A soluble chloroplast protein catalyzes ribulosebisphosphate carboxylase/oxygenase activation in vivo

Ribulosebisphosphate carboxylase/oxygenase (EC 4.1.1.39) (rubisco) must be fully activated in order to catalyze the maximum rates of photosynthesis observed in plants. Activation of the isolated enzyme occurs spontaneously, but conditions required to observe full activation are inconsistent with those known to occur in illuminated chloroplasts. Genetic studies with a nutant of Arabidopsis thaliana incapable of activating rubisco linked two chloroplast polypeptides to the activation process in vivo. Using a reconstituted light activation system, it was possible to demonstrate the participation of a chloroplast protein in rubisco activation. These results indicate that a specific chloroplast enzyme, rubisco activase, catalyzes the activation of rubisco in vivo.     

Geometric design improvements for femoral graft-artery junctions mitigating restenosis

The present study is based on the hypothesis that nonuniform hemodynamics, represented by large time-averaged wall shear stress gradients, trigger abnormal biological processes leading to rapid restenosis, i.e. excessive tissue overgrowth and renewed plaque formation, and hence early graft failure. It implies that this problem may be significantly mitigated by finding graft-artery bypass configurations for which the wall shear stress gradient is approximately zero and hence nearly uniform hemodynamics is achieved. These fluid flow and geometric design considerations are applied to four different end-to-side anastomoses for the distal end of a femoral artery bypass with an appropriate test input pulse and a typical 20–80 flow division. A validated finite-volume code has been used to compute the transient three-dimensional velocity vector fields, wall shear stress distributions and surface contours of the wall shear stress gradients. It is shown that large anastomotic flow areas, small continuously changing bifurcation angles, and smooth junction wall curvatures reduce local time-averaged wall shear stress gradients significantly and hence should mitigate restenosis.     

Inhibited light activation of fructose and sedoheptulose bisphosphatase in spinach chloroplasts exposed to osmotic stress

The light activation of fructose-1,6-bisphosphatase (EC 3.1.3.11) and sedoheptulose-1,7-bisphosphatase (EC 3.1.3.37) was inhibited in isolated intact spinach (Spinacia oleracea L.) chloroplasts exposed to reduced osmotic potentials. Decreases in the velocity and magnitude of light activation correlated with the overall reduction in CO₂ fixation rates. Responses of osmotically stressed chloroplasts to both varying pH and exogeous dihydroxyacetone phosphate (DHAP) or 3-phosphoglycerete (PGA) were examined. In the presence of DHAP, the absolute rate of CO₂ fixation was increased and this increase was most pronounced at alkaline pH. Enhanced light activation of these enzymes was also observed under these conditions. However, in the presence of PGA, similar increases in photosynthetic rate and enzyme activation were not evident. Light-dependent stromal alkalization was unaffected by the stress treatments. Inhibition of light activation under hypertonic conditions is discussed in terms of substrate availability, possible alterations of the redox state of ferredoxin and associated electron carriers, and inhibited enzyme-enzyme or enzyme-substrate interactions involved in the light activation process.Abbreviations and symbols DHAP dihydroxyacetone phosphate - PGA 3-phosphoglycerate - _s osmotic potential     

Plant-feeding and non-plant feeding phytoseiids: differences in behavior and cheliceral morphology

In previous studies plant feeding behavior of plant- and non-plant feeding phytoseiids was never examined directly. Moreover, in these studies the cheliceral morphology of phytoseiids was not associated with their ability to feed on plants. In the present study, we monitored the plant-feeding behavior of Euseius scutalis and Amblyseius swirskii. Only E. scutalis was observed penetrating the leaf surface with the movable digit and feeding. Second, using a dye and coloring the gut as an indicator for feeding, we found that E. scutalis pierced an artificial membrane and fed whereas A. swirskii did not. Finally, to identify morphological characteristics typical of plant feeders versus non-plant feeders, we used scanning electron microscopy to examine the adaxial (inner) profile of the chelicerae in 13 phytoseiid species. The only parameter that distinguished between plant- and non-plant feeders was the ratio of the dorsal perimeter length of the fixed digit to the ventral perimeter length of the movable digit. Plant-feeders were characterized by ratio values greater than one whereas the values for non plant-feeders were lower than one. We suggest that a shorter and less curved movable digit, expressed by a high ratio, will facilitate the penetration of the leaf surface. Cheliceral traits proposed here as typical of plant feeders, were observed for five genera, indicating that plant-feeding may be more common in the Phytoseiidae than previously reported. We propose that the ability to feed on plants be added as a cross type trait of phytoseiid life-style types.     

Phenology and polyploidy in annual Brachypodium species (Poaceae) along the aridity gradient in Israel

Local adaptation of plants along environmental gradients provides strong evidence for clinal evolution mediated by natural selection. Plants have developed diverse strategies to mitigate stress, for example, drought escape is a phenological strategy to avoid drought stress, while polyploidy was proposed as a genomic adaptation to stress. Polyploidy as an adaptation to aridity (an environmental parameter integrating temperature and precipitation) was previously documented in annual Brachypodium spp. (Poaceae) in the Western Mediterranean. Here, we examined whether polyploidy or phenology are associated with aridity in annual Brachypodium spp. along the aridity gradient in the Eastern Mediterranean. Using flow cytometry, we determined ploidy levels of plants from natural populations along the Israeli gradient, spanning ∼424 km from mesic Mediterranean to extreme desert climates. In a common garden we recorded time of seedling emergence, flowering and senescence. We tested whether the proportion of allotetraploids in the populations and phenological traits were associated with aridity. Contrary to a previous study in the Western Mediterranean, we found no effect of aridity on the proportion of allotetraploids and diploids within populations. Interestingly, phenology was associated with aridity: time of emergence was later, while flowering and senescence were earlier in desert plants. Our results indicate that in the Eastern Mediterranean, adaptation of Brachypodium to aridity is mediated mainly by phenology, rather than ploidy level. Therefore, we suggest that genome duplication is not the main driver of adaptation to environmental stress; rather, phenological change as a drought escape mechanism may be the major adaptation.     

