Role of the midgut gland in purine excretion in the robber crab,Birgus latro (Anomura: Coenobitidae)

White fecal strands of Birgus latro are composed of small spherules of uric acid with a mean diameter of 1.6 ± 0.6 μm. Large numbers of membrane‐bound spherules with concentric lamellae are present in the R cells of the midgut gland, so we suggest that lengths of white feces are produced by coordinated secretion of these spherules into the lumen of the midgut gland tubules. There are four cell types in the tubules with embryonic (E) cells at the distal tip, B cells in a narrow band at the distal end and R cells making up the bulk of the tubules and gland. F cells are sparsely scattered among the R cells. Midgut gland tissue was assayed for activities of xanthine dehydrogenase and xanthine oxidase, the two forms of xanthine oxidoreductase. Contrary to previous reports, we found that the midgut gland of B. latro contains only high activities of xanthine dehydrogenase. If proteinase inhibitors were omitted from the assays, however, significant activity of xanthine oxidase was measured, a result we regard as an artifact attributable to the partial conversion of xanthine dehydrogenase to xanthine oxidase by endogenous proteinases. R cells were demonstrated to contain peroxisomes, which may be involved in lipid metabolism rather than synthesis of uric acid. J. Morphol. 241:227–235, 1999 © 1999 Wiley‐Liss, Inc.     

HISTOCHEMISTRY AND ULTRASTRUCTURE OF THE CRYPT CELLS IN THE DIGESTIVE GLAND OF APLYSIA PUNCTATA (CUVIER, 1803)

The crypt cells lining the Aplysia punctata digestive tubulescomprise of three types of cell; calcium, excretory, and thincells. The calcium cells play a role in osmoregulation, mineral storage,exocrine secretion, iron detoxification, and excretion processes.They possess well- developed microvilli and a basal labyrinth,suggesting a role in absorption. The Golgi apparatus is involvedin the production of two main components of calcium spherules;the fibrillar material and mineralized granules. Golgi complex,rough endoplasmic reticulum (RER), ribosomes, and altered mitochondriaare involved in the formation of calcium spherules. Secretoryactivity is indicated by the formation of dense granules containingiron and calcium salts. Lipofuscin pigment has been found inlarge concretions which may arise from cytoplasmic areas surrounded byendoplasmic reticulum, RER and Golgi tubules. There are threestages of excretory cells, called early, mature, and post-excretorycells. This study traces the development of granulofibrillarvacuoles up to the formation of the lipofuscin concretions andshows that excretory cells are in fact degenerating calciumcells. The fine structure of thin cells suggests that they areyoung calcium cells. (Received 29 December 1997; accepted 15 November 1998)     

Sieve-Element Ontogeny in the Aerial Shoot of Equisetum hyemale L.

The aerial shoots of Equisetum hyemale L. var. affine (Engelm.)A. A. Eat. were examined with the electron microscope as partof a continuing study of sieveelement development in the lowervascular plants. Young E. hyemale sieve elements are distinguishablefrom all other cell types within the vascular system by thepresence of refractive spherules, proteinaceous bodies whichdevelop within dilated portions of the endoplasmic reticulum(ER). Details of cell wall thickening differ between protophloemand metaphloem sieve elements. Following cell wall thickeningthe ER increases in quantity and aggregates into stacks. Shortlythereafter, nuclear degeneration is initiated. During the periodof nuclear degeneration some cytoplasmic components-dictyosomes,microtubules and ribosomes-degenerate and disappear, while organellessuch as mitochondria and plastids persist. The latter undergostructural modifications and become parietal in distribution.Eventually the massive quantities of ER are reduced, leavingthe lumen of the cell clear in appearance. At maturity the plasmalemma-linedsieve element contains a parietal network of tubular ER, aswell as mitochondria, plastids, and refractive sphemh At thistime many of the spherules are discharged into the region ofthe wall. Sieveelement pores occur in both lateral and end walls.At maturity many pores are traversed by large numbers of ERmembranes. The metaphloem sieve elements of the mid-internodalregions apparently are sieve-tube members. The connections betweenmature protophloem sieve elements and pericycle cells are associatedwith massive wall thickenings on the pericyclecell side.     

