Fractional boundary value problems: Analysis and numerical methods

This is the author's PDF of an article published in Fractional calculus and applied analysis 2011. The original publication is available at www.springerlink.comThis journal article discusses nonlinear boundary value problems.Fundacao para a Ciencia e Tecnologi

Advances in understanding the mechanism of action of the auxin permease AUX1

In over 40 years of research on the cellular uptake of auxin it is somewhat chastening that we have elabourated little on the original kinetic descriptions of auxin uptake by plant cells made by Rubery and Sheldrake in 1974. Every aspect of that seminal work has been investigated in detail and the uptake activity they measured is now known to be attributed to the AUX1/LAX family of permeases. Recent pharmacological studies have defined the substrate specificity of AUX1, biochemical studies have evaluated its permeability to auxin in plant cell membranes, and rigourous kinetic studies have confirmed the affinity of AUX1 for IAA and synthetic auxins. Advances in genome sequencing have provided a rich resource for informatic analysis of the ancestry of AUX1 and the LAX proteins and, along with models of topology, suggest mechanistic links to families of eukaryotic proton co-transporters for which crystal structures have been presented. The insights gained from all the accumulated research reflect the brilliance of Rubery and Sheldrake’s early work, but recent biochemical analyses are starting to advance further our understanding of this vitally important family of auxin transport proteins

Single-chain glycopolymer folding via host-guest interactions and its unprecedented effect on DC-SIGN binding

Reversible self-folding actions of natural biomacromolecules play crucial roles for specific and unique biological functions in Nature. Hence, controlled folding of single polymer chains has attracted significant attention in recent years. Herein, reversible single-chain folded glycopolymer structures in α-shape with different density of sugar moieties in the knot were created. The influence of folding as well as the sugar density in the knot was investigated on the binding capability with lectins, such as ConA, DC-SIGN and DC-SIGNR. The synthesis of triblock glycocopolymers bearing β-CD and adamantane for the host-guest interaction and also mannose residues for the lectin interaction was achieved using the reversible addition-fragmentation chain transfer (RAFT) polymerization technique. The reversible single-chain folding of glycopolymers was achieved under a high dilution of an aqueous solution and the self-assembled folding was monitored by 2D nuclear overhauser enhancement spectroscopy (NOESY) NMR and dynamic light scattering. The lectin binding profiles consistently provided an unprecedented effect of single chain folding as the single-chain folded structures enhanced greatly the binding ability in comparison to the unfolded linear structures

The supply of fish oil to aquaculture: a role for transgenic oilseed crops?

The importance of an alternative and sustainable supply of omega-3 long chain polyunsaturated fatty acids (LC omega-3) has long been established. As these biologically active fatty acids have a role in nutrition and health, there is an ever increasing demand for oils containing LC omega-3 e.g. eicosapentaenoic (EPA) and docosahexaenoic acid (DHA). These fatty acids are produced by micoroganisms and enter our diet through the consumption of fish. However, in order that the nutritional requirements of fish in aquaculture are met and sufficient levels are deposited to meet the requirements of human consumers, EPA and DHA must be supplied in excess. Given the importance of the aquaculture industry in delivering healthy foodstuff, the question of how to resource the supply of LC omega-3 then arises; traditional sources of EPA and DHA (fish oil) are challenged, whilst vegetable oils do not contain EPA or DHA. Therefore research efforts have focused on the successful reconstitution of LC omega-3 biosynthesis in oilseed crops. The production of EPA and DHA in the seed oil of agricultural crops has the capacity to deliver large volumes of these fatty acids. The expression of optimised combinations of the genes required to produce these fatty acids in the seed of the crop Camelina sativa has been achieved and the utility of this approach demonstrated. This represents a significant breakthrough – the provision of an effective alternative to the use of omega-3 fish oil by the global aquaculture industry

Radio Observations of SN 1980K: Evidence for Rapid Presupernova Evolution

New observations of SN 1980K made with the VLA at 20 and 6 cm from 1994 April through 1996 October show that the supernova (SN) has undergone a significant change in its radio emission evolution, dropping by a factor of ~2 below the flux density S \propto t^{-0.73} power-law decline with time t observed earlier. However, although S at all observed frequencies has decreased significantly, its current spectral index of \alpha= -0.42\pm0.15 (S \propto \nu^{+\alpha}) is consistent with the previous spectral index of \alpha=-0.60_{-0.07}^{+0.04}. It is suggested that this decrease in emission may be due to the SN shock entering a new region of the circumstellar material which has a lower density than that expected for a constant speed (w), constant mass-loss rate (Mdot) wind from the progenitor. If such an interpretation is correct, the difference in wind and shock speeds appears to indicate a significant evolution in the mass-loss history of the SN progenitor ~10^4 years before explosion, with a change in circumstellar density (\propto Mdot/w) occurring over a time span of \lesssim 4 kyr. Such features could be explained in terms of a fast ``blue-loop'' evolutionary phase of a relatively massive pre-SN progenitor star. If so, we may, for the first time, provide a stringent constraint on the mass of the SN progenitor based solely on the SN's radio emission.Comment: 22 pages, 3 figures, to appear in Ap

