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1.
J. Lightner Ellen Lark D. James John Browse 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,94(8):975-981
The fab2-1 mutant of Arabidopsis is an extreme dwarf as a direct result of an increase in the levels of stearate (18 : 0) in membrane lipids. We isolated
a series of lines in which second-site suppressor mutations partly alleviate the dwarf phenotype. In all four of the suppressor
lines examined, restoration of more normal morphology is accompanied by decreases in leaf 18 : 0 content. Three of the isolated
suppressors suppress the high stearate phenotype in both leaves and seeds. The effects of one of the suppressors, TW2-1, is
limited to the leaves. A second allele at the fab2 locus, fab2-2, was also identified and plants homozygous for this allele where intermediate in both plant size and 18 : 0 content between
wild-type Arabidopsis and fab2-1 mutants. The alleles at fab2 and the suppressor mutations provided a total of nine genotypes which were analyzed to demonstrate a clear-cut relationship
between leaf 18 : 0 content (0.7–19.6% of total leaf fatty acids) and reductions in plant size (24–4 mm). These results illustrate
the utility of suppressor analysis for addressing problems in biochemistry and plant biology. They also indicate that the
genetic control of plant lipid composition is more complex than previously appreciated.
Received: 24 January 1997 / Accepted: 14 February 1997 相似文献
2.
Evidence for NO-dependent vasodilation in the trout (Oncorhynchus mykiss ) coronary system 总被引:1,自引:0,他引:1
T. Mustafa C. Agnisola J. K. Hansen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):98-104
The effects of l-arginine, and its analogues N
ω-nitro-l-arginine methyl ester and N
ω-nitro-l-arginine on vascular resistance were investigated in the intact coronary system of an isolated non-working trout heart preparation.
l-Arginine, at 10–8 mol · l–1induced a slight vasodilatory effect (max 10%). N
ω-nitro-l-arginine methyl ester and N
ω-Nitro-l-arginine in the range 10–8–10–4 mol · l–1 caused dose-dependent increases in coronary resistance. The vasodilatory action of l-arginine was abolished when the preparation was pretreated with 10–4 mol · l–1
N
ω-nitro-l-arginine or N
ω-nitro-l-arginine methyl ester. Nitroprusside alone at 1 mmol · l–1 induced a maximum vasodilation (30%) of the coronary system. Methylene blue a known inhibitor of guanylate cyclase, induced
a strong vasoconstriction (already significant at 10–5 mol · l–1) and was able to overcome the vasodilative effect of nitroprusside. The endothelial nitric oxide agonists acetylcholine and
serotonin, established in mammalian vessels, also mediate vasodilation in trout coronary system. In 50% of preparations, acetylcholine
induced a biphasic response with vasodilation at low concentration (max 15% at 10–8 mol · l–1). Serotonin displayed a dose-response vasodilation in the range 10–8–10–4 mol · l–1 (max 20%). These vasodilative effects were reduced or abolished by 10–4 mol · l–1
l-NA. These data support the existence of NO-mediated vasodilation mechanisms in the trout coronary system.
Accepted: 1 July 1996 相似文献
3.
Transpiration and whole-tree conductance in ponderosa pine trees of different heights 总被引:17,自引:0,他引:17
M. G. Ryan B. J. Bond B. E. Law R. M. Hubbard D. Woodruff E. Cienciala J. Kucera 《Oecologia》2000,124(4):553-560
Changes in leaf physiology with tree age and size could alter forest growth, water yield, and carbon fluxes. We measured tree
water flux (Q) for 14 ponderosa pine trees in two size classes (12 m tall and ∼40 years old, and 36 m tall and ∼ 290 years old) to determine
if transpiration (E) and whole-tree conductance (g
t) differed between the two sizes of trees. For both size classes, E was approximately equal to Q measured 2 m above the ground: Q was most highly correlated with current, not lagged, water vapor pressure deficit, and night Q was <12% of total daily flux. E for days 165–195 and 240–260 averaged 0.97 mmol m–2 (leaf area, projected) s–1 for the 12-m trees and 0.57 mmol m–2 (leaf area) s–1 for the 36-m trees. When photosynthetically active radiation (I
P) exceeded the light saturation for photosynthesis in ponderosa pine (900 μmol m–2 (ground) s–1), differences in E were more pronounced: 2.4 mmol m–2 (leaf area) s–1 for the 12-m trees and 1.2 mmol m–2 s–1 for the 36-m trees, yielding g
t of 140 mmol m–2 (leaf area) s–1 for the 12-m trees and 72 mmol m–2 s–1 for the 36-m trees. Extrapolated to forests with leaf area index =1, the 36-m trees would transpire 117 mm between 1 June
and 31 August compared to 170 mm for the 12-m trees, a difference of 15% of average annual precipitation. Lower g
t in the taller trees also likely lowers photosynthesis during the growing season.
