No evidence of carbon limitation with tree age and height in Nothofagus pumilio under Mediterranean and temperate climate conditions

Background and Aims

Trees universally decrease their growth with age. Most explanations for this trend so far support the hypothesis that carbon (C) gain becomes limited with age; though very few studies have directly assessed the relative reductions of C gain and C demand with tree age. It has also been suggested that drought enhances the effect of C gain limitation in trees. Here tests were carried out to determine whether C gain limitation is causing the growth decay with tree age, and whether drought accentuates its effect.

Methods

The balance between C gain and C demand across tree age and height ranges was estimated. For this, the concentration of non-structural carbohydrates (NSCs) in stems and roots of trees of different ages and heights was measured in the deciduous temperate species Nothofagus pumilio. An ontogenetic decrease in NSCs indicates support for C limitation. Furthermore, the importance of drought in altering the C balance with ontogeny was assessed by sampling the same species in Mediterranean and humid climate locations in the southern Andes of Chile. Wood density (WD) and stable carbon isotope ratios (δ¹³C) were also determined to examine drought constraints on C gain.

Key Results

At both locations, it was effectively found that tree growth ultimately decreased with tree age and height. It was found, however, that NSC concentrations did not decrease with tree age or height when WD was considered, suggesting that C limitation is not the ultimate mechanism causing the age/height-related declining tree growth. δ¹³C decreased with tree age/height at the Mediterranean site only; drought effect increased with tree age/height, but this pattern was not mirrored by the levels of NSCs.

Conclusions

The results indicate that concentrations of C storage in N. pumilio trees do not decrease with tree age or height, and that reduced C assimilation due to summer drought does not alter this pattern.     

Allergen-Specific Immunotherapy Alters the Frequency,as well as the FcR and CLR Expression Profiles of Human Dendritic Cell Subsets

Allergen-specific immunotherapy (AIT) induces tolerance and shifts the Th2 response towards a regulatory T-cell profile. The underlying mechanisms are not fully understood, but dendritic cells (DC) play a vital role as key regulators of T-cell responses. DCs interact with allergens via Fc receptors (FcRs) and via certain C-type lectin receptors (CLRs), including CD209/DC-SIGN, CD206/MR and Dectin-2/CLEC6A. In this study, the effect of AIT on the frequencies as well as the FcR and CLR expression profiles of human DC subsets was assessed. PBMC was isolated from peripheral blood from seven allergic donors before and after 8 weeks and 1 year of subcutaneous AIT, as well as from six non-allergic individuals. Cells were stained with antibodies against DC subset-specific markers and a panel of FcRs and CLRs and analyzed by flow cytometry. After 1 year of AIT, the frequency of CD123⁺ DCs was increased and a larger proportion expressed FcεRI. Furthermore, the expression of CD206 and Dectin-2 was reduced on CD141⁺ DCs after 1 year of treatment and CD206 as well as Dectin-1 was additionally down regulated in CD1c⁺ DCs. Interestingly, levels of DNGR1/CLEC9A on CD141⁺ DCs were increased by AIT, reaching levels similar to cells isolated from non-allergic controls. The modifications in phenotype and occurrence of specific DC subsets observed during AIT suggest an altered capacity of DC subsets to interact with allergens, which can be part of the mechanisms by which AIT induces allergen tolerance.     

The dystonia gene THAP1 controls DNA double-strand break repair choice

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Multiple properties of the splicing repressor SRp38 distinguish it from typical SR proteins

The SR protein SRp38 is a general splicing repressor that is activated by dephosphorylation during mitosis and in response to heat shock. Here we describe experiments that provide insights into the mechanism by which SRp38 functions in splicing repression. We first show that SRp38 redistributes and colocalizes with snRNPs, but not with a typical SR protein, SC35, during mitosis and following heat shock. Supporting the functional significance of this association, a micrococcal nuclease-sensitive component, i.e., an snRNP(s), completely rescued heat shock-induced splicing repression in vitro, and purified U1 snRNP did so partially. SRp38 contains an N-terminal RNA binding domain (RBD) and a C-terminal RS domain composed of two subdomains (RS1 and RS2 domains). Unexpectedly, an RS1 deletion mutant derivative specifically inhibited the second step of splicing, while an RS2 deletion mutant retained significant dephosphorylation-dependent repression activity. Using chimeric SRp38/SC35 proteins, we show that SC35-RBD/SRp38-RS can function as a general splicing activator and that the dephosphorylated version can act as a strong splicing repressor. SRp38-RBD/SC35-RS, however, was essentially inactive in these assays. Together, our results help to define the unusual features of SRp38 that distinguish it from other SR proteins.     

The analysis of fatty acid binding to protein using a modified equilibrium dialysis method: detailed analysis of chromophore-fatty acid-protein interactions

In this paper we extend our previous analysis of fatty acid-chromophore-protein interactions using a modified equilibrium dialysis method described previously. A more rigorous mathematical treatment is combined with a micro-dialysis method using a maximum volume of dialyzate of between 250 microliters and 400 microliters to examine the suitability of different chromophores (mepacrine, quinine, chloroquine, chlorpromazine, methylene blue, rhodamine 6G, 6-carboxyfluorescein) for studying the binding of fatty acid to protein. The macro- and micro-methods of dialysis are compared, and the binding of fatty acid to bovine serum albumin and beta-lactoglobulin discussed as examples of the method. Problems associated with propagated errors in the measurements and obtaining the number of binding sites and the binding constants from curve-fitting are also considered.     

