Elevated atmospheric [CO2] promotes frost damage in evergreen tree seedlings

Growth under elevated [CO₂] promoted spring frost damage in field grown seedlings of snow gum ( Eucalyptus pauciflora Sieb. ex Spreng.), one of the most frost tolerant of eucalypts. Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO₂] (– 5·7 °C versus – 4·3 °C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO₂ fertilization and may affect predictions of vegetation change based on increasing temperature.     

Effects of Different Semipermeable Membranes on In Vitro and In Vivo Performance of Microdialysis Probes

The in vitro and in vivo performance of three different semipermeable microdialysis membranes was compared: a proprietary polycarbonate-ether membrane made by Carnegie Medecin; cuprophan, a regenerated cellulose membrane; and polyacrylonitrile. When microdialysis probes were tested in a stirred in vitro solution, large and statistically significant differences among the three membranes in extraction of acid metabolites (3,4-dihydroxyphenylacetic acid, 5-hydroxyindoleacetic acid, and homovanillic acid) and acetaminophen were found. Polyacrylonitrile had the highest extractions in vitro. In contrast, when microdialysis probes were implanted in vivo (in rat striatum), extraction of acid metabolites and acetaminophen did not differ significantly among the different membranes. These results are consistent with predictions made by a mathematical model of microdialysis and can be explained by the fact that in vitro the main factor limiting extraction is membrane resistance to diffusion, whereas tissue resistance to diffusion plays a more dominant role in vivo. These findings suggest that (aside from differences in surface area), the choice of semipermeable membrane will generally have little effect on in vivo microdialysis results. Furthermore, in vitro measurements of microdialysis probe extractions are not a reliable way of calibrating in vivo performance.     

A method for the preparation of high-molecular-weight DNA from marine and freshwater triclads (Platyhelminthes, Turbellaria)

Although the last decade has seen much activity devoted to the phylogeny of the Platyhelminthes, such activity has relied in the main on traditional anatomical, ultrastructural, and developmental data. Extension of these studies to the molecular level has been impeded by the lack of a reliable method for the isolation of DNA from these organisms, especially marine triclads whose DNA is particularly difficult to isolate using methods currently used with other eukaryotic or prokaryotic organisms. We report here the details of a method that results in the rapid isolation of relatively pure DNA in good yields from small amounts of material. The method involves the treatment of the animals with high concentrations of NaDodSO4 followed by phenol extraction, resulting in a product that is an excellent substrate for restriction endonuclease digestion and Southern blotting.     

Linkage relationships of the gene for apolipoprotein CII with loci on chromosome 19

Two common restriction fragment length polymorphisms detected with cloned gene probes for apolipoprotein CII (apo CII) have been used to study the inheritance of the gene in families segregating for loci on chromosome 19. Lod scores for APOC2 with the gene for complement component 3 (C3) exclude close linkage and give a maximum at a male recombination fraction of 0.25-0.30. Lod scores for APOC2 and FHC, the gene causing familial hypercholesterolaemia, are negative in males and suggest the genes may not be linked. However, it appears that APOC2 may be closely linked to the blood group loci Lutheran (Lu) and Secretor (Se), and probably less closely linked to Lewis (Le). These data are consistent with the gene order: FHC-----C3-----(Lu, Se, APOC2)     

Sperm competition games: a prospective analysis of risk assessment.

We develop the logic of assessment of sperm competition risk by individual males where the mechanism of sperm competition follows a ''loaded raffle'' (first and second inseminates of a female have unequal prospects). Male roles (first or second to mate) are determined randomly. In model 1, males have no information about the risk associated with individual females and ejaculation strategy depends only on the probability, q, that females mate twice. Evolutionarily stable strategy (ESS) ejaculate expenditure increases linearly from zero with q, and reduces with increasing inequality between ejaculates, though the direction of the loading (which role is favoured) is unimportant. In model 2, males have perfect information and can identify each of three risk states: females that will (1) mate just once (''no risk''), (2) mate twice but have not yet mated (''future risk''), and (3) mate twice and have already mated (''past risk''). The ESS is to ejaculate minimally with ''no risk'' females, and to expand equally with ''past'' and ''future'' risk females; the direction of the competitive loading is again unimportant. Expenditure again increases with risk, but is now non-zero at extremely low risk. Model 3 examines three cases of partial information where males can identify only one of the three risk states and cannot distinguish between the other two: they therefore have just two information sets or ''contexts''. Expenditure in both contexts typically rises non-linearly from zero with q, but (whatever the loading direction) expenditure is higher in the context with higher risk (e.g. if contexts are ''mated'' and ''virgin'', males spend more with mated females). However, in highly loaded raffles, sperm expenditure can decrease over part of the range of risk. Also, the direction of the loading now affects expenditure. Biological evidence for the predictions of the models is summarized and discussed.     

Ultrastructural observations on the sporogony of Eimeria maxima

Pittilo R. M. and Ball S. J. 1985. Ultrastructural observations on the sporogony of Eimeria maxima. International Journal for Parasilology15: 617–620. Sporogony in Eimeria maxima was found to commence with a contraction of the oocyst cytoplasmic mass which was limited by a single membrane. By 9 h (at 29°C) dense bodies, surrounded by polysaccharide granules, were closely applied to the zygote limiting membrane. By 12 h nuclear division had occurred and by 15 h separate sporoblasts could be discerned. Sporozoite formation occurred from 21 to 30 h.     

Neighboring-nucleotide effects on the rates of germ-line single-base-pair substitution in human genes.

The spectrum of single-base-pair substitutions logged in The Human Gene Mutation Database (HGMD), comprising 7,271 different lesions in the coding regions of 547 different human genes, was analyzed for nearest-neighbor effects on relative mutation rates. Owing to its retrospective nature, HGMD allows mutation rates to be estimated only in relative terms. Therefore, a novel methodology was devised in order to obtain these estimates in iterative fashion, correcting, at the same time, for the confounding effects of differential codon usage and for the fact that different types of amino acid replacement come to clinical attention with different probabilities. Over and above the hypermutability of CpG dinucleotides, reflected in transition rates five times the base mutation rate, only a subtle and locally confined influence of the surrounding DNA sequence on relative single-base-pair substitution rates was observed, which extended no farther than 2 bp from the substitution site. A disparity between the two DNA strands was evidenced by the fact that, when substitution rates were estimated conditional on the 5' and 3' flanking nucleotides, a significant rate difference emerged for 10 of 96 possible pairs of complementary substitutional events. Mutational bias, favoring substitutions toward flanking bases, a phenomenon reminiscent of misalignment mutagenesis, was apparent and exhibited both directionality and reading-frame sensitivity. No specific preponderance of repeat-sequence motifs was observed in the vicinity of nucleotide substitutions, but a moderate correlation between the relative mutability and thermodynamic stability of DNA triplets emerged, suggesting either inefficient DNA replication in regions of high stability or the transient stabilization of misaligned intermediates.     

Hypersensitivity to Some Nematode Antigens

Immediate and delayed skin reactions to antigens derived from Ascaris suum, Necator americanus, and Toxocara canis are described in three subjects and related to eosinophil counts and serum IgE levels. One, who had laboratory contact with ascarides but no known infection, gave positive immediate reactions to all three antigens. Another, following repeated experimental infection with necator, gave positive immediate reactions to all three antigens and a delayed reaction to necator alone. The third, following a single recent infection with necator, gave no immediate or delayed reaction.