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  • 11
    Electronic Resource
    Electronic Resource
    The development and structure of the zoospore vesicle in Bulbochaete hiloensis (1970)
    Springer
    Archives of microbiology 72 (1970), S. 223-237 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Zoospore mother cells in Bulbochaete are shown to be surrounded by a structure interposed between the plasmalemma and the cell wall which is interpreted as the precursor of the vesicle which temporarily surrounds the zoospore on its release. 2. As this vesicle precursor matures it thickens apically to form a ring consisting of a core and two layers. These two layers envelope the young zoospore as its vesicle. Later a space, referred to as the sub-ring, develops within the middle layer of the ring. 3. Histochemical tests indicate that the vesicle precursor and ring are highly proteinaceous with a small carbohydrate component. 4. Dehiscence is apical and thought to be assisted by the apical ring. Upon release of the zoospore, its vesicle is essentially composed of the inner layer of its precursor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00412174
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  • 12
    Electronic Resource
    Electronic Resource
    Reproduction in Bulbochaete hiloensis (Nordst.) Tiffany (1972)
    Springer
    Archives of microbiology 86 (1972), S. 265-280 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The ellipsoid to subspherical zoospore of Bulbochaete hiloensis (Nordst.) Tiffany consists of a green body surmounted by a dome-shaped colourless head, around the base of which is a ring of flagella. 2. The body cytoplasm is characterized by a reticulated chloroplast which contains stacked thylakoids; incipient, developing and mature pyrenoids; and microtubules. The remaining cytoplasm contains active ER-Golgi complexes, coated vesicles, dense bodies, cored bodies, a mitochondrial nest, large central nucleus and lipid-like bodies, adjacent to the large vacuoles. 3. The colourless head, packed with mitochondria, has an extensive ER-Golgi system and a mass of vesicles thought to contain mucopolysaccharides. 4. The flagellar apparatus contains approximately forty regularly-spaced basal bodies situated below a banded fibrous ring. Between the basal bodies are located striated ascending roots, microtubular descending roots and supporting structures. 5. Zoospores are positively phototactic and it is suggested that motility is directed either through differential flagellar activity or by an internal steering mechanism affected by reorientation of the flagellar apparatus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00424984
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  • 13
    Electronic Resource
    Electronic Resource
    Reproduction in Bulbochaete hiloensis (Nordst.) Tiffany (1973)
    Springer
    Archives of microbiology 90 (1973), S. 343-364 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Sexual reproduction in Bulbochaete hiloensis (Nordst.) Tiffany is mediated by the production of dwarf males and oogonia. 2. Mature dwarf males have a stipe cell and a variable number of antheridia, each divided by a septum separating two spermatozoids. 3. Each spermatozoid consists of a head and body surmounted by a flagellar apparatus with a ring of six to nine flagella. 4. The spermatozoid body is characterized by a large nucleus with chromatin but without an apparent nucleolus, and a highly reduced chloroplast with stroma starch but no pyrenoids. 5. Each spermatozoid is surrounded by a fibrous vesicle and an electron dense layer which are thought to be functional in the sequential release of the spermatozoids from the antheridium. 6. A vegetative photosynthetic cell undergoes division to eventually give rise to an oogonium and primary and secondary suffultory cells. 7. The suffultory cells have highly vacuolate, degenerate cytoplasm with no chloroplast. 8. Within the oogonium, the nucleus becomes located near an extracytoplasmic, fibrogranular mass of mucosubstances laid down in the vicinity of a partial wall discontinuity. These mucosubstances are possibly functional in splitting the wall to form the fertilization pore. 9. The plug progressively disperses as the oogonial cytoplasm rounds off, receding from the cell wall in the apical and basal regions. 10. Following fertilization the oogonial contents refill the enclosing cell wall. The nucleus returns to the centre of the cell and the cytoplasm becomes dominated by numerous closely-packed, lipid-like bodies. Stages in the development of the seven-layered oospore wall are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00408929
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  • 14
    Electronic Resource
    Electronic Resource
    Ultrastructural investigations in the stigonemataceae (cyanophyta) (1972)
