共查询到20条相似文献,搜索用时 15 毫秒
1.
Temporal auditory mechanisms were measured in killer whales ( Orcinus orca ) by recording auditory evoked potentials (AEPs) to clicks. Clicks were presented at rates from 10/sec to 1,600/sec. At low rates, clicks evoked an AEP similar to the auditory brainstem response (ABR) of other odontocetes; however, peak latencies of the main waves were 3–3.7 msec longer than in bottlenose dolphins. Fourier analysis of the ABR showed a prominent peak at 300–400 Hz and a smaller one at 800–1,200 Hz. High-rate click presentation (more than 100/sec) evoked a rate-following response (RFR). The RFR amplitude depended little on rate up to 400/sec, decreased at higher rates and became undetectable at 1,120/sec. Fourier analysis showed that RFR fundamental amplitude dependence on frequency closely resembled the ABR spectrum. The fundamental could follow clicks to around 1,000/sec, although higher harmonics of lower rates could arise at frequencies as high as 1,200 Hz. Both RFR fundamental phase dependence on frequency and the response lag after a click train indicated an RFR group delay of around 7.5 msec. This corresponds to the latency of ABR waves PIII-NIV, which indicates the RFR originates as a rhythmic, overlapping ABR sequence. The data suggest the killer whale auditory system can follow high click rates, an ability that may have been selected for as a function of high-frequency hearing and the use of rapid clicks in echolocation. 相似文献
2.
G. Gomez R. Voigt J. Atema 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,185(5):427-436
To understand how chemoreceptor organs may extract temporal information from odor plumes, we investigated the frequency filter
properties of lobster chemoreceptor cells. We used rapid stimulation and high-resolution stimulus measurement for accurate
stimulus control and recorded extracellular responses from chemoreceptors in the lobster lateral antennule in situ. We tested
16 hydroxyproline-sensitive cells with a series of ten 100-ms pulses at 10, 100 and 1000 μmol l−1 at stimulation frequencies from 0.5 Hz to 4 Hz. Receptor cell responses could accurately encode 10 μmol l−1, but not 100 or 1000 μmol l−1 pulses, delivered at rates of 4 Hz. Flicker-fusion frequency and synchronization with the stimulus pulse train were concentration
dependent: performance rates above 1 Hz became poorer both with increasing pulse amplitude and frequency. Flicker fusion frequency
was 3 Hz for 100 μmol l−1 pulses and 2 Hz for 1000 μmol l−1 pulses. Individual cells showed differences in their stimulus pulse following capabilities, as measured by the synchronization
coefficient. These individual differences may form a basis for coding temporal features of an odor plume in an across-fiber
pattern.
Accepted: 7 July 1999 相似文献
3.
Morten Buhl Jørgensen Jakob Christensen-Dalsgaard 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(5):493-502
We studied the directionality of spike rate responses of auditory nerve fibers of the grassfrog, Rana temporaria, to pure tone stimuli. All auditory fibers showed spike rate directionality. The strongest directionality was seen at low
frequencies (200 – 400 Hz), where the spike rate could change by up to nearly 200␣spikes s−1. with sound direction. At higher frequencies the directional spike rate changes were mostly below 100 spikes s−1. In equivalent dB SPL terms (calculated using the fibers' rate-intensity curves) the maximum directionalities were up to
15 dB at low frequencies and below 10 dB at higher frequencies. Two types of directional patterns were observed. At frequencies
below 500 Hz relatively strong responses were evoked by stimuli from the ipsilateral (+90o) and contralateral (−90o) directions while the weakest responses were evoked by stimuli from frontal (0o or +30o) or posterior (−135o) directions. At frequencies above 800 Hz the strongest responses were evoked by stimuli from the ipsilateral direction while
gradually weaker responses were seen as the sound direction shifted towards the contralateral side. At frequencies between
500 and 800 Hz both directional patterns were seen. The directionality was highly intensity dependent. No special adaptations
for localization of conspecific calls were found.
Accepted: 23 November 1996 相似文献
4.
