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1.
The Pseudomonas aeruginosa leuB gene, encoding 3-isopropylmalate dehydrogenase, was identified upstream of asd, encoding aspartate-β-semialdehyde dehydrogenase. Genetic analysis indicated that leuB is identical to the previously mapped gene defined by the leu-10 allele. The chromosomal leuB locus was inactivated by gene replacement. The insertions had no adverse effect on expression of the downstream asd gene but resulted in leucine auxotrophy. The leuB gene encodes a protein containing 360 amino acids (with a molecular weight of 39153), which was expressed in Escherichia coli as a M, 42000 protein. The results suggested that, in contrast to the situation in other bacteria (E. coli, Salmonella typhimurium and Bacillus subtilis) the P. aeruginosa leuB gene is physically separated from the genes encoding the other enzymes of the isopropylmalate pathway.
Received: 15 August 1996 / Accepted: 23 October 1996 相似文献
2.
Oxygen consumption in the foraging honeybee depends on the reward rate at the food source 总被引:1,自引:1,他引:0
L. Moffatt Josué A. Núñez 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):36-42
Oxygen consumption of the honeybee Apis mellifera ligustica was measured as a function of the flow rate supply of sucrose solution at an automatic feeder located inside a respirometric
chamber. Trained bees freely entered the respirometric chamber and collected the sucrose solution supplied. The mean value
of the O2 consumption rate per visit increased with the sucrose flow rate, and for a given flow rate, with increasing locomotor activity.
However, when no locomotor activity was displayed, O2 consumption also increased with increasing nectar flow rate. Crop load attained at the end of the visit showed a positive
relationship with the nectar flow rate; however, for a given flow rate, O2 consumption showed either no correlation or a negative one with the final crop load attained. It is concluded that the energy
expenditure of the foraging bee is controlled by a motivational drive whose intensity depends on the reward rate at the food
source.
Accepted: 30 July 1996 相似文献
3.
E. R. Wood D. E. Wiel J. C. Weeks 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):639-657
The larval proleg withdrawal reflex of the hawk moth, Manduca sexta, exhibits robust habituation. This reflex is evoked by deflecting one or more mechanosensory planta hairs on a proleg tip.
We examined neural correlates of habituation in an isolated proleg preparation consisting of one proleg and its segmental
ganglion. Repeated deflection of a single planta hair caused a significant decrease in the number of action potentials evoked
in the proleg motor nerve (which carries the axons of proleg retractor motor neurons). Significant response decrement was
seen for interstimulus intervals of 10 s, 60 s and 5 min. Response decrement failed to occur in the absence of repetitive
stimulation, the decremented response recovered spontaneously following a rest, and electrical stimulation of a body wall
nerve facilitated the decremented response (a neural correlate of dishabituation). Adaptation of sensory neuron responses
occurred during repeated hair deflections. However, when adaptation was eliminated by direct electrical stimulation of sensory
neurons, the response in the proleg motor nerve still decreased significantly. Muscle recordings indicated that the response
of an identified proleg retractor motor neuron decreased significantly during habituation training. Thus, habituation of the
proleg withdrawal reflex includes a central component that is apparent at the level of a single motor neuron.
Accepted: 20 December 1996 相似文献
4.
S. Egginton 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(2):129-134
The physiological responses to forced exercise were studied in yellowbelly and marbled rockcod (Notothenia coriiceps and N. rossii), and the haemoglobinless icefish (Chaenocephalus aceratus), from blood samples obtained via indwelling catheters. The maximal exertion tolerable by N. coriiceps was 3–5 min, although N. rossii was not fully exhausted by this effort, and it proved difficult to elicit sustained maximal activity in C. aceratus. Arterial O2 tension reflected the relative degree of exhaustion, showing a significant fall in the case of N. coriiceps, little change in N. rossii, and even a rise in C. aceratus as a result of hyperventilation. Such changes in the red-blooded species were not caused by altered O2 carrying capacity, as there was no change in haematocrit. In Notothenia spp. the decrease in arterial pH was better correlated with a rise in arterial CO2 tension than with blood lactate concentration, which is reflected in a modest net metabolic acid load. In contrast, the icefish
showed an attenuated hypercapnia and a more pronounced lactacidosis, but an insignificant net metabolic acid load. Disturbance
in ionoregulation following exercise was limited to an elevated [Cl−] in Notothenia, while circulating catecholamine levels remained unusually low in all specimens. The response to stress appears to reflect
lifestyle and/or endemic speciation, rather than specific adaptations to the stenothermal environment.
