Trends and uncertainties in Siberian indicators of 20th century warming

Estimates of past climate and future forest biomass dynamics are constrained by uncertainties in the relationships between growth and climatic variability and uncertainties in the instrumental data themselves. Of particular interest in this regard is the boreal-forest zone, where radial growth has historically been closely connected with temperature variability, but various lines of evidence have indicated a decoupling since about the 1960s. We here address this growth-vs.-temperature divergence by analyzing tree-ring width and density data from across Siberia, and comparing 20th century proxy trends with those derived from instrumental stations. We test the influence of approaches considered in the recent literature on the divergence phenomenon (DP), including effects of tree-ring standardization and calibration period, and explore instrumental uncertainties by employing both adjusted and nonadjusted temperature data to assess growth-climate agreement. Results indicate that common methodological and data usage decisions alter 20th century growth and temperature trends in a way that can easily explain the post-1960 DP. We show that (i) Siberian station temperature adjustments were up to 1.3 °C for decadal means before 1940, (ii) tree-ring detrending effects in the order of 0.6–0.8 °C, and (iii) calibration uncertainties up to about 0.4 °C over the past 110 years. Despite these large uncertainties, instrumental and tree growth estimates for the entire 20th century warming interval match each other, to a degree previously not recognized, when care is taken to preserve long-term trends in the tree-ring data. We further show that careful examination of early temperature data and calibration of proxy timeseries over the full period of overlap with instrumental data are both necessary to properly estimate 20th century long-term changes and to avoid erroneous detection of post-1960 divergence.     

The Assimilation of Nitrogen from Ammonium Salts and Nitrate by Fungi

1. The assimilation of inorganic nitrogen by Scopulariopsis brevicaulisand some physiologically similar species has been studied. Theirfailure to assimilate completely from ammonium sulphate hasbeen shown to be due to the fall in pH of the medium inducedby the initial uptake of ammonia.
2. Complete assimilation ofammonia takes place in the presenceof the neutral salts ofeach of thirteen organic acids investigated.The organic acidsact primarily through their buffering effectwhich preventsor slows down the fall in pH. They are not specificallyrequiredfor ammonia assimilation by these fungi and can beeffectivelyreplaced by certain inorganic buffers.
3. The influence of severalexternal factors on the rate of assimilationof ammonia, nitrate,and nitrite has been studied in S. brevicaulis.In correspondingconditions the mycelium assimilates ammoniamore rapidly thannitrate over a wide range of conditions.
4. Ammonia, even invery low concentration, completely suppressesnitrate assimilationwhen both sources of nitrogen are presenttogether. Nitrite,however, is assimilated simultaneously withammonia. It is thereforeconcluded that ammonia blocks the reductionof nitrate to nitriteby the fungus.
5. The suppression of nitrate assimilation inthe presence of ammoniais common to many mould fungi besidesS. brevicaulis, and isbelieved to have adaptive significancein natural habitats.
6. The nitrate-reducing and assimilatingsystem is formed, evenwhen S. brevicaulis is grown in completeabsence of nitrate(ammonia medium with organic acid). It comesinto action rapidlywhen the inhibiting effect of ammonia isremoved. Similarly,nitrate-grown mycelium is capable of assimilatingammonia atmaximal rate without any adaptive lag.

     

Extra-pair paternity in the strongly monogamous Wandering Albatross Diomedea exulans has no apparent benefits for females

Although 92% of avian species are socially monogamous, extra-pair copulation (EPC), resulting in extra-pair paternity (EPP), is a common reproductive strategy in birds. Among seabirds, in which the rate of social monogamy reaches 100%, Procellariiformes (albatrosses and petrels) show low EPP rates, with the noticeable exception of the only albatross investigated in this regard, the Waved Albatross Phoebastria irrorata . This species, in which forced copulations are known to occur, showed a surprisingly high rate of EPP (25% of chicks). We investigate here EPP rates in another albatross species, the Wandering Albatross Diomedea exulans , subject to a demographic survey conducted for 38 years. We combined data on pair bonds with analysis of ten microsatellite loci and found that 10.7% of 75 chicks had an extra-pair sire. Although there was some evidence for inbreeding avoidance, within-pair and extra-pair chicks showed similar levels of heterozygosity, and the incidence of EPP was independent of age, experience or past reproductive success. Hence, we found no evidence that females benefit from EPCs. Owing to the male-biased sex ratio in adults, widowed and divorced males required more time to find a new mate (+28 and +72%, respectively) than did females. Combined with high sexual size dimorphism, this phenomenon might promote the forced copulations observed in this species. Our data therefore suggest that EPC is beneficial to unpaired males but occurs at random in females, consistent with the hypothesis that EPP results solely from forced EPCs. However, the importance of the latter for EPP and the part played by solitary males require further investigation.     

Preparation of mycoplasma immunogens from plants and a comparison of polyclonal and monoclonal antibodies made against primula yellows MLO-associated antigens

A method is described for obtaining from plants partially purified preparations of mycoplasma-like organisms (MLO) which are suitable for use as immunogens for polyclonal or monoclonal antibody production, and as antigens for directly coating ELISA plates. Using this method a mouse monoclonal antibody to primula yellows MLO was prepared, and its characteristics compared with those of primula yellows polyclonal antibodies from rabbits and also against polyclonal antibodies made to similar preparations of European aster yellows MLO. No serological distinction was obtained between any of the homologous or heterologous combinations of antibody and MLO preparation using ELISA, fluorescence microscopy with FITC-labelled antibodies, or immunoprobes of western blots of partially purified MLO preparations. By contrast, there were no cross-reactions between the primula or aster yellows antibodies or MLO preparations and preparations of clover phyllody or tomato big bud MLOs or their respective polyclonal antibodies. The primula yellows MLO monoclonal and polyclonal antibodies, and also the European aster yellows MLO polyclonal antibodies, all appeared to recognize only a single major antigen of approximate M, = 22 400 daltons. Some possible explanations for the apparent specificity of the polyclinic antisera for a single antigen, and the relevance to MLO preparation procedures are discussed.     

