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1.
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Observations by transmission electron microscopy of wood samples of Populus tremula inoculated with the white rot fungus Phanerochaete chrysosporium showed that, at certain stages of their growth cycle, hyphae were encapsulated by a sheath which seems to play an active role in the wood cell wall degradation. Chemical and immunochemical techniques and C nuclear magnetic resonance spectroscopy were applied to demonstrate the beta-1,3-1,6-d-glucan nature of the sheath. Double-staining methods revealed the interaction between the extracellular peroxidases involved in lignin degradation and the glucan mucilage. The glucan was also shown to establish a material junction between the fungus and the wood cell wall. It was concluded that, by means of these interactions, the sheath provides a transient junction between the hyphae and the wood, thus establishing a point of attachment to the site of the degradation. The association of peroxidases to the glucan matrix is in favor of the role of the sheath as a supporting structure. Furthermore, that the sheath was hydrolyzed during the attack demonstrated its active role both in providing the H(2)O(2) necessary to the action of peroxidases and in providing a mode of transport of the fungal enzymes to their substrates at the surface of the wood cell wall. 相似文献
3.
Cell proliferation has been induced from the cambial zone of a branch of Acacia senegal, kept on the basal Knop and Ball medium in the presence of auxin. Transferred on the more complete nutrient medium of Schenk and Hildebrandt, the colonies gave rise to several cell lines. One of the friable lines, consisting of aggregates of parenchymatous cells, gave a cell suspension culture in an agitated liquid medium which is maintained as a strain of illimited growth. The heterogeneous suspension did not undergo noticeable changes after eight transfers. Aggregates collected on a 1000-m nylon seive were able to grow on a solid medium and gave back a friable callus similar to the initial colonies. 相似文献
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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
6.
Structure of the Primary Cell Walls of Suspension-Cultured Rosa glauca Cells: I. Polysaccharides Associated with Cellulose 总被引:3,自引:3,他引:0
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Cell walls of suspension-cultured cells of Rosa glauca were fractionated by two different extraction procedures. The first involved a stepwise fractionation scheme based on alkaline extraction. The second took advantage of the powerful cellulose solvent system N-methylmorpholine N-oxide/dimethyl sulfoxide which is capable of solubilizing whole cell walls. From the analytical composition of each solubilized fraction and of the corresponding residues, the fate of each type of cell wall polysaccharide constituent was followed at each step of the extraction scheme and the mode of action of the extractant was interpreted. Although the two fractionation procedures were very different, they yielded very similar cellulosic complex residues and extracts, thus delimiting two blocks of polysaccharides in the cell wall. The cellulose residues still comprised uronic acid-containing polysaccharides and hemicelluloses in association with cellulose. Graded acid hydrolysis provided evidence for the central role of a homogalacturonan core interconnecting xyloglucans and arabinogalactans. A tentative model showing the possible interaction existing between the constituent polysaccharides still associated to cellulose after alkaline extraction is presented. Hydrogen bonding between xyloglucan and cellulose is confirmed, and glycosidic linkages between xyloglucans and pectic polymers are suggested. 相似文献
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The substitution pattern of the water-soluble l-arabino-(4-O-methyl-d-glucurono)-d-xylan from redwood (Sequoia sempervirens) has been studied by enzymic degradation. Exhaustive hydrolysis by an endo-xylanase (EC 3.2.1.8) from a Basidiomycete Sporotrichum dimorphosporum left a residue accounting for 20% of the original d-xylan. In the dialyzable material, oligosaccharides having arabinose or 4-O-methylglucuronic acid residues attached to the non-reducing d-xylosyl end-group of xylobiose or xylotriose, respectively, were the smallest branched oligomers released. Action of the xylanase appears to involve a region of the polysaccharide backbone having three xylosyl residues. A mode of action is proposed that requires unsubstituted hydroxyl groups at C-2, C-3, and C-2′ of a xylobiosyl residue. The binding site seems to correspond to a shallow cavity. The composition and structure of the final residue of attack shows that the enzyme has no action when the xylosyl residues branched through O-2 are separated by only one, unsubstituted xylose residue. This pattern of action, the nature of the dialyzable products, and the production of a final residue in which the substituents are accumulated, suggest that the arabinosyl and glucosyl-uronic groups are irregularly distributed on the main chain of the xylan from redwood and that in some regions they are in close vicinity when not actually on adjacent xylosyl residues. 相似文献
9.
With a view to visualizing the ultrastructural distribution of syringyl lignins in secondary plant cell walls, a polyclonal antibody raised from a synthetic DHP polymer consisting only of syringyl propane units was prepared. To test the reactivity of the antiserum, a mini-dot-blot immunoassay reducing the amounts of substrates and antiserum was developed. A characteristic attribute of the S-antiserum appears to be its specific recognition of sequences of three or more consecutive syringyl units. On ultra-thin sections of model plants of Arabidopsis thaliana, Populus and tobacco, the antiserum allowed us to demonstrate a higher concentration of syringyl epitopes in fibres than in vessels. Variations in the distribution pattern of these epitopes between the three plants examined suggest that the synthesis of syringyl lignins in angiosperms depends on the species. 相似文献
10.