Screening Pigment Research Articles

The role of pigments in light color variation of the firefly Photinus pyralis.

Fireflies use bioluminescent signals to communicate with their mates. Luciferase has been thought to be the sole contributor to light color; however, populations of the Photinus pyralis firefly display variation in the color of their emitted signals yet have identical luciferase sequences. Here, we examined whether pigments could be present in the light organs of the twilight-active species P. pyralis and contribute to this variation. We detected patterns of expression that suggest ommochrome and pterin screening pigments are expressed in P. pyralis light organs and could filter light emitted by luciferase and play a role in signal tuning. There were no significant differences between the pigment gene expression of P. pyralis individuals with yellower and greener signals. Our study provides alternative mechanisms that could influence pigments in P. pyralis light organs that could also play a role in modifying signal color.

Non-invasive recording of electroretinogram from both compound eyes in the cockroach <i>Periplaneta americana L.<i> in response to light stimuli

The paper presents an original method of non-invasive registration of electroretinogram from both compound eyes of an insect. The method demonstrated high reliability and repeatability of the results. Using this method, it was shown that the magnitude of the light responses obtained from mutant cockroaches devoid of screening pigment, pearl, was about 4 times greater than those of wild-type insects. The time to peak of the response decreased with increasing light intensity, both for short-wavelength and long-wavelength stimuli. The pearl cockroaches exhibited a faster time to peak response than wild-type cockroaches; the results of covariance analysis indicate that these differences cannot be fully explained by an increase in the number of photons reaching the photoreceptor membranes and suggest additional differences in the compound eye physiology of mutant and wild-type insects. The positive voltage wave after the end of light stimulation depends on light intensity and reflects hyperpolarization of receptor cells. The photovoltaic effect, which distorts the amplitude and the shape of the response can be eliminated by using a gold wire as a recording electrode.

Retinal Pigment Epithelium Pigment Granules: Norms, Age Relations and Pathology.

The retinal pigment epithelium (RPE), which ensures the normal functioning of the neural retina, is a pigmented single-cell layer that separates the retina from the Bruch's membrane and the choroid. There are three main types of pigment granules in the RPE cells of the human eye: lipofuscin granules (LG) containing the fluorescent "age pigment" lipofuscin, melanoprotein granules (melanosomes, melanolysosomes) containing the screening pigment melanin and complex melanolipofuscin granules (MLG) containing both types of pigments simultaneously-melanin and lipofuscin. This review examines the functional role of pigment granules in the aging process and in the development of oxidative stress and associated pathologies in RPE cells. The focus is on the process of light-induced oxidative degradation of pigment granules caused by reactive oxygen species. The reasons leading to increased oxidative stress in RPE cells as a result of the oxidative degradation of pigment granules are considered. A mechanism is proposed to explain the phenomenon of age-related decline in melanin content in RPE cells. The essence of the mechanism is that when the lipofuscin part of the melanolipofuscin granule is exposed to light, reactive oxygen species are formed, which destroy the melanin part. As more melanolipofuscin granules are formed with age and the development of degenerative diseases, the melanin in pigmented epithelial cells ultimately disappears.

Functional Anatomy of Split Compound Eyes of the Whirligig Beetles Dineutus mellyi (Coleoptera: Gyrinidae).

The functional anatomy of the split compound eyes of whirligig beetles Dineutus mellyi (Coleoptera: Gyrinidae) was examined by advanced microscopy and microcomputed tomography. We report the first 3D visualization and analysis of the split compound eyes. On average, the dorsal and ventral eyes contain 1913 ± 44.5 facets and 3099 ± 86.2 facets, respectively. The larger area of ventral eyes ensures a higher field of vision underwater. The ommatidium of the split compound eyes is made up of laminated cornea lenses that offer protection against mechanical injuries, bullet-shaped crystalline cones that guide light to the photoreceptive regions, and screening pigments that ensure directional light passage. The photoreceptive elements, made up of eight retinular cells, exhibit a tri-tiered rhabdom structure, including the upper distal rhabdom, a clear zone that ensures maximum light passage, and an enlarged lower distal rhabdom that ensures optimal photon capture.

