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991.
992.
Patrelle C Ohst T Picard D Pagano A Sourice S Dallay MG Plötner J 《Molecular ecology resources》2011,11(1):200-205
We describe a non‐invasive, PCR‐RFLP‐based method that allows reliable determination of the European water frog species Pelophylax lessonae and Pelophylax ridibundus and the hybrid form Pelophylax esculentus. Maximum‐likelihood analysis of ITS2 sequences revealed two robust monophyletic clades corresponding to water frogs of the P. lessonae and P. ridibundus groups. Three restriction enzymes (KpnI, HaeII, and SmaI) were used to digest three conserved ITS2 domains. Taxonomic identification was unambiguous; the three restriction enzymes gave the same results. A French reference sample was identified using allozyme electrophoresis. Our PCR‐RFLP method confirmed circa 83% of identification of the allozyme method. We conclude that the difference between identifications was caused by introgression. 相似文献
993.
Hatschekia plectropomi , an ectoparasitic copepod found on the gills, infected Plectropomus leopardus from Heron Island Reef with 100% prevalence ( n = 32) and a mean ± s . e . infection intensity of 131·9 ± 22·1. The distribution of 4222 adult female parasites across 32 individual host fish was investigated at several organizational levels ranging from the level of holobranch pairs to that of individual filaments. Parasites demonstrated a site preference for the two central holobranchs (2 and 3). Along the lengths of hemibranchs, filaments near the dorsal and ventral ends and those in the proximity of the bend region were rarely occupied. The probability of coming into contact with a suitable attachment site and the ability to withstand ventilation forces at that site were proposed as the major factors affecting distribution. Two H. plectropomi morphotypes were identified based on the direction of body curvature. Regardless of morphotype, 99·9% of individuals were attached such that the convex side of the body was oriented towards the oncoming ventilating water currents. Further, 93·3% of individuals attached to the posterior faces of filaments, leading to a predictable pattern of attachment for this species. It is suggested that the direction of body curvature develops in response to the direction of the ventilating water currents. 相似文献
994.
A cohesion/tension model for the gating of aquaporins allows estimation of water channel pore volumes in Chara 总被引:2,自引:2,他引:0
The water permeability (hydraulic conductivity; Lp) of turgid, intact internodes of Chara corallina decreased exponentially as the concentration of osmolytes applied in the medium increased. Membranes were permeable to osmolytes and therefore they could be applied on both sides of the plasma membrane at concentrations of up to 2.0 m (5.0 MPa of osmotic pressure). Organic solutes of different molecular size (molecular weight, MW) and reflection coefficients (σs) were used [heavy water HDO, MW: 19, σs: 0.004; acetone, MW: 58, σs: 0.15; dimethyl formamide (DMF), MW: 73, σs: 0.76; ethylene glycol monomethyl ether (EGMME), MW: 76, σs: 0.59; diethylene glycol monomethyl ether (DEGMME), MW: 120, σs: 0.78 and triethylene glycol monoethyl ether (TEGMEE), MW: 178, σs: 0.80]. The larger the molecular size of the osmolyte, the more efficient it was in reducing cell Lp at a given concentration. The residual cell Lp decreased with increasing size of osmolytes. The findings are in agreement with a cohesion/tension model of the osmotic dehydration of water channels (aquaporins; AQPs), which predicts both reversible exponential dehydration curves and the dependence on the size of osmolytes which are more or less excluded from AQPs (Ye, Wiera & Steudle, Journal of Experimental Botany 55, 449–461, 2004). In the presence of big osmolytes, dehydration curves were best described by the sum of two exponentials (as predicted from the theory in the presence of two different types of AQPs with differing pore diameters and volumes). AQPs with big diameters could not be closed in the presence of osmolytes of small molecular size, even at very high concentrations. The cohesion/tension theory allowed pore volumes of AQPs to be evaluated, which was 2.3 ± 0.2 nm3 for the narrow pore and between 5.5 ± 0.8 and 6.1 ± 0.8 nm3 for the wider pores. The existence of different types of pores was also evident from differences in the residual Lp. Alternatively, pore volumes were estimated from ratios between osmotic (Pf) and diffusional (Pd) water flow, yielding the number of water molecules (N) in the pores. N-values ranged between 35 and 60, which referred to volumes of 0.51 and 0.88 nm3/pore. Values of pore volumes obtained by either method were bigger than those reported in the literature for other AQPs. Absolute values of pore volumes and differences obtained by the two methods are discussed in terms of an inclusion of mouth parts of AQPs during osmotic dehydration. It is concluded that the mouth part contributed to the absolute values of pore volumes depending on the size of osmolytes. However, this can not explain the finding of the existence of two different types or groups of AQPs in the plasma membrane of Chara. 相似文献
995.
