The visual response from the compound eye of Oncopeltus fasciatus: Effects of temperature and sensory adaptation

The effects of temperature (10–30°C) on response latency and amplitude were determined in the dark- and light-adapted compound eye of the milkweed bug, Oncopeltus fasciatus. Response amplitude was an inverse function of temperature under dark-adapted conditions, but was nearly independent of temperature when superimposed on a background field. Response amplitude to a test stimulus (S₂) was maximum at 15–20°C when presented 10 sec after an adapting stimulus (S₁). The optimum temperature (10°C or less) for maximum response amplitude from dark-adapted eyes was far below the temperature at which the animals were grown (19–25°C) and lower than previously reported for insect compound eyes. These results are discussed in terms of the adaptive implications for diurnal, terrestrial ectotherms.Response latency from dark-adapted eyes was an inverse exponential function of temperature with an apparent activation energy of 13·6 kcal mole⁻¹. No change in activation energy could be attributed to light adaptation.Reductions of S₂ response latency and amplitude, during the adaptation régimes employed in this study, were different functions of temperature. Adapting stimuli, which were equally effective at reducing S₂ latency, had different effects on S₂ response amplitude. Recovery of S₂ response latency and amplitude were not related at either 20 or 10°C. Therefore, changes in S₂ response latency as a function of adaptation appeared independent of changes in S₂ response amplitude.     

Current- and Voltage-Clamped Studies on Myxicola Giant Axons : Effect of tetrodotoxin

A new dissection procedure for preparing Myxicola giant axons for observation under voltage clamp is described. Preparation time is generally 40–45 min. 65–70% of the preparations attempted may be brought through the entire procedure, including insertion of the long internal electrode, and support an initial action potential amplitude of 100 mv or greater. Mean values for axon diameter, resting membrane potential, action potential amplitude, maximum peak inward transient current, and resting membrane resistance are 560 µ, —66.5 mv, 112 mv, 0.87 ma/cm² and 1.22 KΩ cm ² respectively. Cut branches do not seem to be a problem in this preparation. Behavior under voltage clamp is reasonably stable over several hours. Reductions in maximum inward transient current of 10% and in steady-state current of 5–10% are expected in the absence of any particular treatment. Tetrodotoxin blocks the action potential and both the inward and outward transient current, but has no effect on either the resting membrane potential or the steady-state current. This selective action of tetrodotoxin on the transient current is taken as an indication that this current component is probably carried by Na.     

CO2-induced changes in the critical fusion frequency of the fly, Sarcophaga bullata

The critical fusion frequency (CFF) for the ERG of a dipteran compound eye was measured under atmospheric conditions of low and high pCO₂. It was found that following an increase in CO₂ concentration to 80%, the CFF decreased from a mean value of 283 to 108 Hz within 60 sec and remained at this lower figure as long as the CO₂ concentration was high. Recovery to control values was observed upon removal of the CO₂. This result is compared with changes in the waveform of the single-flash ERG resulting from an identical CO₂ increase. The low CFF is associated with a single, monophasis negative wave isolated by CO₂ from the normally complex ERG. This negative wave is identified as the receptor cell component.It is suggested that two mechanisms are responsible for the frequency-dependent response characteristics of the dipteran eye. One resides at the level of the receptor cells and is responsible for the CFF recorded at 80% CO₂, while the second involves ganglionic feedback upon the receptor cells and is necessary for the maintenance of the higher CFF recorded under normal atmospheric conditions.     

