Sensory innervation of the tentacles of the polychaete,Sabella pavonina

Summary Following observation of conical groups of stiff, but motile cilia on the tentacles of the branchial crown of Sabella pavonina, these were examined with the electron microscope. The bundles consist of about 40 unenclosed standard cilia supported by one or two primary sense cells with centrally directed axons of 0.1–0.2 diameter. Axons in the distal portions of the branchial crown occur in small bundles surrounded by a basement membrane. More centrally, glial elements appear and the nerves are surrounded by a collagenous sheath. The branchial nerve trunk shows similarities in organisation to other previously investigated annelid central nervous tissue in that the whole nerve is surrounded by a fibrous sheath central to which there is a layer of glial cells with processes penetrating a central neuropile. The 0.1–0.2 axons commonly occur in glial-enveloped groups of < 40 whilst other axons of larger and mixed diameter are found together.Each tentacle has two branchial nerves on the oral side, and each nerve gives rise to two small 75-axon branches running to each pinnule. The branchial nerves fuse to form the branchial nerve trunk running to the supra-oesophageal ganglia.Sections of the branchial nerves of the branchial crown at progressively more central levels show that the branchial nerve trunk contains enough axons of 0.1–0.2 diameter to account for all the sensory cells on the tentacles. This is taken as evidence for the sensory cells having axons terminating within the central nervous system and that there is no peripheral confluence or fusion of these afferent axons.     

Ultrastructural localization of silver deposits in the receptacle cells of carnation flowers

Carnations were treated with a silver thiosulphate complex to prevent wilting of the flowers. The ultrastructural localization of silver and sulphur in the receptacle tissue was investigated by electron microscopy. Electron-dense deposits were present in the receptacle tissue. Coarse-grained deposts (diam. 60–100 nm) were predominantly observed at the inner side of the cell wall, whereas fine-grained deposits (diam. 20–60 nm) were predominantly present inside the cell-wall region and in the intercellular spaces. These particles were analyzed for chemical elements by X-ray analytical electron microscopy (Philips EM 400 plus Edax energy dispersive analyzer, type 711). In both types of deposits, the presence of silver and sulphur was verified. Point analysis revealed that in both precipitates the S/Ag ratio was of the same order.Abbreviations CTEM conventional transmission electron microscope - STEM scanning transmission electron microscope The AEM unit is a joint unit of the Erasmus University of Rotterdam, the University of Leyden, and the Health Organization TNO. The analytical microscope was purchased with a grant from the Dutch Organization for Pure Scientific Research (ZWO) through BION     

Penetration of chemicals into the Malus leaf cuticle

The adaxial leaf cuticle of Malus pumila was examined by electron microscopy to determine possible avenues for transcuticular movement of foliarly applied chemicals. Cutin-embedded polysaccharide microfibrils originated at the outer epidermal cell wall and occasionally extended to the cuticle surface. Lamellae, ca. 4 nm wide, usually were oriented parallel to the cuticle surface. When oriented perpendicular to the surface, they extended nearly to the subjacent wall layer from the surface. Aqueous solutions of uranyl acetate, silver nitrate and phenyl mercuric acetate applied to the cuticle surface of leaf segments floated on solutions of phosphate salts or thiocarbohydrazide (TCH) reacted within the cuticle to form insoluble electron-opaque deposits indicative of their avenues of transcuticular movement. Uranyl phosphate deposits were observed only in the polysaccharide microfibrils of chloroform: methanolextracted leaves. Silver-TCH deposits were observed in the microfibrils of both extracted and nonextracted leaf cuticles. Phenyl mercuric acetate-TCH deposits were randomly dispersed throughout the extracted cuticle and not associated with the polysaccharide microfibrils.Abbreviations TCH thiocarbohydrazide - PMA phenyl mercuric acetate     

A nearly complete respiratory,circulatory, and excretory system preserved in small Late Cretaceous octopods (Cephalopoda) from Lebanon

