Response of antennal cold receptors of the catopid beetles,Speophyes lucidulus Delar. andCholera angustata Fab. to very slowly changing temperature

Summary The antennal cold cells in larval black-hair sensilla of the cave beetle,Speophyes lucidulus Delar., clearly respond to rates of temperature change 5 to 10 times lower than any tested on insect cold cells so far: often below 0.0005° C/s or 2° C/h. At a given ambient temperature between 11° C and 15° C, cold-cell impulse frequency was higher when temperature was falling at these rates than when it was rising at them in every one of the twelve cells examined. The mean differential sensitivity to the rate of change was -3340±1071 (imp/s)/(° C/s), in each case two to 5 times greater (sign ignored) than in any cold cell observed previously (Loftus 1969; Corbière-Tichané and Loftus 1983). The differential sensitivity to ambient temperature,-6.8 (imp/s)/° C, was statistically indistinguishable, on the other hand, from the earlier values forSpeophyes.Antennal cold cells of six first-stage larvae of another Catopid beetle,Choleva angustata Fab., displayed very similar responses to the same stimuli. Its mean differential sensitivities were -8.1+3.9 (imp/s)/° C to ambient temperature and-3790+2190 (imp/s)/(° C/s) to the rate of temperature change. UnlikeSpeophyes this beetle spends only part of its life cycle in caves.Abbreviations dT/dt rate of temperature change in °C/s - F impulse frequency in impulses/s (imp/s) - T temperature in ° C To Sylvie Deleurance, a helpful friend who dedicated much of her life to the study of cave insects     

Response characteristics of a cold receptor in the stick insectCarausius morosus

Summary The cold cell in the easily identified mound-shaped sensillum on the 12th segment ofCarausius morosus' antennae responds to downward temperature (T) steps from about 15 °C with a sharp rise in impulse frequency (F). Responses to similar steps from higher initial temperatures are smaller (Figs. 1, 3, 4). As initialT increases from 16 °C to 31 °C, differential sensitivity to downward steps falls off by a factor of 27: to yield an average increase inF of 1 imp/s, steps down from 31 °C must increase by 1.7 °C; steps down from 16 °C, by only 0.06 °C (Fig. 5). Resolving power forT-steps at mid-range initial temperatures is about 0.7 °C, i.e. the probability that a single cold cell at average differential sensitivity will correctly discriminate between twoT steps 0.7 °C apart is 90% when the cell is presented with each step just once.The same cold cell also displays a clear dependence on steadyt between 14 °C and 24 °C (Figs. 7, 8). The static discharge rate of a single cell at average differential sensitivity has a resolving power of about 0.9 °C for steadyT. — The static discharge is not affected by the amount of water vapor in the stimulating air (Fig. 9).Abbreviations F impulse frequency in impulses per second (imp/s) - Pw partial pressure of water vapor in torr - r correlation coefficient - T temperature in °C - T step change inT     

Antennal warm and cold receptors of the cave beetle,Speophyes lucidulus delar., in sensilla with a lamellated dendrite

Summary Electrophysiological examination of the 2 black-hair sensilla on the antennae of both larval stages of the cave beetle,Speophyes lucidulus, has revealed in each a pair of antagonistic thermal receptors (Fig. 1). Each sensillum was known to house the dendrites of 2 sensory cells which are associated with the extensively lamellated dendrite of a third (Corbière-Tichané 1971). One unit, a cold receptor, responds to temperature drops of 1 to 7 °C from initial temperatures between 9 and 14 °C with impulse frequencies up to 200 imp/s (Figs. 3, 4). Its antagonist, encountered less than 10% as often, is a warm receptor which responds with similar impulse frequencies to rapid rises in temperature from the same 9–14 °C (Figs. 3, 6). As indicated by the average gain of 24 imp/s for an increase of 1 °C in temperature drop, the cold unit appears almost twice as sensitive to sudden temperature change as the warm unit (14 (imp/s) °C). Examination of response scatter indicates that the average cold unit should on the basis of a single pair of responses be able to designate the greater of two temperature drops between 1 and 7 °C with 90% probability when they differ by 0.7 °C (Fig. 5). Though not yet definitive, evidence is accumulating that the third physiological unit is a dry air receptor.Abbreviations F impulse frequency in imp/s - Fc F as calculated - Fm F as measured - imp impulses - Pw partial pressure of water vapor in air - Ps saturation pressure of water vapor - r regression coefficient - T temperature - difference in Supported by the Deutsche Forschungsgemeinschaft, Sonder forschungsbereich 4, Projekt DThe authors wish to express their indebtedness to Dr. Renate Beinhauer, Faculty of Natural Sciences I — Mathematics, Univ. of Regensburg, for her help in applying statistical methods in determining resolving power.     