Robert W. Howarth 《中国科学C辑(英文版)》2005,48(Z2)
Two-thirds of the coastal rivers and bays in the United States are degraded from nutrient pollution, and nitrogen inputs these waters continue to increase. The nitrogen comes from a variety of sources, including runoff from agricultural fields, concentrated animal feeding operations, atmospheric deposition from fossil fuel combustion, and sewage and septic wastes.Technical solutions for nitrogen pollution exist at reasonable cost. That most of these solutions have not yet been implemented to any significant extent across the United States suggests that new policy approaches are necessary. The best solution may involve a combination of voluntary and mandatory approaches, applying different approaches to different sources of nitrogen poilution. A watershed-based approach that relies heavily on voluntary mechanisms (such as crop-yield insurance to reduce over-fertilization) is likely to be the most effective for some sources of nitrogen (such as runoff from agricultural fields), while a uniform national regulatory approach may be better for others (such as NOx emissions from fossil fuel combustion). Implementation of management strategies should be carefully coupled to monitoring programs to assess the effectiveness of these strategies. While both nitrogen and phosphorus are important to control, the focus should be on nitrogen management, in part because nitrogen is more generally the causal agent of coastal eutrophication. Also, while nitrogen-control practices tend to also reduce phosphorus pollution, phosphorus-control practices often have little effect on nitrogen.Although current scientific and technical knowledge is sufficient to begin to make substantial progress toward solving coastal nitrogen pollution, progress will be made more quickly and more cost effectively with increased investment in appropriate scientific research. 相似文献
996.
Utah chub Gila atraria , a temperate freshwater minnow, formed valid otolith annuli (annual growth rings), even when raised in a constant‐temperature desert spring environment. This suggests that factors other than seasonal variation in water temperature control annual otolith marking. 相似文献
997.
Hydrophilins from distant organisms can protect enzymatic activities from water limitation effects in vitro 总被引:2,自引:0,他引:2
998.
A method for direct estimation of percentage apoplastic water volume (% APO) in conifer needles is described. The method presented here, and designated the pressure-needle (P-N) method, measures the relative water content of the needles to develop a curve similar to the pressure-volume (P-V) curve. P-V and P-N curves were developed for Picea pungens Engelm. cv. Hoopsi, Pinus sylvestris L., Abies gradis (Dougl.) L., and Pseudotsuga menziesii (Mirb) Franco. The % APO estimated by the two procedures varied as much as 2-fold, while other parameters were similar. The P-V method generated consistently higher and more variable % APO than the P-N method, due to the inclusion of the apoplastic water of the stem in the P-V method. For conifers, the P-N method offers a more accurate and precise method for determining % APO. 相似文献
999.
CO2 exchange components of a temperate semi-desert sand grassland ecosystem in Hungary were measured 21 times in 2000–2001 using a closed IRGA system. Stand CO2 uptake and release, soil respiration rate (R
s), and micrometeorological values were determined with two types of closed system chambers to investigate the daily courses of gas exchange. The maximum CO2 uptake and release were –3.240 and 1.903 mol m–2 s–1, respectively, indicating a relatively low carbon sequestration potential. The maximum and the minimum R
s were 1.470 and 0.226 mol(CO2) m–2 s–1, respectively. Water shortage was probably more effective in decreasing photosynthetic rates than R
s, indicating water supply as the primary driving variable for the sink-source relations in this ecosystem type. 相似文献
1000.
Effects of grazing on photosynthetic characteristics of major steppe species in the Xilin River Basin,Inner Mongolia,China 总被引:2,自引:0,他引:2
Species composition and photosynthetic characteristics of dominant species of ungrazed plot (UG), overgrazed plot (OG), and
restored grazed plot (RG) were determined in the Xilin River Basin, Inner Mongolia, China. Both heavily grazing and restoration
significantly affected the composition of different species and life forms. Leymus chinensis, Stipa grandis, and Cleistogenes polyphylla, three dominant perennial grasses in UG plot, contributed 58.9 % aboveground biomass to that of whole community, and showed
higher net photosynthetic rate (P
N), transpiration rate (E), and intrinsic water-use efficiency (WUE). In OG plot, relative biomass of L. chinensis and S. grandis significantly decreased, while relative biomass of three shrubs/sub-shrubs, Caragana microphylla, Artemisia frigida, and Kochia prostrata, obviously increased. Heavy grazing significantly decreased P
N, E, and WUE of L. chinensis and S. grandis, while shrubs/sub-shrubs showed significantly higher photosynthetic activity and WUE than the grasses. After 18-year restoration,
photosynthetic activities of L. chinensis and S. grandis were significantly higher than those in the OG plot. The proportion of L. chinensis, S. grandis, and C. microphylla significantly increased, and relative biomass of C. polyphylla, A. frigida, and K. prostrata markedly declined in RG plot. We found close relationships between physiological properties of species and their competitive
advantage in different land use types. Higher photosynthetic capability means more contribution to total biomass. The variations
in physiological characteristics of plants could partly explain the changes in species composition during degrading and restoring
processes of Inner Mongolia typical steppes. 相似文献