D. A. Llano A. S. Feng 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(4):371-385
We examined the auditory response properties of neurons in the medial geniculate body of unanesthetized little brown bats
(Myotis lucifugus). The units' selectivities to stimulus frequency, amplitude and duration were not significantly different from those of neurons
in the inferior colliculus (Condon et al. 1994), which provides the primary excitatory input to the medial geniculate body,
or in the auditory cortex (Condon et al. 1997) which receives primary input from the medial geniculate body. However, in response
to trains of unmodulated tone pulses, the upper cutoff frequency for time-locked discharges (64 ± 46.9 pulses per second or
pps) and the mean number of spikes per pulse (19.2 ± 12.2 pps), were intermediate to those for the inferior colliculus and
auditory cortex. Further, in response to amplitude-modulated pulse trains, medial geniculate body units displayed a degree
of response facilitation that was intermediate to that of the inferior colliculus and auditory cortex inferior colliculus:
1.32 ± 0.33; medial geniculate body: 1.75 ± 0.26; auditory cortex: 2.52 ± 0.96, P < 0.01). These data suggest that the representation of isolated tone pulses is not significantly altered along the colliculo-thalamo-cortical
axis, but that the fidelity of representation of temporally patterned signals progressively degrades along this axis. The
degradation in response fidelity allows the system to better extract the salient feature in complex amplitude-modulated signals.
Accepted: 9 January 1999 相似文献
5.
T. Yazawa J. L. Wilkens M. J. Cavey H. E. D. J. ter Keurs M. J. Cavey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):529-537
“Venous” blood enters the crustacean heart through bivalved ostia. Each ostium is a discrete anatomical unit that remains
functional even when isolated from the heart. Muscle fibers produce overshooting action potentials that have a plateau of
variable duration in response to nervous drive from the cardiac ganglion or during trains of electrical stimuli. Contractions
show summation and facilitation when stimulated by trains of stimuli delivered at rates greater than 0.5 s−1 and 0.2 s−1, respectively. Contraction amplitude increases with stimulating impulse frequency and train duration. Maximum force occurs
at 1.2 times the slack length. The morphology of ostial fibers resembles that of myocardial fibers. Interconnected bundles
of myofilaments occur in both the ostial fibers and the myocardial fibers. In ostial and myocardial fibers, the myofilament
bundles are invested by perforated sheets of sarcoplasmic reticulum, and these sheets interface with a network of sarcolemmal
tubules to form dyadic interior couplings at the level of the sarcomeric H-bands. The contractile apparatus originates and
terminates at intermediate junctions on the transverse cellular boundaries, and the lateral surfaces of the muscle fibers
are linked by a modest number of communicating (gap) junctions.
Accepted: 10 August 1999 相似文献
6.
7.
J. Tougaard 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,183(5):563-572
The interception of a pheromone filament induces flying moths to surge briefly nearly straight upwind; in the absence of
pheromone moths cease upwind progress and zigzag crosswind. We tested males of the almond moth, Cadra cautella (Lepidoptera, Pyralidae), in a low-turbulence wind tunnel in wind velocities of 20, 40 and 80 cm s−1. A mechanical pulse generator was set to produce plumes either with same pheromone pulse frequency (pulse generation frequency
of 2.9 Hz, interpulse distances from 7 cm to 28 cm) or plumes with same interpulse distance across the three wind velocities
(interpulse distance of 14 ± 2 cm, pulse generation frequency of 1.7–5.0 Hz). In plumes of similar pulse frequency, the faster
the speed of the wind the slower the ground speed of flight. However, in plumes of similar interpulse distance, ground speed
remained relatively constant independent of the wind speed. A `realized' frequency of pulse interception for males flying
along the various combinations of pulse frequencies and wind velocities was calculated using the males' average airspeed and
the spatial distribution of pheromone pulses in the plume. Realized frequency of pulse interception ranged from 1.3- to 3.0-fold
higher than the frequency of pulse generation. The flight tracks of males reflected the regime of realized pulse interception.