THE FUNCTIONAL MORPHOLOGY OF THE DIGESTIVE SYSTEM OF LYONSIA HYALINA CONRAD, 1831 (BIVALVIA: ANOMALODESMATA: PANDOROIDEA)

The anatomy and histology of the digestive tract of the suspensionfeeding bivalve Lyonsia hyalina were examined using microdissectionand conventional light microscopy. Lyonsia hyalina has a typeIV stomach which contains a major typhlosole that does not penetratethe left pouch, as in other members of the Pandoroidea. Theventral and posterior sorting areas of the stomach are sitesof vigorous ciliary activity. The gastric shield is locatedon the left and posterior stomach walls, underlain by tall basophiliccells with microvilli that project into the gastric shield.The style sac and midgut are combined, and contain the morphologicalcell types A-D seen in other bivalves. Many ciliated cells ofthe digestive tract appear to have high densities of apicalmitochondria. The ducts within the digestive diverticula arelined by epithelia containing a conspicuous brush border. Bothcrypt cells and digestive cells exist in the digestive tubules.The presence of numerous fragmentation spherules throughoutthe digestive diverticula indicates that intracellular digestionoccurs there. (Received 21 April 1992; accepted 1 October 1992)     

Developmental Ultrastructure of Cells and Plastids in the Petals of Wallflower (Erysimum cheiri)

An ultrastructural study of petal cells of wallflower (Erysimumcheirii) of the family Brassicaceae shows that the adaxial epidermalcells are of the conical papillate type whereas the cells ofthe abaxial epidermis are lenticular in shape. The abaxial epidermiscontains stomata, which are solitary and lack any obvious subsidiarycells. Pigmentation is apparent in both epidermal and internalmesophyll cells and results from the presence of both chromoplastsand large cytoplasmic vesicles containing pigment. These pigmentedvesicles are very obvious in preparations of fixed isolatedpetal cells. Chromoplasts are of the globular type and are presentin significant numbers in both epidermal and mesophyll cells.Division of chloroplasts in young petals prior to bud breakappears to give rise to the populations of chromoplasts observedin mature petals since there was no evidence of chromoplastdivision itself. The development of wallflower petals and theirchromoplasts is discussed in relation to development of petalsin the related species Arabidopsis thaliana. Copyright 1999Annals of Botany Company Wallflower, Erysimum cheiri, Chieranthus, petal development, chromoplasts, chloroplast differentiation.     

Morphological Diversity of the Rod Spherule: A Study of Serially Reconstructed Electron Micrographs

Purpose

Rod spherules are the site of the first synaptic contact in the retina’s rod pathway, linking rods to horizontal and bipolar cells. Rod spherules have been described and characterized through electron micrograph (EM) and other studies, but their morphological diversity related to retinal circuitry and their intracellular structures have not been quantified. Most rod spherules are connected to their soma by an axon, but spherules of rods on the surface of the Mus musculus outer plexiform layer often lack an axon and have a spherule structure that is morphologically distinct from rod spherules connected to their soma by an axon. Retraction of the rod axon and spherule is often observed in disease processes and aging, and the retracted rod spherule superficially resembles rod spherules lacking an axon. We hypothesized that retracted spherules take on an axonless spherule morphology, which may be easier to maintain in a diseased state. To test our hypothesis, we quantified the spatial organization and subcellular structures of rod spherules with and without axons. We then compared them to the retracted spherules in a disease model, mice that overexpress Dscam (Down syndrome cell adhesion molecule), to gain a better understanding of the rod synapse in health and disease.

Methods

We reconstructed serial EM images of wild type and Dscam^GoF (gain of function) rod spherules at a resolution of 7 nm in the X-Y axis and 60 nm in the Z axis. Rod spherules with and without axons, and retracted spherules in the Dscam^GoF retina, were reconstructed. The rod spherule intracellular organelles, the invaginating dendrites of rod bipolar cells and horizontal cell axon tips were also reconstructed for statistical analysis.

