Effects Of Light Adaptation Research Articles

Experimental outdoor studies with Ulva fasciata Delile. I. Interaction of light and nitrogen on nutrient uptake, growth, and biochemical composition

The effects of algal density, light adaptation, and interaction of light and nitrogen on nutrient uptake, growth, and biochemical composition of Ulva fasciata Delile were investigated in outdoor continuous cultures. With increasing plant densities, specific growth rates decreased exponentially from 0.36 to 0.02 doublings · day −1. In contrast, yields increased to a maximum of 4.7 g C · m −2 · day −1 at the intermediate density and then decreased. Plants grown under low (62 ly · day −1) and high (324 ly · day −1) light conditions were subsequently exposed to medium light (282 ly · day −1). Initially, plants from low light conditions had twice the chlorophyll a content and yield than plants from high light conditions. Within 1 wk, all plants showed no difference with regard to chlorophyll a and yield. Growth of U. fasciata did not saturate up to the highest light intensities used (255 ly · day −1). Nitrogen (NO 3 −) additions at low light did not affect growth but at high light there was increasing growth with increasing nitrogen. This interaction between light and nitrogen was apparent when growth was measured as specific growth rate (doublings · day −1), activity coefficient (mg C · g C −1 · day −1) and yield (g C · m −2 · day −1). These growth measures all significantly correlated with %C and ash content but not with %N, the C:N or C: Chl a ratios. Photosynthetic rate (g C · g Chl a −1 · day −1) showed no interaction between light and nitrogen because it corrected for increases in chlorophyll a content caused by nitrogen additions. This growth measure correlated with %N and the C: N and C: Chl a ratios as well as %C and ash content. Photosynthetic efficiency of U. fasciata was positively correlated with %N and chlorophyll a content and was affected by light intensity only at low nitrogen levels. Uptake of NO 3 − by U. fasciata depended mostly on the daily loadings of this nutrient, but was also inversely proportional to light intensity.

Brightness exponent as a function of retinal eccentricity in the peripheral visual field: effects of dark and light adaptation.

Using a method of direct magnitude estimation, the exponent of the brightness power function was determined under dark and light adaptation at luminance levels well above threshold. The exponent was estimated for functions describing the brightness of stimuli presented at the fovea and the following peripheral retinal loci: 10, 20, 30, 40, and 50 deg nasally eccentric to the fovea along the horizontal meridian of the right eye. The exponent for a 1-sec flash was found to be approximately .33 at the fovea and increased slightly with increasing retinal eccentricity.The effect of adaptation on the brightness exponent was not so large when the target luminance was set well above threshold.

The effect of light adaptation on the dynamic properties of phototransduction in the fly, Phormia regina

The static and dynamic characteristics of phototransduction were studied in photoreceptors of the compound eye of the fly Phormia regina (Calliphoridae) using a green light emitting diode driven by a controlled current source. The LED provides sufficiently intense light to investigate the behaviour of the receptors over about half of the dark adapted range of the response versus log intensity curve. The effects of constant adapting light intensities upon the step response and upon the frequency response and coherence functions were examined. Using both methods the effect of light adaptation upon receptor sensitivity can be closely approximated by a similar linear dependence of log sensitivity upon log adapting intensity. However, there was no reliably detectable effect of light adaptation upon the time constant of the response over the range of adapting intensities used.

Primate cone sensitivity to flicker during light and dark adaptation as indicated by the foveal local electroretinogram

During light and dark adaptation the primate foveal local electroretinogram (LERG) was monitored in response to yellow sinusoidally flickering stimuli. Since the foveal LERG is dominated by the late receptor potential (LRP) under these stimulus conditions, we were most likely monitoring cone photoreceptor activity. (1) Relative threshold vs intensity ( tvi) functions were obtained for stimuli flickering at 40, 20 and 5 Hz. Each of these functions achieves a unit slope at moderate to high intensities. Changes in phase relations between the stimulus and response occur only at those adaptation levels where photopigment bleaching is relatively ineffective as an adaptational mechanism. (2) The time course of dark adaptation was monitored for stimuli flickering at various frequencies between 5 and 50 Hz. At frequencies between 5 and 20 Hz, the time course of recovery of log relative sensitivity follows a nonexponential course; a break at 1.5 min sometimes occurs in the 5 Hz function. At higher frequencies the functions are exponential with time constants smaller than found for photopigment regeneration. These results are inconsistent with a simple linear relation relating log sensitivity and photopigment regeneration. (3) A Crawford type of transform indicates a non-equivalence between the effects of prior bleaching and steady-state light adaptation. (4) Absolute amplitude sensitivity functions obtained at various times after a bleach have low and high frequency branches. After compensating for the reduction in photon catch due to photopigment depletion the high frequency sensitivity changes little during dark adaptation, but the low frequency sensitivity changes markedly.1

