Distal invaginations and the renewal of cone outer segments in anuran and monkey retinas

Summary Although it is now clear that the outer segments of mature vertebrate cones are regularly renewed, it is not known how a cone outer segment can maintain a tapered shape if its narrower tip is periodically lost by shedding. This problem was addressed by morphological examination of photoreceptors in retinas of anurans (Xenopus laevis) and monkeys (Macaca fascicularis). Light microscopy revealed a marked daily change in the shape of cone outer segments in X. laevis: at light offset they were long and conical, at light onset they had shed their narrow tips, were sharply truncated, and 40% shorter. Electron microscopy revealed previously undescribed fine-structural features in these mature cone outer segments, most notably the presence of many partial membrane infoldings within their distal lamellae. The growth of each of these distal invaginations apparently split 1 pre-existing distal lamella into 2 daughter lamellae of reduced width. The formation of distal invaginations at various heights within a cone outer segment would thus make it longer and narrower. Similar ultrastructural features were also found in cone outer segments of monkey retinas. These findings suggest that during outer segment renewal the tapered shape of mature cone outer segments is maintained via a remodelling process that accompanies the formation of distal invaginations.Portions of this work have been published in abbreviated or preliminary form (Eckmiller 1988, 1989b, c)     

A light and electron microscopic study of the blue-green algae living either in the coralloid roots of « Macrozamia communis » or isolated in culture

Abstract

The present work is a study of the blue-green algae living in the coralloid roots of Macrozamia communis and isolated from Macrozamia communis in culture.

The light and electron microscopic study pointed out the distribution of these microorganisms in the cortical area of coralloids and did not reveal any cells invaded by bacteria. On the basis of their aspect the blue-green algae living either in the coralloid roots or in culture were classified as belonging to the genus Nosloc, with some features of Nosloc commune.

Inside the coralloids the cells of the blue-green algae were surrounded by abundant mucilage and contain granulations. In culture the blue-green algae were on the contrary very poor in mucilage and rich in polyphosphate granules. Numerous phycobilosomes were ranged along the outside of the thylakoid membranes in alternate arrangement to the granules of the neighbouring lamellae.     

Heterocyst structure in Chlorogloea fritschii

Summary Heterocysts of Chlorogloea fritschii were studied with the aid of light and electron microscopy. Two main types of heterocyst were recognized. One of these, termed here the H.1 cell, is the only type in filaments, but occurs also among endospore groups. The other, the H.3 cell, is restricted to endospore groups. The transition from one type of heterocyst to the other, therefore, does not coincide exactly with the transition in arrangement of vegetative cells from filaments to endospores. Both types of heterocyst differ considerably from other published accounts of heterocysts.The differences between H.1 and H.3 cells reside mainly in the arrangement, and relative development or disappearance of the various cell organelles.A summary is given of other types of cell seen with the electron microscope which share some features with typical heterocysts. Some of these would probably be recognized as heterocysts by light microscopy, whereas others would not.     

Reflector cells in the skin of Octopus dofleini

Summary The cells that form the reflecting layer beneath the chromatophore organs of the octopus are conspicuous elements of its dermal chromatic system. Each flattened, ellipsoidal reflector cell in this layer bears thousands of peripherally radiating, discoidal, reflecting lamellae. Each lamella consists of a proteinaceous reflecting platelet enveloped by the plasmalemma. The lamellae average 90 nm in thickness and have variable diameters with a maximum of about 1.7 m. Sets of reflecting lamellae are organized into functional units called reflectosomes. The lamellae in each reflectosome form a parallel array - similar to a stack of coins. The average number of lamellae in a reflectosome is 11. Adjacent lamellae are uniformly separated by an extracellular gap of about 60 nm in embedded specimens. The reflectosomes are randomly disposed over the surface of the reflector cell.The observed organization of the reflectosome is compatible with its role as a quarter-wave thin-film interference device. The alternating reflecting lamellae and interlamellar spaces constitute layers of high and low refractive indices. Using measurements of the thicknesses and refractive indices of the platelets and interlamellar spaces, we have calculated that the color of reflected light should be blue reen, as seen in vivo.The sequence of events leading to the definitive arrangement of the reflectosomes is uncertain.The reflector cells of O. dofleini are compared and contrasted with the iridophores of squid.This investigation was supported in part by grant 5-TO1-HD-0026 from the National Institute of Health     

