146 search hits
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Bedeutung der Baumart für die Aktivität, Diversität und Abundanz methanoxidierender Bakterien in temperaten Waldböden
(2010)
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Daniela Degelmann
- Die mikrobielle Oxidation atmosphärischen Methans ist in Nadelwaldböden bis zu drei Mal niedriger als in Laubwaldböden. Ziel dieser Dissertation war es, anhand von drei deutschen Waldstandorten (Solling, Steigerwald und Unterlüß) mit jeweils benachbarten Beständen der Rotbuche (Fagus sylvatica L.) und der Gemeinen Fichte (Picea abies L.), die Umweltparameter zu identifizieren, die diese unterschiedlichen Methanoxidationsraten hervorrufen, und deren Auswirkungen auf die Diversität und Abundanz der methanotrophen Lebensgemeinschaft zu bestimmen. Die Aufnahme von Michaelis-Menten-Kinetiken an intakten Bodenkernen bei konstanter Methankonzentration, Temperatur sowie konstantem Matrixpotenzial ergab, dass die kinetischen Parameter Vmax(app) und KM(app) in Fichtenwaldböden bis zu 65% niedriger waren als in entsprechenden Buchenwaldböden. In situ Methanaufnahmeraten und atmosphärische Methanoxidationsraten gestörter Bodenproben waren in Böden unter Fichte ebenfalls niedriger. Die maximale methanotrophe Aktivität war im Oa-Horizont (Buche) oder in den ersten fünf Zentimetern des Mineralbodens lokalisiert. Unter Fichte wurde im Oa-Horizont keine Methanoxidation detektiert. Im Oi- und Oe-Horizont wurde in keinem der beiden Waldbodentypen methanotrophe Aktivität verzeichnet. Die Gasdiffusion durch die organische Auflage der Böden, der pH-Wert und die Ammoniumkonzentration waren in beiden Waldbodentypen ähnlich und schieden somit als regulierende Faktoren für die atmosphärische Methanoxidation in Laub- und Nadelwaldböden aus. Die Produktion von Ethylen unter oxischen Bedingungen war vernachlässigbar, so dass Ethylen ebenfalls ausgeschlossen werden konnte. β-Pinen, welches in Fichtennadeln und -wurzeln vorkommt und eine sehr hohe inhibitorische Wirkung auf die Methanoxidation zeigt, inhibierte die Oxidation von Methan in Bodenaufschlämmungen des Steigerwalds vollständig bei einer Konzentration, die dem Fünffachen der in situ Konzentration entsprach. Die von Fichten freigesetzten Monoterpene können die verminderte Methanaufnahme in Fichtenwaldböden erklären. Der Einfluss der Baumart auf die Zusammensetzung der methanotrophen Lebensgemeinschaft wurde durch vergleichende Analyse der Gene der partikulären Methanmonooxygenase (pmoA) untersucht. Von den insgesamt 366 analysierten pmoA-Genen waren 82% Upland Soil Cluster alpha (USCα) zuzuordnen, dem global am häufigsten detektierten pmoA-Genotyp in Waldböden. Durch Vergleich der PmoA-Sequenzen mit den entsprechenden 16S rRNA-Gensequenzen bekannter methanotropher Isolate wurde ein distanzbasierter „Cut-off“ von 7% auf Proteinebene zur Differenzierung methanotropher OTUs auf Artenebene kalkuliert. Unter Anwendung dieses „Cut-offs“ konnten in Buchenwaldböden sieben OTUs innerhalb von USCα unterschieden werden. Außerdem wurden zwei tiefabzweigende Genotypen (Cluster 6 und Cluster 7) detektiert, die nur entfernt verwandt zu bekannten PmoA-/AmoA-Sequenzen waren. In Fichtenwaldböden waren dagegen nur vier USCα-OTUs sowie Cluster 6 detektierbar. Die erniedrigte Diversität Methanotropher in Fichtenwaldböden wurde durch statistische Analysen bestätigt. Genfragmente von mmoX und der pmoA von methanotrophen Verrucomicrobia wurden nicht detektiert. amoA-Gene mit hoher Verwandtschaft zur amoA von Nitrosospira briensis wurden gelegentlich kodetektiert. Die Abundanz der pmoA-Gene von USCα, der Anteil von USCα an der bakteriellen Gemeinschaft sowie die zellspezifische Aktivität von USCα waren in Böden unter Fichte niedriger als unter Buche. Die ermittelten Werte für die zellspezifische Aktivität von USCα lagen unterhalb des theoretischen Mindestwerts, der für das Überleben einer methanotrophen Zelle bei Oxidation von atmosphärischem Methan notwendig ist. Dies lässt vermuten, dass USCα neben atmosphärischem Methan auf alternative Kohlenstoff- und Energiequellen angewiesen sein könnte. Zusammenfassend lassen die Ergebnisse dieser Disseration den Schluss zu, dass von Fichten freigesetzte Monoterpene die Aktivität, Diversität und Abundanz atmosphärischer Methanoxidierer reduzieren und so die atmospherische Methanaufnahme von Fichtenwaldböden verringern.
