Broad Range Of Light Intensities Research Articles

Enhancement for the synthesis of bio-energy molecules (carbohydrates and lipids) in Desmodesmus subspicatus: experiments and optimization techniques

Microalgae are regarded as renewable resources of energy, foods and high-valued compounds using a biorefinery approach. In the present study, we explored isolated microalgae (Desmodesmus subspicatus) for the production of bio-energy molecules (carbohydrate and lipid). Optimizations of media (BG-11) components have been made using the Taguchi orthogonal array (TOA) technique to maximize biomass, carbohydrate and lipid production. Optimized results showed that biomass, carbohydrates and lipid productivity increased by 1.3 times at optimal combinations of media components than standard BG-11 media. Further, the influence of various carbon and nitrogen sources as nutritional supplement with optimum media composition under different light intensities was investigated for productivity of carbohydrate and lipid. Results demonstrated that 1.5 times higher productivity of carbohydrate and lipids were achieved in the presence optimum BG-11 under a broad range of light intensities (84–504 µmol m−2 s−1). Among different nitrogen sources, glycine was found to give higher productivity (1.5 times) followed by urea. Use of the cellulose as a carbon source in the media significantly increases biomass (2.4 times), carbohydrates (2.3 times) and lipids (2.3 times) productivity. Investigations revealed that cultivating Desmodesmus subspicatus under optimum culture conditions has the potential for large-scale bio-ethanol and bio-diesel production.

Cryo-EM structures of thylakoid-located voltage-dependent chloride channel VCCN1.

In the light reaction of plant photosynthesis, modulation of electron transport chain reactions is important to maintain the efficiency of photosynthesis under a broad range of light intensities. VCCN1 was recently identified as a voltage-gated chloride channel residing in the thylakoid membrane, where it plays a key role in photoreaction tuning to avoid the generation of reactive oxygen species (ROS). Here, we present the cryo-EM structures of Malus domestica VCCN1 (MdVCCN1) in nanodiscs and detergent at 2.7 Å and 3.0 Å resolutions, respectively, and the structure-based electrophysiological analyses. VCCN1 structurally resembles its animal homolog, bestrophin, a Ca2+-gated anion channel. However, unlike bestrophin channels, VCCN1 lacks the Ca2+-binding motif but instead contains an N-terminal charged helix that is anchored to the lipid membrane through an additional amphipathic helix. Electrophysiological experiments demonstrate that these structural elements are essential for the channel activity, thus revealing the distinct activation mechanism of VCCN1.

Light intensity and spectral composition drive reproductive success in the marine benthic diatom Seminavis robusta

The properties of incident light play a crucial role in the mating process of diatoms, a group of ecologically important microalgae. While species-specific requirements for light intensity and photoperiod have been observed in several diatom species, little is known about the light spectrum that allows sexual reproduction. Here, we study the effects of spectral properties and light intensity on the initiation and progression of sexual reproduction in the model benthic diatom Seminavis robusta. We found that distinct stages of the mating process have different requirements for light. Vigorous mating pair formation occurred under a broad range of light intensities, ranging from 10 to 81 µE m−2 s−1, while gametogenesis and subsequent stages were strongly affected by moderate light intensities of 27 µE m−2 s−1 and up. In addition, light of blue or blue–green wavelengths was required for the formation of mating pairs. Combining flow cytometric analysis with expression profiling of the diatom-specific cyclin dsCyc2 suggests that progression through a blue light-dependent checkpoint in the G1 cell cycle phase is essential for induction of sexual reproduction. Taken together, we expand the current model of mating in benthic pennate diatoms, which relies on the interplay between light, cell cycle and sex pheromone signaling.

Shedding light on dark adaptation.

