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1.
Booth DT Thompson MB Herring S 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(4):269-276
Eggs of two small Australian lizards, Lampropholis guichenoti and Bassiana duperreyi, were incubated to hatching at 25 °C and 30 °C. Incubation periods were significantly longer at 25 °C in both species, and
temperature had a greater effect on the incubation period of B. duperreyi (41.0 days at 25 °C; 23.1 days at 30 °C) than L. guichenoti (40.1 days at 25 °C; 27.7 days at 30 °C). Patterns of oxygen consumption were similar in both species at both temperatures,
being sigmoidal in shape with a fall in the rate of oxygen consumption just prior to hatching. The higher incubation temperature
resulted in higher peak and higher pre-hatch rates of oxygen consumption in both species. Total amount of oxygen consumed
during incubation was independent of temperature in B. duperreyi, in which approximately 50 ml oxygen was consumed at both temperatures, but eggs of L. guichenoti incubated at 30 °C consumed significantly more (32.6 ml) than eggs incubated at 25 °C (28.5 ml). Hatchling mass was unaffected
by either incubation temperature or the amount of water absorbed by eggs during incubation in both species. The energetic
production cost of hatchling B. duperreyi (3.52 kJ · g−1) was independent of incubation temperature, whereas in L. guichenoti the production cost was greater at 30 °C (4.00 kJ · g−1) than at 25 °C (3.47 kJ · g−1). Snout-vent lengths and mass of hatchlings were unaffected by incubation temperature in both species, but hatchling B. duperreyi incubated at 30 °C had longer tails (29.3 mm) than those from eggs incubated at 25 °C (26.2 mm). These results indicate that
incubation temperature can affect the quality of hatchling lizards in terms of embryonic energy consumption and hatchling
morphology.
Accepted: 27 January 2000 相似文献
2.
Ultraviolet-B (UV-B, 280–320 nm) radiation may have severe negative effects on plants including damage to their genetic information.
UV protection and DNA-repair mechanisms have evolved to either avoid or repair such damage. Since autotrophic plants are dependent
on sunlight for their energy supply, an increase in the amount of UV-B reaching the earth’s surface may affect the integrity
of their genetic information if DNA damage is not repaired efficiently and rapidly. Here we show that overexpression of cyclobutane
pyrimidine dimer (CPD) photolyase (EC 4.1.99.3) in Arabidopsis thaliana (L.), which catalyses the reversion of the major UV-B photoproduct in DNA (CPDs), strongly enhances the repair of CPDs and
results in a moderate increase of biomass production under elevated UV-B. 相似文献
3.
The vertical profile of stable carbon isotope ratios (δ13C) of leaves was analyzed for 13 tree species in a cool-temperate deciduous forest in Japan. The vertical distribution of
long-term averaged δ13C in atmospheric CO2 (δa) was estimated from δ13C of dry matter from NADP-malic enzyme type C4 plant (Zea mays L. var. saccharata Sturt.) grown at a tower in the forest for 32␣days, assuming constant Δ value (3.3‰) in Z. mays against height. The δa value obtained from δ13C in Z.␣mays was lowest at the forest floor (−9.30 ± 0.03‰), increased with height, and was almost constant above 10␣m (−7.14 ± 0.14‰).
Then leaf Δ values for the tree species were calculated from tree leaf δ13 C andδa. Mean leaf Δ values for the three tall deciduous species (Fraxinus mandshurica, Ulmus davidiana, and Alnus hirsuta) were significantly different among three height levels in the forest: 23.1 ± 0.7‰ at the forest floor (understory), 21.4 ± 0.5‰
in lower canopy, and 20.5 ± 0.3‰ in upper canopy. The true difference in tree leaf Δ among the forest height levels might
be even greater, because Δ in Z. mays probably increased with shading by up to ∼‰. The difference in tree leaf Δ among the forest height levels would be mainly
due to decreasing intercellular CO2 (C
i) with the increase in irradiance. Potential assimilation rate for the three tree species probably increased with height,
since leaf nitrogen content on an area basis for these species also increased with height. However, the increase in stomatal
conductance for these tree species would fail to meet the increase in potential assimilation rate, which might lead to increasing
the degree of stomatal limitation in photosynthesis with height.
