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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 136 (1987), S. 37-48 
    ISSN: 1615-6102
    Keywords: Chara ; Fine structure ; Growth ; Heavy metals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The toxicity of some heavy metals to the common macrophytic freshwater algaChara vulgaris was studied under laboratory conditions. For experiments, apical tips of algae containing two internodes were cultivated for fourteen days in the presence of various concentrations of cadmium, mercury or lead (as triethyl lead or lead nitrate). Fifty percent growth inhibition occurred with concentrations of 8.5×10−8 M (9.5 ppb) cadmium, 7.5×10−7M (150ppb) mercury, 1.6×10−6 M (330ppb) organic lead or 4× 10−5 M (8000 ppb) inorganic lead. Sublethal concentrations of these metals caused alterations in the fine structure of internodal cells which turned out to be at least partly metal-specific or in the case of lead, the effects depended on whether the lead was ionic or organically bound. Cadmium and inorganic lead induced disorders of cell wall microfibrils which resulted in local wall protuberances. Mercury affected the chloroplasts which mostly showed considerably increased grana stacks. In addition, mercury caused a dilation of the endoplasmic reticulum and of the mitochondrial tubuli. Organic lead damaged the membrane system of chloroplasts; sheet- or tubule-like thylakoids were disarranged and showed whorl-like structures. At higher concentrations of organic lead, tubular invaginations of the plasmalemma (“charasomes”) disappeared. The fine structure of nuclei was not altered by any of the metals.
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  • 2
    ISSN: 1435-1536
    Keywords: RNA polymerase ; small-angle ; X-ray
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 3
    ISSN: 1615-6102
    Keywords: Immunolocalization ; H+-ATPase ; Tip growth ; Lilium longiflorum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A heterogeneous distribution of H+-ATPase was visualized in germinated pollen ofLilium longiflorum using monoclonal antibodies raised against plasma membrane H+-ATPase. Immunolocalization studies of protoplasts and subprotoplasts derived from pollen tubes and sectioned pollen grains and pollen tubes show that H+-ATPases are abundant in the plasma membrane of pollen grains but are absent or sparsely distributed in the plasma membrane of pollen tubes. This polar distribution of H+-ATPases is probably the basis of the endogenous current pattern measured in growing lily pollen and involved in pollen tube tip growth.
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  • 4
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Microwave-enhanced fixation of animal tissues for electron microscopy has gained in interest in recent years. Attempts to use microwave irradiation for the preparation of plant tissues are rare. In this study, I report on microwave conditions which allow a high quality preservation of plant cell structure. Tissues used were: internodes of Chara vulgaris, leaves of Hordeum vulgare, root tips of Lepidium sativum. Microwave irradiation was done with a commercial microwave oven (Sharp R-5975). Fixatives used were: 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer, pH 7.2 and 1% osmium tetroxide in veronal/acetate buffer, pH 7.2. Conventional fixations with glutaraldehyde/osmium were compared with microwave fixations. Examinations of thin sections showed that microwave fixation (glutaraldehyde or sequential aldehyde/osmium) is an attractive and rapid alternative method for processing plant tissues for electron microscopy. The optimal conditions found were: microwave oven at power level 50 W, 6.5 ml of fixative solution, irradiation times between 32–34 s, final temperature between 40° C and 47° C.
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  • 5
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Electron dense deposits (EDD) were observed on the extracellular side of the plasmalemma of Chara internodal cells by a calcium-glutaraldehyde fixation technique. The number and size of EDD were greatly increased when cells had been preincubated in Ca2+-enriched medium before fixation. The addition of Na+, Mg2+, or La3+ instead of Ca2+ in incubation and fixation media produced no deposits at all, Sr2+ caused deposits with similar distribution to those formed by Ca2+, and Ba2+ addition resulted in deposits localized at different sites within the cell. Microprobe analysis of single EDD from Ca2+ incubated cells ascertained the presence of calcium in these deposits. Possible functions of the Ca2+-binding sites at the plasma membrane of Chara cells are discussed.