Accepted: 9 August 1996 相似文献
5.
T. Jellema W. J. Heitler 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):659-669
The cuticle strain which develops in the hindleg tibiae when a locust prepares to kick, or when the tibia thrusts against
an obstacle, is detected by two campaniform sensilla, which reflexly excite the fast extensor tibiae motoneuron, some of the
flexor tibiae motoneurons and nonspiking interneurons. The reflex excitation is adaptive for the extensor motoneuron during
both co-activation and thrusting, but is only adaptive for the flexor motoneurons during co-activation, and is maladaptive
during thrusting. We show that the femoral chordotonal organ, which monitors tibial position, controls the efficacy of the
strain feedback. The campaniform sensilla-induced depolarization in the extensor motoneuron is about twice as large when the
tendon is in mid position (reflecting a tibial-femoral angle of 90°) than when fully stretched (reflecting tibial flexion),
while in the flexors the reverse is true. The amplitudes of excitatory postsynaptic potentials evoked by single campaniform
sensilla spikes, are, however, not affected. Our data suggests that the chordotonal organ modulates the gain of the strain
feedback onto the motoneurons by exciting interneuronal circuits whose output sums with the former. Thrusting typically occurs
with the tibia partially extended, therefore the actions of the chordotonal organ support the production of a maximal thrusting
force.
Accepted: 27 December 1996 相似文献
6.
DeForest Mellon Jr. 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):553-565
The cellular substrates of antennular flicking behavior in the crayfish Procambarus clarkii were investigated. Flicking involves fast downward movements of the external filament of each biramous antennule (1st antenna),
and is mediated by phasic contractions of a short muscle, the external filament depressor. Phasic contractions of the external
filament depressor depend upon stereotyped impulse bursts in a single motorneuron (P1). These bursts have a characteristic
impulse frequency profile that is consistent upon successive occurrences. The temporal characteristics of the impulse burst
suggest that the central depolarizations generating each burst may be similar to driver potentials described for motor neurons
in crustacean cardiac ganglia. Responses of the external filament to odorants have a long latency and are characterized by
repetitive bursts and tonic activity in some external filament depressor fibers. Tonic activity in a slowly contracting muscle,
the antennular depressor muscle, is also evoked by chemical stimulation. Flicking is consistently evoked only by mechanical
or hydrodynamic stimulation of the cephalothorax, antennae and antennules. The sensitivity and short latency of the hydrodynamic
antennule-generated flick reflex is consistent with the sensitivity of rapidly conducting, hydrodynamically activated mechanoreceptor
neurons in both antennular filaments. I propose that antennular flicking, which has been shown to enhance the dynamic response
characteristics of olfactory receptor neurons on the external antennular filament, has evolved as a response to the turbulence
associated with fluid movement, within which chaotic odorant concentration fronts may be imbedded.
Accepted: 23 October 1996 相似文献
7.
Blinda E. McClelland Walter Wilczynski A. Stanley Rand 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):451-462
We examined auditory tuning and the morphology of the anatomical structures underlying acoustic communication in female Hyla microcephala and H. ebraccata and compared our findings to data from a previous study (Wilczynski et al. 1993) in which we showed species differences in
the traits that in males relate to differences in the species-typical calls. Female species differences in the best excitatory
frequency (BEF) of the basilar papilla (BP) were similar to the differences seen in males, and females had a significantly
lower BEF in H. ebraccata, but not H. microcephala. In both species, females had lower BP thresholds. Snout-vent length, head width, and tympanic membrane diameters were sexually
dimorphic in both species and larger in females, whereas laryngeal components were sexually dimorphic and larger in males.
