Estimating canopy gross primary production by combining phloem stable isotopes with canopy and mesophyll conductances

Gross primary production (GPP) is a key component of the forest carbon cycle. However, our knowledge of GPP at the stand scale remains uncertain, because estimates derived from eddy covariance (EC) rely on semi-empirical modelling and the assumptions of the EC technique are sometimes not fully met. We propose using the sap flux/isotope method as an alternative way to estimate canopy GPP, termed GPP_iso/SF, at the stand scale and at daily resolution. It is based on canopy conductance inferred from sap flux and intrinsic water-use efficiency estimated from the stable carbon isotope composition of phloem contents. The GPP_iso/SF estimate was further corrected for seasonal variations in photosynthetic capacity and mesophyll conductance. We compared our estimate of GPP_iso/SF to the GPP derived from PRELES, a model parameterized with EC data. The comparisons were performed in a highly instrumented, boreal Scots pine forest in northern Sweden, including a nitrogen fertilized and a reference plot. The resulting annual and daily GPP_iso/SF estimates agreed well with PRELES, in the fertilized plot and the reference plot. We discuss the GPP_iso/SF method as an alternative which can be widely applied without terrain restrictions, where the assumptions of EC are not met.     

Factors affecting sedimentational separation of bacteria from blood

Rapid diagnosis of blood infections requires fast and efficient separation of bacteria from blood. We have developed spinning hollow disks that separate bacteria from blood cells via the differences in sedimentation velocities of these particles. Factors affecting separation included the spinning speed and duration, and disk size. These factors were varied in dozens of experiments for which the volume of separated plasma, and the concentration of bacteria and red blood cells (RBCs) in separated plasma were measured. Data were correlated by a parameter of characteristic sedimentation length, which is the distance that an idealized RBC would travel during the entire spin. Results show that characteristic sedimentation length of 20 to 25 mm produces an optimal separation and collection of bacteria in plasma. This corresponds to spinning a 12-cm-diameter disk at 3,000 rpm for 13 s. Following the spin, a careful deceleration preserves the separation of cells from plasma and provides a bacterial recovery of about 61 ± 5%.     

Distinct clinical phenotypes associated with a mutation in the mitochondrial translation elongation factor EFTs

The 13 polypeptides encoded in mitochondrial DNA (mtDNA) are synthesized in the mitochondrial matrix on a dedicated protein-translation apparatus that resembles that found in prokaryotes. Here, we have investigated the genetic basis for a mitochondrial protein-synthesis defect associated with a combined oxidative phosphorylation enzyme deficiency in two patients, one of whom presented with encephalomyopathy and the other with hypertrophic cardiomyopathy. Sequencing of candidate genes revealed the same homozygous mutation (C997T) in both patients in TSFM, a gene coding for the mitochondrial translation elongation factor EFTs. EFTs functions as a guanine nucleotide exchange factor for EFTu, another translation elongation factor that brings aminoacylated transfer RNAs to the ribosomal A site as a ternary complex with guanosine triphosphate. The mutation predicts an Arg333Trp substitution at an evolutionarily conserved site in a subdomain of EFTs that interacts with EFTu. Molecular modeling showed that the substitution disrupts local subdomain structure and the dimerization interface. The steady-state levels of EFTs and EFTu in patient fibroblasts were reduced by 75% and 60%, respectively, and the amounts of assembled complexes I, IV, and V were reduced by 35%–91% compared with the amounts in controls. These phenotypes and the translation defect were rescued by retroviral expression of either EFTs or EFTu. These data clearly establish mutant EFTs as the cause of disease in these patients. The fact that the same mutation is associated with distinct clinical phenotypes suggests the presence of genetic modifiers of the mitochondrial translation apparatus.     

SPAK Isoforms and OSR1 Regulate Sodium-Chloride Co-transporters in a Nephron-specific Manner

STE20/SPS-1-related proline-alanine-rich protein kinase (SPAK) and oxidative stress-related kinase (OSR1) activate the potassium-dependent sodium-chloride co-transporter, NKCC2, and thiazide-sensitive sodium-chloride cotransporter, NCC, in vitro, and both co-localize with a kinase regulatory molecule, Cab39/MO25α, at the apical membrane of the thick ascending limb (TAL) and distal convoluted tubule (DCT). Yet genetic ablation of SPAK in mice causes a selective loss of NCC function, whereas NKCC2 becomes hyperphosphorylated. Here, we explore the underlying mechanisms in wild-type and SPAK-null mice. Unlike in the DCT, OSR1 remains at the TAL apical membrane of KO mice where it is accompanied by an increase in the active, phosphorylated form of AMP-activated kinase. We found an alterative SPAK isoform (putative SPAK2 form), which modestly inhibits co-transporter activity in vitro, is more abundant in the medulla than the cortex. Thus, enhanced NKCC2 phosphorylation in the SPAK knock-out may be explained by removal of inhibitory SPAK2, sustained activity of OSR1, and activation of other kinases. By contrast, the OSR1/SPAK/M025α signaling apparatus is disrupted in the DCT. OSR1 becomes largely inactive and displaced from M025α and NCC at the apical membrane, and redistributes to dense punctate structures, containing WNK1, within the cytoplasm. These changes are paralleled by a decrease in NCC phosphorylation and a decrease in the mass of the distal convoluted tubule, exclusive to DCT1. As a result of the dependent nature of OSR1 on SPAK in the DCT, NCC is unable to be activated. Consequently, SPAK^−/− mice are highly sensitive to dietary salt restriction, displaying prolonged negative sodium balance and hypotension.     

