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  • Sieve tube  (3)
  • Torpor  (3)
  • Springer  (6)
  • American Geophysical Union (AGU)
  • American Institute of Physics (AIP)
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  • Springer  (6)
  • American Geophysical Union (AGU)
  • American Institute of Physics (AIP)
Years
  • 1
    Electronic Resource
    Electronic Resource
    Ecology of natural hibernation in the marsupial mountain pygmy-possum (Burramys parvus) (1998)
    Springer
    Oecologia 113 (1998), S. 170-178 
    Details
    ISSN: 1432-1939
    Keywords: Key words Alpine ; Natural hibernation ; Marsupial ; Pygmy-possum ; Torpor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The hibernating marsupial mountain pygmy-possum (Burramys parvus, 40 g) has to raise its slow-growing offspring during a short alpine summer. Only females provide parental care, while after mating males emigrate to marginal habitats often at lower altitudes which can sustain only low possum densities. We predicted that the hibernation strategies in mountain pygmy-possums are distinct from those of similar-sized placental hibernators, because of the developmental constraints in marsupials and because hibernation differs between the sexes. Using temperature-sensitive radio transmitters, we studied the hibernation patterns of free-living male and female mountain pygmy-possums living in a north- and a south-facing boulder field (Kosciusko National Park) for two consecutive winters. Individual possums commenced hibernation several months before the snow season. As in other hibernators, torpor in the mountain pygmy-possum was interrupted by periodic arousals which occurred most often during the late afternoon. Torpor bouts initially lasted a few days when the hibernacula temperature (T hib) ranged from 4 to 7°C. As the hibernation season progressed, torpor bouts became longer and possum body temperatures (T b) approached 2°C. The T bs of females were significantly lower and torpor bouts were longer in the second half of the hibernation season than in males. Between torpor bouts, both sexes were often active and left hibernacula for periods of up to 5 days. Especially during the first months of the hibernation season, possums also frequently changed hibernacula sites probably in an attempt to select a site with a more suitable microclimate. Emergence from hibernation was closely coupled with the disappearance of snow from the possum habitat (September 1995, October 1996) and the limited fat stores probably dictate an opportunistic spring emergence. However, in 1995, spring was early and males emerged significantly earlier than females. In 1996, when snow melt was delayed, this difference vanished. Testes are regressed in males during hibernation and the time needed for testes growth and spermatogenesis favours an earlier emergence for males which was probably achieved by their preference for the more sun exposed north-facing boulder field. A sexual dimorphism in hibernation strategies and spring emergence therefore enables mountain pygmy-possums to cope with their harsh alpine environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050365
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  • 2
    Electronic Resource
    Electronic Resource
    Seasonal changes in energetics and torpor patterns in the subtropical blossom-bat Syconycteris australis (Megachiroptera) (1998)
    Springer
    Oecologia 113 (1998), S. 467-473 
    Details
    ISSN: 1432-1939
    Keywords: Key words Energetics ; Torpor ; Subtropical ; Nectar availability ; Thermoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Little is known about how animals from tropical and subtropical climates adjust their energy expenditure to cope with seasonal changes of climate and food availability. To provide such information, we studied the thermal physiology, torpor patterns and energetics of the nocturnal blossom-bat (Syconycteris australis 18 g) from a subtropical habitat in both summer and winter. In both seasons, S. australis frequently entered daily torpor at ambient temperatures between 12 and 25°C when food and water were withheld. Unlike patterns observed in temperate animals, mean minimum metabolic rates during torpor were lower in summer (0.47 ± 0.07 ml O2 g−1 h−1) than in winter (0.75 ± 0.11 ml O2 g−1 h−1). Body temperatures during torpor were regulated at 19.3 ± 1.0°C in summer and at 23.4 ± 2.0°C in winter. Torpor bout duration was significantly longer in summer (7.3 ± 0.6 h) than in winter (5.5 ± 0.3 h), but in both seasons, bout duration was not affected by ambient temperature. Consequently, average daily metabolic rates were also significantly lower in summer than in winter. Body temperatures and metabolic rates in normothermic bats did not change with season. Our findings on seasonal changes of torpor in this bat from the subtropics are opposite to those made for many species from cold climates which generally show deeper and longer torpor in winter and are often entirely homeothermic in summer. More pronounced torpor in subtropical S. australis in summer may be due to low or unpredictable nectar availability, short nights which limit the time available for foraging, and long days without access to food. Thus, the reversed seasonal response of this subtropical bat in comparison to temperate species may be an appropriate response to ecological constraints.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050399
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  • 3
    Electronic Resource
    Electronic Resource
    Microautoradiographic studies of phloem loading and transport in the leaf of Zea mays L. (1983)
    Springer
    Planta 159 (1983), S. 193-206 
    Details
    ISSN: 1432-2048
