Kinetics of excited states of pigment clusters in solubilized light-harvesting complex II: photon density-dependent fluorescence yield and transmittance.

Relative fluorescence yield, phi F, and transmittance, T, were measured in solubilized light-harvesting complex II (LHCII) as a function of photon density, Ip, of monochromatic 645-nm laser pulses (duration: approximately 2.5 ns). Special efforts were made in constructing an optical set-up that allows the accurate determination of the fluorescence from an area of constant Ip, phi F(Ip) starts to decline at approximately 10(14) and drops to values below 0.01% at maximum Ip (approximately 10(19) photons cm-2 pulse-1). T(Ip) decreases only slightly at photon densities of approximately 10(15) but increases steeply at values of > 10(17) photons cm-2 pulse-1. The interpretation of the phi F(Ip) data using the saturation limit of Mauzerall's multiple hit model leads to a unit size of about 10-15 chlorophyll molecules. One interpretation is to attribute this result to a very fast exciton-exciton annihilation of multiple excited states generated within this small domain. Alternatively, based on the assumption that delocalized cluster states within the monomeric/trimeric subunit of LHCII exist, the results can be consistently described by a kinetic model comprising ground, monoexcitonic, and biexcitonic states of clusters and a triplet state that is quenched by carotenoids in LHCII. Within the framework of this model the annihilation of multiple excitations is explained as ultrafast radiationless relaxation of higher excited cluster states. Comparative measurements in diluted acetonic Chl a solution are consistently described by the depletion of the ground state, taking the absorption cross section at the used wavelength.     

Global mangrove root production,its controls and roles in the blue carbon budget of mangroves

Mangroves are among the most carbon-dense ecosystems worldwide. Most of the carbon in mangroves is found belowground, and root production might be an important control of carbon accumulation, but has been rarely quantified and understood at the global scale. Here, we determined the global mangrove root production rate and its controls using a systematic review and a recently formalised, spatially explicit mangrove typology framework based on geomorphological settings. We found that global mangrove root production averaged ~770 ± 202 g of dry biomass m⁻² year⁻¹ globally, which is much higher than previously reported and close to the root production of the most productive tropical forests. Geomorphological settings exerted marked control over root production together with air temperature and precipitation (r² ≈ 30%, p < .001). Our review shows that individual global changes (e.g. warming, eutrophication, drought) have antagonist effects on root production, but they have rarely been studied in combination. Based on this newly established root production rate, root-derived carbon might account for most of the total carbon buried in mangroves, and 19 Tg C lost in mangroves each year (e.g. as CO₂). Inclusion of root production measurements in understudied geomorphological settings (i.e. deltas), regions (Indonesia, South America and Africa) and soil depth (>40 cm), as well as the creation of a mangrove root trait database will push forward our understanding of the global mangrove carbon cycle for now and the future. Overall, this review presents a comprehensive analysis of root production in mangroves, and highlights the central role of root production in the global mangrove carbon budget.     

Functional cis-element sequence requirements for suppression of gene expression by the TNPA protein of the Zea mays transposon En/Spm

TNPA, one of the two transposition proteins encoded by the En/Spm transposable elements of Zea mays, suppresses the expression of genes that contain an appropriate cis element. Suppression can be monitored in tobacco protoplasts in a transient expression assay as follows. The plant promoter-driven expression of the Escherichia coli-glucuronidase (GUS)-encoding gene, uidA, is repressed in the presence of TNPA if the GUS gene contains a functional cis element in the untranslated RNA leader sequence. Earlier, we found that the minimal cis element is composed of two 12 by sequences in a tail-to-tail inverted orientation. Each 12 by sequence is sufficient to bind TNPA in vitro and can be thought of as a half-site in the cis element. Here, we investigated the sequence requirements of the minimal cis element. Our observations support our expectations that a functional cis element must provide a template to which two TNPA molecules can bind in the correct orientation. Sequences within the half-sites can be altered as long as the eight bases that make up the consensus binding sites are not changed. However, we found the following unexpected sequence specificities. Firstly, some changes to the consensus binding sequence can be tolerated in one half-site, as long as the other site matches the consensus. Secondly, although the region between the half-sites can vary in sequence and in length between two and four bases, a thymidine residue is not tolerated directly 5′ preceding the second half-site. Since many variants of the cis element sequence remain functional, the suppressor response element provides a flexible tool for artificially manipulating the expression of genes.     

Molecular cloning and functional expression of bacteriophage PK1E-encoded endoneuraminidase Endo NE

Homopolymeric α-2,8-linked sialic acid (PSA) has been found as a capsular component of sepsis- and meningitis-causing bacterial pathogens, and on eukaryotic cells as a post-translational modification of the neural cell adhesion molecule (NCAM). The polysaccharide is specifically recognized and degraded by a phage-encoded enzyme, the endo-N-acetylneuraminidase E (Endo NE). Endo NE therefore has become a valuable tool in the study of bacterial pathogenesis and eukaryotic morphogenesis. In this report we describe the molecular cloning of Endo NE and the expression of a functionally active recombinant enzyme. The cloned DNA sequence (2436 bp) encodes a polypeptide of 811 amino acids, which at the 5′ end contains a totally conserved neuraminidase motif. Expressed in Escherichia coli, the enzyme migrates as a single band of approximately 74 kDa in SDS-PAGE. A central domain of 669 amino acid residues is about 90% homologous to the recently cloned Endo NF. Both phage-induced lysis of bacteria and the catalysis of PSA degradation by the recombinant enzyme are efficiently inhibited by a polyclonal antiserum raised against the intact phage particle. The C-terminal region seems to be essential to enzymatic functions, as truncation of 32 amino acids outside the homology domain completely abolishes Endo NE activity. Our data also indicate that the 38 kDa protein, previously assumed to be a subunit of the Endo NE holoenzyme, is the product of a separate gene locus and is not necessary for in vitro depolymerase activity.     

