Can weed hosts increase aggressiveness of Phytophthora infestans on potato?

Potato late blight, caused by Phytophthora infestans, is a major disease in potato production throughout the world. In southern Sweden, hairy nightshade (Solanum physalifolium), an alternative non-crop host to the pathogen, is an increasing weed problem. Single-lesion leaves infected by P. infestans were collected from potato and hairy nightshade to determine phenotypic and genotypic population differentiation of P. infestans between the two hosts. Genotypic variation was estimated using microsatellites as markers. The results showed no genotypic differentiation in the samples between the two hosts. Aggressiveness tests were performed using the sampled isolates to cross-inoculate potato and hairy nightshade. The proportion of infected leaves, latency period, lesion growth rate, and sporulation capacity were measured. For isolates from hairy nightshade, the odds of infection were higher on both hosts combined. When tested on potato leaves, isolates from hairy nightshade showed a significantly shorter latency period and higher sporulation capacity compared with isolates from potato. This indicates that an alternative host can filter populations of P. infestans toward a higher aggressiveness, which could lead to increasing problems in controlling potato late blight.

Flux-tunable heat sink for quantum electric circuits.

Superconducting microwave circuits show great potential for practical quantum technological applications such as quantum information processing. However, fast and on-demand initialization of the quantum degrees of freedom in these devices remains a challenge. Here, we experimentally implement a tunable heat sink that is potentially suitable for the initialization of superconducting qubits. Our device consists of two coupled resonators. The first resonator has a high quality factor and a fixed frequency whereas the second resonator is designed to have a low quality factor and a tunable resonance frequency. We engineer the low quality factor using an on-chip resistor and the frequency tunability using a superconducting quantum interference device. When the two resonators are in resonance, the photons in the high-quality resonator can be efficiently dissipated. We show that the corresponding loaded quality factor can be tuned from above 105 down to a few thousand at 10 GHz in good quantitative agreement with our theoretical model.

Hepatocellular uptake of 3H-dihydromicrocystin-LR, a cyclic peptide toxin.

The cellular uptake of microcystin-LR, a cyclic heptapeptide hepatotoxin from the cyanobacterium Microcystis aeruginosa, was studied by means of a radiolabelled derivative of the toxin. 3H-dihydromicrocystin-LR. The uptake of 3H-dihydromicrocystin-LR was shown to be specific for freshly isolated rat hepatocytes whereas the uptake in the human hepatocarcinoma cell line Hep G2 as well as the mouse fibroblast cell line NIH-3T3, and the human neuroblastoma cell line SH-SY5Y, was negligible. By means of a surface barostat technique it was shown that the membrane penetrating capacity (surface activity) of microcystin-LR was low, indicating that the toxin requires an active uptake mechanism. The hepatocellular uptake of microcystin-LR could be inhibited in the presence of bile acid transport inhibitors such as antamanide (5 microM), sulfobromophthalein (50 microM) and rifampicin (30 microM). The uptake was also reduced in a concentration dependent manner when the hepatocytes were incubated in the presence the bile salts cholate and taurocholate. A complete inhibition of the hepatocellular uptake was achieved by 100 microM of either bile salt. The overall results indicate that the uptake of microcystin-LR is through the multispecific transport system for bile acids. This mechanism of cell entry would explain the previously observed cell specificity and organotropism of microcystin-LR.

Determination of hydrazine in hydralazine by capillary gas chromatography with nitrogen-selective detection after benzaldehyde derivatization.

A method for the determination of hydralazine substance is described. Hydrazine is derivatized in aqueous media with benzaldehyde to benzalazine. After extraction to an organic phase containing a homologue as marker, the sample is subjected to capillary column gas chromatography with nitrogen-selective detection. A prolonged reaction with 0.1 M benzaldehyde of 20 min or more led to an increased level of benzalazine when hydralazine was analysed. An increase was also observed if the aqueous hydralazine sample had been allowed to stand for some time before analysis. The final method involved the use of a 5-min reaction time, fresh solutions and the standard addition principle. The levels of hydrazine found in hydralazine hydrochloride were below 1 ppm (as bases, 1 ng/mg).

Cholesterol oxidase catalyzed oxidation of cholesterol in mixed lipid monolayers: effects of surface pressure and phospholipid composition on catalytic activity.

