Light Adaptation Research Articles

Short‐Wave Infrared Synaptic Phototransistor with Ambient Light Adaptability for Flexible Artificial Night Visual System

AbstractFlexible organic monitoring system that can work in short‐wave infrared (SIR) region has great potential in autonomous driving, night driving safety, military encryption, biomedical imaging, and robot engineering. Especially, the development of infrared artificial vision system device that can autonomously improve the computing speed and adapt to different brightness ambient light is very important. However, it is a challenge for mimicking infrared visual adaptation because of the need for infrared absorbing materials and the need to control the concentration of carriers. In this study, inorganic quantum dot material is combined with organic materials to promote carrier separation and introduce interface defects that adjust the carrier concentration in transistors, which induce the synaptic behavior under SIR (1100 nm) light in darkness and the ability to adapt to white ambient light. Furthermore, the device array realizes the image recognition of SIR light at night with white ambient light of different brightness, exhibiting good self‐adaptability, and strong anti‐interference ability. These results demonstrate promising applications of the infrared synaptic phototransistors in adapted bionic optoelectronic devices.

HIV-1 CD4-binding site germline antibody–Env structures inform vaccine design

BG24, a VRC01-class broadly neutralizing antibody (bNAb) against HIV-1 Env with relatively few somatic hypermutations (SHMs), represents a promising target for vaccine strategies to elicit CD4-binding site (CD4bs) bNAbs. To understand how SHMs correlate with BG24 neutralization of HIV-1, we report 4.1 Å and 3.4 Å single-particle cryo-EM structures of two inferred germline (iGL) BG24 precursors complexed with engineered Env-based immunogens lacking CD4bs N-glycans. Structures reveal critical Env contacts by BG24iGL and identify antibody light chain structural features that impede Env recognition. In addition, biochemical data and cryo-EM structures of BG24iGL variants bound to Envs with CD4bs glycans present provide insights into N-glycan accommodation, including structural modes of light chain adaptations in the presence of the N276gp120 glycan. Together, these findings reveal Env regions critical for germline antibody recognition and potential sites to alter in immunogen design.

New prospectives on light adaptation of visual system research with the emerging knowledge on non-image-forming effect

Light adaptation is very important to keep the visual system acutely sensitive to scene content over a wide range of illumination, and has strong influence on brightness perception, visual performance and glare evaluation. The estimation method for the light adaptation state under real circumstances is a big pending topic for lighting industry. The discovery of Intrinsically Photosensitive Retinal Ganglion Cells (ipRGCs) has offered us an exciting entry point to comprehend how light adaptation is regulated. In this paper, we made a comprehensive and thorough analysis of forty-five studies focusing on light adaptation with the emerging knowledge on non-image-forming effect (NIF), to help researchers facilitate the research on light adaptation under complex luminance distribution. From the review, we can have the following outputs: 1) NIF may directly mediate the function of luminance adaptation, and we can take pupillary light reflex (PLR) as an objective indicator for the adaptation; 2) the action spectra of light adaptation may not be a fixed formula like V(λ), but may vary dynamically with luminance level; 3) there is high necessity to conduct research on light adaptation within a natural and complex environment. All these outputs can provide us a new perspective on light adaptation in visual system research.

Frmpd1 Facilitates Trafficking of G-Protein Transducin and Modulates Synaptic Function in Rod Photoreceptors of Mammalian Retina.

Trafficking of transducin (Gαt) in rod photoreceptors is critical for adaptive and modulatory responses of the retina to varying light intensities. In addition to fine-tuning phototransduction gain in rod outer segments (OSs), light-induced translocation of Gαt to the rod synapse enhances rod to rod bipolar synaptic transmission. Here, we show that the rod-specific loss of Frmpd1 (FERM and PDZ domain containing 1), in the retina of both female and male mice, results in delayed return of Gαt from the synapse back to outer segments in the dark, compromising the capacity of rods to recover from light adaptation. Frmpd1 directly interacts with Gpsm2 (G-protein signaling modulator 2), and the two proteins are required for appropriate sensitization of rod-rod bipolar signaling under saturating light conditions. These studies provide insight into how the trafficking and function of Gαt is modulated to optimize the photoresponse and synaptic transmission of rod photoreceptors in a light-dependent manner.

