Inhibition of Aspartate Aminotransferase by Glycation In Vitro Under Various Conditions

Incubation of 50 mM d -glucose with aspartate aminotransferase (AST, EC 2.6.1.1) preparations (purified pig heart enzyme or a rat liver 20,000 × g supernatant) at 25°C had no effect on enzyme activity. 50 mM d -fructose or d -ribose gradually inhibited pig heart AST under the same conditions to zero activity after 14 days. 50 mM dl -glyceraldehyde decreased enzyme activity to zero after 6 days of incubation. The inhibition of pig heart AST by 50 mM d -fructose or d -ribose was marked even at a temperature of 4°C but it was less pronounced than at 25°C. There was no effect of 0.5 mM 2-oxoglutarate on AST activity during incubation, while the presence of 25 mM l -aspartate decreased it rapidly. 0.5 mM 2-oxoglutarate partly prevented inhibition of AST by d -ribose or d -fructose, while an analogous experiment with 25 mM aspartate resulted in a rapid decline similar to that in the absence of sugars.     

Winter energy deficits and the importance of fruit versus insects in a tropical island bird population

The sedentary population of 200 to 500 silver-eyes on Heron Island, Australian Great Barrier Reef, experiences high mortality during the winter non-breeding season. The omnivorous silvereyes feed mainly on small insects gleaned from foliage, and on fruits, especially the fig Ficus opposita. Estimates of the energy content of food items reveal that small insects (2–5 mm long) provide little assimilable energy (9 J), whereas large insects (>8 mm) and bites of fig provide most assimilable energy (217 J and 181 J respectively). An analysis of the average daily intakes and expenditures (estimated by the time-budget method) for three sampling occasions showed that the rates of insect consumption (10,15 and 11 kJ day^-1) were significantly less than the energy requirements (37, 38 and 37 kJ day^-1). While many individuals may have been able to balance their energy budgets by eating figs, the calculated fruit intake rates (38, 9 and 0.5 kJ day^-1 respectively), together with high inter-individual variation in fig consumption, suggest that figs were often in short supply. The birds visited fig trees most frequently during the first 2 h after sunrise, and the feeding success rate in fig trees (approximately 20% of visits successful) during this time was significantly greater than that during the rest of the day (approximately 10% of visits successful). Alternative hypotheses for these patterns, based on protein requirements, on diurnal rhythms imposed by insect availability, or on satiation, are considered and rejected. These results indicate that the pre-breeding population size is limited by winter energy shortage, the extent of which is dependent on the size and phenology of the fig crop. Natural selection should favour individual strategies for maximization of net energy intake.     

Histocompatibility Gene Organization and Mixed Lymphocyte Reaction

TRANSFORMATION of allogenic lymphocytes in mixed cultures depends chiefly on an incompatibility between the lymphocyte donors at the major histocompatibility locus in man (HL-A), mouse (H-2) and rat (H-l)¹. Although the mouse H-2 locus can be divided into several regions each of which controls one or more antigenic specificities² and two or more subloci control HL-A antigens in man³, it is not known whether all parts of the major histocompatibility locus are equally important in eliciting transformation in mixed lymphocyte cultures. We now show that capacity to elicit lymphocyte transformation is different for different parts of the mouse H-2 locus.     

The extent and differences in mitotic activity of the root tip ofVicia faba L.

Mitotic activity does not stop for different meristematic cells of the root apex at the same distance from the initials. The differences are connected with the functional heterogeneity of the apical meristem of the root. The arrangement of vascular bundles,i.e. the alternation of independent xylem and phloem groups, is of major importance. In broad bean roots, the protophloem sieve elements stop dividing first. The centre of the stelei. e. late metaxylem elements stop dividing next. Division in the stele gradually ceases centrifugally, while it ceases centripetally in the peripheral part of the root. The cylindrical region with prolonged cell division includes internal layers of the cortex including endodermis, pericycle and adjoining cells of the stele. Proximally apical meristem is reduced to isolated strands of cells adjacent to the protoxylem poles. Pericycle cells stop dividing last at a distance of approx. 9–10 mm from the initials. The number of the division cycles is limited and is specific for individual cell types. Epidermal and cortical cells divide in broad bean roots transversely approximately seven times, cells of late metaxylem approximately five times. Root apical meristem is an asynchronous cell population with a different duration of the mitotic cycle. We determined local variations in the duration of the mitotic cycle in the apical meristem of broad bean root by means of colchicine-induced polyploidy. The cells of the quiescent centre had the longest mitotic cycle after colchicine treatment. The region of the proper root adjacent to the quiescent centre was mixoploid (2n and 4n). Isolated cells with a long cycle occurred also in the cortex and in the central cylinder. Cells with a division cycle of 18h were found in the root cap, in the epidermis, in the cortex and in the central cylinder. Relatively numerous cells with the shortest division cycle, approx. 12 h, occurred farther of the quiescent centre in the epidermis, in the cortex, in the pericycle, and in adjacent layers of the stele through-out the entire meristematic region. The results derived from the analysis of the apical meristem are discussed in connection with the ontogenesis of different types of cells taking part in the primary structure of the root.     

