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71.
Correlations between Potassium Uptake and Hydrogen Efflux in Barley Varieties : A POTENTIAL SCREENING METHOD FOR THE ISOLATION OF NUTRIENT EFFICIENT LINES 总被引:2,自引:0,他引:2
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Rates of hydrogen ion secretion and potassium (86Rb) absorption by intact roots of twenty-four barley varieties were measured in solutions containing K2SO4 (1 × 10−4 to 1 × 10−3 molar) plus 5 × 10−4 molar CaSO4, at initial pH values in the range 5.3 to 5.5. Fluxes of H+ and K+ were strongly correlated in short-term experiments (up to 15 minutes) as well as in long-term experiments (lasting 24 hours). The observed correlations provide the basis for a preliminary screening method, designed to segregate varieties with high rates of potassium uptake by the use of an acid-base indicator (methyl red). 相似文献
72.
Different base per unit length ratios exist in single-stranded RNA and single-stranded DNA. 总被引:1,自引:1,他引:0
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A significant difference was found to exist in the number of bases per unit length of single-stranded RNA as compared to single-stranded DNA when single-stranded RNA or DNA molecules of known nucleotide sequence were measured by electron microscopy using a cytochrome spreading technique. Using this technique, single-stranded RNA was found to have 17.5% more bases per unit of length than single-stranded DNA. These ratios were verified using four different denaturing conditions for the RNA: 80% formamide, 80% formamide plus glyoxal, 80% formamide/4M urea and 80% formamide/4M urea plus glyoxal. Molecules ranging in size from 1541 to 5386 nucleotides were examined and the number of bases per unit length was found to vary inversely with micrometer was consistent when RNA and DNA molecules of the same length were compared. 相似文献
73.
Mogens L. Glass James W. Hicks Marvin L. Riedesel 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1979,131(4):353-359
Summary In late February, seven box turtles were collected with body temperatures between 7 and 9°C. Ventilation, gas exchange and end-tidal
and
were recorded at 5, 10, 15 and 25°C, the animals being at each temperature for 2 to 3 weeks. There was a pronounced diurnal rhythm of breathing frequency at all temperatures. At 5°C the mean 24-h frequency was only 3.7 breaths h–1. At 15°C the frequency was 16 times higher with a 17-fold increase of ventilation. Oxygen uptake only changed from 3.4 to 12.7 ml·kg–1·h–1. Consequently, the ratio (ventilation, ml BTPS/O2 uptake, ml STPD) increased from 12.5 at 5°C to 48 at 15°C, but decreased to 24 at 25°C. The decrease of this ratio during cold exposure contrasts with an increase of the ratio during cooling earlier reported for fresh water turtles,Pseudemys. Cutaneous CO2 elimination was important at low temperature. This caused a decrease of the pulmonary gas exchange ratio so that end-tidal
remained low at 5°C in spite of an end-tidal
of only 54 Torr. 相似文献
74.
Summary A mathematical model is presented for phase locking of a biological oscillator to a sinusoidal stimulus. Analytical, numerical and topological considerations are used to discuss the patterns of phase locking as a function of the amplitude of the sinusoidal stimulus and the relative frequencies of the oscillator and the sinusoidal stimulus. The sorts of experimental data which are needed to make comparisons between theory and experiment are discussed. 相似文献
75.
76.
Treatment of preimplantation mouse embryos in vitro with 10(-3) to 10(-1) mug actinomycin D/ml for 2 hr showed that (i) postimplantation development in vitro was inhibited most when embryos were treated at the morula stage and (ii) after the morula stage actinomycin D inhibited trophoblast outgrowth less than inner cell mass development. 相似文献
77.
78.
Techniques of cell separation were used to isolate murine erythroid precursors at different states of maturation. Cells were studied before and after short-term incubation in the presence or absence of erythropoietin. Complementary results were obtained by direct examination of the cell fractions and by the short-term culture experiments. Indices of heme synthesis, including incorporation of 59Fe or [2-14C]glycine into heme and activity of delta-aminolevulinic acid synthetase, were already well developed in the least mature cells, chiefly pronormoblasts. Activity then rose moderately in the cell fractions consisting primarily of basophilic and polychromatophilic normoblasts, and fell off with further increases in cell maturity. On short-term culture in the presence of erythropoietin, activity declined with increasing cell maturation except in the least mature fraction where the original level of activity was maintained. By contrast, synthesis of labeled hemoglobin ([3H]leucine) was very low in the least mature cell fractions and rose progressively with increasing cell maturity. The rate of hemoglobin synthesis increase in cells at all stages of maturation when cultured in the presence of erythropoietin. Despite the different patterns observed for heme synthesis and hemoglobin synthesis, both synthetic activities were consistently higher in cells cultured with erythropoietin as compared to controls. These findings suggest that erythropoietin stimulates biochemical differentiation of erythroid precursors at various stages of maturation. They also demonstrate an asynchronism between heme synthesis and hemoglobin syhthesis; heme synthesis is already well developed in the least mature erythroid cells and begins to diminish as the capacity for hemoglobin synthesis continues to rise. 相似文献
79.
Manzoor Elahi Richard W. Glass Clinton O. Chichester Kenneth L. Simpson 《Phytochemistry》1975,14(1):133-138
The inhibitory effect of a series of analogs of CPTA, 2-(4-chlorophenylthio)-triethylamine-HCl, and ammonia derivatives on carotenoid biosynthesis in Phycomyces blakesleeanus mutants was studied. The types of inhibition exhibited allowed no firm conclusions about the biosynthetic route to β-carotene from either β-zeacarotene or lycopene. However, the evidence suggests at present that both pathways are operative. It was found that a slight change in structure of inhibitor resulted in a different type of action. Conclusions based on a single inhibitor could be cited as “evidence” for a certain pathway. 相似文献
80.
M R Glass R W Shaw W R Butt R L Edwards D R London 《BMJ (Clinical research ed.)》1975,3(5978):274-275
Fourteen patients with amenorrhoea and hyperprolactin-anemia but no evidence of pituitary tumours were each given an intramuscular injection of 1 mg oestradiol benzoate. Thirteen patients failed to release luteinizing hormone in response to the oestrogen. This hypothalamic abnormality may help to explain the menstrual disturbances in subjects with hyperprolactinaemia. 相似文献