The influence of extracellular calcium on the response of fly photoreceptors

Summary This paper presents a systematic investigation of the influence of the extracellular concentration of calcium ([Ca²⁺]₀) on the electrophysiological response of the fly's photoreceptors (R1–R6) to light. The hemisected heads of flies were perfused with a standard medium containing 10^–4 mol/1 CaCl₂ and in this medium the intracellularly recorded response of the cell was virtually identical to the normal response obtained in vivo. All the effects of changing the [Ca²⁺]₀ could be reversed within 5 min by perfusing the eye with the standard medium.Changing the [Ca²⁺]₀ did not influence the frequency with which quantum bumps occurred or the resting membrane potential, but did lead to changes in the latency and amplitude of the response and, most significantly, in the repolarization time (t _r). The plot oft _r versus the [Ca²⁺]₀ revealed that the value oft _r changes significantly in two distinct regions representing a [Ca²⁺]₀ of between 2×10^–8 and 10^–7 mol/l and 10^–4 and 10^–2 mol/l, respectively. Lowering the [Ca²⁺]₀ did not affect the amplitude of the response but did lead to a drastic increase int _r which was accompanied by an increase in latency and peak time. Raising the [Ca²⁺]₀ led to a reduction in the duration and amplitude of the response. The latter effect is evidence of reduction in the sensitivity of the photoreceptor cell which is dependent on the [Ca²⁺]₀.It is postulated that two types of binding site for calcium exist, high affinity binding sites (HABS) and low affinity binding sites (LABS), which modulate the functioning of ion channels in the cell membrane that are activated as a consequence of light absorption. The results indicate that the sensitivity of the photoreceptor cell is determined by the degree of saturation of the LABS.     

Ocean acidification and responses to predators: can sensory redundancy reduce the apparent impacts of elevated CO2 on fish?

Carbon dioxide (CO₂) levels in the atmosphere and surface ocean are rising at an unprecedented rate due to sustained and accelerating anthropogenic CO₂ emissions. Previous studies have documented that exposure to elevated CO₂ causes impaired antipredator behavior by coral reef fish in response to chemical cues associated with predation. However, whether ocean acidification will impair visual recognition of common predators is currently unknown. This study examined whether sensory compensation in the presence of multiple sensory cues could reduce the impacts of ocean acidification on antipredator responses. When exposed to seawater enriched with levels of CO₂ predicted for the end of this century (880 μatm CO₂), prey fish completely lost their response to conspecific alarm cues. While the visual response to a predator was also affected by high CO_2, it was not entirely lost. Fish exposed to elevated CO_2, spent less time in shelter than current‐day controls and did not exhibit antipredator signaling behavior (bobbing) when multiple predator cues were present. They did, however, reduce feeding rate and activity levels to the same level as controls. The results suggest that the response of fish to visual cues may partially compensate for the lack of response to chemical cues. Fish subjected to elevated CO₂ levels_, and exposed to chemical and visual predation cues simultaneously, responded with the same intensity as controls exposed to visual cues alone. However, these responses were still less than control fish simultaneously exposed to chemical and visual predation cues. Consequently, visual cues improve antipredator behavior of CO₂ exposed fish, but do not fully compensate for the loss of response to chemical cues. The reduced ability to correctly respond to a predator will have ramifications for survival in encounters with predators in the field, which could have repercussions for population replenishment in acidified oceans.     

Behavioral evidence of a latency code for stimulus intensity in mormyrid electric fish

Mormryid electric fish (Gnathonemus petersii) respond to novel stimuli with an increase in the rate of the electric organ discharge (EOD). These novelty responses were used to measure the fish's ability to detect small changes in the amplitude and latency of an electrosensory stimulus. Responses were evoked in curarized fish in which the EOD was blocked but in which the EOD motor command continued to be emitted. An artificial EOD was provided to the fish at latencies of 2.4 to 14.4 ms following the EOD motor command.Novelty responses were evoked in response to transient changes in artificial EOD amplitude as small as 1% of baseline amplitude, and in latency as small as 0.1 ms. Changes in latency were effective only at baseline delays of less than 12.4 ms.The sensitivity to small changes in latency supports the hypothesis that latency is used as a code for stimulus intensity in the active electrolocation system of mormyrid fish. The results also indicate that a corollary discharge signal associated with the EOD motor command is used to measure latency.Abbreviations EOD electric organ discharge - ELL electrosensory lateral line lobe - epsp excitatory post synaptic potential     

