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Christian Wilhelm

Publications and source records attributed to Christian Wilhelm.

At least 19 recordsLinked to original sources
PubMed2006

SALL4 is directly activated by TCF/LEF in the canonical Wnt signaling pathway.

The SALL4 promoter has not yet been characterized. Animal studies showed that SALL4 is downstream of and interacts with TBX5 during limb and heart development, but a direct regulation of SALL4 by TBX5 has not been demonstrated. For other SAL genes, regulation within the Shh, Wnt, and Fgf pathways has been reported. Chicken csal1 expression can be activated by a combination of Fgf4 and Wnt3a or Wnt7a. Murine Sall1 enhances, but Xenopus Xsal2 represses, the canonical Wnt signaling. Here we describe the cloning and functional analysis of the SALL4 promoter. Within a minimal promoter region of 31bp, we identified a consensus TCF/LEF-binding site. The SALL4 promoter was strongly activated not only by LEF1 but also by TCF4E. Mutation of the TCF/LEF-binding site resulted in decreased promoter activation. Our results demonstrate for the first time the direct regulation of a SALL gene by the canonical Wnt signaling pathway.

Animals↗
PubMed2006

Discordant results of flow cytometric ZAP-70 expression status in B-CLL samples if different gating strategies are applied.

BACKGROUND: Recent studies have identified ZAP-70 expression status as an excellent prognostic parameter in chronic lymphocytic leukemia (CLL). ZAP-70 expression can be determined by direct antibody staining followed by flow cytometric analysis. However, there are currently several different gating strategies for analysis. We compared those strategies for ZAP-70 expression analysis. METHODS: One hundred and one patients with B-CLL were analyzed employing a directly labeled alexa-fluor-488-ZAP-70-antibody. In 27 cases, we additionally measured and analyzed ZAP-70 expression, together with healthy controls as described previously. RESULTS: Applying either T-/NK-cell isotype or healthy control analysis strategies on patient samples that were processed in parallel revealed discrepant results in 48% (12/25) of all cases. Taken together with the 74 B-CLL patients, who were analyzed with regard to average reference values, disconcordant results were obtained in 58% of the samples. We demonstrate that high variances in ZAP-70 T-/NK-cell staining within B-CLL patients, paired with a close proximity of ZAP-70 B-cell values to the suggested cut-off levels, may lead to interpretation difficulties of ZAP-70 status. CONCLUSIONS: We conclude that different gating strategies for determining flow cytometric ZAP-70 expression status produce highly discordant results. Further standardization is required before ZAP-70 can be used as a reliable prognostic parameter in immunophenotyping of B-CLL.

Adult↗
PubMed2006

Lipid dependence of diadinoxanthin solubilization and de-epoxidation in artificial membrane systems resembling the lipid composition of the natural thylakoid membrane.

In the present study, the solubility and enzymatic de-epoxidation of diadinoxanthin (Ddx) was investigated in three different artificial membrane systems: (1) Unilamellar liposomes composed of different concentrations of the bilayer forming lipid phosphatidylcholine (PC) and the inverted hexagonal phase (H(II) phase) forming lipid monogalactosyldiacylglycerol (MGDG), (2) liposomes composed of PC and the H(II) phase forming lipid phosphatidylethanolamine (PE), and (3) an artificial membrane system composed of digalactosyldiacylglycerol (DGDG) and MGDG, which resembles the lipid composition of the natural thylakoid membrane. Our results show that Ddx de-epoxidation strongly depends on the concentration of the inverted hexagonal phase forming lipids MGDG or PE in the liposomes composed of PC or DGDG, thus indicating that the presence of inverted hexagonal structures is essential for Ddx de-epoxidation. The difference observed for the solubilization of Ddx in H(II) phase forming lipids compared with bilayer forming lipids indicates that Ddx is not equally distributed in the liposomes composed of different concentrations of bilayer versus non-bilayer lipids. In artificial membranes with a high percentage of bilayer lipids, a large part of Ddx is located in the membrane bilayer. In membranes composed of equal proportions of bilayer and H(II) phase forming lipids, the majority of the Ddx molecules is located in the inverted hexagonal structures. The significance of the pigment distribution and the three-dimensional structure of the H(II) phase for the de-epoxidation reaction is discussed, and a possible scenario for the lipid dependence of Ddx (and violaxanthin) de-epoxidation in the native thylakoid membrane is proposed.

