Mathematical Modelling of Auxin Transport in Plant Tissues:Flux Meets Signalling and Growth

Plant hormone auxin has critical roles in plant growth, dependent on its heterogeneous distribution in plant tissues. Exactly how auxin transport and developmental processes such as growth coordinate to achieve the precise patterns of auxin observed experimentally is not well understood. Here we use mathematical modelling to examine the interplay between auxin dynamics and growth and their contribution to formation of patterns in auxin distribution in plant tissues. Mathematical models describing the auxin-related signalling pathway, PIN and AUX1 dynamics, auxin transport, and cell growth in plant tissues are derived. A key assumption of our models is the regulation of PIN proteins by the auxin-responsive ARF-Aux/IAA signalling pathway, with upregulation of PIN biosynthesis by ARFs. Models are analysed and solved numerically to examine the long-time behaviour and auxin distribution. Changes in auxin-related signalling processes are shown to be able to trigger transition between passage and spot type patterns in auxin distribution. The model was also shown to be able to generate isolated cells with oscillatory dynamics in levels of components of the auxin signalling pathway which could explain oscillations in levels of ARF targets that have been observed experimentally. Cell growth was shown to have influence on PIN polarisation and determination of auxin distribution patterns. Numerical simulation results indicate that auxin-related signalling processes can explain the different patterns in auxin distributions observed in plant tissues, whereas the interplay between auxin transport and growth can explain the `reverse-fountain' pattern in auxin distribution observed at plant root tips

Herbivore induction of the glucosinolate-myrosinase defense system: major trends, biochemical bases and ecological significance

Like many other plant defense compounds, glucosinolates are present constitutively in plant tissues, but are also induced to higher levels by herbivore attack. Of the major glucosinolate types, indolic glucosinolates are most frequently induced regardl

Homogenization approach to water transport in plant tissues with periodic microstructures

Water flow in plant tissues takes place in two different physical domains separated by semipermeable membranes: cell insides and cell walls. The assembly of all cell insides and cell walls are termed symplast and apoplast, respectively. Water transport is pressure driven in both, where osmosis plays an essential role in membrane crossing. In this paper, a microscopic model of water flow and transport of an osmotically active solute in a plant tissue is considered. The model is posed on the scale of a single cell and the tissue is assumed to be composed of periodically distributed cells. The flow in the symplast can be regarded as a viscous Stokes flow, while Darcy's law applies in the porous apoplast. Transmission conditions at the interface (semipermeable membrane) are obtained by balancing the mass fluxes through the interface and by describing the protein mediated transport as a surface reaction. Applying homogenization techniques, macroscopic equations for water and solute transport in a plant tissue are derived. The macroscopic problem is given by a Darcy law with a force term proportional to the difference in concentrations of the osmotically active solute in the symplast and apoplast; i.e. the flow is also driven by the local concentration difference and its direction can be different than the one prescribed by the pressure gradient.Comment: 31 page

The search for exudates from Eurasian watermilfoil and hydrilla

Secondary metabolites are produced by aquatic plants, and in some instances, exudation of these metabolites into the surrounding water has been detected. To determine whether infestations of Eurasian watermilfoil or hydrilla produce such exudates, plant tissues and water samples were collected from laboratory cultures and pond populations and were analyzed using solid phase extraction, HPLC, and various methods of mass spectrometry including electrospray ionization, GC/MS, electron impact and chemical ionization. Previously reported compounds such as tellimagrandin II (from Eurasian watermilfoil) and a caffeic acid ester (from hvdrilla), along with a newly discovered flavonoid, cyanidin 3 dimalonyl glucoside (from hydrilla), were readily detected in plant tissues used in this research but were not detected in any of the water samples. If compounds are being released, as suggested by researchers using axenic cultures, we hypothesize that they may be rapidly degraded by bacteria and therefore undetectable