Received: 19 April 1999 / Accepted: 23 March 2000 相似文献
4.
Beta–catenin is a multi–functional molecule that is involved in both cell–cell adhesion and signaling. We analyzed changes in β–catenin gene expression during mouse molar tooth development by in situ hybridization. Prominent up–regulation of the expression of this gene was evident exclusively in the enamel knot at the early cap stage. During the cap and bell stages, the enamel knot, inner dental epithelium, and differentiating stratum intermedium expressed the β–catenin gene more strongly than other parts of the enamel organ. During these stages, the strength of the gene expression changed heterogeneously within the inner dental epithelium and stratum intermedium. However, the heterogeneity was not evident at the late bell stage, when the cells in the inner dental epithelium had differentiated into ameloblasts at the cusp tip. No spatiotemporal change in β–catenin gene expression was apparent in the dental papilla except for the cells that differentiated into odontoblasts, which became negative for the expression of the gene after their differentiation. Thus, the up-regulated expression of the β–catenin gene was strongly associated with epithelial morphogenesis. These findings raise the possibility that the up–regulation of the gene expression and the stabilization of the protein by Wnt signaling play a role in the regulation of the activities of β–catenin in tooth morphogenesis. 相似文献
5.
Ole Rintek Madsen Ulrik Birk Lauridsen Andreas Hartkopp Ole Helmer S?rensen 《European journal of applied physiology and occupational physiology》1997,75(3):239-245
Dual energy x-ray absorptiometry (DEXA) offers the possibility of assessing regional soft tissue composition, i.e. lean mass (LM) and fat
mass : LM may be considered a measure of muscle mass. We examined age-related differences in LM, percentage fat (%fat) and
muscle strength in 100 healthy non-athletic women aged 18–87 years. Relationships between muscle strength and leg LM in 20
elite female weight lifters and in 18 inactive women with previous hip fractures were also studied. The LM and %fat of the
whole body, trunk, arms and legs were derived from a whole body DEXA scan. Isokinetic knee extensor strength (KES) and flexor
strength (KFS) at 30° · s–1 were assessed using an isokinetic dynamometer. The women aged 71–87 years had 35% lower KES and KFS than the women aged 18–40
years (P < 0.0001). Differences in LM were less pronounced. The LM of the legs, for instance, was 15% lower in the old than in the
young women (P < 0.0001). In a multiple regression analysis with age, body mass, height and leg LM or KES as independent variables and KES
or leg LM as the dependent variable, age was the most important predictor of KES (r
partial = −0.74, P < 0.0001). The same applied to KFS. Body mass, not age, was the most important predictor of leg LM (r
partial = 0.65, P < 0.0001) and of LM at all other measurement sites. The LM measured at different regions decreased equally with increasing
age. The KES:leg LM ratio was negatively correlated with age (r = −0.70, P < 0.0001). The weight lifters had significantly higher KES:leg LM ratios than age-matched controls (+12%, P < 0.0001) and vice versa for the women with previous hip fractures (–36%, P < 0.0001). In conclusion, from our study it would seem that in healthy nonathletic women, age is a more important determinant
of muscle strength than is LM as measured by DEXA. Muscle strengthening exercises and inactivity seem to have a considerably
stronger influence on muscle strength than on LM.
Accepted: 27 August 1996 相似文献
6.
7.
