Transplantation of eyes to the adult rat brain: Histological findings and light-evoked potential response

Entire eyes were transplanted from fetal rats into the brains of blind adults. In most cases, grafts placed deep within the brain grew and differentiated, and were found to contain retinal cells when examined histologically. Grafts placed within the cerebral cortex infrequently survived. The grafts were found to be sensitive to light, in that electrical potentials similar to electroretinograms (ERGs) or partial ERGs were evoked by flashes of light. It is concluded that fetal eyes can develop a form of light sensitivity when transplanted to the adult rat brain.     

Role of intracellular calcium and sodium in light adaptation in the retina of the honey bee drone (Apis mellifera, L)

In the honey bee drone, the decrease in sensitivity to light of a retinula cell exposed to background illumination was found to be accurately reflected by the difference in amplitude between the initial transient depolarization and the lowest steady depolarization evoked by the background light. It is shown that both the decrease in sensitivity to light and the accompanying drop in potential from the transient to the plateau can be prevented by injecting EGTA intracellularly. A decrease in duration and amplitude of responses to short test flashes such as observed immediately after illumination was found to occur too when Ca or Na, but not K, Li, or Mg injected into dark-adapted retinula cells. Injection of EGTA into a retinula cell maintained a steady state of light adaptation, was found to cause an increase in amplitude and duration of the response to a short test flash, thus producing the effects of dark adaptation. It is suggested that, in the retina of the honey bee drone, an increase in intracellular calcium concentration plays a central role in light adaptation and that an increase in intracellular sodium concentration, resulting from the influx of sodium ions during the responses to light, could lead to this increase in intracellular free calcium.     

Spectral Sensitivity of the Planarian Ocellus

The ocellar potential (OP) of planaria was recorded using microelectrode techniques. The action spectrum and spectral sensitivity of the OP are described. Maximum OP sensitivity was found with 508 nm light. A moderate increase in sensitivity to blue light was observed. This is typical of many invertebrate photoreceptors and was shown, by selective chromatic adaptation, not to indicate the presence of a second pigment.     

Blue Light-Induced Lethality of a Cell Wall-Deficient Mutant of the Unicellular Green Alga Chlamydomonas reinhardtii

When synchronized cultures of a cell wall-deficient Chlamydomonasreinhardtii mutant strain were grown under heterotrophic conditionsand subsequently transferred to the light, a considerable decreaseof the cell number was observed during transition to the celldivision phase. Lethality of the wall-deficient cells was inducedby blue light, but not by red or far-red light, and could notbe prevented by addition of the photosystem II inhibitor DCMU.The light-induced lethality was found to be restricted to wall-deficientcells which were agitated by bubbling with filtered air or nitrogenor vigorously shaken during the transition to the cell divisionphase. Therefore, a (blue) light-induced sensitivity to anymechanical stress seems to be the cause for cell death. In heterotrophicallygrowing cultures of the Chlamydomonas wild-type, illuminationwith blue or white light did not cause a decrease of the cellnumber but only a delay of cell divisions. The latter effectwas also observed in case of the wall-deficient mutant. Bothblue light effects are observed during the transition to thecell division phase and can be induced during the same periodof the cell cycle. Furthermore, the (blue) light-induced lethalityof wall-deficient cells was found to be prevented when the transitionto the cell division phase was inhibited by addition of antibiotics.Therefore, we assume that there is a connection between theblue light-induced sensitivity to mechanical stress and theblue light-induced delay of cell divisions. (Received September 3, 1993; Accepted November 12, 1993)     