Diatoms↗
PubMed2006

Molecular basis of Kindler syndrome in Italy: novel and recurrent Alu/Alu recombination, splice site, nonsense, and frameshift mutations in the KIND1 gene.

Kindler syndrome (KS) is a rare autosomal recessive disorder characterized by skin blistering in childhood followed by photosensitivity and progressive poikiloderma. Most cases of KS result from mutations in the KIND1 gene encoding kindlin-1, a component of focal adhesions in keratinocytes. Here, we report novel and recurrent KIND1 gene mutations in nine unrelated Italian KS individuals. A novel genomic deletion of approximately 3.9 kb was identified in four patients originating from the same Italian region. This mutation deletes exons 10 and 11 from the KIND1 mRNA leading to a truncated kindlin-1. The deletion breakpoint was embedded in AluSx repeats, specifically in identical 30-bp sequences, suggesting Alu-mediated homologous recombination as the pathogenic mechanism. KIND1 haplotype analysis demonstrated that patients with this large deletion were ancestrally related. Five additional mutations were disclosed, two of which were novel. To date, four recurrent mutations have been identified in Italian patients accounting for approximately approximately 75% of KS alleles in this population. The abundance of repetitive elements in intronic regions of KIND1, together with the identification of a large deletion, suggests that genomic rearrangements could be responsible for a significant proportion of KS cases. This finding has implications for optimal KIND1 mutational screening in KS individuals.

Adolescent↗
PubMed2006

Light emission originating from photosystem II radical pair recombination is sensitive to zeaxanthin related non-photochemical quenching (NPQ).

We have used chlorophyll fluorescence, delayed luminescence and thermoluminescence measurements to study the influence of an artificial DeltapH in the presence or absence of zeaxanthin on photosystem II reactions. Energization of the pea thylakoid membranes induced non-photochemical fluorescence quenching and an increase in the overall luminescence emission of PSII during delayed luminescence and thermoluminescence measurements. This DeltapH-induced overall luminescence increase was caused by a strongly enhanced delayed luminescence in the seconds range before sample heating. In the subsequent thermoluminescence measurements the intensity of the B-band decreased after one and increased after two or more single turnover flashes. We propose that strong membrane energization shifted the redox potential of photosystem II radical pairs to more negative values causing the high delayed luminescence. The zeaxanthin-dependent non-photochemical fluorescence quenching component, however, did not alter thermoluminescence B-bands but decreased the delayed luminescence intensity by 30%. To our knowledge this is the first report that the radiative radical pair recombination, exhibited as delayed luminescence but not thermoluminescence emission, is sensitive to the antenna located zeaxanthin related non-photochemical fluorescence quenching. Our data can be interpreted within the frame of the exciton/radical pair equilibrium model that describes photosystem II as a shallow trap and incorporates the transfer of energy from the re-excitated reaction centre to the antenna of photosystem II.

Chlorophyll↗
PubMed2006

Uphill energy transfer from long-wavelength absorbing chlorophylls to PS II in Ostreobium sp. is functional in carbon assimilation.

From the algal genus Ostrobium two species are known which express a chlorophyll antenna absorbing between 710 and 725 nm to a different extent. In a comparative study with these two species it is shown that quanta absorbed by this long wavelength antenna can be transferred to PS II leading to significant PS II-related electron transfer. It is documented that under monochromatic far red light illumination growth continues with rather high efficiency. The data show that the uphill-energy transfer to PS II reduces the quantum yield under white light significantly. It is discussed that this strategy of energy conversion might play a role in special environments where far red light is the predominant energy source.

Absorption↗
PubMed2006

Parallel analysis of transcript levels and physiological key parameters allows the identification of stress phase gene markers in Chlamydomonas reinhardtii under copper excess.

Excessive copper concentrations, known to induce reactive oxygen species (ROS) formation, have been tested with respect to their effects on transcript abundance and related proteins involved in oxidative stress responses. The results show that the stromal photosynthetic functions were more ROS sensitive than the membrane-located reactions. The rbcL over-expression compensated for the damage only at 10 microM Cu, whereas the genetic stimulation of alpha-tocopherol biosynthesis led to the protection of membrane reactions up to 50-100 microM Cu. For this reason, the gradual growth drop of Chlamydomonas reinhardtii cultures observed under increasing Cu(2+) concentrations matched better with the loss of photosynthetic capacity than with those of photosynthetic quantum yields. According to Larcher's stress concept, the results allow the identification of gene markers for the alarm (rbcL), the hardening (FeSOD, VTE3) and the exhaustion [cyclin-dependent protein kinase (cdk), psbA] phases. These genes can be used to rapidly evaluate the state of oxidative stress in algae and putatively in other plant cells.

