Effects of elevated atmospheric CO2 on net ecosystem CO2 exchange of a scrub–oak ecosystem

We report the results of a 2‐year study of effects of the elevated (current ambient plus 350 μmol CO₂ mol^?1) atmospheric CO₂ concentration (C_a) on net ecosystem CO₂ exchange (NEE) of a scrub–oak ecosystem. The measurements were made in open‐top chambers (OTCs) modified to function as open gas‐exchange systems. The OTCs enclosed samples of the ecosystem (ca. 10 m² surface area) that had regenerated after a fire, 5 years before, in either current ambient or elevated C_a. Throughout the study, elevated C_a increased maximum NEE (NEE_max) and the apparent quantum yield of the NEE (φ_NEE) during the photoperiod. The magnitude of the stimulation of NEE_max, expressed per unit ground area, was seasonal, rising from 50% in the winter to 180% in the summer. The key to this stimulation was effects of elevated C_a, and their interaction with the seasonal changes in the environment, on ecosystem leaf area index, photosynthesis and respiration. The separation of these factors was difficult. When expressed per unit leaf area the stimulation of the NEE_max ranged from 7% to 60%, with the increase being dependent on increasing soil water content (W_soil). At night, the CO₂ effluxes from the ecosystem (NEE_night) were on an average 39% higher in elevated C_a. However, the increase varied between 6% and 64%, and had no clear seasonality. The partitioning of NEE_night into its belowground (R_below) and aboveground (R_above) components was carried out in the winter only. A 35% and 27% stimulation of NEE_night in December 1999 and 2000, respectively, was largely due to a 26% and 28% stimulation of R_below in the respective periods, because R_below constituted ca. 87% of NEE_night. The 37% and 42% stimulation of R_above in December 1999 and 2000, respectively, was less than the 65% and 80% stimulation of the aboveground biomass by elevated C_a at these times. An increase in the relative amount of the aboveground biomass in woody tissue, combined with a decrease in the specific rate of stem respiration of the dominant species Quercus myrtifolia in elevated C_a, was responsible for this effect. Throughout this study, elevated C_a had a greater effect on carbon uptake than on carbon loss, in terms of both the absolute flux and relative stimulation. Consequently, for this scrub–oak ecosystem carbon sequestration was greater in the elevated C_a during this 2‐year study period.     

Processing of secretogranin II by prohormone convertases: Importance ofPC1 in generation of secretoneurin

Secretoneurin is a recently characterized neuropeptidepresent in the primary amino acid sequence of secretogranin II. We investigated the proteolytic processing of secretogranin II by prohormone convertases in vivo in a cellular system using the vaccinia virus system. Both PC1 and PC2 can cleave the secretogranin II precursor at sites of pairs of basic amino acids to yield intermediate-sized fragments. Other convertases like PACE4, PC5 and furin were not active. For the formation of the free neuropeptide secretoneurin a different pattern was found. Only PC1 but none of the other convertases tested including PC2 were capable of generating secretoneurin. Our results demonstrate that the prohormone convertases PC1 and PC2 are involved in proteolytic processing of secretogranin II. The neuropeptide secretoneurin can only be generated by PC1 suggesting tissue-specific processing of secretogranin II in neurons expressing different subsets of the prohormone convertases.     

The Psb27 assembly factor binds to the CP43 complex of photosystem II in the cyanobacterium Synechocystis sp. PCC 6803

