Guanine Crystals Research Articles

Guanine-Type retinal tapetum of three species of mormyrid fishes

The eye of mormyrid fishes (Marcusenius andGnathonenius) contains a retinal tapetum composed of guanine crystals. InMarcusenius, the quantity of guanine is about 2 mg cm−2 of the retinal surface area. The retina is duplex, and the cones and rods are grouped in bundles. Each bundle is surrounded by pigment epithelial cell processes which contain numerous guanine reflectors. Two kinds of reflector are present: brick-shaped and rodlet. Mormyrids may use their high sensitivity for nocturnal activities. The retinal features of mormyrid fishes were compared with those of other fish species belonging to the Notopteroidei such as the Hiodontidae, Notopteridae and Gymnarchidae, and related to the chemical nature of notopterid and gymnarchid tapetum.

The Herring: A Successful Species?

The herring has an elaborate racial system closely linked to its spawning habits. Its demersal eggs are laid in a wide range of environments from the deeper parts of the continental shelf to the intertidal zone and in a wide range of salinities and temperatures between latitudes 35 and 70°N. Depending on the race, spawning occurs in all months of the year and the relationship between fecundity and egg size is correlated with the season, with high fecundity and small eggs in the summer and fall and low fecundity and large eggs in the winter and spring. The herring is specially adapted in other respects. There is a complex camouflage system based on silvery layers of guanine crystals in the skin, a specialised retina, and a very complex acoustico-lateralis system linked to the swimbladder. It is physostomous, allowing rapid vertical movements of wide amplitude, and strongly schooling in habit with the facility to switch from particulate to filter-feeding. Filter-feeding can continue in darkness. Although many herring stocks have been overfished, there is no reason to suppose that they cannot recover, to the historical high levels, if properly managed. The stock size varies from millions to hundreds of tonnes, depending on the race, and this has interesting implications for the stock-recruitment relationship.

The herring swimbladder: loss and gain of gas

The herring is a physostome with no gas secretion mechanism in the swimbladder. The swimbladder volume was measured in fish from about 3–33 cm in length. It was rarely large enough to give the fish neutral buoyancy at the sea surface. Swimbladder volumes were also measured after periods of up to 1 week at pressures from 1·9 to 5·5 ATA (0·9–4·5atm above atmospheric pressure) in a laboratory pressure vessel and in a sub-surface cage in the sea. The swimbladder gas was lost within a few hours in the larval herring and in a few days in smaller juvenile fish; no change was found in older fish under experimental conditions. The findings were in accord with measurements of the guanine content of the swimbladder wall which was low in those fish which lost gas quickly. This supports the view that gas diffusion is limited by guanine crystals. While it seems likely that larger fish can exist for several weeks without the need to replenish the swimbladder gas some large spawning herring were caught at sea with empty swimbladders, suggesting a long stay near the sea bed. Analysis of swimbladder gas showed that oxygen tended to diffuse out more quickly than nitrogen. Behaviour experiments showed that fish with artificially emptied swimbladders could refill them by swallowing air at the surface, in some cases very quickly and efficiently. Fish with empty swimbladders and no access to the surface suffered a high mortality. The ecological implications of these results and their relevance to the interpretation of sonar ‘target strength’ measurements are discussed.

Guanine in Balanus balanoides (L.) and Balanus crenatus Bruguière

Intracellular guanine crystals in the tergoscutal flaps and 2nd and 3rd cirri of Balanus balanoides (L.) and B. crenatus Bruguière have been identified with the use of thin-layer chromatography and ultraviolet spectrophotometry. This is the first time that the presence of intracellular crystalline guanine has been recorded in a crustacean. The guanine crystals are much smaller than tyrosine crystals which are also found in the cirri. B. balanoides allowed to grow both ihtertidally and on a raft for the same time have the same concentration of guanine in their tergoscutal flap tissue. There is, however, a higher concentration of guanine in the 2nd and 3rd cirri of those animals from the raft. It is suggested that the stored guanine is dietary in origin.