Physical and ultrastructural basis of blue leaf iridescence in four Malaysian understory plants

Iridescent blue leaf coloration in four Malaysian rain forest understory plants, Diplazium tomentosum Bl. (Athyriaceae), Lindsaea lucida Bl. (Lindsaeaceae), Begonia pavonina Ridl. (Begoniaceae), and Phyllagathis rotundifolia Bl. (Melastomataceae) is caused by a physical effect, constructive interference of reflected blue light. The ultrastructural basis for this in D. tomentosum and L. lucida is multiple layers of cellulose microfibrils in the uppermost cell walls of the adaxial epidermis. The helicoidal arrangement of these fibrils is analogous to that which produces a similar color in arthropods. In B. pavonina and P. rotundifolia the blue-green coloration is caused by parallel lamellae in specialized plastids adjacent to the abaxial wall of the adaxial epidermis. The selective advantage of this color production, if any, is unknown.     

Cytomorphological characters supporting the taxonomic validity ofCyanothece (Cyanoprokaryota)

The fine structure of the type species of the genusCyanothece Komárek 1976,C. aeruginosa, is described and compared with the main cytological characteristics of morphologically related members of the generaCyanobium, Cyanobacterium andSynechococcus. Several morphological features, such as cell walls with thick outer layers containing a special type of vesicles, position of thylakoids, keritomy (net-like appearance of protoplast caused by arrangement of thylakoids, net-like nucleoids and/or by tendency to form intrathylakoidal spaces) and a special structure of mucilaginous envelopes were found to be characteristic of this genus, supporting its separate position among coccal cyanoprokaryotes (cyanobacteria, cyanophytes). The taxonomic significance of ultrastructural features in all mentioned genera is discussed.     

CYANOPHYTE AND CYANELLE DNA: A SEARCH FOR THE ORIGINS OF PLASTIDS1

Cyanophyte-like prokaryotes are widely presumed to be the progenitors of eukaryote plastids. A few rare protistan species bearing cyanophyte-like cyanelles may represent intermediate stages in the evolution of true organelles. Cyanophyte DNA disposition in the cell, so far as is known from electron microscopy, seems uniform within the group and distinctly different from the several known arrangements of DNA in plastids. Therefore a survey of representative cyanophytes and protistan cyanelles was undertaken to determine whether forms reminiscent of plastids could be found. DNA-specific fluorochromes were utilized, along with epifluorescent microscopy, to study the DNA arrangement in situ in whole cells. Only the endospore (baeocyte)-forming Cyanophyta contained more than one, centrally located DNA skein per cell, and then only for the period just preceding visible baeocyte formation. Such forms might, with modification, presage the “scattered nucleoid” DNA disposition found in plastids of several groups, including Rhodophytes, Cryptophytes, Chlorophytes and higher plants. The DNA arrangement in cyanelles of two protists, Cyanophora and Glaucocystis, appear different from each other and possibly related to, respectively, the cyanophytes Gloeobacter and Synechococcus. Cyanelles of the third protist, Glaucosphaera, like the cells of the unique prokaryote Prochloron, appear to have multiple sites of DNA, somewhat similar to those of the “scattered nucleoid” line of plastid evolution. No obvious precursor of the “ring nucleoid” or other types of plastid DNA conformation was found.     

Functional differentiation of the anterior pituitary cells in the fetal pig

Summary The fetal porcine pituitary was investigated by means of ultrastructural immunocytochemistry (1) to identify the first cells synthesizing the adenohypophyseal hormones, (2) to follow their differentiation during fetal development, and (3) to compare their ultrastructural characteristics with those of mature adult cells.The first ACTH-cells, which produced and stored ACTH, -LPH, -MSH, and - and -endorphin in the same granules, were very numerous at day 34 and displayed a uniform morphology. At day 50 and thereafter, until the end of gestation, the ACTH-cells differed in their appearance probably reflecting various stages of differentiation of one cell type. The GH-cells gained rapidly ultrastructural features comparable to those of mature GH-cells. In contrast, in the case of PRL-cells, which appeared only at the end of the gestation period as immature elements containing very small secretory granules, the morphological maturation seemed to take place only after birth. The first cells synthesizing the glycoprotein hormones (LH, LH, FSH and TSH) displayed ultrastructural features of immature cells. At day 50, their ultrastructural organization started to show a different pattern. At the end of gestation, the TSH-cells and the gonadotropic cells displayed the ultrastructural features of mature cells.     

