High Light Exposure Research Articles

Dark Anaerobic Conditions Induce a Fast Induction of the Xanthophyll Cycle in Chlamydomonas reinhardtii When Exposed to High Light

Background: Dark anaerobiosis promotes the acidification of the thylakoid lumen and a reduction in the plastoquinone (PQ) pool. The relationship between the reduction in the PQ pool in the dark and the induction of the xanthophyll cycle under high light stress was investigated in Chlamydomonas reinhardtii. Methods: To achieve a comprehensive oxidative/reductive (aerobic/anaerobic conditions) state of the PQ pool, cultures were bubbled with air or nitrogen for 4 h. To induce the xanthophyll cycle, the cultures were then irradiated with 1200 µmolphotons m−2 s−1 white light for 1 h. Results: The anaerobic cultures exhibited a stronger induction of the xanthophyll cycle with a 3.4-fold higher de-epoxidation state than the aerobic cultures. Chlorophyll fluorescence measurements showed that this response was influenced by the previous redox state of the PQ pool, and that dark anaerobiosis triggers physiological responses, such as exposure to high light. Thus, the photosynthetic apparatus in anaerobic cultures was already alerted, at the moment of high light exposure, to give an appropriate response to the stress with a stronger induction of the xanthophyll cycle than in aerobic cultures. Conclusions: Our results provide new information on the importance of the redox signaling pathway and highlight the importance of the reductive conditions of the PQ pool in regulating the physiological responses of photosynthetic organisms to stress.

Identification and Expression Analysis of TCP Transcription Factors Under Abiotic Stress in Phoebe bournei

The TCP gene family encodes plant transcription factors crucial for regulating growth and development. While TCP genes have been identified in various species, they have not been studied in Phoebe bournei (Hemsl.). This study identified 29 TCP genes in the P. bournei genome, categorizing them into Class I (PCF) and Class II (CYC/TB1 and CIN). We conducted analyses on the PbTCP gene at both the protein level (physicochemical properties) and the gene sequence level (subcellular localization, chromosomal distribution, phylogenetic relationships, conserved motifs, and gene structure). Most P. bournei TCP genes are localized in the nucleus, except PbTCP9 in the mitochondria and PbTCP8 in both the chloroplast and nucleus. Chromosomal mapping showed 29 TCP genes unevenly distributed across 10 chromosomes, except chromosome 8 and 9. We also analyzed the promoter cis-regulatory elements, which are mainly involved in plant growth and development and hormone responses. Notably, most PbTCP transcription factors respond highly to light. Further analysis revealed three subfamily genes expressed in five P. bournei tissues: leaves, root bark, root xylem, stem xylem, and stem bark, with predominant PCF genes. Using qRT-PCR, we examined six representative genes—PbTCP16, PbTCP23, PbTCP7, PbTCP29, PbTCP14, and PbTCP15—under stress conditions such as high temperature, drought, light exposure, and dark. PbTCP14 and PbTCP15 showed significantly higher expression under heat, drought, light and dark stress. We hypothesize that TCP transcription factors play a key role in growth under varying light conditions, possibly mediated by auxin hormones. This work provides insights into the TCP gene family’s functional characteristics and stress resistance regulation in P. bournei.

The interplay between LHCSR and PSBS proteins provides photoprotection in Chlamydomonas reinhardtii pgr5 mutant under high light

Cyclic electron transport (CET) is a vital alternative route that protects against photodamage and aids in energy production. This process depends on proton gradient regulation 5 (PGR5) and PGRL1-dependent pathways associated with CET. The exact roles of these proteins in photosystem I photochemistry under prolonged high light conditions are not fully understood. Continuous light adaptation hinges on two critical mechanisms: alterations in the proton motive force (pmf) and adjustments in the ratio of proteins activated by high light that dissipate excess light through non-photochemical quenching (NPQ). To explore this, we studied pgrl1 and pgr5 mutants to gauge their roles in balancing photochemistry and photoacclimation. These mutants showed inhibited growth, reduced photosynthetic efficiency, and a lowered pmf, leading to diminished non-photochemical energy quenching (qE) under high light. Prolonged high light exposure slowed down unregulated energy losses Y(NO), and relaxation helped regulate photosynthetic activity by increasing photoinhibitory quenching (qI), thus preventing further damage to the photosystem. The precise balance between the two pmf components, ΔpH and Δψ, is critical for controlling photochemistry and photoacclimation, yet remains elusive. In pgr5 reduced pmf led to an accumulation of cytochrome b6f under high light, and a decrease in the ΔpH component increased the Δψ component's role in photosynthetic acclimation. Notably, light-harvesting complex stress response protein 3 (LHCSR3) showed decreased expression in pgrl1, whereas pgr5 exhibited no expression of both LHCSR3 and LHCSR1 under high light conditions. Moreover, continuous increase in PSBS protein accumulation in pgr5 suggests enhanced photoprotection in the absence of LHCSR3 under high light. The study provides significant insights into how cyclic electron transport (CET) regulates photoprotective proteins LHCSR and PSBS, influencing Chlamydomonas' survival strategies.

