University of Konstanz

About: University of Konstanz is a education organization based out in Konstanz, Baden-Württemberg, Germany. It is known for research contribution in the topics: Population & Visualization. The organization has 12115 authors who have published 27401 publications receiving 951162 citations. The organization is also known as: University of Constance & Universität Konstanz.

Protein targeting into complex diatom plastids: functional characterisation of a specific targeting motif

Abstract: Plastids of diatoms and related algae evolved by secondary endocytobiosis, the uptake of a eukaryotic alga into a eukaryotic host cell and its subsequent reduction into an organelle. As a result diatom plastids are sur- rounded by four membranes. Protein targeting of nucleus encoded plastid proteins across these membranes depends on N-terminal bipartite presequences consisting of a signal and a transit peptide-like domain. Diatoms and crypto- phytes share a conserved amino acid motif of unknown function at the cleavage site of the signal peptides (ASA- FAP), which is particularly important for successful plastid targeting. Screening genomic databases we found that in rare cases the very conserved phenylalanine within the motif may be replaced by tryptophan, tyrosine or leucine. To test such unusual presequences for functionality and to better understand the role of the motif and putative receptor proteins involved in targeting, we constructed prese- quence:GFP fusion proteins with or without modifications of the ''ASAFAP''-motif and expressed them in the diatom Phaeodactylum tricornutum. In this comprehensive muta- tional analysis we found that only the aromatic amino acids phenylalanine, tryptophan, tyrosine and the bulky amino acid leucine at the +1 position of the predicted signal peptidase cleavage site allow plastid import, as expected from the sequence comparison of native plastid targeting presequences of P. tricornutum and the cryptophyte Guil- lardia theta. Deletions within the signal peptide domains also impaired plastid import, showing that the presence of F at the N-terminus of the transit peptide together with a cleavable signal peptide is crucial for plastid import.

Light induction of carotenoid biosynthesis genes in the green alga Haematococcus pluvialis: regulation by photosynthetic redox control

Abstract: The unicellular green alga Haematococcus pluvialis accumulates large amounts of the red ketocarotenoid astaxanthin when exposed to various stress situations such as salt stress and high light intensities. Here, the light regulation of Haematococcus carotenoid biosynthesis was examined. Isolation and characterization of the lycopene β cyclase gene involved in carotenoid biosynthesis was carried out using a functional complementation approach. Subsequently, gene expression of lycopene cyclase, phytoene synthase, phytoene desaturase and carotenoid hydroxylase was analysed in green flagellate cells. All four genes revealed higher transcript levels in response to increased illumination. Not only the induction of astaxanthin biosynthesis but also carotenoid gene expression was found to be correlated with the redox state of the photosynthetic electron transport. In accordance with this result, increased transcript levels for carotenoid biosynthesis genes were detected under both blue and red light conditions. The application of different inhibitors of the photosynthetic electron flow indicated that the photosynthetic plastoquinone pool functions as the redox sensor for the up-regulation of carotenoid biosynthesis genes. These results suggested that in Haematococcus not only the specific astaxanthin pathway but also general carotenoid biosynthesis is subject to photosynthetic redox control.

Compartmentation and complexation of metals in hyperaccumulator plants.

Abstract: Hyperaccumulators are being intensely investigated. They are not only interesting in scientific context due to their “strange” behaviour in terms of dealing with high concentrations of metals, but also because of their use in phytoremediation and phytomining, for which understanding the mechanisms of hyperaccumulation is crucial. Hyperaccumulators naturally use metal accumulation as a defence against herbivores and pathogens, and therefore deal with accumulated metals in very specific ways of complexation and compartmentation, different from non-hyperaccumulator plants and also non-hyperaccumulated metals. For example, in contrast to non-hyperaccumulators, in hyperaccumulators even the classical phytochelatin-inducing metal, cadmium, is predominantly not bound by such sulfur ligands, but only by weak oxygen ligands. This applies to all hyperaccumulated metals investigated so far, as well as hyperaccumulation of the metalloid arsenic. Stronger ligands, as they have been shown to complex metals in non-hyperaccumulators, are in hyperaccumulators used for transient binding during transport to the storage sites. This confirmed that enhanced active metal transport, and not metal complexation, is the key mechanism of hyperaccumulation. Hyperaccumulators tolerate the high amount of accumulated heavy metals by sequestering them into vacuoles, usually in large storage cells of the epidermis. This is mediated by strongly elevated expression of specific transport proteins in various tissues from metal uptake in the shoots up to the storage sites in the leaf epidermis. However, this mechanism seems to be very metal specific. Non-hyperaccumulated metals in hyperaccumulators seem to be dealt with like in non-hyperaccumulator plants, i.e. detoxified by binding to strong ligands such as metallothioneins.

Filter mesh size and food particle uptake by Daphnia

Abstract: Food size selection of four Daphnia, species (D. magna, D. hyalina, D. galeata, D. pulicaria) was investigated using spherical plastic beads as artificial food and with small bacteria. The size of the particles ranged from 0.1 to 35 μm with special emphasis to the particle diameters between 0.1 and 1 μm. In one set of experiments a mixture of differently sized particles was offered as food suspension and the selectivity of filtering was determined by comparing the size spectrum of the particles found in the gut contents with the spectrum in the food suspension. In a second series of experiments suspensions of uniformly sized particles were offered to single animals and their feeding activity was observed directly. In both types of experiments the mesh sizes of the filtering apparatus of the respective animals studied were measured after the experiments by, scanning electron microscopy. The mean sizes of the filter meshes were about 0.4–0.7 μm. In all experiments the size of the particles found in the gut or those which caused high feeding activities were larger than the smallest mesh sizes of the filters. As a consequence simple mechanical sieving provides a sufficient explanation for the mechanism of particle retention of the filtering process in Daphnia. D. magna was found to feed with high efficiency on suspended freshwater bacteria, the residual species investigated showed low filtering efficiencies when bacteria were offered as food.