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91.
The hyaline layer (HL) surrounding the sea urchin blastula appears to dissolve in 1 M glycine. However, after this treatment, there persists over the surfaces of the blastomeres a layer of material, referred to here as the apical lamina (AL), that sloughs off as an adhesive convoluted bag upon gradual dissociation of the embryo. Isolated hyaline layers, referred to as HL-AL complexes, were analyzed by urea-SDS-polyacrylamide gel electrophoresis. A major protein of the HL-AL complex, hyalin, bands or precipitates in the stacking gel. Two other major proteins, both strongly PAS positive, migrate with apparent molecular weights of 175K and 145K daltons. As with intact embryos, the glycine wash removes the hyalin protein from the isolated HL-AL complex, leaving the undissolved AL which consists primarily of the 175K- and 145K-dalton proteins. The embryo's own perivitelline-localized cortical granule peroxidase heavily radioiodinates the proteins of the HL-AL complex, further verifying their apical, extracellular location. Unlike hyalin, the AL proteins do not precipitate with calcium ions. Compared to the entire HL-AL complex, the AL contains a greater percentage of carbohydrate. No sialic acid is associated with the HL-AL complex, but the AL contains some sulfate. In contrast to a published report based on ultrastructural staining, no biochemical evidence was found in this study for the presence of collagen or significant glycosaminoglycan within the HL-AL complex. No developmental differences were observed in AL proteins from 1-hr-old embryos compared to those from blastulae. However, there is evidence suggesting heterogeneity and developmental differences in hyalin. The possible organization of hyalin and the AL proteins into separate layers surrounding the embryo is discussed. The influence of the AL proteins in morphogenesis and cell adhesion is considered, and hypothetical roles attributed to the HL and hyalin are critically questioned. 相似文献
92.
Abstract. Tree size and age structures, treefall and canopy gap characteristics, and regeneration responses to treefalls were compared for three stands of old-growth beech (Nothofagus) forest dominated by N. fusca and N. menziesii on the South Island, New Zealand. Treefall gaps (up to 1000 m2) were most often caused by standing trees killed by drought and/or insect attack, or by trees snapped by wind. The causes of gap formation and the size and age distributions of treefall gaps varied between localities because of spatial and temporal differences in the histories of disturbance. At Fergies Bush where drought-related dieback had produced many large gaps with standing dead trees, gaps were generally young. Conversely, at Station Creek, small, old gaps formed by bolesnap dominated the disturbance regime. At Rough Creek, gaps of all ages and sizes were found along with an almost complete fern cover, and abundant shrubs and occasional subcanopy hardwood trees. Although overall patterns of regeneration were unrelated to differences in gap size, the relative abundance of N. fusca and N. menziesii varied between localities according to the seemingly minor differences in forest structure and disturbance history described above. Interpretations of regeneration response to gap parameters, therefore, need to account for differences in disturbance history between sites. Differences in the disturbance history between localities will also influence rates of gap closure, and because closure rates are used to estimate forest turnover times, meaningful comparisons of disturbance regimes for different forest types can only be made if this intersite variability is addressed. 相似文献
93.
Bruce L. Wilson Glenn L. Albright Ph.D. Solomon S. Steiner John L. Andreassi 《Applied psychophysiology and biofeedback》1991,16(1):45-53
In the present study 36 police officers were exposed to a psychological stressor (IQ quiz) and to cold pressor stress while several cardiovascular variables were monitored. Impedance cardiography was used to provide measures of heart rate, stroke volume, cardiac output, myocardial contractility, and total peripheral resistance. In addition, measures of systolic and diastolic blood pressure and peripheral skin temperature were obtained. A multivariate analysis of variance (MANOVA) indicated that significant increases in diastolic and systolic blood pressure during the cold pressor test were mediated by large increases in total peripheral resistance, whereas blood pressure elevation during the IQ quiz were accompanied by significant increases in heart rate and, to a lesser extent, cardiac output. Peripheral skin temperature decreased in response to each stressor. Additional analysis indicated a degree of stimulus specificity for several variables. For example, diastolic blood pressure showed greater increases to cold pressor than quiz, whereas systolic blood pressure increased more with the psychological than the physical stressor. Directional fractionation occurred for both myocardial contractility and cardiac output. 相似文献
94.
David D. Reed Elizabeth A. Jones Hal O. Liechty Glenn D. Mroz Martin F. Jurgensen 《International journal of biometeorology》1992,36(1):51-57
The response of four northern deciduous tree species to annual climate variation is quantified at two intensively measured sites in northern Michigan, USA. Response to changes in temperature and moisture differ with the species and is dependent on other site conditions. Relationships identified in these field studies indicate that projected climate changes may have dramatic effects on the productivity of at least some commercially important tree species in the northern United States. 相似文献
95.
Two techniques, electroporation and conjugation, have been used to introduce the RK2-based broad-host-range plasmids pRK415 and pLAFR3 into strains of the bacterial genus Acidiphilium. Using electroporation, cells were also transformed with a series of chimeric plasmids constructed by cloning cryptic Acidiphilium plasmids into the Escherichia coli vector pBR328. Various parameters affecting electroporation were investigated. Transformation efficiency varied widely with different recipient strains. Growth at an elevated temperature (37 degrees C) prior to electroporation increased transformation efficiency 10-fold compared with growth at 32 degrees C. For three strains tested, optimum transformation efficiency was obtained with field strengths of 10-15 kV/cm. Transformation efficiency increased linearly with increasing DNA concentration up to 10 micrograms/mL. Transformation efficiencies in these experiments ranged up to 10(4) transformants/micrograms DNA. Mobilization of pRK415 and pLAFR3 from E. coli strain S17.1 into several Acidiphilium strains was achieved following incubation for 3 h on nutrient agar medium (pH 7.0). Conjugation frequencies in the range of 10(-5)-10(-9) per recipient cell were obtained. Conjugation frequency was also dependent on recipient strain. 相似文献
96.