Application of fertilization in changing light adaptability and improving growth of Aralia elata (Miq.) Seem. seedlings under various light conditions in temperate forests

Non-timber forest plants have always played a significant role in livelihood security by providing valuable non-timber forest products, especially in less-developed countries. Artificial cultivation is a key approach to sustainably develop non-timber forest plants, for which, in-forest planting is vital. Light conditions in forests severely affect in-forest planting, and the growth of many plants may be restricted due to inappropriate light conditions. Thus, to fully and effectively utilize forest spaces with various light environments, fertilization, as an important practice to supply nutrients for promoting plant growth, was selected to mitigate light constraints in forests. Aralia elata (a valuable non-timber forest plant species) was chosen as the subject to explore the effects of fertilization on photosynthetic and morphological adaptation to light and the growth of in-forest planted seedlings by simulating different light environments. The results showed that the effects of fertilization on light adaptability (i.e., photosynthesis and leaf traits) of A. elata seedlings were limited; that is, only the variations in light-saturated photosynthetic net rate (PNmax), specific leaf area (SLA), and chlorophyll (Chl) content of A. elata seedlings between different shade intensities were noticeably affected by fertilization. Fertilization was positive for growth, and a half fertilization treatment (50 g per plot) was optimum for improving the growth of A. elata seedlings under light conditions of 0–75% shade intensities. These results can provide some practical references for the application of fertilization in in-forest planting and management of transplanted non-timber forest plant seedlings under various light conditions in the forests.

Monitoring the photosynthetic performance of grape leaves using a hyperspectral-based machine learning model

Photosynthesis is a direct expression of the crop growth status and an important indicator predicting yield and quality. Rapid and accurate monitoring of the dynamics of photosynthetic is key to field management. In this study, we obtained photosynthetic pigments and water status parameters at the leaf scale during different growth periods of grape. The potential maximum quantum yield (Fv/Fm) of photosystem II (PSII) under dark adaptation and the light response curve (LRC) of the PSII electron transfer rate (ETR) under light adaptation were measured using a pulse amplitude modulated (PAM) chlorophyll fluorometer, while leaf spectral information was recorded using a hyperspectral imager. The maximum ETR (ETRmax) and initial quantum efficiency (kα) were calculated using the LRC model. A Bayesian neural network (BNN) model (implemented in Tensorfolw2.8) was developed to predict Fv/Fm, ETRmax and kα by quantifying the spectral response indices of photosynthetic pigments and water status parameters. A comparison was made with the partial least squares (PLS) and photochemical reflectance index (PRI). The results show that BNN, PLS model and PRI have better predictive performance for Fv/Fm than ETRmax and kα. Compared with the PLS and PRI, the BNN model was able to significantly improve the prediction accuracy, where the validation results for Fv/Fm were R2 of 0.78, ETRmax of 0.57 and kα of 0.53. In addition, the importance of the BNN model input features varied with Fv/Fm, ETRmax and kα, with the vegetation index describing the photosynthetic pigments having the highest importance. The PRI had the worst predictive performance probably because the de-epoxidation state of the xanthophyll cycle pigments is strongly influenced by temporal changes. The model developed in this paper for monitoring photosynthetic performance parameters in grape leaves can simplify the complex photosynthetic reaction process, expand the application of PAM technology and provide a method for rapid and accurate monitoring of photosynthetic performance.

The Impact of Cameraria ohridella (Lepidoptera, Gracillariidae) on the State of Aesculus hippocastanum Photosynthetic Apparatus in the Urban Environment

The paper presents the results on resistance of Aesculus hippocastanum Linnaeus, 1753 trees to Cameraria ohridella Deschka & Dimić, 1986 (Lepidoptera, Gracillariidae) impact under conditions of a modern urban environment on the example of Dnipro city as the largest industrial city in Ukraine. Field experiments were conducted in all park areas of the city, which allowed covering the full gradient of the existing urban environment and considered the different degrees of the tree settlement by the invasive insect species. The research of the impact of C. ohridella caterpillars’ vital activity on the photosynthetic apparatus state was carried out by applying a chlorophyll fluorescence induction technique. Diagnosis of photosynthetic dysfunction of fresh Ae. hippocastanum leaves was conducted using a portable “Floratest” fluorometer manufactured in Ukraine. Interpretation of the obtained Kautsky curves showed that significant changes in their critical parameters associated with the degree of leaf damage by C. ohridella caterpillars were not detected. The influence of tree growth site conditions on the following 4 main indicators of chlorophyll fluorescence induction was established: the initial value of fluorescence induction after irradiation; the value of “plateau” fluorescence induction; the maximum value of fluorescence induction; the stationary value of fluorescence induction after light adaptation of the plant leaf. It was found that the efficiency coefficients of photochemical processes in Ae. hippocastanum trees growing in low terrain levels differed significantly, which can probably be interpreted as their response to the specific characteristics of the urban environment.

