Showing papers by "University of Freiburg published in 1971"

An Analysis of Phytochrome-mediated Anthocyanin Synthesis

Abstract: Phytochrome (far red form) alone can mediate anthocyanin synthesis in the mustard seedling (Sinapis alba L.). Complete photoreversibility and reciprocity, for both red and far red light exposures over a period of at least 5 minutes, demonstrate this phytochrome involvement.The duration of the initial lag-phase is constant (about 3 hours at 25 C) for seedlings more than 30 hours old and is specific for the system, being independent of the dose or quality of light. Since a complete reversal by far red of a red light induction is possible only during a 5 minute period, phytochrome (far red form) obviously mediates anthocyanin synthesis during the lag-phase although the actual synthesis of pigment can proceed only after the lag-phase is overcome. We suggest that phytochrome (far red form) exerts a double function during the initial lag-phase. It mediates both the build up of a biosynthetic potential ("capacity") and anthocyanin synthesis. However, the sequence of events leading to anthocyanin is arrested at some intermediate stage until this "capacity" is built up after 3 hours. Once "capacity" is achieved it does not decay readily. Therefore, no significant "secondary lag-phase" occurs if the seedling, under appropriate conditions, is reirradiated after an intervening dark period. The rate or extent of synthesis for both anthocyanin and lipoxygenase, previously reported (32), are functions of the amount of phytochrome (far red form). No "phytochrome paradoxes," i.e., nonrational relationships between the amount of phytochrome (far red form) and rate or extent of response, were detected. This fact suggests that the mustard seedling is especially well suited for investigating the biophysical and molecular mechanisms of phytochrome action.

Outet mitochondrial membrane continuous with endoplasmic reticulum

Abstract: Continuity of outer mitochondrial membrane with tubular profiles of endoplasmic reticulum (ER) character is found in rat liver hepatocytes and in the ciliateTetrahymena pyriformis. Such membrane continuity is evident from thin sections through intact cells and isolated fractions as well as with negatively stained isolated mitochondria. The ER-profiles continuous with the outer mitochondrial membrane appear predominantly “smooth”, whereas in some cases they showed a few ribosomes associated with them. The observations are discussed as another indication of the close structural and chemical relationship between the outer mitochondrial membrane and the ER. In addition, it is hypothesized that this cisternal continuity provides a route for transfer of special proteins (and possibly lipid components, too) from the rough ER into the mitochondria.

N-1-napthylphthalamic-acid-binding activity of a plasma membrane-rich fraction from maize coleoptiles.

Abstract: Plasma membrane-rich fractions were prepared from maize coleoptiles by low-shear homogenization and differential and sucrose-gradient centrifugation. Plasma membrane fragments were identified using a specific cytochemical stain based on phosphotungstic acid prepared in chromic acid. In a comparison of 10 different cell fractions of varying plasma membrane content, the N-1-napthylphthalamic-acid (NPA)-binding activity of the fractions was directly proportional to the content of plasma membrane. The NPA binding appears to be strong K M between 10(-8) and 10(-7) M) but non-covalent. NPA is known to inhibit auxin transport efficiently and quickly. Thus, the results are consistent with the localization of auxin transport sites at the plasma membrane of plant cells.

Conformation of amylose in aqueous solution: Optical rotatory dispersion and circular dichroism of amylose–iodine complexes and dependence on chain length of retrogradation of amylose