Understanding the Mechanism of Light-Induced Age-Related Decrease in Melanin Concentration in Retinal Pigment Epithelium Cells.

It is known that during the process of aging, there is a significant decrease in the number of melanosomes in the retinal pigment epithelium (RPE) cells in the human eye. Melanosomes act as screening pigments in RPE cells and are fundamentally important for protection against the free radicals generated by light. A loss or change in the quality of melanin in melanosomes can lead to the development of senile pathologies and aggravation in the development of various retinal diseases. We have previously shown that the interaction between melanin melanosomes and superoxide radicals results in oxidative degradation with the formation of water-soluble fluorescent products. In the present study, we show, using fluorescence analysis, HPLC, and mass spectrometry, that visible light irradiation on melanolipofuscin granules isolated from RPE cells in the human eye results in the formation of water-soluble fluorescent products from oxidative degradation of melanin, which was in contrast to lipofuscin granules and melanosomes irradiation. The formation of these products occurs as a result of the oxidative degradation of melanin by superoxide radicals, which are generated by the lipofuscin part of the melanolipofuscin granule. We identified these products both in the composition of melanolipofuscin granules irradiated with visible light and in the composition of melanosomes that were not irradiated but were, instead, oxidized by superoxide radicals. In the melanolipofuscin granules irradiated by visible light, ions that could be associated with melanin oxidative degradation products were identified by applying the principal component analysis of the time-of-flight secondary ion mass spectrometry (ToF-SIMS) data. Degradation of the intact melanosomes by visible light is also possible; however, this requires significantly higher irradiation intensities than for melanolipofuscin granules. It is concluded that the decrease in the concentration of melanin in RPE cells in the human eye with age is due to its oxidative degradation by reactive oxygen species generated by lipofuscin, as part of the melanolipofuscin granules, under the action of light.

Kinetic Extraction of Fucoxanthin from Undaria pinnatifida Using Ethanol as a Solvent.

Fucoxanthin (Fx) has been proven to exert numerous biological properties, which makes it an interesting molecule with diverse industrial applications. In this study, the kinetic behavior of Fx was studied to optimize three variables: time (t-3 min to 7 days), temperature (T-5 to 85 °C), and concentration of ethanol in water (S-50 to 100%, v/v), in order to obtain the best Fx yield from Undaria pinnatifida using conventional heat extraction. The Fx content (Y1) was found through HPLC-DAD and expressed in µg Fx/g of algae sample dry weight (AS dw). Furthermore, extraction yield (Y2) was also found through dry weight analysis and was expressed in mg extract (E)/g AS dw. The purity of the extracts (Y3) was found and expressed in mg Fx/g E dw. The optimal conditions selected for Y1 were T = 45 °C, S = 70%, and t = 66 min, obtaining ~5.24 mg Fx/g AS; for Y2 were T = 65 °C, S = 60%, and t = ~10 min, obtaining ~450 mg E/g AS; and for Y3 were T = 45 °C, S = 70%, and t = 45 min, obtaining ~12.3 mg Fx/g E. In addition, for the selected optimums, a full screening of pigments was performed by HPLC-DAD, while phenolics and flavonoids were quantified by spectrophotometric techniques and several biological properties were evaluated (namely, antioxidant, antimicrobial, and cholinesterase inhibitory activity). These results could be of interest for future applications in the food, cosmetic, or pharmaceutical industries, as they show the Fx kinetic behavior and could help reduce costs associated with energy and solvent consumption while maximizing the extraction yields.

Intense light unleashes male-male courtship behaviour in wild-type Drosophila.