Virtual reality training improves accommodative facility and accommodative range.

To evaluate the effects of virtual reality (VR) training on different parameters of vision. Sixty individuals ranged 18-60 years old with asthenopia were randomly divided into short-term (n=40) and long-term (n=20) treatment groups. They were given a specially designed VR training device only once for 15min or 3-4 times a day for 15min each time for 1mo. The visual acuity, spherical equivalent, accommodative range, accommodative facility, pupil size, and visual fatigue were evaluated before (control) and after VR training. The visual acuity, accommodative range, and accommodative facility increased in subjects of the short-term treatment group, whereas their pupil size contracted significantly. No significant changes in spherical equivalent and visual fatigue were observed. The changes in distant vision and corrected visual acuity were positively correlated with those in pupil size, but not with spherical equivalent. The accommodative range and accommodative facility improved significantly in subjects of the long-term treatment group. No significant changes in visual acuity, spherical equivalent, pupil size, and visual fatigue were noted. VR training can improve the accommodative range and accommodative facility of human eyes. Although short-term VR training can transiently improve vision, which probably due to bright light adaptation, there is no evidence that it can improve myopia.

Effects of Nitrogen and Phosphorus Addition on Agronomic Characters, Photosynthetic Performance and Anatomical Structure of Alfalfa in Northern Xinjiang, China

The productivity of alfalfa is associated with a large amount of nitrogen (N) and phosphorus (P); the addition of exogenous N and P fertilizers can fully exploit the growth potential of alfalfa. However, there is uncertainty about the relationship between changes in alfalfa productivity and photosynthetic physiology and anatomy. We conducted field fertilization experiments on alfalfa in the second and third years under drip irrigation, as well as measurement of the photosynthetic physiology, anatomical structure and agronomic traits of alfalfa at different levels of N (0, 120 kg·ha−1) and different levels of P2O5 (0, 50, 100 and 150 kg·ha−1). The results showed that the dry matter yield (DMY), crude protein (CP), net photosynthetic rate (Pn) and specific leaf weight (SLW) were increased by 2.10~11.82%, 4.95~11.93%, 4.71~7.59% and 2.02~7.12% in the N application treatment compared with the non-N application treatment, while the DMY, CP, Pn and SLW were increased by 3.19~17.46%, 1.99~8.42%, 6.15~24.95% and 2.16~11.90% in the P application treatment compared with the non-P application treatment. N and P increase the thickness of the spongy tissue (ST) of alfalfa, which will facilitate the entry and exit of gas and water, and will further affect the photosynthetic indexes, such as stomatal conductance (Gs) and transpiration rate (Tr), of alfalfa leaves. Increased palisade tissue (PT) thickness will also enhance the adaptability of plant leaves to strong sunlight, thereby increasing the maximum net photosynthetic rate (Pmax) and light saturation point (LSP). Fertilization treatment showed the highest utilization efficiency for low light and better adaptation to strong light, but the Rd decreased. The comprehensive scores of principal component analysis for anatomical structure, photosynthetic performance and agronomic traits were N1P2 > N0P2 > N1P3 > N1P1 > N0P3 > N0P1 > N1P0 > N0P0. Therefore, the application of N and P fertilizers contributed to the adaptive changes in alfalfa leaf anatomy and the improvement of photosynthetic capacity, which were beneficial to the improvement of alfalfa dry matter yield, growth traits and nutritional quality, with the most obvious improvement effect obtained with the application of 120 kg·ha−1 of N and 100 kg·ha−1 of P2O5.

The Use of Optical Coherence Tomography to Demonstrate Dark and Light Adaptation in a Live Moth.

