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11.
Internal transport of O2 from the aerial tissues along the adventitious roots of intact maize plants was estimated by measuring the concentrations of adenine nucleotides in various zones along the root under an oxygen-free atmosphere. Young maize plants were grown in nutrient solution under conditions that either stimulated or prevented the formation of a lysigenous aerenchyma, and the roots (up to 210 mm long) were then exposed to an anaerobic (oxygen-free) nutrient solution. Aerenchymatous roots showed higher values than non-aerenchymatous ones for ATP content, adenylate energy charge and ATP/ADP ratios. We conclude that the lysigenous cortical gas spaces help maintain a high respiration rate in the tissues along the root, and in the apical zone, by improving internal transport of oxygen over distances of at least 210 mm. This contrasted sharply with the low energy status (poor O2 transport) in non-aerenchymatous roots.Abbreviation AEC
adenylate energy charge 相似文献
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When nucleosome cores reconstituted from chicken erythrocyte histones and a 160 bp DNA molecule are exposed to echinomycin, a bis-intercalating antitumour antibiotic, the DNA appears to rotate with respect to the histone octamer by about half a turn. New bands appear in patterns of DNAase I digestion at positions approximately mid-way between those characteristic of control core samples, while the control pattern is largely suppressed. Similar (but not identical) changes are produced when nucleosome cores are exposed to distamycin, a non-intercalating DNA-binding antibiotic. The effects of both ligands can be explained in terms of a change in rotational orientation of the core DNA, so as to place antibiotic binding sites on the inward-facing (concave) surface of the DNA supercoil. Presumably this serves to optimise non-bonded contacts with the polynucleotide backbone. These results establish that the positioning of DNA about the histone octamer is not absolutely determined by its nucleotide sequence, but may be modified by the binding of such relatively small molecules as antibiotics. 相似文献
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Effect of metabolic inhibitors and temperature on uptake and translocation of ca and k by intact bean plants 总被引:1,自引:0,他引:1
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The dependence of Ca uptake and translocation by intact roots of Phaseolus vulgaris on concurrent root metabolism was investigated using 45Ca-labeled Hoagland solutions at one-half and one-twentieth strength (2.5 and 0.25 mM Ca2+). Adsorbed and absorbed 45Ca fractions in the roots were distinguished on the basis of the time course of exchange with the outer solution. Uptake of 42K, of which the characteristics are better known, was measured for comparison. The absorbed 45Ca fraction showed a markedly nonlinear increase with time in contrast to the near linear increase in 42K. Exposure of roots to cyanide, arsenate, 2,4-dinitrophenol, or low temperatures caused only slight reductions in 45Ca absorption by roots, but significant reductions of 42K. In all treatments involving inhibitors and low temperatures, the translocation to shoots of both 45Ca and 42K was strongly inhibited. The conclusion that much of the absorbed 45Ca fraction in the root tissue is taken up by processes which are not rate-limited by metabolism is discussed. 相似文献
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Characterization of gamma-aminobutyric acid and dopamine overflow following acute implantation of a microdialysis probe 总被引:7,自引:0,他引:7
The present study characterized the voltage and calcium dependence of gamma-aminobutyric acid and dopamine overflow after the acute implantation of a microdialysis probe. Probes were implanted in dorsolateral striatum and globus pallidus. Experiments were performed under light halothane anesthesia. Basal, extracellular levels of GABA were not affected by tetrodotoxin (TTX) and were increased to 140 percent of basal values by calcium free Ringer. Basal, extracellular levels of dopamine were reduced to 14 percent of basal values by the addition of TTX and to 30 percent of basal values by the removal of calcium from the Ringer solution. The results suggest that in this in vivo preparation basal extracellular dopamine is largely of vesicular origin while GABA is not. 相似文献