Distribution and development of rodlet cells in the gills and pseudobranch of the bass, Dicentrachus labrax (L)

Rodlet cells in various stages of development were found in large numbers in the bass gill and pseudobranch. In the gill, rodlet cells were found in the epithelium at the base of the secondary lamellae and on the filament between adjacent lamellae, whilst in the pseudobranch they were found over the whole area of the secondary lamellae as well as in the filament epithelium.
During early development, rodlet cells are characterised by their amorphous cell inclusions, prominent supranuclear Golgi complex and network of granular endoplasmic reticulum. Later, with formation of a fibrous border the arrangement of the cell organelles undergoes reorganisation; the endoplasmic reticulum becomes distended, numerous vesicles appear and the mitochondria aggregate in the apical region of the cell. One of the most striking features is the development of club-shaped sacs containing electron dense cores, which are orientated towards the open apex of the cell.
Various staining properties of rodlet cells for light and electron microscopy were compared with those of mucous cells found in the same tissues. Possible functions of the cell are discussed.     

Growth and gas-vacuole development in vegetative cells of Anabaena flos-aquae

Summary Gas-vacuoles consisting of collections of gas-cylinders, and continuity of the plasma membrane with lamellae, are observed at all stages of growth of Anabaena flos-aquae. In day+4 cells, increased numbers of invaginations of the plasma membrane are observed and the lamellae tend to lie parallel to the cell wall. Some evidence is presented which suggests an associated synthesis of -granules and gas-cylinders by lamellae. Features of older cells are increased numbers of gascylinders, -granules, structured granules, and large intralamellar vesicles which appear to correlate with the presence of pinkish vacuoles as observed with the light microscope. The mean percentage of the volume of cells occupied by gas-vacuoles is about 20% during exponential growth when the doubling time is 56.5 hours, increasing to 34% in day+24 cells when growth is stationary.     

Effect of blue-green light on growth rate and chemical composition of three diatoms

The diatomsChaetoceros sp.,Skeletonema costatum andThalassiosira pseudonana were grown with different irradiances of white and of blue-green light, and with a mixture of blue-green plus 6.5 mol m^–2 s^–1 of white light. Exponential growth rates were higher in mixed blue for the first two, whileT. pseudonana grew faster in white light but, in all cases, mean cell division rates did not differ with increasing irradiances. Harvesting in stationary, rather than in late exponential growth phase, resulted in higher protein contents forChaetoceros sp. andS. costatum, but forT. pseudonana the highest value was in the exponential phase. The highest protein content was in blue-green light for the three species and it increased with irradiance. As to other fractions, the three strains showed different responses, related to quality and quantity, as well as to culture ages.     

ULTRASTRUCTURAL STUDY ON MICROSPORE WALL MORPHOGENESIS IN ISOETES JAPONICA (ISOETACEAE)

Spore wall morphogenesis of the microspore of Isoetes japonica was studied by transmission electron microscopy. The microspore wall consists of four layers: the perispore, outer exospore, inner exospore, and endospore. The perispore consists of electron-dense materials. The exospore is divided into outer and inner sections, with a large gap between the two. The outer exospore appears as an undulating plate consisting of tripartite lamellae with homogeneous sporopollenin. The inner exospore consists of an accumulation of tripartite lamellae on the microspore cell membrane. Immediately after meiosis, the tripartite lamellae of the outer exospore forms around the microspore. The lamellated inner exospore forms next, which adheres to the cell membrane of the microspore. The deposition of homogeneous sporopollenin material on the tripartite lamellae causes the plates of the outer exospore to thicken. Some homogeneous material may also be deposited on the inner exospore. Lastly, the electron-dense perispore is deposited on the outer exospore, and the electron-lucent endospore forms beneath the inner exospore. We conclude that the lamellae of the outer exospore, inner exospore, and endospore are formed and derived, in that order, from the gametophytic microspore cytoplasm. The homogeneous sporopollenin material of the outer exospore and perispore may be derived from the sporophytic tapetal cytoplasm.     