The retina is famous for its ability to operate under a broad range of light intensities. This is partly due to the presence of two types of photoreceptor cells, rods and cones. Rods are used mostly for dim light vision, and cones are used for bright light and colour vision. These cells are also able to adapt to a broad range of light intensities using light- and dark-adaptation mechanisms. Dark adaptation is used by the vertebrate retina to increase its visual sensitivity when moving from a brightly lit environment to a dark environment. The brighter the surrounding light, the longer it takes for the retina to adapt to the dark. Most retina biologists have studied dark adaptation by exposing animals to a 90% bleach, meaning that 90% of the light-sensing proteins in these photoreceptor cells have been activated, followed by transfer of these animals to a dark room and analysis of their light sensitivity using electrophysiological methods. In this report, we introduce the basic elements of the visual system and describe how the system might operate during dark adaptation. We also introduce a novel role for cAMP-mediated phosphorylation of G protein-coupled receptor kinase 1 (GRK1), a major kinase in visual signalling.

Performance Bounds on Passive Indoor Positioning Using Visible Light

In this article, a novel method for passive indoor localization using LED luminaires is proposed where explicit user participation is not required. This approach measures changes in the impulse response between sources and receivers and estimates a location based on optical channel sounding data. An exponential integrating-sphere model is used to represent object impulse response (OIR) from each luminaire source-receiver pair, which is obtained by subtracting impulse response (IR) of the room background (i.e., without an object) from IR when the object is present inside the room. This model is represented as a function of 3D position of the object and depends on both source and receiver parameters and the physical geometry of the room. An analytical expression of the Cramér-Rao lower bound (CRLB) on the proposed passive indoor localization method is derived. The position is also estimated by using a maximum likelihood (ML) estimator which gives the position estimate by maximizing the log-likelihood function of the received noisy OIR waveforms. The results show that the signal-to-noise ratio (SNR) and number of source-receiver pairs used in the estimation, play a crucial role in performance. Typical localization root-mean squared error is less than 10 cm over a broad range of light intensities and object locations.

Highly sensitive in situ-synthesized cadmium sulfide (CdS) nanowire photosensor for chemiluminescent immunoassays

Highly sensitive in situ-synthesized cadmium sulfide (CdS) nanowires (NWs) for the detection of chemiluminescence in immunoassays with a photoresist (PR) layer to stabilize the CdS NWs before and after coating with a parylene film were developed. The thickness of the PR layer was controlled by adjusting the viscosity of the PR solution used for spin-coating. PR2005 was the optimal PR for passivation of the NW surface. After the addition of a parylene coating on the CdS NWs, the photocurrent increased by as much as 50% over a broad range of light intensities, and the additional PR layer increased the photoresponse over the whole range of light intensities. When the photoresponses of the CdS NWs with and without the parylene film were compared after the addition of a PR layer, significant differences were observed in the photocurrent behavior after the incident light was turned off. For the CdS NWs with a parylene film and PR layer, the photocurrent reached the baseline within milliseconds of the incident light being turned off. However, the CdS NWs without a parylene film but with a PR layer required >60 s to reach the baseline level. This difference was due to the capacitance arising from the contact between the NWs. The in situ-synthesized CdS NW photosensor passivated by the parylene film and a PR layer was used in a chemiluminescence-based immunoassay. Finally, the detection of human immunodeficiency virus antibodies was demonstrated via a chemiluminescent enzyme-linked immunosorbent assay based on the CdS NW photosensor in comparison with the optical-density measurement for the chromogenic reaction of TMB(3,3′,5,5′-Tetramethylbenzidine).

Nonreciprocity in Photonic Structures with Phase-Change Components

We consider the scattering problem for an asymmetric composite photonic structure with a component experiencing a thermally driven phase transition. Using a numerical example, we show that if the heating is caused by the incident light, the transmittance can become highly asymmetric within a broad range of light intensities. This effect can be utilized for directional light transmission, asymmetric optical limiting, or power switching.

Dim Light Exposure and Myopia in Children.

