Mechanisms of hyperosmotic acclimation in Xenopus laevis (salt,urea or mannitol)

The acclimation of the clawed toad Xenopus laevis to hyperosmotic solutions of NaCl (balanced solution of sea salt), urea or mannitol was studied. The animals could not be acclimated to salt solutions more concentrated centrated than 400 mosm·l^-1. Urea was tolerated till 500 mmol·l^-1. Plasma osmolality was always hyperosmotic to the environmental solution, but with diminished osmotic gradient at the highest tolerated solutions. Plasma urea concentration approached 90 mmol·l^-1, similar in the three solutions of acclimation. Urine volume was very small under all conditions. Serum aldosterone and corticosterone did not differ significantly, although there was a slight tendency towards lower aldosterone in the NaCl solution. In vivo water uptake in tap water acclimated animals was very small, and was higher in the other groups. Only the salt- and urea-acclimated, but not the tap water and mannitol-acclimated groups responded with a clear increase following injection of oxytocin or theophylline. In vitro urea fluxes were similar and invariable in both directions under all conditions. No significant effect of theophylline was observed. Sodium transport measured by the short-circuit technique in vitro was lower in salt- and mannitol-acclimation conditions, and was stimulated significantly under all conditions in response to serosal oxytocin or theopylline. It is concluded that Xenopus laevis can osmoregulate at a limited range of external solutions. It is limited in the increase of its plasma urea concentration; the transport properties of the skin do not change very much upon acclimation, except for the hydroosmotic response to oxytocin.Abbreviations I _sc short circuit current - PD potential difference - SW balanced sea water - TW tap water     

Physico-chemical characteristics of a permanent Spanish hypersaline lake: La Salada de Chiprana (NE Spain)

La Salada de Chiprana Lake, located in the Ebro River basin, northeastern Spain, is the only permanent and deep water hypersaline ecosystem in all of western Europe. With a total surface of 31 ha and a maximum depth of 5.6 m, it has several basins bounded by elongated sandstone-bodies or ribbons which are paleochannels of Miocene age. Its salinity varied from 30 to 73 g 1^–1 during the 1989 hydrological cycle and the most abundant ions were magnesium and sulphate. Depth-time distributions of major physico-chemical variables demonstrated that the lake was stratified in two distinctive layers during most of the year. The chemocline disappeared only in October, with the complete overturn of the water column. In the deep water, three conditions occurred which allowed development of green sulphur bacteria populations: (1) oxygen depletion, (2) presence of hydrogen sulphide and (3) presence of light. Benthic microbial mats covered the sediments of shallow shores of moderate slope.     

An ecosystems approach to base-rich freshwater wetlands,with special reference to fenlands

A survey of base-rich wetlands in The Netherlands is presented. The main area of their occurrence is the low-lying Holocene part of the country, until some thousand years ago a large and coherent wetland landscape: the Holland wetland. The development of various parts of the Holland wetland into marshes, fens and bogs can be understood from hydrological relations in mire basins, as recognized in the distinction of primary, secondary and tertiary mire basin stages. Presently, the remnants of the Holland wetland are separate base-rich wetlands. The succession of their vegetation reflects various abiotic conditions and human influences. Three main developmental periods are distinguished as regards these factors. The first, geological period of mire development is seen as a post-glacial relaxation, with the inertia due to the considerable mass of wetland as a stabilizing factor. Biological “grazing” influences, as an aspect of utilization by humans, converted base-rich wetlands to whole new types in the second, historical period. Presently, mass and harvesting have decreased in importance, and actual successions in terrestrializing turbaries seem to reflect rapidly changing environmental conditions. Human control could well become the most important factor in the future development of wetland nature. The present value of open fen vegetation strongly depends on the continuation of the historical harvesting. The development of wooded fen may help to increase the mass of wetland in the future. Best results in terms of biodiversity are expected when their base state is maintained through water management. The vegetation and hydrology of floating fens in terrestrializing turbaries is treated in some more detail. Various lines and phases in the succession are distinguished. Open fen vegetation at base-rich, yet nutrient-poor sites is very rich in species threatened elsewhere. The fast acidification of certain such fens is attributed to hydrological and management factors. This acidification is illustrated in the profile of a floating raft sample. At the scale of these small fens, the elemental structure comprising base-rich fen, transitional fen and bog vegetation, is not as stable as it was in the large Holland wetland. A critical role seems to be played by the supply of bases with the water influx. The changing base state is supposed to change the nutrient cycling to such an extent that it would be correct to call this trophic excitation of the ecosystem, rather than just eutrophication. Eutrophication indicates a quantitative reaction to an increased nutrient supply, the internal system being unaltered. The drainage of fens, resulting in an increased productivity of the vegetation, provides another example of excitation, to the effect that the functional system is dramatically changed internally.     

