Histological Study of Seed Coat Development in Arabidopsis thaliana

Arabidopsis seed coat development using light and transmission electron microscopy revealed major morphological changes associated with the transition of the integuments into the mature seed coat. By the use of a metachromatic staining procedure, cytological events such as the production of phenolic compounds and acidic polysaccharides were followed. Immediately after fertilization, the cells of the inner epidermis of the inner integument became vacuolated and subsequently accumulated pigment within them. This pigment started to disappear from the cytoplasm at the torpedo stage of the embryo, as it became green. During the torpedo stage, mucilage began to accumulate in the cells of the external epidermis of the outer integument. Furthermore, starch grains accumulated against the central part of the inner periclinal wall of these cells, resulting in the formation of small pyramidal domes that persisted until seed maturity. At the maturation stage, when the embryo became dormant and colourless, a new pigment accumulation was observed in an amorphous layer derived from remnants of crushed integument layers. This second pigment layer was responsible for the brown seed colour. These results show that seed coat formation may proceed in a coordinated way with the developmental phases of embryogenesis. Received 25 May 1999/ Accepted in revised form 10 February 2000     

ULTRACYTOCHEMICAL LOCALIZATION OF PLASMA MEMBRANE-ASSOCIATED PHOSPHATASE ACTIVITY IN DEVELOPING TOBACCO SEEDS

Plasma membrane-associated phosphatase activity was found in integumentary cells of developing tobacco ovules from the megaspore tetrad stage to seed maturity. Enzyme activity is greatest in the innermost layers of the integument from the mature megagametophyte stage on. The egg, zygote, and synergids almost totally lack plasma membrane-associated reaction product, while the antipodals show some activity at their chalazal ends. The endosperm has much plasma membrane-associated phosphatase activity in most of its cells during development, but it is primarily the outermost plasma membranes of the surface cells of the embryo that have associated reaction product. It is concluded that the plasma membrane-associated phosphatase activity is related to active transport of assimilates and that the integument is the most important site of active transport in the young ovule. After fertilization, in addition to the innermost layers of the integument, the endosperm and the outermost cells of the embryo become involved in active transport, which continues to seed maturity.     

Early Development of the Seed Coat of Soybean (Glycine max)

Although the development of the soybean ovule has been fairlywell studied, knowledge of the sequence of events in the seedcoat during the first 3 weeks after flowering is incomplete.The goal of the present study was to document, using light microscopy,the early development of the soybean seed coat with respectto changes in structure and histochemistry. At anthesis, theseed coat consists of an outer layer of cuboidal epidermal cellssurrounding several layers of undifferentiated parenchyma (whichtogether constitute the outer integument), and an inner layerof cuboidal endothelial cells (the inner integument). At 3 dpost anthesis (dpa), the inner integument has expanded to includethree to five layers of relatively large cells with thick, heavily-stainingcell walls immediately adjacent to the endothelium. By 18 dpa,the outer integument has developed into a complex of tissuescomprised of an inner layer of thick-walled parenchyma, an outerlayer of thin-walled parenchyma containing vascular tissue whichhas grown down from the lateral vascular bundles in the hilumregion, a hypodermis of hourglass cells, and palisade layer(epidermis). The thick-walled parenchyma of the inner integumenthas become completely stretched and compressed, leaving a single,deeply staining wall layer directly above the endothelium. At21 dpa, the outermost cells of the endosperm have begun to compressthe endothelium. At 45 dpa (physiological maturity) the seedcoat retains only the palisade layer, hourglass cells, and afew layers of thin-walled parenchyma. The innermost layer ofthe endosperm, the aleurone layer, adheres to the inside ofthe seed coat. This knowledge will be invaluable in future studiesof manipulation of gene expression in the seed coat to modifyseed or seed coat characteristics. Copyright 1999 Annals ofBotany Company Soybean, Glycine max, seed coat, development, aleurone.     