Drosophila courtship studies have elucidated several principles of the neurogenetic organization of complex behaviour. Through an integration across sensory modalities, males perform stereotypic patterns of chasing, courtship song production and copulation attempts. Here we report a serendipitous finding that intense light not only enhances courtship toward female targets but also triggers unexpected courtship behaviours among male flies. Strikingly, in wild-type male-only chambers, we observed extreme behavioural manifestations, such as 'chaining' and 'wheeling', resembling previously reported male-male courtship behaviours in fruitless mutants and in transformants with ectopic mini-white+ overexpression. This male-male courtship was greatly diminished in a variety of visual system mutants, including disrupted phototransduction (norpA), eliminated eye-colour screening pigments (white), or deletion of the R7 photoreceptor cells (sevenless). However, light-induced courtship was unhampered in wing-cut flies, despite their inability to produce courtship song, a major acoustic signal during courtship. Unexpectedly the olfactory mutants orco and sbl displayed unrestrained male-male courtship. Particularly, orco males attained maximum courtship scores under either dim or intense light conditions. Together, our observations support the notion that the innate male courtship behaviour is restrained by olfactory cues under normal conditions but can be unleashed by strong visual stimulation in Drosophila.

Electron-transfer MALDI MS methodology for microalgae/phytoplankton pigments analysis

The method describes pigment analysis from microalgae/phytoplankton extracts using electron-transfer Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (ET MALDI MS). Current microalgae/phytoplankton pigment analysis requires resource- and time-intensive chromatographic methods due to the broad polarity range of the target analytes. On the other hand, traditional MALDI MS chlorophyll analysis, using proton-transfer matrices such as 2,5-dihydroxybenzoic acid (DHB) or α-cyano-4-hydroxycinnamic acid (CHCA), results in central metal loss and phytol–ester cleavage. ET MALDI MS is an alternative for the rapid screening and detection of pigments in microalgae extracts.•MALDI matrices with ionization energies above 8.0 eV guarantee electron-transfer processes from photosynthetic and photoprotective pigments whose ionization energies lay below 7.5 eV.•ET MALDI MS pigment analysis agrees with data gathered from conventional chromatographic techniques (HPLC) and optical microscopy for pigment extracts from C. vulgaris cultures and freshwater phytoplankton samples.•The ET MALDI MS method allows fast and reliable detection of pigments in microalgae cultures and freshwater phytoplankton samples.

Opponent processing in the retinal mosaic of nymphalid butterflies.

The eyes of nymphalid butterflies, investigated with incident illumination, show colourful facet reflection patterns—the eye shine—which is uniform or heterogeneous, dependent on the species. Facet colours suggest that the ommatidia contain different sets of photoreceptors and screening pigments, but how the colours and the cell characteristics are associated has not been clearly established. Here, we analyse the retinae of two nymphalids, Apatura ilia, which has a uniform eyeshine, and Charaxes jasius, a species with a heterogeneous eye shine, using single-cell recordings, spectroscopy and optical pupillometry. Apatura has UV-, blue- and green-sensitive photoreceptors, allocated into three ommatidial types. The UV- and blue-sensitive cells are long visual fibres (LVFs), receiving opponent input from the green-sensitive short visual fibres (SVFs). Charaxes has an expanded set of photoreceptors, allocated into three additional, red-reflecting ommatidial types. All red ommatidia contain green-sensitive LVFs, receiving opponent input from red receptors. In both species, the SVFs do not receive any opponent input. The simple retina of Apatura with three ommatidial types and two colour-opponent channels can support trichromatic vision. Charaxes has six ommatidial types and three colour-opponent channels. Its expanded receptor set can support tetrachromatic vision.This article is part of the theme issue ‘Understanding colour vision: molecular, physiological, neuronal and behavioural studies in arthropods’.

A HPLC‐DAD method for identifying and estimating the content of fucoxanthin, β‐carotene and chlorophyll a in brown algal extracts

Seaweeds are photosynthetic organisms that have high contents of pigments. The coloration of each alga is defined by the content and combination of pigments synthesized, which varies among species and environmental conditions. The most abundant pigments in algae are chlorophylls and carotenoids, lipophilic molecules that can be used as natural colorants and have high acceptance by consumers. In this work, a simple and short hands-on time HPLC-DAD method for identifying and estimating the pigment content of algal extracts, specifically fucoxanthin, β-carotene and chlorophyll a was carried out. Using this optimized method, a pigment screening was performed on the ethanolic extracts obtained by ultrasound-assisted extraction from nine brown algal from the Atlantic coastline: Ascophyllum nodosum, Bifurcaria bifurcata, Fucus spiralis, Himanthalia elongata, Laminaria saccharina, Laminaria ochroleuca, Pelvetia canaliculata, Sargassum muticum and Undaria pinnatifida. HPLC results permitted to highlight L. saccharina and U. pinnatifida as promising sources of these three target pigments containing a total amount of 10.5 – 11.5 mg per gram of dry weight. Among them, the most abundant one was fucoxanthin, an added-value compound with a high potential to be commercially exploited by different industries, such as the food, cosmetic, and pharmaceutical sectors.