Yurixhi Maldonado–López Edelmira Linares–Mazari Robert Bye Guillermo Delgado Francisco J. Espinosa–García 《Economic botany》2008,62(2):161-170
Mexican Arnica Anti–Inflammatory Action: Plant Age Is Correlated with the Concentration of Anti–inflammatory Sesquiterpenes
in the Medicinal Plant
Heterotheca inuloides
Cass. (Asteraceae). Mexican árnica (Heterotheca inuloides Cass.) is a widely used anti–inflammatory medicinal plant in Mexican folk medicine. Although it has been suggested that plant
age, fertilization, and harvesting regime influence the concentration of secondary compounds affecting the therapeutic activity
of the plant, the effect of these variables on the concentration of the Mexican árnica anti–inflammatory compounds was not
known. We quantified anti–inflammatory sesquiterpenes (caryolan–1, 9β–diol, cadalen–15–oic acid, 7–hydroxycadalene, 4–hydroxy–2–isopropyl–4,
7–dimethyl–1[4H] naftalinone, 7–hydroxy–4αH–3, 4–dihydrocadalene, β–caryophyllene, and β–caryophyllene epoxide) in Mexican
árnica plants subjected to fertilization and successive harvests of flowering stems, conditions that mimic the cultivation
and harvesting for árnica in México. Fertilization and successive harvesting and their interaction had no significant effect
on the concentration of anti–inflammatory compounds. However, the concentrations of these compounds were 60% higher in flowering
stems from 15–month–old plants than in those from 4– or 8–month–old plants and was independent of the number of harvests and
fertilization regime applied. 相似文献
8.
Akihisa Torii Antony S. Harold Takakazu Ozawa Yukio Iwatsuki 《Ichthyological Research》2003,50(2):129-139
This study redescribes Bregmaceros mcclellandi Thompson, 1840, based on one specimen (74.4 mm SL) from the Bay of Bengal and 66 specimens (30.0–84.7 mm SL) from Mumbai
(Bombay), India, because the type specimens have apparently been lost. The present specimens are characterized by having black
dorsal, pectoral, and caudal fins and show the following morphology: caudal fin slightly forked; body chromatophores present
mainly at the dorsal part; no scales on cheek; vertebrae 52–55 (13–15 + 38–41); dorsal rays 52–59; anal rays 54–60; pectoral
rays 18–20; caudal rays 27–31 (principal rays 14); transverse scales 14–15. In the 66 Mumbai specimens, it was confirmed that
the distinctive black fin pigmentation developed sequentially with growth, with complete pigmentation first on the anterior
lobe of the dorsal fin, then simultaneously on the posterior lobe of the dorsal fin, the caudal fin, and the pectoral fin,
and last, on the anal fin. This species is known only from the Arabian Sea, Bay of Bengal, and Gulf of Thailand. A review
of 16 nominal Bregmaceros species indicates that, besides B. mcclellandi, the distinctive dark fin pigmentation is found in B. atripinnis (Tickell), B. atlanticus Goode and Bean, B. japonicus Tanaka, and B. lanceolatus Shen. B. atripinnis is considered a junior synonym of B. mcclellandi, and the others are clearly distinct from B. mcclellandi. Comments are made on some of the characters to more fully characterize the species and for reference in future revisionary
and phylogenetic studies.
Received: June 17, 2002 / Revised: December 2, 2002 / Accepted: December 24, 2002 相似文献
9.
The accumulation of different precursors of carotenoid biosynthesis in carotenoid-deficient mutants of Chlamydomonas reinhardtii was studied by HPLC-analysis. ζ-Carotene accumulated in several ac5 mutants, this character cosegregated with mutations in the ac5 gene. Two groups of ac5 mutants differing in ζ-carotene accumulation were distinguished. One (ac5–1) accumulated ζ-carotene in the dark but not in the light. The other (ac5–2) accumulated ζ-carotene under both dark and light conditions. ac5–2 strains accumulated more ζ-carotene in the dark than ac5-1 strains. Genetic data suggested that the mutations ac5–1 and ac5–2 were allelic. Pleiotropic effects of mutations in the ac5 gene included decreased levels of chlorophyll a and b and acetate requirement. The results are consistent with the presence
of a defective ζ-carotene desaturase in ac5 mutants.
Received: 27 October 1998 / Revision received: 1 February 1999 / Accepted: 16 February 1999 相似文献
10.
Heat and mass exchange processes between the surface of the human body and ambient air at various altitudes 总被引:1,自引:0,他引:1
I. M. Kandjov 《International journal of biometeorology》1999,43(1):38-44
The rates of convection and evaporation at the interface between the human body and the surrounding air are expressed by
the parameters convective heat transfer coefficient h
c, in W m–2°C–1 and evaporative heat transfer coefficient h
e, W m–2 hPa–1. These parameters are determined by heat transfer equations, which also depend on the velocity of the airstream around the
body, that is still air (free convection) and moving air (forced convection). The altitude dependence of the parameters is
represented as an exponential function of the atmospheric pressure p: h
c∼p
n and h
e∼p
1–n, where n is the exponent in the heat transfer equation. The numerical values of n are related to airspeed: n=0.5 for free convection, n=0.618 when airspeed is below 2.0 ms–1 and n=0.805 when airspeed is above 2.0 ms–1. This study considers the coefficients h
c and h
e with respect to the similarity of the two processes, convection and evaporation. A framework to explain the basis of established
relationships is proposed. It is shown that the thickness of the boundary layer over the body surface increases with altitude.