Although they are rare, fossilized gills are well known in Mesozoic coleoid cephalopods. In the Late Jurassic Solnhofen (South Germany) and Late Cretaceous Hâkel and Hâdjoula (Lebanon) plattenkalks, the feather-like gill remains are usually preserved as a yellowish staining. Small coleoids from Hâkel—tentatively determined as octopods—attracted our attention because these stains occur throughout the entire mantle sac in an unusual symmetrical pattern. Actualistic comparisons point to a compound of diverse vascular structures that most likely reflect central parts of the venous blood system (afferent branchial vessels, branchial hearts, vena pallialis, blood sinus) as well as the nephridial sacs. The nephridial sacs are clearly separated, which confirms the octopod nature of the fossils. A reticulated staining pattern in the rear of the mantle, which may reflect the gonad capillary system, suggests the presence of mature small-sized octopods. Based on its colour, its amorphous habit, and energy-dispersive X-ray spectroscopy (EDX) elemental analyses, the major components of the coelomic cavities have been replicated by an iron-rich phase (presumably goethite; copper was not detected). The goethite does not replace the tissues; rather, it traces their gross form as a well-defined “stain”. It is assumed the goethite is secondary after pyrite, which precipitated as a consequence of the oxygen-binding capacity of the copper-bearing haemocyanin and its ability to locally regulate redox potentials immediately postmortem.     

Ultrastructure of the heart muscle cells of the cuttlefish Rossia macrosoma (Delle Chiaje) (Mollusca: Cephalopoda)

Summary The muscle cells of the ventricle, the branchial heart and the branchial heart appendages of Rossia macrosoma (Delle Chiaje) are studied. The ventricle myocardium has three muscle layers, while the other two organs exhibit a loose arrangement of muscle cells. The muscle cells of the ventricle, the branchial heart and the branchial heart appendages are similar in structure. The nuclei are surrounded by myofibrils. In the myofibrils A-, I- and discontinuous Z-bands are seen. The diameters of the thick filaments are 300–400Å, their length varies from 1.7 to 3.9 . Thin filaments have a diameter of approximately 85Å. The ratio between thick and thin filaments is roughly 1 to 11.The SR runs mostly as a longitudinal network within the myofibrils. A few short T-tubules are observed in the Z-regions. Peripheral and internal couplings exist. The latter are few in number.Intercalated discs are small and rarely observed. They have been found in all three organs. A difference in the function of these organs is not reflected in the ultrastructure of the intercalated discs. These discs are often of the interdigitating type with interfibrillar junctions and unspecialized regions. Peripheral couplings are seen at the unspecialized regions. The intercalar surfaces of the muscle cells shoulder off into the lateral surface, and the transition between the two surfaces is not a sharp one. Attachment plaques are found scattered over the whole sarcolemma.     

Heterostyly inPrimula. 1. Fine-structural and cytochemical features of the stigma and style inPrimula vulgaris huds

Summary The stigmas of the heterostylous genusPrimula are of the dry type without a free-flowing surface secretion. The papillae of the stigma surface cells of the two morphs, in pin (stigma exserted) and thrum (stamens exserted), bear a thin proteinaceous surface pellicle, overlying a discontinuous cuticle. The vacuoles of the papillate cells contain tannins, and tannin cells extend in files through the stigma heads and form a loose sheath surrounding the pollen-tube transmitting tract in the styles. The cells of the transmitting tissue in the stigma heads have a normal complement of organelles, and abundant ribosomal endoplasmic reticulum. The intercellular spaces contain an internal secretion which reacts cytochemically for both carbohydrate and protein. The transmitting tract in the styles forms a central core surrounded by several vascular strands. The cells are elongated, and the intercellular spaces here also have a carbohydrate-protein content. In a compatible pollination, thrum pollen tubes enter the stigma by penetrating the cuticle at the tip or on the flank of the pin papilla. Pin tubes on the thrum stigma enter between adjacent papillae, penetrating the thin cuticle at the base. The tubes grow through the transmitting tracts in the intercellular material.     

Integument and sensory nerve differentiation ofDrosophila leg and wing imaginal discs in vitro

Summary An ultrastructural analysis is presented of the cuticular and neural structures formed by the prothoracic leg and wing imaginal discs of maleDrosophila melanogaster larvae during culture in vitro with 0.2 g/ml of -ecdysone. A pupal cuticle, and subsequently an imaginal cuticle with a well-defined epicuticle and a laminated endocuticle is formed. The ultrastructure of the epidermis and of cuticular structures such as bristles, trichomes, apodemes, and tracheoles is very similar to that found in situ. Dendrites and nerve cell bodies are formed in vitro, and sensory axons form nerve bundles similar to those of normal appendages in situ, despite their isolation from the central nervous system. It is concluded that at the ultrastructural level, differentiation in vitro closely parallels the normal course of development.     