Effect of photosystem II reaction center closure on nanosecond fluorescence relaxation kinetics

The fluorescence decay of chlorophyll in spinach thylakoids was measured as a function of the degree of closure of Photosystem II reaction centers, which was set for the flowed sample by varying either the preillumination by actinic light or the exposure of the sample to the exciting pulsed laser light. Three exponential kinetic components originating in Photosystem II were fitted to the decays; a fourth component arising from Photosystem I was determined to be negligible at the emission wavelength of 685 nm at which the fluorescence decays were measured. Both the lifetimes and the amplitudes of the components vary with reaction center closure. A fast (170–330 ps) component reflects the trapping kinetics of open Photosystem II reaction centers capable of reducing the plastoquinone pool; its amplitude decreases gradually with trap closure, which is incompatible with the concept of photosynthetic unit connectivity where excitation energy which encounters a closed trap can find a different, possibly open one. For a connected system, the amplitude of the fast fluorescence component is expected to remain constant. The slow component (1.7–3.0 ns) is virtually absent when the reaction centers are open, and its growth is attributable to the appearance of closed centers. The middle component (0.4–1.7 ns) with approximately constant amplitude may originate from centers that are not functionally linked to the plastoquinone pool. To explain the continuous increase in the lifetimes of all three components upon reaction center closure, we propose that the transmembrane electric field generated by photosynthetic turnover modulates the trapping kinetics in Photosystem II and thereby affects the excited state lifetime in the antenna in the trap-limited case.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - HEPES 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid - PQ plastoquinone - PSI and PSII Photosystem I and II - Q_A and Q_B primary and secondary quinone acceptor of PSII     

Microbial Community Changes in a Perturbed Agricultural Soil Investigated by Molecular and Physiological Approaches

Changes in soil microbial activity and diversity after incubation either with nitrogen or with a mixture of methane and air were examined. The perturbation by methane and air were characterized in detail and led to reduced diversity and enrichment of methanotrophs which were identified by denaturing gradient gel electrophoresis and 16S rRNA sequencing.     

Spectroscopic investigations on the binding site of bovine hepatic fatty acid binding protein. Evidence for the existence of a single binding site for two fatty acid molecules

The hydrophobic region of the binding site of a bovine fatty acid binding protein (pI 7.0-FABP) has been characterized using fluorescence and circular dichroism (CD) spectroscopy. Blue-shifts of fluorescence emission maxima and increased lifetimes of naphthylamine dyes, anthroyloxy-fatty acids, pyrene nonanoic acid and trans-parinaric acid indicated a hydrophobic interaction with FABP. The fluorescence quenching of various anthroyloxy-fatty acids by iodide and acrylamide showed lower accessibility to the fluorophore linked to the carbon adjacent to the carbonyl group and towards the methyl end of the fatty acid. Binding stoichiometries were different for fatty acids and their bulky fluorescent analogues. trans-Parinaric acid when bound to FABP showed a complex induced CD-spectrum, which is explained by a close proximity of two ligands in the same binding site. Fluorescent derivatives of phosphatidylcholine with trans-parinaric acid and cholesteryl trans-parinarate did not bind to FABP. Thus, the binding site appears to be constructed for high affinity binding of long chain fatty acids.     

Fossiliferous methane-seep deposits from the Cenozoic Talara Basin in northern Peru

Thirteen fossiliferous limestone deposits from Cenozoic strata in the Talara Basin in northern Peru are identified as ancient methane-seep deposits. Planktonic foraminifera and the existing stratigraphical framework of the Talara Basin indicate an early Oligocene, or possibly late Eocene, age of these deposits. They are found in three distinct areas – Belén, Cerro La Salina and Cerros El Pelado – and differ in their petrography, stable isotope signatures, and lipid biomarker and macrofaunal contents. At Belén, the carbon stable isotope signature of the carbonate and the abundance of n-alkanes indicates the possibility of oil seepage in addition to methane seepage; for Belén and Cerro La Salina the high abundance of the biomarker crocetane indicates a dominance of anaerobic methane-oxidizing archaea of the ANME-2 group, whereas the rather small combined crocetane/phytane peak of a Cerros El Pelado limestone agrees with mixed ANME-1/ANME-2 input. The macrofauna consists mainly of molluscs; the Cerro La Salina sites include mostly infaunal thyasirid and lucinid bivalves and only few vesicomyid bivalves; gastropods include Provanna antiqua, the limpet Pyropelta and several vetigastropods. The Belén site is dominated by the elongate vesicomyid bivalve Pleurophopsis lithophagoides. The most common bivalve at the Cerros El Pelado sites is an undetermined, possible vesicomyid, and a smooth provannid gastropod. Biogeographically the faunas are most similar to those of the northwestern United States, as indicated by two joint species; similarities on the genus level (Conchocele, Lucinoma, Pleurophopsis, Provanna, Colus) exist also with Japan and the Caribbean region.