Comparative Analysis of Phytohormone Biosynthesis Genes Responses to Long-Term High Light in Tolerant and Sensitive Wheat Cultivars.

Phytohormones are vital for developmental processes, from organ initiation to senescence, and are key regulators of growth, development, and photosynthesis. In natural environments, plants often experience high light (HL) intensities coupled with elevated temperatures, which pose significant threats to agricultural production. However, the response of phytohormone-related genes to long-term HL exposure remains unclear. Here, we examined the expression levels of genes involved in the biosynthesis of ten phytohormones, including gibberellins, cytokinins, salicylic acid, jasmonic acid, abscisic acid, brassinosteroids, indole-3-acetic acid, strigolactones, nitric oxide, and ethylene, in two winter wheat cultivars, Xiaoyan 54 (XY54, HL tolerant) and Jing 411 (J411, HL sensitive), when transferred from low light to HL for 2-8 days. Under HL, most genes were markedly inhibited, while a few, such as TaGA2ox, TaAAO3, TaLOG1, and TaPAL2, were induced in both varieties. Interestingly, TaGA2ox2 and TaAAO3 expression positively correlated with sugar content but negatively with chlorophyll content and TaAGP expression. In addition, we observed that both varieties experienced a sharp decline in chlorophyll content and photosynthesis performance after prolonged HL exposure, with J411 showing significantly more sensitivity than XY54. Hierarchical clustering analysis classified the phytohormone genes into the following three groups: Group 1 included six genes highly expressed in J411; Group 2 contained 25 genes drastically suppressed by HL in both varieties; and Group 3 contained three genes highly expressed in XY54. Notably, abscisic acid (ABA), and jasmonic acid (JA) biosynthesis genes and their content were significantly higher, while gibberellins (GA) content was lower in XY54 than J411. Together, these results suggest that the differential expression and content of GA, ABA, and JA play crucial roles in the contrasting responses of tolerant and sensitive wheat cultivars to leaf senescence induced by long-term HL. This study enhances our understanding of the mechanisms underlying HL tolerance in wheat and can guide the development of more resilient wheat varieties.

Species-specific effects of light and temperature on photosynthesis and respiration among Symbiodiniaceae (Dinophyceae)

Coral reefs are exposed to various environmental stressors that cause bleaching events, whereby endosymbiotic microalgae (Symbiodiniaceae) disassociate from coral hosts. Bleached corals are compromised and face mortality. The combination of high-light exposure and elevated seawater temperature often lead to coral bleaching. The physiological properties of the Symbiodiniaceae within the coral tissues contribute to the thermal tolerance of the holobiont (the host and all its symbionts). The present study aimed to investigate the effects of light and temperature stress on four Symbiodiniaceae species from three genera with respect to photosynthetic oxygen production and consumption. Under control conditions, the species displayed predominantly low-to-moderate light requirements for photosynthesis with increased photoinhibition at higher photon flux rates. After 30 days of heat acclimation at 32 °C, maximum photosynthetic activity declined in Effrenium voratum, doubled in Fugacium kawagutii, and remained unchanged in Breviolum psygmophilum. In subsequent acute heating assays, species-specific effects on maximum photosynthetic activity were observed. Photosynthesis in all species declined across a temperature gradient between 25 and 39 °C in the acute heating assays; full inhibition occurred at 37 °C in B. psygmophilum and E. voratum and at 39 °C in B. aenigmaticum and F. kawagutii. In contrast, respiration remained largely constant in all species across temperatures. Our data point to species-specific photophysiological traits that lead to different thermal tolerances among Symbiodiniaceae.

