Ice premelting during differential scanning calorimetry

Premelting at the surface of ice crystals is caused by factors such as temperature, radius of curvature, and solute composition. When polycrystalline ice samples are warmed from well below the equilibrium melting point, surface melting may begin at temperatures as low as -15 degrees C. However, it has been reported (. Biophys. J. 65:1853-1865) that when polycrystalline ice was warmed in a differential scanning calorimetry (DSC) pan, melting began at about -50 degrees C, this extreme behavior being attributed to short-range forces. We show that there is no driving force for such premelting, and that for pure water samples in DSC pans curvature effects will cause premelting typically at just a few degrees below the equilibrium melting point. We also show that the rate of warming affects the slope of the DSC baseline and that this might be incorrectly interpreted as an endotherm. The work has consequences for DSC operators who use water as a standard in systems where subfreezing runs are important.     

Effects of climate change on productivity of cereals and legumes; model evaluation of observed year-to-year variability of the CO2 response

The effect of elevated [CO₂] on the productivity of spring wheat, winter wheat and faba bean was studied in experiments in climatized crop enclosures in the Wageningen Rhizolab in 1991–93. Simulation models for crop growth were used to explore possible causes for the observed differences in the CO₂ response. Measurements of the canopy gas exchange (CO₂ and water vapour) were made continuously from emergence until harvest. At an external [CO₂] of 700 μmol mol^?1 Maximum Canopy CO₂ Exchange Rate (CCERmax) at canopy closure was stimulated by 51% for spring wheat and by 71% for faba bean. At the end of the growing season, above ground biomass increase at 700 μmol mol^?1 was 58% (faba bean), 35% (spring wheat) and 19% (winter wheat) and the harvest index did not change. For model exploration, weather data sets for the period 1975-88 and 1991–93 were used, assuming adequate water supply and [CO₂] at 350 and 700 μmol mol^?1. For spring wheat the simulated responses (35–50%) were at the upper end of the experimental results. In agreement with experiments, simulations showed smaller responses for winter wheat and larger responses for faba bean. Further model explorations showed that this differential effect in the CO₂ response may not be primarily due to fundamental physiological differences between the crops, but may be at least partly due to differences in the daily air temperatures during comparable stages of growth of these crops. Simulations also showed that variations between years in CO₂ response can be largely explained by differences in weather conditions (especially temperature) between growing seasons.     

Seasonal changes in the response of winter wheat to elevated atmospheric CO2 concentration grown in Open-Top Chambers and field tracking enclosures

Winter wheat was grown at ambient and elevated (ambient plus 350 μL L^–1) CO₂ concentrations in open top chambers and in field-tracking sun-lit climatized enclosures (elevated is 718 μL L^–1). There was no significant effect of CO₂ concentration on sheath, leaf and root biomass and leaf area in the early spring (January to April). 24-h canopy CO₂ exchange rate (CCER) was not significantly affected either. However, elevated CO₂ concentration increased CCER at midday, decreased evapotranspiration rate and increased instantaneous water-use-efficiency during early spring. Leaf, sheath and root nitrogen concentration per unit dry weight decreased and nonstructural carbohydrate concentration increased under elevated CO₂, and N-uptake per unit ground area decreased significantly (– 22%) towards the end of this period. These results contrast with results from the final harvest, when grain yield and biomass were increased by 19% under elevated CO₂. N concentration per dry weight was reduced by 5%, but N-uptake per unit ground area was significantly higher (+ 11%) for the elevated CO₂ treatment. 24-h and midday-CCER increased significantly more in late spring (period of 21 April to 30 May) (respectively by + 40% and 53%) than in the early spring (respectively 5% and 19%) in response to elevated CO₂. Midday evapotranspiration rate was reduced less by elevated CO₂ in the late spring (– 13%) than in early spring (– 21%). The CO₂ response of midday and 24-h CCER decreased again (+ 27% and + 23% resp.) towards the end of the growing season. We conclude that the low response to CO₂ concentration during the early spring was associated with a growth-restriction, caused by low temperature and irradiance levels. The reduction of nitrogen concentration, the increase of nonstructural carbohydrate, and the lower evapotranspiration indicated that CO₂ did have an effect towards the end of early spring, but not on biomass accumulation. Regression analysis showed that both irradiance and temperature affected the response to CO₂.     

