Critical points in edge tunneling between generic FQH states

A general description of weak and strong tunneling fixed points is developed in the chiral-Luttinger-liquid model of quantum Hall edge states. Tunneling fixed points are a subset of `termination' fixed points, which describe boundary conditions on a multicomponent edge. The requirement of unitary time evolution at the boundary gives a nontrivial consistency condition for possible low-energy boundary conditions. The effect of interactions and random hopping on fixed points is studied through a perturbative RG approach which generalizes the Giamarchi-Schulz RG for disordered Luttinger liquids to broken left-right symmetry and multiple modes. The allowed termination points of a multicomponent edge are classified by a B-matrix with rational matrix elements. We apply our approach to a number of examples, such as tunneling between a quantum Hall edge and a superconductor and tunneling between two quantum Hall edges in the presence of interactions. Interactions are shown to induce a continuous renormalization of effective tunneling charge for the integrable case of tunneling between two Laughlin states. The correlation functions of electronlike operators across a junction are found from the B matrix using a simple image-charge description, along with the induced lattice of boundary operators. Many of the results obtained are also relevant to ordinary Luttinger liquids.Comment: 23 pages, 6 figures. Xiao-Gang Wen: http://dao.mit.edu/~we

Influence of uniaxial tensile stress on the mechanical and piezoelectric properties of short-period ferroelectric superlattice

Tetragonal ferroelectric/ferroelectric BaTiO3/PbTiO3 superlattice under uniaxial tensile stress along the c axis is investigated from first principles. We show that the calculated ideal tensile strength is 6.85 GPa and that the superlattice under the loading of uniaxial tensile stress becomes soft along the nonpolar axes. We also find that the appropriately applied uniaxial tensile stress can significantly enhance the piezoelectricity for the superlattice, with piezoelectric coefficient d33 increasing from the ground state value by a factor of about 8, reaching 678.42 pC/N. The underlying mechanism for the enhancement of piezoelectricity is discussed

Cerebellar Modules and Their Role as Operational Cerebellar Processing Units

The compartmentalization of the cerebellum into modules is often used to discuss its function. What, exactly, can be considered a module, how do they operate, can they be subdivided and do they act individually or in concert are only some of the key questions discussed in this consensus paper. Experts studying cerebellar compartmentalization give their insights on the structure and function of cerebellar modules, with the aim of providing an up-to-date review of the extensive literature on this subject. Starting with an historical perspective indicating that the basis of the modular organization is formed by matching olivocorticonuclear connectivity, this is followed by consideration of anatomical and chemical modular boundaries, revealing a relation between anatomical, chemical, and physiological borders. In addition, the question is asked what the smallest operational unit of the cerebellum might be. Furthermore, it has become clear that chemical diversity of Purkinje cells also results in diversity of information processing between cerebellar modules. An additional important consideration is the relation between modular compartmentalization and the organization of the mossy fiber system, resulting in the concept of modular plasticity. Finally, examination of cerebellar output patterns suggesting cooperation between modules and recent work on modular aspects of emotional behavior are discussed. Despite the general consensus that the cerebellum has a modular organization, many questions remain. The authors hope that this joint review will inspire future cerebellar research so that we are better able to understand how this brain structure makes its vital contribution to behavior in its most general form

The Lycopodium alkaloids

Lycopodium alkaloids are quinolizine, or pyridine and α-pyridone type alkaloids. Some Lycopodium alkaloids are potent inhibitors of acetylcholinesterase (AChE). Huperzine A (HupA) is reported to increase efficiency for learning and memory in animals, and it shows promise in the treatment of Alzheimer's disease (AD). 201 Lycopodium alkaloids from 54 species of Lycopodium (sensu lato) have been reported so far. This review is intended to cover the chemical, pharmacological and clinical research on Lycopodium alkaloids reported in the literature from the spring of 1993 to August 2004. Structures of 81 new Lycopodium alkaloids are presented, classified and analyzed. The structural characters and biogenetic relationships of the four major Lycopodium alkaloid groups (lycopodine, lycodine, fawcettimine and miscellaneous) are discussed. Bioactivities of Lycopodium alkaloids, especially HupA, are summarized. In particular, the effect of HupA and other cholinesterase inhibitors (anti-AD drugs) on acetylcholine esterase (AChE) activity in the rat cortex and butylcholine esterase activity are compared. Structure-activity relationships and structure modifications of HupA and its analogs are described. Information on clinical trials with HupA and its derivative ZT-1 is presented. The state of HupA availability and recent advances in in vitro propagation of HupA producing plants are outlined. Finally, hypotheses about Lycopodium alkaloid biosynthetic pathways are discussed