Received: 30 September 1995 / Accepted: 25 October 1996 相似文献
4.
Cation sensitivity and kinetics of guard-cell potassium channels differ among species 总被引:8,自引:0,他引:8
in ward rectifying
g uard
c ell
K
+
c hannel, GCKC1in, from three major crop plants Solanum tuberosum L., Nicotiana tabacum L., and Vicia faba L. Selecting guard cells for our analyses we aimed to test whether K+ channels of the same cell type differ among species. The channels shared basic features including voltage-dependence, selectivity
and single-channel conductance. They activated at hyperpolarization (V
1/2 ≈ −164 mV) with single channels of 7 pS underlying the whole-cell current. The channel density in S. tuberosum was higher than in V. faba and N. tabacum while the activation and deactivation kinetics were faster in the latter two species. Among different monovalent cations
the K+ channels discriminated strongly against Na+, Li+, and Cs+. The sensitivity to Cs+ was similar for the three species. Extracellular Ca2+ blocked the V.␣faba K+ channel at concentrations ≥1 mM but only affected its functional homologs in S. tuberosum and N.␣tabacum at higher concentrations and more-negative membrane potentials. Like the differences in Ca2+-sensitivity, protoplasts from the three species differed remarkably in their response towards extracellular pH changes. Whereas
protons neither altered the open probability nor the kinetic parameters of the V. faba GCKC1in, in S. tuberosum and N. tabacum this cation affected the voltage-dependent properties strongly. An increase in proton concentration from pH 8.5 to 4.5 shifted
the potential of half-maximal open probability to less-negative values with a maximum effect around pH 6.2. The pH modulation
of the K+ channels could be described assuming a two-state model where the open and closed channel can be protonated. The observed
differences in cation-sensitivity and voltage-dependent kinetics between K+ channels reflect the diversification of guard-cell channels that may contribute to species-specific variations in the control
of stomatal aperture.
Received: 19 July 1997 / Accepted: 2 October 1997 相似文献
5.
Thermal acclimation of locomotor performance in tadpoles of the frog Limnodynastes peronii 总被引:3,自引:0,他引:3
R. S. Wilson C. E. Franklin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(6):445-451
Previous analyses of thermal acclimation of locomotor performance in amphibians have only examined the adult life history
stage and indicate that the locomotor system is unable to undergo acclimatory changes to temperature. In this study, we examined
the ability of tadpoles of the striped marsh frog (Limnodynastes peronii) to acclimate their locomotor system by exposing them to either 10 °C or 24 °C for 6 weeks and testing their burst swimming
performance at 10, 24, and 34 °C. At the test temperature of 10 °C, maximum velocity (Umax) of the 10 °C-acclimated tadpoles was 47% greater and maximum acceleration (Amax) 53% greater than the 24 °C-acclimated animals. At 24 °C, Umax was 16% greater in the 10 °C-acclimation group, while there was no significant difference in Amax or the time taken to reach Umax (T-Umax). At 34 °C, there was no difference between the acclimation groups in either Umax or Amax, however T-Umax was 36% faster in the 24 °C-acclimation group. This is the first study to report an amphibian (larva or adult) possessing
the capacity to compensate for cool temperatures by thermal acclimation of locomotor performance. To determine whether acclimation
period affected the magnitude of the acclimatory response, we also acclimated tadpoles of L. peronii to 10 °C for 8 months and compared their swimming performance with tadpoles acclimated to 10 °C for 6 weeks. At the test
temperatures of 24 °C and 34 °C, Umax and Amax were significantly slower in the tadpoles acclimated to 10 °C for 8 months. At 10 °C, T-Umax was 40% faster in the 8-month group, while there were no differences in either Umax or Amax. Although locomotor performance was enhanced at 10 °C by a longer acclimation period, this was at the expense of performance
at higher temperatures.
Accepted: 25 June 1999 相似文献
6.