Middle and inner ear volumes were not sexually dimorphic. Despite the significant species differences in laryngeal morphology
seen in males, female larynges are not significantly different. Furthermore, the interaction of species and sex differences
resulted in significantly different degrees of sex dimorphism in the species, particularly for the larynx, which is more sexually
dimorphic in H. microcephala, and measures of body size, which are more dimorphic in H. ebraccata.
Accepted: 6 December 1996 相似文献
8.
Stuart I. Cromarty Charles D. Derby 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):481-491
The aim of our paper was to investigate whether single olfactory receptor neurons (ORNs) of the spiny lobster Panulirus argus functionally express more than one type of receptor, examine the consequences of this on coding of mixtures, and compare
principles of odorant mixture coding by spiny lobsters with that by the channel catfish, which has been studied extensively
using the same experimental and analytical procedures (Caprio et al. 1989; Kang and Caprio 1991). We examined responses of
individual taurine-sensitive ORNs to binary mixtures of excitatory compounds, either competitive agonists (taurine, β-alanine,
hypotaurine) or non-competitive agonists (taurine, l-glutamate, ammonium chloride, adenosine-5′-monophosphate). Responses to mixtures were compared to two indices: mixture discrimination
index (MDI) and independent component index (ICI). Binary mixtures of competitive agonists had MDI values close to 1.0, as
expected for competitors. Mixtures of non-competitive agonists had ICI values averaging 0.83, indicating the effects of the
components are not independent. We conclude that individual olfactory cells of spiny lobsters can express more than one type
of receptor mediating excitation, one of which typically has a much higher density or affinity, and that spiny lobster and
catfish olfactory cells encode mixtures of two excitatory agonists using similar rules.
Accepted: 20 December 1996 相似文献
9.
Peter J. Simmons F. Claire Rind 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(3):203-214
The LGMD2 belongs to a group of giant movement-detecting neurones which have fan-shaped arbors in the lobula of the locust
optic lobe and respond to movements of objects. One of these neurones, the LGMD1, has been shown to respond directionally
to movements of objects in depth, generating vigorous, maintained spike discharges during object approach. Here we compare
the responses of the LGMD2 neurone with those of the LGMD1 to simulated movements of objects in depth and examine different
image cues which could allow the LGMD2 to distinguish approaching from receding objects. In the absence of stimulation, the
LGMD2 has a resting discharge of 10–40 spikes s−1 compared with <1 spike s−1 for the LGMD1. The most powerful excitatory stimulus for the LGMD2 is a dark object approaching the eye. Responses to approaching
objects are suppressed by wide field movements of the background. Unlike the LGMD1, the LGMD2 is not excited by the approach
of light objects; it specifically responds to movement of edges in the light to dark direction. Both neurones rely on the
same monocular image cues to distinguish approaching from receding objects: an increase in the velocity with which edges of
images travel over the eye; and an increase in the extent of edges in the image during approach.
Accepted: 23 October 1996 相似文献
10.
Photoperiodic time measurement regulating larval diapause in the pitcher-plant mosquito, Wyeomyia smithii, varies in a close relationship with latitude. The critical photoperiod mediating the maintenance and termination of diapause
is positively correlated with latitude (r
2 = 0.977) among six populations from southern (30–31° N), intermediate (40° N), and northern (46–49° N) latitudes in North
America. The developmental response to unnaturally short and to unnaturally long photoperiods declines with increasing latitude,
so that longer critical photoperiods are associated with a downward rather than a lateral shift in the photoperiodic response
curve. Exotic light and dark cycles of varying period (T) with a short (10 h) photophase and a scotophase ranging from 14
(T = 24) to 62 (T = 72) h, reveal two geographic patterns: a decline in perturbability of the photoperiodic clock with increasing
latitude, and no change with latitude in the 21-h period of rising and falling development with increasing T. These results
show (1) that there is a rhythmic component to photoperiodic time measurement in W. smithii, (2) that the period of this rhythm is about 21 h in all populations, and (3) that more northern populations show decreasing
responsiveness to photoperiod and increasing stability against perturbation by exotic period lengths (T > 24). Previous studies
on W.␣smithii indicate that this single temperate species of a tropical and subtropical genus has evolved from south to north. We therefore
conclude that the evolution of increasing critical photoperiod in W. smithii during its adaptive radiation into North America has more likely involved the amplitude and not the period of the underlying
circadian pacemaker.