These results suggest that upwind flight orientation of male C. cautella to pheromone in different wind velocities is determined by the flux of filament encounter.
Accepted: 3 September 1997 相似文献
8.
Joseph P. Weir Dennis A. Keefe Jason F. Eaton Robert T. Augustine Dawn M. Tobin 《European journal of applied physiology and occupational physiology》1998,78(6):555-559
We examined the effect of fatigue of the quadriceps muscles on coactivation of the hamstring muscles and determined if the
response is different between two isokinetic speeds in ten males and ten females with no history of knee pathology. Electromyographic
data were recorded from the vastus lateralis and biceps femoris muscles during 50 maximal knee extensions at isokinetic speeds
of 1.75 rad · s−1 (100° · s−1) and 4.36 rad · s−1 (250° · s−1). A greater degree of coactivation was apparent at the higher speed, but the increase in coactivation of the hamstring muscles
was similar at both speeds. The results revealed that: (1) coactivation is greater at a higher isokinetic speed, and (2) coactivation
increases during fatigue, but the rate of increase is independent of contraction velocity.
Accepted: 15 June 1998 相似文献
9.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
10.
G. I. Rozhkova V. Y. Vedenina G. Kämper 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(2):161-167
The bilateral pairs of cercal interneurons 10-2a and 10-3a in the cricket terminal ganglion are supposed to constitute a
functional system for measuring the direction of air-borne signals, based on their phase-locked responses and selective directional
sensitivity. The purpose of this study was to obtain information on the frequency and intensity characteristics and thus the
potential working range of this system. By recording intracellularly from the axons of the interneurons we measured responses
for stimuli of varying frequency, intensity, and direction. Typically, the stimulus frequency range examined extended from
5 to 600 Hz, at intensities of 0.03–30 mm s−1 (peak-to-peak air-particle velocity). The results show that interneurons 10-2a and 10-3a preserved their level of activity,
response type, and direction tuning in the whole frequency range tested. Stimulus-response cross-correlograms revealed that
spike trains were synchronized with stimulus waves at even higher frequencies, at least up to 1000 Hz. At a given air-particle
velocity in the range of about 2–2.5 logarithmic units, the spike number responses of the interneurons were nearly constant
over a wide frequency range. Directional diagrams appeared to be independent of stimulus frequency, both in orientation and
in amplitude.
Accepted: 14 October 1998 相似文献
11.
Optical study of spatiotemporal inhibition evoked by two-tone sequences in the guinea pig auditory cortex 总被引:1,自引:0,他引:1
J. Horikawa Y. Hosokawa M. Nasu I. Taniguchi 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,181(6):677-684
Spatiotemporal response patterns in the anterior and dorsocaudal fields of the guinea pig auditory cortex after two-tone
sequences were studied in anesthetized animals (Nembutal 30 mg kg−1) using an optical recording method (voltage-sensitive dye RH795, 12 × 12 photodiode array). Each first (masker) and second
(probe) tone was 30 ms long with a 10-ms rise-fall time. Masker-probe pair combinations of the same or different frequencies
with probe delays of 30–150 ms were presented to the ear contralateral to the recording side. With same-frequency pairs, responses
to the probe were inhibited completely after probe delays of less than 50 ms and the inhibition lasted for more than 150 ms,
and the inhibition magnitudes in different isofrequency bands of the anterior field were essentially the same. With different-frequency
(octave-separated) pairs, responses to the probe were not inhibited completely even after probe delays as short as 30 ms,
and the inhibition lasted only for 110–130 ms. Inhibition magnitudes were different from location to location.
Accepted: 4 August 1997 相似文献
12.