Warm and cold receptors of two sensilla on the foreleg tarsi of the tropical bont tickAmblyomma variegatum

Summary A pair of antagonistic thermal receptors has been identified in each of two long, tapering, poreless setae located distally on the foreleg tarsi of the tropicalbont tick,Amblyomma variegatum (Fig. 1). One, the cold receptor, responds to a rapiddrop in temperature (T) with a sudden rise in impulse frequency (F). The other, a warm receptor, responds to a rapidrise inT with a sudden rise inF (Figs. 2, 4). These two units are unusual for sharing their seta with two other units which are mechanosensitive. The four are distinguishable on the basis of spike amplitude and form (Fig. 3). Hence the thermal sensitivity displayed is hardly attributable to the pair of cells with tubular bodies but rather to the two extending up into the seta (for structure, see Hess and Vlimant 1982, 1983 a).As based on the first 100 ms of the response, differential sensitivity to rapidT change is –16.1± 10.4 (imp/s)/°C for cold units, 17.6 ± 9.5 (imp/s)/°C for warm (Table 1). As progressively larger segments of the spike train are employed to determineF, differential sensitivity of the warm unit drops off much more quickly than that of the cold (Table 2, Figs. 5, 6). In the cold unit resolving power (the difference in rapid temperature change discriminable with 90% probability by a pair of responses of a single unit at average sensitivity) continues to increase as the segment of the spike train determiningF is lengthened (from 0.58 °C for 100 ms segments to 0.41 °C for 1,100 ms segments). Resolving power of the warm unit, on the other hand, tends to decrease as longer segments are employed (from 0.52 °C for the first 100 ms to 0.80 °C for the first 1,100 ms). These relationships provoke the question of whether the spike trains may be evaluated in the CNS in different fashions.Abbreviations b slope of characteristic curve - F impulse frequency in impulses per second (imp/s) - n number of individuals examined - Pw partial pressure of water vapor in Torr - r correlation coefficient - s SD of responses from characteristic curve - SD standard deviation - T temperature in °C - T difference inT Refers to difference between initial and end temperature in abruptT changes     

A comparison of proline, thiol levels and GAPDH activity in cyanobacteria of different origins facing temperature-stress

Three cyanobacterial strains originating from different habitats were subjected to temperature shift exposures and monitored for levels of proline, thiol and activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Thermophile Mastigocladus laminosus (growth optimum, 40 °C), raised the proline level 4.2-fold at low temperature (20 °C), for the psychrophile Nostoc 593 (growth optimum, 20 °C), it was raised 8-fold at 40 °C while in the mesophile Nostoc muscorum (growth optimum, 30 °C), the imino acid level increased 2.3-fold during temperature shiftdown to 20 °C or 3.5-fold in sets facing shiftup (40 °C). Alterations in thiol levels in the above strains were in line with proline. It is suggested that such fluctuations reflect metabolic shifts as a response to stress. Interestingly, GAPDH activity was maximum at the respective growth temperature optimum of M. laminosus (122 nmol NADPH oxidized min ^–1 mg ^–1 protein) and Nostoc 593 (141 nmol NADPH oxidized min ^–1 mg ^–1 protein) while in N. muscorum, it increased at 40 °C (101 nmol NADPH oxidized min ^–1 mg ^–1 protein) and to 93.3 nmol NADPH oxidized min ^–1 mg ^–1 protein (20 °C) relative to 86 nmol NADPH oxidized min ^–1 mg ^–1 protein at 30 °C. It seems that extremophiles maintain the GAPDH activity/level during growth at their respective temperatures optimal while the mesophile increases it in order to cope up with temperature-stress.     

