Verbreitung und Ökologie derVaucheria-Arten (Tribophyceae) des Elbe-Ästuars und der angrenzenden Küste

From the Elbe estuary and the adjacent North Sea coast, 19 species ofVaucheria are on record. Their horizontal and vertical distribution pattern as well as their association with macrophyte communities are described. With regard to ecological salinity tolerance and distribution below or above mean high water, 7 ecological groups ofVaucheria species are defined. Dominating species which form extensive algal mats in the upper eulittoral zone areVaucheria compacta var.dulcis (freshwater and oligohalinic section of the estuary),V. compacta var.compacta (mesohalinic section) andV. velutina together withV. subsimplex (polyhalinic and euhalinic section). The rare speciesV. vipera is recorded for the first time from the German coast.

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Herrn Dr. Dr. h. c. Peter Kornmann zum 80. Geburtstag gewidmet.

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Adressat für Sonderdruckwünsche: Prof. Dr. L. Kies.     

Ultrastructure ofCyanoptyche gloeocystis f.dispersa (Glaucocystophyceae)

Cyanoptyche gloeocystis f.dispersa (Geitler)Starmach is a palmelloid colonial alga that contains prokaryotic blue-green endocytobionts (cyanelles) instead of chloroplasts. The periphery of the host cell shows a peculiar lacunae system with underlying microtubules. Vegetative cells possess two rudimentary flagella. Zoospores are dorsiventrally shaped with two heterokont and heterodynamic flagella which originate from a subapical depression. This depression can also be seen in vegetative cells. Both flagella possess non-tubular mastigonemes. Main reserve product is starch lying freely in the cytoplasm. Cyanelles, enclosed singly in a host vesicle, are provided with a remnant cell wall. Thylakoids are arranged concentrically. The central part of each cyanelle harbours its DNA and one large polyhedral body, probably a carboxysome.Cyanoptyche gloeocystis f.dispersa shares all taxonomically essential characters with the monadoidCyanophora, the palmelloidGloeochaete, and the coccoidGlaucocystis. All of them are members of the cyanelle-bearing small algal classGlaucocystophyceae. Members of this class serve as model organisms for the evolution of chloroplasts from cyanophycean ancestors.Dedicated to Prof. DrLothar Geitler on the occasion of his 90th birthday.     

Enzymatic and nonenzymatic degradation of myelin basic protein

A procedure for large scale isolation of myelin basic protein (BP) has been modified to insure BP preparations free of neutral proteinase activity. Fractions were monitored by electrophoretic analysis of BP solutions incubated under various conditions of temperature and pH. Maximum degradation of human BP prepared by the old batch procedure occurs at pH 7, 47°C. BP preparations obtained by the new procedure, as well as BP preparations purified by CM-cellulose chromatography, are stable under these conditions. The latter, however, do undergo significant breakdown at pH 9, 100°C. The results suggest that the degradation observed under these conditions is non-enzymatic in nature.Special Issue dedicated to Dr. Elizabeth Roboz-Einstein.     

A New Form of Myelin Basic Protein Found in Human Brain

Human myelin basic protein was subjected to ion-exchange chromatography at high pH to separate the differently charged components. Polyacrylamide gel electrophoretic patterns of the fractions showed that the less basic fractions 3, 4, and 5 contained significant amounts of a protein somewhat smaller than the more common 18.5-kDa form. Fraction 3 consisted of approximately equal amounts of this smaller polypeptide and component 3, the 18.5-kDa form found in other mammalian myelin basic protein preparations. The two proteins in fraction 3 were separated by fast protein liquid chromatography. Both have blocked N termini and identical C termini (-Met-Ala-Arg-Arg). When the tryptic digests of the two proteins were fractionated by HPLC, the elution profiles were similar, except that four peaks found in the chromatogram of the larger protein were missing from the chromatogram of the smaller one. In addition, an extra peak was found in the elution pattern of the latter chromatogram. Amino acid analysis of the individual tryptic peptides indicated that the smaller protein lacked residues 106-116 (-Gly-Arg-Gly-Leu-Ser-Leu-Ser-Arg-Phe-Ser-Trp-). The deleted portion corresponds exactly to the amino acid sequence encoded by exon 5 of the mouse basic protein gene. This new form of myelin basic protein has a molecular weight of 17,200, calculated from its amino acid composition.     

Role of phosphorylation in conformational adaptability of bovine myelin basic protein.