Animals↗
PubMed2005

The importance of a highly active and DeltapH-regulated diatoxanthin epoxidase for the regulation of the PS II antenna function in diadinoxanthin cycle containing algae.

The present study focuses on the regulation of diatoxanthin (Dtx) epoxidation in the diadinoxanthin (Ddx) cycle containing algae Phaeodactylum tricornutum, Thalassiosira pseudonana, Cyclotella meneghiniana and Prymnesium parvum and its significance for the control of the photosystem II (PS II) antenna function. Our data show that Dtx epoxidase can exhibit extremely high activities when algal cells are transferred from high light (HL) to low light (LL). Under HL conditions, Dtx epoxidation is strongly inhibited by the light-driven proton gradient. Uncoupling of the cells during HL illumination restores the high epoxidation rates observed during LL. In Ddx cycle containing algae, non-photochemical quenching of chlorophyll fluorescence (NPQ) is directly correlated with the Dtx concentration and independent of the presence of the proton gradient. This means that a fast conversion of PS II from the heat dissipating state back to the light-harvesting state can only be realized by an efficient removal of the quenching pigment Dtx. It is proposed that the high Dtx epoxidation rates during LL illumination serve exactly this purpose. The inhibition of Dtx epoxidation by the DeltapH, on the other hand, ensures rapid increases in the Dtx concentration when photoprotection under conditions of HL illumination is required. The regulation of the PS II antenna function in Ddx cycle containing algae is different to that in violaxanthin (Vx) cycle containing plants, where for the zeaxanthin (Zx)-dependent NPQ the presence of a proton gradient is mandatory. In the green alga Chlorella vulgaris conversion of PS II from the heat dissipating state back to the light-harvesting state is controlled by the DeltapH, whose relaxation after a transition from HL to darkness or LL rapidly abolishes the thermal dissipation of excitation energy, including the Zx-dependent NPQ. Due to the inability of Zx to quench fluorescence in the absence of the DeltapH a fast epoxidation of Zx to Vx in LL is not needed and is missing in Chlorella vulgaris.

Algal Proteins↗
PubMed2005

Evidence for a rebinding of antheraxanthin to the light-harvesting complex during the epoxidation reaction of the violaxanthin cycle.

In the present study, we investigated the epoxidation reaction of the violaxanthin (Vx) cycle in intact cells of Chlorella vulgaris. Our results show that the overall epoxidation is slightly slower in darkness compared to the epoxidation during high light (HL) illumination. The calculation of the rate constants of the two epoxidation steps revealed that, for both conditions, the first epoxidation step from zeaxanthin (Zx) to antheraxanthin (Ax) is faster than the second epoxidation step from Ax to Vx. However, the most noteworthy result of our present study is that Ax, which is transiently formed during the epoxidation reaction, participates in non-photochemical quenching of chlorophyll fluorescence (NPQ). A correlation between NPQ and the de-epoxidized xanthophyll cycle pigments during the time-course of the epoxidation reaction can only be achieved when NPQ is plotted versus the sum of Zx and Ax. The accumulation of significant amounts of Ax during the epoxidation reaction further indicates that Ax-dependent quenching proceeds with a similar efficiency compared to the Zx-mediated NPQ. As the xanthophyll-dependent NPQ relies on the presence of de-epoxidized xanthophylls in the PS II antenna, Ax-dependent NPQ is only possible under the assumption that Ax rebinds to the light-harvesting complex (LHC) II during the epoxidation reaction.

Chlorella vulgaris↗
PubMed2005

Role of hexagonal structure-forming lipids in diadinoxanthin and violaxanthin solubilization and de-epoxidation.

