共查询到20条相似文献,搜索用时 31 毫秒
1.
It has been found by reversed-phase chromatography that humic acids obtained from vermicomposts of different duration of vermicomposting consist of a hydrophilic and a hydrophobic fractions, the hydrophobic fraction having a substantially lower content of charged, probably carboxylic, groups. A change in the sign of the temperature dependence of the heat capacity of diluted aqueous solutions of humic acids at approximately 58 degrees C has been found by differential scanning microcalorimetry, which indicates an increase in the hydration of hydrophobic groups. A jumpwise increase in heat capacity in the temperature range from 86 to 90 degrees C was also found, which is due likely to the hydration of hydrophobic groups in the interior of "micelles", due to the "devitrification" of the hydrophobic nucleus of micelle-like structures. It was shown that increasing the duration of vermicomposting leads to an increase in the relative content of the hydrophobic fraction of humic acids and in the cooperativity of the thermodynamic transition, which manifests itself in a jump of heat capacity, which probably results from the increase in the "micelle" size. 相似文献
2.
Characterization of thermal tolerances of ants, which are both abundant and important in most terrestrial ecosystems, is needed
since thermal constraints can inform how a species may respond to local climatic change. Here we identified the thermal tolerances
of 16 common ant species of the Northeastern United States and determined relationships between body size, desiccation, and
thermal tolerance among species. We hypothesized that maximum heat tolerances of these species would differ and be related
to body size and capacity to resist desiccation. We identified four distinct groups of species belonging to one of three subfamilies,
Dolichoderinae, Formicinae, or Myrmicinae, with different maximum thermal tolerances. Group “a” had a mean thermal tolerance
of approximately 43°C (±1°C), group “b” had a mean thermal tolerance of 40°C (±1°C), group “c” had a mean thermal tolerance
of 38°C (±0°C), and group “d” had a mean thermal tolerance of 36°C (±0°C). Groups “a” and “d” consisted of a single species
(in the subfamilies Myrmicinae and Formicinae, respectively), while groups “b” and “c” were a mix of species in the subfamilies
Myrmicinae, Formicinae, and Dolichoderinae. In the subfamily Formicinae, thermal tolerance increased with body size and critical
water content, a metric of desiccation tolerance. In contrast, in the subfamily Myrmicinae, higher thermal tolerance was correlated
with intermediate body size and lower critical water content. These findings suggest that the two dominant subfamilies in
Northeastern deciduous forests have different relationships between body size, capacity to tolerate desiccation, and thermal
tolerances across species. This variation in thermal tolerance suggests that climatic change may impact species differently. 相似文献
3.
Binder H 《European biophysics journal : EBJ》2007,36(4-5):265-279
The ordering and H-bonding characteristics of the hydration water of the lipid 1-palmitoyl-2-oleoylphosphatidylcholine (POPC)
were studied using polarized infrared spectroscopy by varying either the temperature or the relative humidity of the ambient
atmosphere of multibilayer samples. The OH-stretching band of lipid-bound water was interpreted by a simplified two-state
model of well-structured, low density “network” water and of less-structured dense “multimer” water. The IR-spectroscopic
data reflect a rather continuous change of the water properties with increasing distance from the membrane and with changing
temperature. Network and multimer water distribute across the whole polar interphase with changing composition and orientation.
Upon dehydration the fraction of network water increases from about 30 to 60%, a value which is similar to that in supercooled
water at −25°C. The highly ordered gel phase gives rise to an increased fraction of structured network water compared with
the liquid crystalline phase. The IR order parameter shows that the water dipoles rearrange from a more parallel towards a
more perpendicular orientation with respect to the membrane normal with progressive hydration.
Dedicated to Prof. K. Arnold on the occasion of his 65th birthday. 相似文献
4.
An equation is derived from the spread of a “state” by contact through a thoroughly mixed population, in which the probability
of transmission depends both on the over-all duration of the process and on the time an individual has been in the “state.”
Cases in which this probability is a function of only one or the other of the two “times” are worked out. It is shown that
in the case of dependence on “private time” alone the asymptotic value of the fraction of the population effected is the same
as that derived by the random net approach. 相似文献
5.