Stem respiration of ponderosa pines grown in contrasting climates: implications for global climate change 总被引:7,自引:0,他引:7
We examined the effects of climate and allocation patterns on stem respiration in ponderosa pine (Pinus ponderosa) growing on identical substrate in the cool, moist Sierra Nevada mountains and the warm, dry, Great Basin Desert. These environments
are representative of current climatic conditions and those predicted to accompany a doubling of atmospheric CO2, respectively, throughout the range of many western north American conifers. A previous study found that trees growing in
the desert allocate proportionally more biomass to sapwood and less to leaf area than montane trees. We tested the hypothesis
that respiration rates of sapwood are lower in desert trees than in montane trees due to reduced stem maintenance respiration
(physiological acclimation) or reduced construction cost of stem tissue (structural acclimation). Maintenance respiration
per unit sapwood volume at 15°C did not differ between populations (desert: 6.39 ± 1.14 SE μmol m−3 s−1, montane: 6.54 ± 1.13 SE μmol m−3 s−1, P = 0.71) and declined with increasing stem diameter (P = 0.001). The temperature coefficient of respiration (Q
10) varied seasonally within both environments (P = 0.05). Construction cost of stem sapwood was the same in both environments (desert: 1.46 ± 0.009 SE g glucose g−1 sapwood, montane: 1.48 ± 0.009 SE glucose g−1 sapwood, P = 0.14). Annual construction respiration calculated from construction cost, percent carbon and relative growth rate was greater
in montane populations due to higher growth rates. These data provide no evidence of respiratory acclimation by desert trees.
Estimated yearly stem maintenance respiration was greater in large desert trees than in large montane trees because of higher
temperatures in the desert and because of increased allocation of biomass to sapwood. By analogy, these data suggest that
under predicted increases in temperature and aridity, potential increases in aboveground carbon gain due to enhanced photosynthetic
rates may be partially offset by increases in maintenance respiration in large trees growing in CO2-enriched atmospheres.
Received: 4 November 1996 / Accepted: 23 January 1997 相似文献
13.
Gas-exchange measurements were performed to analyze the leaf conductances and assimilation rates of potato (Solanum tuberosum L. cv. Desireé) plants expressing an antisense construct against chloroplastic fructose-1,6-bisphosphatase (FBPase, EC 3.1.3.11)
in response to increasing photon flux densities, different relative air humidities and elevated CO2 concentrations. Assimilation rates (A) and transpiration rates (E) were observed during a stepwise increase of photon flux
density. These experiments were carried out under atmospheric conditions and in air containing 500 μmol mol−1 CO2. In both gas atmospheres, two levels of relative air humidity (60–70% and 70–80%) were applied in different sets of measurements.
Intercellular CO2 concentration, leaf conductance, air-to-leaf vapour pressure deficit, and instantaneous water-use efficiency (A/E) were determined.
As expected, assimilation rates of the FBPase antisense plants were significantly reduced as compared to the wild type. Saturation
of assimilation rates in transgenic plants occurred at a photon flux density of 200 μmol m−2 s−1, whereas saturation in wild type plants was observed at 600 μmol m−2 s−1. Elevated ambient CO2 levels did not effect assimilation rates of transgenic plants. At 70–80% relative humidity and atmospheric CO2 concentration the FBPase antisense plants had significantly higher leaf conductances than wild-type plants while no difference
emerged at 60–70%. These differences in leaf conductance vanished at elevated levels of ambient CO2. Stomatal response to different relative air humidities was not affected by mesophyll photosynthetic activity. It is suggested
that the regulation of stomatal opening upon changes in photon flux density is merely mediated by a signal transmitted from
mesophyll cells, whereas the intercellular CO2 concentration plays a minor role in this kind of stomatal response. The results are discussed with respect to stomatal control
by environmental parameters and mesophyll photosynthesis.
Received: 24 September 1998 / Accepted: 9 February 1999 相似文献
14.