    Springer
    Archives of microbiology 82 (1972), S. 283-299 
    Details
    ISSN: 1432-072X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The general cytoplasmic features of Fischerella muscicola, Stigonema hormoides and cells of Stigonema mamillosum found as a phycobiont in the lichen Ephebe lanata are similar to those found in other cyanophyte cells. 2. In all instances the outer surface of the quadrilayered cell wall bears a series of ridges. The membrane-like outermost layer (L IV) also exhibits a number of evaginations thought to represent sites of extrusion of material from the cytoplasm through the wall into the enveloping fibrous mucilage. 3. Cross walls are formed by inward growth of the two inner layers of the lateral walls, the daughter cells subsequently moving apart through the inward intrusion of the two outer wall layers and a bulk of mucilage. 4. The daughter cells remain connected by a persistent central region of the original septum. This septum is penetrated by pores, although these do not pierce the underlying plasma membranes and no direct connection of the protoplasts is achieved. 5. An apical cell of S. hormoides was found to be capped by remnants of a cross wall, presumably by the disruption of a previously distal cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00424933
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  • 15
    Electronic Resource
    Electronic Resource
    The effect of ionophore A 23187 and ruthenium red on tentacle contraction and ultrastructure inDiscophrya collini: Evidence of calcium fluxing from intracellular reservoirs (1983)
    Springer
    Protoplasma 117 (1983), S. 158-166 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Contraction ; Discophrya ; Ionophore A 23187 ; Ruthenium red ; Tentacle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The suctorian protozoonDiscophrya collini has contractile tentacles with microfilaments and a central microtubule-lined canal (axoneme). The role of calcium fluxing in tentacle contraction has been investigated using the Ca2+ ionophore A 23187 and ruthenium red (RR), a known inhibitor of certain Ca2+ membrane transport events. Treatment with CaCl2 alone caused tentacle contraction with a threshold at 5 × 10−3 M CaCl2 and a maximum at 5 × 10−2 M CaCl2 with contraction to 32.8% of the original length. In the presence of 5 μM ionophore A 23187 the threshold was lowered to 5 × 10−6 M CaCl2 with a maximum to 19.6% original length at 5 × 10−2 M CaCl2. A 23187 alone induced contraction with a threshold of 3.0 μM and a maximum to 30.5% original length at 10 μM A 23187. Treatment with RR alone had little effect on tentacle length. However, a 10 μM A 23187-induced contraction was partially counteracted by the simultaneous application of RR with a threshold at 2 μM RR and a maximum at 8 μM RR. Removal of the ionophore after induced tentacle contraction resulted in partial re-extension, which was inhibited by RR. Ultrastructural observations indicated that the ionophore and CaCl2-induced contraction processes are indistinguishable. The CaCl2/ionophore treatments led to axonome disruption, interpreted as a consequence of supranormal levels of intracellular Ca2+. X-ray microanalysis of cytoplasmic membrane-bound elongate dense bodies (EDB) showed a high level of Ca2+ in CaCl2-treated cells, little Ca2+ in ionophore-treated cells and intermediate levels in the RR-treated, ionophore/RR-treated and untreated control cells. It is suggested that A 23187 enhances both the uptake of extracellular Ca2+ and the release of Ca2+ from the EDB, the latter being counteracted by RR. These observations support the proposal that the EDB act as Ca2+ reservoirs, and that their Ca2+ fluxing moderates cytosolic Ca2+ levels which mediate a Ca2+-dependent tentacle contraction mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288354
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  • 16
    Electronic Resource
    Electronic Resource
    Electrically induced tentacle contraction in the suctorian protozoonTrichophrya collini (1989)
    Springer
    Protoplasma 148 (1989), S. 33-40 
    Details
    ISSN: 1615-6102
    Keywords: Contraction ; Electrical stimulation ; Microtubules ; Suctoria ; Trichophrya