Results

Stereotypical rod (R1) spherules occupy the outer two-thirds of the outer plexiform layer (OPL), where they present as spherical terminals with large mitochondria. This spherule group is highly uniform and composed more than 90% of the rod spherule population. Rod spherules lacking an axon (R2) were also described and characterized. This rod spherule group consists of a specific spatial organization that is strictly located at the apical OPL-facing layer of the Outer Nuclear Layer (ONL). The R2 spherule displays a large bowl-shaped synaptic terminal that hugs the rod soma. Retracted spherules in the Dscam^GoF retina were also reconstructed to test if they are structurally similar to R2 spherules. The misplaced rod spherules in Dscam^GoF have a gross morphology that is similar to R2 spherules but have significant disruption in internal synapse organization.

Conclusion

We described a morphological diversity within Mus musculus rod spherules. This diversity is correlated with rod location in the ONL and contributes to the intracellular differences within spherules. Analysis of the Dscam^GoF retina indicated that their R2 spherules are not significantly different than wild type R2 spherules, but that their retracted rod spherules have abnormal synaptic organization.     

CYCLIC ACTIVITY AND EPITHELIAL RENEWAL IN THE DIGESTIVE GLAND TUBULES OF THE MARINE PROSOBRANCH MAORICRYPTA MONOXYLA (LESSON)

Three cell types are present in tubules of the digestive glandof the marine prosobranch Maoricrypta monoxyla (Lesson). Histochemistry,and feeding and starvation experiments established that themain type, the digestive cell, is involved in endocytotic uptakeof food material from the lumen. Digestion of this materialoccurs within vacuoles, and indigestible material (indicatedby the dye trypan blue) accumulates in basal residual bodiescontaining lipofuscin pigment. Another cell type, the cryptcell, appears to secrete a glycoprotein, probably enzymaticin function. The third cell type contains large vacuoles butit has not been Established whether the contents are secretoryor excretory. The tubules undergo a cycle of digestive activity not relatedto the tidal cycle as in some marine molluscs, but probablyan indirect result of the feeding regime. The cycle begins withimmature tubules in which some endocytosis occurs. These developinto absorbing tubules involved mainly in food uptake. In maturetubules intracellular digestion occurs. At a later stage thetubules fragment to produce spherules which may conserve usefulmaterial, and finally they, disintegrate completely. Eighty per cent of the dividing cells in the epithelium occurin crypts, which are therefore considered to be the main sitesof epithelial renewal. The processes by which tubules may bereformed after breakdown are discussed (Received 28 September 1978;     

Within-bunch Variability in Banana Fruit Weight: Importance of Developmental Lag Between Fruits

Within-bunch (inflorescence) variability in banana fruit weightis of great importance: distal fruits (at the bottom of thebunch) are 30 to 40% smaller than basal fruits at the top. Wehypothesize that this variability is related to a developmentallag between fruits. To validate this hypothesis, histologicalstudies (evolution in number of cells along the fruit radius,starch granule number and size) associated with physiologicalmeasurements (pulp dry weight, dry matter and starch concentration)were carried out. Fruit development stages were dated in cumulativedegree-days (dd) from flower emergence to 3 weeks after theharvest stage (1300 dd). For a fruit located at the top of thebunch, cell divisions ceased around 350 dd and cells began tofill with starch as soon as they appeared. A developmental lagbetween fruits at the top and bottom of the bunch was observed:cell divisions started and stopped approx. 70 dd later in bottom(distal) compared to top (basal) fruits. At the end of celldivisions, basal fruits had a higher number of cells along thefruit radius. This difference in cell number may be due to increasedcompetition for assimilates between fruits when cell divisionoccurs in distal fruits. Variability in cell number may be relatedto variability in pulp dry weight. We conclude that within-bunchvariability in banana fruit weight is related to a differencein cell number and age. Copyright 2001 Annals of Botany Company Musa acuminata, banana, fruit development, fruit growth, cell number, starch accumulation, fruit quality, fruit green-life, fruit-fruit competition     

