Institut für Biochemie und Biologie
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In experiments with axenic cultures of Microcystis aeruginosa, we tested whether this cyanobacterium incorporates leucine, a compound that is often used for the measurement of heterotrophic bacterioplankton production. Microcystis showed significant leucine incorporation, and the uptake of exponentially growing cells was higher than the uptake of cells in stationary growth phase. Therefore, the leucine method may not be suitable for measuring bacterial production in highly eutrophic waters with a dominance of cyanobacteria.
Die Wüste Atacama
(2000)
Simulated long-term vegetation response to alternative stocking strategies in savanna rangelands
(2000)
Mixotrophy is a widespread phenomenon among planktonic protists. It involves the combination of autotrophy and heterotrophy in varying degrees. Many phytoflagellate species ingest bacteria as a means of obtaining nutrients for photosynthesis or for supplementing their carbon budget under light limitation. Ciliates either sequester the plastids of their algal prey or harbour endosymbiotic algae. In the saline lakes of the Vestfold Hills and in Lakes Hoare and Fryxell in the McMurdo Dry Valleys the dominant phytoflagellates ingest bacteria, and there is evidence to suggest that during the winter months they lack chlorophyll and may become entirely heterotrophic. In Lake Fryxell phagotrophic pyhtoflagellates (cryptophytes) made a significant impact on bacterial production, removing up to 13% of the bacterial biomass day-1. These cryptophytes suffered predation from Plagiocampa (a ciliate), which appears to harbour them for a significant period before digesting them. We suspect that this may be equivalent to an intermediate stage in the evolution of mixotrophy. A significant number of the planktonic ciliates in Antarctic lakes were mixotrophic. The final evolutionary end point is the situation seen in Mesodinium rubrum, which now relies entirely on its cryptophycean endosymbiont and no longer ingests food. Mesodinium is the dominant ciliate in many of the saline lakes of the Vestfold Hills, which are of marine origin. It can reach abundances in excess of 60,000l-1 in Ace Lake, This ciliate is a ubiquitous member of the marine plankton worldwide and has successfully adapted to the lacustrine environment in Antarctica. The evidence suggests that among the survival strategies seen in Antarctic lake plankton, mixotrophy plays and important role among a number of the dominant protozoan species.
The growth rates of heterotrophic nanoflagellates (HNAN), mixotrophic cryptophytes, dinoflagellates and ciliates in field assemblages from Ace Lake in the Vestfold Hills (eastern Antarctica) and Lakes Fryxell and Hoare (McMurdo Dry Valleys, western Antarctica), were determined during the austral summers of 1996/1997 and 1997/1998. The response of the nanoflagellates to temperature differed between lakes in eastern and western Antarctica. In Ace Lake the available bacterial food resources had little impact on growth rate, while temperature imposed an impact, whereas in Lake Hoare increased bacterial food resources elicited an increase in growth rate. However, the incorporation of published data from across Antarctica showed that temperature had the greater effect, but that growth is probably controlled by a suite of factors not solely related to bacterial food resources and temperature. Dinoflagellates had relatively high specific growth rates (0.0057-0.384 h(-1)), which were comparable to Antarctic lake ciliates and to dinoflagellates from warmer, lower latitude locations. Temperature did not appear to impose any significant impact on growth rates. Mixotrophic cryptophytes in Lake Hoare had lower specific growth rates than HNAN (0.0029-0.0059 h(-1) and 0.0056-0.0127 h(-1), respectively). They showed a marked seasonal variation in growth rate, which was probably related to photosynthetically active radiation under the ice at different depths in the water column. Ciliates' growth rates showed no relationship between food supply and mean cell volume, but did show a response to temperature. Specific growth rates ranged between 0.0033 and 0.150 h(-1) for heterotrophic ciliates, 0.0143 h(-1) for a mixotrophic Plagiocampa species and 0.0075 h(-1) for the entirely autotrophic ciliate, Mesodinium rubrum. The data indicated that the scope for growth among planktonic Protozoa living in oligotrophic, cold extreme lake ecosystems is limited. These organisms are likely to suffer prolonged physiological stress, which may account for the highly variable growth rates seen within and between Antarctic lakes.
Population biologists have long been interested in the oscillations in population size displayed by many organisms in the field and Laboratory. A wide range of deterministic mathematical models predict that these fluctuations can be generated internally by nonlinear interactions among species and, if correct, would provide important insights for understanding and predicting the dynamics of interacting populations. We studied the dynamical behavior of a two- species aquatic Laboratory community encompassing the interactions between a demographically structured herbivore population, a primary producer, and a mineral resource, yet still amenable to description and parameterization using a mathematical model. The qualitative dynamical behavior of our experimental system, that is, cycles, equilibria, and extinction, is highly predictable by a simple nonlinear model.
