Quantitative Studies on Pigment Migration and Light Sensitivity in the Compound Eye at Different Light Intensities

Comparative electrophysiological and histological studies were made on the functional significance of the secondary iris pigment migration for the sensitivity of the eye in the noctuid moth Cerapteryx graminis. The pigment position at different adapting light intensities was studied as well as the influence of different positions on the sensitivity of the eye. Adapting light intensities above a certain value hold the pigment in light position. At a 3 log units lower intensity the pigment is brought into dark position and at light intensities between these limiting values the pigment attains intermediate positions. The results indicate that at light intensities between the limiting values the pigment shifts closely follow the changes in intensity of the environmental light. With the pigment in dark position the eye is about 1000 times more sensitive than when the pigment is in light position, there being a close relationship between the sensitivity of the eye and the position of the pigment at intermediate positions.     

Light-Induced Dopamine Release from Teleost Retinas Acts as a Light-Adaptive Signal to the Retinal Pigment Epithelium

In the retinal pigment epithelium (RPE) of lower vertebrates, melanin pigment granules migrate in and out of the cells' long apical projections in response to changes in light condition. When the RPE is in its normal association with the retina, light onset induces pigment granules to disperse into the apical projections; dark onset induces pigment granules to aggregate into the cell bodies. However, when the RPE is separated from the retina, pigment granule movement in the isolated RPE is insensitive to light onset. It thus seems likely that a signal from the retina communicates light onset to the RPE to initiate pigment dispersion. We have examined the nature of this retina-to-RPE signal in green sunfish, Lepomis cyanellus. In isolated retinas with adherent RPE, light-induced pigment dispersion in the RPE is blocked by treatments known to block Ca2+-dependent transmitter release in the retina. In addition, the medium obtained from incubating previously dark-adapted retinas in the light induces light-adaptive pigment dispersion when added to isolated RPE. In contrast, the medium obtained from incubating dark-adapted retinas in constant darkness does not affect pigment distribution when added to isolated RPE. These results are consistent with the idea that RPE pigment dispersion is triggered by a substance that diffuses from the retina at light onset. The capacity of the conditioned medium from light-incubated retinas to induce pigment dispersion in isolated RPE is inhibited by a D2 dopamine antagonist, but not by D1 or alpha-adrenergic antagonists. Light-induced pigment dispersion in whole RPE-retinas is also blocked by a D2 dopamine antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)     

Further evidence that the pigment in the Dubin-Johnson syndrome is not melanin

The pigment in the Dubin-Johnson syndrome (DJS) is shown unequivocally not to be a typical melanin or closely related polymer. In electron spin resonance (ESR) studies of DJS pigment from a hepatoma, it is shown that, unlike true melanins, the pigment associated with the DJS syndrome has no free radical in the absence of light. Exposure to even low levels of visible light over a broad frequency range induces a free radical in the DJS pigment. Previous studies did not appreciate the sensitivity to light of this pigment and therefore erroneously concluded that the DJS pigment had a permanent free radical. The light induced ESR signal in DJS tissue has spectroscopic properties that differ significantly from any known melanins. The pigment is not extracted by lipophilic solvents and is centrifuged down at 50,000g, but not at 5,000g.     

Studies of fluorescence inDrosophila compound eyes: changes induced by intense light and vitamin A deprivation

Summary Ultraviolet light excites a red fluorescence fromDrosophila R1–6 rhabdomeres which is superimposed on a blue background emission. Metarhodopsin (M570) pigment generates some or all of the vitamin A dependent red emission. However, the excitation spectrum for red emission peaks in the UV. This suggests that the pigment which sensitizes R1–6's visual pigment to UV light (sensitizing pigment) absorbs the UV light, sensitizing metarhodopsin's fluorescence by energy transfer. Blue emission is neither from sensitizing pigment nor from visual pigment as shown by vitamin A deprivation studies.Very intense UV or blue stimulation causes these changes: (1) conversion of visual pigment into a fluorescent product; (2) destruction of this fluorescent product; (3) a decrease in the blue background fluorescence (even in vitamin A deprived flies); and (4) a permanent destruction of visual pigment and retinal degeneration. The first effect requires intensities 3 log units brighter than needed to interconvert rhodopsin and metarhodopsin 1/2 way to photoequilibrium. UV light is about 5 times as effective as blue light for the conversion of visual pigment into fluorescent product.     

