Dynamics of CO2 efflux from the substrate root system of container-grown plants associated with irrigation cycles

In intensive horticultural crops, the choice of growing media and the adequate management of irrigation must ensure an optimal trade-off between aeration and water supply to roots. The proportion of gas-filled pores and their composition can be strongly affected by the water status and hence by irrigation. In this context, continuous measurement of gas exchange and water status of the growing medium could bring out some insights into how irrigation events affect root activity and aeration in a time scale of minutes to several hours. For this purpose, a measuring system was developed that measured the CO₂ efflux rate from the entire substrate root system of pot plants while their shoots were kept outside, undisturbed. It was able to monitor four plants at a time for several weeks at a rate of one measurement per plant every 10 min, thus tracing the dynamics of CO₂ efflux through a great many irrigation cycles. The results showed a marked pattern of CO₂ efflux around each irrigation event, consisting mainly of a sharp, conspicuous peak followed by a depression until a threshold in substrate water potential was reached. Analysis of these data suggests that the pattern is imposed mainly by the effects of irrigation and water content on the mobility of gases in the growing medium. The peak can be explained by the CO₂-enriched air being displaced by the water added to the growing medium in the pot, and the following depression can be the result of the reduced mobility of gases when substrate water content is high. In spite of the great variation in the instantaneous efflux rate of CO₂, the integration of these CO₂ values for the entire day provides a rather predictable value given the root biomass and does not seem to be affected by the number of irrigation events that occur in a given day.     

Genetic variation in prehistoric Sardinia

We sampled teeth from 53 ancient Sardinian (Nuragic) individuals who lived in the Late Bronze Age and Iron Age, between 3,430 and 2,700 years ago. After eliminating the samples that, in preliminary biochemical tests, did not show a high probability to yield reproducible results, we obtained 23 sequences of the mitochondrial DNA control region, which were associated to haplogroups by comparison with a dataset of modern sequences. The Nuragic samples show a remarkably low genetic diversity, comparable to that observed in ancient Iberians, but much lower than among the Etruscans. Most of these sequences have exact matches in two modern Sardinian populations, supporting a clear genealogical continuity from the Late Bronze Age up to current times. The Nuragic populations appear to be part of a large and geographically unstructured cluster of modern European populations, thus making it difficult to infer their evolutionary relationships. However, the low levels of genetic diversity, both within and among ancient samples, as opposed to the sharp differences among modern Sardinian samples, support the hypothesis of the expansion of a small group of maternally related individuals, and of comparatively recent differentiation of the Sardinian gene pools. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Extreme individual marker F<Subscript>ST </Subscript>values do not imply population-specific selection in humans: the <Emphasis Type="Italic">NRG1</Emphasis> example

Extreme population differentiation, as measured by the F_ST value, has been suggested as an indicator of recent population-specific positive selection. Elevated F_ST values indicating high differentiation between continental groups were previously reported on a linkage disequilibrium region in the Neuregulin 1 gene, a gene which has been associated to schizophrenia. In the present study we show evidence that high F_ST values may not necessarily imply the action of selection, in particular positive selection, neither globally nor regionally, using the example of the NRG1 gene.     

Photosynthesis and photoprotection responses to water stress in the wild-extinct plant Lysimachia minoricensis

Lysimachia minoricensis is an endemic species of the Balearic Islands that has become extinct in the wild, but persists in botanical gardens. Attempts of re-introducing the species into its natural habitat, which consisted in temporary dry streams, have failed. Low genetic variability has been reported for the garden individuals, suggesting that a reduced potential to adapt to environmental changes could be among the reasons for its extinction. In the present study, we particularly test whether photosynthesis and photoprotection responses of this species to water stress could help explaining the lack of success of this species in its natural habitat.

Plants of L. minoricensis were grown in pots in a growth chamber. Soil water depletion was imposed over 20 days by stopping irrigation. Early stomata closure was observed in response to soil water depletion while leaves desiccated progressively. Although net photosynthesis was low in irrigated plants, due to a remarkably low mesophyll conductance to CO₂, substantial photosynthetic activity was kept at severe drought, where leaf relative water content was as low as 50%, suggesting that L. minoricensis is a very drought-tolerant species. In parallel with decreased photosynthesis, thermal dissipation of the excess light and photorespiration progressively increased. The former was linearly related to increased de-epoxidation of the xanthophylls cycle. Photoprotection was effective, as pre-dawn maximum photochemical efficiency was maintained higher than 0.75 through the entire experiment. Moreover, photosynthetic capacity was largely (80%) recovered only 24 h after re-watering. These results show that stomatal regulation, photosynthetic metabolism and photoprotection in L. minoricensis are well adapted to water stress, suggesting that additional factors may be responsible for its status as a wild-extinct plant.     

