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151.
Edwin M. Everham III Randall W. Myster Eric VanDeGenachte 《American journal of botany》1996,83(8):1063-1068
Field experiments were conducted to investigate the effects of light, moisture, temperature, and litter on the regeneration of two early-, one mid-, and two late-successional tropical tree species. High light and litter seem to be universally good cues for regeneration, increasing seed/seedling survival for all species except for Cecropia (an early-successional species) whose small seeds may not be able to penetrate the litter layer. In addition, the high temperature environment in both artificially shaded and nonshaded areas of a natural gap exhibits less seed loss, an increase in the percent and rate of germination, and an increase in seedling survival for Dacryodes (a late-successional species), than the lower temperature environment under an intact canopy. Low soil water is also a good cue for Dacryodes germination as it is for Prestoea and Cecropia. Finally, the lower temperature environment found under the forest canopy (compared to the natural gap) leads to less seed loss and more germination for Guarea (a mid-successional species). Our results suggest that a good patch for regeneration of many species in this forest, early- as well as late-successional species, would have high light and a litter layer that moderates temperature and moisture extremes. The substantial variation in suitability among regeneration filters and species could: (1) contribute to low establishment success, i.e., most dispersed propagules do not become trees, (2) make it difficult to group species into germination strategies, and (3) make it hard to generalize about a net effect of any specific environmental variable on establishment. We suggest that tropical disturbances should be viewed in terms of their impact on a variety of environmental cues, which may signal germination and impact subsequent growth and survival. 相似文献
152.
Pei-Wen Chiang SuQing Wang Paul Smithivas Woo-Joo Song Saravanan Ramamoorthy Joseph Hillman Sheryl Puett Margaret L. Van Keuren Eric Crombez Arun Kumar Thomas W. Glover Diane E. Miller Chun-Hui Tsai C.Clare Blackburn Xiao-Ning Chen Zhiguang Sun Jan-Fang Cheng Julie R. Korenberg David M. Kurnit 《Genomics》1996,34(3):328
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156.
Calcium ions play critical roles in neuronal differentiation. We have recorded transient, repeated elevations of calcium in embryonic Xenopus spinal neurons over periods of 1 h in vitro and in vivo, confocally imaging fluo 3-loaded cells at 5 s intervals. Calcium spikes and calcium waves are found both in neurons in culture and in the intact spinal cord. Spikes rise rapidly to approximately 400% of baseline fluorescence and have a double exponential decay, whereas waves rise slowly to approximately 200% of baseline fluorescence and decay slowly as well. Imaging of fura 2-loaded neurons indicates that intracellular calcium increases from 50 to 500 nM during spikes. Both spikes and waves are abolished by removal of extracellular calcium. Developmentally, the incidence and frequency of spikes decrease, whereas the incidence and frequency of waves are constant. Spikes are generated by spontaneous calcium-dependent action potentials and also utilize intracellular calcium stores. Waves are produced by a mechanism that does not involve classic voltage-dependent calcium channels. Spikes are required for expression of the transmitter GABA and for potassium channel modulation. Waves in growth cones are likely to regulate neurite extension. The results demonstrate the roles of a novel signaling system in regulating neuronal plasticity, that operates on a time scale 104 times slower than that of action potentials. © 1995 John Wiley & Sons, Inc. 相似文献
157.
Eric Hbert Michel Monsigny 《Biology of the cell / under the auspices of the European Cell Biology Organization》1994,81(1):73-76
Summary— The increase in galectin-3 lectin content observed in tumours or in in vitro transformed cells suggests that this lectin is important in the transformation process. In the present study, we investigated the mRNA expression level of the galectin-3, galectin-I and macrophage mannose receptor in normal and ras-transformed NIH 3T3 cells in relation to their transformation state. The galectin3 mRNA content in ras-transformed cells is increased in fully transformed cells, with a maximum in ras-transformed cells that have lost their growth anchorage-dependence. Under the same conditions, the galectin-1 mRNA level which was high in normal cells, increased slightly in transformed cells. The mRNA for the macrophage mannose receptor was not detected in 3T3 cells or in their ras-transformed counterparts. 相似文献
158.
Eric Dufour Paul Robert Dominique Bertrand Tomasz Haertlé 《Journal of Protein Chemistry》1994,13(2):143-149
Fourier transform infrared spectroscopy has been applied to investigate the secondary structural changes of-lactoglobulin in water/ethanol mixtures. The studies were carried out at two differentpHs and at high protein concentrations. The spectra were recorded using an attenuated total reflection cell. The amide I band of-lactoglobulin in water reveals large amounts of intra extended-sheet structure. About 20% ethanol,-lactoglobulin unfolds and-strand formation is observed.-Helices are built up by increasing the ethanol concentration up to 30%. In 50% ethanol,-lactoglobulin gels providing the apparent pH are neutral. The secondary structural changes of-lactoglobulin were observed on the similarity maps obtained by Principal Component Analysis. 相似文献
159.
Theoretical Basis of Protocols for Seed Storage III. Optimum Moisture Contents for Pea Seeds Stored at Different Temperatures 总被引:6,自引:1,他引:5
In previous work, we demonstrated that there was an optimummoisture level for seed storage at a given temperature (Vertucciand Roos, 1990), and suggested, using thermodynamic considerations,that the optimum moisture content increased as the storage temperaturedecreased (Vertucci and Roos, 1993b). In this paper, we presentdata from a two year study of aging rates in pea (Pisum sativum)seeds supporting the hypothesis that the optimum moisture contentfor storage varies with temperature. Seed viability and vigourwere monitored during storage under dark or lighted conditionsat relative humidities between 1 and 90%, and temperatures between-5 and 65°C. The optimum moisture content varied from 0·015g H2O g-1 d.wt at 65°C to 0·101 g H2O g-1 d.wt at15°C under dark conditions and from 0·057 at 35°Cto 0·092 g H2O g-1 d.wt at -5°C under lighted conditions.Our results suggest that optimum moisture contents cannot beconsidered independently of temperature. This conclusion hasimportant implications for 'ultra-dry' and cryopreservationtechnologies.Copyright 1994, 1999 Academic Press Seed storage, seed aging, seed longevity, water content, temperature, glass, desiccation damage, ultradry, Pisum sativum L., pea, cryopreservation 相似文献
160.
Eric Glasgow †Robert K. Druger †Chana Fuchs †Edward M. Levine †Suzanne Giordano † Nisson Schechter 《Journal of neurochemistry》1994,63(2):470-481
Abstract: In efforts to determine the primary structure of intermediate filament proteins in the goldfish visual pathway, we isolated clones from a retinal λgt11 cDNA expression library that represent goldfish vimentin. We show that there are at least two forms of goldfish vimentin, designated as vimentin α and vimentin β. RNase protection assays indicate that vimentin α mRNA is expressed in low amounts in retina, optic nerve, and brain and in higher amounts in spinal cord. In contrast, vimentin β mRNA is expressed in low amounts in retina, optic nerve, brain, and spinal cord and in very high amounts in eye lens. Immunohistochemical studies show that in the optic nerve, vimentin α is mainly restricted to blood vessels, meninges, and septa. Light staining is observed with this antibody in an astrocytic glial pattern throughout the optic nerve. Two-dimensional gel analysis shows that all of these goldfish vimentins are low abundant components of optic nerve cytoskeletal preparations. 相似文献