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881.
The water permeability of periderm membranes stripped from mature trees of Betula pendula Roth was investigated. The diffusion of water was studied using the system water/membrane/water, and transpiration was measured using the system water/membrane/water vapor. Betula periderm consists of successive periderm layers each made up of about 5 heavily suberized cell layers and a varying number of cell layers that are little suberized, if at all. It is shown that these layers act as resistances in series. The permeability coefficient of the diffusion of water (P
d) can be predicted with 79% accuracy from the reciprocal of the membrane weight (x in mg cm-2) by means of the linear equation P
d=14.69·10-7
x-0.73·10-7. For example, the P
d of a periderm membrane having a weight of 10 mg cm-2 (approx. 250 m thick) is 7.4·10-8 cm s-1, which is comparable to the permeability of cuticles. This comparison shows that on a basis of unit thickness, Betula periderm is quite permeable to water as cuticles have the same resistance with a thickness of only 0.5 to 3 m. It is argued that this comparatively high water permeability of birch periderm is due to the fact that middle lamellae and the primary walls of periderm cells are not at all, or only incompletely suberized and, therefore, form a hydrophilic network within which the water can flow. This conclusion is based on the following observations: (1) Middle lamellae and primary walls stain strongly with toluidine blue, which shows them to be polar. (2) If silver ions are added as tracer for the flow of water, they are found only in the middle lamellae, primary walls, and in plasmodesmata, while no silver can be detected in the suberized walls. (3) Permeability coefficients of transpiration strongly depend on water activity. This shows conclusively that water flows across Betula periderm via a polar pathway. It is further argued that liquid continuity is likely to be maintained under all physiological conditions in the network formed by middle lamellae and primary walls. On the other hand, the lumina of periderm cells, intercellular air spaces in the lenticels, and even the pores in the suberized walls (remainders of plasmodesmata) will drain at a humidity of 95% and below. Due to the presence of intercellulars the permeability coefficient of lenticels is much greater than that of the periderm. A substantial amount of the total water, therefore, flows as vapor through lenticels even though they cover only 3% of the surface.Abbreviations PM
perideron membrane
-
P
d
permeability coefficient for diffusion of water
-
P
tt
permeability coefficient of transpiration
- MES
(N-morpholino)ethane sulfonic acid 相似文献
882.
Physiological conditions necessary for the formation of plastocyanin and the concurrent cessation of cytochrome c-553 formation were studied in cells of copper-deficient Scenedesmus acutus after the addition of copper. Plastocyanin is formed after a lag-phase, leaving constant the content of plastidic cytochrome c-553. Therefore, the concentration of plastocyanin per cell increases and the concentration of cytochrome c-553 decreases during growth. Formation of plastocyanin during the induction period studied is dependent on light intensity. In the dark, there is a 90% inhibition, whereas under light intensities above 50 Wm-2, a ratio of 1.3 molecules plastocyanin per 1,000 molecules chlorophyll is attained.Plastocyanin formations is inhibited by the uncoupler carbonylcyanide-p-trifluoromethoxy phenylhydrazone (FCCP), but not by moderate concentrations of 3-[3,4-dichlorophenyl]-1,1-dimethylurea (DCMU), and by keeping the algae under a nitrogen atmosphere without CO2. Concurrently, the cultures treated with FCCP show a decreased endogenous ATP level. The ATP is necessary for plastocyanin formation.Abbreviations FCCP
carbonylcyanide-p-trifluoromethoxyphenylhydrazone
- DCMU
3-[3,4-dichlorophenyl]-1,1-dimethylurea
- pcv
packed cell volume 相似文献
883.
Following oral administration of 9,11- 3H-17α-cyano-methylestra-1,3,5(10)-triene-3,17-diol 3-methyl ether, urinary metabolites were studied in man, baboon, beagle dog, minipig and rat. The metabolite pattern revealed remarkable species differences, especially in quantitative respects. 17α-Cyanomethylestra-1,3,5(10)-triene-3,17-diol, 17α-cyanomethylestra-1,3,5(10)-triene-2,3,17-triol 2-methyl ether, 17α-hydroxymethylestra-1,3,5(10)-triene-3,17-diol and 17α-cyanomethylestra-1,3,5(10)-triene-3,16,17-triol were isolated as principal metabolites. In rat bile, a metabolite was tentatively identified as aγ-lactone of a 17α-carbozymethyl-16α-hydroxy compound. 相似文献
884.
Analysis of a drosophila tRNA gene cluster 总被引:23,自引:0,他引:23
885.
