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  • 1
    ISSN: 1432-2048
    Keywords: Cytochromes ; Energy charge ; Germination (pollen) ; Mitochondrial development ; Pollen ; Protein synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Bi-and trinucleate pollen generally differ in the extent of their mitochondrial development at anther dehiscence and in the rate of their attainment of maximum-phosphorylative capacity during germination in vitro, as judged from experiments with representatives of both groups. The typically trinucleate pollen of Aster tripolium L. immediately respired at a high rate, maintaining a high energy charge. Mitochondria attained maximum electron-transducing capacity within 2 min of incubation, while tube growth started within 3 min. In contrast, the binucleate pollen of Typha latifolia L. only gradually reached a relatively low rate of respiration, concomitant with a temporary decrease in energy charge, upon immersion in the germination medium. Development of the mitochondrial, electrontransducing system occurred in about 75 min, after which the first pollen tubes emerged. Starting from a poor differentiation, mitochondria became increasingly normal in appearance as germination proceeded. The binucleate pollen of Nicotiana alata Link et Otto and Tradescantia paludosa Anders. et Woods. showed intermediate characteristics: Nicotiana resembled Typha but mitochondria developed at a higher rate; Tradescantia germinated more rapidly and resembled the trinucleate pollen of Aster. Inhibitors of mitochondrial or cytoplasmic protein synthesis failed to affect the development of the mitochondrial, respiratory capacities during pollen germination. It is concluded that the duration of the lag period is determined by the level and rate of mitochondrial development and not by the division of the generative cell.
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  • 2
    ISSN: 1432-2048
    Keywords: Germination (pollen) ; Pollen ; Polyribosomes ; Protein synthesis ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Under humid conditions, both bi- and trinucleate pollen species incorporate, on the average, very low amounts of leucine, e.g., 0.4 pmol min-1mg pollen-1. During germination in vitro, however, the two types of pollens greatly differ in their capacity for protein synthesis. Binucleate pollen species such as Typha, which are characterized by slow respiration in humid air and prolonged lag periods during germination in vitro, contain large amounts of monoribosomes at dehiscence. Polyribosomes are formed soon after the pollen is wetted in the germination medium, and a considerable incorporation of leucine is initiated after 10–15 min. More rapidly respiring, binucleate pollen showing a short lag period, such as Tradescantia, may already contain many polysomes at dehiscence and incorporate leucine within 2 min of germination. However, rapidly respiring, trinucleate Compositae pollen contains very limited amounts of ribosomal material and never attains any substantial level of incorporation. Cycloheximide completely inhibits both protein synthesis and tube emergence and growth in the slowly respiring, binucleate pollen species. The more rapidly respiring types are less dependent on protein synthesis, while germination of the phylogenetically advanced, trinucleate Compositae pollen proceeds completely independently. It is concluded that the level of phylogenetic advancement of the male gametophyte is characterized by its overall state of metabolic development at dehiscence rather than by the number of its generative cells.
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  • 3
    ISSN: 1432-2145
    Keywords: Narcissus poeticus ; Papaver rhoeas Typha latifolia ; Free fatty acids ; Lipid deesterification Lysophospholipids ; Pollen storage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Declining viability of pollen during storage at 24° C in atmospheres of 40% relative humidity (RH) and 75% RH was studied, with special emphasis on lipid changes. Pollens of Papaver rhoeas and Narcissus poeticus, characterized by a high linolenic acid content, were compared with Typha latifolia pollen which has a low linolenic acid content. The rationale behind this was to answer the question of whether lipid peroxidation is involved in the rapid viability loss and reduced membrane integrity of, in particular, the unsaturated-lipid pollen types. Viability and membrane integrity degraded more rapidly at 75% RH than at 40% RH. All pollen species showed deesterification of acyl chains of lipids but no detectable peroxidation at both RH levels. Considerable amounts of lipid-soluble antioxidants were detected that did not degrade during storage. Free fatty acids and lysophospholipids were formed during storage, the effects of which on membranes are discussed. These degradation products were very prominent in the short-lived Papaver pollen. The loss of viability does coincide with phospholipid deesterification. A significant decrease of the phospholipid content occurred at 75% RH, but not at 40% RH. Based on compositional analyses of phospholipids and newly formed free fatty acids, it was concluded that the deesterification of acyl chains from the lipids occurred at random. We suggest that, due to the low water content of the pollen, free radicals rather than unspecific acyl hydrolases are involved in the deesterification process.