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Extracellular electrical stimulation ofTrichophrya collini induces tentacle contraction. There is an inverse relationship between stimulus duration and voltage in producing a threshold response, and at a set voltage the response is graded depending upon duration of stimulus. With a threshold stimulus (6.3 V, 1,000 ms) the response is restricted to the anodal tentacles, and with increasing stimulus intensity or duration the response spreads to the cathodal and finally the intermediate tentacles. With a stimulus of 15 V, 1,000 ms the mean tentacle length is reduced to 28% of the control within 1.2 s. Recordings using intracellular microelectrodes give resting membrane potentials between −10mV and −40mV. Intracellular hyperpolarizing currents of 1nA and 2nA induce tentacle contraction to 50% and 25% of the control length respectively, but depolarizing currents do not induce contraction. SEM studies show that in the initial stages of contraction, only the central region of the tentacle shaft becomes shortened, but on full contraction shortening involves the whole of the shaft. TEM studies show that on contraction no depolymerization of tentacle axoneme microtubules occurs, but that the entire axoneme passes down into the body cytoplasm. These observations are discussed in relation to the possible mechanisms of tentacle contraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01403989
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  • 17
    Electronic Resource
    Electronic Resource
    Quantified elemental changes inAspidisca cicada andVorticella convallaria after exposure to aluminium, copper, and zinc (1997)
    Springer
    Protoplasma 198 (1997), S. 143-154 
    Details
    ISSN: 1615-6102
    Keywords: Aluminium ; Copper ; Electron probe X-ray microanalysis ; Protozoa ; Zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Data on metal-induced elemental changes in eukaryotic unicellular organisms, such as protozoa, are rare. This study focused on two species of ciliate protozoa,Aspidisca cicada andVorticella convallaria, both common and abundant in activated sludge. Elemental changes in cells exposed to aluminium, copper, and zinc were determined by scanning electron microscopy-electron probe X-ray microanalysis. X-ray emission spectra obtained from cells 2 h after resuspension in Chalkley's medium (control) showed clear, characteristic peaks for magnesium, silicon, phosphorus, sulphur, potassium, and copper. These elements were also routinely detected in all cells resuspended in metal solution. Spectra obtained from cells treated with aluminium or zinc showed additional distinct peaks for aluminium and zinc. In copper-treated cells enhanced copper peaks were seen. Mean aluminium levels were low inA. cicada control cells (0.14mg/g of dry weight) but higher in cells treated with 0.50 ppm (0.69 mg/g of dry weight) and 2.00 ppm aluminium (2.07 mg/g of dry weight).A. cicada was ten times more sensitive to copper than to the other metals, and thanV. convallaria. There was a significantly higher concentration of copper inA. cicada cells treated with 0.20 ppm copper (2.94 mg/g of dry weight) than in control cells (2.16 mg/g of dry weight). InA. cicada cells treated with 0.50 and 2.00 ppm zinc significantly higher levels of zinc (2.41 and 2.07 mg/g of dry weight, respectively) were observed than in the control (0.41 mg/g of dry weight). After treatment with 0.50 ppm and 2.00 ppm aluminium, aluminium was significantly higher in the treatedV. convallaria cells (1.58 and 0.67 mg/g of dry weight, respectively) than in control cells (0.14 mg/g of dry weight). After treatment with 2.00 ppm copper there was significantly more copper in treatedV. convallaria cells (3.63 mg/g of dry weight) than in controls (2.08 mg/g of dry weight). InV. convallaria cells treated with 0.50 ppm and 2.00 ppm zinc there was an increase in the amount of zinc in cells (1.30 and 2.68 mg/g of dry weight, respectively) compared with control cells (0.34 mg/g of dry weight). Data on other changes in intracellular elements in both species, after 2 h exposure to aluminium, copper, and zinc medium are given. In both species, there was uptake and/or accumulation of aluminium, copper, and zinc when the external concentration of the metal was increased. Intracellular elemental levels were altered by sublethal and toxic external concentrations of the metals studied.A. cicada was ten times more sensitive to copper than to aluminium or zinc, and thanV. convallaria to the metals studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287563
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  • 18
    Electronic Resource
    Electronic Resource
    Asexual reproduction in the suctorianDiscophrya collini (1982)
    Springer
    Protoplasma 111 (1982), S. 195-205 
    Details
    ISSN: 1615-6102
