The statistics of calcium-mediated focal excitations on a one-dimensional cable

It is well known that various cardiac arrhythmias are initiated by an ill-timed excitation that originates from a focal region of the heart. However, up to now, it is not known what governs the timing, location, and morphology of these focal excitations. Recent studies have shown that these excitations can be caused by abnormalities in the calcium (Ca) cycling system. However, the cause-and-effect relationships linking subcellular Ca dynamics and focal activity in cardiac tissue is not completely understood. In this article, we present a minimal model of Ca-mediated focal excitations in cardiac tissue. This model accounts for the stochastic nature of spontaneous Ca release on a one-dimensional cable of cardiac cells. Using this model, we show that the timing of focal excitations is equivalent to a first passage time problem in a spatially extended system. In particular, we find that for a short cable the mean first passage time increases exponentially with the number of cells in tissue, and is critically dependent on the ratio of inward to outward currents near the threshold for an action potential. For long cables excitations occurs due to ectopic foci that occur on a length scale determined by the minimum length of tissue that can induce an action potential. Furthermore, we find that for long cables the mean first passage time decreases as a power law in the number cells. These results provide precise criteria for the occurrence of focal excitations in cardiac tissue, and will serve as a guide to determine the propensity of Ca-mediated triggered arrhythmias in the heart.     

Plant improvement for tolerance to aluminum in acid soils – a review

Development of acid soils that limit crop production is an increasing problem worldwide. Many factors contribute to phytotoxicity of these soils, however, in acid soils with a high mineral content, aluminum (Al) is the major cause of toxicity. The target of Al toxicity is the root tip, in which Al exposure causes inhibition of cell elongation and cell division, leading to root stunting accompanied by reduced water and nutrient uptake. Natural variation for Al tolerance has been identified in many crop species and in some crops tolerance to Al has been introduced into productive, well-adapted varieties. Aluminum tolerance appears to be a complex multigenic trait. Selection methodology remains a limiting factor in variety development as all methods have particular drawbacks. Molecular markers have been associated with Al tolerance genes or quantitative trait loci in Arabidopsis and in several crops, which should facilitate development of additional tolerant varieties. A variety of genes have been identified that are induced or repressed upon Al exposure. Most induced genes characterized so far are not specific to Al exposure but are also induced by other stress conditions. Ectopic over-expression of some of these genes has resulted in enhanced Al tolerance. Additionally, expression of genes involved in organic acid synthesis has resulted in enhanced production of organic acids and an associated increase in Al tolerance. This review summarizes the three main approaches that have been taken to develop crops with Al tolerance: recurrent selection and breeding, development of Al tolerant somaclonal variants and ectopic expression of transgenes to reduce Al uptake or limit damage to cells by Al.     

Palladium(II) and platinum(II) complexes with polypyridylbenzene ligands

The ligands 1,3-bis(3-pyridyl)benzene (1), 1,3-bis(4-pyridyl)benzene (2) and 1,3,5-tris(4-pyridyl)benzene (3) have been prepared by Stille coupling of 3- or 4-trimethylstannylpyridine with the appropriate bromoarene. Ligands 1 and 2 react with [M(OTf)₂(dppp)] (M=Pd, Pt) to produce the dipalladium- or diplatinum-containing macrocycles [M₂(μ-1)₂(dppp)₂](OTf)₄ or [M₂(μ-2)₂(dppp)₂](OTf)₄. These have been characterized by NMR spectroscopy and mass spectrometry and, in the case of [Pd₂(μ-1)₂(dppp)₂](OTf)₄, by X-ray crystallography. The molecular structure of the [Pd₂(μ-1)₂(dppp)₂]⁴⁺ cation reveals a shallow arrangement of the aromatic rings, with the palladium atoms lying above and below. The tridentate ligand 3 reacts with [Pd(OTf)₂(dppp)] to produce a trimetallic species of the form [Pd₃(μ₃-3)₂(dppp)₃](OTf)₆.     