Juozas Kulys Kastis Krikstopaitis Arturas Ziemys 《Journal of biological inorganic chemistry》2000,5(3):333-340
N -substituted phenothiazines (PTs) and phenoxazines (POs) catalyzed by fungal Coprinus cinereus peroxidase and Polyporus pinsitus laccase were investigated at pH 4–10. In the case of peroxidase, an apparent bimolecular rate constant (expressed as k
cat/K
m) varied from 1 ×107 M−1 s−1to 2.6×108 M−1 s−1 at pH 7.0. The constants for PO oxidation were higher in comparison to PT. pH dependence revealed two or three ionizable
groups with pK
a values of 4.9–5.7 and 7.7–9.7 that significantly affected the activity of peroxidase. Single-turnover experiments showed
that the limiting step of PT oxidation was reduction of compound II and second-order rate constants were obtained which were
consistent with the constants at steady-state conditions. Laccase-catalyzed PT and PO oxidation rates were lower; apparent
bimolecular rate constants varied from 1.8×105 M−1 s−1 to 2.0×107 M−1 s−1 at pH 5.3. PO constants were higher in comparison to PT, as was the case with peroxidase. The dependence of the apparent
bimolecular constants of compound II or copper type 1 reduction, in the case of peroxidase or laccase, respectively, was analyzed
in the framework of the Marcus outer-sphere electron-transfer theory. Peroxidase-catalyzed reactions with PT, as well as PO,
fitted the same hyperbolic dependence with a maximal oxidation rate of 1.6×108 M−1 s−1 and a reorganization energy of 0.30 eV. The respective parameters for laccase were 5.0×107 M−1 s−1 and 0.29 eV.
Received: 20 September 1999 / Accepted: 24 February 2000 相似文献
15.
Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances 总被引:6,自引:0,他引:6
The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco;
EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF1) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice
(Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m−2 · s−1, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m−2 · s−1 was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity
were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater
in the plants grown at 350 μmol · m−2 · s−1, whereas Cyt f and CF1 contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited
rate of photosynthesis measured at 350 μmol · m−2 · s−1 was the same or only a little higher in the plants grown at 350 μmol · m−2 · s−1 and that CO2-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent
changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of
the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because
there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential
N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing
a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants
as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf.
Received: 23 February 1997 / Accepted: 8 May 1997 相似文献
16.
P. Pfeiffer B. M. Culik 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(2):143-148
We used a still-water swim channel in conjunction with open-flow oxygen and carbon dioxide respirometry to examine the energy
requirements of river-otters (Lutra lutra L.) swimming voluntarily underwater in Neumünster Zoo (Germany). While at rest on land (5 °C), river-otters had a respiratory
quotient of 0.77 and a resting metabolic rate of 4.1 W kg−1. This increased to an estimated 6.4 W kg−1 during rest in water (11–15 °C) and to 12.3 W kg−1 when the animals were feeding in the channel. River-otters swimming under water preferred a mean speed of 0.89 m s−1, and their energy requirements attained 11.6 W kg−1. Cost of transport, however, was minimal at 1.3 m s−1 and amounted to 0.95 J N−1 m−1.
Accepted: 3 November 1997 相似文献
17.
Daniela Soares dos Santos Vívian Tamaki Catarina Carvalho Nievola 《In vitro cellular & developmental biology. Plant》2010,46(6):524-529
Acanthostachys strobilacea (Schult. f.) Klotzsch is an ornamental species of Bromeliaceae that may show an elongated stem when cultivated in vitro. This work reports a micropropagation protocol for A. strobilacea using nodal segments. Seeds were placed in Murashige and Skoog’s medium with macronutrients diluted to 1/5. Nodal segments
isolated from the stems of in vitro elongated plants were subcultured in the same medium and kept in different light intensities (14, 41, and 50 μmol m−2 s−1) or continuous darkness. Another group of nodes was subcultured according to the position in the mother seedling. The plants
that showed the most stem elongation were those that were cultured in 14 μmol m−2 s−1 or that came from isolated nodal segments in the median and basal regions of the mother plant. After 2 mo, all of the plants
originating from the development of lateral buds were transferred to a greenhouse. Only those that were not elongated survived
ex vitro and flowered after 1 yr. 相似文献
18.
