Rapid, Blue-Light Induced Transpiration in Avena

The transpiration responses of primary Avena leaves to blue-light pulses were investigated. Only light with wave length shorter than 524 nm can produce the rapid transpiration response. The action spectrum has a maximum around 450 nm. The rapid transpiration response induced by blue-light pulses successively disappeared in long-term experiments if the plant was kept in darkness between the pulses. However, if visible light was given to the plant between the pulses, the rapid response was restored. The magnitude of the rapid transpiration response was investigated under different conditions of background illumination and blue-light exposure. Saturation of the response was obtained with an irradiation level of 1.5–2 mW.cm^?2 (5 min pulses) and with a pulse duration of 4 min (pulse irradiance 2 mW.cm^?2). A pulse duration of 3 s was sufficient to produce a significant rapid response at an irradiation level of 2 mW.cm^?2.     

Effect of heat shock on courtship behavior,sound production,and learning in comparison with the brain content of LIMK1 in Drosophila melanogaster males with altered structure of the limk1 gene

In this paper we present results of a comprehensive analysis of the effect of heat shock at different stages of ontogenesis (adult stage, development of mushroom bodies and the central complex) on courtship behavior (latency, duration and efficacy of courtship), sound production (pulse interval, dispersion of interpulse interval, percentage of distorted pulses, the mean duration of the pulse samples), learning and memory formation compared with the content of LIMK1 isoforms in male Drosophila melanogaster with altered structure of the limk1 gene. The heat shock is shown to affect the behavior parameters and LIMK1 content in the analyzed strains of Drosophila. The most pronounced effect of the heat shock was observed at the stage of development of the central complex (CC). Heat shock at CC and adults restores the ability of learning and memory formation in the mutant strain agn ^ts3 that normally is unable to learn and form memory. Correlations between changes of content of LIMK1 isoforms and behavioral parameters due to heat shock have not been established.     

Phycomyces: Phototropism and light-growth response to pulse stimuli

The relationship between phototropism and the light-growth response of Phycomyces blakesleeanus (Burgeff) sporangiophores was investigated. After dark adaptation, stage-IVb sporangiophores were exposed to short pulses of unilateral light at 450 nm wavelength. The sporangiophores show a complex reaction to pulses of 30 s duration: maximal positive bending at 3·10^-4 and 10^-1 J m^-2, but negative bending at 30 J m^-2. The fluence dependence for the light-growth response also is complex, but in a different way than for phototropism; the first maximal response occurs at 1.8·10^-3 J m^-2 with a lesser maximum at 30 J m^-2. A hypertropic mutant, L85 (madH), lacks the negative phototropism at 30 J m^-2 but gives results otherwise similar to the wild type. The reciprocity rule was tested for several combinations of fluence rates and pulse durations that ranged from 1 ms to 30 s. Near the threshold fluence (3·10^-5 J m^-2), both responses increase for pulse durations below 67 ms and both have an optimum at 2 ms. At a fluence of 2.4·10^-3 J m^-2, both responses decrease for pulse durations below 67 ms. The hypertropic mutant (madH), investigated for low fluence only, gave similar results. In both strains, the time courses for phototropism and light-growth response, after single short pulses of various durations, show no clear correlation. These results imply that phototropism cannot be caused by linear superposition of localized light-growth responses; rather, they point to redistribution of growth substances as the cause of phototropism.     

Rhesus monkey behavior during exposure to high-peak-power 5.62-GHz microwave pulses

