Medicago truncatula mutants demonstrate the role of plant calcium oxalate crystals as an effective defense against chewing insects

Calcium oxalate is the most abundant insoluble mineral found in plants and its crystals have been reported in more than 200 plant families. In the barrel medic Medicago truncatula Gaertn., these crystals accumulate predominantly in a sheath surrounding secondary veins of leaves. Mutants of M. truncatula with decreased levels of calcium oxalate crystals were used to assess the defensive role of this mineral against insects. Caterpillar larvae of the beet armyworm Spodoptera exigua Hübner show a clear feeding preference for tissue from calcium oxalate-defective (cod) mutant lines cod5 and cod6 in choice test comparisons with wild-type M. truncatula. Compared to their performance on mutant lines, larvae feeding on wild-type plants with abundant calcium oxalate crystals suffer significantly reduced growth and increased mortality. Induction of wound-responsive genes appears to be normal in cod5 and cod6, indicating that these lines are not deficient in induced insect defenses. Electron micrographs of insect mouthparts indicate that the prismatic crystals in M. truncatula leaves act as physical abrasives during feeding. Food utilization measurements show that, after consumption, calcium oxalate also interferes with the conversion of plant material into insect biomass during digestion. In contrast to their detrimental effects on a chewing insect, calcium oxalate crystals do not negatively affect the performance of the pea aphid Acyrthosiphon pisum Harris, a sap-feeding insect with piercing-sucking mouthparts. The results confirm a long-held hypothesis for the defensive function of these crystals and point to the potential value of genes controlling crystal formation and localization in crop plants.     

Systems virology identifies a mitochondrial fatty acid oxidation enzyme, dodecenoyl coenzyme A delta isomerase, required for hepatitis C virus replication and likely pathogenesis

We previously employed systems biology approaches to identify the mitochondrial fatty acid oxidation enzyme dodecenoyl coenzyme A delta isomerase (DCI) as a bottleneck protein controlling host metabolic reprogramming during hepatitis C virus (HCV) infection. Here we present the results of studies confirming the importance of DCI to HCV pathogenesis. Computational models incorporating proteomic data from HCV patient liver biopsy specimens recapitulated our original predictions regarding DCI and link HCV-associated alterations in cellular metabolism and liver disease progression. HCV growth and RNA replication in hepatoma cell lines stably expressing DCI-targeting short hairpin RNA (shRNA) were abrogated, indicating that DCI is required for productive infection. Pharmacologic inhibition of fatty acid oxidation also blocked HCV replication. Production of infectious HCV was restored by overexpression of an shRNA-resistant DCI allele. These findings demonstrate the utility of systems biology approaches to gain novel insight into the biology of HCV infection and identify novel, translationally relevant therapeutic targets.     

Uptake of dissolved organic nitrogen by size-fractionated plankton along a salinity gradient from the North Sea to the Baltic Sea

The Baltic Sea is known for its ecological problems due to eutrophication caused by high nutrient input via nitrogen fixation and rivers, which deliver up to 70% of nitrogen in the form of dissolved organic nitrogen (DON) compounds. We therefore measured organic nitrogen uptake rates using self produced ¹⁵N labeled allochthonous (derived from Brassica napus and Phragmites sp.) and autochthonous (derived from Skeletonema costatum) DON at twelve stations along a salinity gradient (34 to 2) from the North Sea to the Baltic Sea in August/September 2009. Both labeled DON sources were exploited by the size fractions 0.2–1.6 μm (bacteria size fraction) and >1.6 μm (phytoplankton size fraction). Higher DON uptake rates were measured in the Baltic Sea compared to the North Sea, with rates of up to 1213 nmol N l^?1 h^?1. The autochthonous DON was the dominant nitrogen form used by the phytoplankton size fraction, whereas the heterotrophic bacteria size fraction preferred the allochthonous DON. We detected a moderate shift from >1.6 μm plankton dominated DON uptake in the North Sea and central Baltic Sea towards a 0.2–1.6 μm dominated DON uptake in the Bothnian Bay and a weak positive relationship between DON concentrations and uptake. These findings indicate that DON is an important component of plankton nutrition and can fuel primary production. It may therefore also contribute substantially to eutrophication in the Baltic Sea especially when inorganic nitrogen sources are depleted.     