Ovule morphogenesis and structure in Menispermaceae,focusing on the development of the single fertile ovule and its systematic significance

Menispermaceae is one of the core groups of Ranunculales. The single fertile ovule in each ovary in Menispermaceae varies greatly in integument number, micropyle formation, and integument lobe. However, data regarding ovule morphogenesis in the family are very limited. In this study, we document ovule development of selected species in the Menispermaceae using scanning electron microscopy and light microscopy. Ovule development in Menispermaceae shows the following characteristics. Two ovules are initiated in a young carpel, one of them degenerates gradually and the other develops into a fertile ovule in subsequent stages. Bitegmic in Sinomenium Diels. and Cocculus DC. and unitegmic in Stephania Lour. The formation of unitegmy is probably due to integumentary shifting. The annularly initiated inner integument is of dermal origin and has 2–3 cell layers in the family, but the semi-annularly initiated outer integument is of both dermal and subdermal origin. Both inner and outer integument are cup-shaped at maturity. The cup-shaped outer integument is formed due to the outer integument's extension to the concave (adaxial) side of the funiculus. The obturator is well developed and consists of 2–3 cell layers in Cocculus or 9–11 cell layers in Stephania. Ovule development of Menispermaceae suggests some common characteristics between Cocculus and Sinomenium, and derived unitegmy supports molecular data that indicate Stephania is one of the late-diverging lineages in the family. Integument lobations are present. The sterile ovule shows variations in the degeneration process. These results will provide evidence for exploring the evolution of ovules in Ranunculales.     

Reversible colour change in Arthropoda

The mechanisms and functions of reversible colour change in arthropods are highly diverse despite, or perhaps due to, the presence of an exoskeleton. Physiological colour changes, which have been recorded in 90 arthropod species, are rapid and are the result of changes in the positioning of microstructures or pigments, or in the refractive index of layers in the integument. By contrast, morphological colour changes, documented in 31 species, involve the anabolism or catabolism of components (e.g. pigments) directly related to the observable colour. In this review we highlight the diversity of mechanisms by which reversible colour change occurs and the evolutionary context and diversity of arthropod taxa in which it has been observed. Further, we discuss the functions of reversible colour change so far proposed, review the limited behavioural and ecological data, and argue that the field requires phylogenetically controlled approaches to understanding the evolution of reversible colour change. Finally, we encourage biologists to explore new model systems for colour change and to engage scientists from other disciplines; continued cross‐disciplinary collaboration is the most promising approach to this nexus of biology, physics, and chemistry.     

A structural investigation of the ovule in sugar beet, Beta vulgaris: Integuments and micropyle

The micropyle and the integuments of sugar beet (Beta vulgaris) ovules have been investigated by light and electron microscopy during differentiation and maturation of the ovule. The micropyle itself is formed by the inner integument which is surrounded by the outer integument at its base. The micropyle containts a fibrillar PAS+ substance and is often covered by a thin sheet or hymen. Both integuments are cuticle-covered thin sheets, each 2-few cell layers in thickness. In the outer integument an increase in starch accumulation occurs during ovule maturation and probably functions as nutrient storage for embryo development. The inner epidermis of the inner integument differentiates as the most conspicuous cell layer of the beet ovule. During growth and maturation of the ovule a system of small perinuclear vacuoles containing dense material increases steadily in these cells. At maturity this system fills up more than half of each cell and very dense material has accumulated in each vacuole. This vacuole content is highly refractive and contains tannins and/or polyphenols.     

Flatfish (Pleuronectiformes) chromatic biology

The following aspects of flatfish skin coloration are reviewed. (1) The variety of chromatophores which contribute to the complex integumentary patterns; their relative sizes and numerical distribution. (2) Interspecific variations and intraspecific changes in skin patterns. (3) Ambicolouration and hypomelanosis and their economic consequences. Discussion of nutrition, illumination, stress, endocrine and paracrine factors which may influence both these phenomena, as well as the normal pattern morphology, including putative melanogenesis stimulating and inhibitory factors within the integument. (4) Cryptic responses to substrate texture and colour, as well as to stressors, involving chromatophore morphological and physiological chromatic interaction. (5) Regulation of pattern changes; the simultaneous production by a single neurone type (adrenergic) of both paling and darkening in different pattern areas through variations in “adrenoceptor transition ranges”.     

Developmental Aspects of Vertebrate Chromatophores

Melanophores, xanthophores, and iridophores are fundamentallydistinct chromatophores in their appearance, composition, andfunction. All migrate from their neural crest site of originto populate the integument. Their respective pigments, melanins,ptendines, and purines are found in organelles designated respectivelyas melanosomes, pterinosomes and reflecting platelets. Theseorganelles are all derived from an endoplasmic reticular vesicle.This is in keeping with a hypothesis about the common originof pigment cells from a stem cell containing a primordial organellewith the potential of becoming any of the circumscribed pigmentaryorganelles. It is believed that chromatoblasts may not be specificallydetermined until they reach a final destination where they willdifferentiate in accordance with a pattern already specifiedin the integument. In leopard frogs, it appears that the initialinduction of pattern in the skin is general, but later it becomeshighly specific.     