Limits on the exposure to high-peak-power, short-duration microwave pulses have only recently been adopted. Additional data, however, are needed to understand the effects that may be produced by exposure to high-peak-power pulsed microwaves. Four male rhesus monkeys (Macaca mulatta) were trained on an operant task for food pellet reward to investigate the behavioral effects of very high-peak-power 5.62 GHz microwaves. The operant task required monkeys to pull one plastic lever on a variable interval schedule (VI-25 s) and then respond to color signals and pull a second lever to obtain food. The monkeys were conditioned to perform a color discrimination task using one of three colors displayed by a fiber-optic cable. A red signal was the discriminative stimulus for responding on the first lever. A response on the second lever when a green signal was presented (1 s duration) delivered a food pellet. If a response on the second lever was made in the presence of a white signal, a 30-s timeout occurred. While performing the behavioral task, the monkeys were exposed to microwave pulses produced by either a military radar (FPS-26A) operating at 5.62 GHz or the same radar coupled to a Stanford linear energy doubler (SLED) pulse-forming device (ITT-2972) that enhanced peak power by a factor of nine by adding a high power pulse to the radar pulse. The effects of both types of pulses were compared to sham exposure. Peak field power densities tested were 518, 1270, and 2520 W/cm² for SLED pulses and 56, 128, and 277 W/cm² for the radar pulses. The microwave pulses (radar or SLED) were delivered at 100 pps (2.8 μs radar pulse duration, ≈ 50 ns SLED pulse duration) for 20 min and produced averaged whole-body SARs of 2,4, or 6 W/kg. Compared to sham exposures, significant alterations of lever responding, reaction time, and earned food pellets occurred during microwave exposure at 4 and 6 W/kg but not 2 W/kg. There were no differences between radar or SLED pulses in producing behavioral effects. ©1994 Wiley-Liss, Inc.

1 This is a US Government work and, as such, is in the public domain in the United States of America.

     

Electrofusion of Mucor circinelloides protoplasts

Summary Electrical parameters were optimized for induction of the fusion of protoplasts formed from two auxotrophic (leu^–, ade^–) Mucor circinelloides strains. These proved to be a pulse voltage of 66 V, a pulse duration of 66 us and six pulses at intervals of 1.0 s. Nutritionally complementing colonies were obtained at an average frequency up to 12.4%, which is substantially higher than achieved earlier with the PEG-Ca²⁺ method.     

Development of resistance in Cronobacter sakazakii ATCC 29544 to thermal and nonthermal processes after exposure to stressing environmental conditions

Aims: The objective was to study the response of Cronobacter sakazakii ATCC 29544 cells to heat, pulsed electric fields (PEF), ultrasound under pressure (Manosonication, MS) and ultraviolet light (UV‐C) treatments after exposure to different sublethal stresses that may be encountered in food‐processing environments. Methods and Results: Cronobacter sakazakii stationary growth‐phase cells (30°C, 24 h) were exposed to acid (pH 4·5, 1 h), alkaline (pH 9·0, 1 h), osmotic (5% NaCl, 1 h), oxidative (0·5 mmol l^?1 H₂O₂, 1 h), heat (47·5°C, 1 h) and cold (4°C, 4 h) stress conditions and subjected to the subsequent challenges: heat (60°C), PEF (25 kV cm^?1, 35°C), MS (117 μm, 200 kPa, 35°C) and UV‐C light (88·55 mW cm^?2, 25°C) treatments. The inactivation kinetics of C. sakazakii by the different technologies did not change after exposure to any of the stresses. The combinations of sublethal stress and lethal treatment that were protective were: heat shock–heat, heat shock–PEF and acid pH–PEF. Conversely, the alkaline shock sensitized the cells to heat and UV‐C treatments, the osmotic shock to heat treatments and the oxidative shock to UV‐C treatments. The maximum adaptive response was observed when heat‐shocked cells were subjected to a heat treatment, increasing the time to inactivate 99·9% of the population by 1·6 times. Conclusions: Cronobacter sakazakii resistance to thermal and nonthermal preservation technologies can increase or decrease as a consequence of previous exposure to stressing conditions. Significance and Impact of the Study: The results help in understanding the physiology of the resistance of this emerging pathogen to traditional and novel preservation technologies.     

