Direct Effect Of Light Research Articles

Maternal entrainment of the developing circadian system in the Siberian hamster (Phodopus sungorus).

The aim of these studies was to investigate maternal entrainment of developing circadian locomotor activity rhythms in the Siberian hamster. In Experiment 1, mothers were transferred from a 16:8 LD cycle into constant dim red light (DD) from the day of parturition, and wheel-running activity of the mother and pups was individually monitored from the time of weaning. The phases of the individual pups' rhythms were found to be synchronized both to the phase of the mother and to the phase of lights off (ZT 12) of the photo cycle that the mother was exposed to until the day of parturition. To investigate whether this synchrony might reflect direct effects of light acting upon the fetal circadian system in late gestation, the experiment was repeated but with mothers placed into DD early in pregnancy (< or = day 7 of gestation). The results were similar to the first study, suggesting that the mother rather than the photo cycle during the latter part of gestation entrains the developing circadian system. The third experiment investigated whether this entrainment occurred during the postnatal period. Breeding pairs were maintained on alternative light-dark cycles, LD and DL, that were 12 h out of phase. Litters born to mothers on one light-dark cycle were exchanged on the day of birth with foster mothers from the reversed light-dark cycle, then raised in DD. Control litters exchanged between mothers from the same light-dark cycle had similar litter synchrony as shown by nonfostered litters of Experiment 1. However, pups cross-fostered with mothers on reversed LD cycles showed a very different distribution of pup phases. Pups were not synchronized to their natural mother but to their foster mother. Moreover, pups were more scattered over the 24-h period and were found to be significantly synchronized to the phase of the reversed LD cycle. These results demonstrate the occurrence of postnatal entrainment in the Siberian hamster. The increased scatter produced by the cross-fostering paradigm results from some litters being completely entrained to the phase of the foster mother, some with an intermediate distribution between the phase of the natural and foster mothers, and a minority being associated with the phase of the natural mother. These results suggest that Siberian hamster pups are initially synchronized either prenatally or at birth but that the mother continues to provide entrainment signals during the postnatal period.

The superior colliculus-pretectum mediates the direct effects of light on sleep.

Light and dark have immediate effects on sleep and wakefulness in mammals, but the neural mechanisms underlying these effects are poorly understood. Lesions of the visual cortex or the superior colliculus-pretectal area were performed in albino rats to determine retinorecipient areas that mediate the effects of light on behavior, including rapid eye movement sleep triggering by lights-off and redistribution of non-rapid eye movement sleep in short light-dark cycles. Acute responses to changes in light conditions were virtually eliminated by superior colliculus-pretectal area lesions but not by visual cortex lesions. Circadian entrainment was evident in both groups with lesions and in normal controls. Thus, acute light-dark effects on sleep and wakefulness appear to be mediated independently from cortical vision or circadian rhythms.

Refinement of Limit Cycle Oscillator Model of the Effects of Light on the Human Circadian Pacemaker

In 1990, Kronauer proposed a mathematical model of the effects of light on the human circadian pacemaker. Although this model predicted many general features of the response of the human circadian pacemaker to light exposure, additional data now available enable us to refine the original model. We first refined the original model by incorporating the results of a dose response curve to light into the model's predicted relationship between light intensity and the strength of the drive onto the pacemaker. Data from three bright light phase resetting experiments were then used to refine the amplitude recovery characteristics of the model. Finally, the model was tested and further refined using data from an extensive phase resetting experiment in which a 3-cycle bright light stimulus was presented against a background of dim light. In order to describe the results of the four resetting experiments, the following major refinements to the original model were necessary: (i) the relationship between light intensity (I) and drive onto the pacemaker was reduced fromI1.3toI0.23for light levels between 150 and 10000 lux; (ii) the van der Pol oscillator from the original model was replaced with a higher-order limit cycle oscillator so that amplitude recovery is slower near the singularity and faster near the limit cycle; (iii) a direct effect of light on circadian period (τx) was incorporated into the model such that asIincreases, τxdecreases, which is in accordance with “Aschoff's rule”.This refined model generates the following testable predictions: it should be difficult to enhance normal circadian amplitude via bright light; near the critical point of a type 0 phase response curve (PRC) the slope should be steeper than it is in a type 1 PRC; and circadian period measured during forced desynchrony should be directly affected by ambient light intensity.