To work effectively, the eyes of nocturnal insects have a problem they must overcome. During the night, the light levels are low, so their eyes need to be very sensitive; but they also need a way of adapting to environmental light conditions, and protecting those sensitive organs, if a bright light is encountered. Human eyes have a pupil that changes size to regulate light input to the eye. Moths (Lepidoptera) use a light absorbing pigment that moves position to limit the light within the eye. This pigment migration is difficult to record because it is a dynamic process and will only occur in a live moth. This paper presents the first use of Ocular Coherence Tomography as a method of viewing anatomical detail in a compound eye. This is noninvasive and does not harm the insect. To demonstrate the effectiveness, this article documents the dynamic process of light adaptation within a moth’s eye.

Distinct mechanisms of light adaptation of elementary responses in photoreceptors of dipteran flies and American cockroach.

Of many light adaptation mechanisms optimizing photoreceptor functioning in the compound eyes of insects, those modifying the single-photon response, the quantum bump (QB), remain least studied. Here, by recording from photoreceptors of the blow fly Protophormia terraenovae, the hover fly Volucella pellucens, and the cockroach Periplaneta americana, we investigated mechanisms of rapid light adaptation by examining how properties of QBs change after light stimulation and multiquantal impulse responses during repetitive stimulation. In P. terraenovae, light stimulation reduced latencies, characteristic durations, and amplitudes of QBs in an intensity- and duration-dependent manner. In P. americana, only QB amplitudes decreased consistently. In both species, time constants of QB parameters' recovery increased with the strength and duration of stimulation, reaching ∼30 s after bright prolonged 10-s pulses. In the blow fly, changes in QB amplitudes during recovery correlated with changes in half-widths but not latencies, suggesting at least two separate mechanisms of light adaptation: acceleration of QB onset by sensitizing transduction channels and acceleration of transduction channel inactivation causing QB shortening and decrease. In the cockroach, light adaptation reduced QB amplitude by apparently lowering the transduction channel availability. Impulse response data in the blow fly and cockroach were consistent with the inferences from the QB recovery experiments. However, in the hover fly V. pellucens, impulse response latencies and durations decreased simultaneously, whereas amplitudes decreased little, even when bright flashes were applied at high frequencies. These findings indicate the existence of dissimilar mechanisms of light adaptation in the microvilli of different species.NEW & NOTEWORTHY By studying light adaptation of elementary responses in photoreceptors of the blow fly and the cockroach we found three distinct mechanisms. In the blow fly, one mechanism speeds quantum bump onset and another accelerates quantum bump inactivation, decreasing its size. In the cockroach, quantum bump amplitude decreases without changes in kinetics, indicating decreased availability of transduction channels. The findings can be explained by expression of different transduction channels in the flies and cockroaches.

Light Regimes Regulate Leaf and Twigs Traits of Camellia oleifera (Abel) in Pinus massoniana Plantation Understory

Camellia oleifera (Abel) is an economic tree species and one of the four largest oil plants in the world. The leaf and twig responses and plasticity indices of C. oleifera were investigated under four light regimes in Pinus massoniana understory plantations, namely, 100% light intensity (CK), 75% of CK (HL), 50% of CK (ML), and 30% of CK (LL). The morphological characteristics, biomass allocation, and physiological characteristics of C. oleifera leaves and twigs under different light regimes, as well as their plasticity indexes, were comprehensively evaluated. The results showed that leaf area, and specific leaf area, leaf total carbon, total nitrogen, total phosphorus and chlorophyll contents, and photosynthesis increased, which indicates that plants have the strongest adaptability under HL. No fruit appeared in twigs under LL and ML. The plastic morphological traits were greater than the biomass allocation and physiological traits. The plasticity of palisade/sponge tissue thickness and lower epidermis thickness were the lowest. In conclusion, C. oleifera have differences in sensitivity and regulation mechanism according to their differences in leaf morphological characteristics, biomass allocation physiological indicators, and response to light regimes. C. oleifera plants showed obvious phenotypic inhibition under CK, while they can adjust their strategies for using light energy to maintain their own growth and development under HL. The wide range of light adaptation and strong plasticity of C. oleifera may be two important reasons for its existence in heterogeneous habitats, but it needs at least 75% light regimes to complete its normal growth development and fruit setting. The study provides insights into the optimum light regimes for the improvement of the quality and efficiency of C. oleifera in P. massoniana understory plantations.