Abstract: The dependence on chain length of two characteristic properties of amylose, i.e., retrogradation and complex formation with iodine, have been studied by using enzymatically synthesized, homodisperse amyloses. The association rates of amyloses in water containing 5% dimethyl sulfoxide have a sharp maximum at a degree of polymerization Pn of 80; shorter and longer molecules are much more soluble. The iodine complexes of amylose exhibit a strong Cotton effect in the range of the long-wave absorption maximum (position depending on chain length) and two weaker Cotton effects at 480 and 350 nm. The long-wave Cotton effect is most intense at about Pn 50 and decreases rapidly for shorter and longer chains. This behavior is unexpected and is not in accordance with the further increase of λmax and λmax. The experiments can best be interpreted by assuming well ordered, stiff chains in the low molecular weight range (Pn 50–80). For longer chains, the findings are discussed in the light of current concepts of amylose conformation in aqueous solution, namely the model of the broken helical chain (alternating stiff helical segments and unordered regions) and the model of a flexible coil without a significant helical content. However, according to the results given in this paper, a wormlike helical chain seems to be the most adequate model for amylose conformation in neutral solution.

Physiological aspects of conjugation in fission yeast.

Abstract: Conjugation was studied in Schizosaccharomyces pombe using liquid media. Nitrogen, which was growth-limiting in a synthetic medium, had to be consumed completely before conjugation could start. Conjugation was preceded by sexual agglutination. Agglutinability was not constitutive in heterothallic strains. It only developed when cells of h (+) and h (-) mating type were grown in mixed culture for at least 2.5 hr before the start of conjugation.

Feedback interaction of mechanical and electrical events in the isolated mammalian ventricular myocardium (cat papillary muscle)

Abstract: Measurements of transmembrane potentials were performed under different contractile conditions on isolated cat papillary muscles. It was found that the duration of the action potential (within limits of about 20%) depends on the mode of contraction. Isotonic shortening tends to prolong, isometric tension development tends to shorten the duration of the action potential. As a result of the action potential alterations negative or positive inotropic mechanical transients are observed during 5–10 subsequent beats. The decrease in action potential duration is roughly proportional to the force development, and the increase of action potential duration is related to the shortening velocity. By applying a controlled stretch the shortening velocity of the contractile element (V CE ) was reduced below its value during purely isometric conditions. A further decrease of the action potential duration was observed. IncreasingV CE by release experiments increased the action potential duration beyond that observed under lightly loaded isotonic contractions. A quick release taking place after repolarization is complete produces a new distinct wave of depolarization (10–15 mV) which can sometimes initiate a new action potential. The quick release experiments fascilitated the estimation of the time delay of the feedback interaction which is less than 10 msecs. The possibility that passive geometrical changes of the plasma membrane is a causitive factor of the described phenomenon was experimentally excluded. Alternative explanations are discussed. It seems likely that a controlling parameter of this excitation contraction feedback system is contained in the force velocity relation of the contractile element influencing the internal Ca++-transients by its mode of contraction.

Reserve carbohydrate metabolism in germinating seeds of trigonella foenum-graecum L. (Leguminosae)

Abstract: Seeds of Trigonella foenum-graecum are examined light microscopically and by chemical analysis at different stages of germination. In the earliest stages of germination the raffinose family oligosaccharides are metabolised both in the endosperm and in the cotyledons of the seed but there is no change in the appearance, amount or composition of the main carbohydrate reserve, a galactomannan localised in the endosperm. About 18 hours after the emergence of the radicle the endosperm galactomannan begins to be mobilised. In a period of 24 hours the polysaccharide is completely degraded and the breakdown products, mainly galactose and mannose, are absorbed by the cotyledons in which sucrose increases and starch is formed. Mobilisation of the galactomannan is accompanied by the formation in the endosperm of a dissolution zone the form of which implies that the aleurone layer is involved in the degradation process.

Disorder in Excitation-Contraction Coupling of Cardiac Muscle from Cats with Experimentally Produced Right Ventricular Hypertrophy

Abstract: The contractile and electrical activity of papillary muscles from hypertrophied right ventricles of cats with artificial stenosis of the pulmonary artery was investigated. Contractility was considerably decreased along the entire force-velocity relationship, whereas no measurable alterations could be detected in the electrical activities as recorded by intracellular microelectrodes. By supramaximal Ca2+ activation, the contractility of both the hypertrophied and the normal control preparations was increased to about the same final value. These findings are consistent with the concept that a disorder in the mechanism of excitation-contraction coupling underlies the depressed contractile state of hypertrophied cardiac muscle. In addition, it could be shown that the increase in volume of each cellular unit is clearly related to the decrease in contractility. This can tentatively be explained by the following assumptions. If the amount of Ca2+ entering the cell per unit area is not changed in hypertrophy, the...