Growth environment determines light sensitivity of shoot hydraulic conductance

Acclimation of light sensitivity of hydraulic conductance of shoots of silver birch (Betula pendula) and hybrid aspen (Populus × wettsteinii) to growth environments with three different air humidities was studied. Hydraulic conductance of shoots kept for 1–2 h in darkness (D) or in light (L) was measured by the pressure chamber method, and light sensitivity was defined as a significant difference between D and L shoots. Light sensitivity of shoots grown in three different air humidities was found to vary. Amongst shoots grown in current natural air, only the hydraulic conductance of the whole shoot and that of the leaf blades of birch upper foliage were significantly light sensitive. Amongst shoots grown in decreased air humidity, hydraulic conductance of the whole shoot, the leaf blades, and the stem and petioles of birch upper foliage, the conductance of the whole shoot and the leaf blades of birch lower foliage, and the conductance of the whole shoot of aspen upper foliage were light sensitive. None of the shoots grown in increased air humidity were significantly light sensitive. We predict that light sensitivity will become more widespread among species in regions where air humidity decreases as a result of global climate change, and vice versa. Low white light always caused the same increase in hydraulic conductance as high white light, and blue and white light always caused an increase in conductance about two times greater than red light, indicating that growth environment did not markedly modify the mechanism of light sensitivity.     

A quantitative comparison of the effects of intracellular calcium injection and light adaptation on the photoresponse of Limulus ventral photoreceptors

Calcium ions were iontophoretically injected into ventral photoreceptors of Limulus by passing current between two intracellular pipettes. Changes in sensitivity and photoresponse time course were measured for both light adaptation and Ca++ injection. We found for some photoreceptors that there was no significant difference in the photoresponse time course for desensitization produced by light adaptation or by Ca++ injection. In other photoreceptors, the time delay of photoresponse for Ca++ injection was slightly longer than for light adaptation. The variability of threshold response amplitude and time delay decreases when the photoreceptor is desensitized by either light adaptation or Ca++ injection. The peak amplitude versus log stimulus intensity relationships for controls, light adaptation, and Ca++ injection all could be described very closely by a single template curve shifted along the log intensity axis. A 40- to 50-fold change in sensitivity is associated with a 2-fold change in photoresponse time delay for both light adaptation and Ca++ injection.     

Role of carbohydrates in diurnal chilling sensitivity of tomato seedlings

Tomato seedlings (Lycopersicon esculentum Mill.) chilled starting at different times during the light/dark cycle were most chilling-sensitive at the end of the dark period (AI King, MS Reid, BD Patterson 1982 Plant Physiol 70: 211-214). Low-temperature tolerance was regained with as little as 10 minutes of light exposure. Low light intensities were less effective than high light intensities in reducing sensitivity, and the length of exposure to light directly influenced sensitivity. Seedlings kept at low night temperatures prior to chilling were also less injured following chilling. Light also restored chilling tolerance to seedlings whose roots were removed. Supplying cut shoots with sucrose, glucose, or fructose reduced chilling sensitivity and largely eliminated the diurnal difference in sensitivity. Endogenous carbohydrate content was correlated with changes in chilling sensitivity; starch and sugar content fell markedly during the dark period. Increased concentrations of sugars were detected 15 minutes after the start of the light period. This evidence all suggests that changes in chilling sensitivity over the diurnal period are regulated by the light cycle. It also suggests that increased sensitivity at the end of the dark period could be due to carbohydrate depletion, and that chilling tolerance following light exposure is likely due to carbohydrate accumulation or closely related events.     

Comparison of helium-neon and dye lasers for the excitation of allophycocyanin

Allophycocyanin (APC) has a broad absorption spectrum permitting several different lasers to be used to excite this dye in a flow cytometer. A comparison was made between a dye laser and a helium-neon (HeNe) laser for the excitation of APC as an immunofluorescent chromophore. The ratio of fluorescence of stained to unstained lymphocytes (signal to background) was used to assess differences in sensitivity. In determining the best wavelength for operating the dye laser, it was found that there was little difference in the ability to separate the positive-labelled cells from the unstained cells using 600 nm or 633 nm light for excitation of APC. A study of the effect of laser power on the signal to background identified a nonlinear relationship. It was found that the sensitivity obtained with 47 mW of 633 nm light from a HeNe laser was near the maximum attainable. This sensitivity was comparable to that obtained using phycoerythrin as an immunofluorescence chromophore. APC had the added advantage of being applicable to the study of highly autofluorescent cells. Exciting this chromophore using red light dramatically decreased the autofluorescence observed even on alveolar macrophages.     