Adaptation of Cyanobacteria to the Endolithic Light Spectrum in Hyper-Arid Deserts.

In hyper-arid deserts, endolithic microbial communities survive in the pore spaces and cracks of rocks, an environment that enhances water retention and filters UV radiation. The rock colonization zone is enriched in far-red light (FRL) and depleted in visible light. This poses a challenge to cyanobacteria, which are the primary producers of endolithic communities. Many species of cyanobacteria are capable of Far-Red-Light Photoacclimation (FaRLiP), a process in which FRL induces the synthesis of specialized chlorophylls and remodeling of the photosynthetic apparatus, providing the ability to grow in FRL. While FaRLiP has been reported in cyanobacteria from various low-light environments, our understanding of light adaptations for endolithic cyanobacteria remains limited. Here, we demonstrated that endolithic Chroococcidiopsis isolates from deserts around the world synthesize chlorophyll f, an FRL-specialized chlorophyll when FRL is the sole light source. The metagenome-assembled genomes of these isolates encoded chlorophyll f synthase and all the genes required to implement the FaRLiP response. We also present evidence of FRL-induced changes to the major light-harvesting complexes of a Chroococcidiopsis isolate. These findings indicate that endolithic cyanobacteria from hyper-arid deserts use FRL photoacclimation as an adaptation to the unique light transmission spectrum of their rocky habitat.

Photosynthetic Responses of Two Woody Halophyte Species to Saline Groundwater Irrigation in the Taklimakan Desert

The study of plant photosynthesis under different degrees of drought stress can provide a deeper understanding of the mechanism of plant drought resistance. In the Taklimakan Desert, saline groundwater is the only local water source with regard to shelterbelt construction and determines plant growth and photosynthetic changes. In this study, daily dynamics of gas exchange parameters and their responses to photosynthetic photon flux density at three irrigation levels (W1 = 17.5, W2 = 25, W3 = 35 mm) were measured for two main species, i.e., Calligonum mongolicum (C) and Haloxylon ammodendron (H). H was better adapted to drought stress than C. Net photosynthetic rate (PN) was mainly related to soil water status in the main root system activity layer. In July, the daily variations of PN and transpiration (Tr) for C were higher than H. C increased water use efficiency (WUE) with increases in PN, while H decreased Tr to obtain a higher WUE. Either C or H, drought reduced the low light and metabolic capacity, and thus decreased the light adaptability and photosynthesis potential. We suggest a prerequisite understanding of physiological mechanisms and possible plant morphological adjustments required to adapt plant species to desert drought conditions.

Gradient illumination scheme design at the highway intersection entrance considering driver’s light adaption

Objective Improving lighting arrangements at the highway intersections can significantly reduce the likelihood of crashes. Meanwhile, a reasonable gradient illumination scheme can increase drivers' safety by avoiding the rapid change of their pupil area when driving from an unlighted area into a lighted area. The purpose of this study is to design illumination transition zones for drivers when approaching the highway intersection, and optimize the illumination increments along the transition zones. Methods This issue is addressed in three stages. First, an indoor simulation platform is built using the UC-win/road software, and its parameters are calibrated using real intersection data collected at night. Second, the variation of pupil area under different increasing rates of illuminance near the driver's eyes (INDE) is analyzed, and a model representing the temporal change of the area in the pupil contraction stage is established. Last, an optimization model is proposed to obtain the optimal luminance increasing rates by minimizing the time needed for drivers to travel through the transition zones under different maximum illuminations and speed limits. Results The findings of this study indicate that the INDE increasing time in the transition zone remains unchanged with a determined illumination at the intersection, and the optimal transition zone length is directly proportional to the speed limit of the intersection. Therefore, the transition zone length needs to be adjusted to accommodate different speed limits: it should be extended or shortened by the same percentage as the increase or decrease of the speed limit. Conclusions It can be concluded that the illumination transition zone is necessary when the INDE of highway intersection and the speed limit exceed 8 lx and 40 km/h, respectively. The INDE increasing rate should be maintained around the optimal value, providing safe and comfortable light adaptation to drivers and preventing traffic accidents. The study will provide a scientific basis for safety implementation of lighting arrangements at highway intersections.

