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991.
992.
Far red end-of-day treatment restores wild type-like plant length in hybrid aspen overexpressing phytochrome A 总被引:4,自引:0,他引:4
Shoot elongation in woody plants is modulated by a multitude of light signals, including irradiance, photoperiod and spectral composition, for which the phytochrome system is the probable photoreceptor. In hybrid aspen ( Populus tremula × tremuloides ) overexpression of the oat phytochrome A ( PHYA ) prevents growth cessation in response to short photoperiod, and plants exhibit dwarf growth that is related to reduced cell numbers and reduced gibberellin contents. End-of-day far-red treatment significantly enhances internode elongation in PHYA overexpressors as well as in the wild type, and this was found here to be caused by stimulation of cell division and cell extension. In PHYA overexpressors the effects were substantially larger than in the wild type, and resulted in complete restoration of wild type-like plant length as well as cell numbers, and gibberellin content was greatly increased. No clear effect of far-red end-of-day treatment on gibberellin levels could be detected in the wild type. It thus appears that the far-red end-of-day treatment might modify the responsiveness of the tissue to GA rather than the GA levels. The observed effects were completely reversed by a subsequent irradiation with red light. The present data show that dwarfism due to PHYA overexpression can be completely overcome by far red end-of-day treatment, and the observations indicate that effects of far red end-of-day treatments appear to be mediated by phytochrome(s) other than phytochrome A. 相似文献
993.
The production of extracellular enzymes by the thermophilic fungus Thermomyces lanuginosus was studied in chemostat cultures at a dilution rate of 0.08 h–1 in relation to variation in the ammonium concentration in the feed medium. Under steady state conditions, three growth regimes were recognised and the production of several extracellular enzymes from T. lanuginosus was recorded under different nutrient limitations ranging from nitrogen limitation to carbon/energy limitation. The range and the production of carbohydrate hydrolysing enzymes and lipase increased from Regime I (NH4Cl 600 mg l–1) to Regime III (NH4CI 1200 mg l–1), whereas production of protease was highest in Regime II (600 mg l–1 < NH4Cl <1200 mg l–1). 相似文献
994.
Ribonucleotide reduction is the only known biological means for de novo production of deoxyribonucleotides, the building blocks of DNA. These are produced from ribonucleotides, the building blocks
of RNA, and the direction of this reaction has been taken to support the idea that, in evolution, RNA preceded DNA as genetic
material. However, an understanding of the evolutionary relationships among the three modern-day classes of ribonucleotide
reductase and how the first reductase arose early in evolution is still far off. We propose that the diversification of this
class of enzymes is inherently tied to microbial colonization of aerobic and anaerobic niches. The work is of broader interest,
as it also sheds light on the process of adaptation to oxygenic environments consequent to the evolution of atmospheric oxygen. 相似文献
995.
Dragoi V 《Biological cybernetics》2002,86(6):419-426
Simple exposure to repeatitive stimulation is known to induce short-term learning effects across a wide range of species.
These effects can be both suppressive and facilitatory depending on stimulus conditions: repeatitive presentation of a weak
stimulus decreases the strength of the response (habituation), whereas presentation of a tonic stimulus following a series
of weak stimuli transiently increases the response strength (dishabituation). Although these phenomena have been comprehensively
characterized at both behavioral and cellular levels, most existing models of nonassociative learning focus exclusively on
the suppressive or facilitatory changes in response, and do not attempt to relate cellular events to behavior. I propose here
a feedforward model of habituation effects that explains both suppressive and facilitatory changes in response relying on
the interaction between excitatory and inhibitory processes that develop in parallel on two different timescales. The model's
properties are used to explain the rate sensitivity property of habituation and recovery and stimulus dishabituation.
Received: 1 June 2001 / Accepted in revised form: 4 December 2001 相似文献
996.
997.
Ethanol production from corn cob hydrolysates by <Emphasis Type="Italic">Escherichia coli</Emphasis> KO11 总被引:2,自引:0,他引:2
de Carvalho Lima KG Takahashi CM Alterthum F 《Journal of industrial microbiology & biotechnology》2002,29(3):124-128
Corn cob hydrolysates, with xylose as the dominant sugar, were fermented to ethanol by recombinant Escherichia coli KO11. When inoculum was grown on LB medium containing glucose, fermentation of the hydrolysate was completed in 163 h and
ethanol yield was 0.50 g ethanol/g sugar. When inoculum was grown on xylose, ethanol yield dropped, but fermentation was faster
(113 h). Hydrolysate containing 72.0 g/l xylose and supplemented with 20.0 g/l rice bran was readily fermented, producing
36.0 g/l ethanol within 70 h. Maximum ethanol concentrations were not higher for fermentations using higher cellular concentration
inocula. A simulation of an industrial process integrating pentose fermentation by E. coli and hexose fermentation by yeast was carried out. At the first step, E. coli fermented the hydrolysate containing 85.0 g/l xylose, producing 40.0 g/l ethanol in 94 h. Baker's yeast and sucrose (150.0
g/l) were then added to the spent fermentation broth. After 8 h of yeast fermentation, the ethanol concentration reached 104.0
g/l. This two-stage fermentation can render the bioconversion of lignocellulose to ethanol more attractive due to increased
final alcohol concentration. Journal of Industrial Microbiology & Biotechnology (2002) 29, 124–128 doi:10.1038/sj.jim.7000287
Received 20 February 2002/ Accepted in revised form 04 June 2002 相似文献
998.
999.
Based on NMR spectroscopic information about the allosamidin-hevamine complex, ab initio MO calculations of the ring current effect of the aromatic moieties of Trp255, Tyr183 and Tyr6 of hevamine were carried out to investigate the role of these amino acid residues in binding interactions with allosamidin in solution. In addition, the intermolecular steric compression effect on the 13C chemical shifts of the allosamizoline carbon atoms and the hydrogen bonding to Glu127 was identified. It can be inferred that the binding forces are strongest in the allosamizoline moiety of allosamidin. 相似文献
1000.
High rates of deforestation in the Brazilian Amazon have the potential to alter the storage and cycling of carbon (C) and nitrogen (N) across this region. To investigate the impacts of deforestation, we quantified total aboveground biomass (TAGB), aboveground and soil pools of C and N, and soil N availability along a land-use gradient in Rondônia, Brazil, that included standing primary forest, slashed primary and secondary forest, shifting cultivation, and pasture sites. TAGB decreased substantially with increasing land use, ranging from 311 and 399 Mg ha–1 (primary forests) to 63 Mg ha–1 (pasture). Aboveground C and N pools declined in patterns and magnitudes similar to those of TAGB. Unlike aboveground pools, soil C and N concentrations and pools did not show consistent declines in response to land use. Instead, C and N concentrations were strongly related to percent clay content of soils. Concentrations of NO3-N and NH4-N generally increased in soils following slash-and-burn events along the land-use gradient and decreased with increasing land use. Increasing land use resulted in marked declines in NO3-N pools relative to NH4-N pools. Rates of net nitrification and N-mineralization were also generally higher in postfire treatments relative to prefire treatments along the land-use gradient and declined with increasing land use. Results demonstrate the linked responses of aboveground C and N pools and soil N availability to land use in the Brazilian Amazon; steady reductions in aboveground pools along the land-use gradient were accompanied by declines in inorganic soil N pools and transformation rates. 相似文献