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101.
Susan M. Howitt Andrew J. W. Rodgers Lyndall P. Hatch Frank Gibson Graeme B. Cox 《Journal of bioenergetics and biomembranes》1996,28(5):415-420
F0F1-ATPase structural information gained from X-ray crystallography and electron microscopy has activated interest in a rotational mechanism for the F0F1-ATPase. Because of the subunit stoichiometry and the involvement of both thea- andc-subunits in the mechanism of proton movement, it is argued that relative movement must occur between the subunits. Various options for the arrangement and structure of the subunits involved are discussed and a mechanism proposed. 相似文献
102.
A field incubation technique with acetylene to inhibit nitrification was used to estimate net N mineralization rates in some grassland soils through an annual cycle. Measurements were made on previously long-term grazed pastures on a silty clay loam soil in S.W. England which had background managements of +/– drainage and +/– fertilizer (200 kg N ha–1 yr–1). The effect of fertilizer addition on mineralization during the year of measurement was also determined. Small plots with animals excluded, and with herbage clipped and removed were used as treatment areas and measurements were made using an incubation period of 7 days at intervals of 7 or 14 days through the year. Soil temperature, moisture and mineral N contents were also determined. Mineralization rates fluctuated considerably in each treatment. Maximum daily rates ranged from 1.01 to 3.19 kg N ha–1, and there was substantial net release of N through the winter period (representing, on average, 27% of the annual release). Changes in temperature accounted for 35% of the variability but there was little significant effect of soil moisture. Annual net release of N ranged from 135 kg ha–1 (undrained soil, no previous or current fertilizer) to 376 (drained soil, +200 kg N ha–1 yr–1 previous and current fertilizer addition). Addition of fertilizer N to a previously unfertilized sward significantly increased the net release of N but there was no immediate effect of withholding fertilizer on mineralization during the year in which measurements were made. 相似文献
103.
Primary partitioning and storage of photosynthate in sucrose and starch in leaves of C4 plants 总被引:1,自引:0,他引:1
A procedure involving pulse labelling of leaves with 14CO2 was developed to measure the primary (initial) partitioning of photosynthate between sucrose and starch. Partitioning of photosynthate into sucrose and starch was determined in leaves of C4 plants and compared with the patterns of storage of carbon in these products during the light period. The ratio of primary partitioning into sucrose and starch varied from about 0.5 in those species that accumulated mostly starch in the leaves (Amaranthus edulis L., Atriplex spongiosa F. Muell. and Flaveria trinervia (Spreng.) C. Mohr) to about 8 in Eleusine indica (L.) Gaertn., which accumulated mostly sucrose. No label was detected in free glucose or fructose. Generally there was a reasonable link between the primary partitioning of photosynthate and the type of carbohydrate stored in the leaf during the day. However, the ratio of carbon initially partitioned into sucrose versus starch was about 3 to 4 times higher in leaves of NADP-malic enzyme-type monocotyledonous species compared with phosphoenolpyruvate carboxykinase-type species, although the ratio of sucrose to starch accumulated in leaves during the day was very similar in the two groups. Sucrose and starch were the principal carbohydrates accumulated in leaves during the day. None of the species examined contained significant amounts of fructan and only one species, Atriplex spongiosa, contained substantial amounts of hexose sugars. In most of the species studied, the proportion of photosynthate partitioned into starch was greater at the end of the day than at the beginning. With the exception of Flaveria trinervia, the rate of CO2 assimilation did not decline during the day, showing that, under our conditions, accumulation of carbohydrate in the leaves did not lead to feedback inhibition of photosynthesis in these C4 species.Abbreviations Chl
chlorophyll
- NAD-ME
NAD-malic enzyme
- NADP-ME
NADP-malic enzyme
- PCK
phosphoenolpyruvate carboxykinase
We thank Prof. H.W. Heldt (Pflanzenphysiologisches Institut, Universität Göttingen) for discussions and advice during the course of this work. 相似文献
104.
Debra L. Ellies David W. Stock Gary Hatch Genny Giroux Kenneth M. Weiss Marc Ekker 《Genomics》1997,45(3):580
To understand the relationship between the expression and the genomic organization of the zebrafishdlxgenes, we have determined the genomic structure of thedlx2anddlx4loci. This led to the identification of the zebrafishdlx1anddlx6genes, which are closely linked todlx2anddlx4,respectively. Therefore, the inverted convergent configuration ofDlxgenes is conserved among vertebrates. Analysis of the expression patterns ofdlx1anddlx6showed striking similarities to those ofdlx2anddlx4,respectively, the genes to which they are linked. Furthermore, the expression patterns ofdlx3anddlx7,which likely constitute a third pair of convergently transcribed genes, are indistinguishable. Thus, the overlapping expression patterns of linkedDlxgenes during embryonic development suggest that they sharecis-acting sequences that control their spatiotemporal expression. The evolutionary conservation of the genomic organization and combinatorial expression ofDlxgenes in distantly related vertebrates suggest tight control mechanisms that are essential for their function during development. 相似文献
105.