Photosynthetic performance of transplanted ecotypes ofEcklonia cava(Laminariales, Phaeophyta)

Young sporophytes of short-stipe ecotype ofEcklonia cavafrom a warmer locality (Tei, Kochi Pref., southern Japan) and those of long-stipe ecotype from a cooler locality (Nabeta, Shizuoka Pref., central Japan) were transplanted in 1995 to artificial reefs immersed at the habitat of long-stipe ecotype in Nabeta Bay, Shizuoka Pref., central Japan. The characteristics of photosynthesis and respiration of bladelets of the transplanted sporophytes of the two ecotypes were compared in winter and summer 1997; the results were assessed per unit area, per unit chlorophyllacontent and per unit dry weight. In photosynthesis-light curves at 10–29 °C, light saturation occurred at 200–400 mol photon m^–2s^–1in sporophytes from both Tei and Nabeta. The maximum photosynthetic rate (P _max) at 10–29 °C and the light-saturation index (I _k) at 25–29 °C in sporophytes from both localities were generally higher in winter than in summer.P _maxat 25–29 °C (per unit area and chlorophylla) were higher in sporophytes from Tei than those from Nabeta in both seasons. The optimum temperature for photosynthesis was 25 °C in winter and 27 °C in summer at high light intensities of 100–400 mol photon m^–2s^–1. However, at lower light intensities of 12.5–50 mol photon m^–2s^–1, it was 20 °C in winter and 25–27 °C in summer for sporophytes from both locations. Dark respiration increased with temperature rise in the range of 10–29 °C in sporophytes from both locations in summer and winter. The sporophytes transplanted from Tei (warmer area) showed higher photosynthetic activities than those from Nabeta (cooler area) at warmer temperatures even under the same environmental conditions. This indicates that these physiological ecotypes have arisen from genetic differentiation.     

Interspecific variation for thermal dependence of glutathione reductase in sainfoin

Summary Understanding the biochemical and physiological consequences of species variation would expedite improvement in agronomically useful genotypes of sainfoin (Onobrychis spp.) Information on variation among sainfoin species is lacking on thermal dependence of glutathione reductase (B.C. 1.6.4.2.), which plays an important role in the protection of plants from both high and low temperature stresses by preventing harmful oxidation of enzymes and membranes. Our objective was to investigate the interspecific variation for thermal dependency of glutathione reductase in sainfoin. Large variation among species was found for: (i) the minimum apparent Km (0.4–2.5 M NADPH), (ii) the temperature at which the minimum apparent Km was observed (15°–5°C), and (iii) the thermal kinetic windows (2°–30°C width) over a 15°–45°C temperature gradient. In general, tetraploid species had narrower (17°C) thermal kinetic windows than did diploid species (30°C), with one exception among the diploids. Within the tetraploid species, the cultivars of O. viciifolia had a broader thermal kinetic window (7°C) than the plant introduction (PI 212241, >2 °C) itself.This work was supported by USDA Specific Cooperative Agreement No. 58-7MN1-8-143 from the Plant Stress and Water Conservation Unit, USDA-ARS, Lubbock, Texas. Joint contribution of Texas Tech University, Lubbock, Texas and the USDA-ARS. TTU Journal No. T-4-291     

The effects of assay temperature upon the pH optima of enzymes from poikilotherms: A test of the imidazole alphastat hypothesis

Summary A study of the thermal responses of Na-ATPase and NaK-ATPase activities in microsomes prepared from gill tissue of rainbow trout (Salmo gairdneri) revealed further evidence that the two activities are distinct from one another. Arrhenius plots of the NaK-ATPase from sea water-adapted fish and the Na-ATPase from fresh water-adapted fish were linear (Fig. 4) with estimated activation energies of 19.5 and 7.7 kcal/mole, respectively. The Na-ATPase and NaK-ATPase both showed optimum activity at 45°C (Figs. 2 and 3). The Mg-ATPase from fresh water fish showed a distinct temperature optimum at 24°C (Fig. 1) while Mg-ATPase activity from sea water fish was optimum at temperatures of about 15–24 °C (Fig. 3). The Na⁺ dependence of the Na-ATPase and the NaK-ATPase was examined at an assay temperature of 37 °C (Fig. 5) and the results compared with those obtained at 13 °C. No apparent differences were noted for the Na-ATPase, but with the NaK-ATPase both theK _0.5 for Na⁺ and optimum Na⁺ concentration increased at the higher assay temperature. Finally, evidence is presented showing the Na-ATPase to be distinct from Mg-ATPase activity in fresh water trout gill microsomes.Abbreviation HEPES N-2-hydroxyethylpiperazine-N-2-ethane-sulfonic acid     