Next-generation sequencing,phylogenetic signal and comparative mitogenomic analyses in Metacrangonyctidae (Amphipoda: Crustacea)

Background

Comparative mitochondrial genomic analyses are rare among crustaceans below the family or genus level. The obliged subterranean crustacean amphipods of the family Metacrangonyctidae, found from the Hispaniola (Antilles) to the Middle East, including the Canary Islands and the peri-Mediterranean region, have an evolutionary history and peculiar biogeography that can respond to Tethyan vicariance. Indeed, recent phylogenetic analysis using all protein-coding mitochondrial sequences and one nuclear ribosomal gene have lent support to this hypothesis (Bauzà-Ribot et al. 2012).

Results

We present the analyses of mitochondrial genome sequences of 21 metacrangonyctids in the genera Metacrangonyx and Longipodacrangonyx, covering the entire geographical range of the family. Most mitogenomes were attained by next-generation sequencing techniques using long-PCR fragments sequenced by Roche FLX/454 or GS Junior pyro-sequencing, obtaining a coverage depth per nucleotide of up to 281×. All mitogenomes were AT-rich and included the usual 37 genes of the metazoan mitochondrial genome, but showed a unique derived gene order not matched in any other amphipod mitogenome. We compare and discuss features such as strand bias, phylogenetic informativeness, non-synonymous/synonymous substitution rates and other mitogenomic characteristics, including ribosomal and transfer RNAs annotation and structure.

Conclusions

Next-generation sequencing of pooled long-PCR amplicons can help to rapidly generate mitogenomic information of a high number of related species to be used in phylogenetic and genomic evolutionary studies. The mitogenomes of the Metacrangonyctidae have the usual characteristics of the metazoan mitogenomes (circular molecules of 15,000-16,000 bp, coding for 13 protein genes, 22 tRNAs and two ribosomal genes) and show a conserved gene order with several rearrangements with respect to the presumed Pancrustacean ground pattern. Strand nucleotide bias appears to be reversed with respect to the condition displayed in the majority of crustacean mitogenomes since metacrangonyctids show a GC-skew at the (+) and (-) strands; this feature has been reported also in the few mitogenomes of Isopoda (Peracarida) known thus far. The features of the rRNAs, tRNAs and sequence motifs of the control region of the Metacrangonyctidae are similar to those of the few crustaceans studied at present.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-566) contains supplementary material, which is available to authorized users.     

The Role of HbA1c Determination in Detecting Unknown Glucose Disturbances in Ischemic Stroke

Objectives

To evaluate the usefulness of hemoglobin A1c (HbA1c) determinations during the acute ischemic stroke (IS) to identify undiagnosed glucose disturbances in a prospective series of patients with first-ever IS.

Methods

Retrospective analysis of a prospective series of first-ever IS patients. Patients with previous diagnosis of diabetes mellitus (DM) were excluded from the study. Patients were classified as non-DM (HbA1c<5.7% and no previous evidence of 2 or more fasting blood glucose> = 126 mg/dL), prediabetes (HbA1c from 5.7% to 6.4%), and new suspected DM (HbA1c> = 6.5% independently of current blood glucose). Medical charts from hospital discharge to July 2014 of all suspected DM patients were reviewed to confirm the DM diagnosis.

Results

The initial cohort included 1283 patients, of which 393 were excluded because of previous DM diagnosis and 136 because HbA1c during acute stroke phase was not available. No demographic differences were observed between patients with and without HbA1c determinations. The final cohort was composed of 754 patients with first-ever IS and unknown DM history. HbA1c determination suggested new DM in 87 cases (11.5%) and detected 273 patients with prediabetes (36.2%). New DM cases were identified in all etiological stroke subtypes. After discharge, DM diagnosis was confirmed in 80.2% of patients with available follow-up.

Conclusions

HbA1c determination detected both undiagnosed DM and prediabetes in IS patients without taking into account the blood glucose values during admission, and independently of etiological stroke subtype. HbA1c determination should be included in the systematic screening of all IS patients.     

METABOLIC FLUX IS A DETERMINANT OF THE EVOLUTIONARY RATES OF ENZYME‐ENCODING GENES

Relationships between evolutionary rates and gene properties on a genomic, functional, pathway, or system level are being explored to unravel the principles of the evolutionary process. In particular, functional network properties have been analyzed to recognize the constraints they may impose on the evolutionary fate of genes. Here we took as a case study the core metabolic network in human erythrocytes and we analyzed the relationship between the evolutionary rates of its genes and the metabolic flux distribution throughout it. We found that metabolic flux correlates with the ratio of nonsynonymous to synonymous substitution rates. Genes encoding enzymes that carry high fluxes have been more constrained in their evolution, while purifying selection is more relaxed in genes encoding enzymes carrying low metabolic fluxes. These results demonstrate the importance of considering the dynamical functioning of gene networks when assessing the action of selection on system‐level properties.