An ultrastructural study of the development of the dermal iridophores and structural pigmentation in Poecilia reticulata (peters).

Three general stages of iridophore development were found in Poecilia reticulata that correspond to the development of structural pigmentation. The first stage was prevalent in fish embryos about to hatch to young fish 4 months old. Dermal cells containing elements of endoplasmic reticulum and a Golgi apparatus developed into iridophores. The endoplasmic reticulum early in iridophore development became a few sparse cisternae, and the Golgi apparatus elaborated long rectangular vacuoles with two membranes. From 5 to 15 vacuoles were arranged in parallel stacks in each developing iridophore. Crystals of guanine were deposited within the inner compartment of each vacuole. At this stage of development, the young fish had only a few dermal iridophores next to the lateral muscle. Fish 4 to 6 months old had a more advanced type of iridophore development including several layers of iridophore cells in the dermis. The innermost iridophores near the muscle had many mature crystal-containing vacuoles (iridosomes). Each cell had upt to three stacks of 10-20 iridosomes with their long axis oriented at a slight oblique angle to the surface of the fish. The outer layers of iridophores resembled the immature developing cells found in very young fish. The third developmental stage was found in sexually functional adults. All dermal iridophores contained 2-3 groups of 10-20 mature iridosomes. In mature iridophores, the Golgi apparatus was not found in the cytoplasm. The thickness of the guanine crystals (70 nm) and cytoplasmic intervals (90 nm) results in a constructive interference reflection of 496 nm (blue-green). This iridescence increased concomitantly with the increase in iridophore cells in the dermis and the maturation of their iridosomes.

Studies on the photoreceptors ofAnchoa mitchilliandA. hepsetus(Engraulidae) with particular reference to the cones

Photoreceptors of anchoviesAnchoa mitchilliandA. hepsetusconsist of normal rods and two unusual kinds of cones. The latter lie in single vertical rows, and the rods lie between them. Both participate in photomechanical movements, and movement of the cones is closely coordinated with that of pigment cell processes. There are long cones having a cuneate outer segment and short cones having a bilobed outer segment. Long and short (bifid) cones alternate within a row and are staggered between adjacent rows. Both kinds possess calycal processes; long cones have a lateral sac or accessory outer segment. The long and short cones are associated to form a structure called a cone unit, which consists of the outer segment and ellipsoid of a long cone joined to two outer segment lobes of two adjacent short cones. The lobes of the latter are partly enclosed by the ellipsoid of the long cone. A cone row consists of a row of cone units isolated from each other by processes of the pigment epithelium containing stacks of guanine crystals which form a tapetum. Dorsal and ventral faces of inner segments have contact zones characterized by subsurface cisternae. Lamellae in the cone outer segments are arranged longitudinally with respect to the cell axis and short and long cone lamellae are perpendicular to each other; lamellae of the rods are transverse. Long cone lamellae are perpendicular to the cone row, and in the central retina are almost horizontal to the long axis of the body. Some vesicular/tubular structures also occur in the cone outer segments. Outer and inner segments of cones are joined by a broad connecting structure containing a stalk and root portion corresponding to a modified and reduced cilium shaft and centriole, respectively. The rod has a typical connecting stalk. Mitochondria of cone ellipsoids have expanded perimitochondrial spaces between outer and inner membranes. The organization of the anchovy cones is compared with that of other vertebrates. It is suggested that the cone unit may be a two channel analyser for the detection of plane polarized light and function in conjunction with the overlying reflector of regularly arranged platelets.

Saturnine gout: lead-induced formation of guanine crystals.