Regulation of Transpiration in Avena. Responses to White Light Steps

The transient responses in transpiration rate of the primary leaf of 8-days-old oat plants were studied when step changes in the white light irradiance were administered to the plants. A light or dark step was achieved by an instant increase or decrease, respectively, of the irradiance on the leaf surface. Usually the light step responses consisted of one rapid response (rise time 1–2 min) and one slow response (rise time 5–10 min). The dark step response had a fall time of about 10 min. At a high irradiance level and in CO₂-free air the slow response disappeared. This could mean that the slow response is CO₂-controlled. The rapid response was still present under these conditions and is therefore probably caused by other processes than the slow response. In long time experiments several cycles of a circadian rhythm (period 26–28 h) could be followed in the light step responses. Thus the rapid response was small at that time of the day when the slow response was most pronounced and vice versa. The endogenous nature of the rhythm was established in phase-shift experiments. It is concluded that experiments on stomatal dynamics must take circadian variations into account.     

Species-specific responses of plant communities to altered carbon and nutrient availability

In a field microcosm experiment, species‐specific responses of aboveground biomass of two California annual grassland communities to elevated CO₂ and nutrient availability were investigated. One community grows on shallow, nutrient‐poor serpentine‐derived soil whereas the other occurs on deeper, modestly fertile sandstone/greenstone‐derived substrate. In most species, CO₂ effects did not appear until late in the growing season, probably because the elevated CO₂ increased water‐use‐efficiency easing, the onset of the summer drought. Responses of aboveground biomass to elevated CO₂ differed depending on nutrient availability. Similarly, biomass responses to nutrient treatments differed depending on the CO₂ status. For the majority of the species, production increased most under elevated CO₂ with added nutrients (N,P,K, and micro nutrients). Some species were losers under conditions that increased overall community production, including Bromus hordeaceus in the serpentine community (negative biomass response under elevated CO₂) and Lotus wrangelianus in both communities (negative biomass response with added nitrogen). Treatment and competitive effects on species‐specific biomass varied in both magnitude and direction, especially in the serpentine community, significantly affecting community structure. Individual resource environments are likely to be affected by neighbouring plants, and these competitive interactions complicate predictions of species' responses to elevated CO₂.     

Nonstomatal inhibition of photosynthesis in sunflower at low leaf water potentials and high light intensities

The inhibition of photosynthesis at low leaf water potentials was studied in soil-grown sunflower to determine the degree to which photosynthesis under high light was affected by stomatal and nonstomatal factors. Below leaf water potentials of −11 to −12 bars, rates of photosynthesis at high light intensities were insensitive to external concentrations of CO₂ between 200 and 400 microliters per liter. Photosynthesis also was largely insensitive to leaf temperature between 10 and 30 C. Changes in CO₂ concentration and temperature had negligible effect on leaf diffusive resistance. The lack of CO₂ and temperature response for both photosynthesis and leaf diffuse resistance indicates that rates of photosynthesis were not limited by either CO₂ diffusion or a photosynthetic enzyme. It was concluded that photosynthesis under high light was probably limited by reduced photochemical activity of the leaves at water potentials below −11 to −12 bars.     

Relationship between the Level of Adenine Nucleotides and the Carboxylation Activity of Illuminated Isolated Spinach Chloroplasts: A Study with Antimycin A

The changes in the levels of intact spinach (Spinacia oleracea L.) chloroplast adenine nucleotides during the time course of light-dependent CO₂ fixation were determined with respect to the effect of antimycin A. This study demonstrated that antimycin A lowered the rate of ATP formation during the induction period of carboxylation. While the steady state levels of ATP and the energy-charge value also decreased in the presence of antimycin, the concomitant increase of the CO₂ fixation activities insured higher ATP turnover rates. Changes in the labeling of CO₂ fixation products during the lag phase suggested a stepwise activation of the Calvin cycle, with fructose 1,6-diphosphate, and ribulose 5-phosphate kinase being activated before ribulose 1,5-diphosphate carboxylase. The possible mechanisms of the enhancement of CO₂ fixation activity by antimycin A in relation to its action on photophosphorylation during the lag phase are discussed.     

