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81.
82.
E.D. Weinberg 《Biometals》2000,13(1):85-89
Successful microbial pathogens must be adept in obtaining growth-essential iron from healthy hosts. Some potential pathogens, however, are sufficiently impaired in iron acquisition ability so as to be dangerous mainly in hosts with such iron loading conditions as alcoholism, asplenia, hemochromatosis, -thalassemia major, or tobacco smoking. The association of six impaired pathogens (Capnocytophaga canimorsis, Yersinia enterocolitica and Y. pseudotuberculosis, Vibrio vulnificus, Tropheryma whippelii, and Legionella pneumophila) with iron loaded humans is described. 相似文献
83.
Leaf and minor vein structure were studied in Arabidopsis thaliana (L.) Heynh. to gain insight into the mechanism(s) of phloem loading. Vein density (length of veins per unit leaf area) is
extremely low. Almost all veins are intimately associated with the mesophyll and are probably involved in loading. In transverse
sections of veins there are, on average, two companion cells for each sieve element. Phloem parenchyma cells appear to be
specialized for delivery of photoassimilate from the bundle sheath to sieve element-companion cell complexes: they make numerous
contacts with the bundle sheath and with companion cells and they have transfer cell wall ingrowths where they are in contact
with sieve elements. Plasmodesmatal frequencies are high at interfaces involving phloem parenchyma cells. The plasmodesmata
between phloem parenchyma cells and companion cells are structurally distinct in that there are several branches on the phloem
parenchyma cell side of the wall and only one branch on the companion cell side. Most of the translocated sugar in A. thaliana is sucrose, but raffinose is also transported. Based on structural evidence, the most likely route of sucrose transport is
from bundle sheath to phloem parenchyma cells through plasmodesmata, followed by efflux into the apoplasm across wall ingrowths
and carrier-mediated uptake into the sieve element-companion cell complex.
Received: 5 October 1999 / Accepted: 20 November 1999 相似文献
84.
Marcotrigiano M 《American journal of botany》2000,87(3):355-361
Many higher plants have shoot apical meristems that possess discrete cell layers, only one of which normally gives rise to gametes following the transition from vegetative meristem to floral meristem. Consequently, when mutations occur in the meristems of sexually reproducing plants, they may or may not have an evolutionary impact, depending on the apical layer in which they reside. In order to determine whether developmentally sequestered mutations could be released by herbivory (i.e., meristem destruction), a characterized genetic mosaic was subjected to simulated herbivory. Many plants develop two shoot meristems in the leaf axils of some nodes, here referred to as the primary and secondary axillary meristems. Destruction of the terminal and primary axillary meristems led to the outgrowth of secondary axillary meristems. Seed derived from secondary axillary meristems was not always descended from the second apical cell layer of the terminal shoot meristem as is expected for terminal and primary shoot meristems. Vegetative and reproductive analysis indicated that secondary meristems did not maintain the same order of cell layers present in the terminal shoot meristem. In secondary meristems reproductively sequestered cell layers possessing mutant cells can be repositioned into gamete-forming cell layers, thereby adding mutant genes into the gene pool. Herbivores feeding on shoot tips may influence plant evolution by causing the outgrowth of secondary axillary meristems. 相似文献
85.
External sucrose, supplied by the endosperm in vivo, is the physiological source of sucrose for Ricinus communis L. seedlings. It is taken up by the cotyledons and exported via the sieve tubes to the growing hypocotyl and root. Two parallel
pathways of external sucrose to the sieve tubes, directly via the apoplasm and indirectly after transit through the mesophyll,
have already been established (G. Orlich and E. Komor, 1992). In this study, we analysed whether a symplasmic flow of sucrose
contributes to phloem loading. Uptake of external sucrose into the mesophyll and into the sieve tubes, and export of total
sucrose were measured with intact and exuding seedlings in the presence of p-chloromercuribenzenesulfonic acid (PCMBS). Sucrose uptake into the mesophyll and into the sieve tubes was inhibited by 80–90%.