M. Galiotou-Panayotou M. Kapantai O. Kalantzi 《Applied microbiology and biotechnology》1997,47(4):425-429
A wild type of Aspergillus sp. ATHUM-3482 produced extracellular polygalacturonase when grown in liquid medium containing citrus pectin as sole carbon
source. A number of factors affecting enzyme activity were investigated. Polygalacturonase activities as high as␣4.3 U␣ml−1(reducing-group-releasing activity) and 17␣U␣ml−1 (viscosity-diminishing activity) were obtained under optimum growth conditions. With sugar-beet as sole carbon source the
respective activities were 6.5 U␣ml−1 and 40 U ml−1, the highest achieved in this work. Under these conditions no pectin lyase or pectinesterase activity was detected. The above
yields of polygalacturonase activity compare favourably with those reported for fungi grown under similar growth conditions.
Received: 5 March 1996 / Received last revision: 29 October 1996 / Accepted: 2 November 1996 相似文献
7.
This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In
total, 13 M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m2 · kg−1 · 10−2, Dubois surface area 2.01 (0.16) m2, %body fatness 14.6 (3.9)%, V˙O2peak 49.0 (4.8) ml · kg−1 · min−1] and 17 F [23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m2 · kg−1 · 10−2, 1.68 (0.13) m2, 20.2 (4.8)%, 43.2 (6.6) ml · kg−1 · min−1, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h−1 followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical
protective clothing (0.29 m2 ·°C · W−1 or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i
m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of
their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min−1 at 105 min (n = 13) compared with 145.1 (14.4) beats · min−1 for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T
re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for
M. Tolerance times were significantly longer for M [142.9 (24.5) min] than for F [119.3 (17.3) min]. Partitional calorimetric
estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1 (6.6) and 46.1 (9.7) W · m−2 for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76 (1.44) kJ · kg−1] compared with M [9.45 (1.26) kJ · kg−1]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times [124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S [8.67 (1.44) and 9.39 (1.05) kJ · kg−1 for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory
disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can
be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness.
Accepted: 31 October 1997 相似文献
8.
A. Ancel L. Petter R. Groscolas 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):533-539
The triggering of transitory egg desertion in fasting and incubating blue petrels (Halobaena caerulea, nocturnal burrowing seabirds living in the subantarctic region) was investigated by continuously monitoring both body temperature
(T
sto) and egg temperature (T
egg) with a telemetry system, and by measuring body mass (BM) loss. The birds were kept captive in their burrow and incubated
day and night without any interruption; there was no day-night cycle in T
sto and T
egg, which averaged 39.9 °C and 32.0 °C, respectively. There was no evidence of hypothermia as a way to save energy in this fasting
situation. Egg desertion occurred at night and was an abrupt and definitive phenomenon reflected by a simultaneous fall in
T
egg and a peak in T
sto. After egg desertion, a distinct day-night cycle of body temperature was observed, T
sto being 0.6 °C higher during night-time (P < 0.05), probably reflecting increased nocturnal activity. BM at egg desertion averaged 166.7 ± 3.8 g in telemetered birds
and 164.4 ± 1.6 g in␣a group of free-living birds. Throughout fasting, the␣specific daily BM loss remained at 46 ± 1 g · kg−1 · day−1, but increased sharply below a critical BM of 160.0 ± 2.5 g. Thus, fasting incubating blue petrels spontaneously desert their
egg when reaching a BM threshold. This BM is very close to a critical value in fasting birds and mammals that corresponds
to a critical depletion of fat stores and to a shift from lipid to protein utilization. This strongly suggests that such a
metabolic shift triggers behavioural changes leading to egg desertion and refeeding, which is of great relevance to the understanding
of the long-term control of food intake and BM.
Accepted: 16 July 1998 相似文献
9.