    Keywords: Assimilate transport ; Leaf (14C transport) ; Phloem loading ; Sieve tube ; Vascular bundle ; Zea (14C transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microautoradiographs showed that [14C]sucrose taken up in the xylem of small and intermediate (longitudinal) vascular bundles of Zea mays leaf strips was quickly accumulated by vascular parenchyma cells abutting the vessels. The first sieve tubes to exhibit 14C-labeling during the [14C]sucrose experiments were thick-walled sieve tubes contiguous to the more heavily labeled vascular parenchyma cells. (These two cell types typically have numerous plasmodesmatal connections.) With increasing [14C]sucrose feeding periods, greater proportions of thick- and thin-walled sieve tubes became labeled, but few of the labeled thin-walled sieve tubes were associated with labeled companion cells. (Only the thin-walled sieve tubes are associated with companion cells.) When portions of leaf strips were exposed to 14CO2 for 5 min, the vascular parenchyma cells-regardless of their location in relation to the vessels or sieve tubes-were the most consistently labeled cells of small and intermediate bundles, and label (14C-photosynthate) appeared in a greater proportion of thin-walled sieve tubes than thick-walled sieve tubes. After a 5-min chase with 12CO2, the thin-walled sieve tubes were more heavily labeled than any other cell type of the leaf. After a 10-min chase with 12CO2, the thin-walled sieve tubes were even more heavily labeled. The companion cells generally were less heavily labeled than their associated thin-walled sieve tubes. Although all of the thick-walled sieve tubes were labeled in portions of leaf strips fed 14CO2 for 5 min and given a 10-min 12CO2 chase, only five of 72 vascular bundles below the 14CO2-exposed portions contained labeled thick-walled sieve tubes. Moreover, the few labeled thick-walledsieve tubes of the “transport region” always abutted 14C-labeled vascular parenchyma cells. The results of this study indicate that (1) the vascular parenchyma cells are able to retrieve at least sucrose from the vessels and transfer it to the thick-walled sieve tubes, (2) the thick-walled sieve tubes are not involved in long-distance transport, and (3) the thin-walled sieve tubes are capable themselves of accumulating sucrose and photosynthates from the apoplast, without the companion cells serving as intermediary cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397525
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  • 4
    Electronic Resource
    Electronic Resource
    Daily torpor and thermoregulation in antechinus (Marsupialia): influence of body mass, season, development, reproduction, and sex (1988)
    Springer
    Oecologia 77 (1988), S. 395-399 
    Details
    ISSN: 1432-1939
    Keywords: Antechinus ; Body mass ; Season ; Torpor ; Thermoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Season and body mass influence torpor in mammals. However, the effects of the two factors are often difficult to distinguish because body mass in many species changes with season. The present study attempted to separate seasonal and body mass related alterations of torpor. Adult female Antechinus stuartii and A. flavipes (Marsupialia), which were about half the size of males of the respective species, showed longer and deeper torpor than males. When the two species were compared, torpor in A. stuartii, the smaller species, was more pronounced than in A. flavipes. Juveniles of both species had lower body temperatures and longer torpor durations than adults. Torpor was most pronounced in juvenile males during summer; in winter, when males had grown to adult size, the use of torpor was reduced. Seasonal changes in torpor of adults were not distinct. These results suggest that the influence of body mass on torpor in these Antechinus species is stronger than that of season.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378050
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  • 5
    Electronic Resource
    Electronic Resource
    Microautoradiographic studies of the role of mesophyll and bundle tissues of the Ricinus cotyledon in sucrose uptake (1991)
    Springer
    Planta 183 (1991), S. 251-257 
    Details
    ISSN: 1432-2048
    Keywords: Companion cell ; Membrane potential ; Ricinus ; Sieve tube ; Spongy mesophyll ; Sucrose (uptake, accumulation)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The aim of the study was to show which tissues and cell types of the cotyledon of Ricinus communis L. are responsible for uptake of sucrose by H+-sucrose symport. The cotyledons were incubated in labelled sucrose for up to 20 min and then the amount of radioactivity in each cell type of the cotyledon was assessed by microautoradiography. It was found that 50% of the label was present in the spongy mesophyll, and 10–15% was in the bundles, the epidermal layers and the palisade parenchyma. The sieve tubes contained only 2–3% of the label. The addition of sucrose to cotyledons depolarized the membrane of spongy-mesophyll cells by 33 mV. Therefore, it was concluded that the previously found H+-sucrose symport is at least partly located at the spongy mesophyll. No precursor-like behaviour of the label in mesophyll or bundle-sheath cells was observed in pulse-chase experiments, which indicates a direct uptake of sucrose by the sieve tube-companion cell complex from the apoplast.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197796
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  • 6
    Electronic Resource
    Electronic Resource
    Loading and transport of assimilates in different maize leaf bundles (1989)
    Springer
    Planta 178 (1989), S. 1-9 
    Details
    ISSN: 1432-2048
    Keywords: Leaf (assimilate transport) ; Phloem loading ; Phloem transport ; Sieve tube ; Vascular bundle ; Zea (assimilate transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The loading and transport functions of vascular bundles in maize (Zea mays L.) leaf strips were investigated by microautoradiography after application of 14CO2. The concentrations of 14C-contents in thin-walled sieve tubes of individual bundles in the loading and transport regions were determined by digital image analysis of silver-grain density over the sieve tubes and compared. In the loading region, relatively high concentrations of 14C-contents were found in the thin-walled sieve tubes of small bundles and in the small, thin-walled sieve tubes of the intermediate bundles; the concentration of 14C-label in large bundles was very low. In the transport region, at a transport distance of 2 cm, all of the small bundles contained 14C-assimilates, but generally less than the same bundles did in the loading region; by comparison, at that distance intermediate and large bundles contained two-to threefold more 14C-assimilates than the same bundles in the loading region. The lateral transfer of assimilates from smaller to larger bundles via transverse veins could be demonstrated directly in microautoradiographs. A reverse transport from larger to smaller bundles was not found. At a transport distance of 4 cm, all large and intermediate bundles were 14C-labeled, but many of the small bundles were not. Although all longitudinal bundles were able to transport 14C-asimilates longitudinally down the blade, it was the large bundles that were primarily involved with longitudinal transport and the small bundles that were primarily involved with loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392520
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