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  • 1
    Electronic Resource
    Electronic Resource
    The possible role of calcitonin deficiency in the development of bone disease due to chronic renal failure (1976)
    Springer
    Calcified tissue international 22 (1976), S. 147-153 
    Details
    ISSN: 1432-0827
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02064056
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  • 2
    Electronic Resource
    Electronic Resource
    Altitudinal changes in the incidence of crassulacean acid metabolism in vascular epiphytes and related life forms in Papua New Guinea (1987)
    Springer
    Oecologia 73 (1987), S. 566-572 
    Details
    ISSN: 1432-1939
    Keywords: δ13C ; CAM ; Epiphytes ; Tropical habitat ; Altitude
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The occurrence of Crassulacean acid metabolism (CAM), as judged from δ13C values, was investigated in epiphytes and some related plant species at a series of sites covering the approximate altitudinal range of epiphytes in Papua New Guinea. Comprehensive collections were made at each site and the occurrence of water storage tissue and blade thickness was also determined. Some 26% of epiphytic orchids from a lowland rainforest (2–300 m.a.s.l) showed δ13C values typical of obligate CAM and possessed leaves thicker than 1 mm. A second group of orchids, mostly with succulent leaves, possessed intermediate δ13C values between -23 and -26% and accounted for 25% of the total species number. Some species of this group may exhibit weak CAM or be facultative CAM plants. The remainder of the lowland rainforest species appeared to be C3 plants with δ13C values between -28 and -35%. and generally possessed thin leaves. Obligate CAM species of orchids from a lower montane rainforest (1175 m.a.s.l) comprised 26% of the species total and mostly possessed thick leaves. The remainder of the species were generally thin-leaved with δ13C values between -26 and -35%. largely indicative of C3 photosynthesis. Orchids with intermediate δ13C values were not found in the lower montane rainforest. Obligate CAM appeared to be lacking in highland epiphytes from an upper montane rainforest and subalpine rainforest (2600–3600 m.a.s.l). However the fern, Microsorium cromwellii had a δ13C value of -21.28%. suggesting some measure of CAM activity. Other highland ferns and orchids showed more negative °13C values, up to-33%., typical of C3 photosynthesis. The highland epiphytic orchids possessed a greater mean leaf thickness than their lowland C3 counterparts due to the frequent occurrence of water storage tissue located on the adaxial side of the leaf. It is suggested that low daytime temperatures in the highland microhabitats is a major factor in explaining the absence of CAM. The increased frequency of water storage tissue in highland epiphytes may be an adaptation to periodic water stress events in the dry season and/or an adaptation to increased levels of UV light in the tropicalpine environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379417
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  • 3
    Electronic Resource
    Electronic Resource
    Photosynthetic pathway, chilling tolerance and cell sap osmotic potential values of grasses along an altitudinal gradient in Papua New Guinea (1990)
    Springer
    Oecologia 84 (1990), S. 280-288 
    Details
    ISSN: 1432-1939
    Keywords: Altitude ; C3/C4 photosynthesis ; Chilling tolerance ; Frost hardiness ; Tropical habitat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A total of 22 grass species were examined from 5 sites spanning the altitudinal range 1550–4350 m.a.s.l. The presence of the C3 or C4 photosynthetic pathway was determined from δ13C values and chilling tolerance was assessed on the basis of electrolyte leakage from leaf slices incubated on melting ice. Most of the grasses studied at the lower altitude sites of 1550 m.a.s.l. (annual mean of daily minimum temperature, 14.6° C) and 2600 m.a.s.l. (9.4° C) possessed C4 photosynthesis and were chill-sensitive. The single except ion was Agrostis avenacea, a montane chill-resistant C3 species which occurred at 2600 m.a.s.l. The three species apparently most sensitive to chilling were Ischaemum polystachyum, Paspalum conjugatum and Saccharum robustum, all occurring at 1550 m.a.s.l. At the higher altitude sites of 3280 (5.6° C), 3580 (4.0° C) and 4350 (−0.7°C) m.a.s.l., most of the grasses exhibited C3 photosynthesis and were chill-resistant. However, an Upland population of the C4 species, Miscanthus floridulus was found at 3280 m.a.s.l. which had acquired chill-resistance as confirmed by additional in vivo variable chlorophyll fluorescence measurements. Cell sap osmotic potential values of the upland grasses at altitudes of 3280–4350 m.a.s.l. were lower (−8.1 to −19.8 bars) than values in grasses from 1550 and 2600 m.a.s.l. (−3.9 to −7.5 bars) due mainly to the presence of non-electrolyte osmoticants, which may be involved in frost avoidance mechanism(s).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318285
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  • 4
    Electronic Resource
    Electronic Resource