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  • 6
    ISSN: 1432-0878
    Keywords: Smooth muscle ; Calcium ; Sarcoplasmic reticulum ; Mitochondria ; Microprobe analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The intracellular localization of calcium by means of cytochemical techniques was studied in smooth muscle cells of mouse intestine. When the lead acetate method according to Carasso and Favard (1966) was used calcium was found in mitochondria and sarcoplasmic reticulum and occasionally between the myofilaments. The active ATP-dependent accumulation of calcium into cell structures was investigated by the oxalate method (Heumann and Zebe, 1967). After appropriate treatment the only structures of smooth muscle cells which contained calcium oxalate (identified by microprobe analysis) were elements of the sarcoplasmic reticulum. The results are discussed in relation to the role of calcium in the control of muscle activity during the contraction-relaxation cycle.
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  • 7
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Der Feinbau der ‚'schräggestreiften“ Fasern aus dem Hautmuskelschlauch des Regenwurms (Lumbricus terrestris) besitzt eine prinzipielle Ähnlichkeit mit der Organisation der quergestreiften Muskeln: dicke und dünne Filamente sind in separaten, ineinandergreifenden Sätzen angeordnet, so daß sich A- und I-Banden sowie H-Zonen unterscheiden lassen. Wegen der ausgeprägten bilateralen Symmetrie der Muskelfaser tritt dies aber nur bei Längsschnitten in Erscheinung, die in einer bestimmten Ebene geführt sind. Längsschnitte in der dazu senkrechten Ebene haben ein völlig anderes Aussehen, da die einzelnen Filamentlagen stark gegeneinander versetzt sind und die Banden deswegen in einem sehr spitzen Winkel zur Faserlängsachse verlaufen. Wegen der gestaffelten Anordnung der Filamentlagen tritt die Gliederung der kontraktilen Elemente auch auf Querschnitten hervor. Dicke und dünne Fasern sind regelmäßig durch Querbrücken miteinander verbunden. Ein weiteres charakteristisches Merkmal der schräggestreiften Muskeln von Lumbricus bildet die stäbchenförmige Ausbildung der Z-Elemente. Bei der Kontraktion gleiten die dünnen Filamente wie bei den quergestreiften Muskeln tiefer zwischen die dicken, bis I-Band und H-Zone verschwinden. Darüber hinaus verschieben sich auch die einzelnen Lagen der dicken Filamente gegeneinander. Als Folge davon verringert sich ihr Versetzungsgrad, und der Winkel, den A- und I-Banden mit der Längsachse bilden, nimmt zu. Extreme Verkürzung hat eine Abbiegung der Enden der dicken Filamente durch die Z-Stäbchen zur Folge. Die Regenwurmfasern verfügen über ein extensiv ausgebildetes sarcoplamatisches Reticulum. Es besteht aus drei verschiedenen Elementen: (1) voluminösen Vesikeln, die unmittelbar unter dem Sarcolemm liegen, (2) peripheren Tubuli, die diese miteinander verbinden und (3) transversalen Tubuli, die von den subsarcolemmalen Vesikeln oder den peripheren Tubuli entspringen, um regelmäßig alternierend mit den Z-Stäbchen quer durch den kontraktilen Apparat zu ziehen. Alle diese Elemente können unter bestimmten Umständen Calciumoxalat akkumulieren. Dies deutet auf eine dem sarcoplasmatischen Reticulum der Wirbeltierskelettmuskeln entsprechende Funktion bei der Regulation der Kontraktionsaktivität hin. Einfaltungen der Plasmamembran von der Art eines Transversalsystems fehlen den schräggestreiften Regenwurmmuskeln dagegen.