PurposeExperimental myopia in animal models suggests that bright light can influence refractive error and prevent myopia. Additionally, animal research indicates activation of rod pathways and circadian rhythms may influence eye growth. In children, objective measures of personal light exposure, recorded by wearable light sensors, have been used to examine the effects of bright light exposure on myopia. The effect of time spent in a broad range of light intensities on childhood refractive development is not known. This study aims to evaluate dim light exposure in myopia.MethodsWe reanalyzed previously published data to investigate differences in dim light exposure across myopic and nonmyopic children from the Role of Outdoor Activity in Myopia (ROAM) study in Queensland, Australia. The amount of time children spent in scotopic (<1–1 lux), mesopic (1–30 lux), indoor photopic (>30–1000 lux), and outdoor photopic (>1000 lux) light over both weekdays and weekends was measured with wearable light sensors.ResultsWe found significant differences in average daily light exposure between myopic and nonmyopic children. On weekends, myopic children received significantly less scotopic light (P = 0.024) and less outdoor photopic light than nonmyopic children (P < 0.001). In myopic children, more myopic refractive errors were correlated with increased time in mesopic light (R = −0.46, P = 0.002).ConclusionsThese findings suggest that in addition to bright light exposure, rod pathways stimulated by dim light exposure could be important to human myopia development. Optimal strategies for preventing myopia with environmental light may include both dim and bright light exposure.

Bumblebees Perform Well-Controlled Landings in Dim Light

To make a smooth touchdown when landing, an insect must be able to reliably control its approach speed as well as its body and leg position—behaviors that are thought to be regulated primarily by visual information. Bumblebees forage and land under a broad range of light intensities and while their behavior during the final moments of landing has been described in detail in bright light, little is known about how this is affected by decreasing light intensity. Here, we investigate this by characterizing the performance of bumblebees, B. terrestris, landing on a flat platform at two different orientations (horizontal and vertical) and at four different light intensities (ranging from 600 lx down to 19 lx). As light intensity decreased, the bees modified their body position and the distance at which they extended their legs, suggesting that the control of landing in these insects is visually mediated. Nevertheless, the effect of light intensity was small and the landings were still well controlled, even in the dimmest light. We suggest that the changes in landing behavior that occurred in dim light might represent adaptations that allow the bees to perform smooth landings across the broad range of light intensities at which they are active.

State transitions redistribute rather than dissipate energy between the two photosystems in Chlamydomonas.

Photosynthesis converts sunlight into biologically useful compounds, thus fuelling practically the entire biosphere. This process involves two photosystems acting in series powered by light harvesting complexes (LHCs) that dramatically increase the energy flux to the reaction centres. These complexes are the main targets of the regulatory processes that allow photosynthetic organisms to thrive across a broad range of light intensities. In microalgae, one mechanism for adjusting the flow of energy to the photosystems, state transitions, has a much larger amplitude than in terrestrial plants, whereas thermal dissipation of energy, the dominant regulatory mechanism in plants, only takes place after acclimation to high light. Here we show that, at variance with recent reports, microalgal state transitions do not dissipate light energy but redistribute it between the two photosystems, thereby allowing a well-balanced influx of excitation energy.

Chlorophyll fluorescence imaging as a tool to monitor the progress of a root pathogen in a perennial plant.

The chlorophyll fluorescence parameter ΦNO is an excellent metric for the non-destructive monitoring of disease progression, measured over a broad range of light intensities. The suitability of the slow induction chlorophyll fluorescence parameters ΦPSII, ΦNPQ, and ΦNO to monitor in vivo disease progression in a host-root pathogen pathosystem was evaluated and compared to the established method of monitoring disease by measuring Fv/Fm. Using the infection of ginseng plants (Panax quinquefolius L.) with Pythium irregulare Buisman as a model, light response curves were used to establish the optimal irradiance for the resolution of differences between fluorescence parameters ΦPSII, ΦNPQ and ΦNO. As infection progressed only changes in ΦNO remained consistent with increased irradiance, and increased as infection progressed. Furthermore, ΦNO showed a high sensitivity for distinguishing increased disease load. In contrast, the magnitude in change of ΦPSII and ΦNPQ were sensitive to irradiance levels. The magnitude of increase in ΦNO per unit disease score was equivalent to the corresponding decline in Fv/Fm values. Thus ΦNO is as sensitive as Fv/Fm in monitoring biotic stress. The ability to measure ΦNO under a wide range of light intensities, including natural light, potentially without the need for dark adaptation, means that it can be used in the development of a general protocol for non-invasive, in vivo monitoring of plant health, from the laboratory to the field scale.

