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11.
Burkhard Becker Dieter Becker Johannis P. Kamerling Michael Melkonian 《Journal of phycology》1991,27(4):498-504
The chemical composition of cell walls (thecae) of three taxa of scaly green flagellates (Prasinophyceae) was investigated. The theca of Tetraselmis striata, Tetraselmis tetrathele, and Scherffelia dubia consists mainly of carbohydrate (80% of dry weight), with proteins (5%), calcium (4%), and sulfate (6%) as minor components. The principal sugars (60% of dry weight) are the 2-keto-sugar acids 3-deoxy-manno-2-octulosonic acid (KDO), 3-deoxy-manno-5-O-methyl-2-octulosonic acid (5OMeKDO), and 3-deoxy-lyxo-2-heptulosaric acid (DHA). Arabinose, gulose, galactose, galacturonic acid, and in S. dubia, xylose and rhamnose were also found. Examination of scale preparations from Mantoniella squamata, Mesostigma viride, Pyramimonas amylifera, and Nephroselmis olivacea revealed that the 2-keto-sugar acids were always associated with the presence of typical prasinophycean scales on the cell surface. In contrast, 2-keto-sugar acids were not detected in the cell wall of Chlamydomonas reinhardtii nor in polymer preparations from the culture medium of Chlamydomonas reinhardtii, Dunaliella bioculata, Dunaliella primolecta, Asteromonas gracilis, Hafniomonas reticulate, Pedinomonas tuberculata, Monomastix sp., and Micromonas pusilla. We conclude that 2-keto-sugar acids are chemical markers for prasinophycean scales. 相似文献
12.
Alexander Christmann Jacqueline Christmann Petra Schiller Burkhard Frenzel 《Trees - Structure and Function》1996,10(5):331-338
Levels of indole-3-acetic acid (IAA) were determined in needles from silver fir (Abies alba Mill.) trees in the northern Black Forest. IAA was quantified by gas chromatography (GC) as 1-heptafluorobutyryl-IAA-methylester
(HFB-IAA-ME) using electron capture detection. Prior to GC analysis, extensive purification of needle extracts was performed
employing two HPLC steps. Peak identity of HFB-IAA-ME was confirmed by combined gas chromatography-mass spectrometry in selected
samples. Levels of IAA in needles belonging to different needle age-classes exhibited a cyclic seasonal pattern with highest
concentrations in winter and lowest levels in spring when bud-break occurred. Such a cyclic seasonal pattern of IAA levels
was also observed in needles from declining fir trees or fir trees suffering from a strong sulfur impact (S-impact) in the
field due to a local SO2 source. Levels of IAA increased with increasing needle age. This age dependency of IAA concentrations was most pronounced
in late autumn when IAA levels were high and nearly disappeared in spring when IAA levels reached their minimum. In needles
from declining fir trees or fir trees suffering from a strong S-impact in the field, IAA levels hardly increased with increasing
needle age. It is suggested that in healthy trees high levels of IAA protect older needles from abscission and that the considerable
losses of older needles of declining fir trees or of fir trees under S-impact are a consequence of the low levels of IAA found
in older needles of such trees.
Received: 4 May 1995 / Accepted: 29 August 1995 相似文献
13.
In potato tubers two starch phosphorylase isozymes, types L and H, have been described and are believed to be responsible for the complete starch breakdown in this tissue. Type L has been localized in amyloplasts, whereas type H is located within the cytosol. In order to investigate whether the same isozymes are also present in potato leaf tissue a cDNA expression library from potato leaves was screened using a monoclonal antibody recognizing both isozyme forms. Besides the already described tuber L-type isozyme a cDNA clone encoding a second L-type isozyme was isolated. The 3171 nucleotide long cDNA clone contains an uninterrupted open reading frame of 2922 nucleotides which encodes a polypeptide of 974 amino acids. Sequence comparison between both L-type isozymes on the amino acid level showed that the polypeptides are highly homologous to each other, reaching 81–84% identity over most parts of the polypeptide. However the regions containing the transit peptide (amino acids 1–81) and the insertion sequence (amino acids 463–570) are highly diverse, reaching identities of only 22.0% and 29.0% respectively.Northern analysis revealed that both forms are differentially expressed. The steady-state mRNA levels of the tuber L-type isozyme accumulates strongly in potato tubers and only weakly in leaf tissues, whereas the mRNA of the leaf L-type isozyme accumulates in both tissues to the same extent. Constitutive expression of an antisense RNA specific for the leaf L-type gene resulted in a strong reduction of starch phosphorylase L-type activity in leaf tissue, but had only sparse effects in potato tuber tissues. Determination of the leaf starch content revealed that antisense repression of the starch phosphorylase activity has no significant influence on starch accumulation in leaves of transgenic potato plants. This result indicated that different L-type genes are responsible for the starch phosphorylase activity in different tissues, but the function of the different enzymes remains unclear. 相似文献
14.