Increased photic sensitivity for phase resetting but not melatonin suppression in Siberian hamsters under short photoperiods

Light regulates a variety of behavioral and physiological processes, including activity rhythms and hormone secretory patterns. Seasonal changes in the proportion of light in a day (photoperiod) further modulate those functions. Recently, short (SP) versus long days (LP) were found to markedly increase light sensitivity for phase shifting in Syrian hamsters. To our knowledge, photoperiod effects on light sensitivity have not been studied in other rodents, nor is it known if they generalize to other circadian responses. We tested whether photic phase shifting and melatonin suppression vary in Siberian hamsters maintained under LP or SP. Select irradiances of light were administered, and shifts in activity were determined. Photic sensitivity for melatonin suppression was examined in a separate group of animals via pulses of light across a 4 log-unit photon density range, with post-pulse plasma melatonin levels determined via RIA. Phase shifting and melatonin suppression were greater at higher irradiances for both LP and SP. The lower irradiance condition was below threshold for phase shifts in LP but not SP. Melatonin suppression did not vary by photoperiod, and the half saturation constant for fitted sigmoid curves was similar under LP and SP. Thus, the photoperiodic modulation of light sensitivity for phase shifting is conserved across two hamster genera. The dissociation of photoperiod effects on photic phase shifting and melatonin suppression suggests that the modulation of sensitivity occurs downstream of the common retinal input pathway. Understanding the mechanistic basis for this plasticity may yield therapeutic targets for optimizing light therapy practices.     

Morphogenesis in Schizophyllum commune. II. Effects of Monochromatic Light

The photoinduction of fruiting bodies by light of defined wavelengths was studied in the fungus Schizophyllum commune Fr. Several properties of the induction were established. (1) The exposure-response relationship for induced fruiting was determined for light of 448 nm. (2) The Bunsen-Roscoe Law of Reciprocity was found to hold for the photoinduction of fruiting bodies for the interval 36 to 2000 sec with light of 448 nm. (3) Light of wavelengths from 320 nm to 525 nm induced fruiting bodies. Although the photoreceptor is unknown, it may be a flavin rather than a carotenoid, because light in the near ultraviolet (350 nm-400 nm) was inductive. (4) Neither red light (660 nm) nor far-red light (730 nm) induced fruiting bodies or affected the sensitivity of the fungus toward photoinduction by blue light (448 nm).     

Light-Induced Anthocyanin Reduces the Extent of Damage to DNA in UV-Irradiated Centaurea cyanus Cells in Culture

Using suspension cultures of Centaurea cyanus L. cells, in whichthe biosynthesis of anthocyanin is induced by illumination withUV-containing white light and in which the level of pigmentcan be controlled, we examined the sensitivity of the cellsto both UV-B and UV-C irradiation and the formation of pyrimidinedimer as a result of exposure to UV light, with a special referenceto the level of accumulation of anthocyanin pigment in the cells.The sensitivity of the cells to UV-B or UV-C decreased as theiranthocyanin content increased. Furthermore, the extent of formationof pyrimidine dimers induced by irradiation with UV-B or UV-Clight was found to be reduced in cells with accumulated anthocyanin.Both the extent of resistance to UV irradiation and the reductionin the extent of formation of dimers as a result of exposureto UV light were correlated with the levels of accumulated anthocyaninpigment in the cells. The results show that anthocyanin, a kindof flavonoid, plays a role in protecting cells from the adverseeffects of UV light. (Received January 28, 1991; Accepted May 19, 1991)     

Evidence for habitat partitioning based on adaptation to environmental light in a pair of sympatric lizard species

Terrestrial habitats exhibit a variety of light environments. If species exhibit evolutionary adaptations of their visual system or signals to habitat light conditions, then these conditions can directly influence the structure of communities. We evaluated habitat light characteristics and visual-signal design in a pair of sympatric species of lizards: Anolis cooki and Anolis cristatellus. We found that each species occupies a distinct microhabitat with respect to light intensity and spectral quality. We measured the relative retinal spectral sensitivity and found significant differences between the species that correlate with differences in habitat spectral quality. We measured the spectral reflectance of the dewlaps (colourful throat fans used in communication), and found that the A. cooki dewlap reflects little ultraviolet (UV), while that of A. cristatellus reflects strongly in the UV. For both species downwelling light (irradiance) is rich in UV. However the background light (radiance) is rich in UV for A. cooki, but low in UV for A. cristatellus. Thus, the dewlap of each species creates a high contrast with the background in the UV. Our findings strongly suggest that these two species are partitioning their habitat through specializations of the visual system and signal design to microhabitat light conditions.     

