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961.
U. Helfenstein 《Biometrical journal. Biometrische Zeitschrift》1991,33(4):411-417
In biology and medicine many substances and drugs enter the system not at regular time intervals but rather according to a random process. In the present article a situation is investigated where input enters a 2-compartment system according to a Poisson process. The arising two random concentration curves y(t), one for the central and one for the peripheral compartment are discussed (shot noise). The equations for E[y(t)] and Var [y(t)] are derived. The dependence of E[y(t)] and Var [y(t)] and of the index of dispersion ID[y(t)] on the rate parameters is analysed and discussed in both compartments. The arising calculations were considerably simplified by means of “Mathematica”, a computer program which allows to perform symbolic calculations. 相似文献
962.
Nickel bioavailability in an ultramafic toposequence in the Vosges Mountains (France) 总被引:1,自引:0,他引:1
A serpentinised harzburgite outcrop located in the Vosges Mountains hosts a population of the Ni-hyperaccumulator Thlaspi caerulescens J. & C. Presl. A complete study was undertaken to relate the variability of Ni availability along the ultramafic toposequence
to pedogenesis, soil mineralogy and functioning with X-Ray Diffraction, Transmission Electron Microscope observations coupled
with Isotopic Exchange Kinetics and diethylenetriamine pentaacetic acid extraction of Ni. The soil profiles ranging from Dystric
Cambisol to Hypermagnesic Hypereutric Cambisol were distributed unevenly along the toposequence probably due to geochemical
variability of the bedrock and also complex quaternary erosion features. The richest soils were characterised by slight mineral
weathering leading to Ni, Cr and Fe accumulation in the B horizons whereas the lowest saturated soils had very low-metal contents.
Most soil minerals were inherited from the parent materials and there were only few traces of formation of secondary minerals.
Primary minerals (e.g. serpentine, chlorite) contained low Ni concentrations (0.2%) whereas neoformed goethite, mainly in the B horizons of the
richest soils, contained up to 4.3% Ni. Ni was probably sorbed onto amorphous Fe oxy−hydroxide particles (oxalate extraction)
rather than incorporated within the crystal lattice of goethite. Ni availability in the B horizon of Hypereutric Cambisols
was extremely high and so was the oxalate extractable Fe. At the toposequence level, there was a high level of Ni availability
in the least weathered soils and a very low-availability level in the more intensively weathered soils (strongly acidic pH).
Ni availability was unexpectedly positively correlated to pH and was controlled by soil mineralogy and Ni-bearing mineral
phases. Ni hyperaccumulation (above 1,000 mg kg−1) by native T. caerulescens was only reached in the Ni-rich soils as a consequence of the local edaphic factors. Ni uptake by T. caerulescens is strongly regulated by Ni availability in soils and therefore related to pedogenesis. 相似文献
963.
Ken Lee Soichi Miwa Kunio Koshimura Hiroshi Hasegawa Keigo Hamahata Motohatsu Fujiwara 《Journal of neurochemistry》1990,55(4):1131-1137
The purpose of the present study is to clarify the effects of hypoxia on catecholamine release and its mechanism of action. For this purpose, using cultured bovine adrenal chromaffin cells, we examined the effects of hypoxia on high (55 mM) K(+)-induced increases in catecholamine release, in cytosolic free Ca2+ concentration ([Ca2+]i), and in 45Ca2+ uptake. Experiments were carried out in media preequilibrated with a gas mixture of either 21% O2/79% N2 (control) or 100% N2 (hypoxia). High K(+)-induced catecholamine release was inhibited by hypoxia to approximately 40% of the control value, but on reoxygenation the release returned to control levels. Hypoxia had little effect on ATP concentrations in the cells. In the hypoxic medium, [Ca2+]i (measured using fura-2) gradually increased and reached a plateau of approximately 1.0 microM at 30 min, whereas the level was constant in the control medium (approximately 200 nM). High K(+)-induced increases in [Ca2+]i were inhibited by hypoxia to approximately 30% of the control value. In the cells permeabilized by digitonin, catecholamine release induced by Ca2+ was unaffected by hypoxia. Hypoxia had little effect on basal 45Ca2+ uptake into the cells, but high K(+)-induced 45Ca2+ uptake was inhibited by hypoxia. These results suggest that hypoxia inhibits high K(+)-induced catecholamine release and that this inhibition is mainly the result of the inhibition of high K(+)-induced increases in [Ca2+]i subsequent to the inhibition of Ca2+ influx through voltage-dependent Ca2+ channels. 相似文献
964.
