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  • 1
    Electronic Resource
    Electronic Resource
    Spatial and temporal variability in forest–atmosphere CO2 exchange (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Seven years of carbon dioxide flux measurements indicate that a ∼90-year-old spruce dominated forest in Maine, USA, has been sequestering 174±46 g C m−2 yr−1 (mean±1 standard deviation, nocturnal friction velocity (u*) threshold 〉0.25 m s−1). An analysis of monthly flux anomalies showed that above-average spring and fall temperatures were significantly correlated with greater monthly C uptake while above-average summer temperatures were correlated with decreased net C uptake. Summer months with significantly drier or wetter soils than normal were also characterized by lower rates of C uptake. Years with above-average C storage were thus typically characterized by warmer than average spring and fall temperatures and adequate summer soil moisture.Environmental and forest–atmosphere flux data recorded from a second tower surrounded by similar forest, but sufficiently distant that flux source regions (‘footprints’), did not overlap significantly showed almost identical temperature and solar radiation conditions, but some differences in energy partitioning could be seen. Half-hourly as well as integrated (annual) C exchange values recorded at the separate towers were very similar, with average annual net C uptake differing between the two towers by 〈6%. Interannual variability in net C exchange was found to be much greater than between tower variability. Simultaneous measurements from two towers were used to estimate flux data uncertainty from a single tower. Carbon-flux model parameters derived independently from each flux tower data set were not significantly different, demonstrating that flux towers can provide a robust method for establishing C exchange model parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2004.00847.x
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  • 2
    Electronic Resource
    Electronic Resource
    High growing temperatures reduce fruit carbohydrate and vitamin C in kiwifruit (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Kiwifruit vines are perennial plants grown in climates varying from maritime to continental. To determine key responses to temperature, vines were heated at different stages of fruit development, and vine growth and fruit composition examined. Heating vines during fruit starch accumulation caused a major shift in partitioning towards vegetative growth and dramatically reduced fruit carbohydrate and vitamin C. In the following season, growth and flowering were severely reduced. Heating vines during fruit cell division had minimal long-term effects, whereas heating during fruit maturation delayed starch degradation and fruit ripening and affected growth in the following season. When vines were removed from heat, fruit dry matter, starch and sugar levels were always reduced but hexose : sucrose ratios and inositol were raised. Heating vines affected expression of two sucrose synthase genes, but this did not correlate with reduction in fruit carbohydrate. Activity and expression of l-galactose dehydrogenase decreased as fruit developed, suggesting some vitamin C biosynthesis must take place in the fruit. Activity and expression of actinidin increased in response to heat. The results of this study have demonstrated both short and long-term plant responses to elevated temperatures in woody perennials, and that the timing of heat exposure has severe consequences for vitamin C levels in fruit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2003.01161.x
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  • 3
    Electronic Resource
    Electronic Resource
    Acid phosphomonoesterase and phytase activities of wheat (Triticum aestivum L.) roots and utilization of organic phosphorus substrates by seedlings grown in sterile culture (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: Wheat seedlings exhibited a differential ability to utilize P from a range of organic P substrates when grown in agar culture under sterile conditions. Plants showed limited ability to obtain P from inositol hexaphosphate (IHP), whereas other monoester substrates such as glucose 1-phosphate (G1P), were equivalent sources of P for plant growth as compared with inorganic phosphate (Pi). Poor utilization of IHP was exemplified by significantly lower rates of dry matter accumulation and reduced P content of tissues, which were generally not significantly different to control plants that were grown in the absence of added P. The inability of wheat seedlings to obtain P from IHP was not associated with poor substrate availability but was due to either insufficient root phytase activity or inappropriate localization of phytase within root tissues. Phytase activities of 4 and 24 mU g−1 root fresh weight (FW) were determined for crude root extracts prepared from plants that were grown with either adequate P or under deficient conditions, respectively. Similar levels of phytase activity (approximately 12 mU g−1 FW) were observed in assays using intact roots, although no secreted activity was detected. By comparison, a secreted acid phosphomonoesterase activity was observed, and activities of between 466 and 1029 mU phosphomonoesterase g−1 root FW were measured for intact roots. On the basis of the differences in enzyme activity, and the observed differences in the ability of wheat seedlings to utilize G1P and IHP, it is evident that low intrinsic levels of phytase activity in wheat roots is a critical factor that limits the ability of wheat to obtain P from phytate when supplied in agar under non-limiting conditions. This hypothesis was further supported by the observation that the ability of wheat to obtain P from IHP was significantly improved when the seedlings were inoculated with a soil bacterium (Pseudomonas sp. strain CCAR59) that possesses phytase activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00557.x
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  • 4
    Electronic Resource
    Electronic Resource