Molecular control of cold acclimation in trees

Frost tolerance is an acquired characteristic of plants that is induced in response to environmental cues preceding the onset of freezing temperatures and activation of a cold acclimation program. In addition to transient acclimation to low non-freezing temperatures and enhancing survival to short frost episodes during the growth season, perennial woody plants need additionally to survive the cold winter months. Trees have evolved a complex dynamic process controlling the development of dormancy and freezing tolerance that secures accurate initiation and termination of the overwintering process. Although the phenology of overwintering has been known for decades, only recently has there been progress in elucidating the molecular mechanisms of dormancy and freezing tolerance development in perennial plants. Current molecular and genomic studies indicate that herbaceous annual and woody perennial plants share similar cold acclimation mechanisms. Both the signal processes controlling cold acclimation and the cold-regulated target genes appear to be shared by herbaceous and woody plants. However, the dormancy development during overwintering brings new players in the molecular control of seasonal cold acclimation of woody perennials.     

Cold acclimation in silver birch (Betula pendula). Development of freezing tolerance in different tissues and climatic ecotypes

A number of environmental cues including short day photoperiod (SD) and low temperature (LT) are known to interact in triggering growth cessation, cold acclimation and other adaptive responses in temperate-zone tree species. Proper timing of these responses is particularly important for survival of trees in the boreal and subarctic regions. Therefore, we used a northern tree species, silver birch ( Betula pendula Roth) as an experimental model to investigate the effect of SD and LT on development of freezing tolerance and on levels of endogenous abscisic acid (ABA) in short-term experiments under controlled conditions. We characterized differences in SD and LT-induced cold acclimation between three different climatic ecotypes from southern, central and northern habitats. The results demonstrated that cold acclimation was rapidly triggered by exposing the plants to SD or LT, and that a combination of the different treatments had an additive effect on freezing tolerance. Freezing tolerance induction was not uniform in the different tissues, the buds and leaves developed freezing tolerance more rapidly than the stem, and the young leaves had a higher freezing tolerance than the old leaves. The ability of the leaves to respond to SD and LT and similarity of the bud and leaf responses indicate that birch leaves provide a rapid and convenient system for studies on molecular mechanisms of cold acclimation. Development of freezing tolerance was dependent on the climatic ecotype, the northern ecotype was clearly more responsive to both SD and LT than the two more southern ecotypes. Development of freezing tolerance induced by SD and LT was accompanied by transient changes in ABA levels. These alterations in ABA levels were ecotype-dependent, the northern ecotype reacting more strongly to the environmental cues.     

Regeneration by seeds in alpine meadow and heath vegetation in sub‐arctic Finland

Abstract. This paper compares the regeneration by seeds of heath and meadow and studies relationships between the floristic composition of phases in the regeneration pathway. Seed densities in the seed rain and seed bank as well as the densities of emerged seedlings in gaps and in closed vegetation were greater in the meadow than in the heath. In the heath, environmental constraints hindered seedling emergence almost completely so seeds accumulated in the seed bank. In the meadow, the decrease in the seed bank was due to high seedling emergence. Within both plant communities, seedling emergence in gaps and in closed vegetation was comparable. In the meadow, the seed rain and seedling emergence in gaps, as well as the seed bank and seedling emergence in gaps were positively correlated. Differences in seed and adult plant sizes were reasons for the low correlation between the standing vegetation and the other phases. In DCA ordination the first axis separated the phase of seedling emergence in closed vegetation and seed bank. The second axis separated the standing vegetation from the other phases. The structure of the seed rain was more heterogeneous than that of other phases. In the heath, the standing vegetation and the seed rain were positively correlated. The ordination of these phases reflected the patchiness of standing vegetation and the ability of the diaspores of Betula nana to disperse over long distances.     

Fecal Microbiota Composition and Frailty

The relationship between fecal microbiota composition and frailty in the elderly was studied. Fecal samples from volunteers with high frailty scores showed a significant reduction in the number of lactobacilli (26-fold). At much higher population levels, both the Bacteroides/Prevotella (threefold) and the Faecalibacterium prausnitzii (fourfold) groups showed a significant reduction in percentage of total number of hybridizable bacteria in the elderly with high frailty scores. In contrast to this, the number of Enterobacteriaceae was significantly higher (sevenfold) in samples from very frail volunteers.     

Men report stronger attraction to femininity in women's faces when their testosterone levels are high

Many studies have shown that women's judgments of men's attractiveness are affected by changes in levels of sex hormones. However, no studies have tested for associations between changes in levels of sex hormones and men's judgments of women's attractiveness. To investigate this issue, we compared men's attractiveness judgments of feminized and masculinized women's and men's faces in test sessions where salivary testosterone was high and test sessions where salivary testosterone was relatively low. Men reported stronger attraction to femininity in women's faces in test sessions where salivary testosterone was high than in test sessions where salivary testosterone was low. This effect was found to be specific to judgments of opposite-sex faces. The strength of men's reported attraction to femininity in men's faces did not differ between high and low testosterone test sessions, suggesting that the effect of testosterone that we observed for judgments of women's faces was not due to a general response bias. Collectively, these findings suggest that changes in testosterone levels contribute to the strength of men's reported attraction to femininity in women's faces and complement previous findings showing that testosterone modulates men's interest in sexual stimuli.