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At least 397 records · Page 22Linked to original sources
PubMed1993

Neuroanatomical substrate for the dorsal light response. II. Effects of kainic acid-induced lesions of the valvula cerebelli on the goldfish dorsal light response.

The dorsal light response (DLR) to the continuously rotating light source was investigated in goldfish that had lesioned the valvula cerebelli. The body inclination was observed and analyzed for every 10 degrees of light rotation. The effects of selective lesions of the medial and lateral valvula cerebelli on the DLR were compared. After the lesion of the medial valvula cerebelli, the fish responded to the rotating light in the similar pattern to that seen preoperatively. However, after the unilateral lesion of the lateral valvula cerebelli, the fish did not respond to light from the side contralateral to the lesion, as if the fish had been unilaterally blindfolded. The lesion induced by kainic acid of the rostral and caudal part of the lateral valvula cerebelli differently influenced on the DLR. The DLR was impaired only after the caudal part of the lateral valvula cerebelli was lesioned by kainic acid. These findings suggest that the lateral valvula cerebelli in goldfish mediate the induction of the visually guided aspects of the DLR.

Animals↗
PubMed2006

A light-emitting diode light source for imaging of neural activities with voltage-sensitive dyes.

We tested the possibility of using a high-power monochromatic InGaN light-emitting diode (LED) as an excitation light source for real-time optical imaging using the voltage-sensitive dye RH-795. Driven with a custom-designed, non-feedback-controlled constant-current circuit, the LED generated stable light with rapid on/off. The LED was comparable with commonly used halogen lamps in exciting RH-795. Acoustically evoked responses in the auditory cortex recorded with the two light sources were highly similar. Our results thus suggest that a high-power LED can be successfully used as an excitation light source for voltage-sensitive dyes, without the need of optical filters and shutters.

Animals↗
PubMed2006

Translational regulation of light-harvesting complex expression during photoacclimation to high-light in Chlamydomonas reinhardtii.

When challenged with excess light, the green alga Chlamydomonas reinhardtii responds, in part, by down-regulating light harvesting capacity at Photosystem II while concomitantly reorganising cellular metabolism to increase sink capacity. We examined the role of translational control during different stages of photoacclimation by analysing polysome profiles of two different light-harvesting complex (LHC) genes encoding a major LHCII component (Lhcbm) and CP29 (Lhcb4) plus iron superoxide dismutase (FeSOD), and through measurement of protein synthesis by in vivo labelling. Within two hours following transfer of low-light (LL) acclimated cultures into high-light (HL), Lhcbm transcripts are off-loaded from polysomes indicating a decline in translational initiation. Lhcbm translational repression at two hours was specific since FeSOD mRNA remained associated with polysomes and in vivo labelling showed an increase in overall protein synthesis. After 4 hours HL exposure, however, a global disassembly of polysomes was detected suggesting a general decline in translational initiation. Interestingly, the decrease in polysomes coincides with maximal FeSOD transcript levels emphasizing that transcript profiles do not always accurately reflect gene expression. Within 8 hours after LL to HL shift, polysomes reform and all transcripts examined are loaded back onto polysomes. Disassembly of polysomes was mimicked by hydrogen peroxide application to non-shifted cultures suggesting that production of hydrogen peroxide due to HL-stress may effect the general decline in polysomes observed during HL acclimation.

Acclimatization↗
PubMed2000

Long-term light history modulates the light response kinetics of luminosity (L)-type horizontal cells in the roach retina.

We have examined the effects of prolonged periods of darkness on the responses of luminosity-type horizontal cells (L-HCs) in the freshwater cyprinid, Rutilus rutilus. Two groups of retinae were compared, those recorded after 10 min dark adaptation (SA) and those recorded after 3 h dark adaptation (LA). The results suggest that long-term light history does not modify the general responsiveness of the L-HCs in this species. However, there are apparent changes in the receptive field of the cells and modifications to the kinetics of the light-evoked response. The kinetics changes involve both a delay in the onset of light response and a selective effect on the hyperpolarizing light-ON response. Thus the mean time constant (tau) for the SA cells was 32.4+/-2.39 ms (n=62), whilst that for the LA cells was 53.4+/-3.03 ms (n=61). These effects occur in the absence of changes in the relative spectral sensitivity or threshold sensitivity of the HCs. The results suggest that in some vertebrate retinae, prolonged darkness (light-history) may regulate long-term plasticity in the kinetics of the cone-HC pathway.

Animals↗
PubMed1996

Effect of light exposure on fracture toughness and flexural strength of light-cured composites.