The impact of the ‘New Zealand flatworm’, Arthurdendyus triangulatus, on earthworm populations in the field

The ‘New Zealand flatworm’, Arthurdendyus triangulatus, is a native of the South Island of New Zealand, which has established in the UK, Ireland and the Faroe Islands. In its introduced range, it is a predator of lumbricid earthworms. To assess the impact of A. triangulatus on earthworm species, flatworm distributions were manipulated into ‘high’, control and ‘low’ densities within a replicated field experiment. Earthworm biomass in the ‘high’ flatworm density treatment was significantly lower than the control or ‘low’ treatments. This was due to a reduction in the anecic species Lumbricus terrestris and, to a lesser extent, Aporrectodea longa. There was little evidence of negative effects on other earthworm species, with even a weakly positive relationship between flatworm density and epigeic biomass. Principal components analysis showed a clear separation of anecic species from A. triangulatus, but the epigeic species Lumbricus festivus and Lumbricus rubellus grouped with A. triangulatus, suggesting that they could be benefitting from reduced intraguild competition. Flatworm densities of 0.8 per m², comparable to natural infestations in grassland, were predicted to give a reduction in total earthworm biomass of c. 20 %. The bulk of this was comprised of a reduction in anecic species biomass. In particular, it is considered that A. triangulatus poses a serious risk to L. terrestris populations, with implications for soil functioning and indigenous earthworm-feeding wildlife.     

Synthesising 30 Years of Mathematical Modelling of Echinococcus Transmission

Background

Echinococcosis is a complex zoonosis that has domestic and sylvatic lifecycles, and a range of different intermediate and definitive host species. The complexities of its transmission and the sparse evidence on the effectiveness of control strategies in diverse settings provide significant challenges for the design of effective public health policy against this disease. Mathematical modelling is a useful tool for simulating control packages under locally specific transmission conditions to inform optimal timing and frequency of phased interventions for cost-effective control of echinococcosis. The aims of this review of 30 years of Echinococcus modelling were to discern the epidemiological mechanisms underpinning models of Echinococcus granulosus and E. multilocularis transmission and to establish the need to include a human transmission component in such models.

Methodology/Principal Findings

A search was conducted of all relevant articles published up until July 2012, identified from the PubMED, Web of Knowledge and Medline databases and review of bibliographies of selected papers. Papers eligible for inclusion were those describing the design of a new model, or modification of an existing mathematical model of E. granulosus or E. multilocularis transmission. A total of 13 eligible papers were identified, five of which described mathematical models of E. granulosus and eight that described E. multilocularis transmission. These models varied primarily on the basis of six key mechanisms that all have the capacity to modulate model dynamics, qualitatively affecting projections. These are: 1) the inclusion of a ‘latent’ class and/or time delay from host exposure to infectiousness; 2) an age structure for animal hosts; 3) the presence of density-dependent constraints; 4) accounting for seasonality; 5) stochastic parameters; and 6) inclusion of spatial and risk structures.

Conclusions/Significance

This review discusses the conditions under which these mechanisms may be important for inclusion in models of Echinococcus transmission and proposes recommendations for the design of dynamic human models of transmission. Accounting for the dynamic behaviour of the Echinococcus parasites in humans will be key to predicting changes in the disease burden over time and to simulate control strategies that optimise public health impact.     

Addition of Rapamycin to Anti-CD3 Antibody Improves Long-Term Glycaemia Control in Diabetic NOD Mice

Aims/Hypothesis

Non-Fc-binding Anti CD3 antibody has proven successful in reverting diabetes in the non-obese diabetes mouse model of type 1 diabetes and limited efficacy has been observed in human clinical trials. We hypothesized that addition of rapamycin, an mTOR inhibitor capable of inducing operational tolerance in allogeneic bone marrow transplantation, would result in improved diabetes reversal rates and overall glycemia.

Methods

Seventy hyperglycemic non-obese diabetic mice were randomized to either a single injection of anti CD3 alone or a single injection of anti CD3 followed by 14 days of intra-peritoneal rapamycin. Mice were monitored for hyperglycemia and metabolic control.

Results

Mice treated with the combination of anti CD3 and rapamycin had similar rates of diabetes reversal compared to anti CD3 alone (25/35 vs. 22/35). Mice treated with anti CD3 plus rapamycin had a significant improvement in glycemia control as exhibited by lower blood glucose levels in response to an intra-peritoneal glucose challenge; average peak blood glucose levels 30 min post intra-peritoneal injection of 2 gr/kg glucose were 6.9 mmol/L in the anti CD3 plus rapamycin group vs. 10 mmo/L in the anti CD3 alone (P<0.05).

Conclusions/Interpretation

The addition of rapamycin to anti CD3 results in significant improvement in glycaemia control in diabetic NOD mice.