Possible species specific courtship sounds by two sympatric cichlid fishes in Lake Malawi, Africa

Sounds were produced by the males of two species of cichlid fishes while courting females. Each courtship sound consisted of a series of distinct pulses occurring in rapid succession. Courtship sounds produced by Tramitichromis cf. intermedius and Copadichromis conophorus were significantly different in pulse rate and individual pulse durations. For C. conophorus calls (n=127) the mean ± sd number of pulses per call was 10 ± 3 and call duration was 181 ± 59 ms. There was a significant positive linear relationship between call duration and the number of pulses (r²=0.912, p < 0.001). The dominant frequency of the pulses in calls was 471 ± 50 (range 372–594) Hz (n=40 calls). T. cf. intermedius also produced a pulsed courtship call; data (mean ± sd) from two male T. cf. intermedius: 9 ± 2 pulses per call and duration 199 ± 44 ms (n=20 calls). The linear regression between call duration and number of pulses was positive (r²=0.463, p=0.001). Pulse rate within calls of T. cf. intermedius compared to C. conophorus were significantly different (p=0.018). Individual pulse durations were also significantly different (p=0.043) between species. However, interpulse intervals were not significantly different (p=0.177). These cichlids produced courtship sounds that were distinct by individual pulse durations and by pulse repition rate in a call.     

TEMPORAL AMMONIUM PATCHINESS AND GROWTH RATE IN CODIUM AND ULVA (ULVOPHYCEAE)1

The growth rates of two chlorophyte macroalgae, Codium fragile and Ulva curvata, are compared in response to varied, but non-random, NH₄⁺ enrichments (pulses). The species were chosen to contrast radically different morphologies. Pulse frequency and pulse duration were varied independently; however, an equivalent mass of NH₄⁺ was added in each treatment. The growth rate of Codium varied neither as a function of pulse frequency nor duration; the growth rate of Ulva varied with pulse frequency, but not pulse duration. These data are combined with life form and physiological characters, and are discussed in the context of the “function form” hypothesis. From the evidence we argue that by virtue of its life form, Ulva is capable of utilizing transiently high NH₄⁺ concentrations and is capable of high growth rates, attributes contributing to its role as a ruderal species. In contrast, Codium's life form does not allow utilization of transiently high NH₄⁺ concentrations or high growth rates, thereby contributing to its role as a persistent species.     

Bat Avoidance in Non-Aerial Insects: The Silence Response of Signaling Males in an Acoustic Moth

While the evasive responses of many flying acoustic insects to aerial‐hawking bats are duly recognized and studied, the responses of non‐aerial insects to gleaning bats are generally overlooked. It has been assumed that acoustic insects are deaf to these predators because gleaning bat echolocation calls are typically low in amplitude, brief (1–3 ms) and very high in frequency (>60 kHz). We tested this assumption in a series of playback experiments with a moth (Achroia grisella) that uses hearing in both predator evasion and mating. We report that ultrasound pulses ≥78 dB peSPL (peak equivalent sound pressure level) and ≥1 ms in duration inhibit stationary males from broadcasting their own ultrasonic advertisement calls, provided that the pulsed stimuli are delivered at a repetition rate ≤30/s. Further analyses suggest that inhibition by pulsed ultrasound comprises two processes performed serially. First, a startle response with a latency <50 ms is elicited by a single pulse ≥1 ms duration. Here, a male misses broadcasting several calls over a 50–100 ms interval. Secondly, the startle may be extended as a silence response lasting several to many seconds if subsequent pulses occur at a rate ≤30/s. Call inhibition cannot represent a simple response to acoustic power because of the inverse interaction between pulse duration and rate. On the other hand, the temporal and energy characteristics of inhibitory stimuli match those of gleaning bat echolocation calls, and we infer that inhibition is a specialized defensive behavior by which calling males may avoid detection by eavesdropping bats.     

