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

Heterologous Expression of a Membrane-Spanning Auxin Importer: Implications for Functional Analyses of Auxin Transporters

Biochemical studies of plant auxin transporters in vivo are made difficult by the presence of multiple auxin transporters and auxin-interacting proteins. Furthermore, the expression level of most such transporters in plants is likely to be too low for purification and downstream functional analysis. Heterologous expression systems should address both of these issues. We have examined a number of such systems for their efficiency in expressing AUX1 from Arabidopsis thaliana. We find that a eukaryotic system based upon infection of insect cells with recombinant baculovirus provides a high level, easily scalable expression system capable of delivering a functional assay for AUX1. Furthermore, a transient transfection system in mammalian cells enables localization of AUX1 and AUX1-mediated transport of auxin to be investigated. In contrast, we were unable to utilise P. pastoris or L. lactis expression systems to reliably express AUX1

Characterization of AXR4 protein function from Arabidopsis thaliana

In plants, polar auxin transport requires the activity of auxin transport carrier which consists of influx and efflux protein (Palme and Galweiler, 2001). Genetic evidence suggests that AXR4 and AUXl are involved in regulation of polar auxin transport (Hobbie and Estelle, 1995; Yamamoto and Yamamoto, 1999; Marchant et al., 1999). AUXl encodes an auxin influx carrier (Yang et al, 2006). AUXl trafficking to the plasma membrane of root cells are dependent on the AXR4 gene product (Dharmasiri et al., 2006). The axr4 mutation selectively disrupts targeting of HA-AUXl but not other known Arabidopsis plasma membrane proteins. This project to characterize the AXR4 protein, the protein function and the basis of its regulation of AUXl trafficking.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Binding of Auxin to the Arabidopsis Auxin Influx Transporter AUX1

The cellular import of the hormone auxin is a fundamental requirement for the generation of auxin gradients that control a multitude of plant developmental processes. The AUX/LAX family of auxin importers, exemplified by AUX1 from Arabidopsis (Arabidopsis thaliana), has been shown to mediate auxin import when expressed heterologously. The quantitative nature of the interaction between AUX1 and its transport substrate indole-3-acetic acid (IAA) is incompletely understood, and we sought to address this in the present investigation. We expressed AUX1 to high levels in a baculovirus expression system and prepared membrane fragments from baculovirus-infected insect cells. These membranes proved suitable for determination of the binding of IAA to AUX1 and enabled us to determine a Kd of 2.6 μM, comparable with estimates for the Km for IAA transport. The efficacy of a number of auxin analogues and auxin transport inhibitors to displace IAA binding from AUX1 has also been determined and can be rationalized in terms of their physiological effects. Determination of the parameters describing the initial interaction between a plant transporter and its hormone ligand provides novel quantitative data for modeling auxin fluxes