Perennial N2 supersaturation in an Antarctic lake

The dry valleys of southern Victoria Land in Antarctica contain several closed basins in which perennially ice-covered lakes are found. One of the most unusual features of these lakes is the occurrence of high O2 concentrations in the water column; values ranging from slightly more than saturation to more than four times saturation have been reported. Recently, we considered a bulk O2 budget for Lake Hoare, Antarctica, which led us to suggest that biological processes alone were not sufficient to explain the observed elevated oxygen levels. Consequently, there must be a non-biological source of O2. We suggested that this source results from the exclusion of O2 during the freezing of aerated meltstream water at the bottom of the ice cover, and predicted that this physical mechanism should also enhance the other atmospheric gases. Here we report the results of a study which, for the first time, documents the supersaturation of N2 in a lake. Dissolved N2 levels of 145% and 163% were determined from samples taken just below the ice cover and at a depth of 12 m, respectively. The relatively importance of biological and abiological sources is reflected in the ratio of N2 concentration to O2 concentration. In Lake Hoare this ratio was 1.20 at ice/water interface and 1.05 at 12 m; considerably different from the ratio in equilibrium with air (approximately 1.8). Based on these results, we have determined that about half of the net O2 production in the lake is the result of biological processes.     

Photoperiodic summation is temperature-dependent inPyrrhocoris apterus (L.) (Heteroptera)

Summary InPyrrhocoris apterus, a low temperature, 15°C, prevented the termination of diapause by long days and, unexpectedly, also the induction of diapause by short days. Both responses were enabled at a higher temperature, 26°C. In contrast to current concepts, it was proved that the summation of photoperiodic signals was temperature-dependent, since the morphogenetic development was prevented by starvation.     

用爆炸波起爆癸烷云雾的两种模式

用垂直激波管研究了400μm癸烷液滴与空气混合物的爆炸波起爆。每种混合物有两个极限起爆能值,即高值Ecu,和低值Ecl。当起爆能的值高于Ecu时,观察到100%发生爆轰;而当其低于Ecl时,就不会发生爆轰。有趣的是,当起爆能水平在Ecu和Ecl之间时观察到对应于不同的起爆能水平有不同的起爆行为。如实验结果所表明的,爆轰的激发不仅是由于直接起爆,而且也由于“爆燃”到爆轰的转变。     

Binding of 11-cis retinaldehyde to the partially purified cellular retinaldehyde binding protein from bovine retinal pigment epithelium

Summary 11-cis retinaldehyde binding analysis was performed on a bovine retinal pigment epithelium preparation of cellular retinaldehyde binding protein (CRALBP), whose purity degree was estimated as 75%. Equilibrium binding studies were carried out measuring the replacement of tritium-labeled with unlabeled 11-cis retinaldehyde at 25°C. Analysis of the experimental data both by a direct curve-fitting procedure utilizing a non linear least square regression analysis and by a conventional Scatchard plot revealed a single non-interacting binding site with an apparent equilibrium constant of 0.9×10^–7 M.A binding stoichiometry of approximately 1 mol of 11-cis retinaldehyde/mol of binding protein can be calculated from the experimental data. Competition studies carried out in the presence of unlabeled trans and cis isomers of Vitamin A derivatives confirm the high degree of specificity of the 11-cis retinaldehyde binding.     

Self-labeling of human polymorphonuclear leucocyte myeloperoxidase with125iodine

In order to obtain a radioimmunoassay (RIA) technique for the measurement of human plasma myeloperoxidase (MPO), we purified the enzyme from polymorphonuclear granulocytes (neutrophils), and compared three methods of labeling it with¹²⁵Iodine: chloramine T, lactoperoxidase, and an original technique of self labeling based on the ability of the enzyme to oxidize and bind¹²⁵I in the presence of H₂O₂. The chloramine T technique produced a degraded protein, as well shown by a high non-specific binding of tracer to antibody. The lactoperoxidase technique did not succeed in labeling MPO with an adequate specific activity. In contrast, the self-labeling method gave a stable tracer with a specific activity of 23 Ci/gmg MPO (85 MBq), a satisfactory level of immunoreactivity, and a low-specific binding (3%). After labeling, purification of tracer was achieved by gel filtration chromatography in phosphate buffer (0.05 M; pH7) to which 0.1% poly-L-lysine was added. The labeled molecule remained stable for 40 days and could be used for RIA with a polyclonal antibody raised in rabbits.     

Evolutionary distinctiveness of the endangered Kemp's ridley sea turtle

The endangered Kemp's ridley sea turtle (Lepidochelys kempi) nests almost exclusively at a single locality in the western Gulf of Mexico, whereas the olive ridley (L. olivacea) nests globally in warm oceans. Morphological similarities between kempi and olivacea, and a geographical distribution that "...makes no sense at all under modern conditions of climate and geography", raise questions about the degree of evolutionary divergence between these taxa. Analysis of mitochondrial (mt) DNA restriction sites shows that Kemp's ridley is distinct from the olive ridley in matriarchal phylogeny, and that the two are sister taxa with respect to other marine turtles. Separation of olive and the Kemp's ridley lineages may date to formation of the Isthmus of Panama, whereas the global spread of the olive ridley lineage occurred recently. In contrast to recent examples in which molecular genetic assessments challenged systematic assignments underlying conservation programmes, our mtDNA data corroborate the taxonomy of an endangered form.     

Effects of a change in the level of inbreeding on the genetic load

"The effects of inbreeding may not be as noticeable in the first generation as the invigoration immediately apparent after crossing". This statement, published in 1919, has received little attention, and has apparently never been tested empirically, although the reduction of the genetic load of populations by inbreeding is well known in theoretical terms. Because inbreeding increases homozygosity, and hence the effectiveness of selection against recessive or partially recessive detrimental alleles, changes in levels of inbreeding can lead to a reduction in the frequencies of such mutant alleles. This results in equilibration at higher population mean fitness and is referred to as 'purging' populations of their genetic load. Severe inbreeding can also reduce genetic load due to overdominant alleles, provided selection coefficients are not symmetrical at all loci, because alleles giving lower fitness will be reduced in frequency at equilibrium. With either fitness model, however, reduction in genetic load takes time, and the initial effect of an increase in inbreeding is reduced fitness due to homozygosity. There are few data relating to the extent to which fitness is reduced during inbreeding in a set of lines and to how long the reduction lasts before increasing again to the initial level, or higher. Inbreeding experiments involving sib mating in mice and Drosophila subobscura, and successive bottlenecks in house flies have yielded some evidence consistent with the purging hypothesis. Here, we report results of an experiment demonstrating a prolonged time-course of recovery of mean fitness under self-fertilization of a naturally outcrossing plant, and also compare our results with expectations derived by computer calculations. Our results show that the genetic load present in an outcrossing population can be explained only with a high mutation rate to partially recessive deleterious alleles, and that inbreeding purges the population of mutant alleles.