. A highly significant correlation was found between the effects of the alcohol on pyruvate concentration and carbon dioxide production. It is assumed that the shift in the redox potential inhibits the function of the tricarboxylic acid cycle of the liver.     

Linker insertion analysis of the FimH adhesin of type 1 fimbriae in an Escherichia coli fimH-null background

Abstract The gene encoding the Escherichia coli FimH adhesin of type 1 fimbriae has been subjected to linker insertion mutagenesis. Amino acid changes were introduced at a number of positions spanning the entire sequence in order to probe the structure-function relationship of the FimH protein. The effect of these mutations on the ability of bacteria to express a D-mannose binding phenotype was assessed in a fimH null mutant (MS4) constructed by allelic exchange in the E. coli K-12 strain PC31. Mutations mapping at amino acid residues 36, 58 and 279 of the mature FimH protein were shown to completely abolish binding to D-mannose receptors. Differences in the level of fimbriation were also observed as a result of some of the mutations in the fimH gene. These mutants may prove useful in dissecting receptor-ligand interactions by defining regions of the FimH protein that are important in erythrocyte binding.     

Genomic organization of a mouse MHC class II region including theH2-M andLmp2 loci

The region encompassing theMa, Mb1, Mb2, andLmp2 genes of the mouse class II major histocompatibility complex (MHC) was sequenced. Since this region contains clusters of genes required for efficient class I and class II antigen presentation, it was interesting to search for putative additional genes in the 21 kilobase gap between theMb1 andLmp2 genes. Computer predictions of coding regions and CpG islands, exon trapping experiments, and cross-species comparison with the corresponding human sequence indicate that no additional functional gene is present in that stretch. However, computer analysis revealed the possible existence of an alternative 3 exon forMb1. Except for the fact that the mouse MHC contains twoMb genes, the genomic organization of theH2-M loci was found to be almost identical to the organization of the humanHLA-DM genes. The promoter regions of theMa andMb genes also resemble classical class II promoters, containing typical S, X, and Y boxes. Like the human genes, the threeH2-M genes displayed very limited polymorphism when we compared the cDNA sequences from six haplotypes. Finally, comparison ofDMB withMb1 andMb2, both at the genomic level and in their coding regions, suggests that theMb gene was recently duplicated, probably only in certain rodents.     

Expression of two heterologous promoters, Agrobacterium rhizogenes rolC and cauliflower mosaic virus 35S, in the stem of transgenic hybrid aspen plants during the annual cycle of growth and dormancy

We monitored, for the first time, the activity of two model heterologous promoters, the Agrobacterium rhizogenes rolC and the cauliflower mosaic virus (CaMV) 35S, throughout the annual cycle of growth and dormancy in a perennial species, hybrid aspen. Each promoter was fused to the uidA -glucuronidase (GUS) reporter gene and the constructs were introduced into the hybrid aspen genome by Agrobacterium-mediated transformation. Both wildtype and transgenic plants were cultivated under different regimes of photoperiod and temperature to induce passage through one growth-dormancy-reactivation cycle, and at intervals GUS staining was assessed in stem sections. In rolC::uidA transformants, GUS activity in rapidly growing current-year shoots was not only tissue-specific, being localized to the phloem, but also cell-specific at the shoot base, where it was present only in the companion cells. However, during the onset of dormancy induced by short photoperiod, GUS activity shifted laterally from the phloem to include the cortex and pith. After subsequent exposure to chilling temperatures to induce the transition between the dormancy stages of rest and quiescence, GUS activity almost disappeared from all stem tissues, but regained its original phloem specificity and intensity after the shoots were reactivated by exposing them to long photoperiod and high temperatures. In contrast, GUS activity in the stem of 35S::uidA transformants was strong in all tissues except for the vascular cambium and xylem, and did not vary in intensity during the growth-dormancy-reactivation cycle. The lateral shift and increased intensity of GUS activity in the stem of rolC::uidA transformants during dormancy induction was shown to be associated with the accumulation of starch, and to be mimicked by incubating stem sections in sucrose, as well as glucose and fructose, but not sorbitol, prior to the GUS assay. Our results demonstrate that the activities of the rolC and 35S promoters varied in very different, unpredictable ways during the annual cycle of growth and dormancy in a perennial species, and indicate that the spatial and temporal variation in rolC promoter activity that we observed in the stem of transgenic hybrid aspen plants is attributable to cellular and seasonal changes in sucrose content.     

Species richness in mammalian herbivores: patterns in the boreal zone

Latitudinal gradients in species diversity are well established for a number of plant and animal taxa. Both historical and present-day environmental factors have been suggested to be responsible for observed patterns. We tested the hypothesis that current environmental features of the environment (primary productivity and regional landscape structure) may explain the longitudinal variation in species richness of mammalian herbivores in the Holarctic boreal zone. Mammalian herbivore species diversity was strongly correlated with a number of environmental variables measured. We reduced the data set by a principal components analysis (PCA), and found that in the Palearctic, species richness is positively related to warm climate (high temperature sum), the number of hardwood species, and the area of boreal forest. In the Nearctic, species richness increases as the length of the growing season and the number of coniferous tree species increase. Thus indirect measures of primary productivity as well as tree species number may accurately predict species richness in mammalian herbivores. In addition, there seems to be a strong species-area effect at the regional level. The larger and more homogeneous in terms of forest coverage a boreal section is, the more species coexist there.