Degradabflity and phenolic components of cell walls of wheat in relation to susceptibility to Puccinia striiforntis

Cell walls of tips and bases of laminae of flag leaves from 11 cultivars of winter wheat of varying susceptibility to Puccinia striiforntis yellow rust) were compared by examining their phenolic components released by treatment with a commercial cellulase. Isolated cell walls of both susceptible and resistant cultivars released water-soluble carbohydrate esters of phenolic acids, the major acid detected being trans-ferulic. There was no relationship between the amount of phenolic esters released by cellulase and susceptibility to yellow rust. The leaf lamina tips, which were much more susceptible to yellow rust than the corresponding bases, had lower cell wall contents than the bases and their walls were more degradable by cellulase. Examination of transverse sections of leaf laminae of cv. Little Joss showed that cells whose walls contained phenolic groups that gave a red colour reaction with p-nitrobenzene diazonium tetrafluoroborate, occupied a larger area of leaf lamina bases than of the tips. A greater percentage of the abaxial epidermal cells of the bases, compared with the tips, had walls that gave this red colour reaction. We suggest that the presence of phenolic groups in these walls may be related to the greater resistance of the bases to P. striiforntis.     

Extrusion of DNA from the Macronucleus of Tetrahymena pyriformis GL

SYNOPSIS Administration of the thymidine analog 5-bromodeoxyuridine to exponentially growing cultures of Tetrahymena pyriformis GL in chemically defined medium results in inhibition of cell multiplication by at least one generation before DNA synthesis stops. Cell multiplication can be restored in these cultures, if they are transferred to fresh growth medium, but although most of the cells in the culture contain close to a G2-amount of DNA, a full DNA replication round is a prerequisite for renewed cell multiplication. Large extrusion bodies are found at the first division after transfer to fresh growth medium. Autoradiographic analysis has revealed that the DNA in the extrusion body is a representative of the DNA in the macronucleus indicating a random distribution of DNA between daughter nuclei and extrusion body.     

THE SYNTHESIS OF 5S RNA AND ITS REGULATION DURING EARLY SEA URCHIN DEVELOPMENT

De novo synthesis of 5S RNA and of transfer RNA (tRNA) has been demonstrated previously to occur by mid-cleavage (128-cell stage) in sea urchin embryos (24). The present study focused on determining more precisely the time of onset of activity of the genes for 5S RNA and for tRNA during sea urchin embryogenesis by preloading the GTP precursor pools of unfertilized eggs. The results showed that newly-made 5S RNA and tRNA could be detected as early as the 32-cell stage. In order to determine whether newly-synthesized 5S RNA accumulates coordinately during development with newly-made 26S (34) and 18S ribosomal RNAs (rRNAs), the relative rates of accumulation of these three RNA molecules were measured and compared at each of several stages of sea urchin embryogenesis. In contrast to the coordinated accumulation of newly-synthesized 26S and 18S rRNAs, newly-made 5S RNA accumulated in excess at the mesenchyme blastula (9-fold excess), midgastrula (5-fold excess) and prism (3-fold excess) stages. The 5S RNA/26S RNA molar ratios only approached unity in advanced (48 hr) plutei. The non-coordinated accumulation of newly-made 5S RNA with that of 26S and 18S rRNAs suggests that the accumulation of these newly-synthesized RNAs is differentially regulated during early sea urchin development.     

X-RAY MICROANALYSIS IN CELL BIOLOGY AND CELL PATHOLOGY

Electron probe X-ray microanalysis has been used for the last 25 years by biologists to obtain information about the distribution of elements at the cell and tissue level. During this period, progress has mainly been made through the development of more adequate techniques for specimen preparation (mainly low temperature techniques) and quantitative analysis, so that accurate analysis of the physiologically important cellular ions can be carried out. Use ofin vitrosystems and cell cultures may further increase the number of problems to which X-ray microanalysis can be applied. Among the numerous applications of X-ray microanalysis in cell biology and cell pathology, applications in the areas of epithelial ion transport, the role of calcium in secretory and contractile cells, and the role of ions in cell proliferation and cancer are discussed in more detail.     

FINDING AUTONOMY IN BIRTH

Over the last several years, as cesarean deliveries have grown increasingly common, there has been a great deal of public and professional interest in the phenomenon of women 'choosing' to deliver by cesarean section in the absence of any specific medical indication. The issue has sparked intense conversation, as it raises questions about the nature of autonomy in birth. Whereas mainstream bioethical discourse is used to associating autonomy with having a large array of choices, this conception of autonomy does not seem adequate to capture concerns and intuitions that have a strong grip outside this discourse. An empirical and conceptual exploration of how delivery decisions ought to be negotiated must be guided by a rich understanding of women's agency and its placement within a complicated set of cultural meanings and pressures surrounding birth. It is too early to be 'for' or 'against' women's access to cesarean delivery in the absence of traditional medical indications – and indeed, a simple pro- or con- position is never going to do justice to the subtlety of the issue. The right question is not whether women ought to be allowed to choose their delivery approach but, rather, taking the value of women's autonomy in decision-making around birth as a given, what sorts of guidelines, practices, and social conditions will best promote and protect women's full inclusion in a safe and positive birth process.