As a medium of the transfer processes, the boundary layer is assumed to be a layer of still air with fixed insulation which
causes a reduction in the intensity of heat and mass flux propagating from the human body surface to its surroundings. The
degree of reduction is more significant at a higher altitude because of the greater thickness of the boundary layer there.
The rate of convective and evaporative heat losses from the human body surface at various altitudes in otherwise identical
conditions depends on the following factors: (1) during convection – the thickness of the boundary layer, plus the decrease
in air density, (2) during evaporation (mass transfer) – the thickness of the boundary layer, plus the increase with altitude
in the diffusion coefficient of water vapour in the air. The warming rate of the air volume due to convection and evaporation
is also considered. Expressions for the calculation of altitude dependences h
c (p) and h
e (p) are suggested.
Received: 23 June 1998 / Accepted: 10 February 1999 相似文献
11.
V. B. Meyer-Rochow W. A. Reid 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1996,166(5):319-324
Fifty randomly selected publications dealing with aspects of crustacean vision had their Materials and methods sections examined. In half of the articles gleaned, only the name of the animal under study was given; the other half mentioned
“adult” or “mature” animals; twelve papers provided information on size or age of the experimental animal and six gave the
sex. In Petrolisthes elongatus, rhabdom microvilli not only become more regular in outline as the animal grows, but also decrease in diameter from 90.4±21.2 nm
in crabs of 5.0–8.9 mm carapace length via 86.6±13 nm in crabs of 9.0–12.9 mm carapace length to 79.7±7 nm in crabs of 13.0–16.9 mm
carapace length. Approximately 400 cross sectional diameters of microvilli from identical regions in four eyes of each size
class were measured and provided the basis for Anova-, Levene-, and t-tests. The three size classes possess microvilli of significantly different diameters and standard deviations. Our observations
show that investigators of the crustacean photoreceptor have frequently neglected to consider the size of their experimental
animals, but that this practice should not be continued as the now documented changes in microvillus diameters may influence
the amount of visual pigment present and, thus, the photoreceptor’s sensitivity to light.
Accepted: 7 May 1996 相似文献
12.
This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with
or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment
(Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O2max = 55.5 (4.4 SD) ml kg−1 min−1]. The RE was measured at 3 m s−1 [65 (6)% V˙O2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined
from prior tests, to maintain body mass (group mean = 17.4 ml min−1). The V˙O2 during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase
in V˙O2 from RE1 to RE2 ranged from 3.4 to 4.7 ml kg−1 min−1 across treatments. In conclusion, the deterioration in RE at 3 m s−1 (65% V˙O2max) after 60 min of running at 80% V˙O2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or
electrolytes, in both a thermoneutral and in a hot, humid environment.
Accepted: 30 October 1997 相似文献
13.
14.
Seasonal changes in fatty acid composition associated with cold-hardening in third instar larvae of Eurosta solidaginis 总被引:1,自引:1,他引:0
Valerie A. Bennett Nancy L. Pruitt Richard E. Lee Jr. 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):249-255
Third-instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) survive extended periods in winter during which tissue water is frozen. Both low temperature and reduced
water activity during freezing present challenges for the structural integrity of cellular lipids. Fatty acids of both phospholipids
and triacylglycerols from fat body cells of E. solidaginis were analyzed throughout fall and early winter, a period that encompasses the acquisition of freeze-tolerance, to determine
if adaptations to freezing include changes in fatty acid unsaturation. The five most abundant fatty acids from both fractions
were (in decreasing order) oleic (40–65%), palmitoleic (18–20%), palmitic (12–17%), linoleic (5–10%), and stearic acids (4 –7%).
This represents a typical complement of Dipteran fatty acids, although oleic acid levels were higher in E. solidaginis than those reported from other Dipterans (˜28%; Downer 1985). From September to November, monounsaturates increased from
59 to 70% in phospholipids at the expense of saturated fatty acids (25% –20%) suggesting activation of a Δ9-desaturase enzyme. These changes resulted in an increase in the ratio of unsaturated to saturated fatty acids (U/S) from
3.0 to 4.2, although there was no change in the average number of double bonds per fatty acid (unsaturation index, UI ≈ 1.2
in phospholipids and 0.9 in triacylglycerols throughout the season). These changes were temporally correlated to decreasing
ambient temperatures and increasing larval and fat body cell freeze-tolerance.