A Denoise Network for Structured Illumination Microscopy with Low-Light Exposure

Super-resolution structured illumination microscopy (SR-SIM) is one of the important techniques that are most suitable for live-cell imaging. The reconstructed SR-SIM images are noisy once the raw images are recorded with low-light exposure. Here, we propose a new network (entitled the ND-SIM network) to denoise the SR images reconstructed using frequency-domain algorithms (FDAs). We demonstrate that ND-SIM can yield artifact-free SR images using raw images with an average photon count down to 20 per pixel while achieving comparable resolution to the ground truth (GT) obtained with high-light exposure. We can envisage that the ND-SIM will be widely applied for the long-term, super-resolution live-cell imaging of various bioprocesses in the future.

Paired metabolomics and volatilomics provides insight into transient high light stress response mechanisms of the coral Montipora mollis

The coral holobiont is underpinned by complex metabolic exchanges between different symbiotic partners, which are impacted by environmental stressors. The chemical diversity of the compounds produced by the holobiont is high and includes primary and secondary metabolites, as well as volatiles. However, metabolites and volatiles have only been characterised in isolation so far. Here, we applied a paired metabolomic-volatilomic approach to characterise holistically the chemical response of the holobiont under stress. Montipora mollis fragments were subjected to high-light stress (8-fold higher than the controls) for 30 min. Photosystem II (PSII) photochemical efficiency values were 7-fold higher in control versus treatment corals immediately following high-light exposure, but returned to pre-stress levels after 30 min of recovery. Under high-light stress, we identified an increase in carbohydrates (> 5-fold increase in arabinose and fructose) and saturated fatty acids (7-fold increase in myristic and oleic acid), together with a decrease in fatty acid derivatives in both metabolites and volatiles (e.g., 80% decrease in oleamide and nonanal), and other antioxidants (~ 85% decrease in sorbitol and galactitol). These changes suggest short-term light stress induces oxidative stress. Correlation analysis between volatiles and metabolites identified positive links between sorbitol, galactitol, six other metabolites and 11 volatiles, with four of these compounds previously identified as antioxidants. This suggests that these 19 compounds may be related and share similar functions. Taken together, our findings demonstrate how paired metabolomics-volatilomics may illuminate broader metabolic shifts occurring under stress and identify linkages between uncharacterised compounds to putatively determine their functions.

Rapid flotation of Microcystis wesenbergii mediated by high light exposure: implications for surface scum formation and cyanobacterial species succession.

Increasing occurrences of Microcystis surface scum have been observed in the context of global climate change and the increase in anthropogenic pollution, causing deteriorating water quality in aquatic ecosystems. Previous studies on scum formation mainly focus on the buoyancy-driven floating process of larger Microcystis colonies, neglecting other potential mechanisms. To study the non-buoyancy-driven rapid flotation of Microcystis, we here investigate the floating processes of two strains of single-cell species (Microcystis aeruginosa and Microcystis wesenbergii), which are typically buoyant, under light conditions (150 μmol photons s-1 m-2). Our results showed that M. wesenbergii exhibited fast upward migration and formed surface scum within 4 hours, while M. aeruginosa did not form visible scum throughout the experiments. To further explore the underlying mechanism of these processes, we compared the dissolved oxygen (DO), extracellular polymeric substance (EPS) content, and colony size of Microcystis in different treatments. We found supersaturated DO and the formation of micro-bubbles (50-200 µm in diameter) in M. wesenbergii treatments. M. aeruginosa produces bubbles in small quantities and small sizes. Additionally, M. wesenbergii produced more EPS and tended to aggregate into larger colonies. M. wesenbergii had much more derived-soluble extracellular proteins and polysaccharides compared to M. aeruginosa. At the same time, M. wesenbergii contains abundant functional groups, which was beneficial to the formation of agglomerates. The surface scum observed in M. wesenbergii is likely due to micro-bubbles attaching to the surface of cell aggregates or becoming trapped within the colony. Our study reveals a species-specific mechanism for the rapid floatation of Microcystis, providing novel insights into surface scum formation as well as succession of cyanobacterial species.

