Do grasslands act as a perpetual sink for carbon?

It is increasingly commonly suggested that grasslands are a perpetual sink for carbon, and that just maintaining grasslands will yield a net carbon sink. I examine the evidence for this from repeated soil surveys, long term grassland experiments and simple mass balance calculations. I conclude that it is untenable that grasslands act as a perpetual carbon sink, and the most likely explanation for observed grassland carbon sinks over short periods is legacy effects of land use and land management prior to the beginning of flux measurement periods. Simply having grassland does not result is a carbon sink, but judicious management or previously poorly managed grasslands can increase the sink capacity. Given that grasslands are a large store of carbon, and that it is easier and faster for soils to lose carbon that it is for them to gain carbon, it is an important management target to maintain these stocks.     

Do ribosomal RNAs act merely as scaffold for ribosomal proteins?

Investigations that are being carried out in various laboratories including ours clearly provide the answer which is in the negative. Only the direct evidences obtained in this laboratory will be presented and discussed. It has been unequivocally shown that the interaction between 16S and 23S RNAs plays the primary role in the association of ribosomal subunits. Further, 23S RNA is responsible for the Binding of 5S RNA to 16S.23S RNA complex with the help of three ribosomal proteins, L5, L18, L15/L25. The 16S.23S RNA complex is also capable of carrying out the following ribosomal functions, although to small but significant extents, with the help of a very limited number of ribosomal proteins and the factors involved in protein synthesis: (a) poly U-Binding, (B) poly U-dependent Binding of phenylalanyl tRNA, (c) EF-G-dependent GTPase activity, (d) initiation complex formation, (e) peptidyl transferase activity (puromycin reaction) and (f) polyphenylalanine synthesis. These results clearly indicate the direct involvement of rRNAs in the various steps of protein synthesis. Very recently it has Been demonstrated that the conformational change of 23S RNA is responsible for the translocation of peptidyl tRNA from the aminoacyl (A) site to the peptidyl (P) site. A model has Been proposed for translocation on the Basis of direct experimental evidences. The new concept that ribosomal RNAs are the functional components in ribosomes and proteins act as control switches may eventually turn out to Be noncontroversial.     

Do N-glycoproteins have preference for specific sequons?

Protein N-glycosylation requires the presence of asparagine (N) in the consensus tri-peptide NXS/T (where X is any amino acid, S is serine and T is threonine). Several factors affect the glycosylation potential of NXS/T sequons and one such factor is the type of amino acid at position X. While proline was shown to negatively affect N-glycosylation, the nature of other amino acids at this position is not clear. Using Markov chain analysis of tri-peptide NXS/T from viral, archaeal and eukaryotic proteins as well as experimentally confirmed N-glycosylated sequons from eukaryotic proteins, we show here that the occurrence of most sequon types differ significantly from the expected probability. Sequon types with F, G, I, S, T and V amino acids are consistently preferred while those with P and charged amino acids are under-represented in all four groups. Further, proteins contained far fewer number of possible sequon types (maximum 20 types for NXS or NXT taken separately) for any given number of sequons, which may be explained based on random sampling. Consistent with the present finding, majority of the over-represented sequons found in two important viral envelope glycoproteins (hemagglutinin of influenza A H3N2 and glycoprotein120 of HIV-1) are indeed preferred sequon types, which may provide a selective advantage. Accordingly, although there seems to be some preference for sequons, this preference may not be unique to N-glycosylation.     

Does the major histocompatibility complex serve as a specific receptor for Semliki Forest virus?

Murine F9 and PCC4 teratoma cells do not express H-2 major transplantation antigens according to virus-specific T-lymphocyte cytotoxic or serological assays. However, such cells can be infected with and readily replicate many types of viruses (coxsackie B 3, mouse hepatitis, Sindbis, Semliki Forest [SFV], lymphocytic choriomeningitis, Pichinde, vesicular stomatitis, herpes simplex type 1) to the same extent as do murine F12 teratoma cells and mouse embryo fibroblasts, all of which express the H-2 determinants. In contrast, F9 and PCC4 cells are not productively infected with murine cytomegalovirus, whereas F12 and mouse embryo fibroblast cells are. In addition to replicating in H-2-negative murine teratoma cells, SFV replicates in H-2-negative murine lymphoblastoid cells. The ability of SFV to infect cells without H-2 antigens and then to effect viral antigenic expression in the cells' cytoplasm and on their surface with similar kinetics and in equivalent amounts as cells with H-2 antigens indicates that the H-2 receptor is not needed for SFV infection. Daudi cells, which lack HLA antigens, block the replication of SFV. This occurs at some point after receptor binding, as demonstrated by diminished viral mRNA. In addition, a possible membrane defect precludes viral exit in Daudi cells transfected with SFV infectious RNA. These results indicate that a cell's possession of H-2 antigens is not a requirement for SFV infection and that major histocompatibility complex antigens are not specific receptors for this virus.     