The genus Oryza to which cultivated rice belongs has 24 species (2n = 24 or 48), representing seven genomes (AA, BB, CC, EE, FF, BBCC and CCDD). The genomic constitution of five of these species is unknown. These five species have been grouped into two species complexes,
the tetraploid ridleyi complex (O. ridleyi, O.␣longiglumis) and the diploid meyeriana complex (O.␣granulata, O. meyeriana, O. indandamanica). To evaluate the genomic structure of these species in terms of divergence at the molecular level vis-à-vis other known
genomes of Oryza, we used the total genomic DNA hybridization approach. Total genomic DNA (after restriction digestion) of 79 accessions of
23 Oryza species, 6 related genera, 5 outgroup taxa (2 monocots, 3 dicots) and 6 F1s and BC1s derived from crosses of O.␣sativa with wild species were hybridized individually with 32P-labeled total genomic DNA from 12 Oryza species: O. ridleyi, O. longiglumis, O. granulata, O.␣meyeriana, O. brachyantha, O. punctata, O. officinalis, O. eichingeri, O. alta, O. latifolia, O. australiensis, and O.␣sativa. The labeled genomic DNAs representing the ridleyi and meyeriana complexes cross-hybridized best to all the accessions of their respective species, less to those representing other genomes
of Oryza and related genera, and least to outgroup taxa. In general, the hybridization differential measured in terms of signal intensities
was >50-fold under conditions that permit detection of 70–75% homologous sequences, both in the presence and in the absence
of O. sativa DNA as competitor. In contrast, when total DNAs representing other Oryza genomes were used as probes, species of the O.␣ridleyi and O.␣meyeriana complexes did not show any significant cross-hybridization (<5%). These results demonstrate that the genome(s) of both of
these complexes are highly diverged and distinct from all other known genomes of Oryza. We, therefore, propose new genomic designations for these two species complexes: GG for the diploid O. meyeriana complex and HHJJ for the allotetraploid O. ridleyi complex. The results also suggest that the uniqueness of these genomes is not restricted to species-specific highly repetitive
DNA sequences, but also applies to dispersed sequences present in single or low to moderate copy numbers. Furthermore these
appear to share relatively more genome-specific repeat sequences between themselves than with other genomes of rice. The study
also demonstrates the potential of total genomic DNA hybridization as a simple but powerful tool, complementary to existing
approaches, for ascertaining the genomic makeup of an organism.
Received: 26 July 1996 / Accepted: 17 September 1996 相似文献
10.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
11.
C. Lydersen K. M. Kovacs M. O. Hammill 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):81-88
In this study we measured growth and milk intake and calculated energy intake and its allocation into metabolism and stored
tissue for hooded seal (Cystophora cristata) pups. In addition, we measured mass loss, change in body composition and metabolic rate during the first days of the postweaning
fast. The mean body mass of the hooded seal pups (n = 5) at the start of the experiments, when they were new-born, was 24.3 ± 1.3 kg (SD). They gained an average of 5.9 ± 1.1.
kg · day−1 of which 19% was water, 76% fat and 5% protein. This corresponds to an average daily energy deposition of 179.8 ± 16.0 MJ.
The pups were weaned at an average body mass of 42.5 ± 1.0 kg 3.1 days after the experiment was initiated. During the first
days of the postweaning fast the pups lost an average of 1.3 ± 0.5␣kg of body mass daily, of which 56% was water, 16% fat
and 28% protein. During the nursing period the average daily water influx for the pups was 124.6 ± 25.8 ml · kg−1. The average CO2 production during this period was 1.10 ± 0.20 ml · g−1 · h−1, which corresponds to a field metabolic rate of 714 ± 130 kJ · kg−1 · day−1, or 5.8 ± 1.1 times the predicted basal metabolic rate according to Kleiber (1975). During the postweaning fast the average
daily water influx was reduced to 16.1 ± 6.6 ml · kg−1. The average CO2 production in␣this period was 0.58 ± 0.17 ml · g−1 · h−1 which corresponds to a field metabolic rate of 375 ± 108 kJ · kg−1 · day−1 or 3.2 ± 0.9 times the predicted basal metabolic rate. Average values for milk composition were 33.5% water, 58.6% fat and
6.2% protein. The pups drank an average of 10.4 ± 1.8␣kg of milk daily, which represents an energy intake of 248.9 ± 39.1
MJ · day−1. The pups were able to store 73.2 ± 7.7% of this energy as body tissue.