    Keywords: Discophrya ; Evaginative budding ; Microtubules ; Reproduction ; Suctoria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Discophrya collini reproduces asexually through the formation of a ciliated swarmer by evaginative budding. This process is initiated by the repeated replication of a single subcortical kinetosome to form a kinetosome field. The epiplasm of the multilayered cortex covering this field becomes reduced in thickness and the whole cortex invaginates to produce an internal embryonic cavity. The kinetosomes become organised into rows, and each produces a cilium which projects into the cavity. On completion of the embryonic cavity its walls are extruded through the cavity opening to form an external ciliated swarmer connected to the parent by a thin bridge of cytoplasm. It is suggested that this evagination is induced by a rapid breakdown of supporting microtubules in the cavity wall and the subsequent hydrostatic pressure exerted by the body cytoplasm. The connecting bridge shows no specialised ultrastructural features and separation of swarmer from parent probably is achieved by the active movement of the swarmer. The cytoplasm of the swarmer is similar in structure to that of the adult cell but contains a number of primordia of tentacle axonemes. The infraciliature resembles that of other suctorian swarmers. On settling, the cilia of the swarmer are lost, at least some by resorption, a stalk may be secreted and the axoneme primordia are extended to form functional tentacles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01281967
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  • 19
    Electronic Resource
    Electronic Resource
    Tentacle contraction and ultrastructure inDiscophrya collini: The response to cations (1982)
    Springer
    Protoplasma 112 (1982), S. 92-100 
    Details
    ISSN: 1615-6102
    Keywords: Discophrya ; Tentacle contraction ; Cations ; Calcium ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Discophrya collini is a suctorian protozoan with contractile tentacles containing a microtubule-lined canal and microfilaments. The effects of a range of cations on tentacle contraction and ultrastructure have been determined. Treatment with 80 mM CaCl2 and 95 mM MgCl2 causes contraction to 28% and 57% of the control length respectively. Re-extension takes over 4 hours in the culture medium, but CaCl2-treated tentacles are re-extended after a 5 minutes treatment with 10−2 M EDTA or 5 × 10−3 M EGTA. CuCl2 causes a significant contraction at 10−5 M (to 77%); LaCl3 at 10−4 M (to 65%); ZnCl2 at 10−2 M (to 65%), but BaCl2, CoCl2, MnCl2, NiCl2, and SrCl2 cause significant changes only at 10−1 M. The cytoplasm of CaCl2-treated cells contains two forms of membraneous structures when viewed in TEM; that of MgCl2-treated cells reveals granular areas of medium electron density. None of these features are seen in control cells. The microtubules of the tentacle canal appear to be intact upon its retraction into the cell with no change occurring in the numbers or relative positions of the microtubules. The tentacle cortex is wrinkled. It is suggested from this and previous work that tentacle contraction may be mediated by a microfilament-based mechanism, and that calcium may be involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280219
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  • 20
    Electronic Resource
    Electronic Resource
    Tentacle contraction inDiscophrya collini: The effects of ionophore A23187 and ruthenium red on Ca2+-induced contraction and uptake of extracellular calcium (1984)
    Springer
    Protoplasma 122 (1984), S. 125-131 
    Details
    ISSN: 1615-6102
    Keywords: Calcium ; Contraction ; Discophrya ; Ionophore A23187 ; Ruthenium red ; Tentacles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The tentacles of the suctorian protozoonDiscophrya collini are stimulated to contract by externally applied Ca2+. The role of extracellular Ca2+ in tentacle contraction was studied by monitoring45Ca2+ uptake, using ionophore A23187 to facilitate membrane transport of calcium and ruthenium red (RR) as an inhibitor of transport. The degree of tentacle retraction was dependent upon external Ca2+ concentration and studies with45Ca2+ using scintillation counting indicated a linear relationship between external Ca2+ concentration and Ca2+ uptake. Uptake of Ca2+ was enhanced in the presence of the ionophore while RR caused little inhibition.45Ca2+ uptake was only partially inhibited by RR when cells were subjected to a Ca2+, ionophore and RR mixture. Grain counts from light microscope autoradiographs after treatment of cells with45Ca2+/ionophore,45Ca2+/RR or45Ca2+ alone showed heavy, light and intermediate labelling respectively. In all instances the grains were evenly distributed within the cell. These observations are interpreted as supporting the suggestion that the ionophore enhances both the uptake of extracellular Ca2+ and release of Ca2+from an internal source, while the RR could only partially prevent movement of Ca2+ through the plasma mebrane. A model is presented suggesting that tentacle retraction is mediated by cytosolic Ca2+ levels which are determined by the fluxing of Ca2+ across the plasma membrane and the membrane of elongate dense bodies which act as internal Ca2+ reservoirs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279445
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