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Exocrine glands in Erotylidae (Coleoptera, Cucujoidea): chemical ecology, morphology and evolution
(2010)
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Kai Drilling
- In most insect orders chemical defence is highly important and a multiplicity of partly spectacular defence mechanisms were described in the last years. It is well known that members of the Erotylidae show a particularly rich equipment of exocrine compound glands. However, morphology and ultrastructure as well as the chemistry of the secretions of these compound glands remain unexplored so far. The cosmopolitan Erotylidae is assigned to the superfamily Cucujoidea (Clavicornia) of the Coleoptera-Cucujiformia and comprises about 3500 described species in 258 genera. Today the family includes both the phytophagous species of the former Languriidae and the mycophagous species of the former Erotylidae s. str. (now ranked as the subfamily Erotylinae). The adult beetles, as well as their larvae, are bounded to different bracket fungi or live under the bark. Most species are striking in appearance, frequently in combination with conspicuous patters of stripes, spots or rings. The present contribution deals with species of this coleopteran family and concerns altogether five different subject areas: (1) Morphological details of the internal structure and ultrastructure of the compound glands were examined in exemplar species of the family (Tritoma bipustulata, Triplax scutellaris) for the first time (SEM, TEM). Each compound gland consists of a central excretory duct and numerous identical gland units. These gland units are composed of two different cells, whereof one forms a cuticular ductule. Thus the glands belong to class III as defined by Noirot and Quennedey (1974, 1991). Furthermore, the glands offered two structural features (lateral appendix, the spongious wall of the ductus), which were previously not known from compound glands of beetles. (2) Hitherto hardly known was the ability of reflex bleeding in these species. The phenomenon is reported, for instance, from the closely related families Coccinellidae and Endomychidae. However, the hemolymph is not, like in the mentioned taxa, released from the joints of the leg, but from the abdominal tip. The chemistry of the reflex blood as well as the discharged secretion of the pronotal glands was examined by GC-MS for the first time. Biological effects of the identified compounds of both secretions were evaluated in bioassays and agar diffusion tests. (3) Furthermore, a study on the role of emitted fungal volatile compounds in recognition of the hostfungus by mycophagous beetles was conducted (GC-EAD, EAG). Beside the two erotylid-species (Tritoma bipustulata and Dacne bipustulata), mycophagous species of the families Tenebrionidae and Ciidae were included in this study. The scents of young as well as aged fungi were tested. The results imply that the species are able to discriminate between fungi of different ages as well as the degree of colonization. (4) Due to the multiplicity of different exocrine compound glands in Erotylidae (within the angles, as well as along the lateral margin of the pronotum, on the prosternal and mesoventral intercoxal processes, anteromesal to the compound eyes, on the subgenal braces, and rarely on the mentum), a comparative analysis on the occurrence of compound glands was carried out. 47 species were included in this analysis. The results were mapped on an existing phylogeny of the family and other phylogenetic hypotheses were discussed. Several glandular characters support the monophyly of the Erotylidae, Erotylinae as well as some tribes of the latter subfamily. Also the postulated position of Languria bicolor (Languriinae) within the Erotylinae is confirmed by glandular characters. (5) Finally, it was possible to identify Brachyserphus parvulus (Proctotrupidae) as a parasitoid of T. bipustulata. Members of this group of Hymenoptera are endoparasites in larvae of numerous families of the Coleoptera, Diptera and Lepidoptera. B. parvulus was hitherto known from species of Nitidulidae, Melandryidae, Phalacridae as well as the erotylid genus Triplax.
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Analyse der physiologischen Funktion von Mitgliedern der Rieske-Typ Eisen-Schwefel-Proteinfamilie in der inneren Plastidenhülle
(2009)
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Sandra Bartsch
