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  • 1
    Electronic Resource
    Electronic Resource
    Imbibitional leakage from anhydrobiotes revisited (1999)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 22 (1999), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Dry desiccation-tolerant organ(ism)s leak cellular solutes when placed in water. Elevated temperatures at imbibition and elevated initial moisture contents reduce the leakage and promote growth. We have re-examined the effects of imbibitional stress imposed on cattail (Typha latifolia L.) pollen as a model anhydrobiotic system. A nitroxide spin probe technique and electron microscopy were used, allowing study of the permeability of the plasma membrane together with its visual intactness. Imbibitional leakage can be transient, or prolonged when associated with membrane damage. During the first 15 s of rehydration in medium, plasma membranes of pre-humidified pollen were highly permeable but became less permeable thereafter. The resulting transient leakage may affect vigour as measured by the rate of fresh weight increase, but did not reduce germination. A permanent, high permeability was observed when dry pollen was plunged into medium at low temperatures. This led to cell death and is associated with a phase change of the membranes from gel to liquid crystalline during imbibition. Freeze-fracture images indicate that the damage to plasma membranes is mechanically imposed by the pressure of the penetrating water rather than occurring structurally by a phase separation of membrane components. We suggest that a high rigidity of the plasma membranes in the gel phase at imbibition underlies imbibitional damage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1999.00491.x
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  • 2
    Electronic Resource
    Electronic Resource
    Water-conducting properties of lipids during pollen hydration (2002)
    Oxford, UK : Blackwell Science, Ltd
    Plant, cell & environment 25 (2002), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Based on the authors’ previous work an attempt has been made to study water flow in the lipid matrix during pollen hydration. The present study has demonstrated that in the presence of small amounts of water, the type of lipids used defined the time of hydration of pollen in vivo on the stigma and in vitro. Several approaches were used including cryo-scanning electron microscopy, magnetic resonance imaging and Fourier transform infrared microspectroscopic imaging, with the purpose of detecting very small amounts of water. The results show that no water is detectable in the lipid matrix. It was observed and concluded that the water for pollen hydration accumulates as a thin layer at the contact side between pollen and stigma, during the normal process of pollination in plant species with a wet stigma. However, using the same species deprived of the stigma by cell ablation, it was shown that the layer of water observed in wild-type plants is not necessary for pollen hydration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2002.00827.x
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  • 3
    Electronic Resource
    Electronic Resource
    Oleosins prevent oil-body coalescence during seed imbibition as suggested by a low-temperature scanning electron microscope study of desiccation-tolerant and -sensitive oilseeds (1997)
    Springer
    Planta 204 (1997), S. 109-119 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Desiccation sensitivity ; Imbibition ; Oil body ; Oleosin ; Recalcitrant seed ; Seed storage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. In order to clarify further the physiological role of oleosins in seed development, we characterized the oil-body proteins of several oilseeds exhibiting a range of desiccation sensitivities from the recalcitrant (Theobroma cacao L., Quercus rubra L.), intermediate (Coffea arabica L., Azadirachta indica A. Juss.) and orthodox categories (Sterculia setigera Del., Brassica napus L.). The estimated ratio of putative oleosins to lipid in oil bodies of Q. rubra was less than 5% of the equivalent values for rapeseed oil bodies. No oleosin was detected in T. cacao oil bodies. In A. indica cotyledons, oil bodies contained very low amounts of putative oleosins. Oil bodies both from C. arabica and S. setigera exhibited a similar ratio of putative oleosins to lipid as found in rapeseed. In C. arabica seeds, the central domain of an oleosin was partially sequenced. Using a low temperature field-emission scanning electron microscope, the structural stability of oil bodies was investigated in seeds after drying, storage in cold conditions and rehydration. Despite the absence or relative dearth of oleosins in desiccation-sensitive, recalcitrant oilseeds, oil bodies remained relatively stable after slow or fast drying. In A. indica seeds exposed to a lethal cold storage treatment, no significant change in oil-body sizes was observed. In contrast, during imbibition of artificially dried seeds containing low amounts of putative oleosins, the oil bodies fused to form large droplets, resulting in the loss of cellular integrity. No damage to the oil bodies occurred in imbibed seeds of Q. rubra, C. arabica and S. setigera. Thus the rehydration phase appears to be detrimental to the stability of oil bodies when these are present in large amounts and are lacking oleosins. We therefore suggest that one of the functions of oleosins in oilseed development may be to stabilize oil bodies during seed imbibition prior to germination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050236
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  • 4
    Electronic Resource
    Electronic Resource
    Nuclear pore dynamics during pollen development and androgenesis in Brassica napus (2000)
    Springer
    Sexual plant reproduction 13 (2000), S. 43-51 
    Details
    ISSN: 1432-2145
