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1.
Inhibition of coupling factor activity of chloroplast membranes by diazonium compounds 总被引:2,自引:0,他引:2
R T Giaquinta B R Selman C L Bering R A Dilley 《The Journal of biological chemistry》1974,249(9):2873-2878
2.
Giaquinta RT 《Plant physiology》1979,63(4):744-748
p-Chloromercuribenzenesulfonic acid markedly inhibited sucrose accumulation into sugar beet source leaves without inhibiting hexose accumulation. The site of inhibition is proposed to be the plasmalemma ATPase, since the ATPase-mediated H+ efflux was completely inhibited by p-chloromercuribenzenesulfonic acid under conditions where intracellular metabolism, as measured by photosynthesis and hexose accumulation, was unaffected. Fusicoccin, a potent activator of active H+/K+ exchange, stimulated both active sucrose accumulation and proton efflux in the sugar beet leaf tissue. These data provide strong evidence for the phloem loading of sucrose being coupled to a proton transport mechanism driven by a vectorial plasmalemma ATPase. 相似文献
3.
Han SK Federico S Grillo A Giaquinta G Herzog W 《Biomechanics and modeling in mechanobiology》2007,6(3):139-150
The integrity of articular cartilage depends on the proper functioning and mechanical stimulation of chondrocytes, the cells
that synthesize extracellular matrix and maintain tissue health. The biosynthetic activity of chondrocytes is influenced by
genetic factors, environmental influences, extracellular matrix composition, and mechanical factors. The mechanical environment
of chondrocytes is believed to be an important determinant for joint health, and chondrocyte deformation in response to mechanical
loading is speculated to be an important regulator of metabolic activity. In previous studies of chondrocyte deformation,
articular cartilage was described as a biphasic material consisting of a homogeneous, isotropic, linearly elastic solid phase,
and an inviscid fluid phase. However, articular cartilage is known to be anisotropic and inhomogeneous across its depth. Therefore,
isotropic and homogeneous models cannot make appropriate predictions for tissue and cell stresses and strains. Here, we modelled
articular cartilage as a transversely isotropic, inhomogeneous (TI) material in which the anisotropy and inhomogeneity arose
naturally from the microstructure of the depth-dependent collagen fibril orientation and volumetric fraction, as well as the
chondrocyte shape and volumetric fraction. The purpose of this study was to analyse the deformation behaviour of chondrocytes
using the TI model of articular cartilage. In order to evaluate our model against experimental results, we simulated indentation
and unconfined compression tests for nominal compressions of 15%. Chondrocyte deformations were analysed as a function of
location within the tissue. The TI model predicted a non-uniform behaviour across tissue depth: in indentation testing, cell
height decreased by 43% in the superficial zone and between 11 and 29% in the deep zone. In unconfined compression testing,
cell height decreased by 32% in the superficial zone, 25% in the middle, and 18% in the deep zones. This predicted non-uniformity
is in agreement with experimental studies. The novelty of this study is the use of a cartilage material model accounting for
the intrinsic inhomogeneity and anisotropy of cartilage caused by its microstructure. 相似文献
4.
The pathway of phloem unloading and the metabolism of translocated sucrose were determined in corn (Zea mays) seedling roots. Several lines of evidence show that exogenous sucrose, unlike translocated sucrose, is hydrolyzed in the apoplast prior to uptake into the root cortical cells. These include (a) presence of cell wall invertase activity which represents 20% of the total tissue activity; (b) similarity in uptake and metabolism of [14C]sucrose and [14C]hexoses; and (c) randomization of 14C within the hexose moieties of intracellular sucrose following accumulation of [14C] (fructosyl)sucrose. Conversely, translocated sucrose does not undergo apoplastic hydrolysis during unloading. Asymmetrically labeled sucrose ([14C](fructose)sucrose), translocated from the germinating kernels to the root, remained intact indicating a symplastic pathway for unloading. In addition, isolated root protoplasts and vacuoles were used to demonstrate that soluble invertase activity (Vmax = 29 micromoles per milligram protein per hour, Km = 4 millimolar) was located mainly in the vacuole, suggesting that translocated sucrose entered via the symplasm and was hydrolyzed at the vacuole prior to metabolism. 相似文献
5.