Individual particularities of examinees at lateralization of stationary and moving sound images (virtual reality: specific manifestations)

Characteristics of subjective auditory space at lateralization of stationary and moving fused sound images (FSI) were studied in 15 examinees. The method of dichotic stimulation with a series of binaurally presented click trains was used, at varying of interaural intensity differences (I) within the limits of ±13 dB. Duration of the click series amounted to 2 s. To establish perception of moving FSI, the value of interaural differences in stimulation time (T ) varied from ±630 µs to zero throughout the time of the sound signal action. Under conditions of stationary and moving FSI we estimated expansion of the subjective auditory space (as the distance between the extreme left and extreme right points of FSI position, %), the site of FSI position in it (% related to the head midline), the rate of FSI moving (deg/s), and variability measured by value of examinees estimates of position of both stationary and moving FSI at the initial and final moments of moving. It was established that under conditions of stationary FSI, at the under border I values (from –13 to 13 dB), expansion of auditory space varied from 50 to 149 degrees. Variability of estimations of the stationary FSI position at I = ±13 dB also differed in various examinees, at values from 3–4 to 17–20 deg. Under conditions of moving FSI, expansion of the subjective auditory space increased to amount to from 107 to 185 deg within the borders of I = ±13 dB, whereas value was even somewhat decreased and amounted to from 2–3 to 12–16 deg. The rate of FSI moving at the same I varied in different examinees from 13 to 43 deg/s. The diversity of quantitative characteristics of the subjective auditory space among the examinees is considered from the point of view of individual differences in structure of the auditory space and of the level of physiological noises in the brain centers responsible for making a particular decision. It is suggested that the presented limits of individual examinees differences might be of essential importance for preparation of operators to corresponding kinds of work.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 40, No. 5, 2004, pp. 441–449.Original Russian Text Copyright © 2004 by Variaguina, Radionova.To the 100-Anniversary of N. N. Traugott     

The physiological ecology of Mytilus californianus Conrad

Summary The rates of oxygen consumption, filtration and ammonia excretion by Mytilus californianus have been related to body size and to ration. The rate of oxygen consumption (VO₂) by individuals while immersed, measured on the shore, resembled rates recorded for mussels starved in the laboratory. VO₂ by M. californianus was relatively independent of change in temperature, with a Q ₁₀ (13–22° C) of 1.20. In contrast, the frequency of heart beat was more completely temperature dependent [Q ₁₀ (13–22° C)=2.10]. Filtration rate showed intermediate dependence on temperature change [Q ₁₀ (13–22° C)=1.49] up to 22° C, but declined at 26° C. Both VO₂ and filtration rate declined during starvation. The utilisation efficiency for oxygen was low (approx. 4%) between 13 and 22° C, but increased to 10% at 26° C. Three components of the routine rate of oxygen consumption are recognised and estimated; viz. a basal rate (0.136 ml O₂ h^-1 for a mussel of 1 g dry flesh weight), a physiological cost of feeding (which represented about 6% of the calories in the ingested ration), and a mechanical cost of feeding which was three times higher than the physiological cost. The ratio oxygen consumed to ammonia-nitrogen excreted was low, and it declined during starvation. These data are compared with previously published measurements on Mytilus edulis, and the two species of mussel are shown to be similar in some of their physiological characteristics, though possibly differing in their capacities to compensate for change in temperature. For M. californianus, the scope for growth was highest at 17–22° C and declined at 26° C; it is suggested that exposure to temperatures in excess of 22° C, as for example during low tides in the summer, might result in a cumulative stress on these populations of mussels by imposing a metabolic deficit which must be recovered at each subsequent high tide. The high mechanical cost of feeding imposes a more general constraint on the scope for activity of the species.     

