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Quenching of the triplet state of tryptophan by cysteine has provided a new tool for measuring the rate of forming a specific intramolecular contact in disordered polypeptides. Here, we use this technique to investigate contact formation in the denatured state of CspTm, a small cold-shock protein from Thermotoga maritima, engineered to contain a single tryptophan residue (W29) and a single cysteine residue at the C terminus (C67). At all concentrations of denaturant, the decay rate of the W29 triplet of the unfolded protein is more than tenfold faster than the rate observed for the native protein (not, vert, similar104 s;1). Experiments on the unfolded protein without the added C- terminal cysteine residue show that this faster rate results entirely from contact quenching by C67. The quenching rate in the unfolded state by C67 increases at concentrations of denaturant that favor folding, indicating a compaction of the unfolded protein as observed previously in single-molecule Foerster resonance energy transfer (FRET) experiments.
In recent years most studies of the benthic microbial food web have either been descriptive or were restricted to the measurement of within sediment process rates. Little is known about benthic-pelagic coupling processes such as recruitment. We, therefore, developed an ex situ core incubation procedure to quantify the potential for microbial recruitment from the benthos to the pelagic in an acidic mining lake, Mining Lake 111 (ML 111; pH 2.6), in eastern Germany. Our data suggest that considerable zooplankton recruitment from the benthos takes place. Heliozoan and rhizopod recruitment in both summer and winter sediment cores was highest when they were incubated at 20°C. Maximum heliozoan recruitment was 23 (± 9 s.e.) individuals cm-2 d-1 (40% initial standing stock daily) in the winter 20°C incubation. Maximum rhizopod recruitment was 6 (± 2 s.e.) individuals cm-2 d-1 in the summer 20°C incubation. Little or no recruitment was apparent for either taxa when winter cores were incubated at 5°C, implying a temperature cue. Conversely, the rotifer, Cephalodella hoodi, exhibited a maximum recruitment of 6 (± 2 s.e.) individuals cm-2 d-1 during the winter 5°C incubation, representing 30% of initial standing stock daily, but little recruitment when incubated at 20°C. Cephalodella may have responded to an increased winter benthic food supply; in situ winter Chl a concentrations in the benthos were 3.4 times higher than those in the summer. The importance of this was reinforced by the poor pelagic food supply available in ML 111. In situ, Heliozoa, rhizopods and Cephalodella were first observed in the epilimnion of ML 111 in spring or early summer, suggesting active or passive recruitment following lateral transport from littoral sediments. Benthic-pelagic coupling via recruitment is potentially important in understanding the pelagic food web in ML 111 and warrants further investigation in this and other aquatic environments.
Mixotrophy in the Antarctic phytoflagellate, Pyramimonas gelidicola (Chlorophyta: Prasinophyta)
(2003)
Grazing by the planktonic, phytoflagellate, Pyramimonas gelidicola McFadden (Chlorophyta: Prasinophyta), and heterotrophic nanoflagellates (HNAN) in meromictic, saline Ace Lake in the Vestfold Hills, Eastern Antarctica, was investigated in the austral summers of 1997 and 1999. Up to 47% of the P. gelidicola population ingested fluorescently labelled prey (FLP). Ingestion rates varied with depth. In January 1997 and November 1999, maximum P. gelidicola ingestion rates of 6.95 and 0.79 FLP;cell-1;h-1, respectively, were measured at the chemocline (6-8 m) where a deep chlorophyll maximum composed of phototrophic nanoflagellates (PNAN DCM), predominantly P. gelidicola, persisted all year. During the summers of 1997 and 1999, the grazing P. gelidicola community removed between 0.4 and approximately 16% of in situ bacterial biomass, equivalent to between 4 and >100% of in situ bacterial production. Due to their higher abundance, the community clearance rates of HNAN in Ace Lake generally exceeded those of P. gelidicola but HNAN removed approximately only 3 to 4% of bacterial biomass, equivalent to between 28 and 32% of bacterial production. P. gelidicola growth rates were highest at the PNAN DCM concomitant with the highest ingestion rates. It is estimated that during the summer P. gelidicola can derive up to 30% of their daily carbon requirements from bacterivory at the PNAN DCM. This study confirms mixotrophy as an important strategy by which planktonic organisms can survive in extreme, polar, lacustrine ecosystems.