The Difference Between Open and Closed Meristems

An open and a closed root meristem have been compared by investigatingthe cell kinetics of small regions of the apices of Helianthusand Zea. The cells of the stelar pole are quiescent in both and thereis no exchange of cells between stele and cortex or stele andcap. The immediately distal cells in the closed meristem (Zea)are also quiescent and the few divisions that do occur can betransverse or longitudinal. In the open meristem (Helianthus)these cells are not quiescent, but they go out of cycle transiently,prolonging the potential cell-doubling time. Their divisionsare transverse. It is a consequence of these differences thatclosed meristems form root caps discrete from the cortex whereasopen meristems force instability in the boundary between theperipheral part of the cap and the cortex. Another consequencein roots with open meristems is a succession of columella complexestransversely displaced from each other by the state of fluxin the meristem during the non-cycling phase of the proximaltier of cells, those immediately distal to the stelar pole. The results are discussed in relation to the ontogenetic onsetof quiescence and the evidence for switches between open andclosed operation of meristems. meristem, root apex, Helianthus annuus, Zea mays L.     

Phosphatidylinositol 3-Kinase-, Actin-, and Microtubule-Dependent Transport of Semliki Forest Virus Replication Complexes from the Plasma Membrane to Modified Lysosomes

Like other positive-strand RNA viruses, alphaviruses replicate their genomes in association with modified intracellular membranes. Alphavirus replication sites consist of numerous bulb-shaped membrane invaginations (spherules), which contain the double-stranded replication intermediates. Time course studies with Semliki Forest virus (SFV)-infected cells were combined with live-cell imaging and electron microscopy to reveal that the replication complex spherules of SFV undergo an unprecedented large-scale movement between cellular compartments. The spherules first accumulated at the plasma membrane and were then internalized using an endocytic process that required a functional actin-myosin network, as shown by blebbistatin treatment. Wortmannin and other inhibitors indicated that the internalization of spherules also required the activity of phosphatidylinositol 3-kinase. The spherules therefore represent an unusual type of endocytic cargo. After endocytosis, spherule-containing vesicles were highly dynamic and had a neutral pH. These primary carriers fused with acidic endosomes and moved long distances on microtubules, in a manner prevented by nocodazole. The result of the large-scale migration was the formation of a very stable compartment, where the spherules were accumulated on the outer surfaces of unusually large and static acidic vacuoles localized in the pericentriolar region. Our work highlights both fundamental similarities and important differences in the processes that lead to the modified membrane compartments in cells infected by distinct groups of positive-sense RNA viruses.All positive-strand RNA viruses replicate their genomes in association with cellular membranes. The formation and activity of the membrane-bound replication complexes (RCs) can result in extensive alteration of membrane structures (11, 40, 48). Different viruses use different cytoplasmic membrane compartments as platforms for replication. Currently, there is only a limited understanding of how the virus-encoded and cellular proteins coordinate the formation of the replication-induced membrane structures. We address the mechanisms of membrane-bound replication with alphaviruses, particularly Semliki Forest virus (SFV). The alphaviruses comprise several human and animal pathogens, including the encephalitogenic alphaviruses (e.g., Western, Eastern, and Venezuelan equine encephalitis viruses) as well as the recently reemerging chikungunya virus, which belongs to the SFV clade of alphaviruses. During the past 5 years, chikungunya virus has caused more than 2 million infections and 500 deaths, and a new strain has spread throughout the areas surrounding the Indian Ocean (50). The alphaviruses use mosquitoes as intermediate hosts and transmission vectors, and at present no vaccines or antivirals are available to control these infections.The cytoplasmic replication of alphaviruses depends on the four viral nonstructural (ns) proteins, nsP1 to nsP4, which are all essential and act as a membrane-bound replication complex. The nsPs are translated from the viral positive-sense RNA genome as one large polyprotein. Cleavages catalyzed by the nsP2 moiety result in the release of the individual proteins. A