Pigment screening, phytochemical test, and cytotoxicity testing of the ethanol extract of Holothuria atra sea cucumber from Lemukutan island waters

Background: Holothuria atra is a type of sea cucumber found in the waters of Lemukutan Island, West Kalimantan, which has economic and ecological benefits. Personal experience found the presence of a water-soluble pigment when isolating sea cucumbers, which was bright red, thus drawing attention. Research on the water-soluble pigment of the ethanol extract of H. atra from Lemukutan Island waters has not been carried out yet. Natural pigments in sea cucumbers have a specific role as part of secondary metabolite compounds with the potential of having antimicrobial, antifungal, anticancer, antitumor, antiviral, anticoagulant, and antioxidant activities.Objective: This study aimed to determine the natural pigments, secondary metabolites, and cytotoxic compounds in the ethanolic extract of H. atra.Methods: Samples of H. atra were extracted with 96% ethanol. The pigment analysis used UV-Vis spectrophotometry while the secondary metabolites were tested by the phytochemical screening method, and the cytotoxicity testing involved the Brine Shrimp Lethal Toxicity (BSLT) method.Results: The obtained optimum absorption was 230 nm, which indicated a melanin pigment. The phytochemical test on the ethanolic extract of H. atra found flavonoid, phenolic, alkaloid, saponin, and triterpenoid compounds. The cytotoxicity test based on LC50 was 6.985 ppm, indicating the extract was categorized as extremely toxic because it was Conclusion: The pigment in H. atra is melanin, the secondary metabolites consist of flavonoids, phenolics, alkaloids, saponins, and triterpenoids, and it has a highly toxic activity.Keywords: Holothuria atra, melanin, phytochemical test, BSLT, cytotoxic IntisariLatar belakang: Holothuria atra adalah salah satu jenis teripang yang ditemukan di Perairan Pulau Lemukutan Kalimantan Barat, memiliki manfaat ekonomi maupun ekologi. Pengalaman saat pengambilan sampel dijumpai adanya pigmen larut air dari tempat sampel, berwarna merah cerah dan menarik perhatian. Penelitian tentang pigmen larut air pada ekstrak etanol H. atra dari perairan Pulau Lemukutan belum pernah dilakukan. Pigmen alami pada teripang memiliki peranan tertentu, sebagai bagian dari senyawa metabolit sekunder berpotensi sebagai antimikroba, antijamur, antikanker, antitumor, antivirus, antikoagulan dan antioksidan.Tujuan: Penelitian ini bertujuan mengetahui pigmen alami, senyawa metabolit sekunder dan potensi sitotoksik pada ekstrak etanol H. atra.Metode: Sampel H. atra diekstraksi dengan etanol 96%. Analisis pigmen menggunakan spektrofotometri UV-Vis, pengujian senyawa metabolit sekunder dengan metode skrining fitokimia dan uji sitotoksik menggunakan metode Brine Shrimp Lethal Toxicity (BSLT).Hasil: Serapan optimum yang dihasilkan oleh ekstrak etanol adalah 230 nm yang merupakan pigmen melanin. Hasil uji fitokimia pada ekstrak etanol H. atra ditemukan senyawa flavonoid, fenolik, alkaloid, saponin dan triterpenoid. Uji sitotoksik berdasarkan LC50 adalah 6,985 ppm menunjukkan ekstrak dengan kategori sangat toksik karena nilainya Kesimpulan: Pigmen pada H.atra yaitu melanin. Kadungan ekstrak etanol metabolit sekunder teridiri dari flavonoid, fenolik, alkaloid, saponin dan triterpenoid serta memiliki aktivitas toksistas yang sangat toksik.Kata kunci: Holothuria atra, melanin, uji fitokmia, BSLT, sitotoksik