Generalized receptor law governs phototaxis in the phytoplankton Euglena gracilis

Phototaxis, the process through which motile organisms direct their swimming toward or away from light, is implicated in key ecological phenomena (including algal blooms and diel vertical migration) that shape the distribution, diversity, and productivity of phytoplankton and thus energy transfer to higher trophic levels in aquatic ecosystems. Phototaxis also finds important applications in biofuel reactors and microbiopropellers and is argued to serve as a benchmark for the study of biological invasions in heterogeneous environments owing to the ease of generating stochastic light fields. Despite its ecological and technological relevance, an experimentally tested, general theoretical model of phototaxis seems unavailable to date. Here, we present accurate measurements of the behavior of the alga Euglena gracilis when exposed to controlled light fields. Analysis of E. gracilis' phototactic accumulation dynamics over a broad range of light intensities proves that the classic Keller-Segel mathematical framework for taxis provides an accurate description of both positive and negative phototaxis only when phototactic sensitivity is modeled by a generalized "receptor law," a specific nonlinear response function to light intensity that drives algae toward beneficial light conditions and away from harmful ones. The proposed phototactic model captures the temporal dynamics of both cells' accumulation toward light sources and their dispersion upon light cessation. The model could thus be of use in integrating models of vertical phytoplankton migrations in marine and freshwater ecosystems, and in the design of bioreactors.

A dynamic scaling algorithm for the optimized digital display of VIIRS Day/Night Band imagery

The VIIRS Day/Night Band (DNB) is a visible and near-infrared sensor that is sensitive to a broad range of light intensities ranging from daylight down to airglow at night. The on-board calibration of the DNB allows for the quantification of radiance values over the full range of the instrument’s sensitivity, unlike the heritage Operational Linescan System (OLS). For scenes that span the day/night terminator, observed DNB radiance values may vary by up to eight orders of magnitude. Consequently, it is impractical to display the full range of radiance values in a single digital image. In this work, an algorithm is presented that scales the observed radiance values between expected maximum and minimum values that are a function of solar and lunar zenith angles as well as the fraction of the lunar disc that is illuminated by the Sun. This dynamic scaling algorithm preserves scene contrast over the full range of solar and lunar illumination conditions, similar to the Near Constant Contrast (NCC) imagery product. Unlike the NCC algorithm, however, the ‘erf-dynamic scaling’ algorithm (so-called for its likeness to the Gauss error function) presented here requires no ancillary information outside of what is included in the DNB data distributed according to the Joint Polar Satellite System (JPSS) program file standards. Results indicate that this algorithm has improved performance over simple methods for displaying DNB imagery and, in some instances, may exceed the performance of the NCC product itself. This algorithm is expected to replace many ad hoc methods of displaying DNB imagery and may serve as a substitute for operational users that do not have access to the NCC product.

Economic photoprotection in photosystem II that retains a complete light-harvesting system with slow energy traps.

The light-harvesting antenna of higher plant photosystem II has an intrinsic capability for self-defence against intense sunlight. The thermal dissipation of excess energy can be measured as the non-photochemical quenching of chlorophyll fluorescence. It has recently been proposed that the transition between the light-harvesting and self-defensive modes is associated with a reorganization of light-harvesting complexes. Here we show that despite structural changes, the photosystem II cross-section does not decrease. Our study reveals that the efficiency of energy trapping by the non-photochemical quencher(s) is lower than the efficiency of energy capture by the reaction centres. Consequently, the photoprotective mechanism works effectively for closed rather than open centres. This type of defence preserves the exceptional efficiency of electron transport in a broad range of light intensities, simultaneously ensuring high photosynthetic productivity and, under hazardous light conditions, sufficient photoprotection for both the reaction centre and the light-harvesting pigments of the antenna.

P‐33: Which Color Gamut Metric Best Predicts Human Display Preference?

