Tolerance of Hordeum marinum accessions to O2 deficiency, salinity and these stresses combined

Background and Aims

When root-zone O₂ deficiency occurs together with salinity, regulation of shoot ion concentrations is compromised even more than under salinity alone. Tolerance was evaluated amongst 34 accessions of Hordeum marinum, a wild species in the Triticeae, to combined salinity and root-zone O₂ deficiency. Interest in H. marinum arises from the potential to use it as a donor for abiotic stress tolerance into wheat.

Methods

Two batches of 17 H. marinum accessions, from (1) the Nordic Gene Bank and (2) the wheat belt of Western Australia, were exposed to 0·2 or 200 mol m⁻³ NaCl in aerated or stagnant nutrient solution for 28–29 d. Wheat (Triticum aestivum) was included as a sensitive check species. Growth, root porosity, root radial O₂ loss (ROL) and leaf ion (Na⁺, K⁺, Cl⁻) concentrations were determined.

Key Results

Owing to space constraints, this report is focused mainly on the accessions from the Nordic Gene Bank. The 17 accessions varied in tolerance; relative growth rate was reduced by 2–38 % in stagnant solution, by 8–42 % in saline solution (aerated) and by 39–71 % in stagnant plus saline treatment. When in stagnant solution, porosity of adventitious roots was 24–33 %; salinity decreased the root porosity in some accessions, but had no effect in others. Roots grown in stagnant solution formed a barrier to ROL, but variation existed amongst accessions in apparent barrier ‘strength’. Leaf Na⁺ concentration was 142–692 µmol g⁻¹ d. wt for plants in saline solution (aerated), and only increased to 247–748 µmol g⁻¹ d. wt in the stagnant plus saline treatment. Leaf Cl⁻ also showed only small effects of stagnant plus saline treatment, compared with saline alone. In comparison with H. marinum, wheat was more adversely affected by each stress alone, and particularly when combined; growth reductions were greater, adventitious root porosity was 21 %, it lacked a barrier to ROL, leaf K⁺ declined to lower levels, and leaf Na⁺ and Cl⁻ concentrations were 3·1–9-fold and 2·8–6-fold higher, respectively, in wheat.

Conclusions

Stagnant treatment plus salinity reduced growth more than salinity alone, or stagnant alone, but some accessions of H. marinum were still relatively tolerant of these combined stresses, maintaining Na⁺ and Cl⁻ ‘exclusion’ even in an O₂-deficient, saline rooting medium.Key words: Aerenchyma, combined salinity and waterlogging, leaf Cl⁻, leaf K⁺, leaf Na⁺, radial O₂ loss, salt tolerance, salinity–waterlogging interaction, sea barleygrass, waterlogging tolerance, wheat, wild Triticeae     

Relationship between body adiposity measures and risk of primary knee and hip replacement for osteoarthritis: a prospective cohort study

Introduction  

Total joint replacement is considered a surrogate measure for symptomatic end-stage osteoarthritis. It is unknown whether the adipose mass and the distribution of adipose mass are associated with the risk of primary knee and hip replacement for osteoarthritis. The aim of the present investigation was to examine this in a cohort study.     

Overexpression of hns in the plant growth‐promoting bacterium Enterobacter cloacae UW5 increases root colonization

Aims: Plant growth‐promoting rhizobacteria (PGPR) introduced into soil often do not compete effectively with indigenous micro‐organisms for plant colonization. The aim of this study was to identify novel genes that are important for root colonization by the PGPR Enterobacter cloacae UW5. Methods and Results: A library of transposon mutants of Ent. cloacae UW5 was screened for mutants with altered ability to colonize canola roots using a thermal asymmetric interlaced (TAIL)‐PCR‐based approach. A PCR fragment from one mutant was reproducibly amplified at greater levels from genomic DNA extracted from mutant pools recovered from seedling roots 6 days after seed inoculation compared to that from the cognate inoculum cultures. Competition assays confirmed that the purified mutant designated Ent. cloacae J28 outcompetes the wild‐type strain on roots but not in liquid cultures. In Ent. cloacae J28, the transposon is inserted upstream of the hns gene. Quantitative RT‐PCR showed that transposon insertion increased expression of hns on roots. Conclusions: These results indicate that increased expression of hns in Ent. cloacae enhances competitive colonization of roots. Significance and Impact of the Study: A better understanding of the genes involved in plant colonization will contribute to the development of PGPR that can compete more effectively in agricultural soils.     

Change in Body Size and Mortality: Results from the Melbourne Collaborative Cohort Study

Background

The association between change in weight or body mass index, and mortality is widely reported, however, both measures fail to account for fat distribution. Change in waist circumference, a measure of central adiposity, in relation to mortality has not been studied extensively.

Methods

We investigated the association between mortality and changes in directly measured waist circumference, hips circumference and weight from baseline (1990–1994) to wave 2 (2003–2007) in a prospective cohort study of people aged 40–69 years at baseline. Cox regression, with age as the time metric and follow-up starting at wave 2, adjusted for confounding variables, was used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for change in body size in relation to mortality from all causes, cardiovascular disease and cancer.