The IgM plaque-forming response to the alpha 1-6 epitope of dextran B512 is linked to the Ig-1 heavy chain allotypes j and b characteristic of CBA and C57BL strains, respectively, and the response typically induces the formation of autoanti-idiotypic antibodies that can distinguish between anti-dextran antibodies of CBA and C57BL origin. Nevertheless, some substrains of Balb/c mice (allotype a) and some Bailey recombinant stains give a PFC response although they do not possess allotypes j or b. The anti-dextran antibodies in these strains lack the idiotypes characteristic of either CBA and C57BL antibodies to dextran, but they possess their own particular idiotype. F1 hybrids between two responder strains possessing different idiotypes on their antibodies against dextran, produce both idiotypes and two different autoanti-idiotypic antibodies. CBA(Ig-1b) mice were high responders to dextran and possessed the idiotype of C57BL, whereas C57BL/6(Ig-1a) mice were low responders. The V(H) recombinant strains BAB.14 and CB-8KN that possess the Ig-1b allotype of C57BL, but have some of the V(H) genes from Balb/c and the rest from C57BL/6 were high responders to dextran, but did not possess the C57BL idiotype, suggesting that the genes determining the response against dextran and the idiotype may have different locations in the heavy chain locus. 相似文献
886.
Conclusions Immobilized vegetative cells ofC. acetobutylicum has a similar product formation pattern when incubated in a simple glucose-salts solution as ordinary growing cells. If vegetative cells of the organism are immobilized in the solvent production phase, solvents are continuously produced on extended incubation.By immobi1izing spores of the organism the disturbance of the cells metabolic activity during the immobilization procedure was avoided. After the outgrowth of viable cells within the gel, the washed gel preparation retained at a high production capacity in the non-growth stage and the results indicate that continuous production might be fully possible. The butanol productivity was also found to be higher with immobilized cells than in a normal batch process. 相似文献
887.
Bo Lönnerdal Barbara O. Schneeman Carl L. Keen Lucille S. Hurley 《Biological trace element research》1980,2(3):149-158
Rat bile and pancreatic fluid were examined for the presence of low molecular weight zinc complexes. Fluids were collected
separately by cannulation, and zinc distribution in collected samples was analyzed by gel filtration on Sephadex G-50. Most
of the zinc in bile was associated with low molecular weight zinc complexes; only a small amount of zinc was present in the
high molecular weight fraction. In contrast, pancreatic secretions did not contain low molecular weight zinc complexes, but
there were considerable amounts of zinc bound to high molecular weight compounds. The addition of zinc to bile resulted in
an increased amount of zinc in the low molecular weight fraction, while the addition of zinc to pancreatic fluid resulted
primarily in an increase in zinc bound to the high molecular weight components. Like pancreatic fluid, homogenates of pancreatic
tissue had no low molecular weight zinc complex. In rats whose bile and pancreatic fluid were removed and not returned into
the intestine, the amount of zinc bound to low molecular weight complexes in intestinal homogenates was reduced. This alteration
of the molecular distribution of zinc in intestinal homogenates by removal of bile and pancreatic fluid suggests the potential
importance of low molecular weight zinc complexes for zinc homeostasis. 相似文献
888.
Carl L. Keen Bo Lönnerdal Theodore N. Stein Lucille S. Hurley 《Biological trace element research》1980,2(3):221-227
The presence of superoxide dismutase in bovine and human milk was investigated by ultrafiltration, gel filtration, and isoelectric
focusing. Conclusive evidence for the presence of this enzyme in both milks is presented. The molecular weight of the enzyme
was estimated by gel filtration on Sephadex G-100 to be 30,000, which is consistent with reported values for the copper, zinc
form of superoxide dismutase. In addition, enzyme activity was inhibited by cyanide, thus eliminating the possibility that
the enzyme was present in the manganese form. Several isoenzymes were detected by isoelectric focusing in polyacrylamide gel,
and the isoenzyme pattern in bovine milk was the same as that found for bovine plasma, suggesting that milk superoxide dismutase
originates from plasma. It may be that the presence of copper, zinc superoxide dismutase in milk is important for the maintenance
of its oxidative stability. 相似文献
889.
A method to quantitate lectin activity based on hemagglutination assay in microtiter plates is described. In addition to the normal method of visual titer evaluation an electronic particle counter is used for counting of nonagglutinated cells in the microtiter wells; this allows a rapid, quantitative determination of the amount of lectin required to agglutinate 50% of the countable single cells. It is also recommended that counting results should be related to a standard curve of concanavalin A to improve the reproducibility of the assay. 相似文献
890.
Pétur Reimarsson Björn Lindman Moshe M. Werber 《Archives of biochemistry and biophysics》1980,202(2):664-666
The anion-binding characteristics of ferredoxin from Halobacterium of the Dead Sea have been studied by 35Cl? NMR. It is found that the binding constant of Cl? to halophilic ferredoxin is ca. 0.09 at 28 °C and that the binding enthalpy is positive. It is also found that the correlation time for chloride ions bound to halophilic ferredoxin is about 10 ns. The effect on the 35Cl?1 NMR signal of adding competing anions is also studied. Halophilic proteins like ferredoxin which have a high negative charge bind anions with low affinity but the 35Cl? quadrupole relaxation technique can conveniently monitor such weak binding. 相似文献