The influence of habitat heterogeneity on Nematoda communities in Posidonia oceanica meadows

Nematodes typically comprise the most abundant phylum in meiofaunal communities. We aim to characterize the specific ecological conditions that influence Nematoda communities in Posidonia oceanica grasslands focusing on three habitats: leaves, matte, and unvegetated adjacent sediment. We hypothesized that the constant flux of nutrients under the canopy would result in a higher concentration of metazoans compared to the unvegetated sediment outside; however, the hypothesis was not confirmed by the obtained results. The habitat heterogeneity played an important role in shaping the community, yielding a greater richness in the matte. The resource specificity of the leaves (microepiphytes) was also expected to shape the community by favoring nematodes capable of exploiting this resource (epistratum feeders with scraping-like structures), such as the family Chromadoridae that dominated this habitat. In addition, the high light exposure of the leaves explains the higher concentration of ocellated nematodes in this habitat. Organic carbon and nitrogen contents had an impact on the Nematoda community composition, meanwhile average grain size only affected the abundance of nematodes with elongated/filiform tails.

Live storage of kelp under stressful conditions led to higher iodine reductions during subsequent blanching

Kelp growers and the food industry, as well as food researchers, are currently finding methods for controlling the iodine content of kelp intended for food as this is one of the major obstacles to entering a profitable market. Kelps are rich sources of dietary iodine since iodine is up-concentrated in algal tissue and utilized as an inorganic antioxidant during exposure to stress. As kelp contains much more iodine than any other food source, it is warranted to reduce the amount of iodine in the biomass prior to consumption, since both iodine deficiency and excess can cause health problems. Iodine is typically removed post-harvest using traditional methods such as blanching. In the present work, we attempted to utilize inherent stressors, i.e., intermediate storage (3 days) with high light exposure and low turnover of water, to reduce the iodine content prior to processing. Furthermore, we assessed the effect on subsequent blanching, comparing samples stored in tanks and not stored samples. The iodine content was slightly reduced when comparing storage to no storage, but in most cases not significantly so. However, after subsequent blanching, there was a pronounced added reduction for stored samples (87 % reduction) compared to not stored samples (80 % reduction). Although the differences are smaller than we expected, our research shows that using post-harvest intermediate storage of kelp may alter the iodine content post-processing. Fine-tuning the stressors and conditions could lead to new possibilities for iodine reduction.

Myopia intervention and ultraviolet radiation related eye diseases: A narrative literature review.

There has been an increased understanding of the protective effect of two or more hours in high lux light on the development and progression of myopia. The aim of myopia management is to reduce the incidence of high myopia and sight-threatening myopic complications. Equally important are the sight-threatening complications of ultraviolet radiation (UVR) on the eye and adnexal structures. This review will analyze the literature for both these epidemics to help guide public health policy. Whilst increasing childhood high lux light exposure is important, consideration of a holistic eye health policy should ensure that UV eye diseases are also prevented. The advent of ultraviolet (UV) fluorescence photography has increased our understanding that significant UV eye damage occurs in childhood, with 81% of children aged 12-15 years having signs of UV eye damage. Hence, the need to reduce myopia and protect from UV-related eye diseases needs simultaneous consideration. Advocating for eye protection is important, particularly as the natural squint reflex is disabled with dark sunglasses lenses. The pathways UV reaches the eye need to be considered and addressed to ensure that sunglasses offer optimum UV eye protection. The design of protective sunglasses that simultaneously allow high lux light exposure and protect from UVR is critical in combating both these epidemics.

Flow velocity and light intensity combination is important for Microcystis aeruginosa physical suppression.

The cyanobacterial response to flow velocity or light intensity deviates from the combined effect of both factors. The responses of Microcystis aeruginosa to different combinations of flow velocities and light intensities were tested. Growth (OD730 and protein), stress (catalase, ascorbate peroxidase, and glutathione peroxidase), and photosynthetic ability (chlorophyll-a and fluorescence) parameters of M.aeruginosa were measured to evaluate the effects of different combinations. Exposure to different flow velocity-light combinations significantly affected the growth and physiology of M.aeruginosa. Flow velocities of 0.4m s-1 showed a prominent influence on most of the measured parameters compared with no flow velocity or higher flow velocity conditions. The 1.2-m s-1 flow velocity and high light intensity (1200 μmol m-2 s-1 ) exposure caused a significant elevation in oxidative stress. Lower velocities are beneficial for M.aeruginosa at light stress, whereas extreme velocities are adverse and elevate the stress. Two categories of light-velocity combinations were identified as preferred and extreme categories, depending on whether they suppressed or supported M.aeruginosa growth. In controlling cyanobacteria blooms using flow or high-intensity light, it is imperative to consider the interaction of these two factors, as their combined effects can significantly vary the stress levels in cyanobacteria. A new system, designed to minimize mechanical damage on M.aeruginosa, was used to generate flow velocities. Additionally, the combined effects of flow velocities and light intensities have been considered for the first time. PRACTITIONER POINTS: Flow velocity can influence the effect of light on Microcystis aeruginosa. High light exposure effect on Microcystis aeruginosa can be reduced by low flow velocity. High flow velocity and high light exposure increase the stress on Microcystis aeruginosa. Different light intensities and flow velocity combinations changed Microcystis aeruginosa stress physiology.