In this study, we have examined the influence of different lipids on the solubility of the xanthophyll cycle pigments diadinoxanthin (Ddx) and violaxanthin (Vx) and on the efficiency of Ddx and Vx de-epoxidation by the enzymes Vx de-epoxidase (VDE) from wheat and Ddx de-epoxidase (DDE) from the diatom Cyclotella meneghiniana, respectively. Our results show that the lipids MGDG and PE are able to solubilize both xanthophyll cycle pigments in an aqueous medium. Substrate solubilization is essential for de-epoxidase activity, because in the absence of MGDG or PE Ddx and Vx are present in an aggregated form, with limited accessibility for DDE and VDE. Our results also show that the hexagonal structure-forming lipids MGDG and PE are able to solubilize Ddx and Vx at much lower lipid concentrations than bilayer-forming lipids DGDG and PC. We furthermore found that, in the presence of MGDG or PE, Ddx is much more solubilizable than Vx. This substantial difference in Ddx and Vx solubility directly affects the respective de-epoxidation reactions. Ddx de-epoxidation by the diatom DDE is saturated at much lower MGDG or PE concentrations than Vx de-epoxidation by the higher-plant VDE. Another important result of our study is that bilayer-forming lipids DGDG and PC are not able to induce efficient xanthophyll de-epoxidation. Even in the presence of high concentrations of DGDG or PC, where Ddx and Vx are completely solubilized, a strongly inhibited Ddx de-epoxidation is observed, while Vx de-epoxidation by VDE is completely absent. This indicates that the inverted hexagonal phase domains provided by lipid MGDG or PE are essential for de-epoxidase activity. We conclude that in the natural thylakoid membrane MGDG serves to solubilize the xanthophyll cycle pigments and furthermore provides inverted hexagonal structures associated with the membrane bilayer, which are essential for efficient xanthophyll de-epoxidase activity.

Diatoms↗
PubMed2005

Estimation of chlorophyll content and daily primary production of the major algal groups by means of multiwavelength-excitation PAM chlorophyll fluorometry: performance and methodological limits.

The performance and methodological limits of the Phyto-PAM chlorophyll fluorometer were investigated with laboratory grown algae cultures and natural phytoplankton from the rivers Saar and Saale. The Phyto-PAM is a 4-wavelength chlorophyll fluorometer with the functional combination of chlorophyll (Chl) estimation and assessment of photosynthetic activity, both differentiated into the main algal groups. The reliability of fluorescence-based Chl estimation strongly depends on the group specific calibration of the instrument and the resulting chlorophyll/fluorescence (Chl/F) ratios in reference algal cultures. A very high reliability of the Chl estimation was obtained in the case of constant Chl/F-ratios. Algae grown at different light intensities showed marked differences in Chl/F-ratios, reflecting differences in pigment composition and Chl a specific absorption (a*). When the Phyto-PAM was calibrated with laboratory grown diatoms, the Chl a in river grown diatoms was underestimated, due a lower content of accessory pigments and stronger pigment packaging. While this aspect presently limits the application of PAM fluorometry in limnology, this limitation may be overcome by future technical progress in the detection of dynamic changes in Chl/F-ratio via fluorescence-based measurements of the functional PS II absorption cross-section. Practically identical Chl/F-ratios were found for the diatom-dominated waters of the rivers Saar and Saale, suggesting that the same instrument calibration parameters may be applied for hydrographically similar surface waters. For this particular case, despite of the present methodological limitations, the potential of PAM fluorometry in limnology could be demonstrated. Light response curves were measured to estimate primary production with a spectrally resolved model in daily courses at two sampling sites. Fluorescence based primary production was closely correlated with measured oxygen evolution rates until midday. In the afternoon, at the water surface the fluorescence approach gave higher rates than the measured oxygen evolution. Possible explanations for the observed differences are discussed.

Chlorophyll↗
PubMed2005

The application of micro-FTIR spectroscopy to analyze nutrient stress-related changes in biomass composition of phytoplankton algae.