Consequently, export of total sucrose slowed down. However, after the addition of PCMBS, sucrose was transiently exported
in such a high amount that could not be accounted for by the residual uptake activity nor by the amount of sucrose confined
to the sieve element-companion cell complex (seccc). From the results, we conclude that most of the sucrose exported transiently
had moved to the sieve tubes from a symplasmic domain larger than the seccc, comprising at least all the cells of the bundle
including the bundle sheath. We suggest that the symplasmic flow of sucrose observed is a mass flow driven by a turgor pressure.
As a structural prerequisite for a symplasmic flow, plasmodesmata interconnect all the cells from the bundle sheath to the
sieve tubes and also occur between the bundle sheath and the mesophyll. The phloem loading pathway of Ricinus cotyledons can thus be classified as a combination of three different routes.
Received: 17 October 1997 / Accepted: 9 March 1998 相似文献
86.
Ultrastructural effects in potato leaves due to antisense-inhibition of the sucrose transporter indicate an apoplasmic mode of phloem loading 总被引:8,自引:0,他引:8
To study the export of sugars from leaves and their long-distance transport, sucrose-proton/co-transporter activity of potato
was inhibited by antisense repression of StSUT1 under control of either a ubiquitously active (CaMV 35S ) or a companion-cell-specific (rolC) promotor in transgenic plants. Transformants exhibiting reduced levels of the sucrose-transporter mRNA and showing a dramatic
reduction in root and tuber growth, were chosen to investigate the ultrastructure of their source leaves. The transformants
had a regular leaf anatomy with a single-layered palisade parenchyma, and bicollateral minor veins within the spongy parenchyma.
Regardless of the promoter used, source leaves from transformants showed an altered leaf phenotype and a permanent accumulation
of assimilates as indicated by the number and size of starch grains, and by the occurrence of lipid-storing oleosomes. Starch
accumulated throughout the leaf: in epidermis, mesophyll and, to a smaller degree, in phloem parenchyma cells of minor veins.
Oleosomes were observed equally in mesophyll and phloem parenchyma cells. Companion cells were not involved in lipid accmulation
and their chloroplasts developed only small starch grains. The similarity of ultrastructural symptoms under both promotors
corresponds to, rather than contradicts, the hypothesis that assimilates can move symplasmically from mesophyll, via the bundle
sheath, up to the phloem. The microscopical symptoms of a constitutively high sugar level in the transformant leaves were
compared with those in wild-type plants after cold-girdling of the petiole. Inhibition of sugar export, both by a reduction
of sucrose carriers in the sieve element/companion cell complex (se/cc complex), or further downstream by cold-girdling, equally
evokes the accumulation of assimilates in all leaf tissues up to the se/cc complex border. However, microscopy revealed that
antisense inhibition of loading produces a persistently high sugar level throughout the leaf, while cold-girdling leads only
to local patches containing high levels of sugar.
Received: 4 March 1998 / Accepted: 7 April 1998 相似文献
87.
We describe a 2‐DE proteomic reference map containing 227 basic proteins in the dorsolateral prefrontal cortex region of the human brain. Proteins were separated in the first dimension on pH 6–11 IPG strips using paper‐bridge loading and on 12% SDS‐PAGE in the second dimension. Proteins were subsequently identified by MS and spectra were analyzed using an in‐house proteomics data analysis platform, Proline. The 2‐DE reference map is available via the UCD 2‐DE Proteome Database ( http://proteomics‐portal.ucd.ie:8082 ) and can also be accessed via the WORLD‐2DPAGE Portal ( http://www.expasy.ch/world‐2dpage/ ). The associated protein identification data have been submitted to the PRIDE database (accession numbers 10018–10033). Separation of proteins in the basic region resolves more membrane associated proteins relevant to the synaptic pathology central to many neurological disorders. The 2‐DE reference map will aid with further characterisation of neurological disorders such as bipolar and schizophrenia. 相似文献
88.
