Biomedical subjects

Christian Wilhelm

Publications and source records attributed to Christian Wilhelm.

22 records · Page 2Linked to original sources

PubMed2003

Longitudinal leaf gradients of UV-absorbing screening pigments in barley (Hordeum vulgare).

In vivo leaf characteristics were examined to describe longitudinal gradients of UV-absorbing screening pigments in barley. Chlorophyll fluorescence properties and in vivo absorption spectra (210-750 nm) of leaves were measured from the base to the tip. Barley leaves showed strong longitudinal gradients of chlorophyll, where chlorophyll concentration increased within the first 5-8 cm from the leaf base, and did not significantly change for the remaining part of the leaf. Fluorescence microscopy was used to localize cell wall bound screening pigments different from flavonoids, since flavonoids lack a blue-green fluorescence emission (Lichtenthaler and Schweiger 1998). Measurements of in vivo chlorophyll fluorescence indicated that the ratio of UV-absorbing screening pigments per leaf area increases from the leaf base to the tip. These gradients were confirmed by in vivo absorption spectra. It is demonstrated that leaves in the early stage of development are less protected against UV-radiation than fully developed mature leaf regions. The experiments show that measurements of in vivo chlorophyll fluorescence are ideally suited as a fast non-invasive tool to estimate the epidermal UV-transmittance in different leaf sections.

Journal Article↗

PubMed2002

Plasminogen activator inhibitor-1 mRNA expression in cultured pigmented ciliary epithelial cells of the porcine eye.

BACKGROUND: Plasminogen activator inhibitor-1 (PAI-1) is a main regulator of the fibrinolytic system. PAI-1 inhibits tissue plasminogen activator and urokinase-type plasminogen activator, resulting in reduced plasminogen activity and attenuated fibrinolysis and proteolysis. The present study was performed to determine the gene expression encoding for PAI-1 in cultured pigmented ciliary epithelial cells of the porcine eye and to detect PAI-1 activity in cell culture supernatants. METHODS: Total mRNA of respective confluent primary cultures of porcine ciliary epithelial cells, porcine liver cells and porcine kidney cells was isolated. Reverse transcribed PAI-1 mRNA was measured by real-time polymerase chain reaction (TaqMan PCR) with PAI-1 primers and probes deduced from the human PAI-1 gene. PAI-1 activity in supernatants of the cell cultures was determined by a specific chromogenic test (Coatest PAI). RESULTS: PAI-1 mRNA was localized in all samples of primary cultures of porcine pigmented ciliary epithelial cells. As a negative control we analyzed total mRNA of porcine kidney cells. PAI-1 mRNA was not detectable in these cells. On the other hand, we established PAI-1 mRNA in porcine liver cells as a positive control. High levels of PAI-1 activity were found in all samples of cell culture supernatants. CONCLUSIONS: Our results indicate that PAI-1 is produced and secreted by the porcine ciliary epithelium. We suggest that PAI-1 together with components of the fibrin/fibrinolytic system may be involved in aqueous humor outflow. Overproduction of PAI-1 may induce less fibrinolysis and extracellular proteolysis in aqueous humor and trabecular meshwork, which could result in an elevated intraocular pressure by increasing the outflow obstruction. Therefore stimulation of PAI-1 production may perhaps contribute to the pathogenesis of primary open-angle glaucoma.

Animals↗

PubMed2002

Flow cytometric discrimination of various phycobilin-containing phytoplankton groups in a hypertrophic reservoir.

BACKGROUND: Knowledge of phytoplankton structure is important information in water quality control. Lake restoration and sanitation measures in particular must be evaluated on the organismic level to valuate biological effects and assess the risk of potentially toxic Cyanobacteria blooms. We used and comparatively tested three independent methods for phytoplankton analysis in a hypertrophic reservoir under restoration. METHODS: Nine unialgal cultures and outdoor samples were examined by high-performance liquid chromatography pigment analysis, microscopical cell counting, and flow cytometric (FCM) light scatter and fluorescence analysis to measure the percentage contribution of the major algal groups to chlorophyll a and biovolume. The FCM instrument settings and identification criteria were developed using a single excitation wavelength at 514 nm to differentiate nine algal species representing the major groups of algae. Fluorescence was detected at 585, 620, 650, and 680 nm. RESULTS: The results show that FCM is the only method for determining changes in the phytoplankton composition on both a chlorophyll a and biovolume basis. CONCLUSIONS: Each of the three methods has specific advantages and disadvantages, and should be chosen depending on the experimental problem. FCM sorting allows the combination of all three and offers further new perspectives.

Cell Separation↗

PubMed2002

Light regulation of carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata.

We have studied carotenoid biosynthesis in the prasinophycean alga Mantoniella squamata, which contains a great variety of carotenoids belonging to both the alpha- and the beta-carotene (Car) biosyntheses pathways. This unusual carotenoid composition allowed us to address the problem of how biosynthesis on the alpha- and the beta-Car pathway is regulated in response to different light regimes. We found that illumination with 4 h of actinic high light (HL, 250 micromol m(-2) s(-1)), and culture growth in permanent light (PL, 60 micromol m(-2) s(-1)). induced the de novo synthesis of violaxanthin (Vx) cycle pigments belonging to the beta-Car pathway. Carotenoid synthesis on the alpha-Car biosynthesis pathway led to a strong accumulation of lutein (L) and dihydrolutein (DhL). Both the newly synthesised Vx cycle pigments and L/DhL can be regarded as intermediate pools of carotenoids that were converted to light-harvesting pigments in low light (LL) periods following the phases of HL illumination. This transition to the light-harvesting pigments included the conversion of Vx to neoxanthin (Nx) on the beta-Car pathway, and the transformation of L/DhL to prasinoxanthin (Px), the main light-harvesting pigment of M. squamata belonging to the alpha-carotenoids. Isolation of light-harvesting complexes from L-enriched M. squamata cells showed that both L and the Vx cycle pigments were loosely bound to the LHC apoprotein. This peripheral binding is in agreement with their proposed role as intermediate pigments in the biosynthesis of light-harvesting pigments, and should allow a smooth detachment from the protein in periods of LL when the synthesis of Nx and Px is stimulated. We conclude that carotenoid synthesis proceeds in general in an economical way: in both, the alpha- and the beta-Car pathway HL induces the formation of photoprotective pigments, which in LL periods following the HL illumination are not degraded, but on the contrary are converted to light-harvesting pigments.

Carotenoids↗