- Höher entwickelte Pflanzen enthalten eine Superfamilie von non-Häm Oxygenasen, deren Mitglieder über identische, konservierte Rieske- und mononukleare Fe-Bindungsdomänen verfügen. Diese Familie umfasst Tic55, PAO, CAO, CMO und ein 52 kDa schweres Protein (PTC52), welches in Assoziation mit dem Präkursor NADPH:Protochlorophyllid (Pchlid) Oxidoreduktase A (pPORA) Translocon vorliegt. Die Expression von AtCAO cDNA in Synechocystis, welches kein CAO-Gen enthält, führte zur Bildung von Chlorophyll b (Chl b) und geringen Mengen an Pchlid b. Pulse labeling Experimente mit dem isolierten PTC-Komplex und dem Pchlid Präkursor 5-Aminolävulinsäure (5-ALA) zeigten, dass PTC52 als Pchlid a Oxygenase agiert. Die gekoppelte in vitro Transkription/Translation von Arabidopsis CAO (AtCAO) bzw. PTC52 (AtPTC52) cDNAs führte zur Bildung von katalytisch aktiven Proteinen, wobei CAO Chlid a in Chlid b umwandelte, wohingegen PTC52 die Umwandlung von Pchlid a zu Pchlid b katalysierte. In Kotyledonen von Gerste und Arabidopsis ist der Import von pPORA von Pchlid abhängig. Während der Membran-Passage interagiert pPORA mit Komponenten des PTC-Komplexes und bildet dabei sog. „junction“-Komplexe zwischen äußerer und innerer Plastidenhülle. CAO wird als größeres Präkursor-Protein synthetisiert, über den Standard-Import-Komplex in den Intermembran-Raum importiert und liegt in seiner prozessierten Form als intrinsisches Protein der Thylakoid-Membranen bzw. der inneren Plastidenhülle vor, wo es mit Tic40, Tic22 und Tic20 interagiert und einen neuen Tic-Subkomplex bildet. Weitere Analysen mit Chloroplasten der Chlorina Mutanten ch1-3 (kein funktionelles CAO-Gen; keine Akkumulation von Chl b bzw. LHC-Proteinen) zeigten keinen Import von pLhcb1 (= Präkursor des LHCII-Apoproteins) bzw. pLhcb4 (= Präkursor des CP29-Apoproteins). PTC52 wird als größeres, ca. 57 kDa schweres Vorstufenprotein synthetisiert, in Chloroplasten importiert und zur endgültigen Größe prozessiert. Das reife, 52 kDa schwere Protein wurde als intrinsisches Membranprotein der inneren Plastidenhülle identifiziert, wo es mit PTC130, PTC90, PTC16/Oep16 und PTC33/Toc33 interagiert und einen funktionellen Protein-Import-Komplex (PTC-Komplex) bildet. Während des substratabhängigen Imports von pPORA katalysiert PTC52 die Oxygenierung von Pchlid a zu Pchlid b. DEPC agiert, indem es konservierte His-Reste im Rieske-Fe-S-Cluster ethoxyformyliert. Während bei geringen DEPC-Konzentrationen allein der Import von pPORA inhibiert war, war dieser in Anwesenheit von 1 mM DEPC nicht nachweisbar, wohingegen die Translokation von Tic55-Import-Substraten um ca. 10 % verringert war. Dies bestätigte die Beteiligung der His-Reste am katalytischen Mechanismus von PTC52 und Teil des PTC-Komplexes. Anhand von zwei PTC52-knockout-Linien (SALK_011945 und SAIL_148.HC5) wurde gezeigt, dass loss-of-function-Mutationen im Arabidopsis PTC52-Gen zu einem embryoletalen Phänotyp führten, so dass heterozygote AtPTC52/Atptc52-Pflanzen zur Analyse der Bedeutung von PTC52 in planta herangezogen wurden. Diese Keimlinge waren empfindlicher gegenüber einer Belichtung, was durch die geringeren Mengen an „light-harvesting“ POR-Pchlid (LHPP) – Komplexen im Prolamellarkörper der Etioplasten erklärbar war. Durch Pigmentanalysen konnte sowohl Pchlid a als auch Pchlid b in Wildtyp-Keimlingen identifiziert werden, wobei deren relative Anteile in AtPTC52/Atptc52-Pflanzen in Richtung Pchlid a verschoben waren. Zusätzlich waren ein Rückgang der Chl-Akkumulation, ein verändertes Chl b/Chl a-Verhältnis und eine Verringerung der LHCII-Mengen während des frühen Ergrünens erkennbar. Mittels Affinitätschromatographie wurden Tic55, PTC52 und PAO als Thioredoxin (Trx)-Targets in der inneren Plastidenhülle identifiziert. Abgesehen von konservierten Rieske- und [2Fe-2S]-Clustern weisen diese Proteine ein CxxC-Motiv auf. Aktivitätsmessungen in An- bzw. Abwesenheit von stromalem Trx f bzw. Trx m lassen darauf schließen, dass PTC52 und PAO aus Gerste reversiblen Oxidations/Reduktionsvorgängen, vermittelt durch redox-aktive SH-Gruppen, unterliegen, wobei die reduzierte Form eine höhere Aktivität aufweist. Um zu verifizieren, ob Trx die Aktivität von Tic55, PTC52 und PAO als Reaktion auf die Licht-Dunkel-Regulation und/oder oxidativen Stress regulieren könnte, verglichen wir die In-Vitro-Import-Kapazitäten der verschiedenen Import-Komplexe in tigrina d12 – Chloroplasten, die aus Pflanzen stammten, die entweder unter kontinuierlichem Weiß-Licht angezogen oder vor der Plastiden-Isolierung verdunkelt bzw. einem Dunkel-Licht-Shift unterworfen worden waren. Tic55, PTC52 und PAO reagierten sensitiv gegenüber einer oxidativen Kontrolle und waren in wiederbelichteten tigrina d12 – Pflanzen inaktiv. In CAO ist kein CxxC-Motiv vorhanden, so dass CAO weder auf das Thioredoxin-System noch auf oxidativen Stress reagiert.
