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41.
Thidiazuron stimulates shoot organogenesis and somatic embryogenesis in white ash (Fraxinus americana L.) 总被引:3,自引:0,他引:3
Sharon Bates John E. Preece Nadia E. Navarrete J. W. Van Sambeek Gerald R. Gaffney 《Plant Cell, Tissue and Organ Culture》1992,31(1):21-29
Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 M thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 M adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 M thidiazuron, followed by transfer to a medium containing 0.05 M 6-benzyladenine and 0.5 M naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.Abbreviations BA
6-benzyladenine
- 2,4-d
2,4-dichlorophenoxyacetic acid
- IBA
indolebutyric acid
- 2iP
isopentenyladenine
- NAA
naphthaleneacetic acid
- TDZ
thidiazuron-N-phenyl-N-1,2,3-thiadiazol-5-ylurea
- WPM
woody plant medium 相似文献
42.
Summary Healthy pecan, Caryaillinoensis (Wang) Koch, tissue was obtained from an 8-year-old grafted Cherokee tree. Dormant buds were gathered and stored until spring
growth. After rigorous surface sterilization, halves of both stored and freshly harvested dormant buds and of actively growing
shoots were plated onto sterile PDA. Corresponding halves wre fixed in FAA and processed for scanning electron microscopy
(SEM). All plated dormant buds (both stored and freshly harvested) showed presence internally of a fungus, and SEM studies
revealed hyphalike strands similar to those of the isolated fungi within cells of those buds. The spring flush was sterile
in culture, and strands were absent in SEM studies. 相似文献
43.
The molecular control of the distribution and motion of acetylcholine receptors in the plasma membrane of developing rat myotubes in primary cell culture was investigated by fluorescence techniques. Acetylcholine receptors were marked with tetramethylrhodamine-labeled α-bungarotoxin and lateral molecular motion in the membrane was measured by the fluorescence photobleaching recovery technique. Three types of experiments are discussed: (I) The effect of enzymatic cleavages, drugs, cross-linkers, and physiological alterations on the lateral motion of acetylcholine receptors and on the characteristic distribution of acetylcholine receptors into patch and diffuse areas. (II) Observation of the distribution and/or motion of fluorescence-labeled concanavalin A receptors, lipid probes, cell surface protein, and stained cholinesterase in acetylcholine receptor patch and diffuse areas. (III) The effect of a protein synthesis inhibitor and electrical stimulation on membrane incorporation of new acetylcholine receptors.Some of the main conclusions are: (a) acetylcholine receptor lateral motion is inhibited by concanavalin A plant lectin and by anti-α-bungarotoxin antibody, but marginally enhanced by treatment with a local anesthetic; (b) patches are stabilized by an immobile cellular structure consisting of molecules other than the acetylcholine receptors themselves; (c) this structure is highly selective for acetylcholine receptors and not for other cell membrane components; (d) acetylcholine receptor patch integrity and diffuse area motion are independent of direct metabolic energy requirements and are sensitive to electrical excitation of myotube; (e) lipid molecules can move laterally in both acetylcholine receptor patches and diffuse areas; and (f) acetylcholine receptor lateral motion in diffuse areas and immobility in patch areas are not altered by specific agents which are known to affect extrinsic cell surface proteins, or cytoplasmic microfilaments and microtubules. 相似文献
44.
45.
The ecological impact of bush encroachment on the yield of grasses in Borana rangeland ecosystem 总被引:1,自引:0,他引:1
Ayana Angassa 《African Journal of Ecology》2005,43(1):14-20
The ecological impact of woody encroachment and the responses of herbage yield to encroachment were assessed at three locations in Borana rangeland at the end of the growing season. The study was carried out in two communal grazing areas (Medhecho and Dubluk) and one Government ranch (Dida‐Tuyura) in bush and/or shrub encroached and non‐encroached sites. In each area, three altitude ranges were distinguished and in each altitude range one transect, covering both encroached and non‐encroached rangeland, was selected. The assessment was based on the yield and botanical composition of the herbaceous layer. The grasses Cenchrus ciliaris, Chrysopogon aucheri and Panicum coloratum were common or dominant in both encroached and non‐encroached sites. Pennisetum mezianum and Pennise‐tum stramineum were typically found in encroached vegetation. The relative yield increased with non‐encroached sites and varied at different altitude ranges from about 106% to about 150%, thus increases ranged from 75% in Medhecho to 350% in Dubluk as determined from the lower values of the ranges. The encroached vegetation had a significantly lower score for herbage yield than the non‐encroached vegetation for most of the sites, although the differences were small. Differences based on altitude range were also significant for Eragrostis papposa and Pennisetum stramineum, while the three areas showed a significant difference for the mean yield of Aristida adscensionis, Cenchrus ciliaris and Eragrostis papposa. 相似文献
46.
47.