Growth of migrating and non-migrating cryptophytes in thermally and chemically stratified experimental columns

• 1 Growth rates of migrating and non-migrating populations of two strains of freshwater cryptophytes, CCAP 979/67 and 979/62, under different light and nutrient regimes were calculated from experiments conducted in laboratory columns which were thermally stratified. During the experiments, cellular carbon, nitrogen, phosphorus, carbohydrate and protein were also analysed. The intention was that the populations would become either phosphorus- or nitrogen-depleted following a period of growth.
• 2 In all experiments, populations of cryptophytes grew but growth appeared of short duration. In a phosphorus depletion experiment with Cryptomonas 979/67, there was a period of rapid growth starting on day 2 and finishing on day 8, during which the estimated growth rate was c. 0.9 div. day^-1. In a nitrogen depletion experiment, the period of rapid growth of C. 979/67 lasted only for 2–3 days with a growth rate of c. 0.85 div. day^-1.
• 3 In a phosphorus depletion experiment with C. 979/62, the onset of a period of rapid growth coincided with the commencement of diel vertical migration. The highest growth rate was estimated as c. 1.0 div. day^-1. In a nitrogen depletion experiment, C. 979/62 did not migrate and attained a growth rate of only 0.28 div. day^-1.
• 4 For C. 979/67 the highest observed growth rate was lower than the maximum potential growth rate of 1.38 div. day^-1 estimated in batch culture. For C. 979/62 the maximum growth rate in the column was similar to the maximum potential growth rate of 0.87 div. day^-1 in batch culture experiments.
• 5 The results suggest that some migrating cryptophytes under favourable conditions in stratified water columns can attain high growth rates supporting the hypothesis of Raven & Richardson (1984) that, based on cost-benefit analysis, diel vertical migrations could increase the growth rate of flagellates. Such growth appears of short duration and its ecological importance still requires further verification.

     

Inorganic self-organisation in precambrian cherts

Silica biomorphs are inorganic self-organized precipitates resulting from a crystal aggregation process controlled by a metal silicate membrane. They display morphological and symmetric properties of living organisms and form under physico-chemical conditions similar to some geochemical conditions suggested for the chemical precipitation of Precambrian chert precursors. In consequence, these inorganic precipitates are proposed as an alternative interpretation to be considered when trying to decipher the biogenicity of putative Precambrian microbiotas.     

Sentinel systems on the razor's edge: effects of warming on Arctic geothermal stream ecosystems

The Earth is experiencing historically unprecedented rates of warming, with surface temperatures projected to increase by 3–5 °C globally, and up to 7.5 °C in high latitudes, within the next century. Knowledge of how this will affect biological systems is still largely restricted to the lower levels of organization (e.g. species range shifts), rather than at the community, food web or ecosystem level, where responses cannot be predicted from studying single species in isolation. Further, many correlational studies are confounded with time and/or space, whereas experiments have been mostly confined to laboratory microcosms that cannot capture the true complexity of natural ecosystems. We used a ‘natural experiment’ in an attempt to circumvent these shortcomings, by characterizing community structure and trophic interactions in 15 geothermal Icelandic streams ranging in temperature from 5 °C to 45 °C. Even modest temperature increases had dramatic effects across multiple levels of organization, from changes in the mean body size of the top predators, to unimodal responses of species populations, turnover in community composition, and lengthening of food chains. Our results reveal that the rates of warming predicted for the next century have serious implications for the structure and functioning of these fragile ‘sentinel’ ecosystems across multiple levels of organization.     

From climate change predictions to actions – conserving vulnerable animal groups in hotspots at a regional scale

Current climate change is a major threat to biodiversity. Species unable to adapt or move will face local or global extinction and this is more likely to happen to species with narrow climatic and habitat requirements and limited dispersal abilities, such as amphibians and reptiles. Biodiversity losses are likely to be greatest in global biodiversity hotspots where climate change is fast, such as the Iberian Peninsula. Here we assess the impact of climate change on 37 endemic and nearly endemic herptiles of the Iberian Peninsula by predicting species distributions for three different times into the future (2020, 2050 and 2080) using an ensemble of bioclimatic models and different combinations of species dispersal ability, emission levels and global circulation models. Our results show that species with Atlantic affinities that occur mainly in the North‐western Iberian Peninsula have severely reduced future distributions. Up to 13 species may lose their entire potential distribution by 2080. Furthermore, our analysis indicates that the most critical period for the majority of these species will be the next decade. While there is considerable variability between the scenarios, we believe that our results provide a robust relative evaluation of climate change impacts among different species. Future evaluation of the vulnerability of individual species to climate change should account for their adaptive capacity to climate change, including factors such as physiological climate tolerance, geographical range size, local abundance, life cycle, behavioural and phenological adaptability, evolutionary potential and dispersal ability.