Ronnitte S. Badar-Goffer Oded Ben-Yoseph Simon J. Dolin Peter G. Morris Gerry A. Smith Herman S. Bachelard† 《Journal of neurochemistry》1990,55(3):878-884
We have applied the 19F-nuclear magnetic resonance (NMR) calcium indicator 1,2-bis(2-amino-5-fluoro-phenoxy)ethane-N,N,N',N'-tetraacetic acid (5FBAPTA) to the measurement of the free intracellular calcium concentration [( Ca2+]i) in superfused brain slices. A mean +/- SD control value of 380 +/- 71 nM (n = 18) was obtained at 37 degrees C using 2.4 mM extracellular Ca2+. Subcellular fractionation studies using [3H]5FBAPTA showed that after loading of its tetraacetoxymethyl ester, approximately 55% was de-esterified, with the other 45% remaining as the tetraester bound to membranes. Of the de-esterified 5FBAPTA, greater than 90% was in the cytosolic fractions, with less than 1% in the mitochondria or microsomes. The NMR-visible de-esterified 5FBAPTA slowly disappeared from the tissue with a t1/2 of 4 h. A time course after loading confirmed that the calculated [Ca2+]i was constant over a 5-h period, although the scatter of individual results was +/- 20%. The [Ca2+]i was increased by a high extracellular K+ concentration ([K+]e), by a low extracellular concentration of Na+, and by the calcium ionophore A23187. On recovery from high [K+]e, the [Ca2+]i "overshot" to values lower than the original control value. The [Ca2+]i was surpisingly resistant to changes in extracellular Ca2+ concentration. 相似文献
965.
Growth and mineral status of 9 Taraxacum microspecies were studied under mineral stress conditions, using a flowing solution of low nutrient concentration. Relative growth rate of (whole) plant dry weight, leaf area, and (whole) plant tissue water were used to describe growth. For 4 microspecies, specific uptake rates of NO− 3 , H2 PO− 4 , K+ , Mg2+ and Ca2+ were investigated.
The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum . These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites.
T. nordstedtii , a microspecies of infertile sites, was most efficient in absorbing NO− 3 , H2 PO− 4 and K+ . T. sellandii and T. eudontum , both occurring in fertile grasslands, showed poor uptake performances for all studied ions. In all Taraxacum microspecies studied, except T. eudontum , internal N concentration appeared to limit growth. Efficiencies in N use, at sub-optimal internal N concentrations, varied with the mineral habitat of the microspecies studied. T. nordstedtii , from infertile sites, and T. sellandii , from fertile sites, were established as high and low extremes, respectively. 相似文献
The applied nutrient condition clearly discriminated between the studied Taraxacum microspecies. With respect to relative growth rate, 3 groups of microspecies could be distinguished: T. nordstedtii > T. lancidens, T. adamii, T. hollandicum, T. taeniatum > T. sellandii, T. eudontum, T. ekmanii, T. ancistrolobum . These categories coincided well with the mineral ecology of the microspecies, going from infertile to fertile sites.
T. nordstedtii , a microspecies of infertile sites, was most efficient in absorbing NO
966.
A glasshouse experiment was conducted to study the effect of Ni on the growth and nutrients concentration in wheat (Triticum aestivum Cv. WH 291) in the presence and absence of applied N as urea. Responses to N application were observed up to 120 g N g–1 soil. No response to Ni was observed in the dry matter yield of wheat tops (leaves + stem) in the absence of applied N while in the presence of applied N, significant yield increases were obtained at 12.5g Ni g–1 soil. Nickel was not toxic to wheat up to 50g Ni g–1 soil in the presence of 120g N g–1 soil. Nitrogen and Ni concentration in wheat tops and roots increased with increasing levels of applied N and Ni, respectively. Applied Ni had an antagonistic effect on N concentration. Similarly, N reduced the Ni concentration in the wheat tissues. Positive growth responses to Ni were associated with 22 and 15g Ni g–1 in wheat tops, in the presence of applied N at 60 and 120g N g–1 soil, while Ni toxicity was associated with 63, 92.5 and 112.5g Ni g–1 in wheat tops, in the absence and presence of applied N at 60 and 120g N g–1 soil, respectively. 相似文献
967.