    Keywords: Key words Brassica napus ; Androgenesis ; Freeze fracturing ; Nuclear pore complex ; Pollen development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Changes in nuclear pore complex (NPC) densities, NPCs/nucleus and NPCs/µm3, are described using freeze-fractured Brassica napus microspores and pollen in vivo and in vitro. Early stages of microspore- and pollen-derived embryogenic cells were also analysed. The results of in vivo and in vitro pollen development indicate an increase in activity of the vegetative nucleus during maturation of the pollen. At the onset of microspore and pollen culture, NPC density decreased from 15 NPCs/µm2 at the stage of isolation to 9 NPCs/µm2, under both embryogenic and non-embryogenic conditions. This implies that the drop in NPC density might be a result of culturing the microspores and pollen rather than an indication for microspore and pollen embryogenesis in Brassica napus. However, after 1 day in culture under embryogenic conditions, the NPC density increased again and stabilised around 13 NPCs/µm2, whereas under non-embryogenic conditions the NPC density remained about 9 NPCs/µm2. This low density of 9 NPCs/µm2 was also found in the nuclei of sperm cells, in contrast to the 19 NPCs/µm2 found in the vegetative nucleus. It means that, although both the vegetative and sperm nuclei are believed to be metabolically rather inactive in mature pollen, the NPC density of vegetative nucleus is twice as high as the NPC density of the sperm nuclei. In a few cases, embryos formed suspensor-like structures with a NPC density of 9 NPCs/µm2, indicating a lower nucleocytoplasmic exchange of the nuclei of the suspensor cells than with the nuclei in the embryo proper. In addition, observations on NPCs and other organelles, obtained by high resolution cryo-scanning microscopy, are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009841
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of anoxia on pollen tube growth and tube wall formation of Impatiens glandulifera (1989)
    Springer
    Sexual plant reproduction 2 (1989), S. 85-89 
    Details
    ISSN: 1432-2145
    Keywords: Pollen tube ; Anoxia ; Impatiens glandulifera ; Cell wall formation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary When pollen of Impatiens glandulifera was cultured in aerated liquid medium for 1 h, 70% of the pollen grains germinated; these attained an average tube length of 1 mm. Subsequently, these aerobic growth conditions were changed to anaerobic by substituting a nitrogen inlet for the air inlet. As a result, the pollen tubes stopped elongating and burst. The ultrastructural changes which occurred upon inducing anoxia were studied with samples taken at 0 s, 45 s, and 4 min after changing the gas. Anoxia caused rapid and considerable changes in the ultrastructure of the dictyosome vesicles involved in cell wall formation. There was an increase in the osmiophyly of the vesicle content, and the presence of fibrillar material became apparent. Simultaneously, the fusion behavior of the dictyosome vesicles changed. Instead of the normal fusion of the dictyosome vesicles with the plasma membrane, there was a premature fusion of the vesicles with each other inside the cytoplasm that resulted in the formation of aggregates. Furthermore, the cell wall precursors that were excreted were not incorporated in their usual configuration into the growing cell wall. Instead of a smooth inner cell wall surface, irregular thickenings were formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00191995
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  • 6
    Electronic Resource
    Electronic Resource
    Membrane permeability, morphology, and desiccation tolerance ofDaucus carota somatic embryos as influenced by drying rate (1998)
    Springer
    Protoplasma 202 (1998), S. 202-212 
    Details
    ISSN: 1615-6102
    Keywords: Abscisic acid ; Daucus carota ; Desiccation tolerance ; Low-temperature scanning electron microscopy ; Membrane permeability ; Somatic embryogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Carrot (Daucus carota) somatic embryos that were treated with abscisic acid during their development have been shown to acquire complete desiccation tolerance when slowly dried, but fail to do so when rapidly dried. We studied plasma membrane permeability by a spin probe technique. On rehydration, the plasma membranes of rapidly dried somatic embryos became permanently leaky, whereas those of slowly dried embryos retained permeability levels as low as for fresh embryos. The leakage was associated with extensive deesterification of the phospholipids. Using low-temperature scanning electron microscopy (LTSEM), we examined (re)hydrated and dry somatic and zygotic embryos. No differences in surface morphology were detected between dry tolerant and intolerant somatic embryos that were obtained by slow and rapid drying, respectively. However, on rehydration, the nonviable somatic embryos had lost turgor and intracellular organization, as revealed by LTSEM images of fractured embryos, whereas the viable somatic embryos had turgescent cells with intact cell structure. In 3-day-imbibed, viable embryos, cell extension was visible. These findings are consistent with the electron paramagnetic resonance data. Somatic embryos always had reduced and abnormal cotyledons, mostly fused, and the surface was irregular. The surface of dry somatic embryo cells was considerably more wrinkled than that of dry zygotic embryo cells. Maturation in polyethylene glycol-containing medium increased the percent dry matter in the fresh somatic embryos and reduced the extent of wrinkling after drying. Wrinkling of the dried embryo cells apparently depends on the filling with dry matter in the hydrated state. We suggest that wrinkling per se does not limit desiccation tolerance of somatic embryos.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01282548
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  • 7
    Electronic Resource
    Electronic Resource
    Freeze-fracture studies on isolated sperm cells ofSpinacia oleracea L. (1990)
    Springer
    Protoplasma 153 (1990), S. 204-207 