Controlled thrombic digestion of a preparation of components 2 + 3 isolated from the 18.5 kDa bovine myelin basic protein (MBP) yielded a polypeptide that was monophosphorylated on threonine 97 (component 3pT97). This is the first posttranslationally phosphorylated MBP isolated in pure form. We studied the effect of this single phosphate on the conformational adaptability of 18.5 kDa bovine MBP by comparing the circular dichroism (CD) spectrum of component 3pT97 with the spectra of highly purified nonphosphorylated components 1 and 2. The CD spectra of nonphosphorylated component 1 and component 2 [monodeamidated form(s) of component 1] were indistinguishable, while component 3pt97 exhibited a different spectrum. The singly phosphorylated MBP component exhibited 13% more ordered conformations than that adopted by nonphosphorylated MBP in dilute aqueous solutions. This was estimated from the CD spectra, and apparently involved about 17 additional amino acid residues in beta-structure(s).     

Characterization of two partially purified xyloglucan endotransglycosylases from parsley (<Emphasis Type="Italic">Petroselinum crispum</Emphasis>) roots

Two forms of xyloglucan endotransglycosylase differing in isoelectric points were isolated from the protein mixture obtained from parsley roots and partially characterized. Both forms were glycoproteins differing in their specific activities but other features were almost the same. Activity and stability of both enzymes in broad pH region were observed with two pH optima, one at acidic pH (5.8) and the second one at basic pH (8.8). The enzymes behaved as typical transglycosylases since no activity was observed in the absence of xyloglucan oligosaccharides in the viscometric assay. Small hetero-transglycosylating activities were observed when hydroxyethyl-or carboxymethyl-celluloses instead of xyloglucan as donor substrate were used as well as when cello-oligosaccharides instead of xyloglucan oligosaccharides were used as the acceptor substrate.     

High rate of Helicobacter pylori reinfection in children and adolescents

AIMS: Primary Helicobacter pylori infection occurs predominantly in childhood. The aims of this study were to establish the rate of H. pylori reinfection after successful eradication in children and adolescents and to determine the risk factors associated with reinfection. PATIENTS AND METHODS: This retrospective study involved 45 children (20 girls, 25 boys) who met the following criteria: eradication of H. pylori confirmed at least 4 weeks after the completion of therapy, and the search for reinfection at least one year after control of eradication of H. pylori. Demographic data, socioeconomic status and living conditions were recorded. RESULTS: Forty-five children aged 1.2-17.6 years (median, 10.9 years) at the time of H. pylori treatment were reviewed 1 to 9 years after H. pylori eradication. Eight children (18%) had been reinfected (5.4% to 6% per patient-year). Six of 25 (24%) children older than 10 years at the time of diagnosis became reinfected. None of the studied risk factors was associated with reinfection. However, having a sibling younger than 5 years was found in four of seven (57%) reinfected children versus five of 24 (21%) nonreinfected children (p = .08). CONCLUSION: Children become reinfected more frequently than adults. Adolescents become reinfected, whereas acquisition of primary H. pylori infection occurs predominantly in early childhood. Close contact with young children, especially siblings, younger than 5 years could be a more important risk factor than the age of the patient at the time of treatment for the high rate of reinfection in childhood.     

Multiple Roles of Soluble Sugars in the Establishment of Gunnera-Nostoc Endosymbiosis