Involvement of respiratory processes in the transient knockout of net CO2 uptake in Mimosa pudica upon heat stimulation

Leaf photosynthesis of the sensitive plant Mimosa pudica displays a transient knockout in response to electrical signals induced by heat stimulation. This study aims at clarifying the underlying mechanisms, in particular, the involvement of respiration. To this end, leaf gas exchange and light reactions of photosynthesis were assessed under atmospheric conditions largely eliminating photorespiration by either elevated atmospheric CO₂ or lowered O₂ concentration (i.e. 2000 μmol mol^?1 or 1%, respectively). In addition, leaf gas exchange was studied in the absence of light. Under darkness, heat stimulation caused a transient increase of respiratory CO₂ release simultaneously with stomatal opening, hence reflecting direct involvement of respiratory stimulation in the drop of the net CO₂ uptake rate. However, persistence of the transient decline in net CO₂ uptake rate under illumination and elevated CO₂ or 1% O₂ makes it unlikely that photorespiration is the metabolic origin of the respiratory CO₂ release. In conclusion, the transient knockout of net CO₂ uptake is at least partially attributed to an increased CO₂ release through mitochondrial respiration as stimulated by electrical signals. Putative CO₂ limitation of Rubisco due to decreased activity of carbonic anhydrase was ruled out as the photosynthesis effect was not prevented by elevated CO₂.     

The effect of elevated CO2 on diel leaf growth cycle, leaf carbohydrate content and canopy growth performance of Populus deltoides

Image sequence processing methods were applied to study the effect of elevated CO₂ on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO₂ for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO₂. Increased final leaf area at elevated CO₂ was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30–40% day^?1 was increased by a factor of two in the elevated CO₂ treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO₂ as the growing season progressed. During this minimum, leaves grown under elevated CO₂ decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO₂, suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO₂. Net CO₂ exchange and starch concentration of growing leaves was higher in elevated CO₂. The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO₂ is discussed.     

Sensory and cognitive components of the CO2 laser evoked cerebral potential

We recorded CO₂ laser evoked cerebral potentials in 6 healthy subjects using both a standard technique and an oddball paradigm. In the standard technique stimuli were aimed at the dorsum of the left hand with the subject passive; in the oddball paradigm, target infrequent stimuli (P = 0.15) were directed to one side of the dorsum of the left hand and the subject was instructed to count their occurrence, the frequent stimulus being delivered to the other side of the hand. In both standard and oddball frequent recordings, CO₂ laser evoked potentials were a well-formed negative-positive complex with a peak latency and amplitude around 305 msec (to positivity) and 32 μV respectively. However, in the oddball target task a later potential was also recorded, with a mean latency and amplitude of 621 msec and 24 μV respectively which we believe to be a laser oddball potential. These results demonstrate that the CO₂ potential is not altered by manipulations of attention to any significant extent and suggests that it is therefore closely related to the primary sensory input. They also provide further evidence of the non-specificity of the oddball potential across sensory modalities.     

Can CO2 enrichment modify the effect of water and high light stress on biomass allocation and relative growth rate of cork oak seedlings?

To test whether the impact of an enriched-CO₂ environment on the growth and biomass allocation of first-season Quercus suber L. seedlings can modify the drought response under shade or sun conditions, seedlings were grown in pots at two CO₂ concentrations × two watering regimes × two irradiances. Compared to CO₂, light and water treatment had greater effects on all morphological traits measured (height, stem diameter, number of leaves, leaf area, biomass fractions). Cork oak showed particularly large increases in biomass in response to elevated CO₂ under low-watered (W−) and high-illuminated conditions (L+). Allocation shifted from shoot to root under increasing irradiance (L+), but was not affected by CO₂. Changes in allocation related to water limitation were only modest, and changed over time. Relative growth rate (RGR) and net assimilation rate (NAR) were significantly greatest in the L+/W+ treatment for both CO₂ concentrations. Changes in RGR were mainly due to NAR. Growth responses to increased light, water or CO₂ were strongest with light, medium with water availability and smallest for CO₂, in terms of RGR. The rise in NAR for light and water treatments was counterbalanced by a decrease in SLA (specific leaf area) and LMF (leaf mass fraction). Results suggest that elevated CO₂ caused cork oak seedlings to improve their performance in dry and high light environments to a greater extent than in well-irrigated and low light ones, thus ameliorating the effects of soil water stress and high light loads on growth.     