Dry matter production and photosynthetic capacity in Gossypium hirsutum L. under conditions of slightly suboptimum leaf temperatures and high levels of irradiance

Summary Gossypium hirsutum L. var. Delta Pine 61 was cultivated in controlled-environment chambers at 1000–1100 mol photosynthetically active photons m^-2 s^-1 (medium photon flux density) and at 1800–2000 mol photons m^-2 s^-1 (high photon flux density), respectively. Air temperatures ranged from 20° to 34°C during 12-h light periods, whereas during dark periods temperature was 25° C in all experiments. As the leaf temperature decreased from about 33° to 27° C, marked reductions in dry matter production, leaf chlorophyll content and photosynthetic capacity occurred in plants growing under high light conditions, to values far below those in plants growing at 27° C and medium photon flux densities. The results show that slightly suboptimum temperatures, well above the so-called chilling range (0–12° C), greatly reduce dry matter production in cotton when combined with high photon flux densities equivalent to full sunlight.Abbreviations DW dry weight - F _v variable fluorescence yield - F _M maximum fluorescence yield - PFD photon flux density (400–700 nm)     

Mathematical modeling of mixing in a horizontal rotating tubular bioreactor: “Spiral flow” model

A horizontal rotating tubular bioreactor (HRTB) was designed as a combination of a thin-layer bioreactor and a biodisc reactor whose interior was divided by O-ring shaped partition walls. For the investigation of mixing in HRTB the temperature step method was applied. Temperature changes in the bioreactor were monitored by six Pt-100 sensors (t ₉₀ response time 0.08 s and resolution 0.002 °C) which were connected with an interface unit and a personal computer. In this work a modified tank in series concept was used to establish a mathematical model. The heat balance of the model compartments was established according to the physical model and the spiral flow pattern. Numerical integration was done by the Runge-Kutta-Fehlberg method. The mathematical mixing model called spiral flow model contained four adjustable parameters (N1, Ni, F _cr and F _p) and five parameters which characterized the plant and experimental conditions. The spiral flow model was capable to describe the mixing in HRTB properly, and its applicability was much better than with the simple flow model, presented earlier.List of Symbols A _ui m² ithpart of inner surface of bioreactor's wall - A _vi m² ith part of outlet surface of bioreactor's wall - C _p kJ kg^–1 K^–1 heat capacity of liquid - c _pr kJ kg^–1 K^–1 heat capacity of bioreactor's wall - D h^–1 dilution rate - E °C°C^–1h^–1 error of mathematical model - F _cr dm³ s^–1 circulation flow in the model - F _p dm³s^–1 back flow in the model - F _t dm³ s^–1 inlet flow in bioreactor - I °C intensity of temperature step, the difference in temperature between the temperature of the inlet liquid flow and the temperature of liquid in bioreactor before temperature step - K1 Wm^–2 K ^–1 heat transfer coefficient between the liquid and bioreactor's wall - K2 Wm^–2 K ^–1 heat transfer coefficient between the bioreactor's wall and air - L m length of bioreactor - m _s kg mass of bioreactor's wall - n min^–1 rotational speed of bioreactor - n _s number of temperature sensors - N1 number of cascades - Ni number of compartments inside cascade - r _u m inner diameter of bioreactor - r _v m outside diameter of bioreactor - s(t) step function - t s time - T °C temperature - T _c °C calculated temperature - T _m °C measured temperature - T _N 1,Ni°C temperature of liquid in defined compartments inside the cascade - T _N 1,S°C temperature of defined part of bioreactor's wall - T _N i,z°C temperature of surrounding air - V _t dm³ volume of liquid in the bioreactor     

Responses and song pattern copying of Omega-type I-neurons in the cricket,Gryllus bimaculatus,at different prothoracic temperatures