Glutamine release from hindlimb and uptake by kidney in the acutely acidotic rat.

The arteriovenous difference (release) for glutamine across the hindlimb increases significantly during acute HCl-induced acidosis. This additional amount release by muscle tissue can account for the extra glutamine taken up by the kidney.     

Differential response to irradiation in offspring of freshwater and seawater substrains of Poecilia (Lebistes) reticulata peters in the “guppy male courtship activity test”

Summary An inbred strain (Istanbul) of guppies was divided into two substrains, one of which was maintained and bred in seawater. The offspring of irradiated animals of both substrains (1000 R X-rays to spermatogonia and oogonia of neonatal fish) were tested in a new gruppy male courtship activity test and compared with control groups. The postirradiation response in the seawater substrain was more intense than in the freshwater substrain.Dedicated to Prof.Dr.Dr.h.c.mult. Curt Kosswig on the occasion of his 75th birthday     

Subunit interaction and function of clathrin-coated vesicle adaptors from the Golgi and the plasma membrane

Clathrin in coated vesicles is linked to transmembrane receptors by adaptor protein complexes. The Golgi-associated adaptor complex HA1 is a tetramer, made up of beta', gamma, 47-kDa, and 20-kDa subunits, whereas the tetrameric plasma membrane adaptor, HA2, contains alpha, beta, 50-kDa, and 16-kDa subunits (Ahle, S., Mann, A., Eichelsbacher, U., and Ungewickell, E. (1988) EMBO J. 7, 919-929). Here we report on the structural organization of adaptor subunits as revealed by proteolytic dissection. We show that the beta' and gamma subunits of HA1 are cleaved into 60-67-kDa "trunk" and 32-44-kDa "head" fragments. Interactions between adaptor subunits involve the trunk domains only. In overall organization of their domains, the Golgi and plasma membrane adaptors are very similar. The similarity encompasses also the location of phosphorylated serine residues in the alpha a, beta, beta', and gamma subunits, which are found in the head domains in all cases. In the alpha a and beta subunits they probably occur in the proline- and glycine-rich hinge region, which connects the head to the trunk. Identical adaptor fragments were obtained by controlled digestion of clathrin-coated vesicles. Under conditions that did not affect the integrity of the clathrin heavy chain, the adaptor head fragments were always quantitatively released from coated vesicles. The release of the bulk of the adaptors occurred concomitantly with the cleavage of their beta-type subunits (beta and beta') and under buffer conditions that prevent aggregation of adaptors. These observations taken together with the results of reconstitution experiments confirm and extend previous data (Ahle, S., and Ungewickell, E. (1989) J. Biol. Chem. 264, 20089-20093) which suggested that adaptors attach to clathrin through their beta-type (beta and beta') subunits. Moreover, high affinity interaction between adaptors and clathrin requires the participation of regions from both the head and trunk domains of the beta-type subunits.     

Structure of adsorbed fibrinogen obtained by scanning force microscopy

It is shown that scanning force microscopy (SFM), operated in the attractive mode, can be used to obtain high resolution pictures of adsorbed fibrinogen molecules on solid surfaces, without the need for staining or special microscope grids. SFM also reveals the three-dimensional structure of the adsorbed molecules. Two forms of adsorbed fibrinogen are demonstrated on hydrophobic silicone dioxide surfaces; a trinodular about 60 nm long and a globular with about a 40 nm diameter. Polymeric networks formed after storage of the surface with adsorbed fibrinogen in PBS for 11 days are also shown. The SFM-results for the trinodular structure suggest the existence of loops or peptide chains extending outside the basic structure of the fibrinogen molecule.     

A Pseudomonas strain accumulating polyesters of 3-hydroxybutyric acid and medium-chain-length 3-hydroxyalkanoic acids

Summary A citronellol-utilizing bacterium was isolated that accumulated a polyester consisting of 3-hydroxybutyric acid (3HB) and of medium-chain-length 3-hydroxyalkanoic acids (3HA_MCL) from various carbon sources up to approximately 70% of the cellular dry matter if the cells were cultivated in ammineral salts medium under nitrogen limitation. In octanoate-grown cells, for instance, the polyester consisted of 87.5 mol% 3HB and 12.5 mol% 3-hydroxyoctanoic acid (3HO), whereas it consisted of 10.3 mol% 3HB, 16.7 mol% 3HO and 73.0 mol% 3-hydroxydecanoic acid (3HD) in gluconate-grown cells. However, the results of various experiments indicated that a blend rather than a copolyester was synthesized in the cell. It was the only strain among 45 different recently isolated citronellol-utilizing bacteria that accumulated such a polyester. All other citronellol-utilizing bacteria behaved like Pseudomonas aeruginosa with respect to their polyhydroxyalkanoic acid (PHA) biosynthetic capabilities and accumulated PHA consisting of 3HA_MCL with 3HO and 3HD as the main constituents from octanoate or gluconate, respectively, whereas 3HB was never present. None of 232 different heavy-metal-resistant bacteria was able to accumulate PHA composed of 3HB plus, for example, 3HO. Only 20.3% did not accumulate any PHA at all, 44.8% accumulated PHB from gluconate, and 34.9% behaved like P. aeruginosa. Many bacteria belonging to the latter group were distinguished from the other by rapid growth in nutrient broth and in gluconate mineral salts medium and by their ability to grow in the presence of a high concentration (up to 1.5%, w/v) of octanoate. Correspondence to: A. Steinbüchel