Litman GW; Rast JP; Shamblott MJ; Haire RN; Hulst M; Roess W; Litman RT; Hinds- Frey KR; Zilch A; Amemiya CT 《Molecular biology and evolution》1993,10(1):60-72
Immunoglobulins are encoded by a large multigene system that undergoes
somatic rearrangement and additional genetic change during the development
of immunoglobulin-producing cells. Inducible antibody and antibody-like
responses are found in all vertebrates. However, immunoglobulin possessing
disulfide-bonded heavy and light chains and domain-type organization has
been described only in representatives of the jawed vertebrates. High
degrees of nucleotide and predicted amino acid sequence identity are
evident when the segmental elements that constitute the immunoglobulin gene
loci in phylogenetically divergent vertebrates are compared. However, the
organization of gene loci and the manner in which the independent elements
recombine (and diversify) vary markedly among different taxa. One striking
pattern of gene organization is the "cluster type" that appears to be
restricted to the chondrichthyes (cartilaginous fishes) and limits
segmental rearrangement to closely linked elements. This type of gene
organization is associated with both heavy- and light-chain gene loci. In
some cases, the clusters are "joined" or "partially joined" in the germ
line, in effect predetermining or partially predetermining, respectively,
the encoded specificities (the assumption being that these are expressed)
of the individual loci. By relating the sequences of transcribed gene
products to their respective germ-line genes, it is evident that, in some
cases, joined-type genes are expressed. This raises a question about the
existence and/or nature of allelic exclusion in these species. The
extensive variation in gene organization found throughout the vertebrate
species may relate directly to the role of intersegmental
(V<==>D<==>J) distances in the commitment of the individual
antibody-producing cell to a particular genetic specificity. Thus, the
evolution of this locus, perhaps more so than that of others, may reflect
the interrelationships between genetic organization and function.
相似文献
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Abstract. In order to test for cumulative effects of fire on Paspalum quadrifarium‐dominated grasslands (‘pajonal’), we analysed the impact of single and repeated fires on the community structure and post‐fire recovery of canopy after a final, simultaneous fire event. Nine plots were defined within a homogeneous pajonal stand, and treatments of low (LF), medium (MF) and high frequency (HF) of fire were defined by the application of one, two or four cold‐season burns, respectively, along a 6‐yr period. Both burned and unburned plots were exposed to grazing by cattle during the summer following the first and the third years of that period. High cattle preference for burned sites conditioned fire temperature and vegetation responses to the following burning events. Cumulative effects between successive burning events were observed for the cover of basal area of the dominant and other sprouting species, the cover and thickness of the litter layer, the seed bank size of the principal recruiter species, and the floristic composition. While light interception by the canopy was positively related to fire frequency during the early growth season, further growth of P. quadrifarium determined a greater light interception in LF than in MF and HF. These patterns of light interception were associated with a faster occupation of the inter‐tussock areas by opportunistic species in plots subjected to frequent fires (HF and MF) than in plots with low fire frequency (LF), and a more lasting regrowth of P. quadrifarium in the LF plot than in the HF ones. High fire frequencies reduced the dominance of P. quadrifarium. Percent of species classified as subordinated graminoids or forbs did not vary among treatments. However, the abundance of different forb species was differentially favoured by contrasting frequencies of fire, describing some coarse relationships between their specific responses and their dispersal strategies. 相似文献
9.
Transport and metabolism of 1'-fluorosucrose, a sucrose analog not subject to invertase hydrolysis 总被引:1,自引:1,他引:0
The novel sucrose derivative 1′-fluorosucrose (α-d-glucopyranosyl-β- d-1-deoxy-1-fluorofructofuranoside) was synthesized in order to help define mechanisms of sucrose entry into plant cells. Replacement of the 1′-hydroxyl by fluorine very greatly reduces invertase hydrolysis of the derivative (hydrolysis at 10 millimolar 1′-fluorosucrose is less than 2% that of sucrose) but does not reduce recognition, binding, or transport of 1′-fluorosucrose by a sucrose carrier. Transport characteristics of 1′-fluorosucrose were studied in three different tissues. The derivative is transported by the sucrose carrier in the plasmalemma of developing soybean cotyledon protoplasts with a higher affinity than sucrose (Km 1′-fluorosucrose 0.9 millimolar, Km sucrose 2.0 millimolar). 1′-Fluorosucrose is a competitive inhibitor of sucrose uptake with an apparent Ki also of 0.9 millimolar, while the Ki of sucrose competition of 1′-fluorosucrose uptake was 2.0 millimolar. Thus, both sugars are recognized at the same binding site in the plasmalemma. Both sucrose and 1′-fluorosucrose show very similar patterns of phloem translocation from an abraded leaf surface through the petiole indicating that recognition of 1′-fluorosucrose by sucrose carriers involved in phloem loading is likely as well. 相似文献
10.
Data are presented which suggest that photosystem II dependent hydrogen ion accumulation and ATP synthesis can occur only after the lamellar membranes have undergone a conformational change. This membrane conformational change is detected by the electron transport dependent incorporation of diazonium benzene[35S]sulfonate into membrane components. Previously it was established that electron flux from the photosystem II primary acceptor to plastoquinone is a necessary event for the occurrence of the diazonium-detected conformational change. These studies indicate that the release of hydrogen ions during photosystem II oxidation of the primary reductant is also a necessary event for the diazonium-detected conformational change. When iodide were substituted for water (or other proton-releasing donors) as the primary reductant of system II the conformational change did not occur even though a substantial rate of electron flow from the primary acceptor to plastoquinone occurred. 相似文献