Intravenous injection of a sublethal dose of lead acetate into a domestic pig resulted in a 4.5-fold increase of guanine in the urine, indicating an impairment in the conversion of guanine to xanthine. This impairment is probably due to the inhibition of guanine aminohydrolase (guanase), since the activity of this enzyme is inhibited by Pb2+ (the inhibition constant being 3.0 X 10(-6)M). Postmortem histological examination revealed concretions of crystalline material in the epiphyseal plate of the femoral head. Extraction of the section containing the concretions showed that they were guanine. The relation of these findings to saturnine gout is discussed.

Fine structure of the retinal epithelium of the spectacled caiman (Caiman sclerops).

The fine structure of the retinal epithelium, Bruch's membrane and choriocapillaries has been studied by electron microscopy in the spectacled caiman (Caiman sclerops). The retinal epithelium throughout most of the retina is morphologically very typical of that described for other vertebrates. This typical appearance involves a single layer of pigmented cuboidal cells with extensive basal (scleral) infoldings and numerous apical (vitreal) processes enclosing photoreceptor outer segments. A semicircular area of the retinal epithelium in the superior fundus is, however, further specialized as a tapetum lucidum. The reflecting material consists of a large array of guanine, diffusely scattered within the epithelial cells. Centrally in the tapetal area, no melanosomes are found, indicating a non-occlusible tapetum. At the edge of the tapetum, however, both guanine crystals and melanosomes are found within the epithelial cells. In most other respects, the morphology of the epithelial layer in the tapetal region is not strikingly different from that in the non-tapetal area. Bruch's membrane everywhere displays the typical pentalaminate structure described for most vertebrates. The choriocapillaris is also typical in that numerous fenestrations are present in the endothelium bordering Bruch's membrane.

The tapetum lucidum in the eye of the big‐eye Priacanthus arenatus Cuvier

The big‐eye Priacanthus arenatus Cuvier contains a tapetum lucidum or reflector which lies in the inner region of the choroid. It extends over the entire surface of the fundus, and it consists of several layers of reflecting cells. The cells contain many layers of thin guanine crystals, and there is about 0.5 mg of guanine in a square cm of tapetum. The retina is duplex, and rods are small and very numerous. The tapetum of the big‐eye is compared with those of selachians and sturgeons, which it much resembles.

The Permeability to Gases of the Swimbladder of the Conger Eel(Conger Conger)

The permeability properties of the silvery walls of the swimbladders of eels(Conger congerandAnguilla anguilld)have been studied. The intact swimbladder wall is very much more impermeable to carbon dioxide, oxygen and nitrogen than ordinary connective tissue. Removal of the silvery layer of the wall, which contains crystals of guanine with a little hypoxanthine, increases the permeability about 100 times and leaves a transparent ‘epithelial’ layer only a little less permeable than connective tissue to these gases. The wall of the pneumatic duct of the conger swimbladder, which is not silvered, has permeability properties similar to those of connective tissue. In long-lasting experiments a production of carbon dioxide not coupled to oxygen usage was detected in the epithelial layer. The ratios between the diffusion constants of CO, N and O for both the silvery and epithelial layers show that diffusion probably takes place through water-filled pathways, and calculations show that impermeable overlapping crystals embedded in the silvery layer could account for its very low permeability. Two deep-sea eels were shown to have swimbladders whose walls contained about 10 times more guanine/unit area than the conger eel. The possibility that layers of guanine crystals may divide fish into compartments is discussed.

On the physical identity of scintillons: bioluminescent particles in Gonyaulax polyedra.

ABSTRACT The physical identity of the bioluminescent particles (‘scintillons’) extracted from the marine dinoflagellate Gonyaulax polyedra was investigated by electron microscopy and particle counts of the active fractions from sucrose density gradients. Membranous structures are abundantly present in purified fractions, while there is a decrease, relative to activity, in the numbers of guanine crystals, which had previously been implicated as bioluminescent structures. The significance of these findings with respect to the in vivo scinrillon is discussed.

Mechanism of reflexion in silvery layers of fish and cephalopods.