large fraction of the synthesized nsPs is involved in genome replication and associates with membranes, but a sizable fraction dissociates and is distributed in different cellular compartments: nsP1 binds to the inner surface of the plasma membrane (PM); nsP2 is translocated into the nucleus; nsP3 seems to form aggregates in the cytoplasm; and most of the extra nsP4, the core RNA polymerase, is degraded by the proteasome. While the major enzymatic functions of the individual nsPs have been elucidated (21), little is known of how they function together in the replication machinery.As in other positive-strand RNA viruses, the RCs of alphaviruses are associated with altered intracellular membranes, which were first described in the late 1960s and early 1970s (13, 14, 18). In these early studies, it was shown that virus replication induces bulb-shaped membrane invaginations with a diameter of ∼50 nm, which were called spherules. The spherules were found on the limiting membranes of large cytoplasmic vacuoles, which were named virus-induced cytopathic vacuoles of type I (CPV-I). On rare occasions, the spherules were seen also at the PM. By electron microscopic (EM) autoradiography, it was also shown that the spherules both at the CPV-I and at the PM could be sites of RNA synthesis (18). Subsequently, Froshauer et al. (15) showed that CPV-I are positive for endosomal and lysosomal markers. Moreover, using EM, they showed that the inside of the spherule is connected to the cytoplasm by a pore from which electron-dense material (which the authors suggest to be the newly synthesized RNA) seems to diffuse into the cytoplasm.During the past decade, our group has addressed the biogenesis of the CPV-I. We demonstrated that the formation of the spherules did not require structural proteins (44) and, more recently, that all four nsPs were associated with the spherules together with newly formed RNA (labeled by bromouridine), strongly suggesting that they were the actual units of RNA replication (RCs) (28). We also suggested as one possibility that the spherules could first arise at the PM; subsequent endocytosis of the spherules could account for the formation of the CPV-I (28, 44). Of the four nsPs, only nsP1 has affinity for membranes, and when expressed alone, it is specifically targeted to the inner surface of the PM (45). NsP1 is a monotopic membrane protein; its affinity for membranes is dictated by an amphipathic alpha helix, located in the central region of the protein (4, 31). NsP1 has a specific affinity for negatively charged phospholipids, which could potentially account for its prevalent localization to the PM, where such lipids are enriched. Later we showed that the membrane binding of nsP1 through the amphipathic helix is essential for alphavirus replication (56).Several groups of positive-sense RNA viruses make spherules, which appear very similar to those made by the alphaviruses. However, for these virus groups, the spherules arise in different locations. For the well-characterized brome mosaic virus (BMV), a plant virus very distantly related to the alphaviruses, the spherules are seen in the endoplasmic reticulum (ER) adjacent to the nucleus (51). For the unrelated nodaviruses, the spherules are localized on mitochondrial surfaces (25). Recent models of the RCs of flaviviruses suggest that their replication complexes also resemble spherules (62). For the Flaviviridae, the RCs are found on the membranes of the secretory pathway.The aim of this study was to clarify the role of different membranes in the formation and maturation of alphavirus RCs, and particularly to test our hypothesis that the RCs (spherules) are formed at the PM and are internalized thereafter. By using confocal microscopy, live-cell imaging, and novel electron microscopic techniques, we demonstrate that the RCs of SFV undergo an unprecedented, highly dynamic trafficking between different cellular compartments. They are first detected at the PM, which serves as the major platform for spherule formation. A specific endocytic event results in the transfer of spherules to the limiting membrane of small cytoplasmic vesicles. Using pharmacological inhibitors, we have been able to block the internalization process, and we found that the exit of spherules from the PM is dependent on the activity of phosphatidylinositol3- kinase (PI3K). Following the intracellular dynamics associated with spherules in live cells, we show the contribution of actin and microtubule-based transport, as well as that of fusion events with preexisting acidic organelles, providing the first complete model for the biogenesis of the large static CPV-I, where spherules are found at later stages of infection.     