Nonlinear optical absorption of photosynthetic pigment molecules in leaves

A mathematical formulation of the relationship between optical absorption coefficient of photosynthetic pigment molecules and light intensity was developed. It showed that physical parameters of photosynthetic pigment molecule (i.e., light absorption cross-section of photosynthetic pigment molecule, its average lifetime in the excited state, total photosynthetic pigment molecules, the statistical weight, or degeneracy of energy level of photosynthetic pigment molecules in the ground state and in the excited state) influenced on both the light absorption coefficient and effective light absorption cross-section of photosynthetic pigment molecules. Moreover, it also showed that both the light absorption coefficient and effective light absorption cross-section of photosynthetic pigment molecules were not constant, they decreased nonlinearly with light intensity increasing. The occupation numbers of photosynthetic pigment molecules in the excited states increased nonlinearly with light intensity increasing.     

Elimination of egg pigment from developing ocular tissues in the frog Rana pipiens

The method by which egg pigment is eliminated from the developing retina, corneal epithelium and lens in Rana pipiens was studied with light and electron microscopy. The retina expells egg pigment into the space between the retina and pigment epithelium. This pigment is then engulfed by the pigment epithelial cells. The corneal epithelium eliminates egg pigment directly to the outside via the free surface of the epithelial cells. Egg pigment accumulates in a few cells in the lens. These cells probably degenerate and are extruded. These ectodermal derivatives in the eye are free of egg pigment long before ectodermal derivatives in other parts of the embryo lose their pigment. The early elimination of egg pigment from ocular tissues may related to the fact that these tissues must be transparent in order that light may pass freely to the photoreceptors.     

Insect pupil mechanisms

Summary The hypothesis that the glow observable in dark adapted butterfly eyes is extinguished upon light adaptation by the action of migrating retinula cell pigment granules (Stavenga, 1975a) has been investigated. Experimental procedures applying optical methods to intact, living animals were similar to those used previously to investigate the migration of retinula cell pigment granules in Hymenoptera (Stavenga and Kuiper, 1977). The data obtained from nymphalid butterflies and Hymenoptera show close parallels, favouring the pigment migration hypothesis.The retinula cell pigment granules control the light flux in the butterfly rhabdom and hence are part of a pupil mechanism. The range of action of this pupil mechanism is about 3 log units of light intensity. The speed of pupil closure is slowed down with longer dark adaptation times. The way in which pupil processes can be distinguished from photochemical processes of the visual pigment is discussed.     

The signaling pathway in photoresponses that may be mediated by visual pigments in erythrophores of Nile tilapia

The ability to increase the synthesis or vary the distribution of pigment in response to light is an important feature of many pigment cells. Unlike other light-sensitive pigment cells, erythrophores of Nile tilapia change the direction of pigment migration depending on the peak wavelength of incident light: light near 365, 400 or 600 nm induces pigment aggregation, while dispersion occurs in response to light at 500 nm. How these phenomena are achieved is currently unknown. In the present study, the phototransduction involved in the pigment dispersion caused by light at 500 nm or the aggregation by light at 600 nm was examined, using pertussis toxin, cholera toxin, blockers of ion channels, various chemicals affecting serial steps of signaling pathways and membrane-permeable cAMP analog. The results show that light-induced bidirectional movements in tilapia erythrophores may be controlled by cytosolic cAMP levels via Gi- or Gs-type G proteins. In addition, RT-PCR demonstrated for the first time the expression of mRNAs encoding red and green opsins in tilapia fins, only where erythrophores exist. Here, we suggest that multiple cone-type visual pigments may be present in the erythrophores, and that unique cascades in which such opsins couple to Gi or Gs-type G proteins are involved in the photoresponses in these pigment cells. Thus, tilapia erythrophore system seems to be a nice model for understanding the photoresponses of cells other than visual cells.     