In vitro studies on the mechanisms of endospore release by Rhinosporidium seeberi

Studies of Rhinosporidium seeberi have demonstrated that this organism has a complex life cycle in infected tissues. Its in vivo life cycle is initiated with the release of endospores into a host's tissues from its spherical sporangia. However, little is known about the mechanisms of sporangium formation and endospore release since this pathogen is intractable to culture. We have studied the in vitro mechanisms of endospore release from viable R. seeberi's sporangia. It was found that watery substances visibly stimulates the mature sporangia of R. seeberi to the point of endospore discharge. The internal rearrangement of the endospores within the mature sporangia, the opening of an apical pore in R. seeberi's cell wall, and the active release of the endospores were the main features of this process. Only one pore per sporangium was observed. The finding of early stages of pore development in juvenile and intermediate sporangia suggested that its formation is genetically programed and that it is not a random process. The stimulation of R. seeberi's sporangia by water supports the epidemiological studies that had linked this pathogen with wet environments. It also explains, in part, its affinities for mucous membranes in infected hosts. The microscopic features of endospore discharge suggest a connection with organisms classified in the Kingdom Protoctista. This study strongly supports a recent finding that placed R. seeberi with organisms in the protoctistan Mesomycetozoa clade. This revised version was published online in June 2006 with corrections to the Cover Date.     

Organization of the olfactory system of the Indian major carp <Emphasis Type="Italic">Labeo rohita</Emphasis> (Ham.): A scanning and transmission electron microscopy study

Catla catla, Labeo rohita, and Cirrhinus mrigala represent important alimentary fish in India. Their reproduction/breeding depends on seasons. Fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in central regulation of reproduction. However, no electron microscopy data are available on organization of olfactory components of these fish. We studied organization of the olfactory organ in male L. rohita using scanning (SEM) and transmission electron microscopy (TEM). This organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The olfactory organ is ovoid in shape and consists of about 47–52 lamellae in adults and about 14–20 lamellae in fingerlings. These lamellae originate from the midline raphe. By SEM, microvillar sensory and ciliated non-sensory cells were observed in the lamellae. TEM revealed microvillar receptor cell with rough endoplasmic reticulum and Golgi apparatus towards apical end. Basal cells were present at the base of receptor cell, supporting cells were located adjacent to the olfactory receptor neurons, while epithelial cells—in the nonsensory part of olfactory epithelium. Mast, blastema, and macrophage cells were also found at the basement membrane. This work is the first publication on ultrastructural organization of the olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of the olfactory system and opens new avenues for further investigation of chemical neuroanatomy, sensory signal processing, and neural regulation of reproduction in the Indian major carp.     

Changes in ultrastructure and photosynthetic capacity withinScenedesmus obliquus mutants C-2 A′, C-6 D,and C-6 E on transfer from dark grown to illuminated conditions

Summary The ultrastructure, pigments and photosynthetic capacities of 3 X-ray induced mutants (C-2 A, C-6 D, and C-6 E) ofScenedesmus obliquus were studied whilst growing heterotrophically in the dark and upon transfer into the light (10,000 lux).Dark grown C-2 A, having no photosynthetic capacity and sparse amounts of chlorophylls a and b, greened at a faster rate than mutant C-6 D which already had photosystem I activity and chlorophyll a in the dark. Ultrastructural development to the wild-type situation was similar in both, but again much faster in C-2 A (24 hours) than in C-6 D (48 hours). In the dark grown C-2 A mutant the single lamellae differed from C-6 D in that they were already perforated. In the light, membrane overlapping took place in both to form first double, and later triple, thylakoid bands. A distinct phase of association of plastid ribosomes in a whorl-like arrangement with the developing thylakoids was shown by both only during the greening process. Over a similar period, mitochondrial appressions to these plastids were observed.In the dark, mutant C-6 E resembled dark grown C-6 D and possessed considerable photosystem I activity but no carotenoids. In the light it did not green, no ultrastructural changes were apparent and the unprotected chlorophyll a was photo-oxidized.All mutants in the dark showed tubular connections, resembling but not identical with the prolamellar bodies of higher plant etioplasts. Occasionally tubular connections similar to those in the dark-grown mutants were also found in the light.     