Massive diurnally modulated photoreceptor membrane turnover in crab light and dark adaptation

1. Effects of light and dark adaptation on the photoreceptor membranes of the rock crabGrapsus have been quantitatively studied using light and electron microscopy to document changes in rhabdom size and their fine structural basis. Some comparative data were also obtained for the ghost crabOcypode. Animals in the laboratory were maintained on a daily light (L)-dark (D)cycle 12L∶12D. Periods of adaptation ranged from 3–28 h (Table 1) and light adaptation was effected at one moderate intensity equal to the light period in the daily sequence. 2. Massive rapid reversible changes in rhabdom size (Fig. 1) comprising mainly diameter modulation (Figs. 2, 3) and some alteration in length, normally resulted in maximum increases in receptor organelle volume of about 20× between a thinner, shorter fully light adapted condition (2×290 μm) to the fully dark adapted state (7.9× 336 μm). 3. Rhabdom growth during dark adaptation (Table 2) was due mainly (Fig. 8) to microvillus elongation (+154%) as well as substantial increase (+117%) in the number of microvilli present in cross sections (Figs. 2, 3, 10); microvillus diameter (Figs. 4, 5, 9) also increased (+14%) but accounts for only a minor part of the overall change commensurate with observed differences in rhabdom length (+16%). Calculation shows that from fully light adapted to fully dark adapted state the area of photoreceptor membrane increased nearly 20× in a few hours. 4. Although duration of adaptation affected its amplitude, six hours of either light or darkness evoked the maximum changes documented; shorter and longer periods had less effect (Figs. 6, 7). 5. Time of day had a strong periodic influence on the amplitude of membrane adaptation produced by a given exposure to dark or light. Thus maximum dark adaptation occurred with 6 h of darkness terminating at midnight and maximum light adaptation with 6 h of light ending at noon of the diurnal light cycle (Fig. 11). 6. Direct effects of light and dark on synthesis and degradation of photoreceptor membrane must therefore be superimposed on indirect or direct cyclic neuroendocrine control presumably coupled to an entrained circadian oscillator.

Effect of light and dark adaptation upon the rhabdom in the compound eye of the mosquito

AbstractDuring the first two hours of light adaptation rhabdom volume in compound eyes of adult mosquitoes is strikingly reduced. In females this involves a net loss of photoreceptor membrane of 500–700 μ2/cell/hour. Concurrently, numerous coated vesicles and multivesicular bodies appear in the cytoplasm adjacent the rhabdom. After longer illumination times (up to 5 hours) membrane loss averages considerably less, 220 μ2/cell/hour. Furthermore, puromycin experiments suggest that it is counter‐balanced by the formation of an equal amount of new membrane. Thus, despite substantial membrane turnover no net change in rhabdom volume takes place.When light‐adapted mosquitoes are dark adapted for 12 to 36 hours there occurs a net increase of rhabdom membrane averaging 75 μ2/cell/hour, and a corresponding increase in rhabdom volume.

Interocular light adaptation effect on the lie “specific threshold”

Interocular light adaptation effect on the lie “specific threshold”

Effect of light-adaptation on the photoreaction of bacteriorhodopsin from Halobacterium halobium

Light-induced formation of the 410 nm intermediate was investigated on dark-and light-adapted bacteriorhodopsin. The amplitude of the light-induced absorption increase at 410 nm of the light-adapted bacteriorhodopsin was twice as large as that of the dark-adapted bacteriorhodopsin. The amount of protons released from bacteriorhodopsin in response to illumination was also enhanced by light-adaptation. The degree of the enhancement was independent of the temperature in the dark-adaptation. The relation between these photochemical events and the isomeric configurations of retinal is discussed.

Spatial summation and light adaptation in the goldfish visual system.

IN attempting to explain how visual acuity improves as illumination increases, Pirenne and Denton1 suggested that the retinal image is sampled by numerous units, each summing the effects of light over a region of the retina. At very low luminances, only units with the largest summation areas are functional, but with increasing luminance smaller units come into play as their thresholds are exceeded. Since that suggestion was made, cells at all levels of the visual system have been studied electrophysiologically and many receptive fields have been described that might form the basis for such units. Goldfish and other cyprinid fishes, have been the subjects of many such studies, and their retinal synaptic connections have been revealed in detail. I report here some psychophysical experiments which show the effects of light adaptation on spatial summation in the goldfish. The results are consistent with the connections made by rods and cones in the cyprinid retina, and with the theory of a progressive recruitment of ganglion cells with smaller receptive field centres as background luminance is raised.