The Nature of the Retinal Action Potential, and the Spectral Sensitivities of Ultraviolet and Green Receptor Systems of the Compound Eye of the Worker Honeybee

1. The retinal action potential consists principally of a sustained negative wave which persists for as long as the stimulus. Transitory negative on-effects and off-effects may also be present, particularly at long wave lengths (green, yellow, and red) and in the light-adapted eye. 2. Only the maintained component of the potential can be elicited under CO₂ anesthesia. The transient components are reversibly eliminated from the response at about the same time as the background noise of nerve and muscle spikes. It is suggested that the sustained component arises from the receptor cells, and the other components from second and higher order neurons. 3. The compound eye does not contain a homogeneous population of receptors. A green receptor system (maximum sensitivity at about 535 mµ) determines the response of the dark-adapted eye throughout most of the spectrum; during adaptation to yellow light, however, an ultraviolet receptor system is revealed, with maximum sensitivity at about 345 mµ. The anatomical bases of these receptor systems are unknown; however, they include both retinula cells and neurons in the optic ganglion. 4. There is no change in spectral sensitivity (Purkinje shift) in the first three logarithmic units above the threshold of the retinal action potential. 5. The relatively great effectiveness of near ultraviolet light in stimulating the positive phototaxis of the bee does not depend on excitation of the ultraviolet receptor of the ocellus.     

Analysis of the middle latency evoked potentials to angular acceleration impulses in man

The middle latency vestibular evoked potential (ML-VsEP) recorded with scalp electrodes in man in response to impulses of angular acceleration is dominated by a forehead positive peak at about 15 ms and a negative peak at about 20 ms; the peak amplitude of this component is about 30 μV. This is followed by slower, smaller amplitude activity. The latency of this initial peak is similar to the latency of the vestibulo-ocular reflex (VOR) in monkeys. The present study was undertaken to elucidate the possible relation between the ML-VsEPs and VOR. This included recordings from forehead-mastoid electrodes (sites used to record VsEP) and other scalp electrodes and the recording of potentials due to eye movement: the electro-oculogram. Direct recording of eye movements was also conducted using an infra-red reflection device in those experiments in which the head was not moved. The recordings were conducted in man during vestibular stimulation eliciting VsEPs, during voluntary eye movements and during caloric and optokinetic stimulation. These experiments indicated that the 15–20 ms component of the ML-VsEP was not due to movements of the eye (corneoretinal dipole). The large amplitude 15–20 ms component of the ML-VsEP was similar in general magnitude, waveform, polarity, duration and rise time to the highly synchronous pre-saccadic spike (neural and/or myogenic) which precedes nystagnys and voluntary saccades. It therefore probably represents vestibular-initiated electrical activity in motor units of the extra-ocular muscles which then produce anti-compensatory saccades.     

Cortical representation of nonclassical parts of the visual system

Cortical evoked potentials and extracellular evoked neuronal activity have been investigated in unanesthetized d-curarine immobilized rats during stimulation of the superior colliculi. The focus of responses was found in the lateral part of the visual neocortex (area 18a according to Krieg [5]). The evoked potential includes a negative and subsequent positive waves, its latency being equal to 7.9 +/- 2.8 msec. With deepening the electrode the amplitude of the response decreases, although its polarity remains unchanged. The neuronal activity is of phasic character. During simultaneous record of the evoked potentials and neuronal activity, temporal correlation between impulse activity and the ascending part of the main negative wave of the EP is observed. The data obtained indicate imcomplete overlapping of the retino-geniculo-cortical and retino-tecto-thalamo-cortical channels in the visual system of rats.     