Identification and genetic diversity of two invasive <Emphasis Type="Italic">Pissodes</Emphasis> spp. Germar (Coleoptera: Curculionidae) in their introduced range in the southern hemisphere

During the first half of the twentieth century, two accidental cases of introduction of Pissodes weevils were recorded from the southern hemisphere. The weevils in South Africa were identified as the deodar weevil (Pissodes nemorensis) and those in South America as the small banded pine weevil (Pissodes castaneus). Wide distribution of the two species in their invasive range, general difficulty in identifying some Pissodes spp., and the varying feeding and breeding behaviours of the species in South Africa has necessitated better evidence of species identity and genetic diversity of both species and population structure of the species in South Africa. Barcoding and the Jerry-to-Pat region of the COI gene were investigated. Morphometric data of the South African species was analysed. Our results confirmed the introduction of only one Pissodes species of North American origin to South Africa. However, this species is not P. nemorensis, but an unrecognized species of the P. strobi complex or a hybrid between P. strobi and P. nemorensis. Only P. castaneus, of European origin, was identified from South America. We identified ten mitochondrial DNA haplotypes from South Africa with evidence of moderate genetic structure among geographic populations. Terminal leader and bole-feeding weevils did not differ at the COI locus. A single haplotype was identified from populations of P. castaneus in South America. Results of the present study will have implications on quarantine, research and management of these insect species.     

Prevalence and associated factors of non-exclusive breastfeeding of infants during the first six months in rural area of Sorro District,Southern Ethiopia: a cross-sectional study

Background

Despite the importance of exclusive breastfeeding, a wide number of mothers practice non-exclusive breastfeeding in Ethiopia. Therefore, this study aimed to identify prevalence and factors associated with non-exclusive breastfeeding in rural area of Sorro District in Southern Ethiopia.

Methods

A community based cross-sectional study was undertaken. The study population consisted of all mothers with infants aged of 0–5 months living in the randomly selected kebeles (lowest administrative unit) in the rural area of Sorro District. The study was conducted on 602 mothers with infants selected by using systematic sampling method from 12 August to 23 August 2015. Both bivariate and multivariable logistic regression analysis were used to assess the association between the study variables and to control possible confounding.

Results

The prevalence of non-exclusive breastfeeding in infants under 6 months was 49.4 %. Being currently unmarried [AOR (95 % CI)?=?3.85 (1.44, 10.27)], index infant’s age being within 2–3 months [AOR (95 % CI)?=?3.63 (2.06, 6.36)] and 4–5 months [AOR (95 % CI) =10.29 (5.60, 18.92)] compared to infant age 0–1 month, initiation of breastfeeding after 1 h of birth [AOR (95 % CI)?=?2.11 (1.37, 3.24)], no antenatal care visit during their last pregnancy [AOR (95 % CI) =2.60 (1.64, 4.10)] and no postnatal care visit after delivery [AOR (95 % CI)?=?1.90 (1.19, 3.04)] were significantly associated with non-exclusive breastfeeding.

Conclusion

In this study a large proportion of mothers with infants under 6 months of age were practicing non-exclusive breastfeeding which is one of the major risks for infant and child morbidity and mortality. Taking measures on identified associated factors with non-exclusive breastfeeding was recommended to improve the status of exclusive breastfeeding in the study area.

     

The phytomelanin layer in traditional members of Bidens and Coreopsis and phylogeny of the Coreopsideae (Compositae)

The phytomelanin layer on the pericarp of cypselae (achenes) of many members of traditional Bidens and Coreopsis, both considered polyphyletic, was studied with the help of scanning electron (SEM) and light (LM) microscopes. It is found to be more prominent in taxa kept within Bidens than in Coreopsis. The black ‘peg‐like’ phytomelanin found in traditional members of Bidens is also found in some members of Coreopsis. Some traditional members of Coreopsis display distinctive pericarp morphology but lack phytomelanin. The pericarp in Bidens is striated, i.e. it is interrupted by longitudinal bands of parenchyma through which the embryo emerges during seed germination. No striation was found in cypselae of traditional Coreopsis. Emergence of the seed in taxa with this type of pericarp morphology is observed to be by rupturing the carpel wall along the sutures. Characteristic morphology of the phytomelanin layer and other cellular secretions on the pericarp in representative species of these genera and segregates as well as the probable adaptive value of this layer and that of the parenchyma is discussed. Coreopsis sect. Tuckermannia (Nutt.) Blake, C. sect. Pugiopappus (A. Gray) Blake, and C. sect. Euleptosyne (A. Gray) Blake, are elevated to the genus Leptosyne DC., while Coreopsis sect. Electra (DC.) Blake is returned to Electra DC. A key to the segregate genera and the remaining sections of Coreopsis as well as new combinations and synonyms are provided.     