Blue light-regulation of cell division in Adiantum protonemata: kinetic properties of the photosystem

Abstract Blue-light-induced cell division in single-celled Adiantum protonemata was studied by using two or three pulses (pulse duration: 30 s) separated by various periods and by using relatively long irradiation (e.g. 30 min). The results showed: (1) that the response is saturated by a single pulse, (2) that after the application of a saturating pulse, the protonemata gradually become responsive to another pulse, showing time-dependent saturation to the second pulse, and (3) that although reciprocity holds in the pulse-induced response, it becomes invalid as the exposure duration extends in the range of minutes. These results were analysed in view of a reaction model in which a molecular component is considered to exist in two forms A and B. The response to a single pulse is considered to result from a light-dependent conversion of the component (A→B), and the restoration response measured by two pulses, from its dark reversion (B→A). The analyses yielded (1) the value of the constant which relates the fluence rate to the rate constant of the light-induced reaction, and (2) the rate constant of the dark reaction. The model was extended to formulate the responses to long irradiations as a function of the integrated concentration of B over time. The responses predicted by the formula by using the parameter values estimated from the pulse responses were able to explain the responses measured for long irradiation.     

Dependence of carbon sequestration on the differential responses of ecosystem photosynthesis and respiration to rain pulses in a semiarid steppe

Precipitation pulses play an important role in regulating ecosystem carbon exchange and balance of semiarid steppe ecosystems. It has been predicted that the frequency of extreme rain events will increase in the future, especially in the arid and semiarid regions. We hypothesize that large rain pulses favor carbon sequestration, while small ones cause more carbon release in the semiarid steppes. To understand the potential response in carbon sequestration capacity of semiarid steppes to the changes in rain pulse size, we conducted a manipulative experiment with five simulated rain pulse sizes (0, 5, 10, 25, and 75 mm) in Inner Mongolia steppe. Our results showed that both gross ecosystem productivity (GEP) and ecosystem respiration (R_e) responded rapidly (within 24 h) to rain pulses and the initial response time was independent of pulse size. However, the time of peak GEP was 1–3 days later than that of R_e, which depended on pulse size. Larger pulses caused greater magnitude and longer duration of variations in GEP and R_e. Differences in the response time of microbes and plants to wetting events constrained the response pattern of heterotrophic (R_h) and autotrophic (R_a) components of R_e following a rain event. R_h contributed more to the increase of R_e in the early stage of rain pulse response, while R_a played an more important role later, and determined the duration of pulse response, especially for large rain events of >10 mm. The distinct responses of ecosystem photosynthesis and respiration to increasing pulse sizes led to a threshold in rain pulse size between 10 and 25 mm, above which post wetting responses favored carbon sequestration. The disproportionate increase of the primary productivity of higher plants, compared with those in the activities of microbial decomposers to larger pulse events suggests that the carbon sequestration capacity of Inner Mongolia steppes will be sensitive to changes in precipitation size distribution rather than just precipitation amount.     

Precipitation pulse use by an invasive woody legume: the role of soil texture and pulse size

Plant metabolic activity in arid and semi-arid environments is largely tied to episodic precipitation events or “pulses”. The ability of plants to take up and utilize rain pulses during the growing season in these water-limited ecosystems is determined in part by pulse timing, intensity and amount, and by hydrological properties of the soil that translate precipitation into plant-available soil moisture. We assessed the sensitivity of an invasive woody plant, velvet mesquite (Prosopis velutina Woot.), to large (35 mm) and small (10 mm) isotopically labeled irrigation pulses on two contrasting soil textures (sandy-loam vs. loamy-clay) in semi-desert grassland in southeastern Arizona, USA. Predawn leaf water potential (Ψ_pd), the isotopic abundance of deuterium in stem water (δD), the abundance of ¹³C in soluble leaf sugar (δ¹³C), and percent volumetric soil water content (θ_v) were measured prior to irrigation and repeatedly for 2 weeks following irrigation. Plant water potential and the percent of pulse water present in the stem xylem indicated that although mesquite trees on both coarse- and fine-textured soils quickly responded to the large irrigation pulse, the magnitude and duration of this response substantially differed between soil textures. After reaching a maximum 4 days after the irrigation, the fraction of pulse water in stem xylem decreased more rapidly on the loamy-clay soil than the sandy-loam soil. Similarly, on both soil textures mesquite significantly responded to the 10-mm pulse. However, the magnitude of this response was substantially greater for mesquite on the sandy-loam soil compared to loamy-clay soil. The relationship between Ψ_pd and δ¹³C of leaf-soluble carbohydrates over the pulse period did not differ between plants at the two sites, indicating that differences in photosynthetic response of mesquite trees to the moisture pulses was a function of soil water availability within the rooting zone rather than differences in plant biochemical or physiological constraints. Patterns of resource acquisition by mesquite during the dynamic wetting–drying cycle following rainfall pulses is controlled by a complex interaction between pulse size and soil hydraulic properties. A better understanding of how this interaction affects plant water availability and photosynthetic response is needed to predict how grassland structure and function will respond to climate change.     