We have investigated the location of the Psb27 protein and its role in photosystem (PS) II biogenesis in the cyanobacterium Synechocystis sp. PCC 6803. Native gel electrophoresis revealed that Psb27 was present mainly in monomeric PSII core complexes but also in smaller amounts in dimeric PSII core complexes, in large PSII supercomplexes, and in the unassembled protein fraction. We conclude from analysis of assembly mutants and isolated histidine-tagged PSII subcomplexes that Psb27 associates with the "unassembled" CP43 complex, as well as with larger complexes containing CP43, possibly in the vicinity of the large lumenal loop connecting transmembrane helices 5 and 6 of CP43. A functional role for Psb27 in the biogenesis of CP43 is supported by the decreased accumulation and enhanced fragmentation of unassembled CP43 after inactivation of the psb27 gene in a mutant lacking CP47. Unexpectedly, in strains unable to assemble PSII, a small amount of Psb27 comigrated with monomeric and trimeric PSI complexes upon native gel electrophoresis, and Psb27 could be copurified with histidine-tagged PSI isolated from the wild type. Yeast two-hybrid assays suggested an interaction of Psb27 with the PsaB protein of PSI. Pull-down experiments also supported an interaction between CP43 and PSI. Deletion of psb27 did not have drastic effects on PSII assembly and repair but did compromise short-term acclimation to high light. The tentative interaction of Psb27 and CP43 with PSI raises the possibility that PSI might play a previously unrecognized role in the biogenesis/repair of PSII.     

Antisense-inhibition of ADP-glucose pyrophosphorylase in Vicia narbonensis seeds increases soluble sugars and leads to higher water and nitrogen uptake

We previously reported on Vicia narbonensis seeds with largely decreased alpha- D-glucose-1-phosphate adenyltransferase (AGP; EC 2.7.7.27) due to antisense inhibition [H. Weber et al. (2000) Plant J 24:33-43]. In an extended biochemical analysis we show here that in transgenic seeds both AGP activity and ADP-glucose levels were strongly decreased but starch was only moderately reduced and contained less amylose. The flux control coefficient of AGP to starch accumulation was as low as 0.08, i.e. AGP exerts low control on starch biosynthesis in Vicia seeds. Mature cotyledons of antisense seeds had increased contents of lipids, nitrogen and sulfur. The protein content was higher due, in particular, to increased sulfur-rich albumins. Globulin fractions of storage proteins had a lower ratio of legumin to vicilin. Isolated cotyledons partitioned less [14C]sucrose into starch and more into soluble sugars with no change in the protein fraction. Respiration of isolated cotyledons and activities of the major glycolytic and carbohydrate-metabolizing enzymes were not affected. Sucrose and the hexose-phosphate pool were increased but UDP-glucose, 3-phosphoglyceric acid, phospho enolpyruvate, pyruvate, ATP and ADP were unchanged or even lower, indicating that carbon partitioning changed from starch to sucrose without affecting the glycolytic and respiratory pathways. Soluble compounds were increased but osmolality remained unchanged, indicating compensatory water influx resulting in higher water contents. Developmental patterns of water and nitrogen accumulation suggest a coupled uptake of amino acids and water into cotyledons. We conclude that, due to higher water uptake, transgenic cotyledons take up more amino acids, which become available for protein biosynthesis leading to a higher protein content. Obviously, a substantial part of amino acid uptake into Vicia seeds occurs passively and is osmotically controlled and driven by water influx.     

Developing and analyzing idealized models for molecular recognition

We study equilibrium aspects of molecular recognition of two biomolecules using idealized model systems and methods from statistical physics. Starting from the basic experimental findings we demonstrate exemplarily how an idealized coarse-grained model for the investigation of molecular recognition of two biomolecules can be developed. In addition we provide details regarding two model systems for the recognition of a flexible and a rigid biomolecule respectively, the latter taking into account conformational changes. We focus particularly on the interplay and influence of the correlations of the residue distributions of the biomolecules on the recognition process.     

DNA extraction from bronchial aspirates for molecular cytology: which method to take?

OBJECTIVE: To date, there are only few systematic reports on the quality of DNA extracted from routine diagnostic cytologic specimens. It was the aim of the present study to evaluate the ability of 50% ethanol/2% carbowax (Saccomanno fixative) to preserve bronchial secretions with high quality genomic DNA as well as to compare different DNA extraction methods. METHODS: DNA was extracted from 45 bronchial aspirates by four different extraction protocols. Beside DNA yield, DNA quality with regard to purity, integrity, and PCR success rate were investigated. RESULTS: No fragmentation of sample DNA due to the fixative was detected. It was preserved as high molecular weight DNA. DNA yield, purity, and integrity were dependent on the DNA extraction method to some extend. Irrespective of the DNA extraction method the PCR success rate for amplification of beta-globin gene fragments (268, 536, and 989 bp) was 100%. CONCLUSION: A fixative containing 50% ethanol/2% carbowax preserves high quality DNA which is well suited for PCR-based assays regardless of the extraction protocol used. The selection of the DNA extraction protocol has to be adjusted to the circumstances of application.     