An unresolved discussion in contemporary ecology deals with the relative importance of competition along environmental gradients. In deserts, local-scale differences in environmental productivity may be caused by the presence of shrubs, which represent a favorable habitat for annual populations within a nutrient-poor matrix. In this study, we attempted to test the hypothesis that facilitation of desert annuals by shrubs increase the intensity of competition among the annual plants. Such negative indirect effects have so far been ignored in studies about plant-plant interactions. We tested our hypothesis by measuring seedling survival and fecundity of four abundant annual plant species with and without neighbors in open areas and under shrub canopies in a sandy desert area. Our findings did not indicate indirect negative effects of shrubs on their understory annuals. Sensitivity to the presence of neighbors varied between species and surprisingly, the species with the smallest seeds was the only one which was not negatively affected by the presence of neighbors. In contrast to our hypothesis, there was no difference between the habitat types shrubs and openings in absolute and relative competition intensity. Our overall results suggest that negative indirect effects of shrubs are unimportant in determining demographic response of understory annual plants.
Recently, numerous studies have pointed to the importance of positive interactions in natural communities. There is now a broad consensus that the balance between negative and positive interactions should shift along environmental gradients, with competition prevailing under environmentally benign conditions and positive interactions dominating under harsh conditions. A commonly cited example of the importance of facilitation in harsh environments is the preference of desert annual plants for the areas under the canopy of shrubs. The recognition of apparently positive effects of desert shrubs on annuals, however, has been mostly based on density measurements, while fitness parameters of the understory plants have been ignored. Also, the temporal consistency of such effects has not been previously tested. Based on conceptual ideas about the balance between interference and facilitation, we predicted that positive effects of the shrubs on the understory should dominate in dry years, while in favorable years, negative effects would be stronger. We tested our hypothesis by measuring the direction and magnitude of the shrub effect on demographic responses of four desert annual plant species during four consecutive seasons of differing rainfall. The results contradicted our initial hypothesis. Depending on the species, the effect of the shrubs shifted from either negative to neutral or from neutral to positive with increasing annual rainfall. However, this trend was stronger for the effect of shrubs on plant reproductive success than on their densities. Our data highlight the importance of measuring fitness parameters in studies of plant-plant interactions. We suggest that the negative effects of shrubs on plant fitness were due to rainfall interception, while positive effects were related to increased nutrient availability beneath shrubs. However, the mechanisms by which the shrubs and annuals interact can only be resolved using an experimental approach. Our results contradict previous hypotheses about the relative importance of positive and negative interactions along environmental gradients. A simple conceptual model summarizing the proposed role of rainfall in determining the direction of shrub effects on their understory annuals is presented.
The fairy circles of Kaokoland (North-West-Namibia) : origin, distribution, and characteristics
(2000)
The phosphoinositide signaling cascade is involved in photoreception in the leech Hirudo medicinalis
(2000)
An algal culture medium was developed which reflects the extreme chemical conditions of acidic mining lakes (pH 2.7, high concentrations of iron and sulfate) and remains stable without addition of organic carbon sources. It enables controlled experiments e.g. on the heterotrophic potential of pigmented flagellates in the laboratory. Various plankton organisms isolated from acidic lakes were successfully cultivated in this medium. The growth rates of an Chlamydomonas- isolate from acidic mining lakes were assessed by measuring cell densities under pure autotrophic and heterotrophic conditions (with glucose as organic C-source) and showed values of 0.74 and 0.40, respectively.
Since 1993 the southern shore of Lake Gülpe in western Brandenburg has been man-aged with Galloway cattle. This is supported by the so called "Vertragsnaturschutz" (i.e. contract nature conservation) in order to preserve the valuable, species-rich vegetation structure. This is an economically justifiable arrangement for the Galloway cattle-farmer. Permanent botanical plots were monitored in the area for four years. For most species, the observed changes in vegetation are considered as mere fluctuations on the basis of their known ecological requirements and data on hydrological dynamics during the study. Only a few species might indicate succession. A continuation of the present form of land management is recommended for the preservation of the current vegetation structure. However it is advisable to continue with monitoring of the vegetation in order to confirm the results over larger timescales. Until then the management with Galloway cattle is to acclaim as a proper treatment to preserve the southern shore of Lake Gülpe.
Since 1992 the southern shore of the Lake Gülpe in western Brandenburg is managed with Galloway cattle to preserve species, vegetation and landscape pattern. This paper presents the vegetation zones which are influenced by the water balance being the most significant and dynamic location factor in the area. Following the plots from dry to wet sites the most important plant communities are: Diantho-Armerietum, Arrhenatheretalia-Gesellschaft (-community), Leonotodon saxatilis -Potentilla anserina-community, Caricetum gracilis as well as Glycerietum aquaticae and Cypero- Samoletum. 23 endangered species were found.
