Water under the BAR

Many cellular processes require the generation of highly curved regions of cell membranes by interfacial membrane proteins. A number of such proteins are now known, and several mechanisms of curvature generation have been suggested, but so far a quantitative understanding of the importance of the various potential mechanisms remains elusive. Following previous theoretical work, we consider the electrostatic attraction that underlies the scaffold mechanism of membrane bending in the context of the N-BAR domain of amphiphysin. Analysis of atomistic molecular dynamics simulations reveals considerable water between the membrane and the positively charged concave face of the BAR, even when it is tightly bound to highly curved membranes. This results in significant screening of electrostatic interactions, suggesting that electrostatic attraction is not the main driving force behind curvature sensing, supporting recent experimental work. These results also emphasize the need for care when building coarse-grained models of protein-membrane interactions. These results are emphasized by simulations of oligomerized amphiphysin N-BARs at the atomistic and coarse-grained level. In the coarse-grained simulations, we find a strong dependence of the induced curvature on the dielectric screening.     

Water Absorbency and Water Retention of the Natural Seed Coat of Seriphidium transiliense

The natural seed coat of Seriphidium transiliense Poljak could indirectly absorb water to almost saturation in 1 to 3 h at different temperatures and different relative humidities (RH). At lower humidifies, temperature almost did not affect the water absorbing rate, but at higher humidities, water absorbency escalated with temperature rise. In drought condition with a RH of 21%, it could still retain 10% of water. The direct water absorbing rate of the natural seed was about 1 500%, while that of the seed without film was only 170%. The natural seed coat made up 11% of the total seed weight. The direct absorbing rate was 12 400%. The water absorbency belonged to monomolecular layer absorption at RH < 70%. The ability of water absorbency was stronger at RH > 70%, and the water absorbency belonged to multimolecular layer absorption. There was a linear correlation between the reciprocal of the water absorbing rate and that of the water absorbing time. According to the classifying analysis and the determination of the seed coat substances using IR, it was initially maintained that the main composition of the seed coat of Seriphidium transiliense Poljak was neither protein, pectine, cellulose, nor starch, but some other polysaccharide composed of aldoses. It also contained a kind of acid-base indicating substance.     

Water: the bloodstream of the biosphere

Water, the bloodstream of the biosphere, determines the sustainability of living systems. The essential role of water is expanded in a conceptual model of energy dissipation, based on the water balance of whole landscapes. In this model, the underlying role of water phase changes--and their energy-dissipative properties--in the function and the self-organized development of natural systems is explicitly recognized. The energy-dissipating processes regulate the ecological dynamics within the Earth's biosphere, in such a way that the development of natural systems is never allowed to proceed in an undirected or random way. A fundamental characteristic of self-organized development in natural systems is the increasing role of cyclic processes while loss processes are correspondingly reduced. This gives a coincidental increase in system efficiency, which is the basis of growing stability and sustainability. Growing sustainability can be seen as an increase of ecological efficiency, which is applicable at all levels up to whole landscapes. Criteria for necessary changes in society and for the design of the measures that are necessary to restore sustainable landscapes and waters are derived.     

白鱀豚:水中传说

<正>"淇淇"死后,长江里再也没有人确认见过白鱀豚。它曾经陪伴了人类23年,却始终孑然一身。2002年7月14日上午8时许,在武汉东湖之滨的白鱀豚馆内,一头名为"淇淇"的白鱀豚永远沉睡。它是全世界唯一人工饲养成功的白鱀豚,从此之后,人们再也无缘见到它的身影。     

The Intracellular Water Activity of Bacteria in Relation to the Water Activity of the Growth Medium

Intracellular water activities ( a _w) calculated from the solute composition of various bacterial cells, are in good agreement with values derived from intracellular freezing point data. Further, and confirming literature results based on freezing points, the intracellular a _w was found to be generally equal to or lower than that of the growth medium.     

Water relations of the pine exine

BACKGROUND AND AIMS: Water adhesion forces, water absorption capacity and permeability of the pine exine were investigated to consider a possible function of sporopollenin coatings in the control of water transport. METHODS: The experiments were carried out with sporopollenin capsules obtained from pine pollen consisting of an empty central capsule and two sacci. Changes in the concentration of excluded dextran molecules in the medium were analysed to quantify water absorption by purified exine fragments and the osmotic volume flow out of the intact central capsule. KEY RESULTS: The contact angle of sporopollenin to water is higher than the one to ethanol and lower than the one to n-heptane. The water-filled pore space in pine sporopollenin amounts to only 20.6 % of the matrix volume. A monosaccharide was excluded from 15 % and a trisaccharide from about 38 % of this space. Shrinkage of the central capsule induced by permeable osmotica was transient, whereas that induced by sodium polyacrylate (2100 g mol(-1)) was stable. Values obtained for the hydraulic conductance L(P) of the exine (0.39-0.48 microm s(-1) MPa(-1)) are comparable in size to those of biomembranes. Sodium sulfate solutions induced a significant osmotic flow through the exine (reflection coefficient at least 0.6). The exine around the central capsule can be ruptured by equilibration of its lumen with a concentrated electrolyte solution and subsequent transfer to water. The denatured protoplast along with the intact intine was ejected when pollen grains were subjected to this osmotic shock treatment. CONCLUSIONS: The pine exine is easily wetted with water and does not represent a significant barrier to water exchange either liquid or gaseous. Through osmotic burst, it can be separated from the intine. The effect of salts and small solute molecules on water fluxes may be functionally significant for rehydration upon pollination.     