Environmental and physiological factors influencing phototactic flight of Bemisia tabaci

Abstract. Experiments were conducted in a glasshouse and in the laboratory to determine the environmental and physiological parameters that affect flight behaviour of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae). The number of whiteflies taking off and exhibiting a positive response to sky light in the glasshouse was greatest from 08.30 to 10.00 hours. During peak flight activity less than 5% of the population engaged in phototactic orientation. Temperature was the best single predictor for the phototactic response, accounting for 75% of the variability in whitefly ascent. Sex ratios were determined for individuals remaining on poinsettia, Euphorbia pulcherrima (Willd.), and for individuals that exhibited phototactic orientation; both groups deviated from an expected 1:1 ratio. Males were more prevalent on the plants (1:0.76), whereas females were much more prevalent (1:3.02) among the whiteflies responding to sky light. A higher percentage of the females displaying a phototactic response contained eggs when compared to females remaining on poinsettia (87 v 65%). The two groups of females did not differ significantly in their weights, but males that remained on the plants were heavier than males that responded to sky light. Mark–recapture studies and experiments where phototactic individuals were removed from the population established that the response was short-lived. Whiteflies exhibiting a phototactic response in the glasshouse were more likely to exhibit long-duration, phototactic flights in a vertical flight chamber when compared to individuals that remained on poinsettia (80.7 ± 6.7 v 36.0 ± 5.8% phototactic response; 7.0 ±3.2 v 0.7±0.2min flights). There was also less deviation in flight across the horizontal plane among the individuals that exhibited a positive response to sky light in the glasshouse in comparison to individuals that remained on their host. However, initial rates of climb were not significantly different between the two groups of whiteflies.     

Maximal ecological diversity exceeds evolutionary diversity in model ecosystems

Understanding community saturation is fundamental to ecological theory. While investigations of the diversity of evolutionary stable states (ESSs) are widespread, the diversity of communities that have yet to reach an evolutionary endpoint is poorly understood. We use Lotka–Volterra dynamics and trait-based competition to compare the diversity of randomly assembled communities to the diversity of the ESS. We show that, with a large enough founding diversity (whether assembled at once or through sequential invasions), the number of long-time surviving species exceeds that of the ESS. However, the excessive founding diversity required to assemble a saturated community increases rapidly with the dimension of phenotype space. Additionally, traits present in communities resulting from random assembly are more clustered in phenotype space compared to random, although still markedly less ordered than the ESS. By combining theories of random assembly and ESSs we bring a new viewpoint to both the saturation and random assembly literature.     

Temperature dependence of thermal inactivation rate constants of bacterial spores in a glassy state

Summary Differential scanning calorimetry data obtained from corn embryos is consistent with the hypothesis of their glassy state. This work extends that hypothesis to explain the speculation about the high heat resistance of bacterial spores. By considering the protoplast to be in a glassy solid-state, it can be assumed that the configurational rearrangements of the key life dependent polymer chain backbones (DNA, etc.) are extremely slow, thereby ceasing thermal motions. It is assumed that at the glass transition temperature, the spore protoplast undergoes a discontinuity in the thermal expansion coefficient, and above this critical temperature, the rate of thermal inactivation of spores is free volume dependent and can be described adequately by the William, Landel and Ferry (WLF) equation. Glass transition temperatures forBacillus stearothermophilus andClostridium botulinum spores, obtained by fitting the inactivation rate data to the WLF equation, indicate a decrease in the inactivation rates with increasing glass-transition temperatures.     