Content,absorption quantities and intracellular storage sites of heavy metals in Diplopoda (Arthropoda)

By means of atomic absorption spectrophotometry, concentrations of more than 2500 mg kg^–1 Pb, 150 mg kg^–1 Zn, and 320 mg kg^–1 Cd could be detected in the intestine tissues of diplopods from a lead and silver smelter's spoil bank. While only small portions of the ingested lead and cadmium are absorbed in the midgut of these diplopods, the zinc uptake into the midgut epithelium reaches 33.8–37.5% of the zinc content in the food pulp when the animals were contaminated acutely. However, after long-term contamination with zinc, absorption and excretion of this metal balanced one another. Absorbed lead and cadmium are predominantly stored in the midgut cells of the diplopods; unspecific precipitation of heavy metal showed the spherites of the resorptive epithelial cells to be the main accumulation sites. Zinc is for the most part localized in or near the cuticle; electron energy loss spectroscopy and ESI electron spectroscopic imaging, however, showed this metal to be present also in the spherites of the midgut's resorption cells. These spherites are assigned to belong to the type A granule group since (i) they are concentrically structured, (ii) they are shown to contain great amounts of calcium and (iii) copper, a class B metal, could not be detected in these deposits.     

Two ultrastructurally distinct types of transporting tissues,the branchiostegal and the gill epithelia,in an estuarine tanaid,Sinelobus stanfordi (Crustacea,Peracarida)

Summary On each lateral side of the cephalothorax segments, the adult Sinelobus stanfordi has a branchial chamber which contains an elongated bag-shaped gill and is covered by a thick branchiostegite. The ultrastructural study revealed that the inner surface of the branchiostegite is composed of a transporting-type epithelium which is morphologically distinct from the gill epithelium. Both epithelia are covered by extremely thin (about 80 nm) cuticle layers, suggesting high permeability to gases, ions, and water. In contrast, the outer surface of the branchiostegite consists of ordinary epithelium covered by a very thick cuticle layer in common with the body surface. The inner branchiostegal epithelium (4–10 m thick) has a shallow (about 1 m deep) apical infolding system of the cell membrane (AIS) and an extensive three-dimensional tubular network (about 120 nm in diameter) which is formed by the invagination of the basolateral cell membrane (TNB). The TNB is associated with slender mitochondria and occupies the majority of the cytoplasmic area of the epithelial cell. The gill epithelium, on the other hand, is about 10 m thick and characterized by an abundance of oval mitochondria, well-developed (4–5 m deep) AIS, and a smooth basal cell membrane lacking any infoldings. These morphological features indicate that not only the gill epithelia, but also the inner branchiostegal epithelia, are involved in the ion-transporting processes. The ultrastructural differences between these two kinds of epithelia also suggest their different roles in the osmoregulation of this animal, since it inhabits estuaries which are subject to extreme changes in salinity.     

Cytochemical and X-ray microanalysis studies of intracellular calcium pools in scale-bearing cells of the coccolithophoridEmiliania huxleyi

Summary Emiliania huxleyi is a coccolithophorid with a life cycle including a stage characterized by the occurrence of a scale-bearing cell type. The scales are composed of organic material and are produced in the cisternae of the Golgi apparatus. The present report deals with the ultrastructural calcium localization in scale-bearing cells using cation-precipitating agents. Cations were precipitated either with potassium pyroantimonate alone or according to a combined procedure in which cells are treated first with potassium oxalate, or potassium carbonate, or potassium phosphate, and then with potassium pyroantimonate. The distribution of electron-opaque deposits was the same when visualized by all four techniques. The most extensive deposits occurred in the Golgi apparatus, the peripheral space (a cellular compartment totally encompassing the protoplast), the multivesicular bodies, and the cell vacuole. X-ray microanalysis revealed that calcium was a constituent of the electron-opaque deposits. The uptake and transport of calcium, as universal functions of the Golgi apparatus, are discussed.     