An anatomical and ultrastructural study of the eye of the luminescent millipede Paraspirobolus lucifugus (Gervais 1836) (Diplopoda, Spirobolida, Spiroboleliidae)

The two forward-looking eyes and their ultrastructural organization of an 18 mm long adult bioluminescent female millipede (Paraspirobolus lucifugus) were investigated by transmission electron microscopy and energy-dispersive X-ray spectroscopy. Each eye contained approximately 23 ommatidia with 50–60 μm wide and 80 um thick corneal lenses that contained calcium and silicon and proximally ended in truncated flat surfaces of around 20 μm in diameter. A maximally 28 μm thick and 25 μm long rhabdom, made up of at least 12–14 retinula cells and a 4 μm thick sleeve of screening pigment granules in a light-adapted position was present. Compared with the eyes of non-luminescent julid millipede species, those of P. lucifugus share their basic anatomy, but also exhibit features like the wide possible binocular frontal visual overlap, somewhat narrower interommatidial angles combined with relatively larger rhabdoms, which suggests that P. lucifugus has more efficient eyes and makes greater use of its photoreceptors. P. lucifugus is negatively phototactic and strictly nocturnal and its activity rhythm is apparently governed by a circadian clock.

Screening of natural pigments from indigenous marine microalgae isolated from different coastal aquafarms of Bangladesh

Globalization demands something new and natural. Natural pigments from microalgae could be something like that. However, it is a long way from a Petri dish to market. However, it is going to happen. So, knowing the pigment concentration among different species is necessary because of its significant role in the global market. The present study is designed to estimate the Chlorophylls, carotenoids and phycobiliproteins (Allophycocyanin, Phycocyanin and Phycoerythrin) contents of four (4) different indigenous marine microalgae species i.e. Chlorella sp., Chaetoceros sp., Nannochloropsis sp. and Tetraselmis sp. The result showed significant differences in the concentration of pigments among the species. However, Tetraselmis sp. produced a significantly higher amount of chlorophyll a (2.68 µg/L ± 0.04), and Chlorophyll b (1.23±0.02 µg/L) where Chaetoceros sp. had higher chlorophyll c (0.29±0.01 µg/L) among all the species. In the case of carotenoids, Chlorella sp. produced the lowest carotenoids (0.56±0.02 µg/L), where the other three showed no significant difference. Allophycocyanin and phycoerythrin were reported significantly higher (0.0197±0.0006 µg/L) and (0.0029 ± 0.0002 µg/L) in Nannochloropsis sp. rather than other three species where no significant difference was found in the concentrations of phycocyanin among all the species. Whatever the amount is, these microalgae are important because of their novel features. The study's findings will help the producer select a definite species according to their target and needs.

Screening, Characterization, and Isolation of Pigments from Bacteria in Mesophotic Depths of the Benham Bank Seamount, Philippine Rise Region

The exploration for pigment-producing bacteria and structurally novel pigment continues to increase, and the marine environment has recently become an attractive research site for these investigations because of its rich yet untapped biodiversity. In this study, 16S rRNA gene sequencing and HPLC (high-performance liquid chromatography) profiling of the microbial pigments produced by marine heterotrophic bacteria were described. Seven phenotypically distinct isolates of marine pigmented heterotrophic bacteria (MPHB) were isolated from near-bottom waters and coral reef sediments at mesophotic depths of the Benham Bank Seamount – namely, isolates BR14, BR61, BR63, BR100, BR101, BR144, and BR146. Four promising isolates were subjected to 16S rRNA gene sequencing and revealed that strains BR61 and BR100 were related to members of the genus Cytobacillus, whereas isolates BR144 and BR146 clustered with Meridianimaribacter flavus and Pseudoalteromonas rubra, respectively. Growth of the seven isolates on three media – natural sea water (NSW) Reasoner’s 2A (R2A), marine agar (MA), and tryptic soy agar – revealed variable pigment production and growth yield. MA appeared to be a superior substrate, resulting in darker pigmentation and higher biomass yield. Through a liquid-liquid partitioning approach, isolates BR14 and BR100 produced pigments that were acetone-soluble, whereas isolates BR101, BR144, and BR146 are hexane soluble. Moreover, the BR146 red pigment was proposed to be a mixture of putative prodiginine analogs. The putative prodiginines produced by isolate BR146 can stain fabrics, supporting a proof-of-concept that marine bacteria can be utilized as fabric colorants. The data presented here provided new insights into the utilization of local Philippine marine microbial resources for natural marine pigments with industrial applications.