Chloride Currents in Skeletal Muscles of Bufo arenarum

Cl⁻ currents (I _Cl) were measured in short fibers (1–2 mm) from the lumbricalis muscle of toads (Bufo arenarum) with two microelectrodes (15°C). Initially the fibers were equilibrated in a high K⁺-containing solution: (mm) K₂SO₄ 68; Na₂SO₄ 20; KCl 60; CaSO₄ 8; MgSO₄ 1; HEPES 2.5. Constant pulses were applied when all the external K⁺ was replaced by Cs⁺: Cs₂SO₄ 68; Na₂SO₄ 20; CsCl 60; CaSO₄ 8; HEPES 2.5 (pH 7.5). Under these conditions about 80–90% of the current is carried by Cl⁻. The current-voltage relation is almost linear implying constant conductance and hence voltage-independent permeability. The voltage dependence of the net Cl⁻ current could be fitted by constant field equation with a P _Cl of 3.3 × 10⁻⁶ cm/sec. In a separate group of experiments a two-pulse technique was used to estimate the availability and the inactivation of the initial I _Cl during a test pulse. After returning the potential to the holding potential for various times, test pulses of the same amplitude and duration of the prepulses were applied. The initial current during the test pulse was 70% of the initial current during the prepulse and the recovery was complete in less than 300 msec with a linear relationship between the current during the test pulse and the amplitude of the preceding prepulse. When the test pulses were preceded by a positive prepulse, the initial current for any given test pulse was larger than with a negative prepulse. If we assumed that the initial current during the test pulse is a measure of the number of channels open at the end of the prepulse, these results suggest that hyperpolarizing pulses inactivate and depolarizing prepulses activate the I _Cl. Received: 31 March 1995/Revised: 27 October 1995     

Ultrasonic bouts of a blind climbing rodent (Typhlomys chapensis): acoustic analysis

ABSTRACT

The peculiar acoustic structure of ultrasonic bouts of blind climbing rodents Typhlomys might provide insight on their potential function. We examined 1481 bouts consisting of 1-6 pulses; 49.7% of them were single-pulse bouts. Bout duration and inter-bout interval depended on the number of pulses per bout, whereas period from start of a previous bout to start of the next bout was constant (80.0±2.9 ms). Ultrasonic pulses (540 pulses measured in a subset of 234 bouts) were short (0.68±0.15 ms) sweeps with fundamental frequency slopes from 127.3±6.3 kHz to 64.1±4.6 kHz and peak frequency at 93.3±7.4 kHz, emitted within bouts with inter-pulse periods of 13.03±3.01 ms. Single pulses and start pulses of multi-pulse bouts were lower in frequency than other pulses of the bouts. In contrast, pulse duration was independent on pulse position within bout. Pulses of Typhlomys were reminiscent of echolocation calls of Murina and Myotis bats, but higher in frequency, much shorter, fainter, displayed a convex contour of frequency modulation and only the fundamental frequency band without harmonics and were organized in bouts, that is not characteristic for bat echolocation. Most probably, Typhlomys uses their ultrasonic pulses for call-based orientation during locomotion, including climbing and jumping among bush branches.     