OBJECTIVES: This study was conducted to investigate the curing characteristics of light-cured composites and their related mechanical properties. METHODS: Single-edge notch specimens [25 mm x 2.5 mm x 5 mm with a 5 mm notch (a/W = 0.5)] were prepared for fracture toughness measurements. For flexural strength testing, a stainless steel mold (25 mm x 2 mm x 2 mm) was used. Light-cured composites were condensed into the mold, and the middle third of the specimen was first activated for 30 s with 400 mW/cm2, for 60 s with 200 mW/cm2, or for 120 s with 100 mW/cm2. Then the remaining thirds were activated at the same intensity and curing time as the middle third. After 24 h storage in 37 degrees C water, three-point bending tests were performed with a span length of 20 mm at a crosshead speed of 0.5 mm/min. A one-way ANOVA, followed by a Newman-Keuls test (p < 0.05), were used to compare the data obtained from each group to test the effect of the curing conditions. RESULTS: Fracture toughness, flexural strength, and flexural modulus varied with resin composites. Among the three curing conditions for each material, there were no significant differences in fracture toughness, flexural strength, or flexural modulus. SIGNIFICANCE: The fracture toughness and the flexural strength were the same when irradiations with the same amount of energy (light intensity multiplied by curing time) were used. It was found that, at lower light intensity, longer curing was required to provide comparable mechanical properties. An accumulated irradiation energy obtained through a product of the light intensity and curing time may serve as a guideline to produce samples exhibiting equivalent fracture toughness as well as flexural strengths.

Analysis of Variance↗
PubMed1998

Light transmittance characteristics of light-cured composite resins.

OBJECTIVES: The purpose of this study was: (1) to examine the light transmittance characteristics of various shades of light-cured composite resins, and (2) to evaluate the effect of light transmittance characteristics on the color of the resins. METHODS: Eleven shades of two composite resins were used. Specimens with four different thicknesses (0.5, 1.0, 2.0 and 3.0 mm) were prepared. The transmittance at wavelengths from 400 to 700 nm was measured. Also, the color values and the color differences among thicknesses of a specimen on the CIE L*a*b* color system were determined by a digital chroma meter. The differences in the transmittance, color values and color difference were determined by using a one-way analysis of variance (ANOVA) combined with a Tukey multiple-range test. RESULTS: Significant differences were found in the wavelength dependence of transmittance between the two materials, and among shades of each material. The transmittances of the darker shades of one material were significantly lower at lower wavelengths than the other shades, but were nearly equal or significantly higher at higher wavelengths. There was a significant correlation between the changing ratio of transmittance and the color difference. Two materials showed significant differences in delta a* and delta b* of the chromatic component of color difference. SIGNIFICANCE: The results of this study indicate that light transmittance characteristics, including the wavelength dependence, play an important role for the color of a composite resin. The significant difference in light transmittance characteristics among materials and shades will affect their clinical appearance.

Analysis of Variance↗
PubMed1992

Light-evoked contraction of red absorbing cones in the Xenopus retina is maximally sensitive to green light.

To test the hypothesis that light-evoked cone contraction in eye cups from Xenopus laevis is controlled through a direct mechanism initiated by the cone's own photopigment, we conducted spectral-sensitivity experiments. We estimate that initiation of contraction of red absorbing cones (611 nm) is 1.5 log units more sensitive to green (533 nm) than red (650 nm) light stimuli. The difference is comparable to that predicted from the spectral-sensitivity function of the green absorbing, principal rod (523 nm). Furthermore, 480-nm and 580-nm stimuli which are absorbed nearly equally by the principal rod have indistinguishable effects on cone contraction. We also found that light blockade of nighttime cone elongation is much more sensitive to green than to red light stimuli. Our observations are inconsistent with the hypothesis tested, and suggest that light-regulated cone motility is controlled through an indirect mechanism initiated primarily by the green absorbing, principal rod.

Animals↗
PubMed1999

Effects of light exposure and sleep displacement on dim light melatonin onset.