Ultrastructural Aspects of the Glandular Cells from the Secretory Trichomes and from the Cell Suspension Cultures of Achillea millefolium L. ssp. millefolium

The ultrastructure of the glandular cells of the floret secretorytrichomes from Achillea millefolium L. ssp. millefolium (yarrow)was examined before and after anthesis and compared with theultrastructure of the cells from the cell suspension culturesobtained from the same plant. The profuse tubular structuresobserved in the plastids of the glandular cells of the trichomesduring the pre-secretory stage were much reduced in the secretorystage and showed an osmiophilic content. Some endoplasmic reticulumprofiles could be seen adjacent to the plastids. Later in thesecretory stage, the secretion appeared in the periplasmic spacebetween the cells of the upper tiers and in the sub-cuticularspace. Finally the secretion was released by rupture of thecuticle. At the lag phase, the cells from the cell suspensioncultures of yarrow were characterized by the presence or plastidswith tubular structures, similar to those observed in the plastidsof the trichomes in the pre-secretory stage. By the end of thelag phase accumulations of starch were observed inside the plastids.At the beginning of the exponential phase, the tubular structuresof the plastids started to show an osmiophilic content and theaccumulations of starch were still present. At the end of thisphase starch disappeared from the plastids and only osmiophilictubular structures were observed. Rough endoplasmic reticulumas well as smooth endoplasmic reticulum profiles were frequentlyin close association with plastids and mitochondria. At thestationary phase a very large vacuole filled the cells, andin the remaining cytoplasm some endoplasmic reticulum profilesand osmiophilic droplets were observed.Copyright 1994, 1999Academic Press Achillea millefolium L. spp. millefolium, yarrow, ultrastructure, trichomes, glandular cells, plant cell suspension cultures     

Evidence that mineralized spherules are involved in the formation of the superficial layer of the elasmoid scale in cichlids Cichlasoma octofasciatum and Hemichromis bimaculatus (Pisces,Teleostei): an epidermal active participation?

Summary The region between the epidermis and the surface of the overlapping part of scales has been studied in two cichlid teleosts using transmission electron microscopy. In a few specimens only, numerous mineralized spherules (1 m in diameter) are observed in the loose dermis and at the scale surface, and form a large part of the superficial outer limiting layer of the scale. In the loose dermis (stratum laxum) and close to the scale surface spherules are either free or included in dermal cells. When free, they are dispersed in the extracellular matrix of the dermis, among the fibrils of anchoring bundles, and fused with the scale surface. When included in cell vacuoles, they lie close to the lamina densa and to the scale surface. Steps in the formation of the mineralized spherules are only seen in the lamina densa of the basement membrane. The spherules contain needle-like mineral crystals radially orientated and an organic matrix of stippled material and dense granules, some of which form concentric lines around the centre of the spherules. The results suggest that mineralized spherules form in the lamina densa and pass through the dermis to the scale surface in which they are incorporated.     

White Vesicles in the Skin of Aplysia californicaCooper: A Proposed Excretory Function

White patches of skin that appear early in the development ofthe shell-less mollusc, Aplysia californica, are composed ofaggregations of vase-shaped vesicles, each a single, large cellwith an enlarged nucleus. Two layers of collagen, at 90°to each other, surround the vesicle membrane, together witha non-contiguous external layer of muscle. Energy dispersivespectroscopy and electron diffraction of the contents with scanningelectron microscopy (SEM) and transmission electron microscopy(TEM) failed to find a signal for halogens (involved with unpalatableskin and, therefore, defence against predation), but did recordprominent signals for calcium. Immature vesicles are filledwith an homogenous material that appeared to mature progressively,likely by nucleation, into numerous, small spherules, visibleby both SEM and TEM. Ultra-thin uranyl acetate stained sectionsof mature vesicles showed that the spherules had an intracrystallinematrix of radially arranged electron-dense material. The vesiclecell had none of the modifications characteristic of calciumor rhogocyte cell-types, which serve as calcium reservoirs forthe movement of this element to sites of shell formation andregeneration. These vesicles are likely involved with the excretionof excess calcium and not, as originally hypothesized, witheither defence against predators or calcium flux. In addition,the spherules that fill the vesicles are possibly composed ofthe less common polymorphs of calcium carbonate, vaterite andamorphous calcium carbonate. Excretion of the vesicle contentsappeared to be passive, since vesicles lacked an abundant contiguouslayer of muscle or a muscular release valve in the vesicle neck,but did have organized layers of collagen just outside the vesiclemembrane. We propose that release of vesicle contents probablyoccurs when the neck of the vesicle is broken. (Received 5 December 2005; accepted 28 April 2006)     