On the activating and depressing effects of light adaptation on the electroretinogram of the frog's eye

A study was made of the dynamics of changes in individual waves of the frog rhythmic ERG after switching off prolonged adaptive illumination. With the ratio of intensity of the test and adaptive light approximating 1, in a wide range, irrespective of the absolute values of intensity, colour and total energy of the adaptive light, the waves “a” and “d” proved sharply increased and gradually diminished in the course of dark adaptation. If the test flashes were ten to fifteen times less intensive than the adaptive light, the “a” and “d” waves proved to be reduced and gradually increased in the course of dark adaptation. ERG wave “b” diminished with any ratio of adaptation intensity and test intensity after the prolonged illumination was switched off. So, there is no correlation in the changes of wave “b”, or “a” and “d” ERG waves after light adaptation has been switched off. This is regarded as proof of the existence of two relatively independent types of adaptation processes in the frog's retina.

Distribution of 3':5'-cyclic AMP and 3':5'-cyclic GMP in rabbit retina in vivo: selective effects of dark and light adaptation and ischemia.

By use of highly sensitive radioimmunoassays, 3':5'-cyclic AMP (cAMP) and 3':5'-cyclic GMP (cGMP) were measured in individual layers of light- and dark-adapted rabbit retinas, and the effects of ischemia were determined. In light-adapted retinas, cGMP levels ranged 50-fold, with over 90% of the total concentrated in the photoreceptor cells. The layer of outer segments contained 95 mumol/kg of dry weight, or three times the concentration present in the remainder of the photoreceptor cell layers. By contrast, levels of cAMP varied only 4-fold; the lowest level (6 mumol/kg of dry weight) was found in the outer segment layer and the highest level (22 mumol/kg of dry weight) in the inner segment layer of the photoreceptor cells. Dark adaptation elevated cGMP levels only in retinal layers containing photoreceptor cells, and the greatest proportional increase was observed in the synaptic layer of photoreceptor cells. Dark adaptation also caused increases of cAMP that were restricted to the outer plexiform and outer nuclear layers. Ischemia lowered cGMP levels, but only in retinal layers containing photoreceptor cells, and elevated cAMP levels, primarily in the inner layers of the retina. The effects of ischemia were greater in the dark-adapted than in light-adapted retinas. These results indicate that cGMP and cAMP levels in retina are influenced by the light adaptational state, that ischemia markedly modifies these processes, and that the effects of both light exposure and ischemia are regionally selective.

The effects of light and dark adaptation on the levels of cyclic nucleotides in retinas of mice heterozygous for a gene for photoreceptor dystrophy

Levels of cyclic AMP and cyclic GMP were measured in light and dark adapted retinas from normal mice (++/++) and from mice heterozygous for the photoreceptor dystrophy gene (rdle/++). In light adapted retinas cyclic GMP levels were 40% lower in the heterozygotes than in the normals, whereas cyclic AMP levels were the same. Dark adaptation elevated cyclic GMP levels 120% in both groups and also elevated cyclic AMP levels 90% in the ++/++ and 45% in the heterozygotes. These data suggest that animals heterozygous for photoreceptor dystrophy have an abnormality of their retinal cyclic GMP system.

Effects of light adaptation on the purple membrane structure of Halobacterium halobium

Absorption, circular dichroism and optical rotatory dispersion of the bacteriorhodopsin containing purple membrane form Halobacterium halobium were studied in regard to the structural stability of this membrane during the photoisomerization of the retinal of the bacteriorhodopsin from the 13-cis to the all-trans configuration. The following conclusions were reached: (a) the macromolecular structure (protein-protein interaction which may result in the possible exciton interaction of the retinal pi-pi* (NV1) transition moments and protein-lipid interaction) are not significantly altered, (b) possibilities of delocalized conformation changes of the apoprotein involving secondary and/or tertiary structure can be ruled out, (c) localized secondary structure conformation changes of the apoprotein must be limited to the involvement of no more than one or two amino acid residues and localized tertiary structure conformation changes of the apoprotein must be limited to a very short segment of the protein chain containing only a few aromatic amino acid residues, and (d) the interaction between the apoprotein and retinal seems to be relatively more pronounced when the retinal is in the all-trans form than the 13-cis from and also the apoprotein seems to impose a more pronounced dissymmetric constraint on the retinal in the all-trans form than in the 13-cis form.