Received: 22 July 1996 / Accepted: 30 September 1996 相似文献
11.
Post-dispersal seed predation and the establishment of vertebrate dispersed plants in Mediterranean scrublands 总被引:4,自引:0,他引:4
Philip E. Hulme 《Oecologia》1997,111(1):91-98
The post-dispersal fate of seeds and fruit (diaspores) of three vertebrate-dispersed trees, Crataegus monogyna, Prunus mahaleb and Taxus baccata, was studied in the Andalusian highlands, south-eastern Spain. Exclosures were used to quantify separately the impact of
vertebrates and invertebrates on seed removal in relation to diaspore density and microhabitat. The three plant species showed
marked differences in the percentage of diaspores removed, ranging from only 5% for C. monogyna to 87% for T. baccata. Although chaffinches (Fringilla coelebs) fed on diaspores, rodents (Apodemus sylvaticus) were the main vertebrate removers of seed and fruit. Two species of ant (Cataglyphis velox and Aphaenogaster iberica) were the only invertebrates observed to remove diaspores. However, the impact of ants was strongly seasonal and they only
removed P. mahaleb fruit to any significant extent. While removal of seed by rodents was equivalent to predation, ants were responsible for
secondary dispersal. However, their role was limited to infrequent, small-scale redistribution of fruit in the vicinity of
parent trees. Rodents and ants differed in their use of different microhabitats. Rodents foraged mostly beneath trees and
low shrubs and avoided open areas while the reverse was true of ants. Thus, patterns of post-dispersal seed removal will be
contigent on the relative abundance and distribution of ants and rodents. Studies which neglect to quantify separately the
impacts of these two guilds of seed removers may fail to elucidate the mechanisms underlying patterns of post-dispersal seed
removal. The coincidence of both increased seed deposition by the main avian dispersers (Turdus spp.) and increased seed predation with increasing vegetation height suggested that selection pressures other than post-dispersal
seed predation shape the spatial pattern of seed dispersal. Rather than providing a means of escaping post-dispersal seed
predators, dispersal appears to direct seeds to microhabitats most suitable for seedling survival. Nevertheless, the reliance
of most vertebrate-dispersed trees on regeneration by seed and the absence of persistent soil seed banks imply that post-dispersal
seed predators may exert a strong influence on the demography of the plants whose seeds they consume. Even where microsites
are limited, the coincidence of the most suitable microhabitats for seedling establishment with those where seed predation
is highest provide a means by which selective seed predators can influence community composition.
Received: 19 August 1996 / Accepted: 25 January 1997 相似文献
12.
V. M. King B. K. Follett 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):541-551
c-fos induction was investigated as a potential component in the avian photic entrainment pathway and as a possible means of locating
the central pacemaker in birds. In both quail (Coturnix coturnix japonica) and starlings (Sturnus vulgaris) exposure to 1 h of light induced Fos-lir in the visual suprachiasmatic nucleus but not in the medial suprachiasmatic nucleus. However, the degree of c-fos induction in the visual suprachiasmatic nucleus was similar at different circadian times despite the fact that the light
pulses caused differential phase shifts in the locomotor rhythm. For golden hamsters the same experiment resulted in significantly
different levels of Fos-lir in the suprachiasmatic nucleus, as well as different phase shifts. Starlings and hamsters were also entrained to T-cycles that caused a large daily phase shift (T = 21.5 h in starlings, T = 22.67 hours in hamsters), or no daily phase shift (T = free running period). No difference in the induced levels of Fos-lir in the visual suprachiasmatic nucleus region was observed between the two groups of starlings, but in hamsters there were
significantly different levels of Fos-lir in the suprachiasmatic nucleus between the two groups.
Accepted: 15 November 1996 相似文献
13.