The highly reflecting structures found in the integuments and eyes of fish and cephalopods were studied. In all cases they consist of alternate layers of high and low refractive index ( n ) material (in fish, guanine and cytoplasm) and the high refractive index material is in the form of discrete plates. The highest reflectivity at a given wavelength λ 0 , together with the widest waveband of high reflectivity, would be given if these alternate layers all had an optical thickness of ¼ λ 0 . We have examined the possibility that fish and cephalopods can make ‘ideal' reflectors of this kind. The thicknesses ( t ) of the discrete plates released by scratching the reflecting layers were measured by interference microscopy, and it was found that although the plates from a region of a given colour sometimes varied greatly in surface area, their thicknesses were approximately constant. With one exception the optical thicknesses ( nt ) of the plates found in all the structures studied were between 100 and 200 nm. Many of the reflecting structures are highly coloured and in these there was almost always a good correlation between the wavebands best reflected and four times the optical thick­nesses of the plates which they contained. The most ventral scales in the juvenile sprat were studied in some detail. At normal incidence these scales reflect best a waveband around 720 nm and the guanine crystals which they contain all have optical thicknesses close to one quarter of this wavelength. The changes in colour with angle of viewing, and with changes in osmotic concentration of the medium in which these scales are placed, support the idea that the spaces between the crystals are ¼ λ 0 spaces. These scales have a high reflectivity to the lights penetrating best into the sea at the oblique angles of incidence from which the strongest intensities of daylight fall in life. Qualitative observations on scales from herring and from other regions on the sprat sup­ported the hypothesis that their guanine crystals were also arranged approximately in ¼ λ 0 stacks. Similar conclusions were reached for coloured surfaces found in the skin of the horse mackerel, the iris of the neon tetra, the reflecting tapeta of the dogfish and the spurdog, and in the eye of the squid, Loligo forbesi . In the scales of the roach, Rutilus rutilus , the crystals are of thicknesses which indicate that if in ‘ideal' ¼ λ 0 stacks they would at normal incidence appear red and at oblique incidence green, whilst in fact they are very little coloured. The crystals from the eyes of Callionymus lyra had 4 nt around 300 nm (in the u. v.) yet the reflexions given by piles of these crystals were bronze coloured. Possible explanations of these facts are given. In cephalopods the high refractive index plates are lozenge-shaped, flexible and of refrac­tive index about 1·56.

The osmotic effects of electron microscope fixatives.

The reflecting cells on the scales of sprat and herring contain ordered arrays of guanine crystals. The spacing of the crystals within these cells determines the wave bands of the light which they reflect, hence volume changes in the reflecting cells can be observed as color changes directly. This property of the scales is used to show that (a) fixation with osmium tetroxide solutions destroys osmotic activity; (b) fixation with aldehyde solutions does not destroy osmotic activity and does not cause volume changes if the aldehydes are made up in salt or sucrose solutions whose osmolarities, discounting the aldehyde, are about 60% of those to which the cells are in equilibrium in life, and (c) after aldehyde fixation the cells are osmotically active but come to a given volume in salt and sucrose solutions of concentrations only 60% of those which give their volume before fixation. Various possible mechanisms underlying the change of osmotic equilibrium caused by aldehyde fixation are discussed.

Fine structure of the dermal luminescent organs, photophores, in the fish, Porichthys notatus.

AbstractPhotophores in Porichthys notatus consist of a cellular lens, an underlying area of photogenic tissue and a deep ensheathing reflector. Lens cells exhibit a dense compacted filamentous cytoplasm. Their processes interdigitate and desmosomes exist along their borders. The photogenic tissue, richly supplied by blood vessels, consists of two main cell types: (1) a presumed “photogenic” cell; and (2) a supportive cell. Photogenic cells are characterized by a highly vesiculated cytoplasm and peripheral microvilli. Frequently, they exhibit lamellar membranous whorls. Some whorls display cytoplasmic cores with vesicles. Many of these vesicles communicate via pores with an extracellular channel that envelops the cells. Supportive cells contain cytoplasmic filaments and extend processes around the photogenic cells. Except for isolated desmosomal contact points, a wide extracellular channel intervenes between supportive and photogenic cells. A prominent basal lamina separates supportive cells from the surrounding connective tissue. The strongly birefringent reflector is composed primarily of cells containing guanine crystals. The crystals lie stacked in groups, each membrane‐bounded crystal being separated from its neighbor by an intervening layer of cytoplasm. Such an arrangement produces constructive interference and accounts for the high reflectivity of this multilayered structure. Possible relationships of the above structural features and the production of light are discussed.