Gunnera plants have the unique ability to form endosymbioses with N₂-fixing cyanobacteria, primarily Nostoc. Cyanobacteria enter Gunnera through transiently active mucilage-secreting glands on stems. We took advantage of the nitrogen (N)-limitation-induced gland development in Gunnera manicata to identify factors that may enable plant tissue to attract and maintain cyanobacteria colonies. Cortical cells in stems of N-stressed Gunnera plants were found to accumulate a copious amount of starch, while starch in the neighboring mature glands was nearly undetectable. Instead, mature glands accumulated millimolar concentrations of glucose (Glc) and fructose (Fru). Successful colonization by Nostoc drastically reduced sugar accumulation in the surrounding tissue. Consistent with the abundance of Glc and Fru in the gland prior to Nostoc colonization, genes encoding key enzymes for sucrose and starch hydrolysis (e.g. cell wall invertase, α-amylase, and starch phosphorylase) were expressed at higher levels in stem segments with glands than those without. In contrast, soluble sugars were barely detectable in mucilage freshly secreted from glands. Different sugars affected Nostoc’s ability to differentiate motile hormogonia in a manner consistent with their locations. Galactose and arabinose, the predominant constituents of polysaccharides in the mucilage, had little or no inhibitory effect on hormogonia differentiation. On the other hand, soluble sugars that accumulated in gland tissue, namely sucrose, Glc, and Fru, inhibited hormogonia differentiation and enhanced vegetative growth. Results from this study suggest that, in an N-limited environment, mature Gunnera stem glands may employ different soluble sugars to attract Nostoc and, once the cyanobacteria are internalized, to maintain them in the N₂-fixing vegetative state.Nitrogen (N) is an essential element for plant growth, but availability of reduced N in the soil is often limiting. Representatives from a wide range of land plants have evolved the ability to form associations with N₂-fixing microbes (Franche et al., 2009). Associations between rhizobia and legume plants are well-characterized examples of plant-bacterial N₂-fixing symbioses. Unlike rhizobia, which generally exhibit narrow host ranges (Kistner and Parniske, 2002), N₂-fixing cyanobacteria are able to form productive associations with a broad range of plants, including bryophytes (hornworts and liverworts), ferns (Azolla), gymnosperms (cycads), and angiosperms (Gunnera; for review, see Rai et al., 2000; Adams et al., 2006). Free-living cyanobacteria within the genus Nostoc can fix N in specialized microoxic cells called heterocysts. The ability of Nostoc to fix N independent of a host environment may facilitate the formation of symbioses with a wide range of plants. Understanding the physiological conditions that enable a plant host to enter into symbiotic associations with cyanobacteria may allow us to extend the benefit of biological N fixation to crops outside the legume family.Nostoc has the ability to differentiate not only into filaments bearing heterocysts but also into transiently motile filaments, known as hormogonia, which enable the cyanobacteria to enter plants (Meeks and Elhai, 2002). Nostoc can be induced to form hormogonia by different environmental stimuli and by a hormogonia-inducing factor released from N-stressed host plants (Meeks and Elhai, 2002; Adams et al., 2006). The attraction of hormogonia to plants is much less specific than that of rhizobia. Hormogonia are attracted to root extracts from either host or nonhost plants and even to certain simple sugars, such as Ara, Glc, and Gal (Nilsson et al., 2006). After entering a plant host, hormogonia revert back to filaments with N₂-fixing heterocysts. Inside the host, further hormogonia formation is suppressed, and heterocysts appear at a frequency of about 30% to 40%, 3- to 4-times higher than that found in free-living Nostoc (Meeks and Elhai, 2002). Although free-living Nostoc species can support N₂ fixation through photosynthesis, under symbiotic conditions they rely on photosynthate from the host plant. In general, the sugars (Suc, Glc, and Fru) known to support heterotrophic growth in the dark by free-living cyanobacteria coincide with those that support nitrogenase activity in Nostoc-plant associations (Meeks and Elhai, 2002). However, the Nostoc-Gunnera association may be exceptional; only Glc and Fru have been shown to sustain nitrogenase activities (Man and Silvester, 1994; Wouters et al., 2000), although Suc anddextrin were able to keep Nostoc alive without light (Wouters et al., 2000). It is evident from cyanobacterial studies that the plant hosts have evolved the ability to regulate cyanobacterial growth and differentiation during symbiotic associations (Meeks and Elhai, 2002).However, because most studies of plant-cyanobacterial associations have focused on the cyanobacterial partner (e.g. Wang et al., 2004; Ekman et al., 2006), the mechanisms through which plant hosts attract, internalize, and maintain cyanobacteria remain to be elucidated (Adams et al., 2006).The Nostoc-Gunnera association is an ideal system with which to study plant-cyanobacteria symbioses, not only because Gunnera is the only genus of angiosperms known to form endosymbioses with N₂-fixing cyanobacteria but also because the association between the two can be readily established in the laboratory (Bergman et al., 1992; Chiu et al., 2005). Nostoc hormogonia enter Gunnera plants through specialized glands located on the stem. As the gland matures, it secretes polysaccharide-rich mucilage that attracts cyanobacteria (Nilsson et al., 2006), supports their growth on the gland surface (Towata, 1985; Chiu et al., 2005), and permits further hormogonia differentiation (Rasmussen et al., 1994). From there, hormogonia enter the gland and penetrate cells near the base of the gland in the stem (Bonnett, 1990; Bergman et al., 1992). Although each gland is only transiently capable of accepting cyanobacteria, new glands continue to form on the stem at the base of each new leaf.In contrast to the development of nodules in legumes, which requires a complex exchange of signals between the two symbiotic partners (Cooper, 2007), stem gland development in Gunnera takes place in the absence of cyanobacteria (Bonnett, 1990). N limitation, however, is a prerequisite for stem gland development (Chiu et al., 2005), as it is for nodulation (Barbulova et al., 2007). We have taken advantage of the N-deficiency-induced gland development in G. manicata to identify factors that enable Gunnera to form endosymbiosis with cyanobacteria. This study investigated changes in the carbohydrate metabolism during Gunnera gland development and discovered that tissue in the mature glands accumulated high levels of soluble sugars prior to the arrival of cyanobacteria. In agreement with this finding, several key genes encoding enzymes for starch/Suc hydrolysis were expressed at higher levels in the gland compared to the stem. Furthermore, we found that various sugars cyanobacteria may encounter as they approach Gunnera glands as opposed to those they would encounter within plant cells differentially affected Nostoc’s ability to form motile hormogonia.