On the issue of transmissibility of Alzheimer disease: A critical review

Results from recent experiments with rodents imply that Alzheimer disease might be inducible by seeding Aβ peptides into recipient animals. In respect to this new experimental data, public health aspects as well as epidemiological data have to be reevaluated. In this article, the available experimental and epidemiological data are reviewed.     

Anergic T lymphocytes selectively express an integrin regulatory protein of the cytohesin family.

It has been proposed that the maintenance of T cell anergy depends on the induction of negative regulatory factors. Differential display of reverse transcribed RNA was used to identify novel genes that might mediate this function in anergic Th1 clones. We report that anergic Th1 clones do indeed express a genetic program different from that of responsive T cells. Moreover, one gene, the general receptor of phosphoinositides 1 (GRP1), was selectively induced in anergic T cells. The GRP1, located in the plasma membrane, regulated integrin-mediated adhesion and was invariably associated with unresponsiveness in multiple models of anergy. T cells expressing retrovirally transduced GRP1 exhibited normal proliferation and cytokine production. However, GRP1-transduced T cells were not stable and rapidly lost GRP1 expression. Thus, although GRP1 may not directly mediate T cell anergy, it regulates cell expansion and survival, perhaps through its integrin-associated activities.     

Rubrifacine fromErwinia rubrifaciens

For the main component of the pigments ofErwinia rubrifaciens, we suggest the hitherto unknown structure of a 3-(3-carboxymethyl-4,5-dihydro-4,5-dioxo-2-pyrrolyl)-4,5,6-trihydroxy-pyridine-2-acetic acid. Its isolation and characterization are described. Inasmuch as arylpyrrolindiones are known to be red, the proposed structure can account for the color of the pigment. The 2,3,4-trihydroxypyridine moiety probably inhibits the electron transport in mitochondria. This could explain the toxic action ofErwinia rubrifaciens onJuglans regia.     

Human lens lipids differ markedly from those of commonly used experimental animals

Electrospray ionisation tandem mass spectrometry has allowed the unambiguous identification and quantification of individual lens phospholipids in human and six animal models. Using this approach ca. 100 unique phospholipids have been characterised. Parallel analysis of the same lens extracts by a novel direct-insertion electron-ionization technique found the cholesterol content of human lenses to be significantly higher (ca. 6 times) than lenses from the other animals. The most abundant phospholipids in all the lenses examined were choline-containing phospholipids. In rat, mouse, sheep, cow, pig and chicken, these were present largely as phosphatidylcholines, in contrast 66% of the total phospholipid in Homo sapiens was sphingomyelin, with the most abundant being dihydrosphingomyelins, in particular SM(d18:0/16:0) and SM(d18:0/24:1). The abundant glycerophospholipids within human lenses were found to be predominantly phosphatidylethanolamines and phosphatidylserines with surprisingly high concentrations of ether-linked alkyl chains identified in both classes. This study is the first to identify the phospholipid class (head-group) and assign the constituent fatty acid(s) for each lipid molecule and to quantify individual lens phospholipids using internal standards. These data clearly indicate marked differences in the membrane lipid composition of the human lens compared to commonly used animal models and thus predict a significant variation in the membrane properties of human lens fibre cells compared to those of other animals.     

Enzymatic reduction of labile iron by organelles of the rat liver. Superior role of an NADH-dependent activity in the outer mitochondrial membrane

The enzymatic system mainly responsible for the reduction of labile iron ions in mammalian cells is still unknown. Using isolated organelles of the rat liver, i.e. mitochondria, microsomes, nuclei and the cytosol, we here demonstrate that Fe(III), added as Fe(III)-ATP complex, is predominantly reduced by an NADH-dependent enzyme system associated with mitochondria (65% of the overall enzymatic Fe(III) reduction capacity within liver cells). Microsomes showed a significantly smaller Fe(III) reduction capacity, whereas the cytosol and nuclei hardly reduced Fe(III). Studying the mitochondrial iron reduction, this NADH-dependent process was not mediated by superoxide, ascorbic acid, or NADH itself, excluding low-molecular-weight reductants. No evidence was found for the involvement of complex I and III of the respiratory chain. Submitochondrial preparations revealed the highest specific activity reducing Fe(III) in the outer membrane fraction. In conclusion, an NADH-dependent mitochondrial enzyme system, most likely the NADH-cytochrome c reductase system, located at the outer membrane, should decisively contribute to the enzymatic reduction of labile iron within liver cells, especially under pathological conditions.