SummaryTo obtain better insight into the mechanisms of selenium hyperaccumulation in Stanleya pinnata, transcriptome‐wide differences in root and shoot gene expression levels were investigated in S. pinnata and related nonaccumulator Stanleya elata grown with or without 20 μm selenate. Genes predicted to be involved in sulphate/selenate transport and assimilation or in oxidative stress resistance (glutathione‐related genes and peroxidases) were among the most differentially expressed between species; many showed constitutively elevated expression in S. pinnata. A number of defence‐related genes predicted to mediate synthesis and signalling of defence hormones jasmonic acid (JA, reported to induce sulphur assimilatory and glutathione biosynthesis genes), salicylic acid (SA) and ethylene were also more expressed in S. pinnata than S. elata. Several upstream signalling genes that up‐regulate defence hormone synthesis showed higher expression in S. pinnata than S. elata and might trigger these selenium‐mediated defence responses. Thus, selenium hyperaccumulation and hypertolerance in S. pinnata may be mediated by constitutive, up‐regulated JA, SA and ethylene‐mediated defence systems, associated with elevated expression of genes involved in sulphate/selenate uptake and assimilation or in antioxidant activity. Genes pinpointed in this study may be targets of genetic engineering of plants that may be employed in biofortification or phytoremediation.

RESUMEEn raison des caracteristiques relatives ala geometrte de oisee des radars aantenne syntbetique (RAAS) montes abard des satellites SEASAT, ERS-1, jERS-1 et RADARSAT, les images acquises par ces capteurs presenteront une sensibilite radiometrique et geometrique a la topograpbie locale nettement superieure aux images optiques correspondantes obtenues apartir des satellites Landsat et SPOT II est absolument essentiel, par consequent, que des modeles numeriques d'eleuation fassent partie integrante de toute analyse des capacites des radars. Get article presente uneformulation analytique unifiee d'une methode d'analyse par simulation des RAAS -incluant le geocodage des donnees et la generation de produits avaleur ajoutee-idont le but est de faciliter l'interpretation de la scene. Les auteurs proposent le concept de facteur d 'ecbelle topograpbique pour quantifier le taux moyen de distorsion geometrique dans une scene RAAS, suppose que l'on connaisse la uariabilite de l'eleuation d'un site. Un prototype de progicielfonde sur ces algoritbmes a ete mis au point apeu de frais al'aide d'un ordinateurpersonnel et a ete utilise pour geocoder deux scenes obtenues apartir du radar aantenne syntbetique monte a bord du satellite SEASAT, qui presentent des distorsions dues au terrain al'ecbelle comprise entre 1 et 1,5 km. Des precisions de l'ordre de 75 a150 mont ete obtenues apartir de modeles numeriques d'eleuation al'ecbelle du 1 : 250000. SUMMARYBecause ofthe viewing geometry characteristics ofspaceborne SARs carried by SEASAT, ERS-1, jERS-1, and RADARSAT, imagesfrom these sensors will exhibit Significantly greater radiometric and geometric sensitivity to local topographic relief than corresponding optical imagesfrom Landsat and SPOT sensors. It is imperative, therefore, that digital elevation models be an integralpart ofany SAR analysis capability. This paperpresents a unified analytic formulation ofa simulation-based approach to spacebome SAR analysis, including image geocoding and "value-added" product generation to aid in subsequent scene interpretation. The concept ofa topographic-scaling factor is proposed to quantify the average level of geometric distortion in a SAR scene given a knowledge ofthe elevation variability over a site. A prototype software package based on these algorithms has been implemented on a low-cost personal computer platform and used to geocode two example SEASAT SAR scenes that exhibit terrain-induced distortions on the scale of1 km to 1.5 km. Final geocoding accuracies of 75 m to 150 m have been achieved using a 1:250 OOO-scale DBMs.

No abstract

No abstract

No abstract