Light induction of the clock-controlled gene ccg-1 is not transduced through the circadian clock in Neurospora crassa.

Ambient light and the circadian clock have been shown to be capable of acting either independently or in an interrelated fashion to regulate the expression of conidiation in the ascomycete fungus Neurospora crassa. Recently several molecular correlates of the circadian clock have been identified in the form of the morning-specific clock-controlled genes ccg-1 and ccg-2. In this paper we report studies on the regulation of ccg-1, an abundantly expressed gene displaying complex regulation. Consistent with an emerging consensus for clock-controlled genes and conidiation genes in Neurospora, we report that ccg-1 expression is induced by light, and show that this induction is independent of the direct effects of light on the circadian clock. Although circadian regulation of the gene is lost in strains lacking a functional clock, expression of ccg-1 is still not constitutive, but rather fluctuates in concert with changes in developmental potential seen in such strains. Light induction of ccg-1 requires the products of the Neurospora wc-1 and wc-2 genes, but surprisingly the requirement for wc-2 is suppressed in conditional mutants of cot-1, a gene that encodes, a cAMP-dependent protein kinase. These data provide insight into a complex regulatory web, involving at least circadian clock control, light control, metabolic control, and very probably developmental regulation, that governs the expression of ccg-1.

Monoterpene emission from ponderosa pine

We explore the variability in monoterpene emissions from ponderosa pine beyond that which can be explained by temperature alone. Specifically, we examine the roles that photosynthesis and needle monoterpene concentrations play in controlling emissions. We measure monoterpene concentrations and emissions, photosynthesis, temperature, and light availability in the late spring and late summer in a ponderosa pine forest in central Oregon. We use a combination of measurements from cuvettes and Teflon bag enclosures to show that photosynthesis is not correlated with emissions in the short term. We also show that needle monoterpene concentrations are highly correlated with emissions for two compounds, α‐pinene and β‐pinene, but that Δ‐carene concentrations are not correlated with emissions. We suggest that direct effects of light and photosynthesis do not need to be included in emission algorithms. Our results indicate that the role of needle concentration bears further investigation; our results for α‐pinene and β‐pinene are explainable by a Raoult's law relationship, but we cannot yet explain the cause of our results with Δ‐carene.

USE OF A SPECIALIZED MAGNETORECEPTION SYSTEM FOR HOMING BY THE EASTERN RED-SPOTTED NEWT NOTOPHTHALMUS VIRIDESCENS

Laboratory experiments were carried out to investigate the effects of varying the wavelength of light on the use of an earth-strength magnetic field for shoreward orientation and for the compass component of homing. In the earlier shoreward orientation experiments, newts tested under full-spectrum and short-wavelength (i.e. 400 and 450 nm) light exhibited shoreward magnetic compass orientation. Under long-wavelength (i.e. 550 and 600 nm) light, newts exhibited magnetic compass orientation that was rotated 90 &deg; counterclockwise to the shoreward direction. This wavelength-dependent shift in magnetic compass orientation was shown to be due to a direct effect of light on the underlying magnetoreception mechanism. In homing experiments, newts tested under full-spectrum and short-wavelength light exhibited homeward magnetic compass orientation. Under long-wavelength light, newts were randomly distributed with respect to the magnetic field. The different effects of long-wavelength light on shoreward orientation and homing confirmed earlier evidence that different magnetoreception systems mediate these two forms of orientation behaviour. The properties of the newt's homing response are consistent with the use of a hybrid magnetoreception system receiving inputs from the light-dependent magnetic compass and from a non-light-dependent intensity (or inclination) detector which, unlike the compass, is sensitive to the polarity of the magnetic field.