Accepted: 31 October 1996 相似文献
15.
Using an exclosure experiment in the willow stage of primary succession on the floodplain of the Tanana River, we tested
the hypothesis that browsing can reduce mycorrhizal infection. We measured the effects winter browsing by moose (Alcesalces) and snowshoe hare (Lepusamericanus) had on mycorrhizal infection and fine root biomass of willow (Salix spp.) and balsam poplar (Populusbalsamifera). We found that protection from winter browsing increased ectomycorrhizal infection by 10% in the top 5 cm of the soil profile,
by 23% at 5–10 cm, and by 42% at the 10–15 cm depth. Mammal browsing in taiga forests is now recognized as a major cause of
the shift from palatable deciduous species such as willow and balsam poplar to less palatable species such as alder and spruce.
We suggest that browsing-induced reduction in ectomycorrhizal infection of salicaceous species plays a central role in this
shift in plant community composition.
Received: 26 March 1996 / Accepted: 26 September 1996 相似文献
16.
R. L. Wolff Bernard Comps Anne M. Marpeau Laurent G. Deluc 《Trees - Structure and Function》1997,12(2):113-118
The fatty acid compositions of the seed oils from ten pine species have been established by capillary gas-liquid chromatography
of the methyl esters. With regard to either normal fatty acids or Δ5-olefinic acids, the general pattern of fatty acids did
not differ from that of other pine seed oils reported previously. The main fatty acid was linoleic (9,12–18:2) acid (44.4–57.1%),
followed by either oleic (9–18:1) acid (13.4–24.5%) or pinolenic (5,9,12–18:3) acid (1.5–25.2%). When applying multivariate
analyses to the chemometric data (13 variables) of 49 pine species (ca. 40% of the living pine species), it was possible to
distinguish between several sections: Pinea, Longifolia, Halepensis, Ponderosa-Banksiana, Sylvestris, and Cembra. The latter section was clearly divided into two sub-groups. A few species that presented a low overall content of Δ5-olefinic
acids, and that grow in warm-temperate regions, were isolated from the bulk of other pine species. It is hypothesized that
Δ5-olefinic acids might be related to cold-acclimation.
Received: 5 June 1997 / Accepted: 17 August 1997 相似文献
17.
In the heterothallic ascomycete Podospora anserina, the mating-type locus is occupied by two mutually exclusive sequences termed mat+ and mat–. The mat+ sequence contains only one gene, FPR1, while the mat– sequence contains three genes: FMR1, SMR1 and SMR2. Previous studies have demonstrated that FPR1 and FMR1 are required for fertilization. Further analyses have led to the hypothesis that mat+ and mat– genes establish a mat+ and mat– nuclear identity, allowing recognition between nuclei of opposite mating type within the
syncytial cells formed after fertilization. This hypothesis was based on the phenotypes of strains bearing mutations in ectopic
mat genes. Here we present an analysis of mutations in resident mat– genes which suggests that, unlike FMR1 and SMR2, SMR1 is not involved in establishing nuclear identity. In fact, mutations in these two genes impair nuclear recognition, leading
to uniparental progeny, while mutations in SMR1 block the sexual process, probably at a step after nuclear recognition. The nuclear identity hypothesis has also been tested
through internuclear complementation tests. In these experiments, the mat– mutants were crossed with a mat+ strain carrying the wild-type mat– genes. Our rationale was that internuclear complementation should not be possible for nuclear identity genes: the relevant
genes should show nucleus-restricted expression, and diffusion of their products to other nuclei should not occur. This test
confirmed that SMR1 is not a bona fide mat gene since it can fulfill its function whatever its location, in either a mat− or a mat+ nucleus, and even when present in both nuclei. SMR2, but not FMR1, behaves like a nuclear identity gene with respect to internuclear complementation tests. A model is proposed that tentatively
explains the ambiguous behaviour of the FMR1 gene and clarifies the respective functions of the three mat– proteins.
Received: 15 October 1996 / Accepted: 25 April 1997 相似文献
18.
