Microelectrode analysis of light responses in the brain of the cricket (Gryllus domesticus)

Electrical activity in response to light stimuli was recorded from the brain of the cricket (Gryllus domesticus) using stainless steel microelectrodes. Four basic types of elements were observed as follows: (1) units which registered ambient light intensity by frequency of firing as well as responding with transient changes in rate to stepwise increases or decreases in intensity; (2) units which fired at a higher frequency in dark than in light; (3) units which fired continuously at low level in light and responded with a transient high frequency burst to light off; and (4) units which responded with a brief burst to on and off, but tended to be “on-dominant” or “off-dominant.” Also observed were synchronized spikes in mushroom body responding primarily to light off, but also on occasion to light on, and often accompanied by single unit responses. The units registering intensity are probably homologous with units showing similar properties recorded from the visual systems of several other arthropods and usually referred to as “sustaining units.” On-off, off, and dark units are also known from other forms. The mushroom body light responses were similar to synchronized spikes recorded in cockroach mushroom body following antennal stimulation.     

Tropic Responses of Funaria Spores to Red Light

The tropic responses of Funaria hygrometrica spores to continuous illumination with red light (610 to 690 mμ) have been studied over the intensity range from 10^-5 through 10⁺⁶ erg/cm² second, using both plane polarized light and partial illumination with unpolarized light. From the relative frequency of outgrowth origin in different directions, the following is inferred. (1). The germination direction of chloronemal filaments is directly influenced by red light over this whole intensity range, while that of rhizoids tends to be opposite the chloronema. (2) Three photoreceptor systems direct chloronemal primordia: (a) A low intensity system acting from 10^-5 to 10^-0.5 erg/cm² second. It favors their growth from a cell's brightest part(s). Its photoreceptors are disoriented, excited by the electric vector, and probably are dispersed phytochrome molecules. (b) A medium intensity system which acts largely alone only at 10^0.5 erg/cm² second but is influential from 10⁰ to 10⁵ erg/cm² second. It likewise favors growth from a cell's brightest part(s); its receptor molecules are also excited electrically, but they are tangentially oriented. (c) A high intensity system which acts alone from 10⁵ to 10⁶ erg/cm² second and is influential down to 10¹ erg/cm² second. It favors growth of the chloronemas from a cell's darkest part. Its receptors probably are magnetically excited and tangentially oriented. The polarotropic responses of the chloronemas resemble those directing their origins. One new feature is that under intense (10⁶ erg/cm² second) plane polarized and vertically directed light, many soon grow to form tight helices.     

Die Belichtungsreaktionen sessiler Crustaceen(Balanus balanus) als Alternative zu den Schutzreaktionen bodenbewohnender mariner Wirbelloser

Shadow responses, including reactions to both increase (on) and decrease (off) in light intensity have been hitherto described in the adults of various bottom-dwelling marine invertebrates. These reactions as expressed by decrease in activity are assumed to be protective (withdrawal responses, kinetic rigidity after v. Buddenbrock, 1952). By contrast, the free-swimming larvae of these species normally show increase in activity to both increase and decrease in light intensity as expressed by negative or positive photoresponses. In the sessile barnacleBalanus balanus L. reactions to increase in light intensity are demonstrated which, contrary to the withdrawal responses or kinetic rigidity, result in an increase of cirral activity. The shadow responses of the barnacles (off responses) are described as withdrawal responses. The light responses are expressed by two different modes of behaviour: (a) If an active barnacle is stimulated by increase in light intensity, the frequency of cirral activity increases; (b) if an inactive barnacle is stimulated by increase in light intensity, the cirral activity arises a short time later. The light responses observed are interpreted as a metamorphosis of larval swimming activity.

