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31.
32.
The chemically induced barley (Hordeum vulgare L.) mutation, agr, was found to be a simple recessive trait resulting in agravitropic roots and normal gravitropic shoots. The total seedling root growth was similar for mutant and wild-type roots, although the mutant had fewer roots per seed and greater elongation per root. Although the concentration of exogenous indole-3-acetic acid (IAA) required to reduce root growth by 50% (GR50) was 12 times greater for the agravitropic mutant, agravitropic and gravitropic roots were equally sensitive to exogenous applications of 2,4-dichlorophenoxyacetic acid (2,4-D) and naphthalene acetic acid (NAA). Root IAA contents, determined by high-pressure liquid chromatography (HPLC), were not different for gravitropes and agravitropes. The greater root elongation rates, lack of sensitivity to exogenous IAA, and normal endogenous IAA levels indicate that auxin-controlled growth regulation may be altered in the mutant. 相似文献
33.
Cell suspension cultures of the Madagascan Periwinkle Catharanthus roseus (L) G. Don were maintained on Gamborg's B5 medium and their growth monitored by measuring cellular fresh and dry weight, cell number and mitotic activity. Samples of cells of different ages and physiological states were subcultured onto an alkaloid production medium and their rates of growth and alkaloid accumulation measured over a period of 30–45 days. In two experiments the rate of biomass accumulation was directly related to the rate of cellular serpentine accumulation. Possible mechanisms underlying this phenomenon are discussed in relation to the properties of cells comprising the inocula. 相似文献
34.
RNA synthesis was measured in toluenized E. coli by the incorporation of radiolabeled precursor into either acid precipitable or phenol extracted RNA. Exposure to captan (100 microM) caused a 2.6 fold increase in the apparent rate of RNA synthesis. When captan was tested for its effect on the initiation of RNA synthesis, using either rifampicin-treated cells or by measuring the incorporation of gamma [32P]ATP or gamma [32P]GTP, no change was observed in the number of RNA chains being initiated. Thus, captan does not exert its influence at the level of initiation of nascent chains. However, captan did have an effect on chain growth. From calculations of the incorporation of precursors molecules, RNAs isolated from treated cells were measured to be an average of 2.7 times longer than those from untreated cells. RNA chain lengths were also analyzed by polyacrylamide gel electrophoresis. By this latter technique it was also shown that cells exposed to captan synthesized RNAs that were longer than those of untreated cells. Alterations in the degradation of RNA molecules do not account for the captan mediated response in RNA synthesis. 相似文献
35.
Laura Manuelidis 《Human genetics》1985,71(4):288-293
Summary The position and arrangement of individual chromosomes in interphase nuclei were examined in mouse-human cell hybrids by in situ hybridization of biotinylated human DNA probes. Intense and even labeling of human chromosomes with little background was observed when polyethylene glycol and Tween-20 were included in hybridization solutions. Human interphase chromosomes were separated from each other in the nucleus, and were confined to well localized domains. Hybrid cells with a single human chromosome showed a reproducible position of this chromosome in the nucleus. Some chromosomes appeared to have a characteristic folding pattern in interphase. Optical section as well as electron microscopy of labeled regions revealed the presence of 0.2 m wide fibers in each interphase domain, as well as adjacent, locally extended 500 nm fibers. Such fibers are consistent with previously proposed structural models of interphase chromosomes. 相似文献
36.
William H. Karasov Edwin Petrossian Laura Rosenberg Jared M. Diamond 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1986,156(4):599-609
Summary What digestive adaptations permit herbivorous nonruminant mammals to sustain much higher metabolic rates than herbivorous lizards, despite gross similarity in digestive anatomy and physiology? We approached this question by comparing four herbivorous species eating the same diet of alfalfa pellets: two lizards (chuckwalla and desert iugana) and two mammals (desert woodrat and laboratory mouse). The mammals had longer small and large intestines, greater intestinal surface area, much higher (by an order of magnitude) food intake normalized to metabolic live mass, and much faster food passage times (a few hours instead of a few days). Among both reptiles and mammals, passage times increase with body size and are longer for herbivores than for carnivores. The herbivorous lizards, despite these much slower passage times, had slightly lower apparent digestive efficiencies than the mammals. At least for chuckwallas, this difference from mammals was not due to differences in body temperature regime. Comparisons of chuckwallas and woodrats in their assimilation of various dietary components showed that the woodrat's main advantage lay in greater assimilation of the dietary fiber fraction. Woodrats achieved greater fiber digestion despite shorter residence time, but possibly because of a larger fermentation chamber, coprophagy, and/or different conditions for microbial fermentation. We conclude with a comparative overview of digestive function in herbivorous lizards and mammals, and with a list of four major unsolved questions. 相似文献
37.