Auxenochlorella protothecoides populations adapted to low phosphate conditions accumulated more non-phosphorus glycerolipids and biomass than wild type progenitors

Biodiesel produced by microalgae has great potential as a portable energy that can replace traditional hydrocarbon sources. One limitation of scaling up algal cultivation is the availability of macronutrients, particularly inorganic phosphate (Pi), which is a finite and dwindling resource. Here, Auxenochlorella protothecoides was adapted to low Pi conditions by continuous cultivation in growth media containing 100 times less Pi (17.15 µM PO4) than replete media for ∼ 40 generations. The low Pi-adapted A. protothecoides populations showed significantly higher growth rates, compared to wild type (WT) (natural, non-mutated) progenitor populations in batch experiments, with average maximum growth rates of 0.72 d−1 and 0.54 d−1, respectively. Total lipid profiling of the adapting A. protothecoides populations indicated a shift to non-phosphorus glycerolipids, based on UPLC/MS analyzes. The proportions of monogalactosyldiacylglycerol (MGDG) and sulfoquinovosyldiacyglycerol (SQDG) fluctuated during adaptation, accumulating 305% and 317% of the WT levels respectively by the final sampling. Time-course transcriptome profiling of A. protothecoides across all adaptation stages revealed initial increases in transcript levels, followed by global decreased expression. The short-term transcriptomic changes, prior to ∼ 11 generations, were associated with major metabolic pathways. The long-term changes indicated increased fatty acid turnover and a decrease in photosynthesis-related gene expression. Transcripts predicted to encode alternative oxidase and pyrophosphate-dependent phosphofructokinase fluctuated during adaptation. The selection of A. protothecoides under low Pi conditions resulted in a microalga variant that after only ∼40 generations utilized Pi more efficiently for growth than its wild type progenitor population, while also producing 1.22 times more biomass. The adaptive processes described herein produced commercially relevant strain material and provide avenues for future, targeted engineering of molecular pathways for increased Pi use efficiency in similar organisms. © 2022 The AuthorsOpen access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Identification of the biosynthetic keystep leading to the biosynthesis of dihydrochalcones in apple (Malus x domestica borkh.)

The apple tree is an agriculturally and economically important tree commonly used in food and beverages. Apple has also drawn attention in recent years due to its potential pharmaceutical and nutraceutical applications which are correlated with secondary metabolites. The major phenolic compounds found in apple belong to the class of dihydrochalcones, represented by various phloretin derivatives (e.g. phloridzin, sieboldin, trilobatin). Beside their contribution to the bitter taste of cider and the colour of apple juices due to oxidation products and they were also associated with health effects of apple fruits, and their processed products. The specific reaction that leads to the synthesis of dihydrocoumaroyl-CoA, the direct precourser of dihydrochalcones has not yet been determined. The availability of apple genomic and transcriptomic resources make apple an ideal plant to elucidate this key reductase activity that leads to the production of many valuable dihydrochalcones in apple but also in other plants. To identify genes involved in the synthesis of dihydrophenolic compounds the existing genome database of the Rosaceae was screened for apple genes with significant sequence similarity to Arabidopsis alkenal double-bond reductase. The functionally expressed apple double bond reductase exhibits p-coumaroyl-CoA reductase activity generating dihydrocoumaroyl-CoA. This finding contributes significantly to our understanding of dihydrophenol formation in plants

Identification and cloning of an NADPH-dependent hydroxycinnamoyl-CoA double bond reductase involved in dihydrochalcone formation in Malus × domestica Borkh