Iridescent colour production in hairs of blind golden moles (Chrysochloridae)

Relative to other metazoans, the mammalian integument is thought to be limited in colour. In particular, while iridescence is widespread among birds and arthropods, it has only rarely been reported in mammals. Here, we examine the colour, morphology and optical mechanisms in hairs from four species of golden mole (Mammalia: Chrysochloridae) that are characterized by sheens ranging from purple to green. Microspectrophotometry reveals that this colour is weak and variable. Iridescent hairs are flattened and have highly reduced cuticular scales, providing a broad and smooth surface for light reflection. These scales form multiple layers of light and dark materials of consistent thickness, strikingly similar to those in the elytra of iridescent beetles. Optical modelling suggests that the multi-layers produce colour through thin-film interference, and that the sensitivity of this mechanism to slight changes in layer thickness and number explains colour variability. While coloured integumentary structures are typically thought to evolve as sexual ornaments, the blindness of golden moles suggests that the colour may be an epiphenomenon resulting from evolution via other selective factors, including the ability to move and keep clean in dirt and sand.     

Histology of melanic flank and opercular color pattern elements in the firemouth cichlid,Thorichthys meeki

Dark melanic color pattern elements, such as bars, stripes, and spots, are common in the skin of fishes, and result from the differential distribution and activity of melanin‐containing chromatophores (melanophores). We determined the histological basis of two melanic color pattern elements in the integument of the Firemouth Cichlid, Thorichthys meeki. Vertical bars on the flanks were formed by three layers of dermal melanophores, whereas opercular spots were formed by four layers (two lateral and two medial) in the integument surrounding the opercular bones. Pretreatment of opercular tissue with potassium and sodium salts effectively concentrated or dispersed intracellular melanosomes. Regional differences in epidermal structure, scale distribution, and connective tissues were also identified. J. Morphol. 2013. © 2013 Wiley Periodicals, Inc.     

AN ANALYSIS OF CALIFORNIA SEA OTTER (ENHYDRA LUTRIS) PELAGE AND INTEGUMENT

The sea otter is associated with a cold, marine habitat, has no insulating fat layer, and relies on its fur layer for insulation. Soiled pelage provides inadequate insulation and can lead to hypothermia and death. Information on sea otter pelage, the surface and bound lipids found in the pelage, and histology of the integument is thus relevant to the development of rehabilitation and management techniques for sea otters soiled with oil. We present detailed data on the sea otter pelage and integument, including hair bundle density (737–2,465 bundles per cm²), hair density per bundle (19–91.1), total hair density (26,413–164,662 hairs per cm²), guardhair length (8.2–26.9 mm), underfur length (4.6–15.8 mm), guardhair diameter (44.0–106.0 μ), underfur diameter (7.6–11.9 μ), angle of hair with respect to the skin (61.9°- 84.3°) and structure of individual hairs as seen with a scanning electron microscope. The hydrocarbon squalene was found to be the major component of the lipids associated with the pelage. Various layers of skin from eight sites on a single animal are described histologically. With the exception of density of the hair coat, sea otter integument is similar to that of domestic carnivores.     

Structure-function relationships in the integument of Salamandra salamandra during ontogenetic development

Morphological, cytological and transport properties of the integument of Salamandra salamandra were investigated during natural ontogenetic development, from birth to adult. Three stages were operationally defined: I, larvae, from birth to metamorphosis; II, metamorphosis (judged externally by the colour change and loss of the gills); and III, post-metamorphosis to adult. Pieces of skin were fixed at various stages for immunocytochemical examinations, and the electrical properties were investigated on parallel pieces. Distinct cellular changes take place in the skin during metamorphosis, and lectin (PNA, WGA and ConA) binding indicates profound changes in glycoprotein composition of cell membranes, following metamorphosis. Band 3 and carbonic anhydrase I (CA I) were confined to mitochondria-rich (MR)-like cells, and were detected only in the larval stage. CA II on the other hand, was detected both in MR-like and in MR cells following metamorphosis. The electrical studies show that the skin becomes more tight (transepithelial resistance increases) upon metamorphosis, followed by manifestation of amiloride-sensitive short-circuit current (I(SC)) indicating that functional Na+ uptake has been acquired. The skin of metamorphosed adults had no finite transepithelial Cl- conductance, and band 3 was not detected in its MR cells. The functional properties of MR-like and MR cells remain to be established.     