Alan J. Lewitus Bonnie M. Willis Kenneth C. Hayes JoAnn M. Burkholder Howard B. Glasgow Jr. Patricia M. Glibert Marianne K. Burke 《Journal of phycology》1999,35(6):1430-1437
The nutritional versatility of dinoflagellates is a complicating factor in identifying potential links between nutrient enrichment and the proliferation of harmful algal blooms. For example, although dinoflagellates associated with harmful algal blooms (e.g. red tides) are generally considered to be phototrophic and use inorganic nutrients such as nitrate or phosphate, many of these species also have pronounced heterotrophic capabilities either as osmotrophs or phagotrophs. Recently, the widespread occurrence of the heterotrophic toxic dinoflagellate, Pfiesteria piscicida Steidinger et Burkholder, has been documented in turbid estuarine waters. Pfiesteria piscicida has a relatively proficient grazing ability, but also has an ability to function as a phototroph by acquiring chloroplasts from algal prey, a process termed kleptoplastidy. We tested the ability of kleptoplastidic P. piscicida to take up 15 N-labeled NH , NO , urea, or glutamate. The photosynthetic activity of these cultures was verified, in part, by use of the fluorochrome, primulin, which indicated a positive relationship between photosynthetic starch production and growth irradiance. All four N substrates were taken up by P. piscicida , and the highest uptake rates were in the range cited for phytoplankton and were similar to N uptake estimates for phagotrophic P. piscicida . The demonstration of direct nutrient acquisition by kleptoplastidic P. piscicida suggests that the response of the dinoflagellate to nutrient enrichment is complex, and that the specific pathway of nutrient stimulation (e.g. indirect stimulation through enhancement of phytoplankton prey abundance vs. direct stimulation by saprotrophic nutrient uptake) may depend on P. piscicida 's nutritional state (phagotrophy vs. phototrophy). 相似文献
89.
Weili Zhou Bingtao WuQianhong She Lina ChiZhenjia Zhang 《Bioresource technology》2009,100(14):3471-3476
Investigation on a full-scale UASB treating industrial wastewater at a low organic loading rate (OLR) was conducted. Excellent treatment performance was achieved when treating the evaporator condensate of distillery wastewater at the OLR of less than 1 kg COD/m3 d. Anaerobic effluent could be discharged without further treatment, which saved energy and running cost considerably. GC–MS analysis showed that the soluble microbial products (SMPs) were decreased to a low level at the low OLR. The main SMP in the anaerobic effluent were long chain carbohydrates and esters, accounting for 55–65% of the total organic matters. Anaerobic SMP was more complex than the aerobic ones. 相似文献
90.
Roles of interstitial fraction and load conditions on the dynamic binding capacity of proteins on capillary‐channeled polymer fiber columns 下载免费PDF全文
Capillary‐channeled polymer (C‐CP) fibers are used as a stationary phase for ion‐exchange chromatography of proteins. Collinear packing of the fibers permits operation at high linear velocities (Uo > 100 mm s?1) and low backpressure (<2,000 psi) on analytical‐scale columns. Rapid solvent transport is matched with very efficient solute mass transfer as fibers are virtually non‐porous with respect to the size of the target protein molecules. Lack of porosity of course limits the equilibrium binding capacity of stationary phases. Breakthrough curves and frontal analysis are used to better understand trade‐offs between the kinetic and thermodynamic properties as C‐CP fibers are applied in preparative situations. Fiber columns packed to different interstitial fraction values affect both the total fiber surface area (e.g., equilibrium binding capacity [EBC]) and the permittivity to flow and mass transport characteristics (e.g., dynamic binding capacity [DBC]). The EBC of the nylon 6 C‐CP fibers was found to be 1.30 mg g?1, with isotherms that were best matched by a Moreau model, showing linearity up to solute concentrations of ~0.4 mg mL?1. Isotherms generated under flow conditions were equally well approximated using Langmuir, Freundlich, and Moreau isotherm models. Fairly linear responses were seen up to the maximum load concentration of 1.2 mg mL?1. Counterintuitively, dynamic studies revealed that conditions of high column porosity yielded a DBC that is ~70% higher than the EBC. These findings point to potential advantages in terms downstream processing applications, where protein throughput and yield are critical metrics. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 31:97–109, 2015 相似文献