Visual sensitivity and the state of adaptation in the antAtta sexdens (Hymenoptera: Formicoidea)

In the worker ant,Atta sexdens, the ERG is cornea negative, shows two phasic and one tonic component and never presents an initial positive deflection. Dark adaptation was found to be complete within 10 min even with the longest pre-adapting duration used. Circadian variations were observed on continuous records, showing a tenfold sensitivity increase of the ERG during the night. Effects of light adaptation were also studied. The ERG amplitude can increase after light exposure. The possible role that pigment migration might play in the described sensitivity changes is discussed.

The effect of long-term light and dark adaptation and stimulus intensity on the receptor potential of the Limulus lateral eye

Intracellular recordings of the receptor potential of the lateral eye of Limulus were made following white light stimuli, to test intensity-dependence and long-term light and dark adaptation. The plot of the peak amplitude of the receptor potential ( h max) versus log I is S-shaped. The linear phase covers ca. 2 log units. The plateau-value ( h e) obviously saturates at higher intensities than h max. The long-term adaptation was tested during sustained background light (10 min) with superimposed test flashes, and subsequently in the dark (64 min). The adaptation was fully reversible; 30 sec after turning off the background light h max has already reached 80% of the reference value. The results are discussed on the basis of the concept that the opening of channels in the cell membrane causes the receptor potential. The observed membrane adaptation effects can be explained by assuming, among other factors, a light-dependent variable amplification of the mechanisms producing the receptor potential. The influence of active and electrogenic transport on adaptation is discussed.

Electrophysiological evidence for rod and cone-based vision in the nocturnal flying squirrel

The flying squirrel (Glaucomys volans) is a strongly nocturnal rodent. Previous anatomical observations suggested that the retina of this animal contains some cone-like receptors in addition to large numbers of rods. Evidence for duplicity of function in this visual system was obtained from an examination of three indices of visual activity: the electroretinogram (ERG), the isolated PIII retinal response, and the visually evoked cortical potential (VECP). The spectral sensitivity of the dark-adapted flying squirrel is similar to that of other mammals — it has a 500 nm peak (Figs. 3, 8). Responses of the ERG and isolated PIII to flickering light indicate the operation of two processes (Figs. 4, 7), one of which is unable to follow flickering light at repetition rates above 10–15 Hz. Spectral sensitivity measurements reveal that these two processes have different spectral sensitivities. The photopic mechanism in the flying squirrel visual system has peak sensitivity at about 520 nm (Figs. 5, 7, 9). The effects of steady light adaptation are much more obvious in the cortical potentials than they are in the retinal potentials.

The interocular light adaptation effect at varying retinal locations

The interocular light adaptation effect can be demonstrated in the fovea and in nonfoveal areas up to 10° temporal to the fovea but not 15° from the fovea. These results substantiate the existence of both cone and rod components in the effect. The effect is similar whether determined in the dominant eye or the non-dominant eye. The interocular light adaptation effect is significant for considerations of cone-rod interactions and binocular vision. The differential effects of monocular and dichoptic preadaptation are considered to be due to afterimages which provide different equivalent backgrounds.

Analysis of “off” latency in insect photoreceptors

1. 1. “Off” latency from the compound eye of the milkweed bug, Oncopeltus fasciatus, was an inverse function of light stimulus intensity and duration. 2. 2. Latency for the “off” response to a 125 msec test stimulus (S 2) was also an inverse function of adapting stimulus (S 1) intensity and duration. This supports the hypothesis that “off” latency to a stimulus is determined by the effects of light adaptation generated during that stimulus.

On the mechanisms of the interocular light adaptation effect

Lansford and Baker recently demonstrated that the adaptation state of the contralateral eye effects the sensitivity of the test eye during dark adaptation. Specifically, a smaller and dimmer contralateral preadapting field which partially overlaps the preadapting field seen by the test eye accelerates subsequent monocular dark adaptation. The present study replicated the interocular light adaptation (Lansford-Baker) effect and produced the same effect under different test conditions. By the use of limited wavelength contralateral preadapting fields it demonstrated the interocular light adaptation effect in both cone and rod segments of the dark adaptation curve and that the rod effect is larger. Both long and short wavelength contralateral preadapting fields enhanced the effect to the point of doubling its magnitude.

Adaptation and temporal characteristics of the insect visual response

The effects of light adaptation on temporal characteristics of the electroretinogram were studied in two species of diurnal insects. Latency and time to reach peak amplitude (T m ) of the initial deflection of the ERG were the temporal measures used. The experimental regime consisted of repeatedly light-adapting the eye with a conditioning stimulus (S1 and determining the effects of eachS1 on the response to a test stimulus (S2). The compound eyes of the flesh flySarcophaga bullata, and the milkweed bug,Oncopeltus fasciatus, were compared since they differ substantially in ERG waveform and latency of response.