Verena Fettinger Frans J. M. Smulders Peter Lazar Irem Omurtag Peter Paulsen 《European Journal of Wildlife Research》2010,56(6):943-947
In two surveys, thighs of a total of 137 hunted hares were tested for the presence of intramuscular shots and femur fractures,
which were detected in 42.7% and 29.2% of 274 thighs, respectively. Femur fractures were significantly associated with the
presence of intramuscular shots. In the second survey (46 hares), 92 thighs were grouped into three categories, “A” (no fractures,
no intramuscular shot), “B” (one intramuscular shot), and “C” (multiple shots and hematoma), with 49.0%, 33.6%, and 17.4%,
respectively. Category “C” was found unfit for human consumption. During 7-day storage of vacuum-packed “A” and “B” thighs,
total aerobic counts increased from initially 3.3 ± 0.3 (mean ± SD) and 4.1 ± 0.6 log cfu/g by ca. 2 log units when stored
at 3–4°C, whereas the increase was clearly <1 log unit at 0°C. In comparison to temperature, differences between “A” and “B”
category were less pronounced. Similar dynamics were observed for Enterobacteriaceae. In all categories, muscle pH values
(mean = 5.83) were similar. It is concluded that storage at temperatures of ca. 4°C, although in compliance with EU legislation,
does not afford keeping microbial contaminants in check, and thus will not preserve microbiological quality of vacuum-packed
hare meat. 相似文献
6.
To calculate the solvation of hydrophobic solutes, we have developed a method based on the fundamental measure treatment of
density functional theory. This method allows us to carry out calculations of density profiles and the solvation energy for
various hydrophobic molecules with high accuracy. We have applied the method to the hydration of various hydrocarbons (linear,
branched and cyclic). The calculations of the entropic and enthalpic parts are also carried out. We have examined the question
of the temperature dependence of the entropy convergence. Finally, we have calculated the mean force potential between two
large hydrophobic nanoparticles immersed in water.
Proceedings of “Modeling Interactions in Biomolecules II”, Prague, September 5th–9th, 2005. 相似文献
7.
Christian Körner 《Oecologia》1998,115(4):445-459
In this review I first compile data for the worldwide position of climate-driven alpine treelines. Causes for treeline formation
are then discussed with a global perspective. Available evidence suggests a combination of a general thermal boundary for
tree growth, with regionally variable “modulatory” forces, including the presence of certain taxa. Much of the explanatory
evidence found in the literature relates to these modulatory aspects at regional scales, whereas no good explanations emerged
for the more fundamental global pattern related to temperature per se, on which this review is focused. I hypothesize that the life form “tree” is limited at treeline altitudes by the potential
investment, rather than production, of assimilates (growth as such, rather than photosynthesis or the carbon balance, being
limited). In shoots coupled to a cold atmosphere, meristem activity is suggested to be limited for much of the time, especially
at night. By reducing soil heat flux during the growing season the forest canopy negatively affects root zone temperature.
The lower threshold temperature for tissue growth and development appears to be higher than 3°C and lower than 10°C, possibly
in the 5.5–7.5°C range, most commonly associated with seasonal means of air temperature at treeline positions. The physiological
and developmental mechanisms responsible have yet to be analyzed. Root zone temperature, though largely unknown, is likely
to be most critical.
Received: 3 October 1997 / Accepted: 14 April 1998 相似文献
8.
The final thermal preference FTP) range in parthenogenetic females of cladoceran Daphnia magna was assessed by “acute” and “chronic” methods. The first method included 4-month acclimation to different temperatures in
the range of 14.2 ± 0.7 to 27.1 ± 0.3°C; the “chronic” method was characterized by long-term acclimation to +20°C. Two ranges
of FTP were found for D. magna, 13.3–15.4°C and 20.2–26.2°C. The thermal preference of daphnids and the temperature of acclimation were correspondingly
linearly. The range of FTP was independent of the season. The searching activity of D. magna rose in April, when the FTP range increased, and the FTP was less pronounced. 相似文献
9.
Based on the meteorological data over a period of 4 years (1980–3), the macro-environment of BenCat Farm situated in the southern
part of Vietnam (27 m above mean sea-level, 11° N and 106° E) was categorized as a “monsoon tropical climate”, due to heavy
rainfall (annual mean 2028.96 mm) and about 32% wet days (annual mean 116.52 days) together with high air temperature (annual
mean daily temperature 28.58, max. 32.33 and min 24.85° C). April was the hottest (monthly mean >35°C) and January the coldest
month (monthly mean <22° C) of the year. The maximum number of wet days were during September and October (mean 18 days.month),
whereas the minimum number of wet days were during January and February (mean <1 day/month). The months of December and January
at Ben-Cat buffalo farm were categorized as the “comfortable (moderate-Dry) period” as the mean daily temperature was <27°
C, while the remaining 10 months of the Calender year (February–November) were categorized as the “hot period” (mean daily
temperature >27° C). On the basis of rainfall and the number of wet days, the hot period was further subdivided into a “hot-dry
period” (February–April, mean of 1.67 wet days/month and mean rainfall 19.43 mm/month) and a “hot-humid period” (May–November,
mean of 15.57 wet days/month and mean rainfall 276.28 mm/month). 相似文献
10.