Systematics of Catenulifera (anamorphic Hyaloscyphaceae) with an assessment of the phylogenetic position of Phialophora hyalina

Catenulifera, typified by C. rhodogena (=Scopulariopsis rhodogena), was established to accommodate the anamorphs of Hyphodiscus (Ascomycota, Helotiales) and to delimit these taxa from members of Phialophora section Catenulatae. Catenulifera rhodogena has been inferred as monophyletic, but its relationship to ascomycetes with poorly differentiated phialidic anamorphs remains enigmatic. To test the hypothesis that C. rhodogena is closely related to morphologically similar species of Phialophora and to further explore the systematics of Catenulifera, we analyzed nuclear rDNA and β-tubulin gene sequences of isolates identified as C. rhodogena, Hyphodiscus hymeniophilus, P. brachyconia, P. brevicollaris and P. hyalina. ITS-LSU and ITS-LSU-β-tubulin phylogenies positioned all isolates except P. hyalina in a single, well-supported clade that consisted of three subclades. Subclade 1 included fungicolous isolates of C. rhodogena and H. hymeniophilus that did not fluoresce when exposed to long-wave UV light. Subclade 2 contained fungicolous and lignicolous strains of C. rhodogena that produced fluorescent colonies and possessed a 366bp indel in the LSU rRNA gene. Neither lineage encompassed the ex-type strains of Cistella rubescens (=H. hymeniophilus) or S. rhodogena, but the former isolate was inferred as sister to Subclade 2. Subclade 3 included all isolates of P. brachyconia, a species recognized here as C. brachyconia comb. nov. A fourth isolate of P. brachyconia that was extralimital to Subclade 3 is described as C. luxurians sp. nov. The positions of C. brevicollaris comb. nov., a species based on P. brevicollaris, and C. luxurians were not resolved in the ITS-LSU phylogeny. P. hyalina is not closely related to Catenulifera.     

Mechanism of Action of an Imidopiperidine Inhibitor of Human Polynucleotide Kinase/Phosphatase

The small molecule, 2-(1-hydroxyundecyl)-1-(4-nitrophenylamino)-6-phenyl-6,7a-dihydro-1H-pyrrolo[3,4-b]pyridine-5,7(2H,4aH)-dione (A12B4C3), is a potent inhibitor of the phosphatase activity of human polynucleotide kinase/phosphatase (PNKP) in vitro. Kinetic analysis revealed that A12B4C3 acts as a noncompetitive inhibitor, and this was confirmed by fluorescence quenching, which showed that the inhibitor can form a ternary complex with PNKP and a DNA substrate, i.e. A12B4C3 does not prevent DNA from binding to the phosphatase DNA binding site. Conformational analysis using circular dichroism, UV difference spectroscopy, and fluorescence resonance energy transfer all indicate that A12B4C3 disrupts the secondary structure of PNKP. Investigation of the potential site of binding of A12B4C3 to PNKP using site-directed mutagenesis pointed to interaction between Trp⁴⁰² of PNKP and the inhibitor. Cellular studies revealed that A12B4C3 sensitizes A549 human lung cancer cells to the topoisomerase I poison, camptothecin, but not the topoisomerase II poison, etoposide, in a manner similar to small interfering RNA against PNKP. A12B4C3 also inhibits the repair of DNA single and double strand breaks following exposure of cells to ionizing radiation, but does not inhibit two other key strand-break repair enzymes, DNA polymerase β or DNA ligase III, providing additional evidence that PNKP is the cellular target of the inhibitor.