Effects of serotonin on the cardio-circulatory system of the European eel (Anguilla anguilla) in vivo

The effects of serotonin on continuously recorded cardiac parameters (heart rate, cardiac output, cardiac stroke volume), ventral and dorsal aortic blood pressures, branchial and systemic vascular resistances were investigated in the European eel in vivo. Intravenous administration of serotonin (30 g · kg^–1) caused a marked bradycardia (45%) and a simultaneous decrease in cardiac output (50%), ventral (35%) and dorsal (50%) aortic blood pressures. Branchial resistance was markedly increased (60%) and systemic resistance decreased (30%). Cardiac stroke volume remained unchanged. The effects of serotonin on cardiac mained unchanged. The effects of serotonin on cardiac parameters were suppressed either by methysergide or a bilateral section of the cardiac vagus. Bradycardia could then be regarded as the consequence of a vagal mechanism triggered by serotonin action on central methysergide-sensitive serotonergic receptors. No inotropic effect of serotonin was observed. This lack of myocardiac contractility modification is discussed. The serotonin-mediated branchial vasoconstriction was attenuated by vagotomy, whereas the residual increase in branchial resistance (40%) was suppressed by methysergide. The serotonin-mediated branchial vasoconstriction could be the consequence of both a passive mechanism (compliance) caused by the decrease in cardiac output and an active mechanism involving methysergide-sensitive serotonergic receptors of the branchial vasculature. A possible involvement of this vasomotor effect in gill oxygen uptake is discussed. The serotonin-induced systemic vasodilation was insensitive either to cardiac vagotomy or to 5-HT_1/2, 5-HT₃ and 5-HT₄ receptor antagonists, suggesting the involvement of a local mechanism which remains to be assessed.Abbreviations CSV cardiac stroke volume - DAP dorsal aortic pressure - HR heart rate - QC cardiac output - VAP ventral aortic pressure - VR _b branchial vascular resistance - VR _s systemic vascular resistance - VR _t total vascular resistance - 5-HT 5-Hydroxytryptamine serotonin - RBI Research Biochemical Incorporated, metoclopramide HCl     

Nucleolus-like structures detected in the cytoplasm ofBrodiaea uniflora: Light- and electron-microscopic surveys during mitosis

Summary Both light- and electron-microscopic studies confirmed the presence of cytoplasmic nucleolus-like structures in the root-tip meristems ofBrodiacea uniflora, Liliaceae. This structures were found to be different from all the types of nucleolus-like structures previously detected in the cytoplasm. The nucleolus-like structures in the present material usually appeared as complex structures with two types of elements, although the two elements sometimes lay separately in the cytoplasm. The two elements were differentially stained by the silver staining technique: one reacted more intensely with silver forming black-stained dot while the other was stained brown. The ultrastructural examination revealed that the black-stained dots were spherical, about 1.0 m in diameter, and consisted of highly electron-dense material in which many lacunar areas were always seen, while the brown-stained spherules were consisted of loosely packed RNP- or ribosome-like granules. The nucleolus-like structures were found almost exclusively at telophase and they were never or seldom detected from interphase to anaphase.Their peculiar behavior during mitosis and their ultrastructural organization are discussed with reference to their origin.     

Carapace movements aid air breathing in the semaphore crab,Heloecius cordiformis (Decapoda: Brachyura: Ocypodidae)