Extraction of organic pigments from tomato (Solanum lycopersicum L.), turmeric (Curcuma longa L.) and red amaranth (Amaranthus tricolor L.) for safe use in agro-products

The utilization of synthetic dyes in food industries is a great concern for food safety and health issues. So, natural pigments can be an excellent substitute for synthetic dyes and also health-friendly for consumers. In the experiment, natural pigments were extracted from tomato (Solanum lycopersicum L.), turmeric (Curcuma longa L.) and red amaranth (Amaranthus tricolor L.). Then the stability and consumer acceptance of the extracted pigments were examined. The highest amount of pigment was extracted from turmeric (2.14 ± 0.30 %) with ethanol solvent, followed by tomato (0.67 ± 0.06 %) with hexane: acetone (1:1) solvent, and red amaranth (0.78 ± 0.05 %) with acetone solvent. Turmeric pigment showed the highest stability in high temperatures and light exposure. All of the pigments were highly stable in a neutral environment; however, tomato pigment showed the highest stability index (84.33 ± 2.52) at pH 3.0, but turmeric pigment showed the highest stability (91.67 ± 1.53) at pH 5.0. The simple preference test revealed that the use of turmeric pigment in boiled rice had the highest acceptance rate, and in terms of taste and flavor, red amaranth pigments in ice cream. So turmeric pigment can be utilized in high-temperature processing and/or acidic foods, but tomato and red amaranth pigments might be in low-temperature processing foods such as the ice-cream and soft drinks processing industry.

Modification in the ascorbate-glutathione cycle leads to a better acclimation to high light in the rose Bengal resistant mutant of Nannochloropsis oceanica

Understanding how to adapt outdoor cultures of Nannochloropsis oceanica to high light (HL) is vital for boosting productivity. The N. oceanica RB2 mutant, obtained via ethyl methanesulfonate mutagenesis, was chosen for its tolerance to Rose Bengal (RB), a singlet oxygen (1O2) generator. Compared to the wild type (WT), the RB2 mutant showed higher resilience to excess light conditions. Analyzing the ascorbate-glutathione cycle (AGC), involving ascorbate peroxidases (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.8.1.7), in the RB2 mutant under HL stress provided valuable insights. At 250 μmol photon m−2 s−1 (HL), the WT strain displayed superoxide anion radicals (O2▪-) and hydrogen peroxide (H2O2) accumulation, increased lipid peroxidation, and cell death compared to normal light (NL) conditions (50 μmol photon m−2 s−1). The RB2 mutant didn't accumulate O2▪- and H2O2 after HL exposure, and exhibited increased APX, DHAR, and GR activities and transcript levels compared to WT and remained consistent after HL treatment. Although the RB2 mutant had a smaller ascorbate (AsA) pool than the WT, its ability to regenerate dehydroascorbate (DHA) increased post HL exposure, indicated by a higher AsA/DHA ratio. Additionally, under HL conditions, the RB2 mutant displayed an improved glutathione (GSH) regeneration rate (GSH/GSSG ratio) without changing the GSH pool size. Remarkably, H2O2 or menadione (a O2▪- donor) treatment induced cell death in the WT strain but not in the RB2 mutant. These findings emphasize the essential role of AGC in the RB2 mutant of Nannochloropsis in handling photo-oxidative stress.