Zelle, Einzeller, Vielzeller
(2000)
Biosensor-Stabilität
(2000)
Planktische Räuber-Beute-Systeme : experimentelle Untersuchungen von ökologischen Synchronisationen
(2000)
Operation of a miniature redox hydrogel-based pyruvate sensor in undiluted deoxygenated calf serum
(2000)
Electrochemical immunoassays
(2000)
Integrierte Immuno-Extraktions-Probenahme und tragbarer Biosensor-Prototyp für vor-Ort Messungen
(2000)
Estimating production in plankton food webs from biomass size spectra and allometric relationships
(2000)
Rieselfelder
(2000)
Water column mixing is known to have a decisive impact on plankton communities. The underlying mechanisms depend on the size and depth of the water body, the nutrient status, and the plankton community structure and they are well understood for shallow polymictic and deep stratified lakes. Two consecutive mixing events of similar intensity under different levels of herbivory were performed in enclosures in a shallow, but periodically stratified, eutrophic lake, in order to investigate the effects of water column mixing on bacteria abundance, phytoplankton abundance and diversity, and rotifer abundance and fecundity. When herbivory by filter-feeding zooplankton was low, water column mixing provoking a substantial nutrient input into the euphotic zone, led to an intense net increase of bacteria and phytoplankton biomass. Phytoplankton diversity was lower in the mixed enclosures than in the undisturbed ones owing to the larger contribution of a few fast-growing species. After the second mixing event at high biomass of filter-feeding crustaceans, the increase of phytoplankton biomass was lower than after the first mixing, and diversity remained unchanged as the enhanced growth of small fast-growing was prevented by zooplankton grazing. Bacteria abundance did not increase after the second mixing, when cladoceran biomass was high. Rotifer fecundity indicated a transmission of the phytoplankton response to the next trophic level. Our results suggest that water column mixing in shallow eutrophic lakes with periodic stratification has a strong effect on the plankton community by enhanced nutrient availability rather than resuspension or reduced light availability. This fuels the basis of the classic and microbial food chain via enhanced phytoplankton and bacteria growth, but the effects on biomass may be dampened by high levels of herbivory.
Stillegungsflächen nehmen einen bedeutenden Anteil der landwirtschaftlich nutzbaren Fläche Deutschlands ein. Kompensiert durch Ausgleichszahlungen entfällt in diesen Bereichen die Produktionsfunktion der Agrarlandschaft, ohne dass andere Landschaftsfunktionen explizit gefördert werden. Dabei können Stillegungsflächen eine wichtige Rolle im ökosystemaren Gefüge einer intensiv genutzten Agrarlandschaft spielen. Die vorgestellte Arbeit untersucht das Potential stillgelegter Flächen als Nahrungsquelle für blütenbesuchende Insekten. Dabei wird von der These ausgegangen, dass Stillegungsflächen besonders attraktiv für Blütenbesucher sind, da sie die einzigen Bereiche in einer intensiv genutzten Agrarlandschaft darstellen, deren Vegetation im Jahresverlauf nicht durch Nutzung beeinträchtigt wird. Es werden erste Ergebnisse einer nahrungsökologischen Studie vorgestellt, bei der das Fraßverhalten dominanter Arten der Syrphidae, einer der individuenreichsten Blütenbesuchergruppen Mitteleuropas, auf verschiedenen Stillegungsflächen untersucht wird. Durch wöchentliche Begehungen von Dauerbeobachtungsflächen wurde die Stärke und Dynamik des Blütendargebotes erfasst. Nektarproben ergaben ein Bild von der Quantität und Verfügbarkeit einzelner Nahrungsressourcen. Über die Untersuchungsperiode hinweg wurden Syrphiden mit einem Kescher gefangen und konserviert. Individuen dominanter Arten wurde mit einer Abdominalpräparation der Verdauungstrakt entnommen und pollenanalytisch aufgearbeitet. Die enthaltenen Pollen wurden determiniert und ausgezählt.