97.
Somatic embryogenesis in soybean via somatic embryo cycling 总被引:4,自引:0,他引:4
Wennuan Liu Patricia J. Moore Glenn B. Collins 《In vitro cellular & developmental biology. Plant》1992,28(3):153-160
Summary The objectives of the present research were: a) to develop an efficient soybean embryogenic regeneration system characterized
by a high frequency of explant response and a large number of somatic embryos per explant; b) to evaluate the factors affecting
somatic embryogenesis via somatic embryo cycling; and c) to identify the origin of somatic embryos in the system. A highly
improved and efficient system for soybean somatic embryogenesis was established using somatic embryo cotyledons and somatic
embryo hypocotyl/radicle explants plated on α-naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D) supplemented
MS basal media. The system included somatic embryo cycling between liquid and solid medium and it consistently gave rise to
a much higher frequency of explant response and a larger number of embryos per responding explant than those obtained from
zygotic cotyledon explant tissues. Genotype, differences were observed for response in some of the treatments with cv “Fayette”
being more responsive than “J103”. Histological studies revealed that somatic embryos induced in the somatic embryo cycling
system originated almost exclusively from epidermal cells on both 2,4-D and NAA inductive media. The cells of the epidermis
proliferated to produce somatic embryos directly without an intervening callus phase. A single-cell origin of somatic embryos
was observed in cultures on a 40 mg/liter 2,4-D treatment. A large number of responding cells in the epidermis was also observed
in the 10 mg/liter NAA treatment. The single-cell origin of somatic embryos from epidermal layers of the explant tissues should
facilitate development of an efficient transformation system for soybean. 相似文献
98.
Edward P. Glenn 《Physiologia plantarum》1981,52(1):59-64
The effect of 300 μ M arginine on growth of sugarcane cell suspensions was studied. Cells transferred to defined media in the stationary growth stage showed a greater requirement for exogenous arginine than cells similarly transferred in the rapidly dividing stage. Cell arginine levels, rates of arginine synthesis, and enzymes of arginine synthesis all decreased in cells entering the stationary stage. It is concluded that stationary stage cells are deficient in their ability to synthesize arginine and are therefore dependent upon an exogenous supply to resume growth in fresh media. 相似文献
99.
Tandem duplication induced by an unusual ampA1-, ampC-transducing lambda phage: A probe to initiate gene amplification 总被引:3,自引:0,他引:3
Thomas Edlund Thomas Grundström Glenn R. Björk Staffan Normark 《Molecular & general genetics : MGG》1980,180(2):249-257
Summary Secondary attachment site -lysogens were isolated in an Escherichia coli strain carrying multiple tandem 9.8 kb repeats. The repeat carried the structural gene for chromosomal -lactamase, ampC. One lysogen produced lysates with amp-transducing activity. Three types of phages with different densities were obtained from this lysogen. The one with the lowest density was found to be a helper cI857S7 phage. The other two phages showed identical restriction endonuclease fragmentation patterns. The difference in density was due to the presence or absence of phage tail. In damp the right cohesive end segment was deleted in a random fashion with the majority ending between 81.0% and 82.4% of . The chromosomal segment of damp was most likely located at the attachment site. The damp DNA was compared to that of a ColE1 hybrid carrying the chromosomal amp segment and a ColE1 hybrid carrying the same 9.8 kb amp repeat as the lysogen from which damp was isolated. It was found that the chromosomal part of damp constituted 9.8 kb, i.e. the size of one repeat. Moreover, the novel joint between adjacent repeats was present. In a attB-deleted E. coli K-12 strain, lysogenic for damp, highly ampicillin-resistant mutants occurred at an exceedingly high frequency. They were found to contain in the chromosome an amplified 9.8 kb repeat. This suggested that integration of the novel joint from damp into the amp region gives rise to an amplifiable duplication. In E. coli lysogenized for damp at attB highly ampicillin-resistant clones were also found at a high frequency. These clones carried multiple tandem repeats of damp DNA, each with an intact right end segment. 相似文献
100.
A protein spot corresponding to l-glycerol-3-phosphate dehydrogenase (α-GPDH, E.C. 1.1.1.8, NAD+ oxidoreductase) has been identified on a two-dimensional gel (isoelectric focusing-SDS gel) containing up to 150 stained protein spots from a crude Drosophila homogenate. Preliminary identification of the α-GPDH spot was made by including a suitable amount of purified Drosophila α-GPDH in crude fly homogenates prior to electrophoresis and observing an intensity enhancement of the corresponding protein spot on the gels. When three purified electrophoretic variants (slow, fast, and ultrafast) were mixed and analyzed by two-dimensional gel electrophoresis, horizontal displacements of the three protein spots were observed. Immunoprecipitation of the enzyme prior to electrophoresis and gene mapping further confirmed the identity of the α-GPDH protein spot. The α-GPDH spot can also be detected by autoradiography of a two-dimensional gel from a single fly extract, where it has been estimated to constitute 0.5–1% of the total soluble protein. Mutants which express no apparent α-GPDH activity were analyzed by two-dimensional gels and immunoelectrophoresis in an attempt to identify and characterize the inactive proteins. It is suggested that these techniques provide a powerful tool for the analysis of CRM+-null activity mutants of a specific gene-enzyme system. 相似文献