    Details
    ISSN: 1615-6102
    Keywords: Spinacia oleracea ; Isolation ; Sperm cell membrane ; Intramembrane particles ; Freeze-fracture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary With freeze-fracturing sperm cells appear to be fractured preferentially through the plasma membranes. Only few fracture planes through the cytoplasm are found. Both the PF as well as the EF side of the sperm cell plasma membranes show a slightly undulating surface and contain intramembrane particles. The particle distribution is irregular and does not show any clustering. The EF side of the plasmamembrane contains approximately 3 times more particles per μm2 than the PF side.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01354005
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  • 8
    Electronic Resource
    Electronic Resource
    Ultrastructural immuno-localization of pectins and glycoproteins inArabidopsis thaliana pollen grains (1992)
    Springer
    Protoplasma 168 (1992), S. 14-19 
    Details
    ISSN: 1615-6102
    Keywords: Arabidopsis thaliana ; Pollen ; Sperm cell ; Immunogold localization ; Glycoprotein ; Pectin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary With the monoclonal antibodies MAC 207 and JIM 8 we could demonstrate the presence and localization of arabino-galactan glycoproteins in pollen grains ofArabidopsis thaliana, with JIM 5 the presence and localization of unesterified pectins. MAC 207 preferentially labels the peripheral plasma membrane of the vegetative cell, whereas JIM 8 specifically labels the area of the sperm cell “wall”. Unesterified pectins are present in the inline layer near the plasma membrane, and in the outer intine region which contains remnants of cytoplasmic channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01332646
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  • 9
    Electronic Resource
    Electronic Resource
    Cytological characterization of isolated sperm cells of perennial ryegrass (Lolium perenne L.) (1994)
    Springer
    Protoplasma 178 (1994), S. 48-56 
    Details
    ISSN: 1615-6102
    Keywords: Perennial ryegrass ; Isolated sperm cells ; Ploidy level ; Cytoplasmic constituents ; Nuclear state ; Intramembrane particles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cytoplasmic content and the distribution of intramembrane particles (IMPs) of the plasma membrane of isolated sperm cells of perennial ryegrass (Lolium perenne L.) have been characterized using flow cytometry, transmission electron microscopy, confocal scanning laser microscopy and freeze-fracture studies. The isolated haploid sperm cells contain a variety of cell organelles with the exception of microtubules. Proplastids and plastids with starch were observed, although only rarely. Vacuoles containing remnants of organelles and stacked lamellae of endoplasmic reticulum with cytoplasmic inclusions were observed frequently, indicating that autophagy takes place. The number of mitochondria varies from 11 to 26 with an average of 17. Generally, the nucleus has a lobed shape and displays various interphasic stages of chromatin condensation. The analysis of the number of mitochondria and the nuclear state did not show evidence of sperm cell dimorphism. The cytological variability observed, could be explained by differences in developmental stages already present in vivo at the moment of isolation. No correlation between the number of mitochondria and the nuclear cross-sectioned area and/or the condensation state of the chromatin could be found. The density of intramembrane particles of the plasma membrane on the exoplasmic fracture face is more than twice that on the protoplasmic fracture face. That is the opposite of what was found for sporophytic cells of perennial ryegrass. These results are discussed in relation to the potential use of these cells for biotechnology and developmental studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01404120
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  • 10
    Electronic Resource
    Electronic Resource
    Improved ultrastructural preservation ofPetunia andBrassica ovules and embryo sacs by high pressure freezing and freeze substitution (1997)
    Springer
    Protoplasma 197 (1997), S. 199-209 
    Details
    ISSN: 1615-6102
    Keywords: Brassica napus ; Embryo sac ; Freeze substitution ; High pressure freezing ; Ovule ; Petunia x hybrida
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In order to improve the ultrastructural preservation of the female gametophyte ofPetunia x hybrida andBrassica napus we tested several cryofixation techniques and compared the results with those of conventional chemical fixation methods. Ovules fixed with glutaraldehyde and osmium tetroxide in the presence or absence of potassium ferrocyanide showed poor cell morphological and ultrastructural preservation. In ovules cryo-fixed by plunging into liquid propane, the cell morphology was well preserved. However, at the ultrastructural level structure-distorting ice crystals were detected in all tissues. Due to the large size of the ovules, cryofixation by plunging in liquid propane is not adequate for ultrastructural studies. In contrast,P. x hybrida andB. napus ovules cryo-fixed by high pressure freezing showed improved cell morphological as well as ultrastructural preservation of the embryo sac and the surrounding integumentary tissues. The contrast of the cellular membranes after freeze substitution with 2% osmium tetroxide and 0.1% uranyl acetate in dry acetone was high. At the ultrastructural level, the most prominent improvements were: straight plasma membranes which were appressed to the cell walls; turgid appearing organelles with smooth surface contours; minimal extraction of cytoplasmic and extracellular substances. In contrast to the chemically fixed ovules, in high pressure frozen ovules numerous microtubules and multivesicular bodies could be distinguished.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288029
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