Summary Omega-type I-neurons (ON/1) (Fig. 1A) were recorded intracellularly with the prothoracic ganglion kept at temperatures of either 8–9°, or 20–22° or 30–33 °C and the forelegs with the tympanal organs kept at ambient temperature (20–22 °C). The neurons were stimulated with synthetic calling songs (5 kHz carrier frequency) with syllable periods (SP in ms) varying between 20 and 100, presented at sound intensities between 40 and 80 dB SPL. The amplitude and duration of spikes as well as response latency decreased at higher temperatures (Figs. 1 B, 2, 6). At lower prothoracic temperatures (8–9 °C) the neuron's responses to songs with short SP (20 ms) failed to copy single syllables, or with moderate SP (40 ms) copied the syllable with low signal to noise ratio (Fig. 3). The auditory threshold of the ON/1 type neuron, when tested with the song model, was temperature-dependent. At 9° and 20 °C it was between 40 and 50 dB SPL and at 33 °C it was less than 40 dB SPL (Fig. 4). For each SP, the slope of the intensity-response function was positively correlated with temperature, however, at low prothoracic temperatures the slope was lower for songs with shorter SPs (Fig. 5). The poor copying of the syllabic structure of the songs with short SPs at low prothoracic temperatures finds a behavioral correlate because females when tested for phonotaxis on a walking compensator responded best to songs with longer SPs at a similar temperature.Abbreviations epsps excitatory postsynaptic potentials - ON/1 omega-type I-neuron - SP syllable period - SPL sound pressure level     

Abscisic acid and mefluidide in the regulation of cold hardiness development in Solanum tuberosum L. potato

Plants of Solanum tuberosum L. potato do not cold acclimate when exposed to low temperature such as 5°C, day/night. When ABA (45 M) was added to the culture medium, stem-cultured plantlets of S. tuberosum, cv. Red Pontiac, either grown at 20°C/15°C, day/night, or at 5°C, increased in cold hardiness from –2°C (killing temperature) to –4.5°C. The increase in cold hardiness could be inhibited in both temperature regimes if cycloheximide (70 M) was added to the culture medium at the inception of ABA treatment. Cycloheximide did not inhibit cold hardiness development, however, when it was added to the culture medium 3 days after ABA treatment.When pot-grown plants were foliar sprayed with mefluidide (50 M), ABA content increased from 10 nmol to 30 nmol g^–1 dry weight and plants increased in cold hardiness from –2°C to about –3.5°C. The increases in free ABA and cold hardiness occurred only in plants grown at 20°C/15°C; neither ABA nor cold hardiness increased in plants grown at 5°C.The results suggest that an increase in ABA and a subsequent de novo synthesis of proteins are required for the development of cold hardiness in S. tuberosum regardless of temperature regime, and that the inability to synthesize ABA at low temperature, rather than protein synthesis, appears to be the reason why S. tuberosum does not cold acclimate.     

Lactate content and lactate dehydrogenase activity inPalaemon serratus abdominal muscle during temperature changes

Summary Lactate concentration was measured in the abdominal muscle of the shrimpPalaemon serratus. Rapid and seasonal temperature changes result in an increase of the lactate content of approximately 3–4 fold.Lactate dehydrogenase from the abdominal muscle exhibits a temperature dependent pyruvate inhibition with pyruvate as substrate.The kinetic parameters of lactate dehydrogenase fromPalaemon serratus are found to vary during rapid temperature changes: V_max increases with temperature from 0.06 mol min^–1 (mg protein)^–1 at 10°C to 0.28 mol min^–1 (mg protein)^–1 at 30°C with lactate as substrate, and from 5.5 mol min^–1 (mg protein)^–1 at 10°C to 26.2 mol min^–1 (mg protein)^–1 at 30°C, with pyruvate (Table 1). The Hill coefficientn _H, decreases with temperature from 2.2 to 1.2 when the pyruvate reduction is examined, but remains near 1.2 when the activity is measured with lactate as substrate (Table 1). The S_0.5 values for lactate show a tendency to increase below 30 °C (18.9 mM l^–1 at 20 °C) whereas the S_0.5 for pyruvate is found to increase greatly with temperature (0.004 mM l^–1 at 10 °C and 0.06 mM l^–1 at 20 °C).Long term temperature changes involve variations of lactate dehydrogenase activity leading to inverse thermal compensation (Table 2).Activation energy (about 56 kJ both with pyruvate and lactate) does not vary during the year, suggesting that temperature adaptation does not induce important catalytic changes (Table 3).Abbreviation LDH lactate dehydrogenase     