Communication between Cells of Different Type

Abstract: MANY types of cells have membrane junctions so organized as to allow the passage of molecules from the interior of one cell to another with little loss to the outside1–6. At least in some cases, a large part if not all of the surface membrane seems to be capable of this organization, for if the junction is broken and the cell pair rejoined at some other place, the system can become fully communicating within seconds or minutes7,8. Evidently the membranes must undergo profound structural changes in such a way that previously impermeable surface regions become highly permeable. This implies a close spatial matching of the joining regions on the two membranes. The question arises whether such matching can be effected between membranes that differ from each other. To find something out about this problem, we have paired cultured cells from different organs and species, measuring the communication between cells electrically.

Phytochrome-mediated flavone glycoside synthesis in cell suspension cultures of Petroselinum hortense after preirradiation with ultraviolet light

Abstract: Ultraviolet light was demonstrated to stimulate flavone glycoside synthesis in Petroselinum cell suspension cultures. The data presented suggest the involvement of phytochrome in this response: Flavone glycoside formation resulting from 1 h of ultraviolet irradiation was increased by subsequent continuous far-red light irradiation. However, the ultraviolet effect was reduced by a subsequent irradiation with 10 min of far-red. This far-red effect was fully reversed by a sub-sequent irradiation with 10 min of red. Red and far-red irradiations were ineffective without ultraviolet preirradiation. It is concluded that in this system ultraviolet irradiation is required in order to change the cells in such a way as to allow a physiological effectiveness of the phytochrome system.

Spontaneous occlusion of a bilateral caroticocavernous fistula studied by serial angiography.

Abstract: A case of angiographically-proven spontaneous bilateral carotico-cavernous fistula is described in a 53-year-old woman. Spontaneous cure with closure of the fistula occurred immediately after carotid angiography, and it was confirmed by clinical examination and followup bilateral carotid angiography about one year later. The pathogenesis and haemodynamics of the bilateral arteriovenous shunt and the possible mechanisms responsible for the spontaneous occlusion following carotid angiography were discussed.

Uterus-Relaxation durch hochaktive Ca++-antagonistische Hemmstoffe der elektro-mechanischen Koppelung wie Isoptin (Verapamil, Iproveratril), Substanz D 600 und Segontin (Prenylamin)