Zone lines in plant tissues

I. The black lines formed by Xylaria polymorpha (Pers.) Grey. in hardwoods. [From THE ANNALS OF APPLIED BIOLOGY, VoL. XX, No. 1, pp. 123 -145, FEBRUARY, 1933.]II . The black lines formed by Armillaria mellea (Vahl) Quel.The two papers presented in this thesis deal chiefly with a single type of zone line, namely, the rind of a pseudosclerotium buried in the tissues of the host. Although this is the commonest kind of zone line, there are several other types of zone line about which very little is known. A. brief outline of these lines has already been given on page 126 of the Xylaria paper, One such line is formed by the deposition of "wound gum" as in the attack by Fom.es applanatus on beech, while another is formed by antagonistic mycelia on the same substratum as has been described by Weir (2) in the case of F F. pinicola and F. fomentarius in birch. This latter phenomenon has also been described as being produced by strains of myxobacteria when colonised some little distance apart on agar (1). The writer has in his possession a zone line reputed to be formed between the rots of Polyporus adustus and F. igniarius but proof of this must await further investigation. Indeed, one of the difficulties of research on zone lines has been the necessity for working out the whole biology of the organisms concerned,as the zone lines, although often a matter for comment, have seldom been investigated.Mary accounts of zone- producing fungi even omit to mention the presence of zone lines in the substratum. Thus before any decision as to the nature of the zone line can be made it is generally necessary to make a complete investigation of the fungus suspected of forming it.This explanation of the zone line as the bounding layer of a peeudosolerotium in the substratum is one which may come to be applied to a large number of fungi. For example, it may be suggested that the black transverse /lines on leaves attacked by Lophodermium pinastri are of such a nature, while it can readily be shown by inoculation that Sclerotinia fructigena will form black zones in apples. The writer believes that it will be possible to demonstrate all stages between the true scierotium, the pseudosclerotium buried in the substratum and the case where part of the host, such as the fruit, forms in effect a sc lerotium for the attacking fungus. Indeed, this study of zone lines is only beginning to uncover facts which may throw more light on the physiology of the fungi and their methods of reproduction

The use of in-situ deployments to examine the success of water quality mitigation measures on a watercress farm

Watercress has long been believed to affect macroinvertebrate communities in chalk streams. Harvesting and washing watercress damages plant tissues and releases isothiocyanates which are potential toxicants to Gammarus pulex (L.). This study examined whether impacts on G. pulex of watercress farm factory wash water could be mitigated by treating via recirculation through the watercress beds

Quantitative permeability imaging of plant tissues

A method for mapping tissue permeability based on time-dependent diffusion measurements is presented. A pulsed field gradient sequence to measure the diffusion encoding time dependence of the diffusion coefficients based on the detection of stimulated spin echoes to enable long diffusion times is combined with a turbo spin echo sequence for fast NMR imaging (MRI). A fitting function is suggested to describe the time dependence of the apparent diffusion constant in porous (bio-)materials, even if the time range of the apparent diffusion coefficient is limited due to relaxation of the magnetization. The method is demonstrated by characterizing anisotropic cell dimensions and permeability on a subpixel level of different tissues of a carrot (Daucus carota) taproot in the radial and axial directions

Host range, purification, and genetic variability in Sweet potato chlorotic fleck virus

Sweet potato chlorotic fleck virus (SPCFV) has recently been classified as a putative new member of the genus Carlavirus (family Flexiviridae) on the basis of its molecular properties. In this study, SPCFV was characterized in terms of host range, physical and biological characteristics, and genetic variability. In addition to sweet potato, SPCFV infected some plant species in the families Convolvulaceae, Chenopodiaceae, and Solanaceae. Limited numbers of virus particles were observed in the assimilation parenchyma cells of infected plant tissues; some cells had a distorted and enlarged endoplasmic reticulum though without any cytoplasmic and amorphous inclusions. The normal length of SPCFV particles was determined to be approximately 800 nm. In enzyme-linked immunosorbent assays, polyclonal antibodies raised against purified SPCFV virions were able to detect the virus in infected sweet potato and indicator plant tissues. In immunoelectron microscopy, SPCFV particles were all strongly decorated when reacted with homologous antiserum. Comparison of the 3′ terminal part of the genome of a range of geographically diverse isolates revealed a high level of genetic diversity. The amino acid sequence identity in the coat protein and the nucleic acid binding protein ranged from 89 to 99.7% and from 75.9 to 99.2%, respectively. Phylogenetic analysis of both proteins showed a geographically associated clustering into two genogroups