The purpose of the study was to induce in two different ways, a phase-angle difference between the circadian pacemaker and the imposed sleep-wake cycle in humans, we intended to: (i) shift the circadian pacemaker by exposure to bright light and keep the timing of the sleep-wake cycle fixed; and (ii) keep the timing of the circadian pacemaker fixed by a constant light-dark cycle and displace sleep. We monitored dim light melatonin onset (DLMO), core body temperature and sleep. DLMO was delayed significantly after 3 days of a 3-h delayed sleep-phase when compared with 3 days of sleep at a normal or 3-h advanced sleep-phase. The shifts in DLMO were not accompanied by shifts in body temperature, changes in waking-up time or by a change in the duration of the first rapid eye movement (REM) sleep episode. Three days of light exposure in the morning or evening resulted in shifts in DLMO of similar magnitude, but this was accompanied by shifts in the rhythm of body temperature, changes in waking-up time and in the duration of the first REM sleep episode. We conclude that the changes observed after light exposure reflect shifts in the circadian pacemaker. In contrast, we propose that the changes observed in DLMO after sleep displacement are not mediated by the circadian pacemaker. These results raise some doubts about the reliability of DLMO as a marker of circadian phase in cases of sleep disturbances. Finally, we initiate a search for changes in sleep that might be responsible for the unexpected effects on DLMO.

Adult↗
PubMed1994

Promoter and leader sequences of the spinach PsaD and PsaF genes direct an opposite light response in tobacco cotyledons: PsaD sequences downstream of the ATG codon are required for a positive light response.

Subunits II and III of the photosystem I reaction centre are encoded by the nuclear genes PsaD and PsaF, respectively. In spinach, the expression of both genes is highly synchronized with regard to time, space and in response to stimulators such as light. Nevertheless, promoter sequences as well as the design and location of regulatory elements are strikingly different. Promoter and leader of PsaF, when fused to the GUS reporter gene, direct a positive light response in the cotyledons of transgenic tobacco seedlings. In contrast, the equivalent PsaD regions confer a negative-light regulation to the GUS gene. If a 6-kb fragment that contains 1802 bp of the promoter, the transcription unit as well as additional 2.5 kb downstream of the PsaD gene is introduced into tobacco, the transcript level from the PsaD transgene is positively light-regulated in tobacco cotyledons. Thus, regulatory elements of the spinach PsaD and PsaF promoters are arranged in a very different way and essential cis-determinants for the positive light response of the PsaD gene can be located within the coding region and/or even further downstream.

Base Sequence↗
PubMed2000

The alternative oxidase in roots of poa annua after transfer from high-light to low-light conditions.

The activity of the alternative pathway can be affected by a number of factors, including the amount and reduction state of the alternative oxidase protein, and the reduction state of the ubiquinone pool. To investigate the importance of these factors in vivo, we manipulated the rate of root respiration by transferring the annual grass Poa annua L. from high-light to low-light conditions, and at the same time from long-day to short-day conditions for four days. As a result of the low-light treatment, the total respiration rate of the roots decreased by 45%, in vitro cytochrome c oxidase capacity decreased by 49%, sugar concentration decreased by 90% and the ubiquinone concentration increased by 31%, relative to control values. The absolute rate of oxygen uptake via the alternative pathway, as determined using the 18O-isotope fractionation technique, did not change. Conversely, the cytochrome pathway activity decreased during the low-light treatment; its activity increased upon addition of exogenous sugars to the roots. Interestingly, no change was observed in the concentration of the alternative oxidase protein or in the reduction state of the protein. Also, there was no change in the reduction state of the ubiquinone pool. In conclusion, the concentration and activity of the alternative oxidase were not changed, even under severe light deprivation.

Carbohydrate Metabolism↗
PubMed1976

Light-chain nephropathy. Renal tubular dysfunction associated with light-chain proteinuria.

We observed idiopathic light-chain proteinuria in a patient with multiple abnormalities of proximal-tubule transport mechanisms (Fanconi syndrome), nephrogenic diabetes insipidus, and distal renal tubular acidosis. Seventeen of the 19 urinary amino acid levels measured were elevated. Uric acid and phosphate clearances were greater than 60 per cent and 50 per cent, respectively, of the simultaneous inulin clearance. When water deprivation was coupled with vasopressin administration, the maximum urinary concentration observed was 384 mOsm per kilogram of water. During ammonium-chloride loading, the level of hydrogen-ion concentration in the urine remained less than 100 times that in the blood. Kappa light-chain excretion was 149 mg per 24 hours. It appears that the concurrence of proximal tubular dysfunction, distal tubular dysfunction and light-chain proteinuria represents a distinct syndrome, which we call "combined light-chain nephropathy." Available evidence indicates that excessive light-chain production with subsequent filtration, reabsorption and catabolism, causes the complex tubular dysfunctions observed.

Acidosis, Renal Tubular↗
PubMed2005

On the gating mechanisms of the light-dependent conductance in Pecten hyperpolarizing photoreceptors: does light remove inactivation in voltage-dependent K channels?