AbstractAdvances in display technology depend on our ability to develop miniscule elements that emit a broad range of light intensities and colors. Existing technologies are limited and face trade‐offs between producing luminance and color. Photometry and colorimetry provide tools to help developers understand those trade‐offs and to set meaningful targets for the future. Uncertainty remains however as to which metrics provide the best guidelines. We examined the relationship between 8 color metrics and human preferences for displays that differed only in color gamut. We found that (1) volume metrics, computed from display luminance and color capacity, outperformed area metrics computed only from color and (2) of the color metrics we considered, CIECAM′02 saturation best predicted viewer preference.

Die Fledermaus: regarding optokinetic contrast sensitivity and light-adaptation, chicks are mice with wings.

BackgroundThrough adaptation, animals can function visually under an extremely broad range of light intensities. Light adaptation starts in the retina, through shifts in photoreceptor sensitivity and kinetics plus modulation of visual processing in retinal circuits. Although considerable research has been conducted on retinal adaptation in nocturnal species with rod-dominated retinas, such as the mouse, little is known about how cone-dominated avian retinas adapt to changes in mean light intensity.Methodology/Principal FindingsWe used the optokinetic response to characterize contrast sensitivity (CS) in the chick retina as a function of spatial frequency and temporal frequency at different mean light intensities. We found that: 1) daytime, cone-driven CS was tuned to spatial frequency; 2) nighttime, presumably rod-driven CS was tuned to temporal frequency and spatial frequency; 3) daytime, presumably cone-driven CS at threshold intensity was invariant with temporal and spatial frequency; and 4) daytime photopic CS was invariant with clock time.Conclusion/SignificanceLight- and dark-adaptational changes in CS were investigated comprehensively for the first time in the cone-dominated retina of an avian, diurnal species. The chick retina, like the mouse retina, adapts by using a “day/night” or “cone/rod” switch in tuning preference during changes in lighting conditions. The chick optokinetic response is an attractive model for noninvasive, behavioral studies of adaptation in retinal circuitry in health and disease.

Diverse Responses to Blue Light via LOV Photoreceptors

Plants utilize light not only as an energy source for photosynthesis, but also as an environmental cue to direct numerous developmental and physiological processes. For this purpose, plants have evolved two main types of photoreceptors: the phytochromes (Franklin and Quail 2010), which sense red/ far-red light, and the ultraviolet (UV)-A/blue light (BL)-sensing photoreceptors, which include cryptochrome (Liu et al. 2011), phototropin (Christie 2007) and other BL receptors described below. In addition, a third class of UV-B receptor, UVR8, was recently identified (Rizzini et al. 2011). The long history of research on BL receptors dates back to the initial observation made by the famous Charles Darwin, in which he found that plants were able to move towards light (Darwin and Darwin 1881). For a long time, the nature of the chromophore in BL receptors was much disputed as to whether it was a flavin or a carotenoid (Senger 1980). This issue was partially resolved through the identification of the first BL receptor, which corresponded to a flavin protein named cryptochrome (Ahmad and Cashmore 1993). Shortly after this discovery, the Briggs group demonstrated that the disrupted gene in Arabidopsis non-phototropic hypocotyl 1 (nph1) mutants encoded a BL receptor required for phototropic response (Huala et al. 1997, Christie et al. 1998). A homolog of NPH1, NON-PHOTOTROPIC HYPOCOTYL-LIKE 1 (NPL1), was soon identified (Kagawa et al. 2001); thereafter, NPH1 and NPL1 were renamed phototropin 1 (phot1) and phot2, respectively. Phototropins mediate diverse plant responses, such as chloroplast relocation movements (Kagawa et al. 2001, Sakai et al. 2001), stomatal opening (Kinoshita et al. 2001), early hypocotyl growth inhibition (Folta and Spaulding 2001), leaf flattening (Sakamoto and Briggs 2002), leaf positioning (Inoue et al. 2005), nuclear positioning (Iwabuchi et al. 2007, Tsuboi et al. 2007), sun tracking (Inoue et al. 2008b) and leaf photomorphogenesis (Kozuka et al. 2011), in which phot1 acts over a broad range of light intensities, whereas phot2 acts as a high-light sensor. These physiological responses contribute towards enhancing photosynthesis in the plant by increasing the absorption of light and CO2 (Takemiya et al. 2005). In addition to the two phototropins, a BL receptor family of proteins characteristically containing one light, oxygen or voltage (LOV) domain, an F-box and a Kelch repeat has been identified in Arabidopsis. These proteins include ZEITLUPE (ZTL), FLAVIN-BINDING KELCH REPEAT F-BOX 1 (FKF1) and LOV KELCH PROTEIN 2 (LKP2), and are proposed to regulate the circadian clock and photoperiodic flowering by controlling BL-dependent protein degradation (Ito et al. 2012). A third type of LOV protein, aureochrome (AUREO), was identified in the stramenopile alga, Vaucheria frigida (Takahashi et al. 2007). AUREO has a basic region/leucine zipper (bZIP) domain as well as a LOV domain, and is thought to act as a BL-regulated transcription factor. Thus, the LOV BL receptor family in plants has divergent members who have a variety of physiological functions triggered by the photochemical reactions of FMN in the LOV domain.