    Characterization of transgenic Trifolium subterraneum L. which expresses phyA and releases extracellular phytase: growth and P nutrition in laboratory media and soil (2004)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 27 (2004), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Transgenic Trifolium subterraneum expressing a phytase gene (phyA) from Aspergillus niger were generated. Five independently transformed lines showed an average 77-fold increase in exuded phytase activity in comparison with null segregant and wild-type controls. Unlike other phosphatases, exuded phytase activity was unaffected by P supply, verifying the constitutive expression of phyA. Transgenic T. subterraneum grown in agar with P supplied as phytate, took up 1.3- to 3.6-fold more P than controls and had equivalent P uptake to plants supplied with orthophosphate. This unique phenotype was compromised when the plants were grown in soil. None of the five lines showed increased shoot biomass or total P uptake in an unfertilized, low-P soil taken from under permanent pasture. With addition of P, one of the five transgenic lines had consistently greater P nutrition compared with control plants. Despite variable growth and P nutrition responses, P uptake per root length was on average greater for transgenic lines. Exudation of phytase by transgenic T. subterraneum allowed utilization of P from phytate in non-sorbing, sterile laboratory media, but was less effective when plants were grown in soil. Release of extracellular phytase is therefore not the only requirement for the acquisition of P from endogenous soil phytate by plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2004.01225.x
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  • 5
    Electronic Resource
    Electronic Resource
    Mismatch repair and the regulation of phase variation in Neisseria meningitidis (2001)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 40 (2001), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Neisseria meningitidis controls the expression of several genes involved in host adaptation by a process known as phase variation. The phase variation frequency of haemoglobin (Hb) receptors among clinical isolates of serogroups A, B and C differed drastically, ranging from ≈ 10−6 to 10−2 cfu−1. Frequencies of phase variation are a genetic trait of a particular strain, as two unlinked Hb receptors, hpuAB and hmbR, phase varied with similar frequencies within a given isolate. Based on these frequencies, six Neisserial clinical isolates could be grouped into three distinct classes; slow, medium and fast. An increase in phase variation frequency was accompanied by high rates of spontaneous mutation to rifampicin and nalidixic acid resistance in one medium and one fast strain. The remaining three medium strains displayed elevated levels of phase variation without increases in overall mutability, as they possessed low rates of spontaneous mutation to drug resistance. The mismatch repair system of N. meningitidis was found to play an important role in determining the overall mutability of the clinical isolates. Inactivation of mismatch repair in any strain, regardless of its original phenotype, increased mutability to a level seen in the fast strain. Insertional inactivation of mutS and mutL in the slow strain led to 500- and 250-fold increases in hmbR switching frequency respectively. Concurrently, the frequency of spontaneous point mutations of mutS and mutL mutants from the slow strain was increased 20- to 30-fold to the level seen in the high strain. The status of Dam methylation did not correlate with either the phase variation frequency of Hb receptors or the general mutability of Neisserial strains. Analysis of an expanded set of isolates identified defects in mismatch repair as the genetic basis for strains displaying both the fast Hb switching and high mutation rate phenotypes. In conclusion, elevated frequencies of phase variation were accompanied by increased overall mutability in some N. meningitidis isolates including strains shown to be mismatch repair defective. Other isolates have evolved mechanisms that seem to affect only the switching frequency of phase-variable genes without an accompanied increased accumulation of spontaneous mutations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2001.02408.x
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  • 6
    Electronic Resource
    Electronic Resource
    Increasing turbidity significantly alters the diet of brown trout: a multi-year longitudinal study (2004)
    Oxford, UK; Malden, USA : Blackwell Science Ltd
    Journal of fish biology 65 (2004), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The stomach contents of adult brown trout Salmo trutta from Lake Sorell, Tasmania, were analysed during 6 years of increasing turbidity to follow changes in the diet associated with dramatic changes in water clarity. Brown trout were sampled from 1996, when turbidity was 26 NTU, to 2001 when turbidity was 141 NTU. The mean relative volume of stomach contents decreased progressively to 2001, by which time it was only one sixth of that in 1996, and the mean diversity of prey in stomachs decreased from an average of more than six species per stomach in 1996 to one species in 2001. The species composition of stomach contents shifted from domination by the phreatoicid isopod Colubotelson sp., to the galaxiid fish Galaxias auratus and the amphipod Austrochiltonia australis, and then the cladoceran Daphnia carinata. To give an indication of diet changes over a typical yearly cycle in the current turbid state of the lake, a sample was taken from each season from December 2000 to September 2001. Two basic diets were found during the year; brown trout specialized on D. carinata in summer and autumn, and G. auratus in winter and spring. Mean diversity of prey was less than two species per stomach in all samples from 2000 to 2001, except for the sample from spring 2001 when it was 2·2 species per stomach, and the mean relative volume of stomach contents was more than three times greater in winter than any other season. The ways in which high turbidity may have influenced the changes in the brown trout diet observed since 1996 and the patterns evident during the seasons of 2000–2001 are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0022-1112.2004.00456.x