Emergent climate and CO2 sensitivities of net primary productivity in ecosystem models do not agree with empirical data in temperate forests of eastern North America

Ecosystem models show divergent responses of the terrestrial carbon cycle to global change over the next century. Individual model evaluation and multimodel comparisons with data have largely focused on individual processes at subannual to decadal scales. Thus far, data‐based evaluations of emergent ecosystem responses to climate and CO₂ at multidecadal and centennial timescales have been rare. We compared the sensitivity of net primary productivity (NPP) to temperature, precipitation, and CO₂ in ten ecosystem models with the sensitivities found in tree‐ring reconstructions of NPP and raw ring‐width series at six temperate forest sites. These model‐data comparisons were evaluated at three temporal extents to determine whether the rapid, directional changes in temperature and CO₂ in the recent past skew our observed responses to multiple drivers of change. All models tested here were more sensitive to low growing season precipitation than tree‐ring NPP and ring widths in the past 30 years, although some model precipitation responses were more consistent with tree rings when evaluated over a full century. Similarly, all models had negative or no response to warm‐growing season temperatures, while tree‐ring data showed consistently positive effects of temperature. Although precipitation responses were least consistent among models, differences among models to CO₂ drive divergence and ensemble uncertainty in relative change in NPP over the past century. Changes in forest composition within models had no effect on climate or CO₂ sensitivity. Fire in model simulations reduced model sensitivity to climate and CO₂, but only over the course of multiple centuries. Formal evaluation of emergent model behavior at multidecadal and multicentennial timescales is essential to reconciling model projections with observed ecosystem responses to past climate change. Future evaluation should focus on improved representation of disturbance and biomass change as well as the feedbacks with moisture balance and CO₂ in individual models.     

Gas exchange and air flow in the lung of the snake,Pituophis melanoleucus

Summary Gas samples from various regions of the lung were obtained throughout the breathing cycle inPituophis melanoleucus. Changes in CO₂ concentration during the interbreath period differed markedly along the length of the lung. In general, the largest and most rapid increases in CO₂ tension were measured at the cranial end of the vascular lung. Further caudad in the vascular lung, the increase was slower and did not reach mixed venous CO₂ tension before exhalation. In animals exhibiting the lowest breathing frequencies and presumably larger tidal volumes, the region of gas exchange extended into the cranial portion of the air sac. There was little or no change in gas tensions within the remaining caudal regions of the air sac. Measurement of exhaled CO₂ and O₂ tensions at the nares confirmed the longitudinal gradient in gas exchange and also demonstrated the sequential emptying of the lung. Large regional differences in the ratio of blood flow to alveolar volume are probably responsible for the gradients in lung gases.Interpretation of N₂ clearance curves in terms of two freely communicating compartments demonstrated the presence of a ventilation inequality. Consistent with this was the lack of body wall contractions between breaths while animals were resting. However, just prior to and during activity body wall contractions not associated with breathing often occurred and resulted in pressure excursions in the lung of ca. five mm H₂O. In addition, the heart beat results in a pressure change within the lung of ca. 0.2 mmH₂O which may be significant in gas mixing.     

Jasmonate‐mediated stomatal closure under elevated CO2 revealed by time‐resolved metabolomics

Foliar stomatal movements are critical for regulating plant water loss and gas exchange. Elevated carbon dioxide (CO₂) levels are known to induce stomatal closure. However, the current knowledge on CO₂ signal transduction in stomatal guard cells is limited. Here we report metabolomic responses of Brassica napus guard cells to elevated CO₂ using three hyphenated metabolomics platforms: gas chromatography‐mass spectrometry (MS); liquid chromatography (LC)‐multiple reaction monitoring‐MS; and ultra‐high‐performance LC‐quadrupole time‐of‐flight‐MS. A total of 358 metabolites from guard cells were quantified in a time‐course response to elevated CO₂ level. Most metabolites increased under elevated CO₂, showing the most significant differences at 10 min. In addition, reactive oxygen species production increased and stomatal aperture decreased with time. Major alterations in flavonoid, organic acid, sugar, fatty acid, phenylpropanoid and amino acid metabolic pathways indicated changes in both primary and specialized metabolic pathways in guard cells. Most interestingly, the jasmonic acid (JA) biosynthesis pathway was significantly altered in the course of elevated CO₂ treatment. Together with results obtained from JA biosynthesis and signaling mutants as well as CO₂ signaling mutants, we discovered that CO₂‐induced stomatal closure is mediated by JA signaling.