Synthesis and Utilization of Trialkylammonium‐Substituted Cyclodextrins as Water‐Soluble Chiral NMR Solvating Agents for Anionic Compounds
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Alison E. Dowey Cira Mollings Puentes Mira Carey‐Hatch Keyana L. Sandridge Nikhil B. Krishna Thomas J. Wenzel 《Chirality》2016,28(4):299-305
Cationic trialkylammonium‐substituted α‐, β‐, and γ‐cyclodextrins containing trimethyl‐, triethyl‐, and tri‐n‐propylammonium substituent groups were synthesized and analyzed for utility as water‐soluble chiral nuclear magnetic resonance (NMR) solvating agents. Racemic and enantiomerically pure (3‐chloro‐2‐hydroxypropyl)trimethyl‐, triethyl‐, and tri‐n‐propyl ammonium chloride were synthesized from the corresponding trialkyl amine hydrochloride and either racemic or enantiomerically pure epichlorohydrin. The ammonium salts were then reacted with α‐, β‐, and γ‐cyclodextrins at basic pH to provide the corresponding randomly substituted cationic cyclodextrins. The 1H NMR spectra of a range of anionic, aromatic compounds was recorded with the cationic cyclodextrins. Cyclodextrins with a single stereochemistry at the hydroxy group on the (2‐hydroxypropyl)trialkylammonium chloride substituent were often but not always more effective than the corresponding cyclodextrin in which the C‐2 position was racemic. In several cases, the larger triethyl or tri‐n‐propyl derivatives were more effective than the corresponding trimethyl derivative at causing enantiomeric differentiation. None of the cyclodextrin derivatives were consistently the most effective for all of the anionic compounds studied. Chirality 28:299–305, 2016. © 2016 Wiley Periodicals, Inc. 相似文献
106.
107.
Mechanism of c(4) photosynthesis: a model describing the inorganic carbon pool in bundle sheath cells 总被引:7,自引:7,他引:0
A theoretical model of the composition of the inorganic carbon pool generated in C4 leaves during steady-state photosynthesis was derived. This model gives the concentrations of CO2 and O2 in the bundle sheath cells for any given net photosynthesis rate and inorganic carbon pool size. The model predicts a bundle sheath CO2 concentration of 70 micromolar during steady state photosynthesis in a typical C4 plant, and that about 13% of the inorganic carbon generated in bundle sheath cells would leak back to the mesophyll cells, predominantly as CO2. Under these circumstances the flux of carbon through the C4 acid cycle would have to exceed the net rate of CO2 assimilation by 15.5%. With the calculated O2 concentration of 0.44 millimolar, the potential photorespiratory CO2 loss in bundle sheath cells would be about 3% of CO2 assimilation. Among the factors having a critical influence on the above values are the permeability of bundle sheath chloroplasts to HCO3−, the activity of carbonic anhydrase within these chloroplasts, the assumed stromal volume, and the permeability coefficients for CO2 and O2 diffusion across the interface between bundle sheath and mesophyll cells. The model suggests that as the net photosynthesis rate changes in C4 plants, the level and distribution of the components of the inorganic carbon pool change in such a way that C4 acid overcycling is maintained in an approximately constant ratio with respect to the net photosynthesis rate. 相似文献
108.
A method is described which is suitable for assessing the effects of relative humidity (RH) on the viability of two unicellular algae in experimental aerosols. Viable cells of Nannochloris atomus collected from the airborne state were detected by plating onto agar surfaces of an appropriate growth medium, whereas viable airborne cells of Synechococcus sp., because of unreliable growth on solid media, were determined by a liquid assay system. The assays were performed at intervals during short-term and prolonged storage of algal aerosols in chambers preconditioned to a selected RH and temperature. Both species showed the greatest loss in viability during the first minute after atomization, and the extent of this inactivation, as a function of RH, reflected the subsequent long-term survival. The airborne eukaryotic alga was unable to survive at an RH below 91%, whereas the airborne prokaryotic alga was comparatively stable over a wide humidity range. Initial inactivation was least and long-term survival best, for both species, at 94% RH. 相似文献
109.
The absence of glutamate transport in glutamine-grown cells of Synechococcus cedrorum R7 was due to feedback inhibition and not repression of transport activity. 相似文献
110.
Interactions of Standard Antibody with Australia Antigens in Au Ag-Ab Radioimmunoassay 总被引:2,自引:0,他引:2
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Harry Daugharty Ruth G. Young Milford H. Hatch Donald W. Ziegler 《Applied microbiology》1974,27(4):756-762
Human antisera against Australia (Au) antigen have been characterized by liquid-phase radioimmunoassay (RIA) for their precipitation of (125)I-labeled Au antigen. The end-point dilutions of sera (anti-Au) which precipitated 50% of (125)I-Au antigen by RIA correlated well with complement fixation titers but had a much wider range, indicating a greater precision and perhaps a better sensitivity of assay. Anti-Au serum diluted to precipitate 50% of (125)I-labeled Au antigen was used as standard antibody in RIA tests to detect either inhibition or enhancement of the reaction by preincubated mixtures of Au antigen and antibody specimens. Without free Au antigen or antibody in the resultant mixtures there was no inhibition or enhancement; the mixtures presumably contained immunoreactively equivalent proportions of Au antigen and antibody. RIA data for diagnostic specimens indicated an end-point sensitivity which was proportional to the dilution of the standard anti-Au sera used in the test. High concentrations of the standard antibody permitted detectable inhibition of (125)I-Au antigen precipitation at lower antigen specimen concentrations. Similarly, low concentrations of the standard antibody permitted detectable enhancement of (125)I-Au antigen precipitation at lower antibody specimen concentrations. Omitting the standard antibody altogether resulted in a more sensitive RIA for Au antibody in test sera. 相似文献