C. F. Baker J. C. Montgomery 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1999,184(5):519-527
The sensory basis of rheotaxis (orientation to currents) was investigated in the blind Mexican cave fish, Astyanax fasciatus. An unconditioned rheotactic response to uniform velocity flows was exhibited, with a threshold of less than 3 cm s−1. Disabling the entire lateral line or the superficial neuromast receptor class increased the rheotactic threshold to greater
than 9 cm s−1. A pharmacological block of the lateral line canal system alone had no effect. These results demonstrate that the superficial
lateral line system controls rheotaxis at low current velocities. The effect of pairing an odor stimulant with the water current
dropped the rheotactic threshold to less than 0.4 cm s−1. This study provides a clear behavioral role for the superficial neuromasts where none previously existed, and also establishes
a link between the mechanosensory lateral line and olfactory systems in the olfactory search behavior of the cave fish.
Accepted: 9 January 1999 相似文献
19.
Mode of depolymerisation of hemicellulose by various mannanases and xylanases in relation to their ability to bleach softwood pulp 总被引:2,自引:0,他引:2
G. M. Gübitz D. Haltrich B. Latal W. Steiner 《Applied microbiology and biotechnology》1997,47(6):658-662
Endo-mannanases and endo-xylanases cleave different heteromannans and xylans yielding mainly dimers and trimers of the corresponding
sugars as end-products. However, in the early stages of hydrolysis, four purified mannanases and four xylanases from fungal
and bacterial origin, examined in this study, showed a different pattern of released oligomers (determined up to the pentamers).
Furthermore, some of these enzymes showed a preference for cleaving the polysaccharides in the middle of the chain while others
acted more at the end. When the increase in the specific fluidity of mannan and xylan solutions per reducing sugar released
(K
v) was measured against the bleaching effect of the enzymes on softwood kraft pulp, a correlation was found. A xylanase from
Penicillium simplicissimum (K
v = 0.15 l mPa−1s−1g−1) and a mannanase from Sclerotium rolfsii (K
v = 0.12 l mPa−1s−1g−1) applied in a O(QX)P bleaching sequence (O = oxygen delignification, X = treatment with hemicellulolytic enzymes, Q = chelation
of metals, P = treatment with hydrogen peroxide in alkaline solution) gave a high brightness increase of 3.0% and 1.9% ISO
respectively. A less significant brightness increase was obtained with enzymes showing lower K
v values, such as a xylanase from Schizophyllum commune (Kv = 0.051 l mPa−1s−1g−1, 0.2% ISO) and a bacterial mannanase (K
v = 0.061 l mPa−1s−1g−1,0.5% ISO).
Received: 19 December 1996 / Received revision: 20 February 1997 / Accepted: 22 February 1997 相似文献
20.
The photomechanic infrared receptor for the detection of forest fires in the beetle Melanophila acuminata (Coleoptera: Buprestidae) 总被引:1,自引:0,他引:1
H. Schmitz H. Bleckmann 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1998,182(5):647-657
We recorded from single units of individual sensilla of the thoracic infrared (IR) pit organs of Melanophila acuminata. When the organ was stimulated with a thermal radiator whose emission spectrum was similar to that of a typical forest fire,
units responded phasically with up to seven spikes within 30–40 ms at a radiation power of 24 mW cm−2. In the experiments all wavelengths shorter than 1.6 μm were excluded by a longpass IR filter. Response latencies were about
4 ms and initial impulse frequencies were up to 250 impulses per second (ips). A single spike could be generated even when
stimulus duration was only 2 ms. Reduction of total radiation power from 24 mW cm−2 to 5 mW cm−2 resulted in increased response latencies of 5–6 ms and the occurrence of only two to three spikes. Initial impulse frequencies
decreased to 125 ips. According to our physiological results and calculations, Melanophila should be able to detect a 10-hectare fire from a distance of 12 km. Mechanical stimuli also evoked responses of the IR sensilla.
All present morphological and physiological findings lead to the conclusion that the IR receptors of Melanophila must function by means of a hitherto undescribed photomechanic mechanism.
Accepted: 1 November 1997 相似文献