Mechanism of a novel antibacterial polymeric film with freshness‐retentive and hygiene‐keeping functions

AbstractThe growing concerns surrounding food loss and waste, coupled with the amplified need for effective antimicrobial technologies due to the COVID‐19 pandemic have highlighted the significance of antimicrobial solutions. This study introduces novel polymer‐based antibacterial films to address such challenges by combining antibacterial properties with durability. Using stearyldiethanolamine (C18DEA) as the active ingredient, the polyethylene‐based (PE) film is designed to prevent bacterial growth on its surface. The present study investigated the antibacterial mechanism, durability, and effectiveness of the films against representative gram‐positive and gram‐negative bacterial strains. The films developed in this study demonstrated notable durability against high water temperatures and harsh light exposure for preserving its antibacterial function on the tested bacteria from both representative groups. Scanning electron microscopy (SEM) analysis of bacteria in contact with film surface revealed damages to cellular structure leading to cell lysis even at the lower tested concentration of 800 ppm C18DEA in the film. Our proposed bactericidal mechanism suggests the alkyl chain of C18DEA disrupts bacterial cell membranes, leading to irreversible damage and cell death. Overall, the films hold significant promise for diverse applications, including extended shelf life for perishable foods and enhanced hygiene management, driven by their durability and potent antimicrobial effects.Highlights Mechanism of action of a PE film with C18DEA as active ingredient was studied. Broad‐spectrum bactericidal effect on gram‐positive and gram‐negative bacteria. Films demonstrated resistance to high water temperatures and light exposure. Study highlights the films' application in hygiene, safety, and food preservation.

Kinetics of the xanthophyll cycle and its role in photoprotective memory and response

Efficiently balancing photochemistry and photoprotection is crucial for survival and productivity of photosynthetic organisms in the rapidly fluctuating light levels found in natural environments. The ability to respond quickly to sudden changes in light level is clearly advantageous. In the alga Nannochloropsis oceanica we observed an ability to respond rapidly to sudden increases in light level which occur soon after a previous high-light exposure. This ability implies a kind of memory. In this work, we explore the xanthophyll cycle in N. oceanica as a short-term photoprotective memory system. By combining snapshot fluorescence lifetime measurements with a biochemistry-based quantitative model, we show that short-term memory arises from the xanthophyll cycle. In addition, the model enables us to characterize the relative quenching abilities of the three xanthophyll cycle components. Given the ubiquity of the xanthophyll cycle in photosynthetic organisms the model described here will be of utility in improving our understanding of vascular plant and algal photoprotection with important implications for crop productivity.

Sleep, light exposure at night, and psychological wellbeing during pregnancy

BackgroundPsychological wellbeing during pregnancy is imperative for optimal maternal outcomes. The present study aimed to determine the association between sleep quality, light exposure at night, and psychological wellbeing in the 2nd and 3rd trimesters of pregnancy.MethodsThis prospective study was conducted in 9 randomly selected government maternity clinics in Kuala Lumpur, Malaysia. Healthy women aged 20–48 years old with single pregnancy were recruited using convenience sampling (n = 169). Sleep quality, light exposure at night, and psychological wellbeing were self-reported using the Pittsburgh Sleep Quality Index (PSQI), Harvard Light Exposure Assessment (H-LEA), and Depression, Anxiety, and Stress Scale (DASS-21) in the 2nd trimester and followed-up at the 3rd trimester.ResultsDuring the 2nd and 3rd trimesters of pregnancy, mild to severe symptoms of stress (10.7 and 11.3%), anxiety (42 and 44.3%), and depression (9.6 and 16.6%) were observed among the participants. Adjusted multiple linear regression revealed that poor sleep quality and higher light exposure at night were attributed to greater stress and depression symptoms in the 3rd trimester. Higher lux level exposed from 10 pm to < 1 am was associated with increased stress (β = 0.212, p = 0.037) and depression (β = 0.228, p = 0.024). Only poor sleep quality was observed to adversely affect anxiety (β = 0.243, p = 0.002) and depression levels (β = 0.259, p = 0.001) in the 2nd trimester.ConclusionsPresent study provided preliminary findings on the association between sleep quality, light at night, and psychological wellbeing of pregnant women. As a recommendation, future research could investigate whether public health interventions aimed at decreasing artificial light at night can benefit sleep quality and the psychological health of pregnant women.

Invited Session II: Myopia and myopia control: Interactions between Light Exposure and Diurnal Rhythms on the Choroid.