Micro-Fourier transform infrared (FTIR) spectroscopy was used to study changes in spectral features of three species of Cyanobacteria (Microcystis aeruginosa, Croococcus minutus, and Nostoc sp.) and two Bacillariophyceae (Cyclotella meneghiniana, and Phaeodactylum tricornutum) in response to nutrient stress. The change of physiological state of the cells was followed during a 4-week starvation period on the basis of physiological key parameters and by means of FTIR spectroscopy. Changes in the integrated FTIR bands of cell spectra assigned to proteins, lipids, carbohydrates and silicate were used to calculate relative biomass composition. The results show that short-term acclimatization become visible at first in pigmentation and photosynthetic efficiency, whereas changes in biomass composition reflect long term modulation in the metabolism. Simultaneous monitoring of short term and long term stress acclimatization showed evidence that the metabolic strategies to cope with increasing nutrient limitation are highly species-specific. This species-specificity can only be resolved in natural phytoplankton samples by single cell techniques. The results show that the FTIR technique has the potential to become applicable for the determination of single cell biomass composition from natural phytoplankton communities.

Biomass↗
PubMed2004

Fourier transform infrared spectroscopy as a new tool to determine rosmarinic acid in situ.

A new procedure has been developed for the in situ FT-IR determination of rosmarinic acid (RA) in suspension cultures of Lavandula officinalis. The method involves sample preparation on ZnSe crystals or microplates from silicon, and measuring absorbance spectra between 4000 and 700 cm(-1). First derivative spectra were analysed after normalisation using partial least square (PLS) algorithm. The correlation between spectral analysis and HPLC measurements of cell extracts shows that the FT-IR procedure is suitable for qualitative and quantitative analyses of RA in cell suspension cultures.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2004

A new type of thermoluminometer: a highly sensitive tool in applied photosynthesis research and plant stress physiology.

Here we describe a newly developed thermoluminescence measuring device that employs flash excitation, peltier heating, and light detection by channel photomultipliers (CPM). The new thermoluminometer is equipped with four sample holders for simultaneous measurements of thermoinduced light emission in the temperature range from -20 degrees C to +180 degrees C. It allows one to measure leaf samples, chloroplasts, thylakoids, algae, or even bioorganic material lacking chlorophyll by means of naturally induced or artificially applied chemilumigenic probes. The temperature range of the thermoluminometer allows one to analyse the thermoinduced radical pair recombination of photosystem II in the lower temperature region as well as chemiluminescence from lipid peroxidation in the higher temperature region. Hence, plant material can be assessed concerning both its photosynthetic and its oxidative stress status. Since the device is equipped with four sample holders and four CPM channels for simultaneous detection of thermoinduced light emission, it facilitates a high throughput. Therefore, the new device is interesting, not only in ecophysiology, but also in the field of plant breeding, as it can be used to study the stress tolerance of various cultivars of cultural crop plants.

Equipment Design↗
PubMed2004

Photophysiology and primary production of phytoplankton in freshwater.

In the last 10 years enormous progress has been made in developing new instruments to collect physiological data from natural phytoplankton. In this review we summarize the motivation which has powered this engagement and focus on new technologies used to measure fluorescence, absorption and biochemical compositions of natural phytoplankton cells from nature. Combining the knowledge of phytoplankton structure along with taxon-specific measurements of photosynthetic activity and biochemical cell composition, can lead to new models which increase the reliability of water quality prediction. Furthermore, recent progress in the analysis of photophysiological fitness of phytoplankton cells has revealed new knowledge about the phylogenetic diversity of metabolic strategies to cope with light and nutrient stress. Future progress in single cell analysing systems will be discussed.

Journal Article↗
PubMed2003

Thermoluminescence as a tool for monitoring ozone-stressed plants.

The effect of ozone (6 h, various concentrations from 0 to 350 ppb) on barley (Hordeum vulgare L., cv. Bomi) and tomato (Lycopersicon esculentum L., cv. Yellow Cherry) leaves was investigated in parallel by thermoluminescence (TL) and fluorescence (FL) methods. Several significant changes were found in TL glow curves measured after excitation by one single turnover flash at +2 degree C in the temperature range from 2 to 170 degree C immediately after ozone exposure. Contrary to TL, ozone induced only negligible changes in FL parameters F0, FM and Fv/FM. Measurements done 24 h after ozone exposure showed partial recovery of ozone-induced changes. The extent of recovery was not the same in different parts of TL curves. Fluorescence parameters were not significantly changed. The results demonstrate that TL parameters are more sensitive to ozone than conventially used FL parameters F0, FM and Fv/FM. Moreover, TL measurements seem to give information not only about the PSII electron transport, but also about the extent of oxidative damage and membrane lipid peroxidation. It is concluded, that TL can be a highly informative tool for monitoring the impact of ozone on plants.

Air Pollutants↗