Accepted: 15 August 1996 相似文献
12.
We report the effect of UV-B radiation (0.8 ± 0.1 mW cm−2) and UV-B radiation supplemented with low-intensity PAR (∼80 μmol photons m−2 s−1) on the photosynthesis, photosynthetic pigments, phosphoglycolipids, oxidative damage, enzymatic antioxidants, and UV-absorbing
compounds in Phormidium tenue, a marine cyanobacterium. UV-B radiation resulted in a decline in photosynthesis and photosynthetic pigments leading to lower
biomass. P. tenue synthesized UV-absorbing compounds like mycosporine-like amino acids (MAAs) and scytonemin in response to UV-B radiation.
Quantity of MAAs and scytonemin was higher when UV-B was supplemented with low-level PAR. UV-B treatment also resulted in
quantitative changes in phosphoglycolipids of the membrane. The UV-B treatment resulted in a slight increase in the level
of peroxidation of cell membrane and very little increase in the activity of superoxide dismutase (SOD). Results indicate
that UV-B affected photosynthesis and that the main protective system was the synthesis of MAAs and scytonemin-like compounds
rather than antioxidant enzymes such as SOD. 相似文献
13.
H. J. Cruz A. S. Ferreira C. M. Freitas J. L. Moreira M. J. T. Carrondo 《Applied microbiology and biotechnology》1999,51(5):579-585
In this work, a BHK21 clone producing a recombinant antibody/cytokine fusion protein was used to study the dependence of
cell metabolism on the glucose and glutamine levels in the culture medium. Results obtained indicate that both glucose and
glutamine consumptions show a Michaelis-Menten dependence on glucose and glutamine concentrations respectively. A similar
dependence is also observed for lactate and ammonia productions. The estimated value of the Michaelis constant for the dependence
of lactate production on glucose (K
Glc
Lac) was 1.4 ± 0.1 mM and for the dependence of ammonia production on glutamine (K
Gln
Amm) was 0.25 ± 0.11 mM and 0.10 ± 0.03 mM, at glucose concentrations of 0.28 mM and 5.6 mM respectively. At very low glucose
concentrations, the glucose to lactate yield decreased markedly, showing a metabolic shift towards lower lactate production.
This␣metabolic shift was also confirmed by the significant increase in the specific oxygen consumption rate also observed
at low glucose concentrations. Although it was␣highly dependent on glucose concentration, the oxygen consumption also increased
with the increase in␣glutamine concentration. At very low glutamine concentrations, the glutamine to ammonia yield increased,
showing a more efficient glutamine metabolism.
Received: 21 August 1998 / Received revision: 11 November 1998 / Accepted: 17 January 1999 相似文献
14.
K. Kirimura T. Sato N. Nakanishi M. Terada S. Usami 《Applied microbiology and biotechnology》1997,47(2):127-131
Interspecific protoplast fusion between␣Aspergillus terreus, an itaconic acid producer, and A.␣usamii, a glucoamylase producer, was done to breed new koji molds producing itaconic acid from starch. Protoplast fusion between auxotrophic mutant strains by poly(ethylene glycol) treatment
produced prototrophic fusants with a fusion frequency of 10−5−10−4. The stabilities of some fusants obtained were confirmed by successive subcultures. Conidial analyses of DNA contents and
the number of nuclei indicated that the fusants obtained were haploids like the parental strains. One of the stable fusants,
F-112, morphologically resembled A. terreus, and produced maximally 35.9 mg/ml itaconic acid from soluble starch (120 mg/ml) at day 6 of cultivation. This productivity
from soluble starch was five times as high as that of A. terreus and 70 % of that of A. terreus from glucose (120 mg/ml).
Received: 28 June 1996 / Received revision: 3 September 1996 / Accepted: 29 September 1996 相似文献
15.