Abstract: 1. Isoptin (Verapamil, Iproveratril) und sein nachster Verwandterα-Isopropyl-α-((N-methyl-N-homoveratryl)-γ-aminopropyl)-3,4,5-trimethoxyphenylacetonitril (Substanz D 600) sowie Segontin (Prenylamin) erweisen sich nicht nur am Saugetiermyokard, sondern auch an den glatten Muskelzellen des isolierten Rattenuterus als hochaktive Ca++-Antagonisten, die die elektro-mechanischen Koppelungsprozesse blockieren und bei gleichzeitiger Dampfung der Membranerregbarkeit eine totale Uterusrelaxation erzwingen. Dementsprechend hemmen die genannten Ca++-Antagonisten schon in einem Konzentrationsbereich von etwa 5×10−6 M/l die mechanischen Reaktionen des Uterus auf isotonische KCl-Losung, kathodische Gleichstrompolarisation, Acetylcholin, Carbaminoylcholin, Oxytocin und BaCl2 mehr oder weniger vollstandig. 2. Bei Reduktion des Ca++-Gehalts der Tyrodelosung (1,8 mM/l) auf ein Viertel der Norm (0,45 mM/l) werden die Relaxationseffekte von Isoptin, Substanz D 600 und Segontin betrachtlich verstarkt. Umgekehrt wird die relaxierende Wirkung der genannten Ca++-Antagonisten prompt neutralisiert und die Ansprechbarkeit der Uterusmuskulatur auf Kontrakturstoffe wieder hergestellt, wenn man den Ca++-Gehalt der Tyrodelosung auf das 4–8fache steigert. Dabei kehrt auch die vorher unterdruckte Spontanaktivitat der Uterusmuskulatur zur Norm zuruck. 3. Auch andere „musculotrope“ Relaxantien der Uterusmuskulatur, wie z.B. Papaverin, Athylpapaverin und Nitroglycerin, sind durch klare Ca++-antagonistische Effekte ausgezeichnet. Dementsprechend kann auch die durch Papaverin, Athylpapaverin oder Nitroglycerin erzwungene Ruhigstellung des Uterus trotz weiterer Anwesenheit dieser Stoffe mittels eines Zusatzes von Extracalcium durchbrochen werden. Dies last vermuten, das das pharmakodynamische Wirkungsprinzip musculotroper Relaxantien generell auf der Ausschaltung physiologischer Ca++-Effekte beruht. 4. Auffalligerweise fuhren die genannten Ca++-Antagonisten auch zu einer Hemmung der bioelektrischen Erregungsphanomene an den glatten Muskelzellen, so das die automatische Impulsbildung, die Fortleitung von Aktionspotentialen sowie das Ausmas der Oxytocin- oder BaCl2-induzierten Membrandepolarisation eingeschrankt wird. Extracalcium wirkt auch auf die bioelektrischen Membranfunktionen restituierend. Hieraus ist auf eine starkere Beteiligung von Ca++-Ionen am Erregungsvorgang der Uterusmuskulatur zu schliesen. 5. Fur die Ausschaltung der Spontanaktivitat des isolierten Rattenuterus sind sowohl „musculotrop“ angreifende Ca++-Antagonisten als auch „neurotrope“ Wirkstoffe—speziell Sympathomimetica mitβ-Receptoren-stimulierenden Eigenschaften — brauchbar. Bei der vergleichenden Prufung einer Vielzahl von Uterusrelaxantien zeigte Substanz D 600 unter den musculotropen Hemmstoffen eine etwa 100mal hohere Wirkungsstarke als Papaverin. Unter den sympathomimetischen Stoffen war Substanz Th 1165a (C. H. Boehringer Sohn, Ingelheim) als Inhibitor der Spontanaktivitat am effektivsten. Die elektro-mechanischen Koppelungsprozesse werden jedoch von den sympathomimetischen Hemmstoffen der Uterusmotilitat crst in 10000fach hoheren Dosen oder uberhaupt nicht beeintrachtigt. Auch gegenuber den Uteruskontrakturen durch KCl oder Oxytocin sind Sympathomimetica praktisch unwirksam. 6. Mit der Auffindung hochaktiver Ca++-Antagonisten ist die Moglichkeit gegeben, das schwache Papaverin auch in der klinischen Therapie durch starkere musculotrope Uterusrelaxantien abzulosen. Besonders vielversprechend ist die Kombination einesβ-adrenergischen Sympathomimeticums mit einem Ca++-antagonistischen Hemmstoff — speziell mit Substanz D 600. Dabei ist mit einer Addition der erwunschten uterusrelaxierenden Effekte zu rechnen, wahrend sich umgekehrt die unerwunschten Nebenwirkungen auf das Herz gegenseitigneutralisieren. Tatsachlich sind dieβ-adrenergischen Myokardeffekte (Steigerung von Herzkraft, Schlagvolumen, Schlagfrequenz, O2-Bedarf; Forderung ektopischer Erregungsbildung) den Wirkungen Ca++-antagonistischer Hemmstoffe (Herabsetzung von Herzkraft, Schlagvolumen, Schlagfrequenz, O2-Bedarf; antiarrhythmische Einflusse) diametral entgegengesetzt.