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Gefördert von der Deutschen Forschungsgemeinschaft     

Kinetic models for phycocyanin production by high cell density mixotrophic culture of the microalga Spirulina platensis

Phycocyanin production by high cell density cultivation of Spirulina platensis in batch and fed-batch modes in 3.7-L bioreactors with a programmed stepwise increase in light intensity program was investigated. The results showed that the cell density in fed-batch culture (10.2 g L⁻¹) was 4.29-fold that in batch culture (2.38 g L⁻¹), and the total phycocyanin production in the fed-batch culture (0.795 g L⁻¹) was 3.05-fold that in the batch culture (0.261 g L⁻¹). An unstructured kinetic model to describe the microalga culture system including cell growth, phycocyanin formation, as well as glucose consumption was proposed. The data fitted the models well (r ² > 0.99). Furthermore, based on the kinetic models, the potential effects of light limitation and photoinhibition on cell growth and phycocyanin formation can be examined in depth. The models demonstrated that the optimal light intensity for mixotrophic growth of Spirulina platensis in batch or fed-batch cultures using a 3.7-L bioreactor was 80160 μE m⁻² s⁻¹, and the stepwise increase in light intensity can be replaced by a constant light intensity mode. Received 28 July 1998/ Accepted in revised form 8 October 1998     

Amplification of small signals by voltage-gated sodium channels in drone photoreceptors

Summary Photoreceptor cells of the drone,Apismellifera , have a voltage-gated Na⁺ membrane conductance that can be blocked by tetrodotoxin (TTX) and generates an action potential on abrupt depolarization: an action potential is triggered by the rising phase of a receptor potential evoked by an intense light flash (Autrum and von Zwehl 1964; Baumann 1968). We measured the intracellular voltage response to a small (9%), brief (30 ms) decrease in light intensity from a background, and found that its amplitude was decreased by 1M TTX. The response amplitude was maximal when the background intensity depolarized the cell to –38 mV. With intensities depolarizing the cell membrane to –45 to –33 mV the average response amplitude was decreased by TTX from 1.2mV to 0.5mV. TTX is also known to decrease the voltage noise during steady illumination (Ferraro et al. 1983) but, despite this, the ratio of peak-to-peak signal to noise was, on average, decreased by TTX. The results suggest that drone photoreceptors use voltage-gated Na⁺ channels for graded amplification of responses to small, rapid changes in light intensity.Abbreviations TTX tetrodotoxin - V _i intracellular potential with respect to the bath - V _o extracellular potential - V _m,V _i-V _o approximate transmembrane potential - S amplitude of the voltage response to an 8.9% decrease in light intensity - N voltage noise, usually measured as root mean square voltage deviation as described in Methods     

The frequency response of the action of light on the membrane potential ofNitella

Summary Cells ofNitella flexilis were illuminated with light of sinusoidally modulated intensity at frequencies between 0.1 and 64 cycles/min and the frequency response of the changes of the membrane potential caused by light were measured. A band-pass characteristic was found which is known from similar investigations inAcetabularia. The slope of the frequency response was of the 1/f²-type. This slope and the band-pass characteristic lead to the conclusion that three poles and one zero are comprised in the network function of the action of light on the membrane potential. It is discussed which models regarding the mechanism of the action of light on the membrane potential account for the frequency response measured.

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Zusammenfassung Der Frequenzgang der Lichtwirkung auf das Membranpotential vonNitella.Internodienzellen der AlgeNitella flexilis wurden mit sinusförmig moduliertem Licht im Frequenzbereich von 0,1 bis 64 Schwingungen/min beleuchtet und der Frequenzgang der durch das Licht verursachten Änderungen der Membranspannung gemessen. Es trat eine Bandpaßcharakteristik auf, die jedoch nicht im Deteil untersucht wurde, da sie schon von Messungen anAcetabularia bekannt ist. Das Interesse lag auf der hochfrequenten Flanke. Es wurde gefunden, daß die Asymptote mit 1/f² abfällt. Aus der Bandpaßcharakteristik und der Flankensteilheit ist zu entnehmen, daß die Netzwerkfunktion der Lichtwirkung auf das Membranpotential im untersuchten Frequenzbereich 3 Polstellen und eine Nullstelle enthält. Es wird diskutiert, welche Schlüsse daraus über den Mechanismus der Lichtwirkung zu ziehen sind.