Removal of nitrate and phosphate ions from water, by using the thermophilic cyanobacterium Phormidium laminosum, immobilized on cellulose hollow fibres in the tubular photobioreactor at 43 °C, was studied by continuously supplying dilute
growth medium for 7 days and then secondarily treated sewage (STS) for 12 days. The concentrations of NO−
3 and PO3−
4 in the effluent from the dilute growth medium decreased from 5.0 mg N/l to 3.1 mg N/l, and from 0.75 mg P/l to 0.05 mg P/l
respectively, after a residence time of 12 h. The concentrations of NO−
3 and PO3−
4 in the effluent from STS decreased from 11.7 mg N/l to 2.0 mg N/l, and from 6.62 mg P/l to 0.02 mg P/l respectively, after
a residence time of 48 h. The removal rates of nitrogenous␣and phosphate ions from STS were 0.24 and 0.11 mmol day−1 l reactor−1 respectively, under the same conditions. Although, among nitrogenous ions, nitrate and ammonium ions were efficiently removed
by P.␣laminosum, the nitrite ion was released into the effluent when STS was used as influent. Treatment of water with thermophilic P. laminosum immobilized on hollow fibres thus appears to be an appropriate means for the removal of inorganic nitrogen and phosphorus
from treated wastewater.
Received: 15 August 1997 / Received last revision: 18 November 1997 / Accepted: 29 November 1997 相似文献
16.
Solute mobilities in cuticular membranes of six species (Hedera helix, Malus domestica, Populus alba, Pyrus communis, Stephanotis floribunda, Strophantus gratus) were measured using plant hormones, growth regulators and other organic model compounds varying in molar volumes from 99
to 349 mL · mol−1 The dependence of mobilities (k*) on molar volume (V
x
) was exponential and could be described with equations of the type log
k*=log
k*0−′
V
x
. The y-intercepts (log
k*0) represent mobilities of a hypothetical solute of zero molar volume. The parameter β′ is a measure of size selectivity of
cuticular membranes and no differences among the six species were observed. At 25 °C the average β′ was 0.0095 mol · mL−1. Solute mobility decreased by about a factor of 8.9 when molar volume increased by 100 mL · mol−1 and the mobility of a compound with V
x
= 100 mL · mol−1 was about 700-fold higher than the mobility of a compound with V
x
= 400 mL · mol−1. Size selectivity decreased with increasing temperatures and for Strophantusβ′-values of 1.6 × 10−2 to 8.0 × 10-4 mol · mL−1 were obtained for 10 and 30 °C, respectively. The-intercepts (log k*0) differed among plant species by 3 orders of magnitude and since size selectivity was the same for all species, solute mobilities
for solutes having zero molar volumes were the sole cause for differences among species in solute mobilities and permeabilities.
We argue that these differences in k*0 are related to tortuosity of the diffusion path. These results were used to derive an equation which predicts rates of cuticular
penetration on the basis of k*0, the average size selectivity of 9.5 × 10−3 mol · mL−1 and the driving forces of penetration.
Received: 25 November 1997 / Accepted: 9 March 1998 相似文献
17.
18.
A versatile plasmid shuttle vector system was constructed, which is useful for genetic complementation of Helicobacter pylori strains or mutants with cloned genes of homologous or heterologous origin. The individual plasmid vectors consist of the
minimal essential genetic elements, including an origin of replication for Escherichia coli, a H. pylori-specific replicon originally identified on a small cryptic H. pylori plasmid, an oriT sequence and a multiple cloning site. Shuttle plasmid pHel2 carries a chloramphenicol resistance cassette (cat
GC) and pHel3 contains a kanamycin resistance gene (aphA-3) as the selectable marker; both are functional in E. coli and H. pylori. The shuttle plasmids were introduced into the H. pylori strain P1 by natural transformation. A efficiency of 7.0 × 10−7 and 4.7 × 10−7 transformants per viable recipient was achieved with pHel2 and pHel3, respectively, and both vectors showed stable, autonomous
replication in H. pylori. An approximately 100-fold higher H. pylori transformation rate was obtained when the shuttle vectors for transformation were isolated from the homologous H. pylori strain, rather than E. coli, indicating that DNA restriction and modification mechanisms play a crucial role in plasmid transformation. Interestingly,
both shuttle vectors could also be mobilized efficiently from E. coli into different H.␣pylori recipients, with pHel2 showing an efficiency of 2.0 × 10−5 transconjugants per viable H. pylori P1 recipient. Thus, DNA restriction seems to be strongly reduced or absent during conjugal transfer. The functional complementation
of a recA-deficient H. pylori mutant by the cloned H. pylorirecA
+ gene, and the expression of the heterologous green fluorescent protein (GFP) in H.␣pylori demonstrate the general usefulness of␣this system, which will significantly facilitate the molecular analysis of H. pylori virulence factors in the future.