RelA/p65 is a molecular target for the immunosuppressive action of protein kinase A. 总被引:14,自引:0,他引:14
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M Neumann T Grieshammer S Chuvpilo B Kneitz M Lohoff A Schimpl B R Franza Jr E Serfling 《The EMBO journal》1995,14(9):1991-2004
Stimulation of the protein kinase A (PKA) signalling pathway exerts an inhibitory effect on the proliferation of numerous cells, including T lymphocytes. In CD4+ T helper cells, stimulation of PKA leads to suppression of interleukin 2 (IL-2) induction, while induction of the genes coding for the lymphokines IL-4 and IL-5 is enhanced. We show that the differential effect of PKA activity on induction of the IL-2 and IL-4 genes is mediated through their promoters. One major target of the suppressive effect of PKA is the kappa B site in the IL-2 promoter. A kappa B site is missing in the IL-4 promoter. Mutations preventing factor binding to the IL-2 kappa B site result in a loss of PKA-mediated suppression of IL-2 promoter activity. Furthermore, activation of the PKA signalling pathway impairs the inducible activity of multiple kappa B sites of the IL-2 promoter, but not of other factor binding sites. The reduction in activity of kappa B sites in activated and PKA-stimulated T cells is accompanied by changes in the concentration and DNA binding of Rel/NF-kappa B factors. Stimulation of the PKA pathway in Jurkat T cells with the PKA activator forskolin leads to an increase in synthesis of c-Rel and p105/p50, while synthesis of p65/RelA remains unchanged. However, nuclear translocation and DNA binding of p65 is distinctly impaired, probably due to a retarded degradation of I kappa B-alpha. In a similar way, stimulation of the PKA signalling pathway inhibits nuclear translocation of p65 and generation of nuclear kappa B complexes in peripheral T lymphocytes from murine lymph nodes. These results indicate that PKA-mediated suppression of NF-kappa B activity plays an important role in the control of activation of peripheral T lymphocytes. 相似文献
15.
Determination of apoplastic K+ in intact leaves by ratio imaging of PBFI fluorescence 总被引:2,自引:0,他引:2
The tetraammonium salt of the K+ binding fluorescent dye benzofuranisophthalate (PBFI) was used to investigate the influence ofpotassium nutrition (0.12.1 mol m3) on apoplasticK+ inVicia faba leaves by means of ratio imaging. As a referencethe infiltration-centrifugation method was used. Both methodsreflected the influence of K+ supply on apoplastic K+ concentration.The abaxial leaf side revealed significantly higher K+ concentrations(20-25 mol m3) than the adaxial side (58 mol m3).Application of CCCP led to an immediate increase in apoplasticK+ demonstrating the reliability of the PBFI method. Key words: Vicia faba, leaf, apoplast, K+, PBFI, ratio imaging, ratiometric fluorescence microscopy 相似文献
16.
Accuracy of predicting protein secondary structure and solvent accessibility from sequence information has been improved significantly by using information contained in multiple sequence alignments as input to a neural 'network system. For the Asilomar meeting, predictions for 13 proteins were generated automatically using the publicly available prediction method PHD. The results confirm the estimate of 72% three-state prediction accuracy. The fairly accurate predictions of secondary structure segments made the tool useful as a starting point for modeling of higher dimensional aspects of protein structure. © 1995 Wiley-Liss, Inc. 相似文献
17.
The use of Congo red as an elective stain for eosinophilic granulocytes and their precursors in tissue sections and autoradiographs is demonstrated and discussed. The 0.5% alcoholic Congo red solution of Highman, normally used for the detection of amyloid, may also be used with only minor changes. This simple method may aid in the diagnosis of special hematological problems and facilitates the recognition of eosinophil granulocytes as well as proliferating and nonproliferating myelocytes in autoradiographs from paraffin sections. 相似文献
18.
Equilibrium constants, defined on the basis of the moles of all reactants and products including water, were found to be 4.6, 1.0 and 0.8 for the esterification of the glycinc cation at 20 degrees in a dilute aqueous sytem, and systems having 0.5 : 1 and 1 : 1 molar ratios of ethanol to water, respectively. When corrections were made for deviations from ideality a value of 5 +/- 1 was obtained for all three systems. Enthalpy changes were determined calorimetrically for the dilute aqueous and equimolar ethanol-water systems, and in each case was close to 1 kcal mole(-). The entropy change was calculated as 6 cal mole(-1) deg(-1).DeltaG(0') for the hydrolysis of the glycine ethyl ester cation at 20 degrees and pH 7 was calculated as -7.5 kcal mole(-1). 相似文献
19.
20.
Clonal descent and microevolution of Neisseria meningitidis during 30 years of epidemic spread 总被引:3,自引:0,他引:3
Giovanna Morelli Burkhard Malorny Kerstin Müller rea Seiler Jian-Fu Wang Jesus del Valle & Mark Achtman 《Molecular microbiology》1997,25(6):1047-1064
Serogroup A meningococci of subgroups III, IV-1 and IV-2 are probably descended from a common ancestor that existed in the nineteenth century. The 10.5 kb sequences spanning five distinct chromosomal loci, encoding cell-surface antigens, a secreted protease or housekeeping genes and intergenic regions, were almost identical in strains of those subgroups isolated in 1966, 1966 and 1917 respectively. During the subsequent two to three decades, all of these loci varied as a result of mutation, translocation or import of DNA from unrelated neisseriae. Thus, microevolution occurs frequently in naturally transformable bacteria. Many variants were isolated only once or within a single geographical location and disappeared thereafter. Other variants achieved genetic fixation within months or a few years. The speed with which sequence variation is either eliminated or fixed may reflect sequential bottlenecks associated with epidemic spread and contrasts with the results of phylogenetic analyses from bacteria that do not cause epidemics. 相似文献