The hyperpolarizing receptor potential of ciliary photoreceptors of scallop and other mollusks is mediated by a cGMP-activated K conductance; these cells also express a transient potassium current triggered by depolarization. During steady illumination, the outward currents elicited by voltage steps lose their decay kinetics. One interesting conjecture that has been proposed is that the currents triggered by light and by depolarization are mediated by the same population of channels, and that illumination evokes the receptor potential by removing their steady-state inactivation. Exploiting the information that has become available on the phototransduction cascade of ciliary photoreceptors, we demonstrated that the same downstream signaling elements are implicated in the modulation of voltage-elicited currents: direct chemical stimulation both at the level of the G protein and of the final messenger that controls the light-dependent channels (cGMP) also attenuate the falling phase of the voltage-activated current. Application of a protein kinase G antagonist was ineffective, suggesting that a cGMP-initiated phosphorylation step is not implicated. To ascertain the commonality of ionic pathways we used pharmacological blockers. Although millimolar 4-aminopyridine (4-AP) suppressed both currents, at micromolar concentrations only the photocurrent was blocked. Conversely, barium completely and reversibly antagonized the transient voltage-activated current with no detectable effect on the light-evoked current. These results rule out that the same ionic pores mediate both currents; the mechanism of light modulation of the depolarization-evoked K current was elucidated as a time-dependent increase in the light-sensitive conductance that is superimposed on the inactivating K current.

Animals↗
PubMed1958

Delayed light action spectra of several algae in visible and ultraviolet light.

Action spectra for delayed light production by several algae were determined from 250 to 750 mmicro incident light. In the visible portion of the spectrum the action spectra resemble those reported by previous workers for photosynthesis and light emission. Blue-green algae had a maximum at 620 mmicro, red algae at 550 mmicro, whereas green and brown algae have action spectra corresponding to chlorophyll and carotenoid absorption. In the ultraviolet portion of the spectrum delayed light is emitted by algae down to 250 mmicro incident light. The action spectra of the different algae are not alike in the ultraviolet portion of the spectrum. This indicates that pigments other than chlorophyll must be sensitizing or shielding the algae in the ultraviolet region.

Eukaryota↗
PubMed1991

Multiple conductance states of the light-activated channel of Limulus ventral photoreceptors. Alteration of conductance state during light.

The properties of light-dependent channels in Limulus ventral photoreceptors have been studied in cell-attached patches. Two sizes of single-channel events are seen during illumination. Previous work has characterized the large (40 pS) events; the goal of the current work was to characterize the small (15 pS) events and determine their relationship to the large events. The small events are activated by light rather than as a secondary result of the change in membrane voltage during light. The mean open time of the small events is 1.34 +/- 0.49 ms (mean +/- SD, n = 15), approximately 50% of that of the large events. The large and small events have the same reversal potential and a similar dependence of open-state probability on voltage. Evidence that these events are due to different conductance states of the same channel comes from analysis of relatively infrequent events showing a direct transition between the 15 and 40-pS levels. Furthermore, large and small events do not superpose, even at positive voltages when the probability of being open is very high, as would be predicted if the two-sized events were due to independent channels. Expression of the different conductance states is not random; during steady illumination there are alternating periods of several hundred milliseconds in which there are consecutive, sequential large events followed by periods in which there are consecutive, sequential small events. At early times during the response to a step of light, the large conductance state is preferentially expressed. At later times, there is an increase in the relative contribution of the low conductance state. These findings indicate that there is a process that changes the preferred conductance state of the channel. This alteration has functional importance in the process of light adaptation.

Animals↗
PubMed2001

Characterization of cDNA of the liverwort phytochrome gene, and phytochrome involvement in the light-dependent and light-independent protochlorophyllide oxidoreductase gene expression in Marchantia paleacea var. diptera.

The cDNA of the phytochrome gene in the liverwort Marchantia paleacea var. diptera (MpdPHY1) was isolated. MpdPHY1 encoded a conventional phytochrome apoprotein. The MpdPHY1 transcript was accumulated in the dark and suppressed in the light. The degradation of the MpdPHY1 transcript by red light irradiation had red/far-red reversibility, suggesting that the liverwort phytochrome gene expression was regulated by a phytochrome. Northern blot analysis of the transcripts in cells irradiated by red/far-red light revealed that the liverwort phytochrome was involved in the expressions of chlB, chlL, chlN, or por, which encode subunits of light-independent and light-dependent protochlorophyllide oxidoreductase, respectively.