Effect of nutrient pulse concentration and frequency on growth ofGracilaria chilensis plants and levels of epiphytic algae

The effect of nutrient pulse concentration and frequency onGracilaria chilensis Bird, McLachlanet O Oliveira growth and epiphyte abundace was investigated for plants grown in an indoor culture facility. The frequency of nutrient pulses (which ranged from 1 pulse to 4 pulses per 14 days) had a strong influence on plant growth, while pulse concentration (from 72 to 143 µM as ammonium) had a lesser influence. Growth became a function of total N flux only when plants received nutrient pulses at least twice per 14 days. Both pulse frequency and pulse concentration affected the abundance of epiphytic algae found attached toGracilaria thalli, but pulse frequency was the more significant of the two factors. Their effects could be combined into the single factor, total N flux. Both reasonableG. chilensis growth and low levels of epiphytes were achieved under these conditions (20 °C, 25 µ mol photon m^–2 s^–1 PAR) if ammonium was pulsed at relatively high concentrations (up to 150 µM) once every 7 days into otherwise nitrogen-depleted seawater.     

Cold shock and fish

Rapid decreases in water temperature may result in a number of physiological, behavioural and fitness consequences for fishes termed ‘cold shock’. Cold‐shock stress occurs when a fish has been acclimated to a specific water temperature or range of temperatures and is subsequently exposed to a rapid decrease in temperature, resulting in a cascade of physiological and behavioural responses and, in some cases, death. Rapid temperature decreases may occur from either natural (e.g. thermocline temperature variation, seiches and storm events) or anthropogenic sources (e.g. varied thermal effluents from power generation and production industries). The magnitude, duration and frequency of the temperature change as well as the initial acclimation temperatures of individuals can influence the extent of the consequences of cold shock on fishes. Early research on cold shock focused on documenting mortality events associated with cold shock. However, in recent years, a shift in research has occurred where the focus of cold‐shock studies now involves characterizing the sublethal effects of cold shock in terms of the stress response in fishes. This shift has revealed that cold shock can actually be used as a tool for fisheries science (e.g. to induce polyploidy). The cold‐shock stress response offers opportunities to develop many exciting research questions, yet to date, cold‐shock research has been largely unfocused. Few studies attempt to link laboratory physiology experiments with ecologically relevant field data on behaviour, growth, bioenergetics and fitness. Additional research will allow for the development of more focused and robust management policies and conservation initiatives. This review synthesizes the sublethal physiological and behavioural consequences of cold‐shock stress on fishes, identifies natural and anthropogenic sources of cold shock, discusses the benefits of cold shock to fisheries science and describes mitigation and management efforts. Existing knowledge gaps and opportunities for future cold‐shock research are presented.     

Effect of continuous rearing on courtship acoustics of five braconid parasitoids,candidates for augmentative biological control of <Emphasis Type="Italic">Anastrepha</Emphasis> species

The courtship acoustics of five species of parasitoid wasps (Hymenoptera: Braconidae), potential candidates for augmentative biological control of Anastrepha (Schiner) species (Diptera: Tephritidae), were compared between recently colonized individuals and those continuously reared 70–148 generations. During courtship, males of these parasitoid species fan their wings and produce a series of low amplitude pulses. The first series of 15 or more continuous courtship pulses was used to measure the pulse duration, frequency, and interpulse interval (IPI) from the beginning, middle, and end of the pulse series. Each parameter was compared between young and old colonies, and among species. Several differences in courtship acoustics were detected in colonies that had been continuously reared. The pulse duration at the end of the pulse series was longer in old colonies for Doryctobracon crawfordi (Viereck) (Hymenoptera: Braconidae), but shorter for old colonies of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae). The IPI of the middle pulse was shorter in old colonies of Opius hirtus (Fischer) (Hymenoptera: Braconidae), and was also shorter at the last pulse for old colonies of both Utetes anastrephae (Viereck) (Hymenoptera: Braconidae) and D. longicaudata. The duration of the middle pulse distinguished the three native species, and separated the two introduced species from each other. We discuss our findings in light of their biological and applied implications, particularly those dealing with quality control of mass-reared parasitoids.     