Received: 22 April 1997 / Accepted: 4 November 1997 相似文献
19.
Michael J. Adams Blake R. Hossack Roland A. Knapp Paul Stephen Corn Stephen A. Diamond Peter C. Trenham Dan B. Fagre 《Ecosystems》2005,8(5):488-500
An increase in ultraviolet-B (UV-B) radiation has been posited to be a potential factor in the decline of some amphibian population.
This hypothesis has received support from laboratory and field experiments showing that current levels of UV-B can cause embryo
mortality in some species, but little research has addressed whether UV-B is influencing the distribution of amphibian populations.
We compared patterns of amphibian presence to site-specific estimates of UV-B dose at 683 ponds and lakes in Glacier, Olympic,
and Sequoia–Kings Canyon National Parks. All three parks are located in western North America, a region with a concentration
of documented amphibian declines. Site-specific daily UV-B dose was estimated using modeled and field-collected data to incorporate
the effects of elevation, landscape, and water-column dissolved organic carbon. Of the eight species we examined (Ambystoma gracile, Ambystoma macrodactylum, Bufo boreas, Pseudacris regilla, Rana cascadae, Rana leuteiventris, Rana muscosa, Taricha granulosa), two species (T. granulosa and A. macrodactylum) had quadratic relationships with UV-B that could have resulted from negative UV-B effects. Both species were most likely
to occur at moderate UV-B levels. Ambystoma macrodactylum showed this pattern only in Glacier National Park. Occurrence of A. macrodactylum increased as UV-B increased in Olympic National Park despite UV-B levels similar to those recorded in Glacier. We also found
marginal support for a negative association with UV-B for P. regilla in one of the two parks where it occurred. We did not find evidence of a negative UV-B effect for any other species. Much
more work is still needed to determine whether UV-B, either alone or in concert with other factors, is causing widespread
population losses in amphibians. 相似文献
20.
J. B. K. Leonard J. F. Norieka B. Kynard S. D. McCormick 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):287-295
To assess the energetics of migration in an anadromous fish, adult American shad (Alosa sapidissima) were swum in a large respirometer at a range of speeds (1.0–2.3 body lengths (BL) s−1, 13–24 °C). Metabolic rate (MO2) was logarithmically related to swimming speed (Bl s−1; r
2 = 0.41, slope = 0.23 ± 0.037) and tailbeat frequency (beats × min−1; r
2 = 0.52, slope = 0.003 ± 0.0003). Temperature had a significant effect on metabolic rate (r
2 = 0.41) with a Q10 of 2.2. Standard metabolic rate (SMR), determined directly after immobilization with the neuroblocker gallamine triethiodide,
ranged from 2.2–6.2 mmolO2 kg−1 h−1 and scaled with mass (W) such that SMR = 4.0 (±0.03)W0.695(±0.15). Comparison of directly determined and extrapolated SMR suggests that swimming respirometry provides a good estimate of SMR
in this species, given the differences in basal activity monitored by the two methods. Overall, American shad metabolic rates
(MO2 and SMR) were intermediate between salmonids and fast-swimming perciforms, including tunas, and may be a result of evolutionary
adaptation to their active pelagic, schooling life history. This study demonstrates variability in metabolic strategy among
anadromous fishes that may be important to understanding the relative success of different migratory species under varying
environmental conditions.
Accepted: 3 March 1999 相似文献