     

Light-Induced Body Movement of Euglena gracilis Coupled to Flagellar Photophobic Responses by Mechanical Stimulation*†

SYNOPSIS. In low viscosity media, Euglena gracilis strain Z responds to a sudden change in light intensity by a cessation of forward movement, followed by a reorientation of the locomotor flagellum which results in turning of the cell around the lateral axis (photophobic response). At a viscosity interface between low [～ 1 cP (centipoise)] and high (4000 cP) media, the cells exhibit avoidance responses or become immobilized in the higher viscosity medium. Upon changing the light intensity, free swimming cells have photophobic responses, while immobilized ones undergo body contractions. For cells immersed in media of varying viscosity, the delay between light stimulation and body contraction (transduction time) is shortest at high viscosities. From 500 to 2000 cP, where the cells are capable of both movement and light-induced body contractions, there is a logarithmic dependence of the transduction time on the viscosity. The transduction time does not vary appreciably with the intensity of the primary light stimulus within a range of 0.14-1.13 kW/m².     

Mathematical modelling of the light response curve of photoinhibition of Photosystem II

The light response curves of the acceptor and donor side mechanisms of photoinhibition of Photosystem II were calculated, using Arabidopsis as a model organism. Acceptor-side photoinhibition was modelled as double reduction of Q_A, noting that non-photochemical quenching has the same effect on the quantum yield of Q_A double reduction in closed PSII centres as it has on the quantum yield of electron transport in open centres. The light response curve of acceptor-side photoinhibition in Arabidopsis shows very low efficiency under low intensity light and a relatively constant quantum yield above light saturation of photosynthesis. To calculate the light response curve of donor-side photoinhibition, we built a model describing the concentration of the oxidized primary donor P₆₈₀⁺ during steady-state photosynthesis. The model is based on literature values of rate constants of electron transfer reactions of PSII, and it was fitted with fluorescence parameters measured in the steady state. The modelling analysis showed that the quantum yield of donor-side photoinhibition peaks under moderate light. The deviation of the acceptor and donor side mechanisms from the direct proportionality between photoinhibition and photon flux density suggests that these mechanisms cannot solely account for photoinhibition in vivo, but contribution of a reaction whose quantum yield is independent of light intensity is needed. Furthermore, a simple kinetic calculation suggests that the acceptor-side mechanism may not explain singlet oxygen production by photoinhibited leaves. The theoretical framework described here can be used to estimate the yields of different photoinhibition mechanisms under different wavelengths or light intensities.     

The importance of grazing intensity and frequency for physiological responses of the tropical seagrass Thalassia hemprichii

Seagrass grazing is an intrinsic disturbance in primarily tropical and subtropical areas. While there is a general parabolic response in seagrass growth to grazing intensity, there is less knowledge on the role of grazing frequency, as well as potential interactions between grazing intensity and frequency. This study experimentally investigated physiological responses in Thalassia hemprichii to simulated (leaf cutting) grazing regimes with different intensities (25% vs. 75%) and frequencies (1 times vs. 3 times) over 35 days in Chwaka Bay (Zanzibar, Tanzania). The results showed that the two high-intensity treatments (75% removal) had 37–41% lower growth rate than the low-intensity/low-frequency treatment, and rhizome sugar and starch content were both affected in a similar way. A 36% lower starch content in the simulated low-intensity/high-frequency regime (25% × 3) compared to the one of low-intensity/low-frequency (25% × 1) also shows an interaction between grazing intensity and frequency. This suggests that high-intensity (and to some extent frequency) grazing regimes, in comparison to low-intensity regimes, could negatively affect T. hemprichii growth, energy reserves, and thereby the ability to deal with additional stress like light limitation or grazing.     

Low temperature and high light dependent dynamic photoprotective strategies in Arabidopsis thaliana