Application of metabolomics to plant genotype discrimination using statistics and machine learning
(2003)
South Africa's endemic Knysna seahorse, Hippocampus capensis Boulenger 1900, is a rare example of a marine fish listed as Endangered by the IUCN because of its limited range and habitat vulnerability. It is restricted to four estuaries on the southern coast of South Africa. This study reports on its biology in the Knysna and Swartvlei estuaries, both of which are experiencing heavy coastal development. We found that H. capensis was distributed heterogeneously throughout the Knysna Estuary, with a mean density of 0.0089 m-2 and an estimated total population of 89 000 seahorses (95% confidence interval: 30 000 to 148 000). H. capensis was found most frequently in low density vegetation stands ( 20% cover) and grasping Zostera capensis. Seahorse density was not otherwise correlated with habitat type or depth. The size of the area in which any particular seahorse was resighted did not differ between males and females. Adult sex ratios were skewed in most transects, with more males than females, but were even on a 10 m by 10 m focal study grid. Only three juveniles were sighted during the study. Both sexes were reproductively active but no greeting or courtship behaviours were observed. Males on the focal study grid were longer than females, and had shorter heads and longer tails, but were similar in colouration and skin filamentation. The level of threat to H. capensis and our limited knowledge of its biology mean that further scientific study is urgently needed to assist in developing sound management practices.
The classical (Levins) metapopulation scenario envisions a species persisting in a network of habitat patches through a balance between frequent local (within-patch) extinctions and recolonizations. Although this is the dominant paradigm for species in fragmented habitats, empirical support is limited and it has been argued that very restrictive conditions on migration rates are required: high enough for recolonization to balance extinctions, but low enough that local populations do not fluctuate in synchrony. Through simulation and analysis of a stochastic spatial model, we argue that the likelihood of persistence via the classical scenario is strongly affected by some basic properties of within- patch successional dynamics whose importance has not been emphasized in metapopulation theory: the distribution of successional stage durations, and whether patches are "refractory" versus immediately available for recolonization after an extinction has occurred. These properties are tied to the biological causes of extinction (e.g., demographic accident versus regular successional changes) and patch recovery (e.g., recolonization by a host species versus regeneration of an exhausted resource base). Our results indicate that metapopulation theory needs to incorporate the patch-dynamics perspective of a landscape in a dynamic mosaic of successional states, with particular attention to links between colonization-extinction processes and local succession.
Ecological and evolutionary dynamics can occur on similar timescales. However, theoretical predictions of how rapid evolution can affect ecological dynamics are inconclusive and often depend on untested model assumptions. Here we report that rapid prey evolution in response to oscillating predator density affects predator-prey (rotifer-algal) cycles in laboratory microcosms. Our experiments tested explicit predictions from a model for our system that allows prey evolution. We verified the predicted existence of an evolutionary tradeoff between algal competitive ability and defence against consumption, and examined its effects on cycle dynamics by manipulating the evolutionary potential of the prey population. Single-clone algal cultures (lacking genetic variability) produced short cycle periods and typical quarter-period phase lags between prey and predator densities, whereas multi-clonal (genetically variable) algal cultures produced long cycles with prey and predator densities nearly out of phase, exactly as predicted. These results confirm that prey evolution can substantially alter predator-prey dynamics, and therefore that attempts to understand population oscillations in nature cannot neglect potential effects from ongoing rapid evolution.
A characteristic vertical sequence of phytoplankton populations was observed below the metalimnetic oxycline of a stratified, mesotrophic lake. Ceratium spp., Closterium acutum and Aphanizomenon flos- aquae were present in the epilimnion but had distinct population maxima in the microaerobic chemocline. Below these populations, Cryptomonas phaseolus, Planktothrix clathrata, Pseudanabaena catenata and Limnothrix sp. followed each other in the transition zone between the chemocline and the sulphide-containing hypolimnion. The dominating populations of P. clathrata and P. catenata caused a deep chlorophyll maximum. Phytoplankton structure was determined by the vertical gradients of sulphide and light. Compared with the epilimnion, nutrient availability was not fundamentally better below the oxycline but the algae might have benefited from reduced grazing pressure in their habitat.