Jing Zhang Yan Liu Dan Yu Hongze Song Jingjin Cui Tao Liu 《Journal of applied phycology》2011,23(2):165-171
Hybridization of gametophytes, continuous self-crossing and targeted selection were utilized to breed a new Laminaria variety. After five-generation selection breeding, the new variety “Rongfu” was obtained. Its male parent “Yuanza No.10”
was the high-yield cultivation variety, and its female parent was variety “Fujian” which could tolerate relatively high seawater
temperature. “Yuanza No.10” and “Fujian” were different but complement in their morphological characteristics and biological
habits. Variety “Rongfu” was bred through their hybridization which exhibited high-yield potential and high seawater temperature
tolerance. The results of traits evaluation in consecutive years showed that “Rongfu” attained higher yields by 24–27% compared
to the control (widely used commercial variety) and also contained considerable amounts of iodine, mannitol, and algin. When
seawater temperature was 18–21°C, the blade growth of “Rongfu” was maintained and tissue loss by abrasion was significantly
lower than the control. Since the adoption of variety “Rongfu” in 2001, its cultivation areas have been extended to Shandong,
Fujian and Guangdong province and have reached 14,133 ha currently, i.e., almost one-tenth of the total cultivation areas
of Laminaria in China. The results of Random Amplified Polymorphic DNA analysis showed that the relationship between “Rongfu” and other
cultivation varieties in China was very close. 相似文献
11.
Cornicchi E Capponi S Marconi M Onori G Paciaroni A 《European biophysics journal : EBJ》2008,37(5):583-590
Through elastic neutron scattering measurements, we investigated the thermal fluctuations of DNA enclosed by glycerol–water
glassy matrices, at different levels of hydration, over the wide temperature range from 20 to 300 K. For all the samples,
the extracted hydrogen mean square displacements (MSD) show a purely vibrational harmonic trend at very low temperatures,
and a first onset of anharmonic dynamics above ∼100 K. Such onset is consistent with the activation of DNA methyl group rotational
motions. Then, at a certain temperature T
d, the MSD show a second onset of anharmonicity, which corresponds to the DNA dynamical transition. The T
d values vary as a function of the hydration degree of the environment. The crucial role of the solvent mobility to activate
the DNA thermal fluctuations is proposed, together with a preferential hydration effect of the DNA phosphate groups. Finally,
a comparison between the average mobility of homologous samples of DNA and the lysozyme protein is considered.
Advanced neutron scattering and complementary techniques to study biological systems. Contributions from the meetings, “Neutrons
in Biology”, STFC Rutherford Appleton Laboratory, Didcot, UK, 11–13 July and “Proteins At Work 2007”, Perugia, Italy, 28–30
May 2007. 相似文献
12.
Effects of different organic waste amendments on soil microaggregates stability and molecular sizes of humic substances 总被引:5,自引:0,他引:5
Three soils which had been amended for several years with pig slurry, cattle slurry, and sewage sludge were dry-sieved to
obtain microaggregates in the size range of 250–125, 125–50, and <50 μm. With amendments, aggregate size distribution of whole
soils was shifted to larger sizes, especially for the most fragile soil, whereas percent content of microaggregates decreased
except for the lower size aggregates of the fragile soil. Particle size distribution of microaggregates revealed an increase
in percent sand and a reduction of percent silt and clay in the <50 μg size fraction for all soils. These results showed the
aggregation effect induced by the organic waste additions. Aggregate stability of microaggregates revealed significant correlation
with humic substances content (humic acids alone and humic plus fulvic acids) and non significant with total organic matter
substantiating the belief that humic substances are the predominant binding agents in this aggregation range. Molecular weight
distribution of humic acids extracted from microaggregates of unamended soils demonstrated that the lower the soil aggregate
size distribution, the larger the contribution of the high molecular weight fraction. All microaggregates from amended soils
showed a progressive increase of the high molecular weight humic acids with decreasing size, reaching a maximum in the <50
μm fraction. In this aggregate size a parallel enhancement of the aggregate stability was also evident. It is concluded that
a close relationship exists between aggregate stability and high molecular weight humic substances. Additions to soils of
organic material containing high molecular weight constituents would represent a useful management practice to improve aggregate
stability. 相似文献
13.