AMPK β subunits display isoform specific affinities for carbohydrates

AMP-activated protein kinase (AMPK) is a heterotrimer of catalytic (α) and regulatory (β and γ) subunits with at least two isoforms for each subunit. AMPK β1 is widely expressed whilst AMPK β2 is highly expressed in muscle and both β isoforms contain a mid-molecule carbohydrate-binding module (β-CBM). Here we show that β2-CBM has evolved to contain a Thr insertion and increased affinity for glycogen mimetics with a preference for oligosaccharides containing a single α-1,6 branched residue. Deletion of Thr-101 reduces affinity for single α-1,6 branched oligosaccharides by 3-fold, while insertion of this residue into the equivalent position in the β1-CBM sequence increases affinity by 3-fold, confirming the functional importance of this residue.     

Do movement behaviors identify reproductive habitat sampling for wild turkeys?

Selection of habitats has regularly been suggested to influence species demography at both local and broad scales. The expectation is that selection behaviors have positive benefits via greater fitness or increased survival. The current paradigm of habitat selection theory suggests a hierarchical process, where an individual first selects where they choose to live (e.g., range) and then searches and selects locations within this range meeting life history needs. Using high‐frequency GPS data collected from reproductively active Rio Grande (n = 21) and Eastern (n = 23) wild turkeys, we evaluated a long‐standing theory for ground‐nesting galliformes, in that movements during the prenesting period are behaviorally focused on sampling available habitats to optimize the selection of nesting sites. Contrary to expectations, we found no evidence that reproductively active females engage in habitat sampling activities. Although most nest sites (>80% for both subspecies) fell within the prenesting range, the average minimum daily distance from nest sites for Rio Grande and Eastern wild turkey females was large [1636.04 m (SE = 1523.96) and 1937.42 m (SE = 1267.84), respectively] whereas the average absolute minimum distance from the nest site for both Rio Grande and Eastern wild turkey females was 166.46 m (SE = 299.34) and 235.01 m (SE = 337.90), respectively, and showed no clear temporal reduction as laying approached. Overall, predicted probability that any female movements before laying were initiated intersected with her nesting range (area used during incubation) was <0.25, indicating little evidence of habitat sampling. Our results suggest that the long‐standing assumption of hierarchical habitat selection by wild turkeys to identify nest sites may be incorrect. As such, habitat selection may not be the proximate driver of nest success and hence population‐level fitness. Rather, based on our results, we suggest that wild turkeys and other ground‐nesting species may be fairly plastic with regard to the selection of reproductive habitats, which is appropriate given the stochasticity of the environments they inhabit.     

Do rivers function as corridors for plant dispersal?

Abstract. We evaluated the importance of dispersal for species frequencies and distribution by comparing dispersal properties of vascular plant species with their frequencies along river banks. We assumed that species with long-floating seeds would be more frequent than species with short-floating seeds. We compiled data on frequencies of vascular plants and their dispersal properties from ten rivers in northern Sweden and compared these with boreal forests and grasslands in the same region. In all rivers, but in none of the reference areas, there was a positive relationship between floating capacity and frequency of species. A comparison of floating capacity between species with and without certain dispersal devices showed that seeds of vegetatively dispersed species had higher floating capacities than other seeds. For other dispersal categories (animal and wind dispersal), floating time did not differ from contrast groups. The results indicate that water dispersal has a certain role in structuring the riparian flora, and provide a basis for explaining species distribution patterns from dispersal characteristics. They also suggest that continuous river corridors are important for maintaining regional biodiversity.     

NMDA receptor signaling: death or survival?

Glutamate-induced neuronal damage is mainly caused by overactivation of N-methyl-D-aspartate (NMDA) receptors.Conversely,normal physiological brain function and neuronal survival require adequate activ...     