Anna Maria Tagliasacchi Laura Maria Costantina Forino Manuela Frediani Silvana Avanzi 《Protoplasma》1983,115(2-3):95-103
Summary The pattern of DNA and RNA puffs in pair VII of polytene chromosomes has been investigated in the suspensor ofPhaseolus coccineus during early embryo development. The pattern of3H-TdR and3H-U incorporation has been also detected. Collected data indicate that: 1. both heterochromatic regions, p11 and q(111+112), of chromosome pair VII, organize large DNA puffs; 2. DNA puffs of both regions are specific of different embryo differentiation steps; 3. a seasonal influence on the DNA puffing seems also to be present, as demonstrated by the comparison of the results collected in two different crops; 4. the incorporation experiment by3H-TdR evidences that not all DNA puffs show clustered labeling; 5. the RNA puffing of the two regions seems also to be specific of determined embryo stages. 相似文献
38.
Glucosylation of Teichoic Acid: Solubilization and Partial Characterization of the Uridine Diphosphoglucose:Polyglycerolteichoic Acid Glucosyl Transferase from Membranes of Bacillus subtilis 总被引:4,自引:2,他引:2 下载免费PDF全文
Polyglycerolteichoic acid:glucosyl transferase (TAG transferase), one of the three enzymes involved in the pathway leading to the glucosylation of teichoic acid in Bacillus subtilis 168, was investigated. During the early stages of the growth of B. subtilis, TAG transferase is predominantly a soluble enzyme found in the cytoplasm. As growth proceeds, the amount of soluble enzyme decreases and the proportion of insoluble, membrane-bound TAG transferase increases, reaching a maximal value at the close of the logarithmic phase. Data are presented which suggest that these are two forms of the same enzyme, or have some common component. The effects of chaotropic agents, such as sodium trichloroacetate and sodium perchlorate, on the cytoplasmic membrane were also studied. These data show that such compounds can effectively remove the TAG transferase from the membrane in a water-soluble form. A study of some of the physical properties of this solubilized enzyme suggests that there is little difference between the two forms of the enzyme. Experiments are described which indicate that the glucosyl transfer by both the membrane-bound and soluble enzymes is not mediated by lipids. 相似文献
39.
Nature of Escherichia coli B(P1) Yielder Cells at the Time of Infection with Restricted T1 总被引:1,自引:1,他引:0 下载免费PDF全文
In the infection of Escherichia coli B(P1) with restricted T1, it was shown that yielder cells consist of both special and nonspecial cells. Special or predetermined yielders occurred only among the earliest yielders. In most instances, yielder-cell formation was most easily explained by assuming that the first step was a chance escape of the restricted phage DNA from the degrading enzyme of the restricting cell. 相似文献
40.
The ultrastructure of the mature spermatozoa and spermatogenesis of the bivalve Scrobicularia plana are described. Support cells extend from the basal lamina to the lumen of the testis and are laterally connected to the germinal epithelium. Germ cells present intercellular bridges and flagella since the spermatogonial stage. While spermatogonia and spermatocytes appear connected to support cells by desmosome-like junctions, elongated spermatids are held at the acrosomal region by support cell finger-like processes. During spermiogenesis, the acrosomal vesicle differentiates from a golgian saccule and then migrates to the nuclear apex. A microtubular manchette arising from centrioles surrounds the acrosomal vesicle, the nucleus, and the mitochondria at the time these three organelles start their elongation, disappearing after that. The mature spermatozoon of S. plana lacks a distinct midpiece because the mitochondria extend from the region of the pericentriolar complex along the nucleus anteriorly for approximately 1.4 μm. The features of this bivalve type of modified spermatozoon are compared with those of other animal groups having similar modifications. 相似文献