The rabbits retina functional state after exposure to low-frequency ultrasound: electroretinogram indicators analysis

Relevance. Currently, several groups of scientists are working on the implementation of low-frequency ultrasound in surgery of the retina and vitreous body. But there are not enough articles on the study of the functional activity of the retina when exposed to this type of energy. Electrophysiological research methods make it possible to analyze and evaluate the safety, effectiveness of surgical interventions, the effect of new drugs at the level of neurons and visual pathways. The electroretinography method makes it possible to record the bioelectrical activity of retinal neurons during light stimulation during dark and light adaptation. The aim of the study is to carry out a comparative analysis of the aand b-wave indices of the rabbit electroretinogram after experimental removal of the vitreous body using low-frequency ultrasound and mechanical action. Materials and Methods. Experiments were carried out in two groups of Chinchilla rabbits (n = 40). In the experimental group, surgery to remove the vitreous body was performed using low-frequency ultrasound, in the control group a fragmentator with guillotine mechanism was used. Before and after the surgery (1, 7, 14, 30 days) an electroretinogram was recorded, the parameters of the amplitude and latency of the aand b-waves were measured. Results and Discussion. In both groups, a sharp decrease in all parameters was observed on day 1. Later, on the 7th day, the dynamics of the latency of aand b-waves slightly decreased than the preoperative values. On the 14th day after the exposure, the amplitude and peak latency of the aand bwaves in both groups remained at the same level as on the 7th day. On the 30th day, the indicators increased, which indicates the restoration of the functions of photoreceptors and Mueller cells in both groups. There were no statistically significant differences between the study groups at all periods of the study. Conclusion. The use of low-frequency ultrasound for vitreous removal can be considered safe and has prospects for further development and application.

The rabbits retina functional state after exposure to low-frequencyultrasound: electroretinogram indicators analysis

Relevance. Currently, several groups of scientists are working on the implementation of low-frequency ultrasound in surgery of the retina and vitreous body. But there are not enough articles on the study of the functional activity of the retina when exposed to this type of energy. Electrophysiological research methods make it possible to analyze and evaluate the safety, effectiveness of surgical interventions, the effect of new drugs at the level of neurons and visual pathways. The electroretinography method makes it possible to record the bioelectrical activity of retinal neurons during light stimulation during dark and light adaptation. The aim of the study is to carry out a comparative analysis of the a- and b-wave indices of the rabbit electroretinogram after experimental removal of the vitreous body using low-frequency ultrasound and mechanical action. Materials and Methods. Experiments were carried out in two groups of Chinchilla rabbits (n = 40). In the experimental group, surgery to remove the vitreous body was performed using low-frequency ultrasound, in the control group a fragmentator with guillotine mechanism was used. Before and after the surgery (1, 7, 14, 30 days) an electroretinogram was recorded, the parameters of the amplitude and latency of the a- and b-waves were measured. Results and Discussion. In both groups, a sharp decrease in all parameters was observed on day 1. Later, on the 7th day, the dynamics of the latency of a- and b-waves slightly decreased than the preoperative values. On the 14th day after the exposure, the amplitude and peak latency of the a- and b-waves in both groups remained at the same level as on the 7th day. On the 30th day, the indicators increased, which indicates the restoration of the functions of photoreceptors and Mueller cells in both groups. There were no statistically significant differences between the study groups at all periods of the study. Conclusion. The use of low-frequency ultrasound for vitreous removal can be considered safe and has prospects for further development and application.

A reinterpretation of critical flicker-frequency (CFF) data reveals key details about light adaptation and normal and abnormal visual processing.