Phyllostictine A : total synthesis, structural verification and determination of substructure responsible for plant growth inhibition

The first total synthesis of phyllostictine A (PA) is reported, which confirms the structure of this fungal metabolite and its (6S,7R,8S)-stereochemistry. Both synthetic PA and an analogue containing the 5-methylene-1,5-dihydro-2H-pyrrol-2-one nucleus exhibit μM inhibitory activity in root growth assays against Arabidopsis thaliana, indicating that this heterocyclic subunit is key to the herbicidal activity of the natural product

Overexpression of an endogenous type 2 diacylglycerol acyltransferase in the marine diatom Phaeodactylum tricornutum enhances lipid production and omega-3 long-chain polyunsaturated fatty acid content

Background: Oleaginous microalgae represent a valuable resource for the production of high-value molecules. Considering the importance of omega-3 long-chain polyunsaturated fatty acids (LC-PUFAs) for human health and nutrition the yields of high-value eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) require significant improvement to meet demand; however, the current cost of production remains high. A promising approach is to metabolically engineer strains with enhanced levels of triacylglycerols (TAGs) enriched in EPA and DHA. Results: Recently, we have engineered the marine diatom Phaeodactylum tricornutum to accumulate enhanced levels of DHA in TAG. To further improve the incorporation of omega-3 LC-PUFAs in TAG, we focused our effort on the identification of a type 2 acyl-CoA:diacylglycerol acyltransferase (DGAT) capable of improving lipid production and the incorporation of DHA in TAG. DGAT is a key enzyme in lipid synthesis. Following a diatom based in vivo screen of candidate DGATs, a native P. tricornutum DGAT2B was taken forward for detailed characterisation. Overexpression of the endogenous P. tricornutum DGAT2B was confirmed by qRT-PCR and the transgenic strain grew successfully in comparison to wildtype. PtDGAT2B has broad substrate specificity with preferences for C16 and LC-PUFAs acyl groups. Moreover, the overexpression of an endogenous DGAT2B resulted in higher lipid yields and enhanced levels of DHA in TAG. Furthermore, a combined overexpression of the endogenous DGAT2B and ectopic expression of a Δ5-elongase showed how iterative metabolic engineering can be used to increase DHA and TAG content, irrespective of nitrogen treatment. Conclusion: This study provides further insight into lipid metabolism in P. tricornutum and suggests a metabolic engineering approach for the efficient production of EPA and DHA in microalgae

Synthetic auxin herbicides : finding the lock and key to weed resistance

Synthetic auxin herbicides are designed to mimic indole-3-acetic acid (IAA), an integral plant hormone affecting cell growth, development, and tropism. In this review, we explore target site genes in the auxin signaling pathway including SCFTIR1/AFB, Aux/IAA, and ARFs that are confirmed or proposed mechanisms for weed resistance to synthetic auxin herbicides. Resistance to auxin herbicides by metabolism, either by enhanced cytochrome P450 detoxification or by loss of pro-herbicide activation, is a major non-target-site resistance pathway. We speculate about potential fitness costs of resistance due to effects of resistance-conferring mutations, provide insight into the role of polyploidy in synthetic auxin resistance evolution, and address the genetic resources available for weeds. This knowledge will be the key to unlock the long-standing questions as to which components of the auxin signaling pathway are most likely to have a role in resistance evolution. We propose that an ambitious research effort into synthetic auxin herbicide/target site interactions is needed to 1) explain why some synthetic auxin chemical families have activity on certain dicot plant families but not others and 2) fully elucidate target-site cross-resistance patterns among synthetic auxin chemical families to guide best practices for resistance management

Orbital Solutions and Absolute Elements of the Massive Algol Binary ET Tauri

We acquired differential UBV photoelectric photometry and radial velocities of the relatively bright, understudied, massive Algol binary ET Tau and utilized the Wilson-Devinney (WD) analysis program to obtain a simultaneous solution of these observations. To improve the orbital ephemeris, the V measurements from the ASAS program were also analyzed. Because of the very rapid rotation of the significantly more massive and hotter component (B2/3 spectral class), only radial velocities of the secondary component, which has a ∼B7 spectral class, could be measured. We derive masses of ${M}_{1}=14.34\pm 0.28\,{M}_{\odot }$ and ${M}_{2}=6.339\pm 0.117\,{M}_{\odot }$ and equal-volume radii of ${R}_{1}=6.356\pm 0.056\,{R}_{\odot }$ and ${R}_{2}=11.84\pm 0.10\,{R}_{\odot }$ for the primary and secondary, respectively. The secondary is filling its Roche lobe, so the system is semi-detached. The effective temperature of the secondary was held fixed at 15,000 K, and the primary\u27s temperature was found to be $\mathrm{30,280}\pm 109$ K. The system, which has a period of 5.996883 ± 0.000002 days, is assumed to have a circular orbit and is seen at an inclination of 79\buildrel{\circ}\over{.} 55\pm 0\buildrel{\circ}\over{.} 05