Effect of Light with Different Spectral Composition on Cell Growth and Pigment Composition of the Membranes of Purple Sulfur Bacteria <Emphasis Type="Italic">Allochromatium minutissimum</Emphasis> and <Emphasis Type="Italic">Allochromatium vinosum</Emphasis>

The effect of light with different spectral composition: white, red and blue-green (the first one is absorbed by all the pigments of the cell, and the second and the third ones are absorbed by bacteriochlorophyll and carotenoids, respectively) on culture growth, carotenoid synthesis, and assembly of the light-harvesting complexes was studied for the purple sulfur bacteria Allochromatium (Alc.) minutissimum MSU and Alc. vinosum ATCC 17899. The working hypothesis on the growth of bacteria under blue-green illumination (absorbed by carotenoids) resulting in the inhibition of cell growth was tested. When equalizing the light by luxes, the intensity of illumination for each luminous flux was 1800 lx (white and red light, 4 W/m²; bluegreen light, 0.4 W/m²). The growth of the cells was recorded in white and red light, while in blue-green light an insignificant increase was observed only for Alc. vinosum at the end of the experiment (7–9 days). Regardless of the spectral composition of the light the B800-850 type LH2 complex was always assembled in Alc. minutissimum membranes, and two short-wave LH2 complexes of В800-820 and В800-840 type were assembled in the membranes of Alc. vinosum. Upon smoothing and increasing the luminous flux up to 6 W/m² for every illumination mode, both cultures grew with approximately equal rates in blue-green light. In the membranes of Alc. minutissimum and Alc. vinosum the same types of LH2 complexes were assembled as in the case of 1800 lx illumination. It was found that blue-green light did not inhibit cell growth. At illumination of the cells collected at the end of the experiment with blue-green light for 6 h, no photooxidation of BChl850 was registered. However, in the membranes from the cells oxygen-saturated at isolation, ~50% of BChl850 was oxidized after 30 minutes of illumination. In the course of cell growth, oxygen is probably completely consumed and anaerobic conditions develop inside the cell. Under these conditions, formation of reactive oxygen species, BChl photooxidation and inhibition of the cell growth become impossible.     

REJUVENATION OF MELOSIRA GRANULATA (BACILLARIOPHYCEAE) RESTING CELLS FROM THE ANOXIC SEDIMENTS OF DOUGLAS LAKE,MICHIGAN, II. ELECTRON MICROSCOPY 1

Detailed cytological changes that accompany the rejuvenation of resting cells of Melosira granulata were studied with the electron microscope. Dormant and viable cells that we previously classified as the condensed state generally contain definable chloroplasts, mitochondria, a nucleus and other cytoplasmic remnants. However, there appears to be a continuous cytoplasmic degradation spectrum and some cells which appear intensely colored with the light microscope have discontinuous chloroplast membranes and few other cytoplasmic remnants. Rejuvenation of viable dormant cells is initially accompanied by the accumulation of both lipids and polyphosphates. In the earliest stages of expansion, these storage products are dispersed throughout the cell. In later stages of expansion, the lipids appear to be coalesced into larger droplets which are easily identified at the light microscope level. The fully expanded stage is characterized by the normal complement of organelles and their arrangement at the periphery of the cells and central cytoplasmic bridge. These cells appear both anabolically and catabolically active as evidenced by the abundance of endoplasmic reticulum, ribosomes and secretory and lytic vesicles. Prior to cell division, both lipids and polyphosphates a re reduced or absent in the cells. The ultrastructural features of the dormant, condensed state in resting cells of M, granulata are similar to those described for hypnospores. A rejuvenation sequence that produces cytological features common to resting state formation could provide a population of cells which could easily revert should environmental conditions become adverse.     