A New Green Tree Frog from Suriname

AMONG the many bright green tree frogs in South America the green coloration may be brought about by two entirely different sets of physiological factors. In one type the skin contains three types of chromatophores arranged in different layers. The most superficial layer is made up of lipophores that are filled with a yellow, fatty material. Deep to the lipophores is a layer of guanophores packed with crystals of guanine, a chemical allied to uric acid. The deepest layer is that of the melanophores. When visible light falls on the skin the light of shorter wave lengths (greens, blues, lavenders) is reflected back by the guanophores while the longer wave lengths (reds, oranges, yellows) are absorbed by the melanophores. As the shorter light rays are reflected by the guanophores back through the lipophores the blues and lavenders tend to be absorbed while the greens are transmitted so that the skin appears green to the human eye. If, however, the lipophores are altered or destroyed by preserving fluid the blues and lavenders are transmitted so that the preserved frog appears blue or some shade of lavender to the human eye. Examples of skin pigmentation of this type are found in Phyllomedusa bicolor (blue in preservative), Phyllomedusa hypochondrialis, and Centrolenella geijskesi (lavender in preservative). In addition to green frogs of this type there are others in which the green coloration is due to an accumulation of a chemical (biliverdin) in the skin rather than to chromatophores. In this latter group the chemical may be altered or destroyed by the preserving fluid so that the specimen fades to a milky white. As examples of this type we can mention Hyla punctata, Hyla granosa, and Sphoenorhynchus aurantiacus. It is one of the latter type that we describe here.

Ultrastructure of guanophores

Guanophores in the back skin of the adult tree frog have been studied with an electron microscope. The cytoplasm is characterized by numerous needle- or platelet-like clear spaces which are incompletely surrounded by their own limiting membranes. These clear spaces are arranged in many groups and run in parallel with each other within the group. However, in extremely thick unstained sections, the cytoplasm is filled up with many dense inclusions, guanine crystals, instead of spaces. It is suggested, therefore, that the clear spaces are empty cavities and represent almost the sites of guanine crystals which were removed away from ultrathin sections probably by mechanical pressure applied during cutting. Except for ordinary cell organelles, fine filaments about 60 Å in bundles are scattered in the cytoplasm.

A Multilayer Interference Reflector in the Eye of the Scallop, Pecten Maximus

ABSTRACT Animals frequently make use of highly reflecting surfaces, as for example in the tapeta of the eyes of many vertebrates, the iridophores and photophores of many marine animals, and the scales of fish. Such surfaces raise the question: how are high reflectivities, often comparable with that of polished metal, achieved using biological materials?

Polarization of light reflected from the silvery exterior of the bleak,Alburnus alburnus

A method is described for measuring, for various angles of incidence, the polarization produced by reflexions from natural surfaces.This method was tested by measurements on matallic surfaces of known properties and then used to study reflexions from the silvery gill cover of the bleakAlburnus alburnus(L.).Althouth the reflecting surfaces of the gill cover are crystals of a dielectric guanine, there is no polarizing angle, and the reflecting properties of the gill cover resemble those of a sputtered aluminium mirrorThe biological significance of these results is briefly discussed.