Evolution of the relaxin-like peptide family

Background  

The relaxin-like peptide family belongs in the insulin superfamily and consists of 7 peptides of high structural but low sequence similarity; relaxin-1, 2 and 3, and the insulin-like (INSL) peptides, INSL3, INSL4, INSL5 and INSL6. The functions of relaxin-3, INSL4, INSL5, INSL6 remain uncharacterised. The evolution of this family has been contentious; high sequence variability is seen between closely related species, while distantly related species show high similarity; an invertebrate relaxin sequence has been reported, while a relaxin gene has not been found in the avian and ruminant lineages.     

The PDZ binding motif of human papillomavirus type 16 E6 induces PTPN13 loss, which allows anchorage-independent growth and synergizes with ras for invasive growth

The human papillomavirus (HPV) oncogene E6 has been shown to perform multiple functions (p53 degradation, telomerase activation, etc.) that play a role in oncogenic transformation. Beyond known E6 functions, an undefined mechanism that allows cellular invasion requires the E6 PDZ binding motif (PDZBM). Here, we show that HPV type 16 (HPV16) E6 interacts with and induces loss of a protein tyrosine phosphatase (PTPN13) in a PDZBM-dependent manner. PTPN13 loss induced either by the presence of E6 or by a short hairpin RNA strategy allows for anchorage-independent growth (AIG) and synergy with a known oncogene, Ras^v12, resulting in invasive growth in vivo. Restoring PTPN13 expression reverses AIG in cells lacking PTPN13. A genomic analysis of colorectal carcinoma has identified an association between PTPN13 loss-of-function mutations and aberrant Ras signaling. Our findings support this correlation and provide methods for further evaluation of the mechanisms by which PTPN13 loss/Ras expression leads to invasive growth, the results of which will be important for treatment of HPV-related and non-HPV cancer.     

Ca2+, annexins, and GTP modulate exocytosis from maize root cap protoplasts

Protoplasts isolated from root cap cells of maize were shown to secrete fucose-rich polysaccharides and were used in a patch-clamp study to monitor changes in whole-cell capacitance. Ca2+ was required for exocytosis, which was measured as an increase in cell capacitance during intracellular dialysis with Ca2+ buffers via the patch pipette. Exocytosis was stimulated significantly by small increases above normal resting [Ca2+]. In the absence of Ca2+, protoplasts decreased in size. In situ hybridization showed significant expression of the maize annexin p35 in root cap cells, differ-entiating vascular tissue, and elongating cells. Dialysis of protoplasts with maize annexins stimulated exocytosis at physiological [Ca2+], and this could be blocked by dialysis with antibodies specific to maize annexins. Dialysis with milli-molar concentrations of GTP strongly inhibited exocytosis, causing protoplasts to decrease in size. GTPgammaS and GDPbetaS both caused only a slight inhibition of exocytosis at physiological Ca2+. Protoplasts were shown to internalize plasma membrane actively. The results are discussed in relation to the regulation of exocytosis in what is usually considered to be a constitutively secreting system; they provide direct evidence for a role of annexins in exocytosis in plant cells.     

Galvechelone lopezmartinezae gen. et sp. nov., a new cryptodiran turtle in the Lower Cretaceous of Europe

Abstract: The Spanish town of Galve (Teruel) is notable because of the abundance of Upper Jurassic and, especially, Lower Cretaceous vertebrates recorded there. Although most groups have been studied in detail, information on turtles is very limited even though the material is relatively abundant. So far, no turtle taxa have been identified at the generic level. The only Lower Cretaceous articulated specimen from Galve is analysed here. It is identified as a representative of Cryptodira, Galvechelone lopezmartinezae gen. et sp. nov. Galvechelone lopezmartinezae is determined as a taxon belonging to the node that groups the turtles traditionally assigned to ‘Macrobaenidae’ and ‘Sinemydidae’, and other taxa such as the members of Panchelonioidea. This node, very abundant in the Lower Cretaceous of Asia, and with a broad subsequent distribution, has recently been recognized in the Lower Cretaceous of Europe. The diversity of basal members of Eucryptodira in the European Late Jurassic (represented by Thalassemydidae, Plesiochelyidae and Eurysternidae) was high. Owing to a relative scarcity of well‐preserved early Cretaceous turtles from Europe, the knowledge of this group of reptiles is limited. The study of the new turtle from Galve, together with the recently described Hoyasemys jimenezi, and the recently completed review of the enigmatic Chitracephalus dumonii demonstrate that members of the cryptodiran node grouping ‘Macrobaenidae’, ‘Sinemydidae’ and Panchelonioidea were also very diverse in this period.