Arabidopsis thaliana has been recognized as a chilling tolerant species based on analysis of resistance to low temperature stress, however, the mechanisms involved in this tolerance are not yet clarified. The low temperature-induced effects are exacerbated when plants are exposed to low temperatures in the presence of high light irradiance but the experimental data on the impact of light intensity during cold stress and its influence during recovery from stress are rather limited. The main objective of this study was to re-examine the photosynthetic responses of A. thaliana plants to short term (6 days) low temperature stress (12/10°C) under optimal (150 μmol m⁻² s⁻¹) and high light (500 μmol m⁻² s⁻¹) intensity and the subsequent recovery from the stress. Simultaneous measurements of the in vivo and in vitro functional performance of both photosystem II (PSII) and photosystem I (PSI), as well as, net photosynthesis, low temperature (77 K) chlorophyll fluorescence and immunoblot analysis of the relative abundance of PSII and PSI reaction center proteins were used to evaluate the role of light in the development of possible protective mechanisms during low temperature stress and the consequent recovery from exposure to low temperature and different light intensities. The results presented clearly suggest that Arabidopsis plants can employ a number of highly dynamic photoprotective strategies depending on the light intensity. These strategies include one based on LHCII quenching and two other quenching mechanisms localized within the PSII and PSI reaction centers, which are all expressed to different extent depending on the severity of the photoinhibitory treatments under low temperature stress conditions.     

The effects of temperature on signalling in ocellar neurons of the desert locust, <Emphasis Type="Italic">Schistocerca gregaria</Emphasis>

In Schistocerca gregaria ocellar pathways, large second-order L-neurons use graded potentials to communicate signals from the ocellar retina to third-order neurons in the protocerebrum. A third-order neuron, DNI, converts graded potentials into axonal spikes that have been shown in experiments at room temperature to be sparse and precisely timed. I investigated effects of temperature changes that a locust normally experiences on these signals. With increased temperature, response latency decreases and frequency responses of the neurons increase. Both the graded potential responses in the two types of neuron and the spikes in DNI report greater detail about a fluctuating light stimulus. Over a rise from 22 to 35°C the power spectrum of the L-neuron response encompasses higher frequencies and its information capacity increases from about 600 to 1,700 bits/s. DNI generates spikes more often during a repeated stimulus but at all temperatures it reports rapid decreases in light rather than providing a continual measure of light intensity. Information rate carried by spike trains increases from about 50 to 185 bits/s. At warmer temperatures, increased performance by ocellar interneurons may contribute to improved aerobatic performance by delivering spikes earlier and in response to smaller, faster light stimuli.     

Effect of light on the formation of atypical fruiting structures inGanoderma lucidum

Ganoderma lucidum develops atypical fruiting structures (AFSs) with non-basidiocarpous basidiospores during the incubation under light on nutrient agar media. To examine the light quality effective in inducing AFSs, 17 isolates ofG. lucidum were incubated on agar media under light from different colored fluorescent lamps. Of the 17 isolates, 13 isolates produced AFSs and basidiospores under fluorescent lamps. Nine isolates formed AFSs in a broad light region from P-B (pure blue) to P-R (pure red) lamps. The remaining 4 isolates produced AFSs under different colored fluorescent lamps. No isolates formed AFSs in the dark or under BLB (black light blue) illumination. The mycelial growth was inhibited by light illumination, especially BLB light. Although the AFSs were induced at a very low light intensity such as 0.5µmol m^–2s^–1, the optimum light intensity for the AFS formation varied depending on the kind of fluorescent lamp and the isolate. The AFS formation inG. lucidum isolates was also tested under monochromatic light produced by the combination of interference filters and colored glass filters.G. lucidum isolates were separable into various types in the responses of AFS formation to monochromatic light, indicating thatG. lucidum is heterogeneous in its photo-response with regard to AFS formation.     

Metabolic flux analysis of a poly-β-hydroxybutyrate producing cyanobacterium,Synechococcus sp. MA19, grown under photoautotrophic conditions

To understand the utilization property of light energy,Synechococcus sp. MA19, a poly-β-hydroxybutyrate (PHB) producer, was cultivated at the different incident light intensities of 15.3, 50.0 and 78.2 W/m² using media with and without phosphate. From the results of metabolic flux analysis, it was found that the cell yield based on ATP synthesis was estimated as 3.5×10⁻³ kg-biomass/mol-ATP in these cultures. Under the examined conditions, there were no significant differences in the efficiency of light energy conversion to chemical energies estimated as ATP synthesis and reducing potential (NADH+NADPH) formation whether the PHB synthesis took place or not. The energy converted from light to ATP was kept relatively high around the energy absorbed by the cells of 2.5–3.0×10⁶ J h⁻¹ kg⁻¹, whereas the energy of reducing potential was hardly changed in the examined range of the energy absorbed by the cells.     