Amino Acid Sequence↗
PubMed2001

Photosynthetic light response of flooded cherrybark oak (Quercus pagoda) seedlings grown in two light regimes.

Two-year-old cherrybark oak (Quercus pagoda Raf.) seedlings raised in full or partial (27%) sunlight were flooded for 30 days to study the effects of light availability and root inundation on photosynthetic light response. Compared with seedlings receiving full sunlight, seedlings receiving partial sunlight developed leaves with 90% greater blade area, 26% less mass per unit volume, and 35% lower nitrogen (N) concentration per unit area, leading to a 15% reduction in leaf photosynthetic capacity when carbon exchange rates were based on blade area. However, when carbon exchange rates were based on leaf mass, leaves acclimated to partial sunlight exhibited a 15% greater photosynthetic capacity realized primarily through an increased initial slope of the photosynthetic light response (A/PPFD) curve and increased net photosynthesis at leaf saturation (Amax). Short-term flooding increased leaf mass per unit area more than 19%, reduced foliar N concentrations per unit dry mass by 19%, and initiated reductions in Amax and apparent quantum yield (phi) of seedlings in both light regimes. Greatest impairment of Amax (56% area basis, 65% mass basis) and phi (40%) were observed in leaves receiving full sunlight, and the declines were concomitant with a 35% decrease in chlorophyll concentration. Flooding also depressed instantaneous photosynthetic N-use efficiency (PPNUE) such that Amax decreased 54%, and the initial slope of PPNUE/PPFD curves decreased 33 and 50% for leaves acclimated to partial and full sunlight, respectively. The A/PPFD patterns indicated that the magnitude of flood-induced inhibition of the photosynthetic mechanism of cherrybark oak seedlings is determined partly by the light environment.

Light↗
PubMed2001

Canopy structure and light interception in Quercus petraea seedlings in relation to light regime and plant density.

Foliage structure was measured on 1- and 2-year-old Quercus petraea (Matt.) Liebl. seedlings grown in 100 or 18% sunlight at a planting density of 2.8 or 25 plants per m(2). A three-dimensional digitizing device was used to acquire the spatial position and orientation of all leaves within the seedlings and of all seedlings within the plot. The data were used to obtain (1) quantitative information on canopy structure, including leaf area index (LAI), seedling leaf area, number of leaves, leaf area density and leaf orientation; and (2) structural information on foliage arrangement from virtual images to estimate light interception by individual seedlings (STAR) and light partitioning among seedlings. During the second year, shading significantly reduced total leaf area and number of leaves but increased individual leaf area. The STAR was greater for seedlings in shade than in full sunlight because of the more horizontal orientation of leaves. Leaf area density was unaffected by the full sun treatments, and changes in leaf area dispersion had no effect on light-interception efficiency. No plant density effect was observed during the first year. During the second year, only the high plant density treatment induced mutual shading between seedlings, resulting in greater competition for light among seedlings in the full sun treatment than in the shade treatment. The small treatment-induced changes in light interception indicate that Q. petraea has low morphological plasticity of foliage structure compared with other species.

Light↗
PubMed1994

Overexpression of Arabidopsis COP1 results in partial suppression of light-mediated development: evidence for a light-inactivable repressor of photomorphogenesis.

Arabidopsis seedlings are genetically endowed with the capability to follow two distinct developmental programs: photomorphogenesis in the light and skotomorphogenesis in darkness. The regulatory protein CONSTITUTIVE PHOTO-MORPHOGENIC1 (COP1) has been postulated to act as a repressor of photomorphogenesis in the dark because loss-of-function mutations of COP1 result in dark-grown seedlings phenocopying the light-grown wild-type seedlings. In this study, we tested this working model by overexpressing COP1 in the plant and examining its inhibitory effects on photomorphogenic development. Stable transgenic Arabidopsis lines overexpressing COP1 were generated through Agrobacterium-mediated transformation. Overexpression was achieved using either the strong cauliflower mosaic virus 35S RNA promoter or additional copies of the wild-type gene. Analysis of these transgenic lines demonstrated that higher levels of COP1 can inhibit aspects of photomorphogenic seedling development mediated by either phytochromes or a blue light receptor, and the extent of inhibition correlated quantitatively with the vivo COP1 levels. This result provides direct evidence that COP1 acts as a molecular repressor of photomorphogenic development and that multiple photoreceptors can independently mediate the light inactivation of COP1. It also suggests that a controlled inactivation of COP1 may provide a basis for the ability of plants to respond quantitatively to changing light signals, such as fluence rate and photoperiod.

Arabidopsis↗