The central grassland region of the United States encompasses major gradients in temperature and precipitation that determine
the distribution of plant life forms, which in turn may influence key ecosystem processes such as nutrient cycling and soil
organic matter dynamics. One such gradient is the threefold increase in precipitation from the eastern Colorado shortgrass-steppe,
in the rain shadow of the Rocky Mountains, to the tallgrass prairie in eastern Kansas. We investigated the relative roles
of plant species and plant cover in influencing soil C and N cycling in three sites along this gradient. Plant cover (i.e.,
the presence or absence of an individual plant) was relatively more important than plant species in explaining variability
in soil properties at the dry site, the Central Plains Experimental Range in␣northeastern Colorado. However, plant species
explained relatively more of the variability in soil properties than did plant cover at the two wetter sites, Hays and Konza,
in central and eastern Kansas. The wetter sites had more continuous plant cover, resulting in less plant-cover-induced variation
in soil C and N, than did the dry site, which had distinct patches of bare ground. Plant species at the wetter sites had higher
and more variable levels of tissue C:N than plant species at the dry site, due to both within species changes and changes
in species composition. Aboveground tissue C:N was better correlated with net nitrogen mineralization rates at the wet sites
than the dry site. Thus, tissue chemistry appears to exert more control on nitrogen dynamics at the wet than the dry sites.
The results suggest that plant species traits that are relevant to nutrient cycling (e.g., tissue C:N ratios, spatial patterns,
productivity) reflect environmental limitations as well as species' physiological potentials. Furthermore, a dominant environmental
driver such as precipitation may ameliorate or exaggerate the importance of individual species traits for nutrient cycling.
Received: 11 July 1996 / Accepted: 5 December 1996 相似文献
14.
Invasive capacity of Tamarix ramosissima in a Mojave Desert floodplain: the role of drought 总被引:1,自引:0,他引:1
Tamarix ramosissima (Tamaricaceae) is a woody phreatophyte that has invaded thousands of hectares of floodplain habitat in the southwestern U.S.
In this study, we examined the response of gas exchange and stem sap flow of Tamarix and three co-occurring native phreatophytes (Pluchea sericea (Asteraceae), Prosopis pubescens (Fabaceae) and Salix exigua (Salicaceae)) to drought conditions in an early successional floodplain community in the Mojave Desert of southern Nevada.
In an analysis of a size/age series of each species across the whole floodplain (both mature and successional stands), stem
growth rate was lowest for Tamarix. However, along the same successional chronosequence, Tamarix came to dominate the 50+ year old stands with dense thickets of high stem density. Xylem sap flow, when expressed on a sapwood
area basis, was highest in Tamarix under early drought conditions, but comparable between the four species toward the end of the summer dry season. Multivariate
analysis of the gas exchange data indicated that the four species differentiated based on water use under early drought conditions
and separated based on plant water potential and leaf temperature (indices of drought effects) at the end of the summer dry
season. This analysis suggests that the invasive Tamarix is the most drought tolerant of the four species, whereas Salix transpires the most water per unit leaf surface area and is the least tolerant of seasonal water stress. Therefore, Salix appears to be well adapted to early successional communities. However, as floodplains in this arid region become more desiccated
with age, Tamarix assumes greater dominance due to its superior drought tolerance relative to native phreatophytes and its ability to produce
high density stands and high leaf area.
Received: 8 August 1996 / Accepted: 29 January 1997 相似文献
15.
Multisegmental motor activity in the segmentally restricted gin trap behavior in Manduca sexta pupae
William C. Lemon Richard B. Levine 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(6):611-619
Stimulation of sensory neurons innervating hairs in the gin traps on the abdomen of Manduca sexta pupae evokes a rapid bending of the abdomen that is restricted to one or more of the three articulating posterior segments.