Fine Structure of the Visual System of Arge similis (Hymenoptera, Argidae).

Simple SummaryArge similis is a notorious pest on rhododendron plants. The fine structure of the compound eyes of A. similis adults were examined by light, scanning, and transmission electron microscopy. Each ommatidium consists of a lamellated cornea, a crystalline cone with eucone type, and a centrally fused rhabdom composed of eight retinular cells.External morphology and ultrastructure of the visual system of Arge similis (Vollenhoven, 1860) adults were investigated by light microscopy, scanning electron microscopy, and transmission electron microscopy. Each compound eye contains 2022 ± 89 (mean ± SE) facets in males and 2223 ± 52 facets in females. Arge similis has an apposition kind of compound eye composed of a cornea, a crystalline cone of four cone cells, and a centrally fused rhabdom made up of the rhabdomeres of eight large retinular cells. Each crystalline cone is surrounded by primary and secondary pigment cells with black spherical screening pigment granules measuring 0.60 ± 0.02 and 0.41 ± 0.01 μm in diameter, respectively. Based on our findings, the compound eye of A. similis can be expected to exhibit high adaptability to light intensity changes.

Screening of Bio-active Pigments, Antioxidant Activity, Total Phenolic and Flavonoid Content of Some Economically Important Medicinal Plants for Ethno-botanical Uses

An experiment was conducted to determinate the phytochemical properties (chlorophyll-a, chlorophyll-b, carotenoids, antioxidant activity, total phenolic and flavonoid content) in ten medicinal plants namely Syal Kata (Argemone mexicana L.), Akanda (Calotropis gigantea (L.) Dryand.), Dumur (Ficus carica L.), Chalmugra (Gynocardia odorata R.Br.), Kata kachu (Lasia spinosa (L.) Thwaites), Shetodrone (Leucas aspera (Wild.)), Khona (Oroxylum indicum (L.) Kurz), Reri (Ricinus communis L.), Ghat kachu (Typhonium trilobatum (L.) Schott) and Bazna (Zanthoxylum rhetsa DC.) for ethno-botanical uses. The young fresh leaves were harvested and were subjected to methanolic (95%) extract. Total phenolic contents were analysed by using Folin - Ciocalteau method where gallic acid was used as standard. Total phenolic content varied from 94.53 mg GAE/100 g FW (C. gigantea) to 484.88 mg GAE/100 g FW (L. aspera). Total flavonoid contents were performed by using Quercetin as standard. Total flavonoid content varied from 137.25 mg QUE /100 g FW (C. gigantea) to 334.27 mg QUE/100 g FW (G. odorata). Antioxidant activity of these extracts was performed by using DPPH free radical scavenging assay. Total anti-oxidant capacity varied from IC50 value 35.37 mg/mL (A. mexicana) to 90.47 mg/mL (F. carica) where ascorbic acid is used as standard. Results indicated that among the ten medicinal plants phenolics rich in L. aspera, flavonoids rich in G. odorata, antioxidant activity rich in A. mexicana. Z. rhetsa leaf rich in chlorophyll-a content (311.67 mg/100 g FW), L. aspera leaf rich in chlorophyll-b content (157 mg/100 g FW), Z. rhetsa rich in chlorophyll- (a+b) content as 439 mg/100 g FW, A. mexicana leaf rich in carotenoids content as 96 mg/100 g FW.

Red-green opponency in the long visual fibre photoreceptors of brushfoot butterflies (Nymphalidae).