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Identification and characterization of Sgo2 interactions - Insights into dynamic chromosomal localization, mechanism of cohesin protection and putative checkpoint function
(2010)
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Bernd Mayer
- Sister chromatids are embraced and held together by a ring-shaped multiprotein complex called cohesin, from the time of their generation in S-phase until their separation in M-phase. Shugoshins protect centromeric cohesin from premature dissociation and, hence, are important regulators of genome stability. This work demonstrates that hSgo2, one of the two shugoshins in humans, first binds to kinetochores in prophase, then localizes to centromeres in prometaphase before finally traveling back to kinetochores in metaphase. It is further shown that (1) chromatin binding requires the C-terminus of hSgo2, (2) the catalytic activity of the aurora B kinase is essential to focus hSgo2 at centromeres, and (3) attachment of microtubules to kinetochores is not only necessary for the metaphase-specific re-localization of hSgo2 but also sufficient; pulling forces are not required. These newly discovered regulations allow to formulate a mechanistic model that explains shugoshin’s dynamic subcellular localization. An existing conflict in the literature concerns the relative importance of mammalian Sgo1 and Sgo2 in mitosis. Cell biological analyses now demonstrate unambiguously that, contrary to earlier claims, hSgo2 is dispensable for several aspects of mitotic cell divisions. Thus, shugoshin functions are strictly separated, being fulfilled by hSgo1 in mitosis and by hSgo2 in meiosis. Initially, it was unclear how shugoshins exert their cohesin protective function at the molecular level. Using a biochemical approach, protein phosphatase 2A (PP2A) was identified as a prominent interactor of shugoshins in this thesis. Shortly thereafter, it was reported that shugoshins protect cohesin by mediating PP2A-dependent dephosphorylation. Nevertheless, it is shown here for the first time that hSgo2 binds PP2A via its N-terminus. A Sgo2 point mutant deficient in PP2A binding is created and characterized by cell biological experiments. Importantly, biochemical assays demonstrate that hSgo2 greatly stimulates PP2A’s enzymatic activity. Shugoshin function therefore extends beyond simple provision of a linkage between cohesin and PP2A. Mitosis and meiosis are chiefly controlled by the spindle assembly checkpoint (SAC), which allows anaphase to take place only after all chromosomes have become properly attached to the mitotic spindle. Central to SAC signaling, kinetochore bound Mad1-Mad2 complex catalyzes a conformational switch of soluble Mad2, thereby allowing its inhibitory binding to the downstream effector protein Cdc20. SAC-dependent inhibition of anaphase correlates well in timing with shugoshin-dependent protection of cohesin. Here, Mad2 is identified as another novel interactor of hSgo2. Precise mapping reveal a conserved Mad2 interaction motif (MIM) in hSgo2, which is shared by the known Mad2 interactors Mad1 and Cdc20. In fact, several lines of evidence show that the Sgo2-Mad2 complex is structurally very similar to the Mad1-Mad2 and the Cdc20-Mad2 complexes. These biochemical studies challenge the current “one source (kinetochore bound Mad1) – one target (Cdc20)” dogma in the field of SAC research. Mad2 binding is conserved in the only Xenopus laevis shugoshin, xSgo1, indicating an important function of this interaction during vertebrate meiosis.
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Secondary Plant Compounds as Feeding Deterrents in the African Subterranean Termite Schedorhinotermes lamanianus Sjöstedt (Isoptera: Rhinotermitidae): A Behavioural and Neurophysiological Approach
(2010)
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Stefan Gross
- In the present study, the influence of plant-derived secondary compounds on feeding behaviour in the subterranean termite Schedorhinotermes lamanianus was investigated. Furthermore, the chemosensory input system responsible for the perception of these compounds was investigated using electrophysiological methods. The obtained results provide evidence that in S. lamanianus a variety of structurally diverse secondary plant compounds (alkaloids and non-alkaloids) other than securinega-alkaloids influence feeding behaviour. These compounds evoke an avoidance of food sources or lower food consumption under choice conditions even at lower concentrations obtained for securinega-alkaloids. Furthermore, these compounds also reduce feeding under no-choice conditions. Termites seem to ingest less food even when they started feeding and no alternative food source is available. Therefore these compounds act as repellents and feeding deterrents in S. lamanianus depending on the test conditions under which they are applied. Furthermore, the present study provides strong evidence that different proximate mechanisms explain feeding inhibition in S. lamanianus: 1) Twelve structurally very diverse alkaloids, including feeding deterrent alkaloids in S. lamanianus, stimulated the taste neuron II/3 in TP II sensilla on antennae of this termite species. Non-alkaloids did not stimulate neuron II/3. Therefore, this neuron II/3 is an "alkaloid cell" negatively influencing feeding behaviour in this termite. 2) Feeding inhibition seems also to be influenced by the inhibition of phagostimulant taste neurons ("water cells") on antennae. 3) A second sensory input system for the perception feeding deterrent plant-derived secondary compounds seems to be evident as some tested compounds (alkaloids and non-alkaloids) are clear antifeedants in S. lamanianus but do not influence feeding behaviour by the former two mechanisms. Hence, in termites feeding inhibition by secondary plant compounds is a very complex process which needs further investigation. Including neurophysiological investigations of the chemosensory input system seems to be a promising approach to better understand feeding inhibition in termites which may lead to improved wood protection and termite management.