Plasticity and steric strain in a parallel beta-helix: Rational mutations in P22 tailspike protein
(2000)
By means of genetic screens, a great number of mutations that affect the folding and stability of the tailspike protein from Salmonella phage P22 have been identified. Temperature-sensitive folding (tsf) mutations decrease folding yields at high temperature, but hardly affect thermal stability of the native trimeric structure when assembled at low temperature. Global suppressor (su) mutations mitigate this phenotype. Virtually all of these mutations are located in the central domain of tailspike, a large parallel beta-helix. We modified tailspike by rational single amino acid replacements at three sites in order to investigate the influence of mutations of two types: (1) mutations expected to cause a tsf phenotype by increasing the side-chain volume of a core residue, and (2) mutations in a similar structural context as two of the four known su mutations, which have been suggested to stabilize folding intermediates and the native structure by the release of backbone strain, an effect well known for residues that are primarily evolved for function and not for stability or folding of the protein. Analysis of folding yields, refolding kinetics and thermal denaturation kinetics in vitro show that the tsf phenotype can indeed be produced rationally by increasing the volume of side chains in the beta-helix core. The high-resolution crystal structure of mutant T326F proves that structural rearrangements only take place in the remarkably plastic lumen of the beta-helix, leaving the arrangement of the hydrogen-bonded backbone and thus the surface of the protein unaffected. This supports the notion that changes in the stability of an intermediate, in which the beta-helix domain is largely formed, are the essential mechanism by which tsf mutations affect tailspike folding. A rational design of su mutants, on the other hand, appears to be more difficult. The exchange of two residues in the active site expected to lead to a drastic release of steric strain neither enhanced the folding properties nor the stability of tailspike. Apparently, side-chain interactions in these cases overcompensate for backbone strain, illustrating the extreme optimization of the tailspike protein for conformational stability. The result exemplifies the view arising from the statistical analysis of the distribution of backbone dihedral angles in known three-dimensional protein structures that the adoption of straight phi/psi angles other than the most favorable ones is often caused by side-chain interactions.
Die Anforderungen an die Stresstoleranz der wichtigsten landwirtschaftlichen Nutzpflanzen werden durch den prognostizierten Klimawandel in vielen Regionen Deutschlands, so auch im Land Branden-burg, weiter wachsen. Zur Sicherung langfristig stabiler Ernteerträge müssen deshalb Sorten bereitge-stellt werden, die sich durch eine hohe Adaptationsfähigkeit gegenüber Witterungsfaktoren auszeich-nen. Da Zea mays als C4-Pflanze während der Hauptentwicklungsphase geringere Ansprüche an die Was-serverfügbarkeit als C3-Pflanzen stellt, dürfte der Maisanbau auch bei abnehmenden Niederschlägen bzw. ausgeprägten Dürreperioden bedeutsam bleiben. Kritisch sind aber, wie wir an der relativ dürre-toleranten Sorte "Bonny" zeigen konnten (Gzik 1997), auch bei dieser Kulturpflanze die Phasen der Keimung und der Keimlingsentwicklung. Zur Beurteilung der Stresstoleranz während dieser frühen Stadien der Entwicklung wurden Untersu-chungen zur Keimung und zum Keimlingswachstum exemplarisch mit fünf zugelassenen Sorten unter Einwirkung von Stressoren (begrenzte Wasserverfügbarkeit, Salzbelastung, erhöhte Temperaturen) durchgeführt. Neben Daten zum Wachstum wurden in den Keimlingsorganen auch verschiedene Stoffwechselparameter erfasst. Alle geprüften Sorten hatten eine Keimbereitschaft von 100%. Bereits milder Trockenstress von -0,2 MPa, induziert durch die Applikation von Polyethylenglykol 6000, verursachte bei allen Sorten einen Keimverzug. Bei einer Stressstärke von -0,4MPa war die Keimung verringert. Die stärkste Beeinflus-sung wurde bei "Bonny", gefolgt von "Diamant" und "Achat", beobachtet. Die Sorte "Helix" zeigte die höchste Toleranz. Auch das Wachstum der Keimlingsorgane war unter Trockenstress stark gehemmt, wobei wiederum die Sorte "Helix" die geringsten Abweichungen von der Kontrolle aufwies. Der Prolingehalt, der für viele Stressoren als Stressindikator gilt, war schon bei sehr mildem Stress (-0,2MPa) in den Keimlingsorganen dramatisch erhöht. Die Akkumulationsraten (im Vergleich zu den Kontrollen) waren bei den Sorten "Achat" und "Diamant" am höchsten und bei "Bonny" am niedrigsten. Der Gehalt an löslichen Zuckern war in den Koleoptilen aller Sorten unter Stress nahezu unverändert, während er in den Primärwurzeln erhöht war. Der Stärkegehalt lag in beiden Keim- lingsorganen bei Stress unter den Werten der Kontrollen. Der Gehalt an freien Aminosäuren stieg unter Stress an. Besonders der Anteil an basischen Aminosäuren war erhöht. Diese Ergebnisse weisen auf einen verstärkten Proteinabbau unter Stressbedingungen hin. Bei den geprüften Stoffwechselparametern konnte keine Korrelation zur Stressempfindlichkeit der Sorten beobachtet werden.
Ecological buffering mechanisms in savannas : a unifying theory of long-term tree-grass coexistence
(2000)
Reversible binding of the starch-related R1 protein to the surface of transitory starch granules
(2000)