Sensory rhodopsin‐controlled release of the switch factor fumarate in Halobacterium salinarium

Halobacterium salinarium responds to blue light by reversing its swimming direction. Fumarate has been proposed as one of the molecular components of this sensory system and is involved in the switching process of the flagellar motor. In order to obtain chemical proof for this role of fumarate, cells were stimulated with a pulse of blue light and lysed by rapid mixing with distilled water. The lysate contained fumarate in free and bound form, which were separated by ultrafiltration. The fumarate concentration in the low-molecular-mass fraction (< 5 kDa) of the lysate was assayed enzymatically and a light-induced increase was observed. Additionally, the total cellular fumarate content decreased in response to light, indicating that fumarate was released from a cellular pool rather than being formed by de novo synthesis. The light-induced release was not detected in a mutant defective in sensory rhodopsin-I and -II. Therefore it is concluded that photoreceptor activation rather than a direct effect of light on the activity of metabolic enzymes causes fumarate release. For each photoactivated sensory rhodopsin-II molecule at least 350 molecules of fumarate were liberated demonstrating efficient amplification. The rate of light-induced fumarate release is at least 10-times faster than the fumarate turnover number of the citric acid cycle which was estimated as approximately 4300 per cell and second. Therefore this metabolic process is not expected to be part of the signal transduction chain in the halobacterial cell.

Light-induced isomerization and dimerization of cinnamic acid derivatives in cell walls

The role of light in the isomerization and cyclodimerization of the cinnamic acid component of plant cell walls has been examined in a number of ways. Cinnamic acid derivatives were extracted from neutral detergent fibre cell walls by alkaline hydrolysis and quantified by GC. Amounts of these acids in leaf and stem tissues of barley straw which had naturally been exposed to very different levels of radiation were compared. Leaf cell walls contained less p-coumaric acid than stem cell walls, but a higher proportion of this was found as the ( Z)-isomer and cyclodimer (4,4′-dihydroxy-α-truxillic acid). Samples of wheat straw from a sequence of 10 consecutive years, grown under conditions where meteorological conditions were the major variable, showed considerable year-to-year differences; the ( Z)-/( E)-ratio and dimer/monomer ratio varied three-fold. Additional studies compared the direct effect of light on the cinnamic acid derivatives in growing barley seedlings (live), freeze-dried seedlings (dead) and freshly harvested straw samples (dead). There were no significant changes in the cinnamic acid derivatives extracted from the cell walls of dead tissue which had been stored in the dark. Storage in light resulted in increased ( Z)-isomer and cyclodimer contents. These changes occurred whether the tissue was alive or dead. They can, therefore, be directly attributed to the effect of light, and do not appear to be mediated by any enzymic reactions.

Behavioural evidence for use of a light-dependent magnetoreception mechanism by a vertebrate

THE Earth's magnetic field provides an important source of directional information for terrestrial organisms1,5, but the sensory receptor or receptors responsible for magnetic field detection have yet to be identified. Theoretical models of the mechanism of magnetoreception have implicated specialized photoreceptors6,7. The proposed mechanisms would amplify the weak interaction of the geomagnetic field with a single electron spin to the level of photon detection, resulting in a modulation of the photoreceptor response to light. Although behavioural8,9 and neurophysiological10–12 studies have established a link between magnetic field sensitivity and the visual system, definitive evidence for the use of a light-dependent magnetoreception mechanism has been lacking. Here we show that magnetic compass orientation in a semiaquatic salamander is affected by the wavelength of light13, and that this wavelength-dependence is due to a direct effect of light on the underlying magnetoreception mechanism.