Crystals of Riboflavin making up the Tapetum Lucidum in the Eye of a Lemur

THE tapetum lucidum of the eye is a specialized layer lying behind, but adjacent to, the light-sensitive cells of the retina. It is specialized to form a reflecting surface so that any light not absorbed during its first passage through the light-sensitive cells is reflected back again and has a second opportunity to be absorbed. The tapetum is the basis of eye-shine in animals; it may be made up of crystals or of regularly arranged fibres1,2. Many fish, for example, have tapeta made of crystals of guanine, carnivores one of crystals of a complex of zinc-cysteine3, while herbivores such as the sheep and cow have fibrous tapeta. Man and the higher apes have no tapetum; but some lemurs have a well-developed one; the brilliant yellow tapetum of Galago monteiri is described by Johnson4, who says “… the background resembles burnished gold”. Rochon-Duvigneaud5 has found that both diurnal and nocturnal lemurs may have a tapetum. Kolmer6 agrees with this and notes that the tapetum of Lemur rufifrons, a diurnal lemur, is both crystalline and yellow. Luck7 has found that the eyes of Galago crassicaudatus agisymbanus, a nocturnal lemur, have a fluid vitreous body and a highly developed cellular tapetum which is brilliant gold in colour.

Zoogeography of the Bathypelagic Fish, Chauliodus

THE MID-DEPTHS of the oceans comprise a significant part of the volume of the biosphere, yet the conditions for life here are so different from those encountered by man that it is difficult to appreciate the factors limiting the distribution of the bathypelagic organisms living there. Catch records, however, indicate that many species are restricted in their geographical distribution. An attempt is made here to study the conditions of life in these mid-depths by centering attention on a group of fish that has a worldwide distribution. There are a number of fish groups which could serve for such a study, among them the gonostomiatids and the myetophids. Although these two groups have a wide distribution and occur in large numbers, their taxonomy has not been sufficiently clarified to make a zoogeographic study possible. The genus Chauliodus was chosen because it fulfilled the requirements. It has a world-wide distribution; large numbers of body measurements are available for the comparison of different populations; physical and chemical data are available for the stations at which the specimens were caught. The Stomiatoidei, the suborder to which Chauliodus belongs, can be considered herring-like fish with photophores and extremely large teeth. The genus Chauliodus has been placed in the family Chauliodontidae by Berg (1940), removing it from the Stomiatidae because the inner ear of Chauliodus lacks a lagena, whereas all the other members of that family have one. These two families make up the superfamily Stomiatoidae in the suborder Stomiatoidel. This suborder of the Clupeiformes is characterized by Berg as being the Clupeoidei, especially near the Alepocephalidae. (p. 431). Although Chauliodus (Plate 1, p. 120) lacks scales, the pattern of the pigment is such that it forms hexagonal areas in which there is a thin deposit of an opalescent substance, which appears under magnification like guanine crystals. The body is covered by a thick transparent coating containing microscopic spheres of unknown composition. This gelatinous layer forms, in part, the base of the adipose fin, and does not seem to be merely a slime secretion. Brauer (1908) was of the opinion that the gelatinous layer is a part of the corneum of the skin, although his earlier observations had led him to believe that it was a slime secretion. The fang-like teeth (Plate 2) appear admirably suited to the capture of the animals found in the mid-depths, and, indeed, stomach analyses show that Chauliodus feeds on chaetognaths (Clemens and Wilby, 1946) and on macroplanktonic crustacea, probably deep-sea prawns (personal observation). It is tempting to speculate that the prey is lured to the mouth by the many lights of the photophores. These light organs are of three types: microscopic spheres without a pigment layer; large spheres with a pigment coat, reflector and lens; and larger, bell-shaped organs with a pigment coat, lens and reflector. The microscopic photophores are scattered over the dorsal surface of the fish, whereas the larger, pigment-covered spherical organs are found in groups within each hexagonal scale area, around the eye socket, and in rows along the dorsal surface of the base of the pectoral and pelvic fins, and the base of the dorsal and anal fins. There is also a lateral row between the rows of bell-shaped organs. The two suborbital photophores (Plate 2) are special types, the more an-