The Conditions for Bacteriochlorophyll Formation and the Ultrastructure of a Methanol-utilizing Bacterium,Protaminobacter ruber,Classified as Non-photosynthetic Bacteria

A methanol-utilizing bacterium, Protaminobacter ruber, formed a green pigment, when it was grown on 1,2-propanediol as a sole carbon and energy source. The pigment was identified as bacteriochlorophyll a by the absorption spectrum resembling the pigment from photosynthetic bacteria and by the exact stoichiometric relationship among the original pigment, the pigment treated to remove magnesium (bacteriopheophytin) and magnesium ion obtained from the pigment. Bacteriochlorophyll formation was stimulated by the exposure to light during the relatively early stage of the growth, while the continuous light exposure completely prevented the pigment formation. Aeration was also necessary for the pigment synthesis as well as the bacterial growth. Electron micrographs of thin section of P. ruber cells cultured in the intermittent light showed the probable existence of a chromatophore-like structure.     

Action Spectra for Step-Up Photophobic Response in Blepharisma

ABSTRACT The cells of Blepharisma which possess red pigment (blepharismin) show step-up photophobic response (temporal ciliary reversal induced by a sudden increase in light intensity). Bleaching of the cells by cold shock raised a threshold light intensity for the response, Oxidation of red pigment that produced blue pigment did not raise the threshold for the response. The action spectrum for the step-up photophobic response of the cells which possess normal red pigment had peaks at about 580, 540 and 490 nm, a value which coincided with peaks of an absorption spectrum of the red pigment. The absorption spectrum of oxidized pigment (blue pigment) shifted 20 nm toward infrared light. The action spectrum for the response of the cells which possess blue pigment also shifted 20 nm toward infrared light. Results suggest that red pigment might be involved in the step-up photophobic response. Key words. Blepharismin, ciliary reversal, photoreceptors, photoresponse.     

Stimulation of Distinct D2 Dopaminergic and α2-Adrenergic Receptors Induces Light-Adaptive Pigment Dispersion in Teleost Retinal Pigment Epithelium

In the retinal pigment epithelium (RPE) of lower vertebrates, melanin pigment granules aggregate and disperse in response to changes in light conditions. Pigment granules aggregate into the RPE cell body in the dark and disperse into the long apical projections in the light. Pigment granule movement retains its light sensitivity in vitro only if RPE is explanted together with neural retina. In the absence of retina, RPE pigment granules no longer move in response to light onset or offset. Using a preparation of mechanically isolated fragments of RPE from green sunfish, Lepomis cyanellus, we investigated the effects of catecholamines on pigment migration. We report here that 3,4-dihydoxyphenylethylamine (dopamine) and clonidine each mimic the effect of light in vivo by inducing pigment granule dispersion. Dopamine had a half-maximal effect at approximately 2 nM; clonidine, at 1 microM. Dopamine-induced dispersion was inhibited by the D2 dopaminergic antagonist sulpiride but not by D1 or alpha-adrenergic antagonists. Furthermore, a D2 dopaminergic agonist (LY 171555) but not a D1 dopaminergic agonist (SKF 38393) mimicked the effect of dopamine. Clonidine-induced dispersion was inhibited by the alpha 2-adrenergic antagonist yohimbine but not by sulpiride. These results suggest that teleost RPE cells possess distinct D2 dopaminergic and alpha 2-adrenergic receptors, and that stimulation of either receptor type is sufficient to induce pigment granule dispersion. In addition, forskolin, an activator of adenylate cyclase, induced pigment granule movement in the opposite direction, i.e., dark-adaptive pigment aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structure and functional aspects of the scotopic compound eye of the sugarcane borer moth

Morphology and functional aspects of the scotopic compound eye of the moth Diatraea saccharalis, studied using light and electron microscopy, is presented. An ommatidium is composed of a laminate corneal lens, four Semper cells, a refractive cone, two primary pigment cells, six screening pigment cells, a crystalline tract that functions as an optical waveguide, and six to eight sensory retinular cells. Accessory light regulators consist of screening pigment cells that, in the dark-adapted position, increase receptor sensitivity by permitting light rays to cross over to adjacent ommatidia and specialized tracheal regions that enhance sensitivity by reflecting light back toward sensory receptors.     