Increasing evidence demonstrates that light exposure and circadian rhythms plays a role in myopia, with high intensity outdoor light being protective. The choroid may be involved in this mechanism. The goals of our studies were to examine the interaction between light exposure and circadian influences on the choroid. In Experiment 1, choroid diurnal rhythms were investigated during monocular light deprivation in adults using spectral domain optical coherence tomography imaging (SD-OCT). The left eye was light deprived for 20 hours. In Experiment 2, the effects of two hours of high intensity outdoor light exposure on retinal and choroid thickness were investigated and compared to indoor illumination and darkness. For Experiment 1, choroid diurnal variation persisted and retinal diurnal variation was eliminated in light deprived eyes. Total retinal and inner segment thicknesses decreased (P < 0.001) and outer segment + RPE thickness increased (P < 0.05) with light deprivation. For Experiment 2, the choroid was significantly thinner during outdoor light exposure compared to indoors and darkness (P < .01), but returned to baseline at follow-up (P > .05). Total retinal thickness was significantly thicker during and after the outdoor compared to indoor and dark conditions (P < .05). These studies demonstrate that the choroid is mediated by both intrinsic circadian mechanisms as well as light exposure. Choroidal thickness rhythms were not impacted by short-term light deprivation. Surprisingly, high intensity sunlight resulted in an unexpected thinning of the choroid. These findings have implications regarding the interaction between light exposure, circadian rhythm, and the choroid on myopia.

Application and stability of fungal pigments using jelly sweets as a food model system

SummaryNatural pigments have seen an increase in usage over the past decades due to their acclaimed safety and active biological properties. This is in line with the shift in consumer market preferences requiring a source replacement for synthetic colourants. Filamentous fungi are amongst the natural sources currently explored for pigment production. In this study, the heat, pH and UV light stability of fungal pigments produced by Penicillium multicolour (dark brown), P. canescens (green) and P. herquie (yellow). Talaromyces verruculosus (red) and Fusarium solani (orange) were evaluated. The antioxidant properties of the pigments as influenced by these conditions were ascertained using the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assay. The pigments were also applied in a jelly sweet formulation and incubated at ambient temperature for 4 weeks. It was demonstrated that the pigment extracts of P. multicolour and T. verruculosus were significantly affected by higher pH (7.0 and 9.0), where the decline in antioxidant activity was observed. As far as high temperature and UV light exposure are concerned, all the pigment extracts, with exception of P. herquie, maintained an antioxidant activity above 35%. On the other hand, the L*a*b* values showed no overall significant change for heat and UV light exposure with the exception of P. canescens across the four pH levels (3.0, 4.0, 7.0 and 9.0), where an increase in the ‐a (green index) coupled with a decline in brightness (L* index) and b* (blue index) was observed. Finally, there was no significant change in colour over the 4 weeks of incubation. In conclusion, fungal pigments are generally stable at normal storage conditions (ambient temperature and normal light) and can be suitably applied in jelly sweets.

Lys264 of the D2 Protein Performs a Dual Role in Photosystem II Modifying Assembly and Electron Transfer through the Quinone-Iron Acceptor Complex.

Bicarbonate (HCO3-) binding regulates electron flow between the primary (QA) and secondary (QB) plastoquinone electron acceptors of Photosystem II (PS II). Lys264 of the D2 subunit of PS II contributes to a hydrogen-bond network that stabilizes HCO3- ligation to the non-heme iron in the QA-Fe-QB complex. Using the cyanobacterium Synechocystis sp. PCC 6803, alanine and glutamate were introduced to create the K264A and K264E mutants. Photoautotrophic growth was slowed in K264E cells but not in the K264A strain. Both mutants accumulated an unassembled CP43 precomplex as well as the CP43-lacking RC47 assembly intermediate, indicating weakened binding of the CP43 precomplex to RC47. Assembly was impeded more in K264E cells than in the K264A strain, but K264A cells were more susceptible to high-light-induced photodamage when assayed using PS II-specific electron acceptors. Furthermore, an impaired repair mechanism was observed in the K264A mutant in protein labeling experiments. Unexpectedly, unlike the K264A strain, the K264E mutant displayed inhibited oxygen evolution following high-light exposure when HCO3- was added to support whole chain electron transport. In both mutants, the decay of chlorophyll fluorescence was slowed, indicating impaired electron transfer between QA and QB. Furthermore, the fluorescence decay kinetics in the K264E strain were insensitive to addition of either formate or HCO3-, whereas HCO3--reversible formate-induced inhibition in the K264A mutant was observed. Exchange of plastoquinol with the membrane plastoquinone pool at the QB-binding site was also retarded in both mutants. Hence, D2-Lys264 possesses key roles in both assembly and activity of PS II.