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  • 7
    Electronic Resource
    Electronic Resource
    Energy flux in a natural population of the land snail, Cepaea nemoralis L. (1975)
    Springer
    Oecologia 19 (1975), S. 141-164 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Energy flux in a population of Cepaea nemoralis L. living on a sand dune system was estimated in 1970 and 1971. Numbers and dynamics of the adults were studied by a capture-mark-recapture method, juveniles by quadrat sampling. Adult numbers were around a mean of 2.14 m-2 (mean annual biomass 14.7 kJ m-2 1970; 13.4 kJ m-2 1971). Eggs were laid in June, July and August and peak numbers of small juveniles (〈6 mm) were present in October (20.7 m-2 1970; 7.8 m-2 1971). Mortality rates of the small animals was high and in the following season (1971) density of the next size class (6–11 mm) was much lower (4.9 m-2). Mean annual biomass of the whole population was 17.0 kJ m-2 in 1970 and 16.4 kJ m-2 in 1971. Growth rates were slow and variable. Adult production was calculated as the yield to carnivores and scavengers plus the continuous mucus production which was almost half the total. Juvenile production was calculated from quadrat sampling data. Total population production was 34.3 kJ m-2 in 1970 and 25.9 kJ m-2 in 1971. Adult respiration was measured in an open flow respirometer with gas analysis by gas chromatograph. Measurements were made in 1971 on field acclimated animals. Juvenile respiration measurements were made in Warburg respirometers. Population respiratory losses were 62.8 kJ m-2 and 41.8 kJ m-2 in the 2 years. In the calculation of population respiration, allowance was made for low metabolic rates during periods of aestivation and hibernation. Population activity was reduced by 90% after 5 days without rain. Population consumption, was estimated at 316.6 kJ m-2 and 239.0 kJ m-2 and assimilation efficiencies were from 30–40% on natural foods. Annual energy budgets were constructed and energy flux (P+R) was 97.0 kJ m-2 in 1970 and 77.6 kJ m-2 in 1971. The plot of log respiration against log production fell lower than that for most long-lived poikilotherms due to the inflation of the production estimate by mucus production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00369098
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  • 8
    Electronic Resource
    Electronic Resource
    Food, feeding rates and assimilation in the land snail Cepaea nemoralis L. (1975)
    Springer
    Oecologia 19 (1975), S. 59-70 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The natural diet of a population of Cepaea nemoralis living in a sand dune system in southwest England was investigated by field observations and examination of crop and faeces contents. The food consisted of dead material from the commoner plants on the site. Very little green matter was eaten and there was little evidence for seasonal variation in the diet. Consumption and egestion rates were measured gravimetrically on natural foods (dead leaves of Taraxacum officinale and Ononis repens) and artificial foods. Consumption rates were temperature dependent over the measured range of 5–20°C and also varied with the food substrate, an artificial food (rat food pellets) being consumed at the highest rate. High variability in the results can probably be linked to the live weight and activity cycles of the snails. Assimilation was estimated as the difference between consumption and egestion, since a trial of the ash-ratio method proved unsuitable with this animal. Assimilation efficiency did not vary with temperature over the range studied, but was dependent on food substrate, the two artificial foods (rat food pellets and lettuce leaves) being assimilated more efficiently (71–73%) than natural foods (30–44%). Faeces produced from the digestive gland could be distinguished and were measured separately. The amount produced was very small compared to the gut faeces, but increased significantly when a relatively indigestible food was used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377590
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  • 9
    Electronic Resource
    Electronic Resource
    Hsp70 and aging (1994)
    Springer
    Cellular and molecular life sciences 50 (1994), S. 1092-1098 
    Details
    ISSN: 1420-9071
    Keywords: Aging ; liver ; transcription ; heat shock transcription factor ; rat ; senescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract An alteration in the ability of cells to express heat shock proteins could be physiologically important in aging because all living organisms show a reduced ability to respond to stress with increasing age. Using hepatocytes freshly isolated from young adult and old rats, we have shown that the induction of hsp70 expression by heat shock is reduced approximately 50% with age. The decrease in hsp70 expression occurs at the level of transcription and appears to arise from a defect in the heat shock transcription factor. Other investigators have also shown that the induction of hsp70 expression by heat shock as well as other stresses declines significantly with age in a variety of tissues from rats as well as mononuclear cells from human subjects. In addition, a decrease in the inducibility of hsp70 is observed with cell senescence in cultured cells. Therefore, it appears that a reduced ability to express hsp70 in response to stress may be a common phenomenon underlying the aging process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01923466
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  • 10
    Electronic Resource
    Electronic Resource
    A photoisomerisation product of dieldrin (1966)
    Springer
    Bulletin of environmental contamination and toxicology 1 (1966), S. 127-132 
    Details
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01844243
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