Structural energetics of the molten globule state

Certain partly ordered protein conformations, commonly called “moltenglobule states,” are widely believed to represent protein folding intermediates. Recentstructural studies of molten globule states ofdifferent proteins have revealed features whichappear to be general in scope. The emergingconsensus is that these partly ordered forms exhibit a high content of secondary structure, considerable compactness, nonspecific tertiary structure, and significant structural flexibility. These characteristics may be used to define ageneral state of protein folding called “the molten globule state,” which is structurally andthermodynamically distinct from both the native state and the denatured state. Despite exaatensive knowledge of structural features of afew molten globule states, a cogent thermodynamic argument for their stability has not yetbeen advanced. The prevailing opinion of thelast decade was that there is little or no enthalpy difference or heat capacity differencebetween the molten globule state and the unfolded state. This view, however, appears to beat variance with the existing database of protein structural energetics and with recent estimates of the energetics of denaturation of α-lactalbumin, cytochrome c, apomyoglobin, and T4 lysozyme. We discuss these four proteins at length. The results of structural studies, together with the existing thermodynamic values for fundamental interactions in proteins, provide the foundation for a structural thermodynamic framework which can account for the observed behavior of molten globule states. Within this framework, we analyze the physical basis for both the high stability of several molten globule states and the low probability of other protential folding intermediates. Additionally, we consider, in terms of reduced enthalpy changes and disrupted cooperative interactions, the thermodynamic basis for the apparent absence of a thermally induced, cooperative unfolding transition for some molten globule states. © 1993 Wiley-Liss, Inc.     

Oxide-Based Solid-State Batteries: A Perspective on Composite Cathode Architecture

The garnet-type phase Li₇La₃Zr₂O₁₂ (LLZO) attracts significant attention as an oxide solid electrolyte to enable safe and robust solid-state batteries (SSBs) with potentially high energy density. However, while significant progress has been made in demonstrating compatibility with Li metal, integrating LLZO into composite cathodes remains a challenge. The current perspective focuses on the critical issues that need to be addressed to achieve the ultimate goal of an all-solid-state LLZO-based battery that delivers safety, durability, and pack-level performance characteristics that are unobtainable with state-of-the-art Li-ion batteries. This perspective complements existing reviews of solid/solid interfaces with more emphasis on understanding numerous homo- and heteroionic interfaces in a pure oxide-based SSB and the various phenomena that accompany the evolution of the chemical, electrochemical, structural, morphological, and mechanical properties of those interfaces during processing and operation. Finally, the insights gained from a comprehensive literature survey of LLZO–cathode interfaces are used to guide efforts for the development of LLZO-based SSBs.     

REPRODUCTION IN MALE ATLANTIC WALRUSES (ODOBENUS ROSMARUS ROSMARUS) FROM THE NORTH WATER (N BAFFIN BAY)

Age at sexual maturity and timing of the mating season were determined in male Atlantic walruses ( Odobenus rosmarus rosmarus , L.) from the "North Water" subpopulation in northern Baffin Bay. Testes and epididymides of 174 male walruses (between 0 and 30 yr old) from NW Greenland (1987–1990) were studied macroscopically and a subset of 57 specimens was analyzed microscopically. In physically mature bulls ( i.e. , ≥12 yr old), sperm or apparently ripe spermatids were found between 9 November and 12 July. In younger walruses these signs of fertility were found in a few specimens (7–11 yr old) collected between 9 January and 28 May. The mating season seems to peak in January—April. The youngest sexually mature individual was 7 yr old and the oldest apparently immature individual was 13 yr old. Average age of sexual maturity was 10.9 yr (95% C.I.: 9–6–12.2 yr) and all were sexually mature by the time they were 14 yr old. The non-spermiogenetic testes and epididymides showed accelerated growth between about the 5–6th and about the 12–15th year of life, indicating that sexual maturation occurs during these years. The length of the baculum increased gradually until about 12–15 yr of age, when physical maturity was reached.     

Responses in stomatal conductance to elevated CO2 in 12 grassland species that differ in growth form

Responses in stomatal conductance (g _st ) and leaf xylem pressure potential ( _leaf ) to elevated CO₂ (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO₂ concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August, _leaf was usually higher in all species at elevated CO₂ and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO₂ resulted in decreased g _st in 10 of the 12 species measured. Greatest decreases in g _st (ca. 50%) occurred in growth forms with the highest potential growth rates (C₃ and C₄ grasses, and C₃ ruderals). In contrast, no significant decrease in g _st was measured in the two C₃ shrubs. During a dry period in September, reductions in g _st at elevated CO₂ were measured in only two species (a C₃ ruderal and a C₄ grass) whereas increased g _st at elevated CO₂ was measured in the shrubs and a C₃ forb. These increases in g _st were attributed to enhanced _leaf in the elevated CO₂ plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g _st were measured in response to elevated CO₂. Thus, there was significant interspecific variability in stomatal responses to CO₂ that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g _st and was greatest (>30%) when water availability was low, but only 6–12% when _leaf was high.The results of this study confirm the importance of considering interactions between indirect effects of high CO₂ of plant water relations and direct effects of elevated CO₂ on g _st , particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g _st to be measured at elevated levels of CO₂.