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991.
992.
Wittwer , S. H., and M. J. Bukovac . (Michigan State U., E. Lansing.) Quantitative and qualitative differences in plant response to the gibberellins. Amer. Jour. Bot. 49(5): 524–529. Illus. 1962.—The comparative biological activities of gibberellins A1 through A9 were evaluated, over a wide concentration range and in several test systems. All gibberellins were effective in promoting stem elongation of dwarf peas (Pisum sativum), and, with the exception of A8, epicotyl growth in Phaseolus vulgaris. Elongation of Cucumis sativus seedlings was strikingly greater with A4, A7, and A9 than with the other gibberellins. With mutant dwarfs of Zea mays, A5 and A9 were the most active gibberellins for d3 and d5, and relatively ineffective compared to A3 on d1. Gibberellins A2, A7, and A8 were less effective than A3 on all dwarfs. Qualitative and quantitative differences among the gibberellins were noted on seedstalk elongation and flowering of Lactuca sativa, with A3 the most active followed by A1, A7, A4, and A9. No flowering or seedstalk elongation occurred with A2, A6 or A8. Parthenocarpic fruit growth in Lycopersicon esculentum was a function of dosage with all gibberellins. At the lowest levels, A5 and A7 were the most active, while at the highest levels all gibberellins with the exception of A8 were equally effective. The results suggest a high degree of species and response specificity among the known fungal and higher plant gibberellins, and demonstrate the importance of utilizing a wide spectrum of plant responses and dosage levels in the biological assay of plant extracts for native gibberellins. 相似文献
993.
L. S. Wolfe Igor Klatzo Jaime Miquel Cornelius Tobias Webb Haymaker 《Journal of neurochemistry》1962,9(2):213-218
994.
995.
Iron uptake was studied using cells enzymically isolated from green tobacco leaves. Absorption was increased both by light and succinate as probable energy sources. Bicarbonate in the incubation mixture was inhibitory, and citrate also reduced absorption presumably by chelation with the metal. Absorption of iron was temperature sensitive and optimal at 25°C. Temperature coefficients and activation energies suggested that absorption was energy mediated. NaN3 and DNP inhibited uptake at concentrations of 10-3M and 10?4M, respectively. The inhibition caused by DNP was not negated by an external supply of ATP. The results suggest that iron absorption is an active metabolic process in cells enzymically isolated from green tobacco leaves. Cells from Fe-chlorotic leaves of PI 54619–5–1 soybean absorbed less iron than those derived from healthy leaves of the same variety, while leaf cells from the variety Hawkeye showed no such differences. 相似文献
996.
Tobias Kieser 《Plasmid》1984,12(1):19-36
Based on the results of a systematic study of factors affecting plasmid yield and purity, a procedure suitable for the rapid screening for and isolation of covalently closed circular DNA from Streptomyces lividans and Escherichia coli was developed. The method consists of lysis of lysozyme-treated bacteria combined with alkaline denaturation of DNA at high temperature. Renaturation of CCC DNA and precipitation of single-stranded DNA together with protein is achieved by the addition of a minimal amount of phenol/chloroform. The screening procedure uses only a single tube and the samples can be analyzed by agarose gel electrophoresis about 30 min after lysis. Removal of phenol and further purification of the plasmid preparation is achieved by consecutive precipitations with isopropanol and spermine, followed by extraction with ethanol, producing samples suitable for restriction endonuclease digestion, ligation, and transformation of S. lividans protoplasts or competent E. coli cells in about 2 h. All steps of the procedure are explained in detail with information about the effects of changing parameters. This should help the experimenter to obtain reproducible results and may be useful if the method has to be adapted to new strains or plasmids. 相似文献
997.
Hormone-sensitive stages in the sexual differentiation of laryngeal muscle fiber number in Xenopus laevis 总被引:2,自引:0,他引:2
The number of muscle fibers in the vocal organ of the adult male African clawed frog, Xenopus laevis, exceeds that of adult females. This sex difference is the result of rapid fiber addition in males between the end of metamorphosis, post-metamorphic stage 0 (PM0) and PM2. At PM0, male and female frogs have similar numbers of laryngeal muscle fibers. Males then add more muscle fibers than females and achieve an adult value that is 1.7 times the female number. Males castrated at PM0 have the same fiber number as females. Ovariectomy at PM0 does not alter muscle fiber addition in females. Gonadectomy at PM2 has no effect on fiber addition in either sex. Females attain masculine muscle fiber number if their ovaries are replaced with a testis at metamorphosis. Exogenous testosterone treatment at PM0 significantly increases fiber number in females but not in males. Exogenous testosterone given at PM2 has no effect on fiber number in females but decreases fiber number in males. We conclude that the testes are necessary for the marked addition of laryngeal muscle fibers seen in male X. laevis between PM0 and PM2. The masculine pattern of muscle fiber addition can be induced in females provided with a testis. Androgen secretion from the testes most probably accounts for masculinization of laryngeal muscle fiber number. After PM2, androgens are no longer necessary for muscle fiber addition and cannot increase fiber number in females. 相似文献
998.
Bernd Jensch Markus Baur Frank Brandstätter Tobias Friz Thomas Kölpin Fabian Schmidt Ralf Sommerlad Karl-Heinz Voigt 《Der Zoologische Garten (in deutscher Sprache / in German)》2009,78(2-3):102-131
The minimum requirements for the keeping of crocodiles in private and public institutions are set up by a collective of authors. Important aspects such as the design of enclosures, secure handling and keeping, thermoregulation, protection of animals, feeding, behavioural enrichment and diseases and their prophylaxis are important topics. The authors critically deal with existing guidelines and give suggestions on how crocodiles can be kept appropriately and according to existing laws at the same time.Special attention is given to the aspects of current legislation. It is stressed that there should be given proper attention to the qualification of the keeping institution as to the biology of the animals as well as to security aspects.A table of species completes the text with a short array of important features to be considered in the keeping of crocodiles. 相似文献
999.
The Validity of the Ussing Flux Ratio Equation in a Three-Dimensionally Inhomogeneous Membrane 下载免费PDF全文
Tobias L. Schwartz 《Biophysical journal》1971,11(7):596-602
Derivations of the Ussing flux ratio equation have, until now, required the membrane to be both bounded by parallel planes and homogeneous, except in the transmembrane direction. These constraints have been necessary for the theoretical demonstration that the equation is independent of membrane parameters in the absence of carriers, coupling, solvent drag, or “single-file” diffusion. In a new derivation, the flux ratio equation is shown to be valid in this kind of diffusion regime without regard to the three-dimensional structure of the membrane. Thus the constraints on both membrane homogeneity and membrane geometry are shown to be unnecessary. The general use of this equation to differentiate between simple, uncoupled diffusion and other membrane transport phenomena is thus placed on a firmer base. However, as in earlier derivations, it is necessary that isopotential, isobaric, constant concentration surfaces exist sufficiently close to the membrane on both of its sides. 相似文献
1000.