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Funktionale Charakterisierung neuer Komponenten der mitochondrialen Morphogenese in Saccharomyces cerevisiae
(2010)
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Miriam Hammermeister
- Die Morphologie und die Dynamik von Mitochondrien spielen eine wichtige Rolle bei der Funktion und Vererbung dieser Organellen. Zum besseren Verständnis der beteiligten Prozesse müssen alle dazugehörigen Komponenten identifiziert und charakterisiert werden. Die Erforschung von zwei Proteinen, Mdm35 und Mdm36, die die mitochondriale Morphologie und Verteilung beeinflussen, und ihre mögliche Eingliederung in den Morphogenesapparat der Mitochondrien war Gegenstand dieser Arbeit. Der erste Teilabschnitt der Arbeit beschäftigte sich mit der Charakterisierung und Ermittlung der Funktion von Mdm36 in der Gestaltgebung von Mitochondrien. Die Dynamik der Mitochondrien wird maßgeblich von den beiden antagonistischen Prozessen Fusion und Teilung bestimmt. Dnm1, eine Dynamin-verwandte GTPase, stellt die Schlüsselkomponente der mitochondrialen Teilung in Hefe dar, die in Zusammenarbeit mit weiteren Komponenten agiert. Teilungsmutanten besitzen netzartige Mitochondrien, die aufgrund der gestörten Teilung bei fortlaufender Fusion entstehen. In dieser Arbeit wurde gezeigt, dass Deletionsmutanten von MDM36 stark verzweigte mitochondriale Netzwerke aufweisen, die denen der Teilungsmutanten sehr ähneln. Doppeldeletionsstudien mit den Fusionskomponenten Fzo1 und Mdm30 lassen annehmen, dass Mdm36 der Fusion entgegengesetzt wirkt. Außerdem ist in delta-mdm36-Mutanten die durch die Depolymerisation des Aktinzytoskeletts induzierte mitochondriale Teilung blockiert und die Anzahl an teilungsaktiven Dnm1-Komplexen reduziert. Das Zellkortex-assoziierte Protein Num1 interagiert mit mitochondrial assembliertem Dnm1 und fördert über die dadurch geschaffene Verankerung der Mitochondrien am Zellkortex die mitochondriale Teilung. Der mitochondriale Phänotyp der delta-mdm36-Mutanten und delta-num1-Mutanten ist fast identisch. Beide Mutanten besitzen netzähnliche, kompakte Mitochondrien, die wenig Nähe zur Zellperipherie aufweisen und hoch dynamisch sind. Durch die Abwesenheit von Mdm36 wird die Kolokalisation von Dnm1 und Num1 aufgehoben. Diese Ergebnisse liefern weitere Einblicke in die mitochondriale Teilungsmaschinerie und legen ein Modell nahe, in dem Mdm36 für die Bildung des Num1/Dnm1-Komplexes und folglich für die Verankerung der Mitochondrien am Zellkortex benötigt wird. Über diesen wird dann die notwendige Spannung entlang des Mitochondrientubulus für die Dnm1-abhängige Teilung erzeugt. Im zweiten Teilabschnitt der vorliegenden Arbeit wurde zunächst die mitochondriale Morphologie der Mutanten der kürzlich identifizierten Twin Cx9C-Protein-Familie analysiert. Anschließend wurde das dabei und durch eine vorhergehende systematische Durchmusterung einer Hefedeletionsstammsammlung auffällig gewordene Protein Mdm35 näher untersucht. Mdm35 ist ein mitochondriales Protein des Intermembranraums, dessen Deletionsmutante zum Großteil sphärische Mitochondrien besitzt und einen Wachstumsdefekt bedingt durch den Verlust von mitochondrialer DNA aufweist. Die Mitochondrien und das instabile mitochondriale Genom der delta-mdm35-Mutante zeigen Ähnlichkeiten zu Zellen auf, denen entweder die mitochondrialen Innenmembranproteine Mdm31 bzw. Mdm32 fehlen, oder die mitochondrialen Außenmembranproteine Mmm2, Mdm10, Mdm12 bzw. das integrale Membranprotein des Endoplasmatischen Retikulums Mmm1. Die gleichzeitige Deletion von MDM35 und MDM31 bzw. MDM32 ist synthetisch letal, was ein Hinweis darauf ist, dass die Proteine an demselben zellulären Prozess beteiligt sind. Für die Deletion von MDM31 und MDM32 konnte bereits eine synthetische Letalität mit MMM1, MMM2, MDM10 und MDM12 gezeigt werden. Mmm1, Mmm2, Mdm10 und Mdm12 bilden einen Komplex aus, der eine Bindung zwischen dem Endoplasmatischen Retikulum und den Mitochondrien herstellt und vermutlich für den Austausch von Calcium und Phospholipiden zuständig ist. Dieser Komplex befindet sich außerdem in Nachbarschaft aktiv replizierender mitochondrialer DNA. Die erhaltenen Ergebnisse deuten darauf hin, dass Mdm35 möglicherweise als Protein des Intermembranraums eine Funktion bei der Vermittlung zwischen dem Mmm1/Mmm2/Mdm10/Mdm12-Proteinkomplex und den Innenmembranproteinen Mdm31/Mdm32 besitzt und so ein koordiniertes mitochondriales Wachstum ermöglicht durch Kopplung der Replikation des mitochondrialen Genoms und der Aufrechterhaltung der mitochondrialen Membranen über den Lipidtransport.