Masculinized dominant females in a cooperatively breeding species

The molecular mechanisms underlying complex social behaviours such as dominance are largely unknown. Studying the cooperatively breeding African cichlid Neolamprologus pulcher, we show that dominant females were similar to dominant males in dominance behaviour, high testosterone levels and brain arginine vasotocin expression (a neuropeptide involved in vertebrate territorial, reproductive and social behaviours) compared to subordinate helpers, but had lower levels of 11-ketotestosterone than males. Furthermore, brain gene expression profiles of dominant females were most similar to those of the males (independent of social rank). Dominant breeder females are masculinized at the molecular and hormonal level while being at the same time reproductively competent, suggesting a modular organization of molecular and endocrine functions, allowing for sex-specific regulation.     

Cathemerality and lunar periodicity of activity rhythms in owl monkeys of the Argentinian Chaco

Although most South American owl monkeys are mainly nocturnal, Aotus azarai azarai of the Argentinean Chaco regularly shows diurnal activity. In this study we examined the strong influence of moonlight on its diurnal and nocturnal activity, as well as the interaction of moonlight effects with other exogenous factors. We analyzed long-term automated activity recordings obtained with accelerometer collars from 7 owl monkeys during 2003 and 2004. Our data show marked lunar periodic and seasonal modulations of the owl monkeys' activity pattern. On full moon days they were active throughout the whole night and displayed reduced activity during the day. With a new moon, activity decreased during the dark portion of the night, peaked during dawn and dusk and extended over the bright morning hours. Waxing and waning moons induced a significant increase in activity during the first and the second half of the night, respectively. During the cold winter months the monkeys displayed twice as much activity throughout the warmer bright part of the day than during the rest of the year. These findings indicate that A. a. azarai is mainly a dark-active species, but is still able to shift a considerable portion of activity into the bright part of the day if unfavourable lighting and/or temperature conditions prevail during the night.     

The molecular evolution of sperm zonadhesin

Based on pioneering work of Hardy and Garbers, zonadhesin has become one of the best studied sperm ligands in boreoeutherian mammals, both from a biochemical and evolutionary perspective. Zonadhesin is a mosaic-type protein that localizes to the apical head of spermatozoa. In pig, cattle, rabbit and primates, zonadhesin precursor essentially consists of two or three MAM (meprin/A5 antigen/mu receptor tyrosine phosphatase) domains, one mucin-like domain, one incomplete and four complete D domains (homologous to vWFD). Mouse zonadhesin is distinguished from this general pattern by 20 extra partial D3 domains. While concerted evolution drives the divergence of the mucin-like domain in the ortholog comparison, MAM and D domains mainly diverge under the influence of drift and positive selection, both in the paralog and ortholog comparison. As can be seen particularly well within a putative binding region in the most C-terminal MAM domain, positive selection not only causes amino acid exchanges, but also promotes changes in the pattern of predicted posttranslational modification. Moving window and correlation analyses of sequence evolution and sexual body dimorphism further suggest that sexual selection, especially sperm competition, drives zonadhesin divergence. However, considering its zona pellucida avidity, female cryptic choice might as well contribute to zonadhesin evolution. Despite the general tendency for divergence of zonadhesin, conservation by negative selection dominates the evolution of most codon sites. In accordance, the distribution of EGF (epidermal growth factor)-like motifs, DP-doublets, single cysteines and CGLC motifs suggests a wide conservation of processing, folding and oligomerization of zonadhesin in pig, rabbit and primates.