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21.
Bjørn Grinde 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(2):140-144
Benzyl alcohol caused a rather complete and selective inhibition of the methylamine sensitive (i.e., the putative lysosomal) pathway of protein degradation in isolated rat hepatocytes. The effect was found to be entirely reversible within 30 min of removing the agent. A morphometric examination of electron micrographs revealed that the inhibition of lysosomal protein degradation coincided with a block in the formation of autophagic vacuoles. The number of acidic vacuoles (i.e., vacuoles induced to swell by adding methylamine) was not drastically reduced. 相似文献
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The simultaneous action of shear deformation and high pressure (SDHP) creates changes in the structure of wood and its main
components (cellulose, hemicelluloses, lignin). The formation of water and alkali soluble polysaccharides under SDHP action,
proceeds in seconds in the solid state, without the use of any reagents and solvents. Therefore, SDHP seems to be a technologically
safe method and friendly to the environment. The amorphization of cellulose crystallites and depolymerization of cellulose
chains were observed under a wide range of pressures (1–6 GPa), both for cellulose samples and the cellulose part of wood.
Similar depolymerization occurs in the hemicellulose part of wood. The decomposition of polysaccharides under SDHP causes
the formation of the water soluble part, whose content increases with pressure and the applied shear deformation. A maximum
solubility of 40% and 55% was registered at 6 GPa following treatment of cellulose and birch wood samples. A higher output
in the case of wood can be explained by a specific role of lignin under SDHP, which acts as a ‘grinding stone’ during cellulose
and hemicelluloses destruction. As shown by high-performance size exclusion chromatography, the water soluble fraction obtained
from cellulose contained glucose (2.6%), cellobiose (9.6%), cellotriose (16.6%) and other higher water soluble oligomers (71%).
Almost complete dissolution (98%) of the treated cellulose sample can be achieved by extraction with 10% NaOH solution. The
SDHP treated birch wood was subjected to submerged fermentation (with Trichoderma viride), and a 13% output of proteins was
obtained. In this case, the water soluble part played the role of the so called ‘start sugars’. Abbreviations: ASF, alkali
soluble fraction; DP, degree of polymerization; EC, energy consumption; HP, high pressure; LMWS, low molecular weight sugars;
MC, moisture content; MCC, microcrystalline cellulose; SD, shear deformation, SDHP, shear deformation under high pressure;
SS, shear strength; WSF, water soluble fraction
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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Oxygen stable isotope ratios of tree-ring cellulose: the next phase of understanding 总被引:3,自引:0,他引:3
Leonel da Silveira Lobo O'Reilly Sternberg 《The New phytologist》2009,181(3):553-562
Analysis of the oxygen isotope ratio of tree-ring cellulose is a valuable tool that can be used as a paleoclimate proxy. Our ability to use this tool has gone through different phases. The first began in the 1970s with the demonstration of empirical relationships between the oxygen isotope ratio of tree-ring cellulose and climate. These empirical relationships, however, did not provide us with the confidence that they are robust through time, across taxa and across geographical locations. The second phase began with a rudimentary understanding of the physiological and biochemical mechanisms responsible for the oxygen isotope ratios of cellulose, which is necessary to increase the power of this tool. This phase culminated in a mechanistic tree-ring model integrating concepts of physiology and biochemistry in a whole-plant system. This model made several assumptions about leaf water isotopic enrichment and biochemistry which, in the nascent third phase, are now being challenged, with surprising results. These third-phase results suggest that, contrary to the model assumption, leaf temperature across a large latitudinal gradient is remarkably constant and does not follow ambient temperature. Recent findings also indicate that the biochemistry responsible for the incorporation of the cellulose oxygen isotopic signature is not as simple as has been assumed. Interestingly, the results of these challenges have strengthened the tree-ring model. There are several other assumptions that can be investigated which will improve the utility of the tree-ring model. 相似文献
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Determinants of Land Degradation and Fragmentation in Semiarid Vegetation at Landscape Scale 总被引:1,自引:0,他引:1
Yolanda Pueyo Concepción L. Alados Olivia Barrantes 《Biodiversity and Conservation》2006,15(3):939-956
The objective of this paper was to investigate the sensitivity to degradation of semiarid plant communities in terms of plant
cover and fragmentation, quantifying relationships between landscape characteristic (physical, socio-economical and historical)
and vegetation degradation. The degradation of vegetation was measured as the degree of coverage of the two dominant vegetation
types (i.e. tall arid brush and tall grass steppe), while fragmentation was measured as patch size and isolation. Data were
obtained using GIS tools, and analyzed by logistic regression and linear multivariate regression. Results showed denser coverage
at more elevated, gradual slopes that were not sea-oriented. Historical elements of the landscape had a significant effect
on current natural vegetation. According to the fragmentation patterns, the vegetation is in fairly good condition (medium
coverage had the largest patches but dense coverage was less isolated) but attention must be given to preserve vegetation,
due to the relationships between fragmentation and human activities. Moreover, the protection plan under way in the area appeared
to favour denser vegetation cover, while human activities had a measurable effect on vegetation degradation. 相似文献