Physiological control of the chromatophores of Austrolestes annulosus (Odonata)

The chromatophore-containing integument of Austrolestes annulosus always changes from a dark to a blue colour phase in vitro and therefore functions independently of a central control mechanism. In isolated abdominal segments, the reverse colour change occurs independently of the presence of central nervous system. The amount of change decreases with the size of the piece of integument; it varies over different parts of the body of the same intact insect, and it varies both in vitro and in vivo with time of day.A variety of experiments, involving ligation of abdominal segments and ablation of their ganglia, show that the terminal ganglion is primarily responsible for the release of a darkening factor which migrates in an anterior direction. Other ventral ganglia have a similar function but are of less importance.Transplants of terminal ganglia and injection of their extracts fail to restore capacity for colour change in ligature-isolated segments which have had their own ganglia removed. These findings, supported by histological observations, suggest that the darkening factor is a neurosecretion.     

Evidence for pyroelectric and piezoelectric sensory mechanisms in the insect integument.

Quantitative pyroelectric (PE) and piezoelectric (PZE) measurements were carried out on the insect integument of live Blaberus giganteus (cockroach) and on dry integument preparations of the same species. Voltage responses to optical pulses of 10--500 ms, absorbed in the live integument, were PE: interference filter measurements showed the responses to be proportional to the absorbed thermal radiation flux and independent of the wavelength. The voltage/time-course of the responses was in agreement with theoretically calculated PE signals. Voltage responses to mechanical pulses were PZE. The responses of the inner and outer integument surfaces always had opposite electric signs. The polar character of the integument was confirmed by means of a separate dielectric heating method. To explain these results, we hypothesize that the PE properties are for the most part localized in the two outermost layers (outer and inner epicuticle) of the integument, which consists mainly of polar lipids and proteins. Parallel alignment of these polar molecules perpendicular to the integument surface is very likely. PE and PZE responses, therefore, will not only occur in live insects but will also be measurable in dead, dry integument preparations as long as the polar tissue texture remains intact. Due to its polar texture, the insect integument will react to rapid changes in temperature, illumination, or uniaxial pressure in the same way as nonbiological PE materials, where the voltage responses depend on dX/dt (X, pressure or temperature). It seems clear, therefore, that the well-known physiological reactions of various arthropods to such physical outside influences may be related to the PE property of their integument.     

Material properties of the skin of the Kenyan sand boa Gongylophis colubrinus (Squamata, Boidae)

On the basis of structural data, it has been previously assumed that the integument of snakes consists of a hard, robust, inflexible outer surface (Oberhäutchen and β-layer) and soft, flexible inner layers (α-layers). The aim of this study was to compare material properties of the outer and inner scale layers of the exuvium of Gongylophis colubrinus, to relate the structure of the snake integument to its mechanical properties. The nanoindentation experiments have demonstrated that the outer scale layers are harder, and have a higher effective elastic modulus than the inner scale layers. The results obtained provide strong evidence about the presence of a gradient in the material properties of the snake integument. The possible functional significance of this gradient is discussed here as a feature minimizing damage to the integument during sliding locomotion on an abrasive surface, such as sand.     

Ontogenic colour change,survival, and mating in the damselfly Agriocnemis pygmaea Rambur (Insecta: Odonata)

1. Damselflies often show intra-specific colour variation, which may represent genetic polymorphism or age-related (ontogenic) colour changes. 2. Such variation has distinct implications for the species' ecology and evolution. Colour variation in females of the damselfly Agriocnemis pygmaea was studied, which range from blue male-like individuals (andromorphs) to those with a distinct red colour (heteromorphs). From preliminary observations, it was hypothesised that this species exhibits ontogenic colour change from heteromorph to andromorph coloration. 3. Mark–recapture experiments and egg counts of dissected females suggested that immature females are heteromorphic and gradually begin to resemble males as they attain sexual maturity. 4. Reflectance spectra of field-caught individuals indicated that, although males are indistinguishable from andromorphs, they could be easily differentiated from heteromorphs. 5. Finally, field observations and mate choice experiments showed that males rarely attempt to mate with heteromorphic females and prefer andromorphs. Together, this study's results suggest that the observed colour variation in A. pygmaea females is ontogenic and is associated with sexual maturity.     