    Notes: Summary The obliquely-striated fibers of earthworm muscles have a finestructural organization fundamentally similar to cross-striated muscle: Thick and thin myofilaments are arranged in separate, overlapping formations so that I and A bands as well as H zones can be distinguished. However, this is obvious only with respect to a certain plane of sectioning, while it is obscured in longitudinal sections cut at right angles to that plane because the layers of filaments are not in register. This latter circumstance is responsible for the fact that individual bands appear oriented at an acute angle to the longitudinal axis. Consequently, sections at right angles to the longitudinal axis, will, in one single section, reveal the cross-sectional images of all bands. For such a section will cut through various levels of the staggered filaments. Thick and thin myofilaments are connected by regularly spaced lateral bridges. The Z material in earthworm muscles is rod-shaped. During contraction, corresponding to cross-striated muscle, the thin filaments slide between the thick filaments until I bands and H zones disappear. In addition, however, the individual layers of thick filaments slide against each other. As a result, the angle at which the bands in the relaxed state are oriented with respect to the longitudinal axis, increases as the muscle contracts. Extreme shortening leads to bending of the ends of the thick myofilaments by the Z rods. The earthworm muscle displays a well developed sarcoplasmic reticulum in which three elements are distinct: (1) large vesicles subjacent to the sarcolemma, (2) tubular elements that interconnect these vesicles, and (3) transversely oriented tubules. These originate from both the large vesicles and the interconnecting tubules and ran parallel to and alternate with the Z rods. All elements of the sarcoplasmic reticulum accumulate calcium oxalate under appropriate experimental conditions. This suggests a function similar to that of the sarcoplasmic reticulum in vertebrate striated muscle, which consists in regulating the contractile activity by means of varying the effective calcium concentration in the sarcoplasm. A transverse tubular system continuous with the plasma membrane does not exist in obliquely-striated earthworm muscle.
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  • 8
    ISSN: 1432-0878
    Keywords: Taste hairs ; Insects ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Die Schmeckhaare der Fliege Phormia terraenovae enthalten fünf Rezeptorzellen (vier Kontaktchemo- und eine Mechanorezeptorzelle), die von zwei Hüllzellen unter Aussparung von Lymphräumen („Vakuole“) umgeben sind. Die Rezeptorzellen gliedern sich in Axon, Zellkörper und Dendrit, der aus Innenglied, Übergangsabschnitt und Außenglied besteht. Der Übergangsabschnitt hat die 9+0-Struktur der modifizierten Cilien mit zwei Basalkörpern. Im Plasma der Außenglieder sind nur Mikrotubuli zu erkennen. Die Außenglieder der Kontaktchemorezeptoren ziehen durch die röhrenförmige Dendritenscheide und den Kanal I des Haarschafts bis zu einem Porus in der Haarspitze, durch den sie mit den Schmeckstoffen in Kontakt kommen (Ort der Primärprozesse). Das Außenglied der Mechanorezeptorzelle enthält einen tubulären Körper und setzt an der Haarbasis an. Die Hüllzelle II (tormogene Zelle) bildet zum großen Sensillenlymphraum hin ein stark gefaltetes Membransystem aus. Der Feinbau wird in Beziehung zur Funktion der Schmeckhaare gesetzt.
    Notes: Summary The tarsal taste hairs of the blowfly contain five receptor cells: four contact chemoreceptors and one mechanoreceptor. These cells are surrounded concentrically by two sheath cells with fluid-filled spaces (“vacuoles”) between them. The receptor cell parts are the axon, the cell body, and the dendrite. The latter has an inner segment, a transitional region, and an outer segment. The transitional region shows the 9+0 configuration of a modified cilium with two basal bodies. In the outer segment only microtubules are found. The outer segments of contact chemoreceptors pass through the tube-like dendrite sheath, then through “canal I” of the hair shaft, to reach the pore at the tip of the hair. The outer segment of the mechanoreceptor contains a “tubular body” and terminates at the hair base. The “sheath cell II” (tormogene cell) forms a folded membrane system toward the main liquor space. The fine structure of the tarsal taste hairs is discussed in relation to their function.