Results

There were 1465 deaths (109 cancer, 242 cardiovascular disease) identified during an average 7.7 years of follow-up from 21 298 participants. Compared to minimal increase in body size, loss of waist circumference (HR: 1.26; 95% CI: 1.09–1.47), weight (1.80; 1.54–2.11), or hips circumference (1.35; 1.15–1.57) were associated with an increased risk of all-cause mortality, particularly for older adults. Weight loss was associated with cardiovascular disease mortality (2.40; 1.57–3.65) but change in body size was not associated with obesity-related cancer mortality.

Conclusion

This study confirms the association between weight loss and increased mortality from all-causes for older adults. Based on evidence from observational cohort studies, weight stability may be the recommended option for most adults, especially older adults.     

Cooperative personalities and social niche specialization in female meerkats

The social niche specialization hypothesis predicts that group‐living animals should specialize in particular social roles to avoid social conflict, resulting in alternative life‐history strategies for different roles. Social niche specialization, coupled with role‐specific life‐history trade‐offs, should thus generate between‐individual differences in behaviour that persist through time, or distinct personalities, as individuals specialize in particular nonoverlapping social roles. We tested for support for the social niche specialization hypothesis in cooperative personality traits in wild female meerkats (Suricata suricatta) that compete for access to dominant social roles. As cooperation is costly and dominance is acquired by heavier females, we predicted that females that ultimately acquired dominant roles would show noncooperative personality types early in life and before and after role acquisition. Although we found large individual differences in repeatable cooperative behaviours, there was no indication that individuals that ultimately acquired dominance differed from unsuccessful individuals in their cooperative behaviour. Early‐life behaviour did not predict social role acquisition later in life, nor was cooperative behaviour before and after role acquisition correlated in the same individuals. We suggest that female meerkats do not show social niche specialization resulting in cooperative personalities, but that they exhibit an adaptive response in personality at role acquisition.     

Cytochrome c3 Mutants of Desulfovibrio desulfuricans

To explore the physiological role of tetraheme cytochrome c₃ in the sulfate-reducing bacterium Desulfovibrio desulfuricans G20, the gene encoding the preapoprotein was cloned, sequenced, and mutated by plasmid insertion. The physical analysis of the DNA from the strain carrying the integrated plasmid showed that the insertion was successful. The growth rate of the mutant on lactate with sulfate was comparable to that of the wild type; however, mutant cultures did not achieve the same cell densities. Pyruvate, the oxidation product of lactate, served as a poor electron source for the mutant. Unexpectedly, the mutant was able to grow on hydrogen-sulfate medium. These data support a role for tetraheme cytochrome c₃ in the electron transport pathway from pyruvate to sulfate or sulfite in D. desulfuricans G20.     

Cbp1, a fungal virulence factor under positive selection,forms an effector complex that drives macrophage lysis

Intracellular pathogens secrete effectors to manipulate their host cells. Histoplasma capsulatum (Hc) is a fungal intracellular pathogen of humans that grows in a yeast form in the host. Hc yeasts are phagocytosed by macrophages, where fungal intracellular replication precedes macrophage lysis. The most abundant virulence factor secreted by Hc yeast cells is Calcium Binding Protein 1 (Cbp1), which is absolutely required for macrophage lysis. Here we take an evolutionary, structural, and cell biological approach to understand Cbp1 function. We find that Cbp1 is present only in the genomes of closely related dimorphic fungal species of the Ajellomycetaceae family that lead primarily intracellular lifestyles in their mammalian hosts (Histoplasma, Paracoccidioides, and Emergomyces), but not conserved in the extracellular fungal pathogen Blastomyces dermatitidis. We observe a high rate of fixation of non-synonymous substitutions in the Cbp1 coding sequences, indicating that Cbp1 is under positive selection. We determine the de novo structures of Hc H88 Cbp1 and the Paracoccidioides americana (Pb03) Cbp1, revealing a novel “binocular” fold consisting of a helical dimer arrangement wherein two helices from each monomer contribute to a four-helix bundle. In contrast to Pb03 Cbp1, we show that Emergomyces Cbp1 orthologs are unable to stimulate macrophage lysis when expressed in the Hc cbp1 mutant. Consistent with this result, we find that wild-type Emergomyces africanus yeast are able to grow within primary macrophages but are incapable of lysing them. Finally, we use subcellular fractionation of infected macrophages and indirect immunofluorescence to show that Cbp1 localizes to the macrophage cytosol during Hc infection, making this the first instance of a phagosomal human fungal pathogen directing an effector into the cytosol of the host cell. We additionally show that Cbp1 forms a complex with Yps-3, another known Hc virulence factor that accesses the cytosol. Taken together, these data imply that Cbp1 is a fungal virulence factor under positive selection that localizes to the cytosol to trigger host cell lysis.     

Synthesis of β-Peptide Standards for Use in Model Prebiotic Reactions

A one-pot method was developed for the preparation of a series of β-alanine standards of moderate size (2 to ≥12 residues) for studies concerning the prebiotic origins of peptides. The one-pot synthesis involved two sequential reactions: (1) dry-down self-condensation of β-alanine methyl ester, yielding β-alanine peptide methyl ester oligomers, and (2) subsequent hydrolysis of β-alanine peptide methyl ester oligomers, producing a series of β-alanine peptide standards. These standards were then spiked into a model prebiotic product mixture to confirm by HPLC the formation of β-alanine peptides under plausible reaction conditions. The simplicity of this approach suggests it can be used to prepare a variety of β-peptide standards for investigating differences between α- and β-peptides in the context of prebiotic chemistry.