THE INWARD H+ PATHWAY IN BACTERIORHODOPSIN: THE ROLE OF M412 AND P(N)560 INTERMEDIATES*

Abstract— In purple bacteriorhodopsin sheets adsorbed onto the phospholipid‐impregnated collodion film, electrogenic stages are identified correlating with decays of the M and N(P)‐type intermediates. It is concluded that both M → N and N → bR transitions are electrogenic.The M decay is shown to be of a complex kinetics. In purple sheets, the lower the light intensity, the higher the rate of “slow M” decay. Such a dependence, which is absent from monomeric bacteriorhodopsin in proteoliposomes and from Triton X‐100‐solubilized protein, may be explained by the inhibiting effect of a light‐induced conformation change in a bacteriorhodopsin molecule upon the M decay in some other bacteriorhodopsin molecules within the same sheet.The light intensity‐independent “slow M” decay in solubilized bacteriorhodopsin is shown to correlate with the decay of the N intermediate and H+ uptake after the flash. In contrast to “fast M”, “slow M” is pH dependent, closely resembling in this respect the N intermediate. It is suggested that there is a fast light‐independent equilibration between M and N so that “slow M” represents the portion of the M pool that monitors the N concentration. The M → N equilibrium is assumed to be involved in the effect of the light‐induced electric field on the M decay. No direct effect of light on the equilibrium was found.

The direct effect of light therapy on endothelial cell proliferation in vitro.

During repair, new blood vessels are formed by the process of angiogenesis. The prerequisite to blood vessel formation is the proliferation of endothelial cells. The purpose of this study was to find out if light therapy is capable of affecting endothelial cell proliferation in vitro. The direct effect of light at wavelengths of either 660 or 820 nm was studied on primary cultures of bovine aortic endothelial cells using varying energy densities, of either 1, 2, 4, or 8 J/cm2. The proliferation of the endothelial cells was assessed over a period of five days after a single irradiation.

Light represses transcription of asparagine synthetase genes in photosynthetic and nonphotosynthetic organs of plants.

Asparagine synthetase (AS) mRNA in Pisum sativum accumulates preferentially in plants grown in the dark. Nuclear run-on experiments demonstrate that expression of both the AS1 and AS2 genes is negatively regulated by light at the level of transcription. A decrease in the transcriptional rate of the AS1 gene can be detected as early as 20 min after exposure to light. Time course experiments reveal that the levels of AS mRNA fluctuate dramatically during a "normal" light/dark cycle. This is due to a direct effect of light and not to changes associated with circadian rhythm. A novel finding is that the light-repressed expression of the AS1 gene is as dramatic in nonphotosynthetic organs such as roots as it is in leaves. Experiments demonstrate that the small amount of light which passes through the soil is sufficient to repress AS1 expression in roots, indicating that light has a direct effect on AS1 gene expression in roots. The negative regulation of AS gene expression by light was shown to be a general phenomenon in plants which also occurs in nonlegumes such as Nicotiana plumbaginifolia and Nicotiana tabacum. Thus, the AS genes can serve as a model with which to dissect the molecular basis for light-regulated transcriptional repression in plants.

Light Represses Transcription of Asparagine Synthetase Genes in Photosynthetic and Nonphotosynthetic Organs of Plants

Asparagine synthetase (AS) mRNA in Pisum sativum accumulates preferentially in plants grown in the dark. Nuclear run-on experiments demonstrate that expression of both the AS1 and AS2 genes is negatively regulated by light at the level of transcription. A decrease in the transcriptional rate of the AS1 gene can be detected as early as 20 min after exposure to light. Time course experiments reveal that the levels of AS mRNA fluctuate dramatically during a "normal" light/dark cycle. This is due to a direct effect of light and not to changes associated with circadian rhythm. A novel finding is that the light-repressed expression of the AS1 gene is as dramatic in nonphotosynthetic organs such as roots as it is in leaves. Experiments demonstrate that the small amount of light which passes through the soil is sufficient to repress AS1 expression in roots, indicating that light has a direct effect on AS1 gene expression in roots. The negative regulation of AS gene expression by light was shown to be a general phenomenon in plants which also occurs in nonlegumes such as Nicotiana plumbaginifolia and Nicotiana tabacum. Thus, the AS genes can serve as a model with which to dissect the molecular basis for light-regulated transcriptional repression in plants.

