No evidence of transmission of grapevine leafroll-associated viruses by phylloxera (Daktulosphaira vitifoliae).

Grapevine leafroll disease is associated with several species of phloem-limited grapevine leafrollassociated viruses (GLRaV), some of which are transmitted by mealybugs and scale insects. The grape phylloxera, Daktulosphaira vitifoliae (Fitch) Biotype A (Hemiptera: Phylloxeridae), is a common vineyard pest that feeds on the phloem of vine roots. There is concern that these insects may transmit one or more GLRaV species, particularly GLRaV-2, a species in the genus Closterovirus. A field survey was performed in vineyards with a high incidence of grapevine leafroll disease and D. vitifoliae was assessed for acquisition of GLRaV. In greenhouse experiments, the ability of D. vitifoliae to transmit GLRaV from infected root sections or vines to co-planted virus-free recipient vines was tested. There were no GLRaV-positive D. vitifoliae in the field survey, nor did D. vitifoliae transmit GLRaV- 1, ?2, ?3, or -4LV in greenhouse transmission experiments. Some insects tested positive for GLRaV after feeding on infected source vines in the greenhouse, however there was no evidence of virus transmission to healthy plants. These findings, in combination with the sedentary behaviour of the soil biotype of D. vitifoliae, make it unlikely that D. vitifoliae is a vector of any GLRaV.DOI: 10.1007/s10658-016-1049-

Thermotropic phase behavior and headgroup interactions of the nonbilayer lipids phosphatidylethanolamine and monogalactosyldiacylglycerol in the dry state

<p>Abstract</p> <p>Background</p> <p>Although biological membranes are organized as lipid bilayers, they contain a substantial fraction of lipids that have a strong tendency to adopt a nonlamellar, most often inverted hexagonal (H_II) phase. The polymorphic phase behavior of such nonbilayer lipids has been studied previously with a variety of methods in the fully hydrated state or at different degrees of dehydration. Here, we present a study of the thermotropic phase behavior of the nonbilayer lipids egg phosphatidylethanolamine (EPE) and monogalactosyldiacylglycerol (MGDG) with a focus on interactions between the lipid molecules in the interfacial and headgroup regions.</p> <p>Results</p> <p>Liposomes were investigated in the dry state by Fourier-transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). Dry EPE showed a gel to liquid-crystalline phase transition below 0°C and a liquid-crystalline to H_IItransition at 100°C. MGDG, on the other hand, was in the liquid-crystalline phase down to -30°C and showed a nonbilayer transition at about 85°C. Mixtures (1:1 by mass) with two different phosphatidylcholines (PC) formed bilayers with no evidence for nonbilayer transitions up to 120°C. FTIR spectroscopy revealed complex interactions between the nonbilayer lipids and PC. Strong H-bonding interactions occurred between the sugar headgroup of MGDG and the phosphate, carbonyl and choline groups of PC. Similarly, the ethanolamine moiety of EPE was H-bonded to the carbonyl and choline groups of PC and probably interacted through charge pairing with the phosphate group.</p> <p>Conclusions</p> <p>This study provides a comprehensive characterization of dry membranes containing the two most important nonbilayer lipids (PE and MGDG) in living cells. These data will be of particular relevance for the analysis of interactions between membranes and low molecular weight solutes or soluble proteins that are presumably involved in cellular protection during anhydrobiosis.</p

Progress report on colloid-facilitated transport at Yucca Mountain: Yucca Mountain site characterization program milestone 3383

To assess colloid-facilitated radionuclide transport in groundwaters at the potential nuclear waste repository at Yucca Mountain, it is very important to understand the generation and stability of colloids, including naturally occurring colloids. To this end, we measured the colloid concentration in waters from Well J-13, which is on the order of 106 particles per milliliter (for particle sizes larger than 100 manometers). At this low particle loading, the sorption of radionuclides to colloids would have to be extremely high before the colloids could carry a significant amount of radionuclides from the repository to the accessible environment. We also performed aggregation experiments to evaluate the stability of silica (particle diameter: 85 nm) and clay colloids (particle diameter: 140 nm) as a function of ionic strength in a carbonate-rich synthetic groundwater. When the concentration of electrolyte is increased to induce aggregation, the aggregation is irreversible and the rate of aggregation increases with increasing electrolyte strength. We used autocorrelation photon spectroscopy to estimate the rate of particle aggregation for both types of colloids. By relating the measured aggregation rate to the Smoluchowski rate expression, we determined the stability ratio, W. Aggregation of silica particles and kaolinite clay particles decreased dramatically for an electrolyte concentration, C{sub NaCl}, below 300 mM and 200 mM, respectively