Carotenoid Synthesis in Leaves of Wheat after Irradiation by Red Light

A short inipulse of red light induces a Carotenoid synthesis in dark-grown wheat leaves. This effect is particularly evident if the leaves, having received a short light impulse, are kept in darkness for six hours prior to a period of continuous irradiation for six hours. During this second period of irradiation much more carotenoids are formed than during an irradiation period of the same length, but not preceded by a pre-irradiation. The main increase in pigment contents can be brought back to β-carotene. For this pigment the short light impulse nearly doubles the pigment synthesis during a subsequent dark and light period of six + six hours as compared to the amount formed during six hours of light without pre-irradiation.     

Effect of light on growth,pigment production and culture morphology of <Emphasis Type="Italic">Monascus purpureus</Emphasis> in solid-state fermentation

The capacity to sense and respond to light is widespread in animals, plants, fungi and bacteria. The effect of light quality on growth and pigment yield of Monascus purpureus was investigated. Incubation in total darkness increased red pigment production from 14. 5 OD/g dry substrate to 22 OD/g dry substrate. In contrast, growth of the fungus in direct illumination resulted in total suppression of pigment production. It was found that both red and blue light influenced pigment yield as well as culture morphology. The authors propose the existence of a light-perception system in Monascus purpureus.     

黑莓果实色素的稳定性分析

研究了光照、温度、pH值、氧化剂（H2O2）和还原剂（Na2SO3）对黑莓（Rubus spp．）果实色素水溶液稳定性的影响。结果表明,黑莓果实色素为水溶性花色苷类化合物,对光和热有较好的耐受性,对pH、H2O2和Na2SO3较敏感,且耐还原性略强于耐氧化性。在小于pH4．0、温度低于50℃及避光条件下黑莓果实色素的稳定性较好,可作为食品色素添加剂使用。     

Genetic study of eye cancer in cattle

Heritabilities, phenotypic, and genetic correlations of lid and corneoscleral pigment and eye lesions associated with "cancer eye" were investigated in 2,831 Herefords from 34 herds in 21 states and one Canadian province. The results indicated that lid and corneoscleral pigment were heritable and genetically correlated. Corneoscleral pigment had a direct protective effect on lesions developing at the corneoscleral junction. Corneoscleral pigment and lesion development were apparently not genetically related, and lesion development was not heritable. These findings lead to the general conclusion that the genetic effect on pigment determines to a large extent the degree to which the eye is susceptible to some carcinogenic agent. The ultraviolet light component of sunlight is the most plausible carcinogenic agent that affects the eye. A genetic-environmental interaction is indicated, whereby an increasing amount of pigment lessens both susceptibility and the probability of lesion development, but whether lesions develop in the absence of pigment depends to a large extent on the amount of ultraviolet light to which the eye is exposed. The findings further indicate that the disease is controllable by selective breeding for increased amounts of lid pigment, which should lead to a correlated increase in lid and corneoscleral pigment and a decrease in lesions.     