Contrast enhancement in a Hermann grid with variable figure-ground ratio.

Abstract: Psychophysical experiments on contrast vision were made using a modified Hermann grid which was graded in two directions. This pattern was composed of intersecting (IG) and intersected stripes (ID) representing 15 shades of a gray scale, and was viewed against 5 uniform backgrounds (BGD) ranging from white to black. Illusory light and dark patches at intersections were essentially limited to IG's that ranged in reflectance between BGD and ID. The illusion was most distinct when the contrast ratio between IG and BGD was minimum, while that between IG and ID was maximum; it was much reduced on intersections formed by equireflectant stripes, such as those in the original Hermann grids. “Brighter” responses were evoked by a white BGD and “darker” responses by a black BGD. Gray BGD's elicited both kinds of responses. The contrast effects were more pronounced for vertical and horizontal than for diagonal grid orientation. An optimum grid was devised that shows maximum brightness changes at almost every intersection, even when fixated foveally. The observations are interpreted in terms of Baumgartner's receptive field hypothesis.

Foveal perceptive fields in the human visual system measured with simultaneous contrast in grids and bars

Abstract: Foveal perceptive fields (center plus surround) for human vision were investigated by means of contrast illusions in grids and bars. The task consisted of determining the size of the retinal area within which photic stimulation of the periphery induces apparent brightness changes of the central portions. The mean of the individual thresholds obtained in four experiments suggests a total field diameter of 17.8 min of arc (with an estimated 4.0′ corresponding to the center) for on-and off-center fields. It is assumed that this average value refers to perceptive fields of retinal ganglion cells. The significance of eye movements and afterimages in contrast vision and their possible influence on these measurements is discussed.

Pattern formation in longitudinal halves of leaf hopper eggs (Homoptera) and some remarks on the definition of “Embryonic regulation”

Abstract: 1. Eggs of the leaf hopperEuscelis plebejus F. were fragmented longitudinally by a novel technique during cleavage. 2. Irrespective of the plane of fragmentation, both fragments may produce germ bands which are either of perfect bilateral symmetry or contain at least some bilaterally symmetrical body segments. With one possible exception, no longitudinal half-patterns were formed. 3. Ventral and lateral egg halves produce either complete germ bands or anterior partial germ bands. The failure to produce posterior body segments is correlated to the absence of special posterior pole materials marked by the symbiont mass. 4. Dorsal egg halves may produce either complete germ bands or posterior partial germ bands. The loss of anterior segments may be due to lack of keimanlagen cells. 5. The results are discussed and compared to those from transverse fragmentations carried out earlier. 6. Aided by a formalized presentation of the results a dilemma of definition is pointed out which results from the common usage of defining embryonic regulation as the alternative of mosaic development and at the same time by reference to the normal result of development.

Durchflußfluorescenzcytophotometrie für ultraschnelle DNS-Messungen an großen Zellpopulationen

Abstract: Ausgehend vom Leitz-Mikroskopphotometer MPV mit Auflicht-Anregung wird ein Durchflusfluorescenzcytophotometer beschrieben, das es gestattet, die relativen Feulgen-DNS-Mengen von bis zu 1000 Zellen pro Sekunde zu bestimmen. Die Meswerte werden in einem Impulshohenanalysator klassifiziert und gespeichert. Auf Abruf wird der Speicherinhalt analog als Histogramm ausgeschrieben oder digital als Zahlenfolge ausgedruckt. Das Vorgehen bei der Zellsuspensionsherstellung, Fixierung, Hydrolyse und Farbung mit dem Feulgen-Farbstoff Akriflavin wird dargelegt. Anwendungsbeispiele werden besprochen.