Gas exchanges of wheat (Triticum aestivum L. cv. Courtot) shoots were measured before and during a water stress. While photosynthesis, transpiration and dark respiration
decreased because of the stress, photorespiration increased initially, up to a maximum of 50% above its initial value. The
CO2 concentration in the intercellular space was calculated from gas-diffusion resistances, and remained approximately constant
before and during the stress. On the other hand, the CO2 concentration in the chloroplast, in the vicinity of Ribulose-1,5-biphosphate carboxylase/oxygenase (Rubisco), was evaluated
from the ratio of CO2 to O2 uptake, using the known kinetic constants of the oxygenation and carboxylation reactions which compete for Rubisco. In the
well-watered plants, the calculated chloroplastic concentration was slightly smaller than the substomatal concentration. During
water stress, this concentration decreased while the substomatal CO2 concentration remained constant. Hypotheses to explain this difference between substomatal and chloroplastic CO2 concentrations are discussed. 相似文献
968.
J K Thibodeaux C A Anzalone S A Voelkel J D Roussel L L Goodeaux 《Journal of medical primatology》1990,19(5):493-499
Refractometer indexes were standardized and found to be highly correlated (r = 0.831) to actual creatinine levels. Urinary estradiol corrected by creatinine levels and refractometer indexes were found to be highly correlated (r = 0.857). Predicted ovulation was the same day in 86% of the ovulatory cycles predicted by creatinine and refractometer corrected estradiol levels. Refractometer indexes may be used in place of creatinine levels to correct for urine concentration fluctuations when predicting ovulation in the rhesus female. 相似文献
969.
Seedlings of two tree species from the Atlantic lowlands of Costa Rica, Ochroma la-gopus Swartz, a fast-growing pioneer species, and Pentaclethra macroloba (Willd.) Kuntze, a slower-growing climax species, were grown under enriched atmospheric CO2 in controlled environment chambers. Carbon dioxide concentrations were maintained at 350 and 675 μl 1−1 under photosynthetic photon flux densities of 500 μol m−2 s−1 and temperatures of 26°C day and 20°C night. Total biomass of both species increased significantly in the elevated CO2 treatment; the increase in biomass was greatest for the pioneer species, O. lagopus . Both species had greater leaf areas and specific leaf weights with increased atmospheric CO2 . However, the ratio of non-pho-tosynthetic tissue to leaf area also increased in both species leading to decreased leaf area ratios. Plants of both species grown at 675 μl 1−1 CO2 had lower chlorophyll contents and photosynthesis on a leaf area basis than those grown at 350 μl 1−1 . Reductions in net photosynthesis occurred despite increased internal CO2 concentrations in the CO2 -enriched treatment. Stomatal conductances of both species decreased with CO2 -enrichment resulting in significant increases in water use efficiency. 相似文献
970.
N. K. Fageria 《Plant and Soil》1985,88(2):237-243
Summary The dry matter production and the concentration of nutrients in rice (Oryza sativa L.) cultivars from soil adjusted to different levels of salinity were evaluated under a greenhouse conditions. Soil salinity levels were produced by applying 0.34 mol l–1 solution of NaCl which resulted in the following levels, control (0.29), 5, 10 and 15 dS m–1 conductivity of saturation extract. The effect of salinity on dry matter production varied from cultivar to cultivar.The concentrations of P and K in the tops of rice cultivars decreased with increasing soil salinity. But the concentrations of Na, Zn, Cu and Mn increased.Significant varietal differences were found in relation to salinity tolerance. Based on dry matter yield reduction, rice cultivars were classified as tolerant, moderately tolerant, moderately susceptible or susceptible. 相似文献