Two genetic linkage maps of tetraploid roses 总被引:11,自引:0,他引:11
S. Rajapakse D. H. Byrne L. Zhang N. Anderson K. Arumuganathan R. E. Ballard 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2001,103(4):575-583
A tetraploid F2 progeny segregating for resistance to black spot, growth habit, and absence of prickles on the stem and petioles was used
to construct genetic linkage maps of rose. The F1 of the progeny, 90–69, was created by crossing a black spot-resistant amphidiploid, 86–7, with a susceptible tetraploid,
82–1134. The F1 was open-pollinated to obtain 115 seedlings. AFLP and SSR markers were used to eliminate seedlings produced through cross-fertilization.
The remaining progeny set of 52 F2 plants was used to study the inheritance of 675 AFLPs, one isozyme, three morphological and six SSR markers. AFLP markers
were developed with three combinations of restriction enzymes, EcoRI/MseI, KpnI/MseI and PstI/MseI. Most of the markers appear to be in simplex or single-dose and segregated 3:1 in the progeny. One linkage map was constructed
for each parent using only the single-dose markers. The map of 86–7 consists of 171 markers assigned to 15 linkage groups
and covering more than 902 cM of the genome. The map of 82–1134 consists of 167 markers assigned to 14 linkage groups and
covering more than 682 cM of the genome. In the AFLP analysis, EcoRI/MseI generated nearly twice as many markers per run than PstI/MseI. Markers developed with three restriction enzyme combinations showed a mixed distribution throughout the maps. A gene controlling
the prickles on the petiole was located at the end of linkage group 7 on the map of 86–7. A gene for malate dehydrogenase
locus 2 was located in the middle of linkage group 4 on the map of 86–7. These first-generation maps provide initial tools
for marker- assisted selection and gene introgression for the improvement of modern tetraploid roses.
Received: 20 June 2000 / Accepted: 13 January 2001 相似文献
19.
The heat increment of feeding in house wren chicks: magnitude, duration, and substitution for thermostatic costs 总被引:3,自引:3,他引:0
Mark. A. Chappell Gwendolyn C. Bachman Kimberly A. Hammond 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(4):313-318
The heat increment of feeding (HIF), a transient postprandial increase in metabolic rate, is the energy cost of processing
a meal. We measured HIF in house wren chicks (Troglodytes aedon) ranging in mass from 1.6 to 10.3 g. This mass range (age 2–10 days) spanned a transition from blind, naked, ectothermic
chicks through alert, endothermic birds with nearly complete feathering. We fed chicks crickets (2.7–10% of chick body mass)
and determined HIF from continuous measurements of oxygen consumption rate (O2) before and after meals. At warm ambient temperatures (T
a) of 33–36 °C, the magnitude of HIF (in ml O2 or joules) was linearly related to meal mass and was not affected by chick mass. HIF accounted for 6.3% of ingested energy,
which is within the range of results for other carnivorous vertebrates. The duration of HIF was inversely related to chick
mass; 10-g chicks processed a standard meal approximately twice as fast as 2-g chicks. HIF duration increased with increasing
meal mass. The peak O2 during HIF, expressed as the factorial increase above resting metabolism, was independent of body mass and meal mass. In
large, endothermic chicks ( > 8 g), HIF substituted for thermoregulatory heat production at low T
a.
Accepted: 11 December 1996 相似文献
20.
A dense accumulation of the phototrophic consortium “Pelochromatium roseum” in a small, eutrophic, freshwater lake (Dagowsee, Brandenburg, Germany) was investigated. Within the chemocline, the number
of epibionts of the consortia represented up to 19% of the total number of bacteria. Per “P. roseum” a mean value of 20 epibionts was determined. Similar to other aquatic habitats, consortia in the Dagowsee were found only
at low light intensities (< 7 μmol quanta m–2 s–1) and low sulfide concentrations (0–100 μM). In dialysis cultures of “P. roseum”, bacterial cells remained in a stable association only when incubated at light intensities between 5 and 10 μmol quanta
m–2 s–1. Intact consortia from natural samples had a buoyant density of 1046.8 kg m–3, which was much higher than that of ambient chemocline water (995.8 kg m–3). Under environmental conditions and without motility, this density difference would result in rapid sedimentation of consortia
toward the lake bottom. Our results indicate that (1) consortia are adapted to a very narrow regime of light intensities and
sulfide concentrations, (2) motility and tactic responses must be of ecological significance for the colonization of the free
water column of lakes, and (3) phototrophic growth of consortia can be explained only by a cycling of sulfur species in the
chemocline, possibly within the consortia themselves.
Received: 27 May 1997 / Accepted: 16 September 1997 相似文献