Summary While on land and recirculating branchial water the Australian semaphore crab Heloecius cordiformis (Decapoda: Ocypodidae), a semi-terrestrial airbreathing mangrove crab, sequentially depresses and elevates its carapace in a regular pump-like manner. The functional role of these carapace movements in aerial oxygen consumption is investigated. Carapace immobilisation (reversible and non-injurious) did not appear to affect branchial water circulation. In dry crabs (branchial water removed) carapace immobilisation had no effect on the rate of oxygen consumption (VO₂), heart rate or whole-body lactate (WBL) levels. In wet crabs (with branchial water) carapace immobilisation caused VO₂ to drop by 38% from 81 to 46 l O₂ · g^-1 · h^-1, heart rate to decline by 32%, from 2.5 to 1.7 Hz, and WBL levels to increase over 2.5-fold, from 0.27 to 0.67 mg · g^-1, after 3 h of carapace immobilisation. The (VO₂) of carapace-immobilised crabs with branchial water was similar to lung-occluded crabs with branchial water. Severe hypoxia induced physiological responses similar to those of carapace-immobilised crabs with branchial water. After 3 h of severe hypoxia, heart rate had declined by 80%, from 2.2 to 0.43 Hz, and the incidence of carapace pumping slowed by 85%, from 2.4 to 0.37 cycles · min^-1. It is concluded that in the absence of carapace movements branchial water in some way inteferes with lung ventilation. Under normal circumstances water circulation and lung ventilation are mutually exclusive processes (due to their singular dependence on the scaphognathites), yet in Heloecius these processes must be carried out simultaneously. Carapace movements may alleviate this conflict.Abbreviations FF, FR, SF, SR fast-forward, fast-reverse, slow-forward, slow-reverse scaphognathite pumping - MEA Milne Edwards aperture - VO₂ rate of oxygen consumption - WBL whole-body lactate     

Ultrastructure of cuticle deposited inPlodia interpunctella wing discs after variousβ-ecdysone treatments in vitro

Summary Wing discs of the Indian meal moth may be cultured for extended periods in vitro. The discs produced a tanned cuticle after continuous incubation with -ecdysone in medium conditioned with fat body or after a 24-h pulse incubation with -ecdysone in plain medium. We investigated the ultrastructure of the cuticle deposited by such discs. We found that the treatment that produced the most complete cuticle in vitro was the 24-h pulse of hormone. We observed that cuticle formation in vitro was not all-or-none. Depending on culture conditions, discs produced cuticulin only, complete epicuticle, epicuticle plus diffuse endocuticle, epicuticle plus lamellate endocuticle, or even multiple layers of cuticle. The ultrastructural evidence suggests that continuous incubation with -ecdysone in plain medium does not always inhibit cuticle formationper se, but does prevent tanning of the partially formed cuticle.     

Microscopic Anatomy and Ultrastructure of Nephridium in the Sipunculan Thysanocardia nigra Ikeda, 1904 from the Sea of Japan

The microscopic anatomy and ultrastructure of nephridium have been studied in the sipunculan Thysanocardia nigra Ikeda, 1904 (Sipuncula, Sipunculidea) from the Sea of Japan using histological and electron microscopic techniques (SEM and TEM). This paper describes ultrastructural features of nephridial epithelium, muscle grid, and coelomic epithelium on the surface of the nephridium, the area of the ciliary funnel, and the tongue. Several types of cells were distinguished in the excretory tube of the nephridium: (1) a columnar epithelium of the excretory bunches; (2) a cubical or flattened epithelium of flask-shaped infoldings; and (3) granulocytes that migrate from the coelom to the extracellular matrix of the nephridial wall. The system of podocytes and multiciliary cells were described in the nephridial coelothelium. Two types of secretion of nephridial epithelium have been discovered: a merocrine secretion of columnar cells and an apocrine secretion of cells of the flask-shaped infoldings. Using ultrastructural data, two zones of filtration through the wall of excretory tube have been found, namely (1) the tips of flask-shaped infoldings (via the extracellular matrix and microvillary canals between the epithelial cells) and (2) areas between the flask-shaped infoldings (via the contacts of podocytes, extracellular matrix, and the basal labyrinth of the columnar cells). Unlike previously studied representatives of the genus Phascolosoma, no coelomic epithelium is present on the tips of the flask-shaped infoldings in Th. nigra. This data on the anatomy and histology allow us to conclude that the funnel only works like a gonoduct.     