Comparative structure of the gas-vacuoles of blue-green algae

Summary An investigation was made of 5 species of blue-green algae reported to contain gas-vacuoles. All organisms were grown and harvested under standard conditions. Gas-vacuoles were characterised as reddish structures which are destroyed by applying pressure. Using a simple direct preparation technique gascylinders were observed with the transmission electron microscope in gas-vacuolate cells. Gas-vacuoles were present in the strains of Anabaena flos-aquae, Gloeotrichia echinulata and Oscillatoria agardhii studied and absent from Microcystis aeruginosa and Nostoc linckia. The reddish, refractile central area of N. linckia and M. aeruginosa cells was tentatively identified as nucleoplasm. Gas-vacuoles are collections of gas-cylinders 70 m wide, which in A. flos-aquae and G. echinulata are clearly bounded by photosynthetic lamellae and associated with -granules. The presence of bounding photosynthetic lamellae in these species is suggested as a causal factor of the unusual optical properties of their gas-vacuoles. The range of lengths of gas-cylinders in G. echinulata and O. agardhii is from 100 m to 500 m and in A. flos-aquae it is from 100 m to 1300 m. The percentage of cell volume occupied by gas-vacuoles was estimated by direct measurement. In A. flos-aquae and G. echinulata it was 22%. In O. agardhii gas-cylinders were not clearly associated with photosynthetic lamellae and -granules and occupied 39% of cell volume. Gascylinder membranes showed reasonable preservation in KMnO₄ and excellent preservation in OsO₄. The widths of membranes after treatment with these two fixatives was 3 m and 2 m respectively.     

Histophysiological studies on the corpus allatum of Leucophaea maderae

Summary The structural differences between active and inactive corpora allata, visible under the light microscope, become more pronounced under the electron microscope. Aside from differences in cellular and nuclear diameters, and nuclearcytoplasmic ratios, there are qualitative characteristics in ultrastructural organization.The cytoplasm of active corpus allatum cells contains numerous sinuous mitochondria, distinct Golgi elements, ergastoplasmic units with a tendency to form whorls, agranular cytomembranes, and free ribosomes. Pleomorphic inclusion bodies resembling lysosomes are more or less numerous. The plump, ovoid nuclei frequently show two prominent nucleoli whose components may form a meshwork harboring chromatin.The marked reduction in the amount of cytoplasm occurring during the organ's return to inactivity is accompanied by a decrease in the number, and a change in the appearance, of some cytoplasmic organelles. The mitochondria tend to be smaller, and the ergastoplasm is reduced to scattered wisps of ribosome-studded membranes. Nuclei of inactive cells have smaller diameters than those of active ones.In all stages of activity, cell boundaries are clearly visible. As a result, the corpus allatum cell can now be characterized as a discrete unit of epithelioid character and rather complex shape. The plasma membrane may become folded when the cellular content shrinks to the inactive level. Aside from changing outlines, all corpus allatum cells have long, gradually thinning processes. These penetrate deeply into the parenchyma where they interlock with those of other cells; many processes eventually seem to reach the surface of the gland where the secretory products are released into the hemolymph. These have to pass through an acellular connective tissue layer that shares tinctorial and ultrastructural properties with those of a boundary (or basement) membrane.This stromal element forms a sheath and branching processes that extend into and permeate the parenchyma. It seems to represent a system of channels, not only for the release of secretory and other cellular products, but for the entry of nutrients and perhaps chemical messenger substances.Neurosecretory material can be observed in the form of structurally distinctive elements, i.e., as electron-opaque granular inclusions within axon terminals that become contiguous with corpus allatum cells.No definite statement can be made on the basis of the present study about the nature of the corpus allatum hormone or hormones, except that the ultrastructural criteria indicative of proteinaceous secretion, such as the appearance of secretory granules in spatial relation with Golgi elements, seem to be missing in the corpora allata of Leucophaea.Supported by Research Grants A-3984 and B-2145 from the U.S.P.H.S.