1. This is a discussion of the applicability to the phytoplankton of the concepts of 'Plant Functional Types' (PFTs) and 'Functional Diversity' (FD), which originated in terrestrial plant ecology. 2. Functional traits driving the performance of phytoplankton species reflect important processes such as growth, sedimentation, grazing losses and nutrient acquisition. 3. This paper presents an objective, mathematical way of assigning PFTs and measuring FD. Ecologists can use this new approach to investigate general hypotheses (e.g. the intermediate disturbance hypothesis (IDH), the insurance hypothesis and synchronicity phenomena), since, for example, in its original formulation the IDH makes its predictions based on FD rather than species diversity.
Recently, much ecological research has focused on predicting invasions of alien species in order to prevent potentially negative effects of such invasions. In this study, we utilize novel methods of landscape ecology for testing the hypothesis that increasing structural diversity correlates with an increasing number of alien plant species. Our overall findings support this hypothesis and suggest that in the studied area (RB Dessau, Sachsen Anhalt, Germany), species richness of neophytes is positively correlated with the diversity in land-use types and structures. However, this relationship between structural diversity and species diversity applied for native spe-cies, too. Furthermore, our results support findings of previous studies which show that neophytes occur mainly in artificially or naturally disturbed areas. Our overall findings highlight the use of landscape-scale ecological methods for studying plant distribution patterns.
Gaps are often important microhabitats for recruitment of herbaceous plants. In the Florida scrub, fires create gaps by top-killing resprouting shrubs. These natural gaps are aboveground gaps (without aboveground vegetation) that may also be complete gaps (if belowground roots and rhizomes are absent). Within three types of gaps (natural gaps, experimental aboveground and experimental complete gaps), we studied seedling recruitment and survival of spontaneous species and seven sown herbs for two years. We created aboveground gaps by clipping vegetation and complete gaps by removing shrub roots and rhizomes. These gaps occurred in two Florida scrub habitats: rosemary scrub and scrubby flatwoods. We also explored factors that can affect recruitment patterns in gaps, such as soil moisture, root water retention and light availability. In addition, we tested effects of supplemental watering on sown seeds in the field since drought in 2000 and 2001 suppressed natural seedling recruitment. The watering treatment increased recruitment in all types of gaps. Over half of all gaps were colonized, but there were few seedlings. Recruitment was highest in watered, complete gaps in scrubby flatwoods, where the soil moisture levels were higher and light levels lower than in the other gap types. Seedlings of a single spontaneously recruited species (Lechea deckertii) were more abundant than sown species. Locally common gap specialists were more abundant than generalists. Because many of these gap specialists are endangered plant species, understanding how disturbances create microsites for their regeneration is critical for conservation and management of the Florida scrub ecosystem. In small-scale conservation projects, artificially created gaps may substitute for post-fire gaps when prescribed burning is impossible.
Köderauslageintervalle und Dauer der Bekämpfung des Kleinen Fuchsbandwurms : eine Modellierstudie
(2003)
Stomatal cell biology
(2003)
Die Biosynthese und Funktion des Galaktolipids Digalaktosyldiacylglycerol in Arabidopsis thaliana
(2003)
Mixotrophs combine resource use to outcompete specialists: Implications for aquatic food webs
(2003)
The majority of species can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such 'mixotrophy' is a widespread phenomenon in aquatic habitats and is observed in many protozoan and metazoan organisms. The strategy requires investment in both photosynthetic and heterotrophic cellular apparatus, but the benefits must outweigh these costs. In accordance with the mechanistic resource competition theory, laboratory experiments revealed that pigmented mixotrophs combined light and prey as substitutable resources. Thereby, they reduced prey abundance below the critical food concentration of competing specialist grazers [Rothhaupt, K. O. (1996) Ecology 77, 716-724]. Here, we demonstrate for the first time the important consequences of this strategy for an aquatic community. In the illuminated surface strata of a lake, mixotrophs reduced prey abundance so steeply that grazers from higher trophic levels, consuming both the mixotrophs and their prey, could not persist. Thus, the mixotrophs escaped from both competition and grazing, and remained dominant. Furthermore, the mixotrophs structured the prey abundance along the vertical light gradient creating low densities near the surface and a pronounced maximum of their algal prey at depth. Such deep algal accumulations are typical features of nutrient poor aquatic habitats, previously explained by resource availability. We hypothesize instead that the mixotrophic grazing strategy is responsible for deep algal accumulations in many aquatic environments.