Organization of a phyllobranchiate gill from the green shore crab Carcinus maenas (Crustacea,Decapoda)

Summary The phyllobranchiate gills of the green shore crab Carcinus maenas have been examined histologically and ultrastructurally. Each gill lamella is bounded by a chitinous cuticle. The apical surface of the branchial epithelium contacts this cuticle, and a basal lamina segregates the epithelium from an intralamellar hemocoel. In animals acclimated to normal sea water, five epithelial cell types can be identified in the lamellae of the posterior gills: chief cells, striated cells, pillar cells, nephrocytes, and glycocytes. Chief cells are the predominant cells in the branchial epithelium. They are squamous or low cuboidal and likely play a role in respiration. Striated cells, which are probably involved in ionoregulation, are also squamous or low cuboidal. Basal folds of the striated cells contain mitochondria and interdigitate with the bodies and processes of adjacent cells. Pillar cells span the hemocoel to link the proximal and distal sides of a lamella. Nephrocytes are large, spherical cells with voluminous vacuoles. They are rimmed by foot processes or pedicels and frequently associate with the pillar cells. Glycocytes are pleomorphic cells packed with glycogen granules and multigranular rosettes. The glycocytes often mingle with the nephrocytes. Inclusion of the nephrocytes and glycocytes as members of the branchial epithelium is justified by their participation in intercellular junctions and their position internal to the epithelial basal lamina.     

The effects of the adrenoreceptor agonists phenylephrine and isoproterenol on the intracellular ion concentrations of branchial epithelial cells of brown trout (Salmo trutta L.)

Brown trout were fitted with indwelling, intraperitoneal catheters and injected with 4–6 mol · kg^-1 of the -receptor agonist phenylephrine or the -receptor agonist isoproterenol. The intracellular concentrations of sodium, chlorine, potassium and phosphorus in the pavement epithelial cells and the mitochondria-rich cells of the branchial epithelium were measured by X-ray microanalysis 1 h after the injection of the adrenoreceptor agonists. Injection with phenylephrine resulted in a significant increase in intracellular chlorine and potassium in mitochondria-rich cells and a significant but relatively smaller increase in chlorine in pavement epithelial cells. Injection with isoproterenol resulted in a significant increase in sodium and chlorine concentration in pavement epithelial cells and a significant decrease in potassium concentration. The only significant effect of isoproterenol injection on mitochondria-rich cells was a decrease in intracellular chlorine concentration. The results suggest that these adrenoreceptor agonists have a direct effect on the influx of Na⁺ and Cl^- across the branchial epithelium. These effects may be a mechanism for acid-base regulation during the severe stress conditions that elicit catecholamine release in vivo. These results corroborate previous studies using X-ray microanalysis which suggested that pavement epithelial cells are the sites of Na⁺ uptake in freshwater fish whilst Cl^- uptake occurs via mitochondria-rich cells.Abbreviations LTSEM low-temperature scanning electron microscope - MR cells mitochondria-rich cells - PE cells pavement epithelial cells - XRMA X-ray microanalysis     

Ultrastructure and function of the labial nephridia and the rectum of Orchesella cincta (L.) (Collembola)

Summary The collembolan Orchesella cincta possesses a well-developed coelomoduct kidney. The presence of podocytes in the wall of the sacculus and the fact that the epithelium of the nephridial tubule has the ultrastructural characteristics of resorbing cells, indicate that this is an ultrafiltration-reabsorption kidney.Apparently also the rectum is lined by a reabsorptive epithelium; the cells possess an extensive system of apical and basal infoldings. This view is sustained by the fact that the stereology of the apical channel system varies in animals kept under different moisture conditions. During the intermoult period, both organs are subject to strong morphological changes, which are obviously related to the feeding rhythm.The authors wish to thank Dr. T. Sminia for his stimulating interest during the investigations, Dr. J.C. Jager for statistical advice and Mr. G.W.H. van den Berg for drawing the figures     

Elektronenmikroskopische und histochemische Untersuchungen zur Funktion des Kiemenherzanhanges (Pericardialdrüse) von Sepia officinalis