Temperature adaptation and the contractile properties of live muscle fibres from teleost fish

Summary The contractile properties of swimming muscles have been investigated in marine teleosts from Antarctic (Trematomus lepidorhinus, Pseudochaenichthys georgianus), temperate (Pollachius virens, Limanda limanda, Agonis cataphractus, Callionymus lyra), and tropical (Abudefduf abdominalis, Thalassoma duperreyi) latitudes. Small bundles of fast twitch fibres were isolated from anterior myotomes and/or the pectoral fin adductor profundis muscle (m. add. p). Live fibre preparations were viable for several days at in vivo temperatures, but became progressively inexcitable at higher or lower temperatures. The stimulation frequency required to produce fused isometric tetani increased from 50 Hz in Antarctic species at 0°C to around 400 Hz in tropical species at 25°C. Maximum isometric tension (P_o) was produced at the normal body temperature (NBT) of each species (Antarctic, 0–2°C; North Sea and Atlantic, 8–10°C; Indo-West Pacific, 23–25°C). P₀ values at physiological temperatures (200–300 kN·m^–2) were similar for Antarctic, temperate, and tropical species. A temperature induced tension hysteresis was observed in muscle fibres from some species. Exposure to <0°C in Antarctic and <2°C in temperate fish resulted in the temporary depression of tension over the whole experimental range, an effect reversed by incubation at higher temperatures. At normal body temperatures the half-times for activation and relaxation of twitch and tetanic tension increased in the order Antarctic>temperate>tropical species. Relaxation was generally much slower at temperatures <10°C in fibres from tropical than temperate fish. Q₁₀ values for these parameters at NBTs were 1.3 2.1 for tropical species, 1.7–2.6 for temperate species, and 1.6–3.5 for Antarctic species. The forcevelocity (P-V) relationship was studied in selected species using iso-velocity releases and the data below 0.8 P₀ iteratively fitted to Hill's equation. The P-V relation at NBT was found to be significantly less curved in Antarctic than temperate species. The unloaded contraction velocity (V_max) of fibres was positively correlated with NBT increasing from about 1 muscle fibre length·s^–;1 in an Antarctic fish (Trematomus lepidorhinus) at 1°C to around 16 muscle fibre lengths·s^–1 in a tropical species (Thalassoma duperreyi) at 24°C. It is concluded that although muscle contraction in Antarctic fish shows adaptations for low temperature function, the degree of compensation achieved in shortening speed and twitch kinetics is relatively modest.Abbreviations ET environmental temperature - m. add. p major adductor profundis - m. add. s. major adductor superficialis - NBT normal body temperature - P ₀ maximum isometric tension - P-V force velocity - SR sarcoplasmic reticulum - T 1/2 a half activation time - T 1/2 r half relaxation time - V _max unloaded contraction     

Cell inactivation,mutation and DNA strand-break induction by γ-rays at very low temperatures

Cell inactivation, mutation and DNA strand-break induction by -radiation have been investigated at very low temperatures (–78° C, –196° C, and –268° C). InEscherichia coli Y _mel ,lacI ⁺ lacI ^– andSalmonella typhimurium TA102,his ^–his ⁺ dose-modifying factors determined for low radiation doses are similar for both mutation induction and cell inactivation. The sensitivity of repair-deficient strainsE. coli polA ^– andE. coli recA ^– was also reduced at low temperature to a comparable extent. This suggests that the lesions which are responsible for cell inactivation and mutagenesis could be strongly mutually related and/or that different types of lesions which are responsible for cell inactivation and mutation induction in bacteria are reduced at low temperature to the same or similar extent. Likewise, a lower yield of DNA strand breaks in plasmids irradiated at low temperature was observed.     

