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1.
Summary The plant root tip represents a fascinating model system for studying changes in Golgi stack architecture associated with the developmental progression of meristematic cells to gravity sensing columella cells, and finally to young and old, polysaccharideslime secreting peripheral cells. To this end we have used high pressure freezing in conjunction with freeze-substitution techniques to follow developmental changes in the macromolecular organization of Golgi stacks in root tips ofArabidopsis andNicotiana. Due to the much improved structural preservation of all cells under investigation, our electron micrographs reveal both several novel structural features common to all Golgi stacks, as well as characteristic differences in morphology between Golgi stacks of different cell types.Common to all Golgi stacks are clear and discrete differences in staining patterns and width of cis, medial and trans cisternae. Cis cisternae have the widest lumina (30 nm) and are the least stained. Medial cisternae are narrower (20 nm) and filled with more darkly staining products. Most trans cisternae possess a completely collapsed lumen in their central domain, giving rise to a 4–6 nm wide dark line in cross-sectional views. Numerous vesicles associated with the cisternal margins carry a non-clathrin type of coat. A trans Golgi network with clathrin coated vesicles is associated with all Golgi stacks except those of old peripheral cells. It is easily distinguished from trans cisternae by its blebbing morphology and staining pattern. The zone of ribosome exclusion includes both the Golgi stack and the trans Golgi network.Intercisternal elements are located exclusively between trans cisternae of columella and peripheral cells, but not meristematic cells. In older peripheral cells only trans cisternae exhibit slime-related staining. Golgi stacks possessing intercisternal elements also contain parallel rows of freeze-fracture particles in their trans cisternal membranes. We propose that intercisternal elements serve as anchors of enzyme complexes involved in the synthesis of polysaccharide slime molecules to prevent the complexes from being dragged into the forming secretory vesicles by the very large slime molecules. In addition, we draw attention to the similarities in composition and apparent site of synthesis of xyloglucans and slime molecules.Dedicated to the memory of Professor Oswald Kiermayer 相似文献
2.
An adaptive, object oriented strategy for base calling in DNA sequence analysis. 总被引:3,自引:1,他引:2 下载免费PDF全文
An algorithm has been developed for the determination of nucleotide sequence from data produced in fluorescence-based automated DNA sequencing instruments employing the four-color strategy. This algorithm takes advantage of object oriented programming techniques for modularity and extensibility. The algorithm is adaptive in that data sets from a wide variety of instruments and sequencing conditions can be used with good results. Confidence values are provided on the base calls as an estimate of accuracy. The algorithm iteratively employs confidence determinations from several different modules, each of which examines a different feature of the data for accurate peak identification. Modules within this system can be added or removed for increased performance or for application to a different task. In comparisons with commercial software, the algorithm performed well. 相似文献
3.
Inhibition of endoplasmic reticulum-to-Golgi traffic by poliovirus protein 3A: genetic and ultrastructural analysis. 总被引:9,自引:8,他引:1 下载免费PDF全文
Poliovirus protein 3A, only 87 amino acids in length, is a potent inhibitor of protein secretion in mammalian cells, blocking anterograde protein traffic from the endoplasmic reticulum (ER) to the Golgi complex. The function of viral protein 3A in blocking protein secretion is extremely sensitive to mutations near the N terminus of the protein. Deletion of the first 10 amino acids or insertion of a single amino acid between amino acids 15 and 16, a mutation that causes a cold-sensitive defect in poliovirus RNA replication, abrogates the inhibition of protein secretion although wild-type amounts of the mutant proteins are expressed. Immunofluorescence light microscopy and immunoelectron microscopy demonstrate that 3A protein, expressed in the absence of other viral proteins, colocalizes with membranes derived from the ER. The precise topology of 3A with respect to ER membranes is not known, but it is likely to be associated with the cytosolic surface of the ER. Although the glycosylation of 3A in translation extracts has been reported, we show that tunicamycin, under conditions in which glycosylation of cellular proteins is inhibited, has no effect on poliovirus growth. Therefore, glycosylation of 3A plays no functional role in the viral replicative cycle. Electron microscopy reveals that the ER dilates dramatically in the presence of 3A protein. The absence of accumulated vesicles and the swelling of the ER-derived membranes argues that ER-to-Golgi traffic is inhibited at the step of vesicle formation or budding from the ER. 相似文献
4.
Flow field-flow fractionation is introduced as a new tool applicable to protein studies. Specific advantages of this method are discussed, including the capability for measuring diffusivities and Stokes radii directly, even for trace components. The theoretical equations of flow FFF are summarized and expanded to include an explicit dependence on the Stokes radius. Several native proteins are retained. The retention is shown to be systematically controllable by changes in cross flow and the results are in quantitative agreement with theory. Fractograms of different rat plasmas are then shown to produce coincident peaks, while human plasma exhibits several systematic peak shifts with respect to the fractogram of the rat plasma. Finally, changes in the Stokes radii of ferritin peaks are shown after various forms of treatment with SDS. Flow FFF in this study demonstrates a capability of working with a mass range of ∼ 105 in a single run. 相似文献
5.
