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Richard E. Kouri Raymond Kiefer Eugene M. Zimmerman 《In vitro cellular & developmental biology. Plant》1974,10(1-2):18-25
Summary Two methods for determining the hydrocarbon-metabolizing enzyme activity of cultured mammalian cells were compared. The method
designed to measure benzo[a]an-thracene-induced aryl hydrocarbon hydroxylase activity could detect and quantify enzyme activities
in low passage rodent cells, but could not reproducibly detect levels in intermediate or high passage mouse, rat, or human
cells. The method designed to measure the ability of a cell to convert benzo[a]pyrene from an organic-soluble to an aqueous
acetone-soluble form proved to be more reproducible. This technique, when modified, was demonstrated to be an effective screening
test for the detection of those lines with higher levels of hydrocarbon-metabolizing enzymes.
Supported by the Council for Tobacco Research and Contract NIH 70-2068 within the Virus Cancer Program, National Cancer Institute,
National Institutes of Health. 相似文献
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Ribosomes, the universal cellular machines, possess spectacular architecture accompanied by inherent mobility, allowing for their smooth performance as polymerases that translate the genetic code into proteins. The site for peptide bond formation is located within a universal internal semi-symmetrical region, which was identified within all contemporary ribosomes. The high conservation of this region implies its existence irrespective of environmental conditions and indicates that it may represent an ancient RNA molecular apparatus. Hence, we named it the “proto-ribosome”. This prebiotic pocket-like RNA entity is suggested to be capable to accommodate substrates whose stereochemistry enables the creation of chemical bonds. It could have evolved from an earlier catalytic RNA entity that we named the “pre-proto-ribosome”, presumed to be a molecular machine capable of performing various essential tasks in the RNA world, which was snatched by the amino acid invaders for producing proteins. 相似文献
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Francesca Fasolo Richard H. Zimmerman Ingrid Fordham 《Plant Cell, Tissue and Organ Culture》1989,16(2):75-87
Leaves taken from micropropagated shoots of several apple (Malus domestica Borkh.) cultivars were cultured in vitro on Linsmaier & Skoog (LS) medium or the rice anther culture medium of Chu et al. (N6) containing various concentrations of either benzyladenine (BA) or thidiazuron (TDZ) plus naphthaleneacetic acid (NAA). Of the TDZ concentrations tested, 10 M was most effective and it was equivalent to, or better than, 22 M BA for both the percentage of leaves regenerating shoots and number of shoots formed per regenerating leaf in almost every experiment. Lower concentrations of NAA (1.1 and 5.4 M) gave best results with both BA and TDZ. N6 medium gave consistently better results than LS. Lowering total salt concentration or total N concentration of LS to that of N6 did not improve the response nor did changing the NO3:NH4 ratio. The 3–4 leaves on the most distal part of the shoot were most responsive and tended to form the most adventitious shoots. Placing the leaf cultures in the dark for the first 2–3 weeks of the culture period produced the best results. Optimum results were obtained by culturing leaves from the distal part of the shoot in the dark for 2 weeks on N6 medium containing 10 M TDZ and 1.1 or 5.4 M NAA, then moving the cultures to 16 h daylight at a photon flux of 60 mol s-1m-2. 相似文献
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A. Michael Powell Allan D. Zimmerman Richard A. Hilsenbeck 《Plant Systematics and Evolution》1991,178(1-2):107-122
The origin ofEchinocereus ×lloydii
Britt. & Rose, pro sp. (Lloyd's Hedgehog Cactus) was investigated using comparative morphology, cytology, biochemistry, and particularly, artificial hybridization. Numerous artificial crosses between the putative parentsE. coccineus
Engelm. (a species of claret-up cactus) andE. dasyacanthus
Engelm. (Texas Rainbow Cactus) were successful, resulting in the production of hundreds of seeds with hybrid embryos. The F1 hybrid progeny (i.e., syntheticE. ×lloydii) grew to sexual maturity in about four and one-half years, whereupon successful backcrosses and F2 generation hybrids were also obtained. The known F1 hybrids closely approximated naturalE. ×lloydii. The fertility of these syntheticE. ×lloydii was high, like their natural counterparts. The populations ofE. ×lloydii in Pecos County, Texas are inferred to have originated as the result of natural interspecific hybridization. It is assumed thatE. ×lloydii or similar plants may arise wherever the parental taxa grow sympatrically. 相似文献
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E. G. Zimmerman 《Genetica》1988,76(2):153-159
Genetic variation at eight polymorphic loci was examined in a population of a subterranean rodent, the plains pocket gopher (Geomys bursarius), sampled over a 10-yr period. Two loci exhibited relatively minor changes in gene frequencies, while the remaining loci demonstrated major shifts in predominant alleles, loss of minor alleles, and addition of alleles due to migration. Significant deviations from Hardy-Weinberg expectations, concomitant to heterozygote deficiencies, were observed for several loci. Temporal heterogeneity, as measured by FST, was high and comparable to that exhibited by local populations sampled over relatively short periods of time. The high degree of temporal genetic variation is consistent with observations that fossorial rodents occur in locally isolated populations with small effective population sizes that are subject to genetic drift, bottlenecking, and inbreeding. 相似文献