Light Regulation of Sink Metabolism in Tomato Fruit

Light/dark effects on growth and sugar accumulation in tomato (Lycopersicon esculentum) fruit during early development were studied on intact plants (in vivo) and in tissue culture (in vitro). Through the use of an in vitro culture of tomato fruit, it was possible to investigate the direct effects of light on sink metabolism by eliminating the source tissue. Similar growth patterns were found in vivo and in vitro. Fruit growth in different sugars indicated that sucrose was the best source of carbon for in vitro fruit growth. Fruit growth increased as sucrose concentration increased up to 8%. Darkening the fruit decreased fruit dry weight about 40% in vivo and in vitro. The differences in the CO(2) exchange rate between light and dark grown fruit indicated that light stimulation of fruit growth was due to mechanisms other than photosynthesis. Supporting this conclusion was the fact that light intensities ranging from 40 to 160 micromoles per square meter per second had no significant influence on fruit growth, and light did not increase growth of fruit cultured with glucose or fructose as a carbon source. However, light stimulated fruit growth significantly when sucrose was used as the carbon source. Light-grown fruit took up 30% more sucrose from the same source and accumulated almost twice as much hexose and starch as dark-grown fruit. A possible expansion of an additional sink for carbon by light stimulation of starch synthesis during early development will be discussed.

The Response of the Rat Urinary Bladder Microcirculation to Photodynamic Therapy

Light activation of dihematoporphyrin ether (photofrin II) has been used in the treatment of bladder tumors, yet the effects of this treatment on the normal urinary bladder microcirculation have not been determined. This study involved the use of in vivo television microscopy to observe the effects of light activation (530 to 560nm., 175mW/cm.2) on the urinary bladder microcirculation of female Sprague-Dawley rats. Animals pretreated with dihematoporphyrin ether 30minutes prior to light activation had high serum and low tissue concentrations of the photosensitizer and activation resulted in a statistically significant reduction of red blood cell column diameter in both arterioles and venules. The reduction was primarily due to mural thrombus formation with the occlusion remaining 60minutes after activation. Animals pretreated 48hours before activation had low serum and high tissue concentrations of dihematoporphyrin ether and activation had no microcirculatory effects apart from occasional platelet aggregation. These results suggest that the photodynamic effect on normal (non-neoplastic) tissue treated more than 48hours after administration of dihematoporphyrin ether is probably due to a direct effect of light and the sensitizer on the smooth muscle of the bladder rather than an effect on the microcirculation. (J. Urol, 142: 865–868, 1989)

Comparative analysis of the biogenesis of photosystem II in the wild-type and Y-1 mutant of Chlamydomonas reinhardtii.

Expression of the genes of the photosystem II (PSII) core polypeptides D1 and D2, of three proteins of the oxygen evolving complex of PSII and of the light harvesting chlorophyll a/b binding proteins (LHCP) has been compared in wild-type (wt) and in the y-1 mutant of Chlamydomonas reinhardtii. Since wt, but not y-1 cells produce a fully developed photosynthetic system in the dark, comparison of the two has allowed us to distinguish the direct effect of light from the influence of plastid development on gene expression. The PSII core polypeptides and LHCP are nearly undetectable in dark-grown y-1 cells but they accumulate progressively during light induced greening. The levels of these proteins in wt are the same in the light and the dark. The amounts of the proteins of the oxygen evolving complex do not change appreciably in the light or in the dark for both wt and y-1. Steady state levels of chloroplast mRNA encoding the core PSII polypeptides remain nearly constant in the light or the dark and are not affected by the developmental stage of the plastid. Levels of nuclear encoded mRNAs for the oxygen evolving proteins and of LHCP increase during light growth in wt and y-1. In contrast to wt, synthesis of LHCP proteins is not detectable in y-1 cells in the dark but starts immediately after transfer to light, indicating that LHCP synthesis is controlled by a light-induced factor or process. While the rates of synthesis of D1 and D2 are immediately enhanced by light in wt, this increase occurs only after a lag in y-1 and thus must be dependent on an early light-induced event in the plastid. These results show that the biosynthesis of PSII is affected by light directly, by the stage of plastid development, and by the interaction of light and events associated with plastid development.