The apple tree (Malus sp.) is an agriculturally and economically important source of food and beverages. Many of the health beneficial properties of apples are due to (poly)phenolic metabolites that they contain, including various dihydrochalcones. Although many of the genes and enzymes involved in polyphenol biosynthesis are known in many plant species, the specific reactions that lead to the biosynthesis of the dihydrochalcone precursor, p-dihydrocoumaroyl-CoA (3), are unknown. To identify genes involved in the synthesis of these metabolites, existing genome databases of the Rosaceae were screened for apple genes with significant sequence similarity to Arabidopsis alkenal double bond reductases. Herein described are the isolation and characterization of a Malus hydroxycinnamoyl-CoA double bond reductase, which catalyzed the NADPH-dependent reduction of p-coumaroyl-CoA and feruloyl-CoA to p-dihydrocoumaroyl-CoA and dihydroferuloyl-CoA, respectively. Its apparent Km values for p-coumaroyl-CoA, feruloyl-CoA and NADPH were 96.6, 92.9 and 101.3 μM, respectively. The Malus double bond reductase preferred feruloyl-CoA to p-coumaroyl-CoA as a substrate by a factor of 2.1 when comparing catalytic efficiencies in vitro. Expression analysis of the hydroxycinnamoyl-CoA double bond reductase gene revealed that its transcript levels showed significant variation in tissues of different developmental stages, but was expressed when expected for involvement in dihydrochalcone formation. Thus, the hydroxycinnamoyl-CoA double bond reductase appears to be responsible for the reduction of the α,β-unsaturated double bond of p-coumaroyl-CoA, the first step of dihydrochalcone biosynthesis in apple tissues, and may be involved in the production of these compound

Dihydrochalcones as natural sweeteners against "modern" diseases

Humans love the taste of sweet foods, a craving likely due to our natural instinct to search for high calorie foods. However, obesity, diabetes and high blood pressure have become common health issues in the modern world, and therefore there is increasing demand for foods containing decreased calories and sugar levels. Fruit trees such as citrus have been bred over thousands of years to bear high sugar content fruit, and thus, while apple fruit is considered healthy for all in some respects (fiber, antioxidants), the high sugar content is a problem for a growing worldwide population suffering from "modern" diseases. One possible strategy/solution is to develop fruits to contain natural low-calorie sweeteners (e.g. dihydrochalcone), which would allow breeding for reduced fruit sugar levels while maintaining sweetness. Dihydrochalcone-glycosides are a family of sweet tasting naturally occurring bicyclic aromatic compounds. For instance, phloretin, a simple dihydrochalcone found in plants, is glycosylated at the 4' position to obtain the sweet tasting trilobatin. Phloretin and trilobatin accumulate in low levels in Malus species, in some tropical citrus species, and in a few other plants (Gosch et al., 2010). Although many of the genes and enzymes involved in polyphenol biosynthesis are known in many plant species, the specific reactions that lead to the biosynthesis of the proposed dihydrochalcone precursor, p-dihydrocoumaroyl-CoA, are unknown. Here we describe the isolation and characterization of a Malus hydroxycinnamoyl-CoA double bond reductase, which catalyzed the NADPH-dependent reduction of p-coumaroyl-CoA and feruloyl-CoA to p-dihydrocoumaroyl-CoA and dihydroferuloyl-CoA, respectively. Its apparent Km values for p-coumaroyl-CoA, feruloyl-CoA and NADPH were 96.6 µM, 92.9 µM and 101.3 µM, respectively. The Malus double bond reductase preferred feruloyl-CoA to p-coumaroyl-CoA as a substrate by a factor of 2.1 when comparing catalytic efficiencies. Expression analysis of the hydroxycinnamoyl-CoA double bond reductase gene revealed that its transcript levels showed significant variation in tissues of different developmental stages, but was expressed when expected for involvement in dihydrochalcone formation. Thus, the hydroxycinnamoyl-CoA double bond reductase appears to be responsible for the reduction of the α,β-unsaturated double bond of p-coumaroyl-CoA, the first step of dihydrochalcone biosynthesis in apple tissues, and may be involved in the production of these compound

Applications of Metabolomics in Agriculture

Biological systems are exceedingly complex. The unraveling of the genome in plants and humans revealed fewer than the anticipated number of genes. Therefore, other processes such as the regulation of gene expression, the action of gene products, and the metabolic networks resulting from catalytic proteins must make fundamental contributions to the remarkable diversity inherent in living systems. Metabolomics is a relatively new approach aimed at improved understanding of these metabolic networks and the subsequent biochemical composition of plants and other biological organisms. Analytical tools within metabolomics including mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy can profile the impact of time, stress, nutritional status, and environmental perturbation on hundreds of metabolites simultaneously resulting in massive, complex data sets. This information, in combination with transcriptomics and proteomics, has the potential to generate a more complete picture of the composition of food and feed products, to optimize crop trait development, and to enhance diet and health. Selected presentations from an American Chemical Society symposium held in March 2005 have been assembled to highlight the emerging application of metabolomics in agricultur