An histochemical and ultrastructural analysis of the dermal chromatophores of the variant ranid blue frog

Integument from blue and green areas of the variant blue frog were analyzed biochemically for pteridines and carotenoids. Solvent extraction and absorption spectrophotometry indicated that β carotene was greatly reduced in the blue skin, and present in high quantities in the green skin of the blue frog. Thin layer and paper chromatography indicated that the pteridines were almost totally lacking in the blue skin, and present in normal quantities in the green skin of the blue frog. Light and electron microscopy indicated that the xanthophore pigment cells were either greatly altered or absent from the blue integument and present in the green integument. The fine structure of the xanthphores of the green integument contained the normal ultrastructural components of xanthopores found in regular green integument. The blue integument contained an abnormal cell type that occupied the position in the dermal chromatophore unit normally held by the xanthophores. The possibility of these cells being abnormal xanthophores or some other cell type is discussed.     

The rhinoceros among Serpents: Comparative anatomy and experimental biophysics of Calabar burrowing python (Calabaria reinhardtii) skin

The Calabar burrowing python (Calabaria reinhardtii) has a unique combination of marked thickness of the integumentary layers, a highly organized lamellate arrangement of the dermal collagen bundles, and a reduction in the size of the interscale hinge region of the integument. Biomechanical testing demonstrates that the skin of C. reinhardtii is more resistant to penetration than the skin of other snakes. The laminar arrangement of the collagen bundles provides for penetrative resistance, even while maintaining the flexibility characteristic of snake skin. Considering the life history of this species, it is hypothesized that the specialized integument of C. reinhardtii is a passive defensive mechanism against penetrative bites from maternal rodents and predators.     

Colour change and visual cues in the sand flathead, Platycephalus arenarius (Ramsay and Ogilby)

This study investigates cryptic coloration and the phenomenon of colour change in the sand flathead, Platycephalus arenarius (Ramsay and Ogilby), a shallow-water marine species. The chromatophore configurations of the dorsal integument are described and the responses to a range of artificial backgrounds studied. Certain visual cues used by this species in colour change are deduced, and the existence of a linear relationship between the shade of the integument and that of the background is proposed.     

Development of the integument of Dasypus hybridus and Chaetophractus vellerosus,and asynchronous events with respect to the postcranium

The integument of extant armadillos (Xenarthra, Cingulata) is a unique organ in which complex glandular systems are associated with pilose follicles, dermal ossifications, and cornified scales. Up to date, papers have focused on neither comparative morphology of the skin (dorsal and ventral) nor chronology of the development of interspecific homolog structures. In order to clarify the way in which events occur during development of the integument structures, maturity of other tissues (e.g. skeletal tissues) should be considered. Therefore, we will be able to identify events that have been pre- or post-displaced during ontogenetic development. The aim of this paper is to describe in a developmental and comparative framework the integumentary system of neonates of Dasypus hybridus and Chaetophractus vellerosus. In order to understand the morphology of the different integumentary structures serial histological sections were prepared. Staining techniques included H–E, Masson Trichrome, PAS, orcein and reticulin. To study ossification of postcranial elements, the specimens were cleared and double-stained with alcian blue and alizarin red. Determinations of ossification centers and their progress were recorded through the early uptake of alizarin. The dorsal dermis of neonates from D. hybridus is clearly differentiated into a superficial and deep layer, as in fetuses of Dasypus novemcinctus. In C. vellerosus, however, these layers could not be identified. This suggests a less connective tissue differentiation in the latter species at this stage. Osteoderms in D. hybridus are well differentiated unlike C. vellerosus where no condensations of osteoprogenitory cells are observed. Conversely, pilose follicles and glandular tissues are less developed in D. hybridus. Regarding postcranial elements, ossification centers are less advanced in C. vellerosus than D. hybridus, this is particularly notorious for the vertebral column, sternal, and pelvic girdle elements. Asynchronies between neonates of both species observed on integumentary and postcranial skeletal tissues could match with specific adaptive strategies related to distribution in different environments, and/or different postnatal care.