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Advanced Technologies in Education - Developing the Science Classroom of the Future
(2010)
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Sofoklis A. Sotiriou
- Information communication technology (ICT) nowadays provides innovative learning systems which although routinely available needs adjustment to real educational environments. Due to the complexity of the task an appropriate integration into everyday classrooms is an important global research challenges focusing on its utilization and effects in both, classroom and non-classroom settings. By rigorous collecting data on teaching methods, classroom characteristics and students learning effects needs analysis by concentrating on selected variables that may determine effectiveness as well as teachers characteristics such as teacherspreparation and professional development. Therefore, the aim of the four presented research papers focuses on envision the science classroom of the future, by constructing a framework for improving current educational practices and learning processes in science and mathematics through the effective implementation of advanced technological tools and applications. Overall this work presents a vision for the science classroom of the future: It will not be an island, a self-contained campus, a counter-world. The classroom of the future will be able to emit and absorb along different wavelengths, be immersed in contemporary culture, be open to the emotions, facts and news of its time. It will be permeated by society, but not unprotected: the relationship between school and society will be one of osmosis, where the pedagogical tools and applications act as a membrane and interface. For this purpose, four empirical studies were carried out in real school environments, based on the use of advanced educational systems. (i) The first system under study is the COSMOS Portal, which is an educational repository that offers access to a network of robotic telescopes across the world. At the same time it offers access to more than 85,000 educational resources. The behaviour of the teachers who are using this system was mapped through the log files of the system database for a period of one year. (ii) The second system, called Lab of Tomorrow, is a wearable device that allows high school students to use their every day life as the field where they will conduct sophisticated experiments and thus will deepen their understanding of the science concepts involved in the activities. The impact of the system on students learning and to the lesson profile was studied for a period of one school year. (iii) The third system, called CONNECT, is also a wearable device that includes an advanced visualization system that augments additional information to the optical view of the user. The system is used in the framework of educational visits in science centres and museums enriching the experiences of the visitors. The effectiveness of the system in supporting the students conceptual change was studied in this case. (iv) The fourth system, called EXPLOAR, evolved from the described CONNECT system to a much more user-friendly handheld device. Taking into account the school curriculum we have designed a series of scenarios of use of these tools. The scenarios of use include classroom activities, field trips in science centres and museums, informal learning activities, professional development opportunities and community building. In all four studies, students cognitive learning is analysed as well as selected teachers tasks on the job. By applying different assessment methods and tools (questionnaires, video captures of lessons, log files and web based data) we monitored the implementation procedure across different European countries. Our working hypothesis is that amending the traditional scientific methodology for experi¬mentation with visualization applications and model building tools will help students to articulate their mental models, make better predictions, and reflect more effectively. Additionally, working to reconcile the gaps and inconsistencies within their mental models, system models, predictions and results, will provide the learners with a powerful, explicit representation of their misconceptions and a means to repair them. Additionally our aim is to support teachers professional development. Apart from the purely technical training, in order for teachers to introduce ICT-enhanced learning methods into their everyday practice, they will have to perform a change in behaviour and to adapt a new culture and philosophy. The use of the new tools asks for systematic and detailed lesson planning procedures and use of student centred approaches. In our work we are demonstrating methods for involving teachers in this process but also tools to monitor this behavioural change.
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Tropical bracken, a powerful invader of pastures in South Ecuador: Species composition, ecology, control measures, and pasture restoration
(2010)
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Kristin Roos
- Bracken (Pteridium spec.) is one of the most wide-spread weeds, especially where fire has been used for forest clearing or maintenance of agricultural areas. Taxonomically, it is considered an aggregate that separates into a northern hemispherical and a southern, tropical complex. Different from the extensively studied northern bracken, the knowledge of ecology and control measures of the tropical species is still fragmentary. The main aims of my thesis were (1) identification and population structure of bracken, (2) ecology of tropical bracken with particular emphasis on its survival of bushfires, and (3) development of an effective bracken control strategy and subsequent re-pasturisation of abandoned areas. The bracken vegetation of the study area consists of mixed stands of Pteridium arachnoideum (KAULF.) MAXON and P. caudatum (L.) MAXON with a proportion of 3:2, and of a hybrid (ca. 2%). Identification was by leaf morphology, allozyme analysis, comparison of particular chloroplastic DNA sequences, and analysis of four genomic and one plastidic microsatellites. Dominance of P. arachnoideum was explained by the fact that P. caudatum, as a lowland species, reaches its upper altitudinal limit in the research area. Analysis of heterozygosity indicated a higher genetic stability of the diploid P. arachnoideum population as compared to the allotetraploid P. caudatum population. Spatial extension of the individual clones is much smaller than reported for the northern bracken, indicating higher significance of sexual reproduction for the tropical fern in comparison to vegetative propagation by rhizome fragmentation. Four weeks after burning the natural rain forest, vigorously sprouting bracken sporophytes were observed. These developed from gametophytes, which germinated from the wind dispersed spores. Fast growth of the young sporophytes established the fern in the areas. After planting pasture grass, bracken was supported by repeated burning of the areas. In the long run, the grass was outcompeted by the fern possibly due to weakening of its vitality by burning and grazing, and the areas have been abandoned. The density of bracken fronds in a settled bracken area of our research site remained constant over years with small