Pupil dilation and visual field in the piked dogfish, Squalus acanthias

The relatively large eye and pupil of the Piked Dogfish, Squalus acanthias, is visually arresting. However, knowledge of its basic visual characteristics lags far behind other areas in this generally well studied species. This study quantifies pupil dilation in a species that is naturally exposed to a broad range of light intensities and finds that the pupil area in the dark adapted state is 35.3% of the total eye area, an increase of 12.4% from the light adapted state. The anterior and posterior extents of the horizontal visual field are assessed and compared with both morphological and electrophysiological techniques and the results are integrated with the measured head yaw to derive the anterior convergence distance and blind area. The position of the eyes and the triangular, pointed snout of S. acanthias provides excellent anterior vision, which likely facilitates foraging upon its mobile prey.

PhycomycesMADB interacts with MADA to form the primary photoreceptor complex for fungal phototropism

The fungus Phycomyces blakesleeanus reacts to environmental signals, including light, gravity, touch, and the presence of nearby objects, by changing the speed and direction of growth of its fruiting body (sporangiophore). Phototropism, growth toward light, shares many features in fungi and plants but the molecular mechanisms remain to be fully elucidated. Phycomyces mutants with altered phototropism were isolated approximately 40 years ago and found to have mutations in the mad genes. All of the responses to light in Phycomyces require the products of the madA and madB genes. We showed that madA encodes a protein similar to the Neurospora blue-light photoreceptor, zinc-finger protein WC-1. We show here that madB encodes a protein similar to the Neurospora zinc-finger protein WC-2. MADA and MADB interact to form a complex in yeast 2-hybrid assays and when coexpressed in E. coli, providing evidence that phototropism and other responses to light are mediated by a photoresponsive transcription factor complex. The Phycomyces genome contains 3 genes similar to wc-1, and 4 genes similar to wc-2, many of which are regulated by light in a madA or madB dependent manner. We did not detect any interactions between additional WC proteins in yeast 2-hybrid assays, which suggest that MADA and MADB form the major photoreceptor complex in Phycomyces. However, the presence of multiple wc genes in Phycomyces may enable perception across a broad range of light intensities, and may provide specialized photoreceptors for distinct photoresponses.

Secondary scattering on the intensity dependence of the capture velocity in a magneto-optical trap

In this work, we consider a three-dimensional model to simulate the capture velocity behavior in a sample of cold-trapped sodium atoms as a function of the trapping laser intensity. We expand on previous work [V. S. Bagnato, L. G. Marcassa, S. G. Miranda, S. R. Muniz, and A. L. de Oliveira, Phys. Rev. A 62, 013404 (2000)] by calculating the capture velocity over a broad range of light intensities considering the secondary scattering in a magneto-optical trap. Our calculations are in a good agreement with recent measured values [S. R. Muniz et al., Phys. Rev. A 65, 015402 (2001)].