Alternating Perturbation Response of the Water Regulatory System in Arena Leaves

The transpiration response of excised primary Avena leaves was studied when pulse perturbations were given to the water regulatory system. Repeated light pulses given to the leaf caused regularly alternating transpiration responses, i.e. the magnitude alternated regularly between a high and a low value. This effect, denoted alternating pulse response, could be recorded under quite different light pulse conditions but was not found when the pulse interval was too long or too short (longer than about 60 min. shorter than about 15 min). Sodium chloride given to the transpiration stream induced and increased the effect. Alternating pulse response could also be recorded when mannitol pulses were given to the root system of intact plants.     

Electrically induced calcium elevation,activation, and parthenogenetic development of bovine oocytes

The influence of electrical stimulation on the level of intracellular Ca²⁺ in bovine oocytes, as well as activation and extent of parthenogenetic development, was investigated. Mature oocytes were electrically stimulated at 29 hr of maturation, and intracellular Ca²⁺ concentration was determined with the Ca²⁺ indicator fura-2 dextran (fura-2 D). The Ca²⁺ response of oocytes to a given electrical pulse was variable. Oocytes responded with either no Ca²⁺ rise from baseline (≈? 12 nM), a short-duration Ca²⁺ rise (from 12 nM to 300 nM) that returned to baseline within 2 min of the pulse, or a long-duration Ca²⁺ rise (from 12 nM to 1,000–2,000 nM) that never returned to baseline during the 8 min period over which the oocytes were monitored. In these oocytes, Ca²⁺ level returned to baseline when oocytes were removed from 0.30 M mannitol and placed in an ionic medium. Increasing field strength or pulse duration tended to increase the proportion of oocytes displaying a Ca²⁺ rise, and at 1.0 kVcm^?1 for 40 μsec, all oocytes displayed a long-duration Ca²⁺ elevation. Direct transfer of oocytes from culture medium to mannitol also triggered a Ca²⁺ rise. Multiple stimulations, either electrical or by transferring to mannitol, produced multiple Ca²⁺ rises. This mannitol-induced Ca²⁺ rise could be inhibited by first washing the oocytes in medium containing equal parts of 0.30 M mannitol and phosphate buffered saline (PBS). The level of Ca²⁺ stimulation affected activation and development of oocytes. Insufficient, or, conversely, excessive Ca²⁺ stimulation impaired development. Optimum development was obtained with (1) three pulses of 0.2 kVcm^?1 for 20 μsec, each pulse 22 min apart, after direct transfer of oocytes from culture medium to mannitol (22% blastocysts) or (2) three pulses of 1.0 kVcm^?1 for 20 μsec after transfer of oocytes from culture medium to medium containing equal parts mannitol and PBS, then to mannitol (24% blastocysts). This procedure avoided induction of a Ca²⁺ rise prior to the pulse. The results indicate that the level of Ca²⁺ stimulation can be regulated by incubation conditions prior to the pulse and, to some extent, by field strength and pulse duration. The level of electrical stimulation influenced oocyte Ca²⁺ response, activation, and parthenogenetic development. © 1993 Wiley-Liss, Inc.     

Orientation ofFucus egg polarity by electric a. c. and d. c. fields

Summary Zygotes of the marine brown alga,Fucus serratus, have been subjected to the different modes of electric fields. 1) The result of a former study with conductive d.c. fields has been confirmed using electrostatic d.c. fields of 0.5 to 4 V/cm: the zygotes develop the cell polarity axis parallel to the imposed field with the rhizoid pole toward the cathode. 2) The frequency response to both, conductive and electrostatic, a.c. fields represents an optimum curve. The response,i.e. rhizoid formation at either or, in rare cases, both cell poles, peaks at square pulse durations,t _E, of 70 to 120 ms. 3) The same frequency response appears if the pulse number is kept constant at 8s^–1 by variation of the interval between the pulses,t _o. Only fort _oo > 200 ms,i.e. a pulse number of 3s^–1 the response declines markedly. The data support our hypothesis that imposed electric fields induce cell polarityvia differential shift of the membrane potential rather than transcellular current flow. Furthermore, the given dose-response curves strikingly resemble those due to the other morphogenetically active signals: percent response consistently approximates the per cent signal intensity gradient which evokes it.