Zusammenfassung Die elektronenmikroskopischen Untersuchungen am Kiemenherzanhang von Sepia officinalis zeigen, daß diesem Organ wie den Venenanhängen exkretorische Funktionen zukommen. Die Pericardialdrüse erweist sich als ein Derivat des Kiemenherzens. Ihre Hauptmasse besteht aus einem polar organisierten Faltenepithel, dessen Ultrastrukturmerkmale (basaler Faltenapparat, Gehalt an Mitochondrien und Lysosomen, sekretorisch aktiver Mikrovillisaum) anderen Exkretionsorganen entsprechend auf aktive Ionentransportvorgänge hindeuten. Es ist dem äußeren Kiemenherzepithel homolog und kommt in ähnlicher Ausbildung auch in anderen Organen (Zentralherz, Kieme) vor. Die polygonalen Zellen der Randzone sind dem zentralen Gewebe des Kiemenherzens zu homologisieren; ihr Reusensystem in Nachbarschaft der Blutlakunen ist ähnlich dem der Podocyten in der Vertebratenniere und macht eine Druckfiltration wahrscheinlich. Als Filtermembranen funktionieren neben dem Plasmalemm auch noch die Basalmembran und Zwischenmembran, die porenartige, für Myofer durchlässige Lücken von 30 Å Weite zeigen. Daneben werden an der Grenze zwischen Epithel und Lakune wie auch in der Intima größerer Gefäße besondere Dichtezellen dargestellt, die ähnlich wie Macrophagen größere Partikel (z.B. Ferritin und Myofer) aufnehmen und intraplasmatisch als dense bodies ablagern.Die enzymhistochemischen Befunde über die Verteilung von G-6-PD, SDH, IDH, MDH und MAO und der sauren und alkalischen Phosphatase in Faltenepithel und Lakunen stützen diese Befunde und sprechen ebenfalls für eine exkretorische Funktion.

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Electron microscopic and histochemical studies on the function of the branchial heart appendage (pericardial gland) in Sepia officinalis (l.)

Summary Our electron microscopic studies of the appendages of the branchial heart and veins of Sepia officinalis suggest an excretory function for these organs. The pericardial gland appears to be a derivate of the branchial heart; it mostly consists of a folded polarized epithelium. Ultrastructural features of the epithelium such as the basal folding system, contents of mitochondria and lysosomes, and secretory microvilli suggest active ion transport in these cells of the pericardial gland. The pericardial gland epithelium is homologous with the external epithelium of the branchial heart; it is also present in a similar form in the central heart and branchia. Polygonal cells present in the peripheral zone of the pericardial gland are homologous with the central branchial heart tissue. The system of basal cell processes of the polygonal cells near blood lacunae is similar to the podocyte-capillary relationship in the vertebrate kidney and suggests the possibility of pressure filtration. The plasmalemma, as well as the basal and intermediate membranes, appear to be filtration membranes; they contain pore-like structures about 30 Å in diameter which are permeable to Myofer. Furthermore, special dense cells are present at the epithelium-lacunae border and in the intima of larger vessels; these cells, similar to macrophages, take up large particles, such as ferritin and Myofer, and deposit them in the cytoplasm as dense bodies.Histochemical findings on the distribution of enzymes G-6-PD, SDH, IDH, MDH, and MAO, and the distribution in the folded epithelium and lacunae of alkaline and acid phosphatases confirm the ultrastructural results and suggest an excretory function of the pericardial gland.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft. — Frau Beyerle-von Wehren sei für wertvolle technische Unterstützung gedankt.     

Mechanisms of stomatal movement in response to air humidity,irradiance and xylem water potential

Turgor, and osmotic and water potentials of subsidiary cells, epidermal cells and mesophyll cells were measured with a pressure probe and a nanoliter osmometer in intact transpiring leaves of Tradescantia virginiana L. Xylem water potential was manipulated by changing air humidity, light, and water supply. In a transpiring leaf the water potential of mesophyll cells was lower, but turgor was higher, than in cells surrounding the stomatal cavity owing to the presence of a cuticle layer which covers the internal surface of subsidiary and guard cells. Cuticular transpiration from the outer leaf surface was negligibly small. When stomata closed in dry air, transpiration decreased despite an increasing vapor-pressure difference between leaf and air, and the water potential of subsidiary cells dropped to the level of the water potential in mesophyll cells. We suggest that the observed decrease of transpiration at increasing vapor-pressure difference can be attributed to a shortage of water supply to the guard cells from subsidiary cells, causing turgor to decrease in the former more than in the latter. The leafs internal cuticle appears to play a special role in channelling the internal water flow during a water shortage.Abbreviations and Symbols VPD Vapor-pressure difference between leaf and air - PFD photon flux density - water potential