Sensitivity to methylmethanesulfonate and nitrous acid of ultraviolet light-sensitive mutants in Saccharomyces cerevisiae

Summary Twenty two ultraviolet light-sensitive mutants isolated byParry andCox (1968) were tested for a possible cross-sensitivity to nitrous acid and methylmethanesulfonate. Eighteen of these mutants showed, in comparison to wild type, an increased sensitivity to methylmethanesulfonate and 16 mutants were cross-sensitive to nitrous acid. Cross-sensitivity between these two chemicals was good even when the degrees of sensitivity were compared; only two major exceptions were found. The degree of sensitivity to the two chemicals on one side and to ultraviolet light was not always the same. Two mutants of extreme sensitivity to chemicals were only weakly sensitive to ultraviolet light whereas in another mutant an extreme sensitivity to ultraviolet light was combined with a low sensitivity to chemicals. These observations are discussed in the light of current views on excision repair models.     

Neuro-pharmacological studies on firefly light organs during metamorphosis

Luminescences in response to electrical stimulation and pharmacological treatment were characterized during progressive degeneration of the larval light organ and differentiation of the adult light organ during metamorphosis. It was found that: (1) neural control of the larval light organ persists during pupation, (2) the differentiating adult light organ, while frequently luminescing, is not directly or neurally excitable until eclosion (3), a gradual loss of postsynaptic receptor chemical responsiveness occurs in parallel with declining neural excitability of the larval light organ, (4) postsynaptic chemical sensitivity of the adult light organ appears prior to establishment of neural control, (5) both larval and adult light organs spontaneously luminesce in the absence of neural control, and (6) synapses between nerve terminals and photocytes of the larval light organ are present throughout pupation.     

Adaptation and facilitation in the barnacle photoreceptor

The barnacle photoreceptor sensitivity may either decrease (light adaptation) or increase (facilitation) after exposure to a conditioning light. The balance between adaptation and facilitation is influenced by at least three factors: initial sensitivity state of the cell, external calcium concentration, and conditioning intensity. Cells of very high sensitivity show mainly adaptation, which appears only for higher conditioning intensities and is suppressed in low-calcium media. Less sensitive cells, or those whose sensitivity is reduced by injury or metabolic decay, exhibit facilitation, expecially in low-calcium media and at intermediate conditioning intensities. Both phenomena show recovery time-courses of seconds-to-minutes. Models are proposed which relate light adaptation, as previously suggested, to increased internal calcium concentration, and facilitation either to decreased internal calcium concentration or to decreased activation "affinity" of ion-channel-blocking sites.     

Physiological basis of phototaxis to near-infrared light in Nephotettix cincticeps

In a previous study of the phototaxis of green rice leafhoppers, Nephotettix cincticeps (Hemiptera, Cicadellidae), we found positive responses to 735 nm light. Here, we investigated the mechanism underlying this sensitivity to near-infrared light. We first measured the action spectrum using a Y-maze with monochromatic lights from 480 to 740 nm. We thus found that the action spectrum peaks at 520 nm in the tested wavelength range, but that a significant effect is still observed at 740 nm, albeit with a sensitivity 5 log units lower than the peak. Second, we measured the spectral sensitivity of the eye, and found that the sensitivity in the long-wavelength region parallels the behaviorally determined action spectrum. We further identified mRNAs encoding opsins of ultraviolet, blue, and green-absorbing visual pigments, and localized the mRNAs in the ommatidia by in situ hybridization. The electrophysiology, molecular biology and the anatomy of the eye together indicate that the eyes of N. cincticeps do not contain true “red” receptors, but rather that the behavioral response to near-infrared light is mediated by the tail sensitivity of the green receptors in the long-wavelength region of the spectrum.     

