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21.
Abstract. The wood-degrading white-rot fungus Phanerochaete chrysosporium , has been the subject of intensive research in recent years and, based upon isolation of the extracellular enzyme ligninase, major advances have now been made toward elucidating the mechanism by which this fungus degrades lignin. From these developments, a model emerges which could explain the process by which wood-degrading fungi in general, attack lignin. 相似文献
22.
A system was established for introducing cloned genes into white clover (Trifolium repens L.). A high regeneration white clover genotype was transformed with binary Agrobacterium vectors containing a chimaeric gene which confers kanamycin resistance. Transformed kanamycin resistant callus was obtained by culturing Agrobacterium inoculated stolon internode segments on selective medium. The kanamycin resistance phenotype was stable in cells and in regenerated shoots. Transformation was confirmed by the expression of an unselected gene, nopaline synthase in selected cells and transgenic shoots and by the detection of neomycin phosphotransferase II enzymatic activity in kanamycin resistant cells. Integration of vector DNA sequences into plant DNA was demonstrated by Southern blot hybridisation. 相似文献
23.
S. B. Hladky 《European biophysics journal : EBJ》1987,15(4):251-255
The transfer of substances across the interface between water and a membrane or between water and a solvent occurs in series with transport up to and away from the interface. These processes have been difficult to resolve. Recently D. M. Miller (Biochim Biophys Acta 856: 27–35, 1986) has used a moving drop technique to measure the rates of transfer of short-chain alcohols and tritiated water between water andn-octanol. This technique produces equivalent unstirred layers which are less than about 10 m thick. Based on the trends in the observed rates of phase transfer, he proposes that the transfer is limited by the actual interfacial step. If so, water-oil interfacial transfer would be sufficiently slow to limit the rate of permeation of lipid membranes by these substances. It is shown here that the observed rates of phase transfer can be explained quantitatively if they are limited by convection or by diffusion across the combination of 5–10 m unstirred layers both inside and outside the moving drops. For water, comparison of the observed rates with the rate of evaporation from a clean surface, suggests that the interfacial step at the water-octanol interface is not rate-limiting. 相似文献
24.
The rate of the electromagnetic energy deposition and the resultant thermoregulatory response of a block model of a squirrel monkey exposed to plane-wave fields at 350 MHz were calculated using a finite-difference procedure. Noninvasive temperature measurements in live squirrel monkeys under similar exposure conditions were obtained using Vitek probes. Calculations exhibit reasonable correlation with the measured data, especially for the rise in colonic temperature. 相似文献
25.
Five plant species were cultivated on a soil from the Neckar alluvial fan near Heidelberg (FRG) polluted by the emissions
of a cement plant. Thallium, cadmium and lead concentrations in seedlings and mature plants were determined by atomic absorption
analysis. AdditionallyBrassica napus L.napus was grown on soils containing 5 different concentrations of heavy metals, achieved by mixing two similar soils, from the
same area but with different metal concentrations.
Thallium and cadmium were shown to be taken up by roots whilst lead which was also absorbed, was deposited mainly on the plant
surface. However during cultivation in the winter months, a remarkable deposit of lead via the roots was found. Thallium in
the soil from a anthrorogen source was more available to plants than thallium of geological origin.
During the lifetime of a plant concentrations of thallium and cadmium were always highest in the seedling. The decrease in
metal concentration with maturity depended on the plant species and the element, but was not a function of the metal concentration
in the soil. 相似文献
26.
Endosymbiotic origin and codon bias of the nuclear gene for chloroplast glyceraldehyde-3-phosphate dehydrogenase from maize 总被引:19,自引:0,他引:19
Henner Brinkmann Pascal Martinez Françoise Quigley William Martin Rüdiger Cerff 《Journal of molecular evolution》1987,26(4):320-328
Summary The nuclei of plant cells harbor genes for two types of glyceraldehyde-3-phosphate dehydrogenases (GAPDH) displaying a sequence divergence corresponding to the prokaryote/eukaryote separation. This strongly supports the endosymbiotic theory of chloroplast evolution and in particular the gene transfer hypothesis suggesting that the gene for the chloroplast enzyme, initially located in the genome of the endosymbiotic chloroplast progenitor, was transferred during the course of evolution into the nuclear genome of the endosymbiotic host. Codon usage in the gene for chloroplast GAPDH of maize is radically different from that employed by present-day chloroplasts and from that of the cytosolic (glycolytic) enzyme from the same cell. This reveals the presence of subcellular selective pressures which appear to be involved in the optimization of gene expression in the economically important graminaceous monocots. 相似文献
27.
28.