Comparative collicular tonotopy in two bat species adapted to movement detection,Hipposideros speoris andMegaderma lyra

Summary The tonotopic organization of the inferior colliculus (IC) in two echolocating bats,Hipposideros speoris andMegaderma lyra, was studied by multiunit recordings.InHipposideros speoris frequencies below the range of the echolocation signals (i.e. below 120 kHz) are compressed into a dorsolateral cap about 400–600 m thick. Within this region, neuronal sheets of about 4–5 m thickness represent a 1 kHz-band.In contrast, the frequencies of the echolocation signals (120–140 kHz) are overrepresented and occupy the central and ventral parts of the IC (Fig. 3). In this region, neuronal sheets of about 80 m thickness represent a 1 kHz-band. The largest 1 kHz-slabs (400–600 m) represent frequencies of the pure tone components of the echolocation signals (130–140 kHz).The frequency of the pure tone echolocation component is specific for any given individual and always part of the overrepresented frequency range but did not necessarily coincide with the BF of the thickest isofrequency slab. Thus hipposiderid bats have an auditory fovea (Fig. 10).In the IC ofMegaderma lyra the complete range of audible frequencies, from a few kHz to 110 kHz, is represented in fairly equal proportions (Fig. 7). On the average, a neuronal sheet of 30 m thickness is dedicated to a 1 kHz-band, however, frequencies below 20 kHz, i.e. below the range of the echolocation signals, are overrepresented.Audiograms based on thresholds determined from multiunit recordings demonstrate the specific sensitivities of the two bat species. InHipposideros speoris the audiogram shows two sensitivity peaks, one in the nonecholocating frequency range (10–60 kHz) and one within the auditory fovea for echolocation (130–140 kHz).Megaderma lyra has extreme sensitivity between 15–20 kHz, with thresholds as low as –24 dB SPL, and a second sensitivity peak at 50 kHz (Fig. 8).InMegaderma lyra, as in common laboratory mammals, Q_10dB-values of single units do not exceed 30, whereas inHipposideros speoris units with BFs within the auditory fovea reach Q_10dB-values of up to 130.InMegaderma lyra, many single units and multiunit clusters with BFs below 30 kHz show upper thresholds of 40–50 dB SPL and respond most vigorously to sound intensities below 30 dB SPL (Fig. 9). Many of these units respond preferentially or exclusively to noise. These features are interpreted as adaptations to detection of prey-generated noises.The two different tonotopic arrangements (compare Figs. 3 and 7) in the ICs of the two species are correlated with their different foraging behaviours. It is suggested that pure tone echolocation and auditory foveae are primarily adaptations to echo clutter rejection for species foraging on the wing close to vegetation.Abbreviations BF Best frequency - CF constant frequency - FM frequency modulated - IC inferior colliculus - HS Hipposideros speoris     

Effects of pre-storage conditions on storage of in vitro cultures of Nephrolepis exaltata (L.) Schott and Cordyline fruticosa (L.) A. Chev.

In vitro cultures of Nephrolepis exaltata and Cordyline fruticosa were stored at 5°, 9° or 13°C, at a low irradiance (3–5 mol m^–2 s^–1) or in darkness. Prior to storage the cultures were subjected to 18°, 21°, 24° or 27°C and 15, 30 or 45 mol m^–2 s^–1 in a factorial combination.The optimal storage conditions for Nephrolepis were 9°C in complete darkness. These cultures were still transferable to a peat/perlite mixture at the end of the experimental period of 36 months.The optimal storage conditions for Cordyline were 13°C and a low light level (±3–5 mol m^-2 s^-1). When the pre-storage conditions were normal growth room conditions (24°C and 30 mol m^-2 s^-1), in vitro cultures could be stored for 18 months. With the most favourable pre-storage treatment (18°C and 15 mol m^-2 s^-1) some cultures still had green shoots after 36 months of storage, but did not survive transfer to peat/perlite.Pre-conditioning before storage was most favourable for Nephrolepis, and not that important, but still favourable, for Cordyline. There was an interaction between pre-storage temperature and pre-storage irradiance. For both species a high irradiance level was less favourable than a low irradiance level when combined with high growth room temperatures.Abbreviations BA 6-benzyladenine - IAA indole-3-acetic acid - NOA 2-naphthoxyacetic acid