Microrheological properties (aggregation and deformability) of erythrocytes separated by centrifugation at 30000×g density gradient into “young” and “old” (the upper and lower fractions, respectively) were studied. The erythrocytes were
taken from physically active persons (PAP) and from those with elevated arterial pressure (EAP). A significant difference
in microrheological properties of the “young” and “old” erythrocytes was found. The aggregation degree of “old” cells was
nearly twice that of “young” cells. The deformability of the erythrocyte subpopulations was significantly different, though
the difference was not so pronounced as in the case of aggregation. The aggregation of “young” and “old” erythrocytes in the
PAP group was the least (28% lower than in the control). Note, that “old” erythrocytes in the PAP group had better microrheological
properties than in the other groups. All erythrocyte populations in the EAP group were characterized by higher aggregation,
decreased deformability, and decreased capacity for oxygen transport. 相似文献
14.
To explore how chemical structures of both nucleobases and amino acids may have played a role in shaping the genetic code,
numbers of sp2 hybrid nitrogen atoms in nucleobases were taken as a determinative measure for empirical stereo-electronic property to analyze
the genetic code. Results revealed that amino acid hydropathy correlates strongly with the sp2 nitrogen atom numbers in nucleobases rather than with the overall electronic property such as redox potentials of the bases,
reflecting that stereo-electronic property of bases may play a role. In the rearranged code, five simple but stereo-structurally
distinctive amino acids (Gly, Pro, Val, Thr and Ala) and their codon quartets form a crossed intersection “core”. Secondly,
a re-categorization of the amino acids according to their β-carbon stereochemistry, verified by charge density (at β-carbon)
calculation, results in five groups of stereo-structurally distinctive amino acids, the group leaders of which are Gly, Pro,
Val, Thr and Ala, remarkably overlapping the above “core”. These two lines of independent observations provide empirical arguments
for a contention that a seemingly “frozen” “core” could have formed at a certain evolutionary stage. The possible existence
of this codon “core” is in conformity with a previous evolutionary model whereby stereochemical interactions may have shaped
the code. Moreover, the genetic code listed in UCGA succession together with this codon “core” has recently facilitated an
identification of the unprecedented icosikaioctagon symmetry and bi-pyramidal nature of the genetic code. 相似文献
15.
Extracellular polypeptides released by both N2-grown [peptide I] and NO3-grown [peptide II]Anabaena L-31 have molecular weight of approximately 3,500 but have distinctly different amino acid composition. Acid hydrolysis of
the peptide I fraction (obtained by separation on Sephadex G-25) yielded ten amino acids whereas that from peptide II fraction
yielded only 3 amino acids. On addition to a freshly inoculated N2-grown culture, the peptide I fraction stimulated pro-heterocyst and to a lesser extent heterocyst differentiation, whereas
the peptide II fraction strongly inhibited differentiation. The inhibitory effect of polypeptide II fraction could not be
relieved by methionine sulphoximine, which by itself enhances differentiation, but was greatly relieved by addition of the
peptide I fraction. The data suggest but does not prove, thatAnabaena L-31 synthesises “inducer” or “inhibitor” peptides which could possibly control pattern formation. 相似文献
16.
The effect of fire on soil humic substances 总被引:1,自引:0,他引:1
Summary High temperature effects on soil humic substances were investigated both in natural and laboratory conditions. Differential
Thermal Analysis and pyrolysis show that only temperatures above 250°C produce changes in the humic acid fraction. The mean
change is a loss of weight due to decarboxylation. Isotachophoretic studies also show that temperatures higher than 250°C
produce alteration in the separation pattern of the different subfractions due to changes in the ‘core’ or/and in the amount
of carboxyl and hydroxyl groups. Isotachophoregrams done on soil samples extracted from an area before and after fire show
no differences. This result is taken as an indication that there was no direct effect of the temperature on the soil humic
substances. 相似文献
17.