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  • 4
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Germplasm must be stored under optimal conditions to maximize longevity and efficiently maintain genetic resources. In order to identify optimal storage conditions, we investigated the effects of temperature (−5 to 45°C) and water content (〈0.17 g H2O g−1 dry weight) on longevity of Typha latifolia L. pollen. Longevity was highest at water contents corresponding to storage relative humidity (RH) of 11-15% which corresponded to the shoulder of water sorption isotherms. Also coinciding with this shoulder were abrupt changes in heat capacity of water present in the pollen. Consistent with changes in isotherms with temperature and the concept of critical RH for storage, optimum water contents increased with decreasing temperature. An attempt was made to explain the aging behavior according to the glass concept. The water content-temperature combinations of optimal storage were found to be below the glass transition curve, indicating that optimum storage conditions are achieved when intracellular glasses are present. We also found a change in activation energy of aging in Arrhenius plots around Tg, demonstrating a change in aging kinetics when the glassy state is lost. We concluL that Tg curves cannot be used solely to predict precise conditions of optimum storage, but might be useful for predictions of storage longevity above optimum water contents. The data imply that too much drying reduces longevity and should be avoided, particularly when cryogenic storage is considered.
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  • 5
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In previous studies on the causes of imbibitional leakage in dry polien we have presented data which suggest that the leakage is due to a gel to liquid crystalline phase transition in membrane phospholipids during the rehydration event. In the present study we greatly extend and confirm those results. A supplemented phase diagram for the hydration dependent transition temperature of membrane phospholipids in pollen is presented. In pollen containing 〉 0.05 g H2O g−1 dry weight at the time of imbibition, this phase diagram for the phospholipids precisely predicts the conditions for rehydration under which germination is maximal and leakage is minimal. However, in extremely dry pollen, containing 〈 0.05 g H2O g−1 dry weight the predictive value of the phase diagram for phospholipids in the pollen is not in agreement with data for germination and leakage. Thus, an alternative explanation must be sought for leakage in these circumstances. We examined the available evidence and suggest here that a modified form of the non-bilayer phase hypothesis proposed by Simon (1974) may apply in the specialized case of extremely dry cells.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 48 (1980), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The equal rates of water vapour absorption by both bi- and trinucleate pollen indicate that their widely-differing rates of respiration have an intrinsic, biochemical basis. This was investigated with various metabolic inhibitors that were previously introduced into dry pollen via anhydrous acetone.The uncoupler, carbonyl cyanide m-chlorophenyl hydrazone, inhibited the O2 uptake of rapidly respiring pollen and stimulated that of slowly respiring types to similar absolute values, that probably reflect the rates of substrate transport across the mitochondrial membranes.The extent of inhibition of the O2 uptake by oligomycin, dicyclohexyl carbodiimide, antimycin A, and salicyl hydroxamic acid, alone and in combinations, indicates that hardly any oxidative phosphorylation and anabolic activities occur in slowly respiring, binucleate pollen species, having low-developed mitochondria and high energy charge values. The presence of the alternative pathway was insignificant.In other binucleate pollen species, characterized by recognizable mitochondria and low energy charge values, a limited ATP synthesis was established. The low energy charge values point to imbalance between phosphorylative and anabolic activities.In rapidly respiring, trinucleate pollen, containing well-developed mitochondria, a significant activity of the alternative oxidase was found. The energy charge values were high notwithstanding the large demand for ATP, mounting to 1.7 μmol h−1 (mg pollen)−1.In some pollen species, oligomycin highly stimulated the flow of electrons through the cytochrome pathway, which made an estimation of the ATP synthesis impossible.
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 34 (1975), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The respiration and vitality of ungerminated bi- and trinucleate pollen were studied in order to determine the influence of relative humidity and temperature on metabolic activity. The gas exchange, germination capacity and staining with tetrazolium bromide were followed under standardized conditions.A constant respiration rate occurred under conditions of high relative humidity (97%). Per mg pollen, the trinucleate grains of Compositae and Gramineae respired 2 to 3 times as intense as 6 species of binucleate grains. Per unit of pollen protein the differences were even larger. In contrast to binucleate pollen, the longevity of trinucleate pollen was very short and the ability to germinate was lost twice as fast as the respiration capacity. This limits the use of tetrazolium bromide as an indicator of viability.At reduced relative humidities respiration was strongly restricted, but the longevity of bi- and trinucleate pollen considerably increased.Pollen of Gramineae, however, was very sensitive to changes in relative humidity; short exposure to low relative humidity decreased both the vitality and the capacity to respire.
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  • 8
    ISSN: 1573-6881
    Keywords: Phase transitions ; phospholipids ; water ; desiccation ; dehydration ; anhydrobiosis ; imbibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Dry phospholipid bilayers are known to undergo transient changes in permeability during rehydration. In this review, we present evidence from which we suggest that this permeability change is due to a gel to liquid-crystaline phase transition accompanying rehydration. If the transition is avoided, as in lipids that remain in gel phase whether dry or rehydrated, the problem of leakage during rehydration is obviated, at least in part. Further, the evidence that the transition temperature for dry bilayers can be depressed by certain sugars is discussed. Finally, we show that these principles can be extended to intact cells. Using pollen grains as a model, we have measured the transition temperature for membrane phospholipids and show that the transition is correlated with physiological measurements including permeability changes and subsequent germination. From theT m values taken from pollen grains at different water contents, we have constructed a phase diagram for the intact pollen that has high predictive value for physiological properties.
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  • 9
  • 10
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