In many butterflies, the ancestral trichromatic insect colour vision, based on UV-, blue- and green-sensitive photoreceptors, is extended with red-sensitive cells. Physiological evidence for red receptors has been missing in nymphalid butterflies, although some species can discriminate red hues well. In eight species from genera Archaeoprepona, Argynnis, Charaxes, Danaus, Melitaea, Morpho, Heliconius and Speyeria, we found a novel class of green-sensitive photoreceptors that have hyperpolarizing responses to stimulation with red light. These green-positive, red-negative (G+R–) cells are allocated to positions R1/2, normally occupied by UV and blue-sensitive cells. Spectral sensitivity, polarization sensitivity and temporal dynamics suggest that the red opponent units (R–) are the basal photoreceptors R9, interacting with R1/2 in the same ommatidia via direct inhibitory synapses. We found the G+R– cells exclusively in butterflies with red-shining ommatidia, which contain longitudinal screening pigments. The implementation of the red colour channel with R9 is different from pierid and papilionid butterflies, where cells R5–8 are the red receptors. The nymphalid red-green opponent channel and the potential for tetrachromacy seem to have been switched on several times during evolution, balancing between the cost of neural processing and the value of extended colour information.

Photoprotection in lichens: adaptations of photobionts to high light

AbstractLichens often grow in microhabitats where they are exposed to severe abiotic stresses such as desiccation and temperature extremes. They are also often exposed to levels of light that are greater than lichen photobionts can use in carbon fixation. Unless regulated, excess energy absorbed by the photobionts can convert ground state oxygen to reactive oxygen species (ROS). These ROS can attack the photosynthetic apparatus, causing photoinhibition and photo-oxidative stress, reducing the ability of the photobionts to fix carbon. Here, we outline our current understanding of the effects of high light on lichens and the mechanisms they use to mitigate or tolerate this stress in hydrated and desiccated states. Tolerance to high light can be achieved first by lowering ROS formation, via synthesizing light screening pigments or by thermally dissipating the excess light energy absorbed; second, by scavenging ROS once formed; or third, by repairing ROS-induced damage. While the primary focus of this review is tolerance to high light in lichen photobionts, our knowledge is rather fragmentary, and therefore we also include recent findings in free-living relatives to stimulate new lines of research in the study of high light tolerance in lichens.

The spectral sensitivity of Drosophila photoreceptors

Drosophila melanogaster has long been a popular model insect species, due in large part to the availability of genetic tools and is fast becoming the model for insect colour vision. Key to understanding colour reception in Drosophila is in-depth knowledge of spectral inputs and downstream neural processing. While recent studies have sparked renewed interest in colour processing in Drosophila, photoreceptor spectral sensitivity measurements have yet to be carried out in vivo. We have fully characterised the spectral input to the motion and colour vision pathways, and directly measured the effects of spectral modulating factors, screening pigment density and carotenoid-based ocular pigments. All receptor sensitivities had significant shifts in spectral sensitivity compared to previous measurements. Notably, the spectral range of the Rh6 visual pigment is substantially broadened and its peak sensitivity is shifted by 92 nm from 508 to 600 nm. We show that this deviation can be explained by transmission of long wavelengths through the red screening pigment and by the presence of the blue-absorbing filter in the R7y receptors. Further, we tested direct interactions between inner and outer photoreceptors using selective recovery of activity in photoreceptor pairs.

Evolution of Insect Color Vision: From Spectral Sensitivity to Visual Ecology.

Color vision is widespread among insects but varies among species, depending on the spectral sensitivities and interplay of the participating photoreceptors. The spectral sensitivity of a photoreceptor is principally determined by the absorption spectrum of the expressed visual pigment, but it can be modified by various optical and electrophysiological factors. For example, screening and filtering pigments, rhabdom waveguide properties, retinal structure, and neural processing all influence the perceived color signal. We review the diversity in compound eye structure, visual pigments, photoreceptor physiology, and visual ecology of insects. Based on an overview of the current information about the spectral sensitivities of insect photoreceptors, covering 221 species in 13 insect orders, we discuss the evolution of color vision and highlight present knowledge gaps and promising future research directions in the field.