However, electrical stimulation of the gin trap sensory nerve in an isolated abdominal nerve cord evokes characteristic motor
neuron activity in every abdominal segment. To determine if the segmentally distributed motor activity also occurred in intact
animals and how it contributed to the segmentally restricted reflex movement, mechanical stimulation of the sensory hairs
in intact animals was used to evoke reflex responses that were recorded as electromyograms synchronized with video recordings
of the behavior. Motor activity was monitored during movements to determine if there was activity in many segments when the
movement was restricted to one segment. Coordinated muscle activity was evoked throughout the abdomen in response to stimulation
of any of the three gin traps, even when movement was restricted to one segment. Differences in the timing of ipsilateral
and contralateral motor activity among segments allowed the closing of gin traps to be segmentally restricted. These findings
suggest that the neural circuit underlying the gin trap reflex is distributed throughout the abdominal nerve cord. This network
generates a complex, yet coordinated, motor pattern with muscular activity in many abdominal segments that produces a localized
bending reflex.
Accepted: 10 January 1997 相似文献
16.
In order to test whether an increased export of carbohydrates by leaves and starch mobilization are critical for floral transition
in Arabidopsis thaliana, the Columbia ecotype as well as its starchless mutant pgm and starch-in-excess mutant sex1 were investigated. Induction of flowering was achieved by exposure of plants to either one long day (LD) or one displaced
short day (DSD). The following conclusions were drawn: (i) Both the pgm and sex1 mutants have a late-flowering phenotype in days shorter than 16 h. (ii) When inductive treatments cause a large percentage
of induced plants, there is always a large, early and transient increase in carbohydrate export from leaves. By contrast,
when an inductive treatment results in only a low percentage of induced plants (pgm plants exposed to one DSD), the export of carbohydrates from leaves is not increased, supporting the idea that phloem carbohydrates
have a critical function in floral transition. (iii) Starch mobilization is not required to obtain an increased carbohydrate
export when induction is by one LD (extended period of photosynthesis), but is absolutely essential when induction is by one
DSD (period of photosynthesis unaffected). (iv) Floral induction apparently increases the capability of the leaf phloem-loading
system.
Received: 27 August 1997 / Accepted: 6 March 1998 相似文献
17.
Lethal mutations in the 0.5 map unit region between dpy-5 and bli-4 on chromosome I in Caenorhabditis elegans were serially rescued using cosmid-containing transgenic strains. All the lethal mutations analyzed came from a set of 495
EMS-induced, sDp2-rescued lethals described previously. Germline transformation with cosmid DNA was used to create 25 transgenic strains bearing
heritable extrachromosomal arrays. These arrays were used as small duplications for the fine-scale mapping of essential genes,
via the rescue of lethal mutations. Lethal mutations in 13 essential genes have been phenotypically rescued, allowing the
alignment of the genetic and physical maps in this region. Extrachromosomal arrays were found to be transmitted 2- to 7-fold
less frequently in oocytes than in hermaphrodite sperm for 12 of the 16 arrays that were examined. Three of these strains
showed a subsequent 4- to 13-fold increase in array stability in oocytes. This phenomenon may be influenced by cosmid sequences.
Early mitotic loss of the arrays was observed in all 17 transgenic strains examined, suggesting that loss of the array can
occur at any time during development when cell divisions are occurring. As a result of this work, 13 of the essential loci
positioned between dpy-5 and bli-4 are anchored to the physical map, thereby providing links between the physical and genetic maps on average every 85 kb.
Received: 8 May 1996 / Accepted: 27 January 1997 相似文献
18.
W. Li P. W. Sorensen 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(4):429-438
(1) Electro-olfactogram recording was used to determine whether the olfactory epithelium of adult sea lamprey is specifically
sensitive to bile acids, some of which have been hypothesized to function as pheromones. Ten bile acids were selected from
38 which had already been pre-screened for olfactory activity. These compounds were first tested on their own, then as adapting
stimuli, and finally as components of mixtures (2) The lamprey-specific bile acids, petromyzonol sulfate and allocholic acid,
were the most potent compounds tested. Five other bile acids were also detectable at picomolar concentrations. Petromyzonol
sulfate had a distinctive dose-response curve. (3) Cross-adaptation demonstrated that sensitivity to bile acids is attributable
to at least four independent classes of olfactory receptor sites and that both the nature and position of conjugating group(s)
are critical to receptor specificity. Notably, petromyzonol sulfate has its own highly specific and independent receptor site.