Induction of spherule formation in Physarum polycephalum by polyols

A method has been developed for inducing spherule formation (spherulation) in the myxomycete Physarum polycephalum by transferring the culture to synthetic medium containing 0.5 m mannitol or other polyols. This morphogenetic process occurred within 12 to 35 hr after the inducer was added. The mature spherules existed as distinct morphogenetic units, in contrast to the clusters of spherules formed during starvation. Ninety per cent of the spherules germinated by 24 hr in synthetic medium. The changes in the synthesis of ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and protein during plasmodial growth, spherulation, and germination of spherules are described. When spherule formation was completed, RNA, protein, and DNA decreased, compared with the values at the beginning of the conversion. The incorporation of (3)H-uridine into trichloroacetic acid-insoluble material was different in each of these periods, and this incorporation was sensitive to actinomycin D. The amount of glycogen increased during growth, whereas it decreased during spherulation. (14)C-glucose could be taken up by the cells in the presence of the inducer, and mannitol could not replace glucose as a source of energy. The mode of action of mannitol and its mechanism of induction are discussed.     

Cell populations in the pineal gland of the viscacha (Lagostomus maximus). Seasonal variations

Pineal samples of the viscacha, which were taken in winter and in summer, were analysed using both light and electron microscopy. The differences found between the two seasons were few in number but significant. The parenchyma showed two main cell populations. Type I cells occupied the largest volume of the pineal and showed the characteristics of typical pinealocytes. Many processes, some of which were filled with vesicles, could be seen in intimate contact with the neighbouring cells. The presence in the winter samples of "synaptic" ribbons and spherules, which were almost absent in the summer pineals, suggests a seasonal rhythm. These synaptic-like structures, as well as the abundant subsurface cisterns present in type I cells, appeared as basic differential features which allowed these cells to be distinguished from type II cells. These latter cells, which can be classified as interstitial cells, showed some other distinguishing features, such as irregular-shaped nuclei, abundant deposits of glycogen-like particles and structures of unknown function consisting of concentric cisterns surrounding a dense body. In the summer, interstitial cells displayed numerous large round bodies, which contributed to increase the cellular volume slightly. Regarding other constituents, like glial cell processes, vessels of non-fenestrated endothelium and sympathetic innervation, no qualitative differences were observed between the two seasons studied. We have presented here some morphological evidences of the circannual rhythm of the viscacha pineal, as well as ultrastructural criteria for distinguishing the main cell populations of this organ, which could be useful for studies carried out in other mammals.     

Functional and Structural Chromosome Analyses in Autotetraploid Silene latifolia

Recent immunocytological and molecular data show that heterochromaticnuclear regions, both constitutive and facultative, are modifieddifferently (cytosine hypermethylation and histone hypoacetylation)and late replicating, when compared to euchromatin. Intrusiveand/or additive (supernumerary) DNA sequences are often functionallysilenced; this is accompanied by their heterochromatinization.In this work we present a number of karyological studies onautotetraploid female cells of Silene latifolia (syn. Melandriumalbum). Immunofluorescence analyses do not indicate any globaldifferences in DNA methylation, histone H4 acetylation, andchromosome replication patterns which could arise as a consequenceof the duplication of the whole chromosome set of the originaldiploid genome. Similarly, the number of silver-positive nucleoliroughly correlates to the ploidy level. Early replication andH4 hyperacetylation have been detected at all subterminal chromosomeregions. This, together with cDNA in situ hybridization patterns,indicates the localization of gene-rich regions. DNA methylationand chromosome replication patterns, but not histone H4 acetylation,show differences among the four X chromosomes present: one tothree X chromosomes were observed as hypermethylated and/orlate replicating. Taken together, the data demonstrate thatthere is no overall silencing of the additional two sets ofautosomes in the tetraploid cells, but the X chromosomes couldbe subject to an irregular dosage compensation. Copyright 1999Annals of Botany Company DNA methylation, histone acetylation, polyploidy, replication patterns, sex chromosomes, Silene latifolia (syn.Melandrium album ).     