Spectral responses of the tsetse fly, Glossina morsitans morsitans

Spectral responses of male Glossina morsitans morsitans Westw, were investigated using behavioural and electrophysiological techniques. Phototactic responses to monochromatic lights of different wavelengths but equivalent intensities (measured either in energy or quantal units) were tested in an apparatus which permitted the simultaneous presentation of pairs of lights to groups of flies. Near ultraviolet light was the most attractive, followed by blue and red, with green and far red light giving no significant responses above control levels. The spectral sensitivity of the compound eye was also determined from the electroretinogram (ERG) recorded from electrodes implanted in the eye which was stimulated with flashes of monochromatic light. Three areas of maximum sensitivity were found by this method in the UV, blue/green and red. The relationship between the behavioural and electrophysiological sensitivity characteristics is explained with reference to visual systems of other Diptera which have previously been described.     

Differences in effects of oncogenes on resistance of gamma rays, ultraviolet light, and heat shock.

The effects of viral or activated cellular oncogenes on sensitivity to gamma rays, ultraviolet light, and heat shock were examined in SHOK (Syrian hamster Osaka-Kanazawa) cells and their transfectants. Resistance to gamma rays was conferred by the introduction of v-mos or c-cot genes, which coded serine/threonine kinase. Cells transfected with v-mos and c-cot genes increased their resistance to ultraviolet light and heat shock compared to their parent cells (SHOK cells). Of the activated ras genes, the N-ras gene developed a SHOK cell phenotype resistant to gamma rays and ultraviolet light. The Ha-ras gene produced SHOK cells resistant to ultraviolet light and heat shock, while introduction of the Ki-ras gene did not affect sensitivity. The v-erbB gene was found to be involved in the development of resistance to heat shock. Transfection with neo, c-myc, and v-fgr genes had little or no effect on cell survival. The karyotypes of SHOK cells and oncogene-containing cells were compared. No alterations were seen after the introduction of a foreign gene. Using cell cycle analysis, we found no apparent difference between SHOK cells and their transfectants. These results suggest that activation of serine/threonine kinase may be involved in common processes occurring after gamma-ray, ultraviolet-light, and heat-shock treatment, and that each oncogene may have a different effect on the development of a resistant phenotype.     

Common steps in the repair of alkylation and radiation damage in yeast

Summary Radiation sensitive mutants of Saccharomyces cerevisiae were exposed to the action of nitrogen mustard (HN2) and methyl methanesulfonate (MMS). Sensitivity to HN2 was found to be correlated with sensitivity to ultraviolet light, whereas sensitivity to MMS was found to be correlated with sensitivity to X-rays. One mutant strain that is sensitive to both UV and X-rays was found to be sensitive also to HN2 and MMS. The latter result shows that there exists a locus in yeast that controls the repair of DNA damaged by all four of these mutagens.     

Synechocystis 6803 mutants expressing distinct forms of the Photosystem II D1 protein from Synechococcus 7942: relationship between the psbA coding region and sensitivity to visible and UV-B radiation

Synechocystis PCC 6803 mutants expressing either the "low light" (D1:1) or the "high light" (D1:2) form of the Photosystem II (PSII) D1 protein from Synechococcus PCC 7942 were constructed and characterized with respect to properties of PSII and sensitivity to visible and UV-B radiation. The AI and AIII mutants (containing only the D1:1 and D1:2 forms, respectively) exhibited very similar PSII characteristics as the control strain and they differed only in the accelerated decay kinetics of flash-induced variable fluorescence measured in the presence of DCMU. However, the mutants showed increased sensitivity to photodamage induced by visible and UV-B radiation, with higher loss of PSII activity in the AI than in the AIII strain. Thus, the difference between strains containing D1:1 and D1:2 found previously in Synechococcus 7942 is maintained after transfer of corresponding psbA genes into Synechocystis 6803 and is directly related to the coding region of these genes. The higher light sensitivity of the AI mutant is caused partly by the higher rate of photodamage and partly by the less efficient PSII repair.