The situation for unconjugated bile acids was more complex and there appeared to be several sub-classes of receptor sites
for these compounds. (4) Mixture studies largely confirmed the cross-adaptation results, describing receptor site independence
for the same four sets of odorants. Mixture enhancement was also seen when expected and there was no evidence of mixture suppression.
(5) Together, these data demonstrate that conspecific bile acids are discriminated by the olfactory epithelium of the sea
lamprey, supporting the possibility that these compounds may function as migratory pheromones.
Accepted: 23 November 1996 相似文献
19.
G. Körtner X. Song F. Geiser 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):631-638
Circadian rhythms have been observed in most mammals, but their importance and function remain controversial with respect
to daily cycles during hibernation. We investigated the timing of arousals from and entries into hibernation for both free-living
and captive mountain pygmy-possums (Burramys parvus). Under both natural and laboratory conditions most arousals and entries were entrained with the light-dark cycle. Entries
occurred mainly during the night and arousals preferably around dusk, which coincides with the onset of the normal activity
phase for the nocturnal pygmy-possums. This entrainment prevailed throughout the hibernation season although only the laboratory
animals were constantly subjected to photoperiodic stimuli, whereas under natural conditions hibernacula are shielded from
photic cues and diurnal temperature fluctuations. Nevertheless, possums left their hibernacula frequently throughout winter
and were occasionally trapped close to the snow surface suggesting that during the periods of post-arousal normothermia they
can be exposed to environmental stimuli. It thus appears that the synchronisation with the photocycle was governed by a temperature-compensated
circadian clock which was reset periodically during short activity periods. For the mountain pygmy-possum, entrainment with
the photocycle probably has two functions:
1. Entrainment ensures that foraging bouts during the hibernation season remain synchronised with the dark phase.
2. Information about the prevailing climatic conditions sampled during short activity periods enables them to time final spring
emergence from hibernation when snow melt begins and ensures that the breeding season can commence as early as possible.
Accepted: 26 August 1998 相似文献
20.
Molecular evolution and functional relevance of the chalcone synthase genes of pea 总被引:12,自引:0,他引:12
M. Ito Y. Ichinose H. Kato T. Shiraishi T. Yamada 《Molecular & general genetics : MGG》1997,255(1):28-37
We have isolated seven genomic chalcone synthase (CHS) genes and six classes of CHS cDNA from elicitor-treated pea tissues. Comparison of the nucleotide sequences of the coding regions revealed the existence
of eight members of the CHS gene family in pea. These can essentially be divided into three groups (PSCHS1, 2 and 8; PSCHS3, 4 and 5; and PSCHS6 and 7) on the basis of nucleotide and/or amino acid sequence comparisons of the coding regions, introns and promoter regions. We
previously reported that the accumulation of CHS mRNAs is induced by elicitor treatment. Accumulation of CHS mRNA was observed mainly in roots and very little was found in floral organs. To specifically detect expression of each CHS gene in various types of pea cells, S1 nuclease protection assays were performed. Interestingly, the classification of the
eight members of the CHS gene family based on the sequence identity was found to reflect their expression patterns as determined by the S1 nuclease
protection assay. The first group of CHS genes, PSCHS1, 2 and 8, was strongly induced not only by elicitor treatment and UV irradiation but is also constitutively expressed in root and
flower tissues. The second group, PSCHS3, 4 and 5, was also strongly induced by elicitor treatment and UV irradiation but is constitutively expressed only in root. Expression
of the third group, PSCHS6 and 7 was barely detectable in any of the organs tested and was not influenced by environmental stimuli such as elicitor or UV.
Furthermore, sequence analysis of the promoter region of each member of the CHS gene family revealed that putative cis-regulatory elements, such as Box-I, Box-II and G-Box, were conserved only in PSCHS1, 2, 3, 4 and 5. From these results we propose that an ancestral CHS gene might have given rise to defense response-related (UV irradiation- and elicitor-responsive) and -unrelated (unresponsive)
genes at an early stage of evolution, followed by divergence within these subclasses based upon the developmental program
in pea.
Received: 5 November 1996 / Accepted: 6 February 1997 相似文献