Colchicine-induced Paracrystals in Root Cells of Wheat (Triticum aestivum L.)

Tubulin conformations other than microtubules in the meristematiccells of wheat roots grown in the presence of 2 mM colchicinesolution were investigated by immunofluorescence and electronmicroscopy. In the affected cells microtubules disappeared andwere replaced by tubulin fluorescent strands that occurred inthe cortical cytoplasm. With increasing time of exposure tocolchicine the tubulin strands became better organized and occurredalso in the subcortical cytoplasm and finally they were restrictedto the area around the nucleus. In prophase and preprophasecells thick strands occupied the cortical cytoplasmic zone wherein normal cells a preprophase microtubule band (PMB) was expectedto be assembled. In the colchicine-treated cells electron microscopy revealedan accumulation of paracrystalline aggregates, which initiallyoccurred along the cell wall and later deeper in the cytoplasm,in the perinuclear regions and the cytoplasmic invaginationsof the nucleus. In transverse planes the paracrystalline strandsappear to consist of hexagonal subunits in a 'honeycomb' arrangement,while in longitudinal and oblique sections they exhibit variableimages. Since their distribution coincides with that of thetubulin strands visualized by immunofluorescence, they are consideredto be the same structure. Therefore, the paracrystals consistof, or at least contain, tubulin. They are most likely to bepolymers of tubulin-colchicine complexes.Copyright 1995, 1999Academic Press Wheat roots, colchicine, immunofluorescence, electron microscopy, tubulin paracrystals, Triticum aestivum L     

Identification of coccidioidomycosis of the lung by fine needle aspiration biopsy

A solitary coin lesion in the lung is a frequent presentation of coccidioidomycosis; these lesions may be radiologically indistinguishable from cancer. In a series of 112 fine needle aspiration (FNA) biopsies performed in the San Joaquin Valley on solitary pulmonary nodules, 8 cases were identified as coccidioidomycosis by the presence of spherules in the aspirated material. The immature sporangia ranged in size from 4 micron to 40 micron. The smaller spherules did not show endospores and could have been confused with red blood cells. A methenamine silver or periodic acid-Schiff stain was helpful in identifying the spherules following decolorization of Papanicolaou-stained material; this was especially important when the background material was bloody. Older nonviable spherules showed a folded collapsed cell membrane, which may be associated with long-standing cavitary disease. A complement fixation titer was frequently not elevated. This study demonstrates the utility of FNA biopsy in the identification of cocci granulomas in the lung.     

Glandular Trichomes on Vegetative and Reproductive Organs of Leonotis leonurus (Lamiaceae)

The types of glandular trichomes, their ontogeny and patternof distribution on the vegetative and reproductive organs ofLeonotis leonurus at different stages of development, are studiedby light and scanning electron microscopy. Two morphologicallydistinct types of glandular trichomes (peltate and capitate)are described. Peltate trichomes, at the time of secretion,are characterized by a short stalk, which is connected witha large spherical head composed of eight cells in a single layer.Capitate trichomes can be divided into various types. Generally,they consist of a four-celled head supported by one or threestalk cells. The two kinds of trichomes differ in the secretionprocess. In the peltate trichomes, the secretory product seemsto remain accumulated in a subcuticular space, unless an externalfactor damages it. In the capitate trichomes, this product probablybecomes released through micropores. On the leaves peltate andcapitate trichomes are abundant, while on the flowers only thepeltate trichomes are numerous and the capitate are rare orabsent.Copyright 1995, 1999 Academic Press Leonotis leonurus R. Br., lion's ear, lion's tail, Lamiaceæ, glandular trichomes, morphology, ontogeny