Do DNA polymerases delta and alpha act coordinately as leading and lagging strand replicases?

The activity ratio of DNA polymerases delta and alpha in calf thymus was found to be invariably 1:1, irrespective of extraction procedure (8 types) and subcellular localization (cytoplasm, nucleus and microsomes). This was established by separation of the two forms by hydroxyapatite chromatography and by their response to specific inhibitors and monoclonal antibodies. This finding supports the dimeric DNA polymerase model [(1980) J. Biol. Chem. 255, 4290-4303], which proposes that DNA polymerases delta and alpha act coordinately as leading and lagging strand enzymes, respectively, at the replication fork.     

Can freshwater mites act as forensic tools?

Determination of post-mortem interval often employs analysis of age structure and diversity of saprophilic arthropods (including mites) that have colonized corpses. The majority of research has focused on decomposition processes in terrestrial situations, with relatively few studies on the utility of freshwater invertebrates as forensic agents. Most freshwater mites are predators, detritivores or algivores, and hence seem unlikely candidates as tools for aging or determining original placement of corpses or other bodily remains. The main exceptions to this are some aquatic Astigmata, which have occasionally been observed feeding on the tissues of moribund aquatic animals. Here I investigate Canadian law literature and published forensic research to determine how frequently freshwater mites are included in court cases or are found attending dead bodies. I found only one questionable report of aquatic mites in over 30 years of material from legal databases. Three published research papers reported mites associated with vertebrate flesh in fresh water. Only one paper provided an identification of mites finer than ‘Acari’ or ‘water mites’. In this case, the mites were identified as Hydrozetes (Oribatida). In none of these papers were mites reported to be high in abundance or biomass, and in two of the three publications methodological problems and/or poor reporting of data raised doubts about interpretation of results. I conclude that based on their biology, there is little expectation that freshwater mites should be of great value as forensic tools, and this survey of legal and scientific literature supports my argument.     

Do environmental changes or juvenile competition act as mechanisms of species displacement in crayfishes?

The Big Creek Crayfish, Orconectes peruncus, is native to the St. Francis River drainage in Missouri, USA and is often absent where the introduced Woodland Crayfish, Orconectes hylas, has established. We performed a field experiment to determine whether effects of current abiotic conditions and interspecific competition with O. hylas were responsible for displacement of O. peruncus from parts of their former range. We examined growth and survival of juvenile male O. peruncus exposed to juvenile male O. hylas in enclosures at two sites in the former range of O. peruncus. Enclosures contained 8 (low density) or 16 individuals (high density) and had O. peruncus only (control) or both species (interspecific treatment). Juvenile O. peruncus were able to survive and grow in portions of their former range, implicating biotic versus abiotic factors in the displacement of O. peruncus. Survival rates of O. peruncus did not differ among treatments at either site. Orconectes peruncus showed significant growth in all treatments and interspecific effects were not greater than intraspecific effects on O. peruncus growth rates. High-density treatments showed significantly reduced O. peruncus growth rates compared to low-density treatments, except in Carver Creek interspecific treatments. When considered in the context of previous studies examining the effects of O. hylas on O. peruncus, results suggest that neither direct competition between juvenile males of the two species or abiotic change are responsible for the decreased range of O. peruncus. Additional research is required to determine the mechanism(s) driving the displacement of O. peruncus.     

What mechanisms underlie involvement of different NMDA receptor subunits in the induction of hippocampal long-term potentiation and long-term depression?

There is a point of view that N-methyl-D-aspartate (NMDA) receptor subunit-specific signaling outcomes determine the direction of modifications of efficacy of synaptic transmission. Activation of NMDA receptors that contain the 2A subunit promotes LTP, while LTD requires activation of NMDA receptors containing 2B subunit. However, this hypothesis is inconsistent with some experimental data. For explanation of these data, we put forward an alternative hypothesis. According to this hypothesis, the activation of diverse subtypes of NMDA receptors can lead to ether LTP or LTD depending on the relation between posttetanic Ca2+ rise and increase in postsynaptic Ca2+ concentration produced by previous stimulation. Activation of NMDA receptors with 2B subunit can promote LTD of excitatory input to the pyramidal cell due to presence of these receptors on inhibitory interneurons, induction of the LTP in interneuron, and potentiation of inhibitory transmission between the interneuron and the target pyramidal cell.