Effects of rare earth elements on growth rate,lipids, fatty acids and pigments in microalgae

The extensive exploitation of rare earth elements (REEs), particularly in electronic technologies and agriculture has concomitantly raised the environmental load. Their resulting effects on primary producers such as microalgae are, however, poorly understood. We have studied these effects on two microalgae of biotechnological interest. The yellow‐green alga Trachydiscus minutus (Eustigmatophyceae, Ochrophyta), and the green alga Parachlorella kessleri (Trebouxiophyceae, Chlorophyta) were cultivated in mineral medium supplemented with 10 μmol L^?1 chlorides of REEs: cerium, gadolinium, lanthanum, lutetium, praseodymium, scandium, and with monazite, which is a mineral rich in those elements. We observed growth rates at different mean light intensities (20, 50, 150 and 300 μmol m^?2 s^?1). The high growth rate of P. kessleri was not affected by the presence of any lanthanide, and decreased proportionally with light intensity (from 0.2 to 0.04 doublings per hour). In contrast, the growth rate of T. minutus was about three times lower compared with P. kessleri, with an optimum at 50 μmol m^?2 s^?1 and decreased at higher or lower light intensities. In the presence of Ce³⁺, La³⁺ and Sc³⁺, the growth rate markedly increased to a value that corresponded to the growth rate in P. kessleri at the same light intensity. The composition and content of pigments and lipids were followed at the optimum light intensity for both species. The lipid content (percentage of dry weight) varied only slightly in the presence of individual rare earths. There was, however, an increase in saturated fatty acids at the expense of polyunsaturated fatty acids. The effect of REEs on pigments was variable: the presence of Ce³⁺, Gd³⁺, La³⁺ and Sc³⁺ caused an increase in the concentrations of major pigments such as lutein, violaxanthin, β‐carotene or chlorophylls, while Pr³⁺ and Lu³⁺ reduced them.     

PHOTOSYNTHESIS IN THE SNOW: THE ALGA CHLAMYDOMONAS NIVALIS (CHLOROPHYCEAE)1

Red blooms of snow algae consisting almost exclusively of large spherical red cells of Chlamydomonas nivalis (Bauer) Wille are widespread during the summer in the Beartooth Mountains in Montana and Wyoming. Field studies designed to examine the effects of temperature, light, and water potential on algal activity were performed with natural populations using photosynthetic ¹⁴C-HCO₃- or ¹⁴CO₂ incorporation as a measure of activity. The algae photo-synthesized optimally at 5.4 × 10⁴ lx, but were not inhibited by increased light intensity up to 8.6 × 10⁴ lx, the maximum observed in the field. Photosynthesis was sensitive to a reduction in water potential, and since low water potentials develop in snow at temperatures below 0 C, it is unlikely that significant algal activity occurs at the sub-0 temperatures which occur throughout winter. Photosynthesis was much lower following melting of the snow, but this was probably due to decreased diffusion of CO₂. The optimal temperatures varied considerably among the different algal populations. Most samples photo-synthesized optimally at 10 or 20 C but retained substantial activity at temperatures as low as 0 or -3 C. Exceptional samples photosynthesized optimally at 0 or -3 C. It is proposed that the varied temperature responses reflect the presence of different temperature strains. Taken together, the data suggest that development of the snow algae can occur only during the summer months.     

Growth of Spirulina platensis enhanced under intermittent illumination

The growth characteristics of microalgae under different light conditions (continuous or intermittent) are essential information for photobioreactor design and operation. In this study, we constructed a thin-layer (10 mm) flat plate photobioreactor device with a light/dark (L/D) alternation system to investigate the growth of Spirulina platensis under two different light regimes: (1) continuous illumination in a wide range of light intensities (1.00-77.16 mW cm⁻²); (2) intermittent illumination in medium frequency (0.01-20 Hz). Specific growth rate and light efficiency based on biomass production were determined for each round of experiment. Four regions (light limited region, intermediate region, light saturated region and light inhibition region) were recognized according to the results under continuous illumination. Under intermittent illumination, when L/D frequency increased from 0.01 Hz to 20 Hz, specific growth rate and light efficiency were enhanced. However, the enhancement was different, depending on the applied light intensity and light fraction. The higher the light intensity, the greater the enhancement would be when L/D frequency increased from 0.01 Hz to 20 Hz; and the higher the light intensity, the lower the light fractions is needed to maintain light efficiency as high as that under continuous illumination in light limited region.     