We used two different techniques to measure the recovery time of Photosystem II following the transfer of a single electron from P-680 to QA in thylakoid membranes isolated from spinach. Electron transfer in Photosystem II reaction centers was probed first by spectroscopic measurements of the electrochromic shift at 518 nm due to charge separation within the reaction centers. Using two short actinic flashes separated by a variable time interval we determined the time required after the first flash for the electrochromic shift at 518 nm to recover to the full extent on the second flash. In the second technique the redox state of QA at variable times after a saturating flash was monitored by measurement of the fluorescence induction in the absence of an inhibitor and in the presence of ferricyanide. The objective was to determine the time required after the actinic flash for the fluorescence induction to recover to the value observed after a 60 s dark period. Measurements were done under conditions in which (1) the electron donor for Photosystem II was water and the acceptor was the endogenous plastoquinone pool, and (2) Q400, the Fe2+ near QA, remained reduced and therefore was not a participant in the flash-induced electron-transfer reactions. The electrochromic shift at 518 nm and the fluorescence induction revealed a prominent biphasic recovery time for Photosystem II reaction centers. The majority of the Photosystem II reaction centers recovered in less than 50 ms. However, approx. one-third of the Photosystem II reaction centers required a half-time of 2–3 s to recover. Our interpretation of these data is that Photosystem II reaction centers consist of at least two distinct populations. One population, typically 68% of the total amount of Photosystem II as determined by the electrochromic shift, has a steady-state turnover rate for the electron-transfer reaction from water to the plastoquinone pool of approx. 250 e− / s, sufficiently rapid to account for measured rates of steady-state electron transport. The other population, typically 32%, has a turnover rate of approx. 0.2 e− / s. Since this turnover rate is over 1000-times slower than normally active Photosystem II complexes, we conclude that the slowly turning over Photosystem II complexes are inconsequential in contributing to energy transduction. The slowly turning over Photosystem II complexes are able to transfer an electron from P-680 to QA rapidly, but the reoxidation of Q−A is slow (t1/2 = 2 s). The fluorescence induction measurements lead us to conclude that there is significant overlap between the slowly turning over fraction of Photosystem II complexes and PS IIβ reaction centers. One corollary of this conclusion is that electron transfer from P-680 to QA in PS IIβ reaction centers results in charge separation across the membrane and gives rise to an electrochromic shift. 相似文献
29.
Methanogenesis by a Syntrophomonas wolfei/ Methanospirillum hungatei coculture was inhibited in presence of ethylene and the hydrogenation catalyst Pd-BaSO4. However, butyrate oxidation by S. wolfei continued and ethylene was reduced to ethane. Per mol of butyrate oxidized, 2.4 mol acetate was produced and 0.8 mol ethylene was reduced. Acetylene, propylene and butene were less effective as H2 acceptors than ethylene, and addition of bromoethanesulfonic acid was necessary to inhibit methanogenesis in the presence of the two longer-chain olefins. Other hydrogenation catalysts were less effective in the order Pd-charcoal < PE-asbestos < Pd-PEI beads < Pt-Al2O3, Pd-CaCO3. Optimal ethylene hydrogenation was achieved with still incubation in presence of 7.2 mg Pd-BaSO4 and 0.7 g sand per ml medium. The higher catabolic rate of S. wolfei in presence of the methanogen indicated that the biological H2 removal mechanism was more efficient than the catalytic olefin reduction.Abbreviations BES
bromoethane sulfonic acid
- VFA
volatile fatty acid 相似文献
30.
Deme formation in scale insects: a test with the pinyon needle scale and a review of other evidence 总被引:2,自引:0,他引:2
ABSTRACT. 1. Deme formation is the transformation of a generalist population into one which is adapted to its local conditions. This adaptation has been inferred from many things but should be inferred from higher survival or fecundity of scale insects on their natal tree compared to that of immigrant scales on the same tree.
2. Transfers of the scale insect Matsucoccus acalyptus Herbert within and between infested host trees ( Pinus monophylla (Torr. & Frem.) resulted in significant differences in scale survivorship among recipient trees. Survival on individual trees was correlated across years, indicating stable differences in tree susceptibility to scale.
3. A significant natal tree colonized tree interaction was observed for late stage scale survival in one experiment but the interaction was not caused by superior survivorship of scales transferred back to the natal tree. Hence, we found no evidence of deme formation in M.acalyptus.
4. Previous studies have concluded that deme formation occurs in the black pineleaf scale based on a significant natal tree by colonized tree interaction in scale survival. We question this conclusion because the experimental design employed did not include transfers back onto the natal tree. Other indirect evidence for deme formation in scale insects is critically discussed. 相似文献
2. Transfers of the scale insect Matsucoccus acalyptus Herbert within and between infested host trees ( Pinus monophylla (Torr. & Frem.) resulted in significant differences in scale survivorship among recipient trees. Survival on individual trees was correlated across years, indicating stable differences in tree susceptibility to scale.
3. A significant natal tree colonized tree interaction was observed for late stage scale survival in one experiment but the interaction was not caused by superior survivorship of scales transferred back to the natal tree. Hence, we found no evidence of deme formation in M.acalyptus.
4. Previous studies have concluded that deme formation occurs in the black pineleaf scale based on a significant natal tree by colonized tree interaction in scale survival. We question this conclusion because the experimental design employed did not include transfers back onto the natal tree. Other indirect evidence for deme formation in scale insects is critically discussed. 相似文献