The effects of acetylcholine (Ach) on growth, the total peroxidase activity and the isoperoxidase spectrum of the roots ofLens culinaris were studied and compared with actual and earlier results obtained with an auxin (IAA) treatment. The general growth and
peroxidase activity patterns of Ach treated roots and IAA treated ones showed many important similarities. 相似文献
6.
Kramer RW Slagowski NL Eze NA Giddings KS Morrison MF Siggers KA Starnbach MN Lesser CF 《PLoS pathogens》2007,3(2):e21
Numerous bacterial pathogens manipulate host cell processes to promote infection and ultimately cause disease through the action of proteins that they directly inject into host cells. Identification of the targets and molecular mechanisms of action used by these bacterial effector proteins is critical to understanding pathogenesis. We have developed a systems biological approach using the yeast Saccharomyces cerevisiae that can expedite the identification of cellular processes targeted by bacterial effector proteins. We systematically screened the viable yeast haploid deletion strain collection for mutants hypersensitive to expression of the Shigella type III effector OspF. Statistical data mining of the results identified several cellular processes, including cell wall biogenesis, which when impaired by a deletion caused yeast to be hypersensitive to OspF expression. Microarray experiments revealed that OspF expression resulted in reversed regulation of genes regulated by the yeast cell wall integrity pathway. The yeast cell wall integrity pathway is a highly conserved mitogen-activated protein kinase (MAPK) signaling pathway, normally activated in response to cell wall perturbations. Together these results led us to hypothesize and subsequently demonstrate that OspF inhibited both yeast and mammalian MAPK signaling cascades. Furthermore, inhibition of MAPK signaling by OspF is associated with attenuation of the host innate immune response to Shigella infection in a mouse model. These studies demonstrate how yeast systems biology can facilitate functional characterization of pathogenic bacterial effector proteins. 相似文献
7.
Prevost, I. and Le PageDegivry, M. Th. 1985. Changesin absicisic acid content in axis and cotyledons of developingPhaseolus vulgaris embryos and their physiological consequences.J.exp. Bot. 36: 19001905.Changes in abscisic acid (ABA)content with time were measured in embryonic axes and in cotyledonsof Phaseolus vulgaris embryos using a radioimmunoassay.During embryogenesis, a similar pattern was observed in bothtissues: ABA increased to a maximum 29 d after an thesis, followedby a decrease as the seed matured. The level of ABA in the cotyledonswas always much higher than that in the axes. In in vitro cultures,the duration of the lag phase before germination of isolatedembryonic axes increased with ABA content. The presence of cotyledonsalways lengthened the lag phase; longer lag phases were associatedwith greater concentrations of ABA in the cotyledons. Moreoverthe presence of cotyledons stimulated the growth of seedlings. Key words: ABA distribution, embryo maturation, axis and embryo germinability 相似文献
8.
The East Kleinemonde Estuary, on the south-east coast of South Africa, typically opens for only short periods, usually <10 days. During a nine-month study in 2006, marine influence persisted for a near-continuous period of three months. This provided an opportunity to explore potential changes in the structure and pattern of the subtidal estuarine macrozoobenthic community. Salinity changes were minimal after mouth opening, decreasing by c. 4 and 8 in the lower and upper estuary, respectively. Salinity decrease was due to river dominance over tidal influence. Two biotic assemblages, structured by sediment characteristics, typified the community throughout the study: a sand-associated group near the mouth and a mud-associated group upstream. Amphipods were proportionally the most abundant group within each assemblage and on each sampling occasion. At the species level, high variability typified the community, with no trends or patterns observed. However, species richness declined from 27–30 to 23 after mouth opening. The number of species returned to former levels at the time of the final survey and just before final mouth closure. An analysis of the subtidal macrozoobenthos in the East Kleinemonde and other temporarily open/closed estuaries (TOCEs) of similar size in the bioregion indicated that communities were typically composed of relatively few, broadly tolerant euryhaline species with no species unique to TOCEs. 相似文献
9.
The ommatidium of the termite mastotermes darwiniensis 总被引:1,自引:0,他引:1
An electron microscope study of the compound eye of the termite Mastotermes darwiniensis shows that the ommatidia have both primitive and specialized features. The ommatidia are of the apposition type with eight similar retinular cells, a fused rhabdom, irregularly orientated rhabdomere tubules and no tracheae. The retinula cells contain lipid. The cone cells have unusual processes, which thicken towards the basement membrane and contain rough endoplasmic reticulum, granules and dense bodies. These processes may act as a primitive transport system for nutrients. 相似文献
10.