Our ability to see flicker has an upper frequency limit above which flicker is invisible, known as the "critical flicker frequency" (CFF), that typically grows with light intensity (I). The relation between CFF and I, the focus of nearly 200 years of research, is roughly logarithmic, i.e., CFF∝log(I)-a relation called the Ferry-Porter law. However, why this law should occur, and how it relates to the underlying physiology, have never been adequately explained. Over the past two decades we have measured CFF in normal observers and in patients with retinal gene defects. Here, we reanalyse and model our data and historical CFF data. Remarkably, CFF-versus-I functions measured under a wide range of conditions in patients and in normal observers all have broadly similar shapes when plotted in double-logarithmic coordinates, i.e., log (CFF)-versus-log(I). Thus, the entire dataset can be characterised by horizontal and vertical logarithmic shifts of a fixed-shape template. Shape invariance can be predicted by a simple model of visual processing built from a sequence of low-pass filters, subtractive feedforward stages and gain adjustment (Rider, Henning & Stockman, 2019). It depends primarily on the numbers of visual processing stages that approach their power-law region at a given intensity and a frequency-independent gain reduction at higher light levels. Counter-intuitively, the CFF-versus-I relation depends primarily on the gain of the visual response rather than its speed-a conclusion that changes our understanding and interpretation of human flicker perception. The Ferry-Porter "law" is merely an approximation of the shape-invariant template.

Fiddler crab electroretinograms reveal vast circadian shifts in visual sensitivity and temporal summation in dim light.

ABSTRACTMany animals with compound eyes undergo major optical changes to adjust visual sensitivity from day to night, often under control of a circadian clock. In fiddler crabs, this presents most conspicuously in the huge volume increase of photopigment-packed rhabdoms and the widening of crystalline cone apertures at night. These changes are hypothesised to adjust the light flux to the photoreceptors and to alter optical sensitivity as the eye moves between light- and dark-adapted states. Here, we compared optical sensitivity in fiddler crab (Gelasimus dampieri) eyes during daytime and night via three electroretinogram (ERG) experiments performed on light- and dark-adapted crabs. (1) Light intensity required to elicit a threshold ERG response varied over six orders of magnitude, allowing more sensitive vision for discriminating small contrasts in dim light after dusk. During daytime, the eyes remained relatively insensitive, which would allow effective vision on bright mudflats, even after prolonged dark adaptation. (2) Flicker fusion frequency (FFF) experiments indicated that temporal summation is employed in dim light to increase light-gathering integration times and enhance visual sensitivity during both night and day. (3) ERG responses to flickering lights during 60 min of dark adaptation increased at a faster rate and to a greater extent after sunset compared with daytime. However, even brief, dim and intermittent light exposure strongly disrupted dark-adaptation processes. Together, these findings demonstrate effective light adaptation to optimise vision over the large range of light intensities that these animals experience.

Leaf anatomy, photosynthesis, and chloroplast ultrastructure of Heptacodium miconioides seedlings reveal adaptation to light environment

Light intensity is a critical factor for the plant survival and early growth. Heptacodium miconioides , a well-accepted ornamental plant, has been endangered due to fragmented habitats in the wild. To better understand the light adaptation mechanisms of H. miconioides , we investigated the morphology, photosynthesis, chloroplast ultrastructure, and chloroplast gene expression of the leaves under high light (HL), moderate light (ML), and low light (LL) conditions. With decreasing light intensity, the specific leaf area and chlorophyll contents of H. miconioides increased, whereas the leaf size first increased followed by a decrease. The maximum net photosynthetic rate under ML and HL treatments were significantly higher than that under LL treatment. However, leaves under ML treatment exhibited the lower dark respiration rate and light compensation point than those under HL treatment. The leaf thickness, palisade tissue, spongy tissue, and stomatal density were obviously reduced with decreasing light intensity. Chloroplast ultrastructure showed the better development in leaves under ML condition, and the size of chloroplast, the number of starch grains and plastoglobules increased significantly. In addition, the expression levels of genes involved in chlorophyll biosynthesis ( HEMA , CLH , CHLI , CHLH , CHLG ) were higher under ML than LL treatment, but lower under HL treatment. The up-regulation of the photosystem II ( PsbB , PsbD , PsbO ) genes expression play an important role in under ML and LL treatments. Taken together, we proposed that the optimal growth of H. miconioides seedlings varies between HL and ML but had poor growth under LL condition. The improvement in H. miconioides growth under moderate shade was mainly through its effects on leaf morphology, chloroplast development, and light capture efficiency of PSII phase. • Adaptation mechanisms to different light intensity were investigated in Heptacodium miconioides . • Seedlings grown under moderate and high light intensities exhibited higher photosynthetic capacity. • Moderate light intensity increased the size of chloroplast and the accumulation of starch grains and plastoglobules. • Moderate light intensity up-regulated chlorophyll biosynthesis and photosystem II (PSII) related gene expression.