The catalytic activity of cholesterol oxidase from Streptomyces sp. in mixed monolayers of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC), N-oleoylsphingomyelin (O-SPM), and cholesterol (CHL) has been determined at lateral surface pressures between 10 and 30 mN/m. The highest cholesterol oxidase activity (determined at 37 degrees C) was observed at surface pressures around 20 mN/m in a POPC/CHL monolayer (50:50 mol %). Above and below this surface pressure, the enzyme activity decreased markedly. A similar optimal activity vs surface pressure relationship was observed also for an O-SPM/CHL monolayer (50:50 mol %). The activity of cholesterol oxidase toward cholesterol in the O-SPM/CHL monolayer was, however, less than in the corresponding POPC mixed monolayer. The surface activity of cholesterol oxidase decreased markedly when the temperature was lowered to 20 degrees C, and hardly any enzyme activity was observed in an O-SPM/CHL monolayer at 25 mN/m or above. With a monolayer containing POPC/O-SPM/CHL (42:18:40 mol %), maximal cholesterol oxidase activity was observed at the lowest surface pressure tested (i.e., 10 mN/m), and the catalytic activity decreased markedly with increasing lateral surface pressures in the monolayer. The results of this study show (i) that the activity of cholesterol oxidase in general is highly dependent on the lateral surface pressure in the substrate membranes and (ii) that sphingomyelin, by interacting tightly with cholesterol, can prevent or restrain the accessibility of cholesterol for oxidation by cholesterol oxidase.

Oxidation of cholesterol in low density and high density lipoproteins by cholesterol oxidase.

The cholesterol oxidase-catalyzed oxidation of cholesterol in native low density (LDL) and high density lipoproteins (HDL3) as well as in monolayers prepared from surface lipids of these particles, has been examined. The objective of the study was to compare the oxidizability of cholesterol, and to examine the effects of lipid packing on oxidation rates. When [3H]cholesterol-labeled lipoproteins were exposed to cholesterol oxidase (Streptomyces sp.), it was observed that LDL [3H]cholesterol was oxidized much faster than HDL3 [3H]cholesterol. This was true both at equal cholesterol concentration per enzyme unit, and at equal amounts of lipoprotein particles per enzyme unit. About 95% of lipoprotein [3H]cholesterol was available for oxidation. The complete degradation of lipoprotein sphingomyelin by sphingomyelinase (Staphylococcus aureus) resulted in a 10-fold increase in the rate of LDL [3H]cholesterol oxidation, whereas the effects on rates of HDL3 [3H]cholesterol oxidation were less dramatic. A monolayer study with LDL surface lipids indicated that degradation of sphingomyelin loosened the lipid packing, because the ceramide formed occupied a smaller surface area than the parent sphingomyelin, and since the condensing effect of cholesterol on sphingomyelin packing was lost. The effects of sphingomyelin degradation on lipid packing in monolayers of HDL3-derived surface lipids were difficult to determine from monolayer experiments. Based on the finding that cholesterol oxidases are surface pressure-sensitive with regard to their catalytic activity, these were used to estimate the surface pressure of intact LDL and HDL3. The cut-off surface pressure of a Brevibacterium enzyme was 25 mN/m and 20 mN/m in monolayers of LDL and HDL3-derived surface lipids, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of cholesterol with synthetic sphingomyelin derivatives in mixed monolayers.

To study the structural requirements of the molecular interactions between cholesterol and sphingomyelins in model membranes, sphingomyelin derivatives were synthesized in which (a) the 3-hydroxy group was replaced with a hydrogen atom or with a methoxy, ethoxy, or tetrahydropyranyloxy group, (b) the N-acyl chain length was varied, and (c) the N-acyl chain length contained an alpha-hydroxy group. The chemical syntheses of these derivatives from DL-erythro-sphingosine are reported. The properties of these sphingomyelin derivatives were examined in monolayer membranes at the air/water interface. The mean molecular area of the pure N-stearoylsphingomyelin derivatives was determined, and the effects of cholesterol on the condensation of sphingomyelin packing in the monolayer were recorded. It was observed that replacement of the 3-hydroxy group of sphingomyelin with a hydrogen atom or its substitution with a methoxy or ethoxy group did not affect the ability of cholesterol to condense the molecular packing in monolayers. Even when a bulky tetrahydropyranyloxy group was introduced at the 3-hydroxy position of egg sphingomyelin, cholesterol was still able to condense the molecular packing of this derivative. The condensing effect of cholesterol on derivatives of N-stearoyl-SPMs was significantly larger than the comparable effect observed with 1,2-distearoyl-sn-glycero-3-phosphocholine or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. Our results with 3-hydroxysphingomyelins having differing N-acyl chain lengths (i.e., N-stearoyl, N-myristoyl, and N-lauroyl), and with 3-hydroxy-N-(alpha-hydroxypalmitoyl)sphingomyelin also indicated that cholesterol was able to induce condensation of the molecular packing.(ABSTRACT TRUNCATED AT 250 WORDS)