A Photoelectron‐spectroscopic investigation of the Homoconjugative Interaction between π‐ and Walsh‐Orbitals in endo‐ and exo‐Cyclopropano‐norbornene

Abstract: Photoelectron spectra of endo- and exo-cyclopropano-norbornene ( = endo- and exo-tricyclo[3.2.1.02.4]octa-6-ene) show that a significant homoconjugation exists between the π-orbital of the double bond and the symmetric Walsh-es-orbital of the cyclopropane ring in the exo-isomer, whereas the interaction is negligeable in the endo-derivative.

Äquivalente und konvalente gesangliche Reaktionen einer extrem regelmäßig singenden Nachtigall (Luscinia megarhynchos L.)

Abstract: 1. Eine Nachtigall (Luscinia megarhynchos L.) trug, ungestort singend, ihre 61 verschiedenen Gesangsstrophen (Abb. 1) in regelmasiger und zyklischer Reihenfolge vor (Abb. 2, 3). Zugleich zeigte die sequentielle Wiederkehr ihrer nach gleichen Anfangen klassifizierten Strophen eine Periodik, die sich nicht aus der zyklischen Strophensequenz ableiten lies (Abb. 4). Diese Periodik mus (entsprechend der Spontanperiodik von Amselstrophen) von einer eigenen „Einfluskomponente“ abhangen. Die Periodik der haufigsten Strophenklasse lag bei 13 Zwischenstrophen. — Der Determinationsgrad der Strophenfolge (=Haufigkeit der Aufeinanderfolge zweier Strophen bezogen auf die Haufigkeit ihres Auftretens) betrug im ungestorten Nachtgesang durchschnittlieh 83%, war aber innerhalb seiner verschiedenen Sequenzbereiche unterschiedlich gros:Wahrend er sich in einem „weniger determiniert“ erseheinenden Sequenzbereich W D nur auf ca. 64% belief, lag er in dem „verstarkt determiniert“ erscheinenden Bereich V D bei 92% (Abb. 2). — Die Tagesgesange der Nachtigall unterschieden sich von den unbeeinflusten Nachtgesangen lediglich in der Lange, nicht dagegen im Aufbau (Tabelle 1). 2. Das Versuchstier reagierte auf ihm vom Tonband vorgespielte sequentiell unveranderte (250- oder 24-Strophen lange) Abschnitte seines Eigengesanges mit aquivalenten (Reaktionszeit: 1–2,2 sec) oder konvalenten (Reaktionszeit: 1–2 sec) (Definitionen s. S. 265) Antworten (Abb. 5–7). — Vorgespielte Strophen des sequentiell besonders festgelegt scheinenden V D-Bereichs wurden vornehmlich mit konvalenten, Strophen des weniger festgelegten W D-Bereiches dagegen fast ausschlieslich mit aquivalenten Reaktionen beantwortet (Abb. 8). Insgesamt lag die Antworthaufigkeit auf Reizstrophen aus V D-Bereichen bei 77%, aus den W D-Bereichen bei 67%. 3. Eine Besonderheit der gesanglichen Reaktion des Versuchstieres lag darin, das es nach einer nicht im Verlauf seiner „normalen“ Strophensequenz liegenden Antwort auf ein Reizmuster keineswegs wieder an jene Sequenzstelle zuruckkehrte, die es mit der Antwort verlassen hatte, sondern das es mit denjenigen seiner Strophen weitersang, die sich sequenzmasig an die Antwortstrophe anschlossen. Nach kurzer Eingewohnung machte die Nachtigall, konfrontiert mit einem aus einzelnen Abschnitten ihres Spontangesangs hergestellten Reizgesang, dessen Sequenzsprunge in 62% aller Falle bereits 1–3 Strophen nach diesen Sprungen mit (Abb. 9, Tabelle 2). — Das Versuchstier schlos sich Sequenzsprungen eines Reizgesangs nicht an, falls diese zu haufig auftraten: Bei seiner Konfrontation mit einem Attrappengesang, der aus experimentell aneinandergereihten Einzelstrophen seines Eigengesangs bestand, diese Strophen aber in einer von seiner Eigensequenz abweichenden Reihenfolge enthielt, liesen sich keine spezifischen gesanglichen Reaktionen nachweisen (Tabelle 1).