deviations caused by particular weather situations. Since this balance holds also for patchy fern canopies, it is assumed that this is due to nutrient shortage of the soil. Most probably, a new leaf can only develop from the nutrients remobilized from a senescing old leaf. Two to three months after a fire, an explosive emergence of new leaves was observed at rates, which substantially exceeded those under undisturbed growth. The newly formed leaves showed an extended life-span, which was attributed to a better nutrient supply from the ash. Subsequent self-thinning reduced the density of the leaves to a stable level within two years. In a laboratory experiment, the effects of heat pulse by a simulated bushfire on the bracken rhizomes were investigated. Separated long and short shoots were heated for a short time either in a water bath or embedded in soil. Subsequent to this heat pulse, they were cultivated in original soil. Short shoots showed a significantly higher heat resistance (up to 80°C) than long shoots (up to 60°C). In addition, the short shoots showed elongation growth and an enhanced frond production, whereas long shoots were not stimulated by the heat pulse. In a bracken control experiment, thirteen control measures (cutting of the fronds, several herbicides, covering with plastic foil and combinations thereof) were applied over a time-period of 23 months. Each treatment was repeated six times and the effects were recorded monthly. Quarterly cutting of the leaves as well as treatment with a customary herbicide mixture (picloram and metsulforon methyl) were the most effective treatments resulting in a reduction of the standing biomass by 65%. Monthly records of the resprouting bracken was necessary to work out the minimum number of treatments required for a clear control effect. For the five most efficient treatments among two to four applications were necessary. However, complete eradication of bracken was not possible. For re-pasturisation, the common pasture grass Setaria sphacelata was planted on the treated areas within a long-term experiment. After nearly two years of observation, the system had stabilized with a cover of S. sphacelata of 75% and of bracken of below 40%. This result demonstrated that the competitive strength of S. sphacelata was sufficient to control bracken once weakened by control treatments. The long-term experiment and, in addition, an experiment in which a gradually bracken-infested area is subjected to controlled burning, are continued.
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Structuring Descriptive Data of Organisms — Requirement Analysis and Information Models
(2007)
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Gregor Hagedorn
- Data that describe organisms in a structured form are indispensable not only for taxonomic and identification purposes, but also many phylogenetic, genetic, or ecological analyses. By analyzing existing information models and performing selected fundamental requirement analyses, the present work contributes to a broadening of the understanding of these forms of data. It falls into an interdisciplinary area between biology and information science. The term “descriptive data” is understood here in a broad sense: As descriptions of individuals, populations, or taxa, intended for various purposes (e. g., genetic, phylogenetic, diagnostic, taxonomic, or ecological), and covering a wide array of observation methods and data types (e. g., morphological, anatomical, genetic, physiological, molecular, or behavioral data). The position of descriptive data in the context of biodiversity framework concepts (covering, e. g., nomenclatural data, specimen collection data, or resource management) is discussed. A number of fundamental problems arise when modeling biological descriptive data. The ways in which existing data exchange formats, information models, and software applications address them are studied and future possible solutions are outlined. One such solution, the information model for the software “DiversityDescriptions (DeltaAccess)” is one of the results of this thesis and fully documented (Ch. 7). This entity relationship model fully supports the concepts of the traditional DELTA data exchange format (Description Language for Taxonomy; TDWG standard since 1986). If further improves on DELTA by introducing “modifiers” as a new terminology class, by introducing a more flexible system of handling statistical measures, by improving the handling of multilingual data sets, by supporting subset and filter features for concurrent collaborative editing (instead of supporting these for report-generation purposes alone), by supporting improved character attributes to create natural language descriptions from structured descriptions, and by adding metadata for a data set to improve the ability of data exchange without external documentation. In preparation of a future improved information model for descriptive data, the results of three requirement analyses are presented: a data-centric analysis of general concepts, a process-centric analysis of identification tools, and a high-level use case analysis. The first analysis (Ch. 4) is a structured inventory of fundamental approaches and problems involved in collecting and summarizing scientific descriptions of organisms. It is informed in part by current practices in information science, comparative data analysis, statistical, descriptive or phylogenetic software applications, and data exchange formats in biodiversity informatics. At the end three topics are discussed in particular detail (“Federation and modularization of terminology”, “Modifiers”, and “Secondary classification resulting in description scopes”). Except for phylogenetic analyses, identification is the most common usage of descriptive data. The second analysis (Ch. 5) therefore studies the processes, data structures, presentational and user interface requirements for printable and computer-aided identification tools (“keys”). Finally, a general use case analysis is performed with the goal of creating a framework of high-level use cases into which present as well as future requirements may be integrated (Ch. 6). All three requirement analyses are explorative and do not fulfill formal criteria of software engineering. They identify many requirements not addressed by the relational DiversityDescriptions model. Some of these could only be explored and await future solutions. For others solutions are proposed (some of which could already be incorporated into the design of SDD, an xml-based TDWG standard since 2005): The traditional data types are changed into an extensible character type model. The importance of data aggregation concepts was recognized to be fundamental. Complementary to data aggregation, the present and potentially future use of data inheritance along the lines of the taxonomic hierarchy is briefly studied. The concept of calculated characters could be addressed only insofar as the mapping between values can potentially be generalized. Character decomposition models are studied, but ultimately the traditional character concept, supplemented with a forest of ontologies for compositional and generalization concept hierarchies, is preferred as a more general concept. Both the traditional character subset and character applicability models can be integrated into concept hierarchies.