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  • 9
    ISSN: 1432-0878
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Die glatten Fasern aus dem vorderen Byssusretraktor (ABRM) der Miesmuschel Mytilus edulis wurden elektronenmikroskopisch untersucht. Unsere besondere Aufmerksamkeit richtete sich dabei auf die Veränderungen, die beim Übergang des erschlafften Zustands in den kontrahierten eintreten. Der kontraktile Apparat, der fast das gesamte Faservolumen einnimmt, besteht aus dicken (170–800 Å) und dünnen (etwa 60 Å) Myofilamenten sowie aus länglichen Z-Elementen, an deren Schmalseiten die dünnen Myofilamente ansetzen. Auf Längsschnitten ist außer einer Parallelorientierung der Myofilamente keinerlei Regelmäßigkeit zu erkennen. Querschnitte zeigen das Vorhandensein von undeutlich umrissenen „A-Zonen“ und „I-Zonen“. Die Kontraktion ist mit einer erheblichen Vermehrung der Myofilamente im Faserquerschnitt und der Dichte ihrer Packung verbunden. Dies kann als ein Anzeichen für eine Verkürzung durch einen Gleitmechanismus angesehen werden. Im Gegensatz zu den erschlafften Fasern sind die kontrahierten uneinheitlich strukturiert. Im Hinblick auf Anordnung und Verteilung der beiden Myofilamenttypen wurden drei verschiedene Muster beobachtet: 1. Dicke und dünne Myofilamente liegen ziemlich gleichmäßig über den ganzen Querschnitt verteilt. 2. Die dicken Myofilamente bilden unregelmäßige und unvollständig voneinander abgegrenzte Gruppen, innerhalb derer die Einzelfilamente vor allem mit ihren Mittelteilen so eng aneinandergelagert sind, daß sich ihr Umriß häufig nur schwierig erkennen läßt. Die Masse der dünnen Filamente liegt in den Zwischenräumen zwischen den Gruppen der dicken. 3. Die dicken Myofilamente finden sich nur in einer zentralen Zone der Faser. Sie liegen hier ebenfalls eng aneinandergepreßt („aggregiert“). Die meisten dünnen Myofilamente sind in eine periphere Zone verlagert. Diese Befunde werden im Hinblick auf mögliche Korrelationen mit den verschiedenen Funktionszuständen des ABRM, also der phasischen Kontraktion und dem Sperrtonus diskutiert.
    Notes: Summary The fine structure of the smooth fibers from the anterior byssus retractor muscle (ABRM) of the mussel Mytilus edulis was investigated in the relaxed and in the contracted state. Most of the fiber volume is occupied by the contractile apparatus. There are thick (between 170 and 800 Å) and thin (about 60 Å diameter) myofilaments. The last ones are attached to spindle shaped Z-elements which lie among the myofilaments at irregular intervals and sometimes appear to be connected with the plasma-membrane. The myofilaments run parallel to each other, but no other regularity is apparent from longitudinal sections. Cross-sections, however, show the presence of irregular “A zones” and “I zones” in these smooth muscle fibers. Contraction leads to a considerable increase in the number of myofilaments per cross-sectional area. This indicates that shortening takes place according to the sliding filament theory. Relaxed fibers seem to be uniform, while contracted ones may differ in their appearence. In those three distinct patterns were observed in the distribution of myofilaments: 1. Thick and thin myofilaments are distributed rather evenly across the whole cross-sectional area. 2. The thick myofilaments are arranged in irregular groups. In each group the filaments touch each other especially in their middle portions. Therefore, it is sometimes difficult to recognize the outline of a particular single filament. Most of the thin filaments occupy the space between the groups of thick filaments. 3. The thick myofilaments are crowded in a central area of the fiber. Here they aggregate, so that little or no interval is left between individual filaments. Most of the thin filaments are found in a peripheral zone of the fiber. These observations are discussed in view of possible correlations to the different functional states of the ABRM: phasic and tonic contraction.
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  • 10
    ISSN: 1432-0487
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Übersicht Es wird die Differentialgleichung, die die Temperaturverhältnisse in einem Zylinderkondensator unter den genannten Bedingungen wiedergibt, aufgestellt und gelöst. Die erhaltenen Ergebnisse werden mit Beispielen aus der Kabeltechnik veranschaulicht. Auch wird gezeigt, wie sich bei Hochspannungskabeln der Wärmedurchschlag berechnen läßt.
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