QTL analysis of fruit components in the progeny of a Rennell Island Tall coconut (Cocos nucifera L.) individual 总被引:2,自引:0,他引:2
Baudouin L Lebrun P Konan JL Ritter E Berger A Billotte N 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2006,112(2):258-268
We investigated the genetic factors controlling fruit components in coconut by performing QTL analyses for fruit component
weights and ratios in a segregating progeny of a Rennell Island Tall genotype. The underlying linkage map of this population
was already established in a previous study, as well as QTL analyses for fruit production, which were used to complement our
results. The addition of 53 new markers (mainly SSRs) led to minor amendments in the map. A total of 52 putative QTLs were
identified for the 11 traits under study. Thirty-four of them were grouped in six small clusters, which probably correspond
to single pleiotropic genes. Some additional QTLs located apart from these clusters also had relatively large effects on the
individual traits. The QTLs for fruit component weight, endosperm humidity and fruit production were found at different locations
in the genome, suggesting that efficient marker-assisted selection for yield can be achieved by selecting QTLs for the individual
components. The detected QTLs descend from a genotype belonging to the “Pacific” coconut group. Based on the known molecular
and phenotypic differences between “Pacific” and “Indo-Atlantic” coconuts, we suggest that a large fraction of coconut genetic
diversity is still to be investigated by studying populations derived from crosses between these groups.
Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users. 相似文献
18.
Under conditions of a few behavioral tests on rats, we examined the psychotropic activity of novel N-uronoyl derivatives of
amino acids: (i) N-(1,2:3,4-di-O-isopropylidene-α-D-galactopyranuronoyl-β-alanine (DAGU-Ala), (ii) DAGU-glycyl-D,L-glutamic
acid (DAGU-Gly-Glu), and (iii) DAGU-glycyl-glycine (DAGU-Gly-Gly) injected i.p. in a 50 mg/kg dose. In an open-field test,
DAGU-Gly-Glu and DAGU-GLy-Gly showed antistress properties (they decreased the intensity of locomotion, decreased the number
of defecation acts, and intensified the research activity), while DAGU-Ala possessed a psychostimulating effect (intensification
of locomotor and research activity and an increase in the number of defecations). In the “black-and-white chamber” test, only
DAGU-Gly-Gly exerted an anxiolytic effect; it somewhat increased the frequency and duration of emergings of animals from the
dark section and duration of visits to the illuminated section of the chamber. DAGU-GLy-Glu manifested antidepressant properties;
it increased the time of active swimming of the animal in the Porsolt test and decreased the duration of passive “hanging”
of rats in the “suspension by the tail” test.
Neirofiziologiya/Neurophysiology, Vol. 39, No. 1, pp. 52–61, January–February, 2007. 相似文献
19.
D. K. Chistyulin O. D. Novikova O. Yu. Portnyagina V. A. Khomenko T. I. Vakorina N. Yu. Kim M. P. Isaeva G. N. Likhatskaya T. F. Solov’eva 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2012,6(3):235-242
The polypeptide profile of the porin protein fraction of Yersinia ruckeri, a Gram-negative bacterium causing yersiniosis in fish, has been shown to depend on cultivation temperature. OmpF-like porins are expressed mainly in the outer membrane (OM) of the “cold” variant (4°C) of the microorganism and OmpC-like proteins are expressed in the OM of the “warm” variant (37°C). Both types of porins are present in the OM of Y. ruckeri at room temperature. The OmpF-like porin of the “cold” variant was isolated and characterized. The molecular weight and primary structure of the protein were determined. The methods of optical spectroscopy (circular dichroism and intrinsic protein fluorescence) have shown that the protein has a spatial structure typical of β-structured porins from the OM of Gram-negative bacteria. The functional activity of isolated protein was characterized by the bilayer lipid membrane (BLM) technique. The most probable level of channel conductivity was 320 ± 60 pS, corresponding to the channel conductivity of OmpF porins of the genus Yersinia. The distinctive feature of OmpF porin from Y. ruckeri is high thermostability of its functionally active conformation: the protein forms stable pores in the BLM even after heating to 85°C. 相似文献
20.
B. B. Kheyfets S. I. Mukhin 《Biochemistry (Moscow) Supplemental Series A: Membrane and Cell Biology》2011,5(4):392-399
Two-phase lipid membrane is modeled with lipids of different bending rigidity of hydrophobic tails: domains consist of “rigid”
lipid liquid condensed phase and are surrounded by the “flexible” lipid liquid expanded phase. Within the framework of the
earlier proposed model of flexible strings, entropic contribution not including mismatch energy is calculated analytically.
“Entropic” line tension is found to be weakly dependent on the domain radius. According to the model, it is shown that merely
“entropic mismatch” is not enough for the domain formation. In the paper it is assumed that lipids at the boundary, on the
average, have larger area than the ones in the volume. This leads to an increase of energy of boundary lipids. Cases of lipids
with nearly the same bending rigidities and with strongly different ones are considered. Free energy is calculated using Taylor
expansion on the difference of area of lipids at the domain’s boundary and in the volume. Based on the calculated boundary
energy domain stability in the finite system is estimated. 相似文献