Aim This study investigates changes in bird communities between 1998 and 2008 in four savanna sites in Swaziland and the extent to which shrub encroachment is responsible for these changes. Location Swaziland, southern Africa. Methods Generalized estimated equations were used to estimate changes in bird species occurrence between 1998 and 2008. Remote sensing of aerial photographs/satellite images was used to assess vegetation changes during the same period. We assessed the role of shrub encroachment for bird communities by testing the relationship between change in species occurrence and species habitat using a general linear model. We also estimated species richness, colonization and extinction and used general linear models to test the effects of vegetation changes on these parameters. Results More than half of the bird species showed a significant change in occurrence between 1998 and 2008: 32 species increased and 29 decreased. Change in species occurrence was significantly explained by species habitat. Species significantly increasing were mainly associated with wooded savanna, whereas species significantly decreasing were mainly associated with open savanna. Species richness decreased significantly, and this decrease was significantly explained by shrub cover increase at the plot scale (from 24% to 44% on average). Extinction at the plot scale was significantly influenced by the loss of grass cover, while colonization at the plot scale was influenced by tree cover increase. Main conclusions This study represents the first evidence of temporal changes in bird communities owing to shrub encroachment in southern Africa. Despite its short time frame (10 years), this study shows dramatic changes in both vegetation structure and bird community composition. This confirms the general concern for southern African bird species associated with open savanna if current trends continue. 相似文献
48.
During the scale‐up of a bioprocess, not all characteristics of the process can be kept constant throughout the different scales. This typically results in increased mixing times with increasing reactor volumes. The poor mixing leads in turn to the formation of concentration gradients throughout the reactor and exposes cells to varying external conditions based on their location in the bioreactor. This can affect process performance and complicate process scale‐up. Scale‐down simulators, which aim at replicating the large‐scale environment, expose the cells to changing environmental conditions. This has the potential to reveal adaptation mechanisms, which cells are using to adjust to rapidly fluctuating environmental conditions and can identify possible root causes for difficulties maintaining similar process performance at different scales. This understanding is of utmost importance in process validation. Additionally, these simulators also have the potential to be used for selecting cells, which are most robust when encountering changing extracellular conditions. The aim of this review is to summarize recent work in this interesting and promising area with the focus on mammalian bioprocesses, since microbial processes have been extensively reviewed. 相似文献
49.
Katrin Paul Katharina Bttinger Bernd M. Mitic Georg Scherfler Christoph Posch Dirk Behrens Christian G. Huber Christoph Herwig 《Engineering in Life Science》2020,20(8):368-378
Large‐scale bioreactors for the production of monoclonal antibodies reach volumes of up to 25 000 L. With increasing bioreactor size, mixing is however affected negatively, resulting in the formation of gradients throughout the reactor. These gradients can adversely affect process performance at large scale. Since mammalian cells are sensitive to changes in pH, this study investigated the effects of pH gradients on process performance. A 2‐Compartment System was established for this purpose to expose only a fraction of the cell population to pH excursions and thereby mimicking a large‐scale bioreactor. Cells were exposed to repeated pH amplitudes of 0.4 units (pH 7.3), which resulted in decreased viable cell counts, as well as the inhibition of the lactate metabolic shift. These effects were furthermore accompanied by increased absolute lactate levels. Continuous assessment of molecular attributes of the expressed target protein revealed that subunit assembly or N‐glycosylation patterns were only slightly influenced by the pH excursions. The exposure of more cells to the same pH amplitudes further impaired process performance, indicating this is an important factor, which influences the impact of pH inhomogeneity. This knowledge can aid in the design of pH control strategies to minimize the effects of pH inhomogeneity in large‐scale bioreactors. 相似文献
50.
Zai Hang Zhang Xin Yu Jia Jing Yi Fang Hao Chai Qun Huang Chang She Peng Jia De Chun Geng Wei Xu 《Journal of cellular and molecular medicine》2020,24(7):4233-4244
The increase in bone resorption and/or the inhibition of bone regeneration caused by wear particles are the main causes of periprosthetic osteolysis. The SOST gene and Sclerostin, a protein synthesized by the SOST gene, are the characteristic marker of osteocytes and regulate bone formation and resorption. We aimed to verify whether the SOST gene was involved in osteolysis induced by titanium (Ti) particles and to investigate the effects of SOST reduction on osteolysis. The results showed osteolysis on the skull surface with an increase of sclerostin levels after treated with Ti particles. Similarly, sclerostin expression in MLO-Y4 osteocytes increased when treated with Ti particles in vitro. After reduction of SOST, local bone mineral density and bone volume increased, while number of lytic pores on the skull surface decreased and the erodibility of the skull surface was compensated. Histological analyses revealed that SOST reduction increased significantly alkaline phosphatase- (ALP) and osterix-positive expression on the skull surface which promoted bone formation. ALP activity and mineralization of MC3T3-E1 cells also increased in vitro when SOST was silenced, even if treated with Ti particles. In addition, Ti particles decreased β-catenin expression with an increase in sclerostin levels, in vivo and in vitro. Inversely, reduction of SOST expression increased β-catenin expression. In summary, our results suggested that reduction of SOST gene can activate the Wnt/β-catenin signalling pathway, promoting bone formation and compensated for bone loss induced by Ti particles. Thus, this study provided new perspectives in understanding the mechanisms of periprosthetic osteolysis. 相似文献