The visual ecology of pupillary action in superposition eyes

The two most common mechanisms of pupillary screening-pigment migration in arthropod superposition eyes are the cone and longitudinal pigment migration mechanisms. The dynamics of each were investigated by optical modelling and by determining experimentally the relationship between eye glow brightness and screening pigment position within the eyes of two representative insect species: the noctuid moth Agrotis infusa and the dung beetle Copris elphenor. During dark adaptation, in both mechanisms, the screening pigment is contracted distally to expose the proximal half of each crystalline cone. During light adaptation the pigment migrates proximally and reduces light flux in the retina. In the longitudinal mechanism, pigment migrates into the clear zone of the eye. In the cone mechanism, pigment never enters the clear zone and is instead restricted to the proximal half of each crystalline cone: a migrating sleeve of pigment creates a small aperture at the end of the crystalline cone, the area of which depends on the degree of light adaptation. According to the model, the cone mechanism provides a limited range of light attenuation (ca. 0.6 log units) for which both good spatial resolution and accuracy of control are maintained, and within this range attenuation is controlled very finely. Beyond this range, whilst attenuation is still possible, diffraction at the pigment aperture and increasing coarseness of control worsen visual performance significantly. In contrast, the longitudinal mechanism provides a much larger useful range of light attenuation (up to several log units) and maintains reasonable fineness of attenuation control over the entire range (although not as fine as the cone mechanism). The experimental results support the model. An extensive survey of arthropods with superposition eyes reveals that the cone mechanism is almost exclusively possessed by those animals experiencing a narrow range of light intensities, and the longitudinal mechanism by those experiencing a wide range.Dedicated to Professor Rolf Elofsson on the occasion of his retirement from the Chair of Zoology in Lund     

光合作用对光和CO2响应模型的研究进展

光合作用对光和CO₂响应模型是研究植物生理和植物生态学的重要工具, 可为植物光合特性对主要环境因子的响应提供科学依据。该文综述了当前光合作用对光和CO₂响应模型的研究进展和存在的问题, 并在此基础上探讨了这些模型的可能发展趋势。光合作用涉及光能的吸收、能量转换、电子传递、ATP合成、CO₂固定等一系列复杂的物理和化学反应过程。光合作用由原初反应、同化力形成和碳同化3个基本过程构成, 任一个过程均可对光合作用速率产生直接的影响。光合作用对光响应模型只涉及光能的转换, 而光合作用的生化模型包含了同化力形成和碳同化这两个基本过程。把光合作用的原初反应, 即把参与光能吸收、传递和转换的捕光色素分子的物理参数(如捕光色素分子数、捕光色素分子光能吸收截面、捕光色素分子处于激发态的平均寿命等)结合到生化模型中, 可能是今后光合作用对光响应机理模型的发展方向。     

夜蛾复眼转化速度与光暗适应的时间关系

夜行蛾类的复眼,随光、暗适应时间而逐步转化,这种转化是可逆的.以屏蔽色素分布范围的大小为指标来判断复眼的转化速度得以下结果:1.从亮眼到暗眼:亮眼进入暗适应后其屏蔽色素随暗适应时间的增加而逐步向远心端方向集中.屏蔽色素的移动是减速进行的.暗适应开始后的前3分钟,每分钟移动百分率为10.7,当暗到10—15分钟时每分钟移动百分率为4.6,再暗到60—150分钟时每分钟移动百分率为0.7.屏蔽色素移动的速度个体间差异较大,完成全过程大多数个体需150分钟,少数个体只需60分钟,另有个别个体经过270分钟暗适应仍尚未完成全过程.2.从暗眼到亮眼:暗眼受光后,其屏蔽色素随光适应时间的增加而向近心端方向扩散,色素移动速度随时间的增加而减缓.转化全过程约需60分钟.     

Direct Action of Light in Naturally Pigmented Muscle Fibers : I. Action spectrum for contraction in eel iris sphincter

Contraction due to light in excised eel irises appears to follow a simple first order law. The action spectrum for contraction has a maximum which agrees with the eel rhodopsin absorption maximum. Inasmuch as rhodopsin is the rod pigment-opsin complex and the iris sphincter pupillae evolves from the pigment epithelium of the retina in the region of the iris, the muscle pigment might be the same as the visual pigment. In the human eye the contraction of the iris sphincter is activated only by light incident on the retina and the pupil diameter varies inversely with the square root of the light intensity. The inverse first power relation observed in the present experiments suggests a more primitive origin for the light reaction in eel irises. Relaxation is a much slower process and can be approximated as the sum of two first order processes.