Impact of Yangtze River Water Transfer on the Water Quality of the Lixia River Watershed,China

To improve water quality and reduce the negative impacts of sudden inputs of water pollution in the Lixia River watershed, China, a series of experimental water transfers from the Yangtze River to the Lixia River were conducted from 2 December 2006 to 7 January 2007. Water samples were collected every six days at 55 monitoring sites during this period. Eight water parameters (water temperature, pH, dissolved oxygen (DO), chemical oxygen demand (COD), potassium permanganate index (COD_Mn), ammonia nitrogen (NH₄ ⁺-N), electrical conductivity (EC), and water transparency (WT)) were analyzed to determine changes in nutrient concentrations during water transfers. The comprehensive pollution index (Pi) and single-factor (Si) evaluation methods were applied to evaluate spatio-temporal patterns of water quality during water transfers. Water quality parameters displayed different spatial and temporal distribution patterns within the watershed. Water quality was improved significantly by the water transfers, especially for sites closer to water intake points. The degree of improvement is positively related to rates of transfer inflow and drainage outflow. The effects differed for different water quality parameters at each site and at different water transfer times. There were notable decreases in NH₄ ⁺-N, DO, COD, and COD_Mn across the entire watershed. However, positive effects on EC and pH were not observed. It is concluded that freshwater transfers from the Yangtze River can be used as an emergency measure to flush pollutants from the Lixia River watershed. Improved understanding of the effects of water transfers on water quality can help the development and implementation of effective strategies to improve water quality within this watershed.     

Water and the cytoskeleton.

The diffusion of intracellular fluid and solutes is mainly limited by the density and the geometry of crossbridges between cytoskeletal polymers mediating the formation of an integrated cytoplasmic scaffold. Evidence for specific relationships between water and cytoskeletal polymers arises from the effect of heavy water on their polymerization process in vitro and on the cytoskeleton of living cells. The hydration of cytoskeletal subunits is modified through polymerization, a mechanism which may be involved in the direct contribution of the cytoskeleton to the osmotic properties of cells together with changes of hydration of polymers within networks. The dynamic properties of the hydration layer of cytoskeletal polymers may reflect the repetitive distribution of the surface charges of subunits within the polymer lattice, thus inducing a local and long range ordering of the diffusion flows of water and solutes inside polymer networks. The interactions between subunits in protofilaments and between protofilaments determine the specific viscoelastic properties of each type of polymer, regulated by associated proteins, and the mechanical properties of the cell through the formation of bundles and gels. Individual polymers are interconnected into dynamic networks through crossbridging by structural associated proteins and molecular motors, the activity of which involves cooperative interactions with the polymer lattice and likely the occurence of coordinated modifications of the hydration layer of the polymer surface. The cytoskeletal polymers are polyelectrolytes which constitute a large intracellular surface of condensed anionic charges and form a buffering structure for the sequestration of cations involved in the regulation of intracellular events. This property allows also the association of cytoplasmic enzymes and multimolecular complexes with the cytoskeleton, facilitating metabolic channelling and the localization of these complexes in specific subdomains of the cytoplasm. The consequences of interactions between membranes and the cytoskeleton in all cellular compartments range from the local immobilization and clustering of lipids and membrane proteins to the regulation of water and ion flows by the association of cytoskeletal subunits or polymers with transmembrane channels. The possibility that the polyelectrolyte properties of the cytoskeletal polymers contribute to the modulation of membrane potentials supports the hypothesis of a direct involvement of the cytoskeleton in intercellular communications.     

这里有一方神奇之水

一道奇特的风景线 冬日的五大连池被茫茫冰雪包裹得严严实实心目中14座火山锥和五池碧水的壮观景象已被眼前的白色取代．天地一色树木、公路．就连老百姓的房顶也被单调的白色笼罩着,别样的心情别样的感受．我努力搜寻着别样的色彩…     

节水应优先于调水

就规划中的南水北调西线工程受水区情况,本刊记者访问了刘昌明院士和陶传进博士。尽管他们对南水北调西线工程的必要性看法不同,却表达了一个共同的声音：受水区应把挖掘自身的节水潜力摆在优先。     

Water,Water, Everywhere

Abstract

Math and Science Across Culture: Activities and Investigations from the Exploratorium. Maurice Bazin, Modesto, and the Exploratorium Teacher Institute. New York: The New Press, 2002. 176 pp. $19.95 (paperback). ISBN 1-56584-541-2

History Beneath the Sea—Nautical Archaeology in the Classroom. K. C. Smith and Amy Douglass (Editors). Washington, D.C.: Society for American Archaeology, 2001. 28 pp. $5.95 (paperback). ISBN 0-932839-17-7.     

Studies Concerning the Prediction of Intracellular Water Activity of Bacteria Grown at Reduced Water Activities

The water activity of various salts, macromolecules and mixed salt-macromolecule solutions has been determined. The results indicate that interactions between salts and macromolecules can be ignored for predicting the water activity of mixed aqueous solutions.