Exkursionsbericht "Exkursion zu den Lübbener Pfaffenbergen und Hartmannsdorfer Wiesen" am 20.07.2002
(2003)
Rivers form the most important natural corridors through the landscape. Certain plant species grow mainly or exclusively in these corridors as it has been observed for about 150 years in Central European lowlands. However, these species do not form a homogenous group in terms of biogeography, site requirements, life form, or any other feature this distribution pattern. Accordingly, first, we give a review of the various hypotheses which have been proposed to explain the river corridor distribution pattern. This includes (1) river corridors acting as routes of migration or invasion, (2) floodplain-specific disturbance providing open sites, (3) temporary anoxic conditions during floods, (4) deviating meso-climatic conditions, (5) specific substrate and nutrient supply, and (6) water supply. In particular, the above hypotheses (2-5) imply that river corridor plants may be well-adapted to specific stress and regeneration conditions in floodplains while other species may be not. This may lead to reduced competition in river corridors. We suggest this mechanism to constitute actual benefits for river corridor plants. Secondly, we present a simple model of multi-species population dynamics to show, that our competition-related framework is, in principle, able to explain river corridor plant species distribution patterns. As, however, none of the above hypotheses (1-6) have been tested experimentally we thirdly present a currently running experimental study on the river corridor plant Juncus atratus (black rush) in north- eastern Germany. We emphasize that much more experimental evidence must be gained on population ecology and meta- population dynamics to understand the distribution patterns of river corridor plants.
Offenlandmanagement durch kontrolliertes Brennen : ein Beitrag aus sozioökonomischer Perspektive
(2003)
1. Anthropogenic changes in the global climate are shifting the potential ranges of many plant species. 2. Changing climates will allow some species the opportunity to expand their range, others may experience a contraction in their potential range, while the current and future ranges of some species may not overlap. Our capacity to generalize about the threat these range shifts pose to plant diversity is limited by many sources of uncertainty. 3. In this paper we summarize sources of uncertainty for migration forecasts and suggest a research protocol for making forecasts in the context of uncertainty.
PURPOSE: CEACAM6, CEACAM1, and human carcinoembryonic antigen (CEA) are coexpressed in normal colorectal epithelia, but show deregulated expression in colorectal cancers (CRC). Upregulation of CEACAM6 expression in hyperplastic polyps and early adenomas represents one of the earliest observable molecular events leading to colorectal tumors. The aim of our study was to evaluate the prognostic relevance of CEACAM6, CEACAM1, and CEA tissue expression in patients with CRC. PATIENTS AND METHODS: Immunohistochemical analysis was carried out on tissue microarrays from 243 paraffin-embedded biopsies from a randomized controlled clinical trial (Swiss Group for Clinical Cancer Research [SAKK] 40/81) of adjuvant fluorouracil-based chemotherapy with CEACAM-specific monoclonal antibodies. The median follow-up was 8 years. Overall survival (OS) and disease-free survival (DFS) were calculated using Kaplan-Meier estimates and hazard ratios (HRs) estimated using Cox proportional hazards models. RESULTS: Tissue expression of CEACAM6, CEACAM1, and CEA was enhanced in 55%, 58%, and 94% of patients, respectively. Multivariate Cox analysis including sex, age, tumor site, stage, differentiation grade, treatment, and nodal status as covariates showed that CEACAM6 overexpression independently predicted poor OS (HR, 1.86; P =.0100) and DFS (HR, 2.00; P =.0028), whereas CEACAM1 or CEA were not significantly related to these outcomes. The data did not provide evidence for or against the hypothesis that the CEACAM6 effect on survival differs according to treatment. CONCLUSION: Expression of the cell adhesion molecule CEACAM6 in CRC is an independent prognostic factor allowing subdivision of patients into low- and high-risk groups. Whether CEACAM6 or CEA and CEACAM1 might be useful as predictive markers of chemotherapy benefit remains unclear.