    Leaf anatomy, water relations and crassulacean acid metabolism in the chlorenchyma and colourless internal water-storage tissue of Carpobrotus edulis and Senecio ?mandraliscae (1987)
    Springer
    Planta 170 (1987), S. 421-432 
    Details
    ISSN: 1432-2048
    Keywords: Carpobrotus (water relations) ; Chlorenchyma ; Crassulacean acid metabolism ; Senecio (water relations) ; Tannin cells ; Water relations (leaf) ; Water-storage tissue
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Both Carpobrotus edulis and Senecio ?mandraliscae possess leaves with a peripheral chlorenchyma and colourless internal water-storage tissue. Water stress in C. edulis growing under semi-natural conditions resulted in the induction of weak Crassulacean acid metabolism (CAM) whereas well-watered plants of S. ?mandraliscae exhibited a similar degree of CAM. Titratable acidity in the separated water-storage tissue was substantially lower than in the chlorenchyma in both species but, nevertheless, increased during the night and decreased during the day either when sampled from the intact plant or from incubated tissue slices. Indeed, the increase in nocturnal titratable acidity produced by the water-storage tissue in situ accounted for approx. 30% of total acidification on a per-leaf basis. It appears that during the night the water-storage tissue in these species is able to fix CO2 which is subsequently released during the day to enter the photosynthetic carbon-reduction cycle of the chlorenchyma. Diurnal rhythms of water potential (Ψ) and osmotic potential (Ψs) were measured in separated chlorenchyma and water-storage tissue by thermocouple psychrometry. Both parameters increased during the latter part of the daytime and initial nocturnal period and decreased during the rest of the night and into the post-dawn period. The chlorenchyma of water-stressed plants of C. edulis appeared to possess a marked negative turgor pressure (as determined from Ψ-Ψs) but this was caused by a severe underestimation in the measurement of the chlorenchyma Ψ. It is suggested that this artefact arose from release of colloidal polysaccharide mucilage, or possibly tannins, from broken tannin cells producing a lowering of water activity when measured using thermocouple psychrometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00395036
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  • 5
    Electronic Resource
    Electronic Resource
    Acclimation of potassium influx in rye (Secale cereale) to low root temperatures (1987)
    Springer
    Planta 171 (1987), S. 377-385 
    Details
    ISSN: 1432-2048
    Keywords: Acclimation (K+ influx) ; Low temperature (root) ; Potassium influx (regulation) ; Secale (K+ influx) ; Shoot/root ratio
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influx of K+(86Rb+) into intact roots of rye (Secale cereale L. cv. Rheidal) exposed to a differential temperature (DT) between the root (8° C) and shoot (20° C) is initially reduced compared with warm-grown (WG) controls with both shoot and root maintained at 20° C. Over a period of 3 d, however, K+-influx rates into DT plants are restored to levels similar to or greater than those of the WG controls, the absolute rates of K+ influx being strongly dependent upon the shoot/root ratio. Acclimation in DT plants results in a reduction of K+ influx into the apical (0–2 cm) region of the seminal root which is associated with a compensatory increase in K+ influx into the more mature, basal regions of the root. Values of V max and apparent K m for K+ influx into DT plants were similar to those for WG plants at assay temperatures of 8° C and 20° C except for an increase in the apparent K m at 8° C. The influx of K+ from solutions containing 0.6 mol·m-3 K+ into both WG and DT plants was found to be linearly related to assay temperature over the range 2–27° C, and the temperature sensitivity of K+ influx to be dependent upon shoot/root ratio. At high shoot/root ratios, the ratio of K+ influx at 20° C:K+ influx at 8° C for WG plants approached a minimum value of 1.9 whereas that for DT plants approached unity indicating that K+ influx into DT plants has a large temperature-insensitive component. Additionally, when plants were grown in solutions of low potassium concentration, K+ influx into DT plants was consistently greater than that into WG plants, in spite of having a greater root potassium concentration ([K+]int). This result indicates some change in the regulation of K+ influx by [K+]int in plants exposed to low root temperatures. We suggest that K+ influx into rye seedlings exposed to low root temperatures is regulated by the increased demand placed on the root system by a proportionally larger shoot and that the acclimation of K+ influx to low temperatures may be the result of an increased hydraulic conductivity of the root system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00398683
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  • 6
    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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  • 7
    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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