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  • 1
    Electronic Resource
    Electronic Resource
    Anhydrobiosis (1992)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 54 (1992), S. 579-599 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.54.030192.003051
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  • 2
    Electronic Resource
    Electronic Resource
    The effects of moisture and temperature on the ageing kinetics of pollen: interpretation based on cytoplasmic mobility (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: This study shows that characterization of the molecular mobility in the cytoplasm of pollen provides a new understanding of the effects of moisture and temperature on ageing rates. Using EPR spectroscopy, we determined the rotational motion of the polar spin probe, 3-carboxy-proxyl, in the cytoplasm of Typha latifolia pollen, under different temperature and moisture content conditions. Increasing the temperature resulted in faster rotational motion, analogous to faster ageing rates. With decreasing moisture content, rotational motion first decreased until a minimum was reached, after which rotational motion slightly increased again. The moisture content at which this minimal rotational motion was observed increased with decreasing temperature, comparable to the pattern of ageing rate. A significant linear relationship was found between ageing rates and rotational motion in the cytoplasm, suggesting that these parameters are causally linked. Upon melting of the intracellular glass, a twofold increase in activation energy of rotational motion and ageing rate was observed. In contrast, melting of the sucrose glass resulted in an increase in rotational motion of five orders of magnitude. The difference in rotational motion upon melting glasses of pollen or sucrose suggests that other molecules beside sugars play a role in intracellular glass formation in pollen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00601.x
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Differential desiccation sensitivity of corn and Pennisetum pollen linked to their sucrose contents (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 12 (1989), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Two pollen species from the Gramineae family were investigated as to their differential sensitivity to desiccation. Germination in vivo ceased to occur after previous drying to 7–8% moisture content in Zea mays and 3% in Pennisetum typhoides. The reduced vitality coincided with extensive membrane damage, as evidenced by the considerable leakage of fluorescein and K+ from the prehumidified grains into liquid media. Further experiments were undertaken to investigate the basis for this interspecific difference: (1) phospholipid analyses revealed little difference in composition and content both before and after drying; (2) free fatty acid contents increased in both species upon drying but levels were generally low; and (3) sucrose was the sole soluble carbohydrate found in both species. Fresh maize pollen contained 5% sucrose, as compared to 14% in Pennisetum pollen. During slow drying (8h) this level went up to 12% and 17%, respectively. Drying corn pollen in the cold (2°C), or at high rate, limited sucrose levels and affected the resistance to drying. The authors conclude that survival of dehydration is correlated with the presence of sucrose. Finally, they tested the ability of sucrose to preserve dry liposomes prepared from phospholipids purified from the two species. When liposomes were dried in the presence of sucrose, fusion and leakage could largely be prevented at mass ratio's of sugar to lipid of 〉 4. Trehalose was also effective but myo-inositol was not. No species differences were observed. The authors suggest that the presence of sucrose is a key factor in preserving membranes in dry pollen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1989.tb01919.x
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  • 5
    Electronic Resource
    Electronic Resource
    Do phospholipids and sucrose determine membrane phase transitions in dehydrating pollen species? (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 15 (1992), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gel-to-liquid crystalline transition temperatures (Tm) of phospholipids of five desiccation tolerant pollen species in vivo were compared at various levels of dehydration. In an attempt to explain chemically the differences in Tm between these species, phospholipids and soluble carbohydrate contents were examined. We observed a negative correlation between the number of double bonds per phospholipid and Tm values for the intact pollen. This negative correlation also applied to Tm and the relative amount of linolenic acid. For the purpose of comparing Tm values of pollen and of unsaturated PCs (from the literature), the relative amounts and degree of unsaturation of pollen PCs were determined. A discrepancy between Tm values of individual PCs and intact pollen is discussed. Sucrose is the major soluble carbohydrate in 15 pollen species tested, generally making up a considerable part of the dry weight. A positive correlation between sucrose content (either as a percentage of the dry weight or as grams sucrose per grams phospholipid) and Tm was established. This unexpected result was explained in terms of alternative adaptive strategies. We suggest that, for desiccation tolerance, pollen either has to contain sucrose for the protection of its phospholipids, or have a high degree of fatty acid unsaturation in its phospholipids. The advantages and disadvantages of the two options are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1992.tb01494.x
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  • 6
    Electronic Resource
    Electronic Resource
    Acquisition of desiccation tolerance in developing wheat embryos correlates with appearance of a fluid phase in membranes (2003)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 26 (2003), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Membrane behaviour in developing wheat (Triticum aestivum cv Priokskaya) embryos was studied in relation to the acquisition of desiccation tolerance, using spin probe techniques. Fresh embryos were able to develop into seedlings at day 15 after anthesis, but it took 18 d before fast-dried, isolated embryos could germinate. On the basis of membrane integrity measurements it was estimated that between 14 and 18 d after anthesis the proportion of embryonic cells surviving fast drying increased and the critical moisture content, to which embryonic cells could be dehydrated, decreased. Apparently, embryonic cells do not acquire the same level of desiccation tolerance simultaneously. Only when all cells had become desiccation tolerant was germination of air-dried embryos possible. Using 5-doxylstearic acid as the probe molecule, an approximately similar lipid–water interface ordering of membranes was observed in all hydrated embryos, irrespective of age. Dehydration had a dual effect on the lipid interface: further ordering of the major part of the interface and the appearance of additional, disturbed regions. The proportion of these regions correlated with the proportion of desiccation-tolerant cells. We propose that the membrane surface disturbance be caused by endogenous amphiphiles that partition from the cytoplasm into membranes during drying. The absence of such disturbed regions in dried, desiccation-sensitive embryos might reflect a lack of sufficient amphiphiles. The relevance of membrane surface disturbance for desiccation tolerance is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2003.01098.x
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  • 7
    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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