Position of targets and period of competence for UV-induction of the malformation "Double Abdomen" in the egg ofSmittia spec. (Diptera, Chironomidae)

Abstract: 1. UV irradiation of anterior pole regions of eggs ofSmittia results in the formation of "double abdomens". The frequency of this malformation has been recorded as a function of developmental stage, size and position of irradiated area, and UV dose. 2. The efficiency of irradiation decreases with increasing longitudinal extent of the irradiated anterior area. 3. Within the anterior fourth of the egg, irradiation of peripheral regions is more effective than irradiation of central regions. 4. The varying efficiency of irradiation is thought to represent a corresponding distribution in the concentration of effective targets or the morphogenetic efficiency of the targets in the irradiated state. Alternative interpretations are discussed. 5. There is a multiplicity of targets distributed symmetrically to the longitudinal egg axis. 6. The effective targets have been proved to be localized in the ooplasm of eggs aged less than 1 h. There is evidence to show that the targets are confined to the ooplasm during all stages studied. 7. The targets are probably stored during oogenesis. 8. The irradiated targets affect the body segment pattern far beyond the irradiated area. 9. Possible relations between the targets for UV-induction of double abdomens and factors that are involved in the formation of the normal body segment pattern are discussed.

Cytomembrane differentiation in a ciliate, Tetrahymena pyriformis. I. Endoplasmic reticulum and dictyosomal equivalents.

Abstract: Various differentiating forms of rough and smooth endoplasmic reticulum (ER), as well as a novel type of a Golgi apparatus-equivalent organelle, are described for the ciliate Tetrahymena pyriformis. Ergastoplasmic stackings and dictyosomal configurations have been studied in particular detail since such structures had hitherto been reported not to occur in these ciliate cells. A Tetrahymena cell can contain several hundred dictyosomes, which are frequently formed at the mitochondrial jacket-ER. The following way of secretory flow is suggested for Tetrahymena: Small patches of rough ER (or of the nuclear envelope) loose their ribosomes and become smooth. From such smooth membrane areas vesicles pinch off which are distinct by greater membrane thickness and electron contrast as well as by an intimate association with characteristic granulo-fibrillar aggregates. Such ER-derived vesicles can then conflux, either to give rise to a stream of vesicles with distally increasing sizes, or to produce a localized “pile up” as more or less comprehensive stacks of flattened cisternae in the typical mode of a dictyosome with forming and secreting face polarity. The observations indicate that processes of cytomembrane differentiation and membrane flow take place in ciliate systems. In addition, the coincidence of vesicle pinching off with the appearance of fenestrae in the cisternae has led to new concepts of how pores in cisternae might generally be formed as a consequence of vesicle production.

MEMBRANE-TO-MEMBRANE CROSS-BRIDGES A Means to Orientation and Interaction of Membrane Faces

Abstract: Electron microscopy has shown various examples of membrane faces which occur in parallel, being separated by a distance of 70-350 A . This distance is constant for a defined cellular situation, although it varies from one type of association to another . Prominent instances of this include the parallel associations (stacks) of cisternae, such as the Golgi apparatus and the so-called \"impaired\" endoplasmic reticulum (ER) cisternae (for literature see 20, 24), as well as cases in which a cisternal (or vesicular) membrane parallels a single membrane ; a particularly clear example of this being the relationship of the plasma membrane with the \"subsurface cisternae\" of various cells (e .g ., 4, 32, 48) and with the alveolar sacs of the pellicle of many ciliates (e .g ., 27, 40, 45) . In a detailed electron microscope screening of such parallel membrane-membrane associations in diverse cell types, intermembranous cross-bridges were consistently observed . This suggests that the cross-bridges function as \"rungs\" for the stabilization of such characteristic membrane arrangements .