Effect of growth conditions on carboxylating enzymes of Zea mays plants

Phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and ribulose-1,5-bisphospate (RuBP) carboxylase (EC 4.1.1.39) activities in leaves of different maize hybrids grown under field conditions (high light intensity) and in a growth chamber (low light intensity) were determined. Light intensity and leaf age affected PEP carboxylase activity, whereas RuBP carboxylase was affected by leaf age only at low light intensity. PEP carboxylase/RuBP carboxylase activity ratio decreased according to light intensity and leaf age. Results demonstrate that Zea mays grown under field conditions is a typical C₄ species in all leaves independently from their position on the stem, whereas it may be a C₃ plant when it is grown in a growth chamber at low light intensityAbbreviations PEP phosphoenolpyruvate - RuBP ribulose-1,5-bisphosphate     

Sinusoidal and delta function responses of visual cells of the Limulus eye

Dynamic responses of visual cells of the Limulus eye to stimuli of sinusoids and narrow pulses of light superimposed on a nonzero mean level have been obtained. Amplitudes and phase angles of averaged sinusoidal generator potential are plotted with respect to frequency of intensity modulation for different mean levels of light adaptation. At frequencies above 10 CPS, generator potential amplitudes decrease sharply and phase lag angle increases. At frequencies below 1 CPS, amplitude decreases. A maximum of amplitude in the region of 1 to 2 CPS is apparent with increased mean intensity. The generator potential responses are compared with those of differential equation models. Variation of gain with mean intensity for incremental stimuli is consistent with logarithmic sensitivity of the photoreceptor. Frequency response of the photoreceptor derived from narrow pulses of light predicts the frequency response obtained with sinusoidal stimuli, and the photoreceptor is linear for small signals in the light-adapted state.     

DIFFERENTIAL EFFECTS OF PHOTOPHASE IRRADIANCE ON METABOLIC AND URINARY STRESS HORMONE CONCENTRATIONS IN BLIND AND SIGHTED RODENTS

The effects of different photophase irradiance levels on the daily rhythms of energy expenditure (DEE, calculated from oxygen consumption, VO₂) and urinary metabolites of stress hormones in sighted (Microtus socialis) and blind (Spalax ehrenbergi) rodents were compared. Five groups of each species were exposed to different irradiance levels (73, 147, 293, 366, and 498 μW/cm²) under short photoperiod (8L:16D) condition with constant ambient temperature 25?±?2°C for 21 days before assessments. As light intensity increased from 73 μW/cm², both species reduced DEE, especially among M. socialis. Cosinor analysis revealed significant ultradian rhythms in VO₂ of M. socialis with period length being inversely related to irradiance level. Conversely, in S. ehrenbergi, robust 24 h VO₂ rhythms were detected at all irradiances. In M. socialis, significant 24 h rhythms in urinary output of adrenaline were detected only at 293 μW/cm², whereas for cortisol, unambiguous rhythms were detected at 73 and 147 μW/cm². Distinct adrenaline daily rhythms of S. ehrenbergi were observed at 73 and 293 μW/cm², whereas this species exhibited significant rhythms in cortisol at 147 and 293 μW/cm². Changes in photophase irradiance levels affected stress hormone concentrations in a dose-dependent manner. There were significant negative and positive correlations of M. socialis and S. ehrenbergi stress hormones, respectively, with increasing irradiance. Our results indicate photophase light intensity is another environmental factor that can significantly affect entrainment of mammalian daily rhythms. Both low and high irradiance conditions can trigger stress responses, depending on the species' natural habitat. (Author correspondence: zubidat3@013.net.il)