Reduction of human sleep duration after bright light exposure in the morning

In 8 subjects the spontaneous termination of sleep was determined after repetitive exposure to either bright or dim light, between 6.00 and 9.00 h, on 3 days preceding sleep assessment. Sleep duration was significantly shorter following bright light than following dim light. During sleep the time course of EEG energy was not affected by the light treatment. Analysis of the time course of body temperature during sleep indicated an earlier rise of body temperature following the bright light treatment. In terms of the two-process model of sleep regulation this can be interpreted as a direct effect of light on the circadian phase of the wake up threshold.

Sudden infant deaths and clear weather in a subtropical environment

Particulate pollution levels were found to decrease, on average, over the 10-day period preceding SIDS incidence in a study of 369 cases over 15 years in Brisbane, Australia. This unexpected association could not be explained by correlations between daily pollution levels and daily precipitation, wind velocity, air temperature or cloud. Of the meteorological variables studied, which might have given rise to the particulate-SIDS associations, only visibility showed associations with SIDS incidence. Average visibility increased prior to SIDS in both summer and winter cases. It is hypothesised that these findings may be due to either direct effects of light, or due to increased outdoor exposure of infants and/or to changes in parental behaviour during clear weather.

Effect of phototherapy on plasma levels of GH, LH and FSH in the newborn

Plasma levels of GH, LH and FSH were measured in 74 three-day-old newborn infants with hyperbilirubinemia before and after exposure to continuous phototherapy (PhT) for 48 h. The results obtained were compared with data observed over the same period of time in 46 newborn infants belonging to the control group having homogeneous characteristics as far as form of delivery (spontaneous), gestation age, chronological age, sex, birth weight and basal blood glucose were concerned, except hyperbilirubinemia and necessity of PhT. Hyperbilirubinemic female newborn showed higher plasma GH concentrations in comparison with hyperbilirubinemic males and with controls. Forty-eight of continuous PhT significantly reduced GH levels which, however, appeared not to be substantially different from those of normal controls of the same age. Moreover, PhT determined a slight trend to increase in FSH of females, and did not modify the physiological decline of LH in both sexes during the first five days of life. The reduction of GH following PhT from abnormal to physiological concentrations may be due to the direct effect of light and/or to continuous light-related disorders of sleep. In conclusion, 48 h of continuous exposure to light (PhT) do not impair the newborn's pituitary functions here studied.

Control of psbA gene expression: in mature Spirodela chloroplasts light regulation of 32-kd protein synthesis is independent of transcript level

Spirodela oligorrhiza plants were used to study direct effects of light on plastid gene expression uncoupled from sequential chloroplast-developmental processes. Specific transcript levels were analysed using chloroplast, gene-fragment probes. Protein synthesis in vivo and in vitro was also measured. In tissue with mature chloroplasts, light/dark regimes had no substantial effect on transcript levels of the psbA gene coding for the 32-kd protein. However, under the same conditions, synthesis of the protein itself was dramatically affected. We conclude that in mature chloroplasts synthesis of 32-kd protein is regulated mainly at a translational level. Transcript levels of the rbcL gene, coding for the large subunit of ribulosebisphosphate carboxylase-oxygenase, were somewhat sensitive to light/dark effects, although not to the same degree as was synthesis of the protein. We conclude that translational events and transcript levels are involved in regulating synthesis of this polypeptide. Carbon deprivation in the dark reduced psbA and rbcL transcript levels appreciably below those found in non-starved, dark-grown tissue. This suggests that starvation and dark effects must be experimentally separated from each other for valid conclusions to be drawn about light/dark regulation of chloroplast gene expression.