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Molecular Characterization of Sugarcane Yellow Leaf Virus (SCYLV) and its Effect on Sucrose Transporters in Sugarcane Saccharum spp. hybrids
(2010)
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Abdelaleim Ismail Ibrahim ElSayed
- Sugarcane is an important crop plant and has served as a source of sugar for hundreds of years, recently it is used to produce bioethanol, a renewable bio-fuel energy source. Sugarcane yellow leaf virus (SCYLV) was detected in the late 1990s first in Hawaii as a causal agent of a sugarcane disease which leads to sugarcane yellow leaf syndrome and reduced sugar yield. The presence of Sugarcane yellow leaf virus was determined by RT-PCR in several sugarcane cultivars, mostly from Hawaii. Interesting was the comparison of so-called susceptible versus resistant cultivars. As expected, the susceptible Hawaiian cultivars H73-6110 and H87-4094 showed strong PCR amplification products of SCYLV, while the virus-free line H87-4094, produced by tissue culture, showed no PCR product. The three resistant cultivars H87-4319, H78-4153 and H78-7750 showed quite different amplification patterns. While H78-4153 and H78-7750 expressed a weak but specific band of the correct size, unexpectedly H87-4319 showed strong amplification product. Three Cuban cultivars (C1051-73, JA-605 and CP52-43) showed low titer of SCYLV. No PCR amplificate was obtained with the moderately susceptible cultivar H65-7052. Aphids feeding on cv. H87-4094 contained sufficient virus to yield a SCYLV-signal similar in strength as from preparations from resistant cultivars. Northern blot analysis supported the results obtained from RT-PCR. The presence of SCYLV in the cultivars with low amount of virus titer (H87-4319, H78-7750 and H78-4153) indicated that they should better be called tolerant for the virus in the sense that they allow a low replication rate for SCYLV. Virus preparations from 3 Hawaiian cultivars (two susceptible and one resistant) were fully sequenced. Quantitative analysis for four different genome regions of SCYLV covering the 6 ORFs has been performed for these 3 cultivars using the GeXP analysis system. The transcript levels of the different regions of SCYLV in these cultivars were present at very different quantities, for example ORF0-1 transcripts were up to 10 times more frequent than transcripts of ORF3-4. The SCYLV-sequences from the 3 Hawaiian cultivars were aligned to published full and partial sequences. The phylograms corroborated previous findings that the so-called YLS-segment coding for the coat protein shows the least genetic diversity, whereas the other sequence fragments A-D, representing the ORFs 0-5, expressed a twofold higher diversity. The phylograms of partial sequences and of the whole genome placed the Hawaiian SCYLV-strains next to the Peru strain, apart from the BRA-strains and well apart from the REU-strains. It is proposed that the Hawaiian SCYLV is considered as own group together with the Peru strain as HAW-PER. The sequences from the two susceptible cultivars had a deletion of 48 to 54 nt in ORF1, which codes for the gene silencing suppressor/RNA-dependent RNA-polymerase complex. It is speculated that this deletion is important for the proliferation rate of the virus in the plant. Sucrose is the main product of sugarcane, which accumulates in the stalk internodes in excess of 50 % of the dry weight. To gain an overview of the physiological status of SCYLV-infected sugarcane compared to virus-free plants, gene expression. Sucrose increased rapidly between internodes 3 and 7, reaching a maximum in internodes 7. Sugars content in leaves, seedling and internodes were increased as effect of the SCYLV-infection. Sucrose phosphate synthase (SPSII) transcript levels were approximately the same in sink, source and internodes with a trend to be higher in the mature internodes. A sucrose transporter of Hawaiian cultivar was isolated and sequenced and classified as ShSUT1A. There is high variability among the SUT1 subfamily with identities of 70-97%. The identity between ShSUT1A and ShSUT1 was 97.4%. It is expressed in sink, source and storage tissues. The ShSUT1A was expressed at approximately similar extent in SCYLV-infected and virus-free sugarcane. In addition a partial sequence of a sucrose transporter belonging to the SUT4 family was first obtained in sugarcane and its transcript levels in plant organs were measured. Quantitative analysis for sucrose transporters (ShSUT1 and ShSUT4) using the GeXP analysis system showed that sucrose transporter ShSUT1 was at a higher transcript expression than ShSUT4 in sink and source leaves, but not in mature internodes. In conclusion, - SCYLV from Hawaiian cultivars was characterized as belonging to an own subgroup (HAW- PER), - A deletion of 48-54 nt was detected in the SCYLV-sequence from susceptible cultivars, which may be correlated to virus proliferation, and - large differences in transcript levels of the viral ORFs were found. - Sucrose transporter transcripts and SPSII transcripts were not strictly correlated to SCYLV- infection and do not explain the pathological effect of SCYLV on sugarcane.
