Phloem sap intricacy and interplay with aphid feeding

Aphididae feed upon the plant sieve elements (SE), where they ingest sugars, nitrogen compounds and other nutrients. For ingestion, aphid stylets penetrate SE, and because of the high hydrostatic pressure in SE, phloem sap exudes out into the stylets. Severing stylets to sample phloem exudates (i.e. stylectomy) has been used extensively for the study of phloem contents. Alternative sampling techniques are spontaneous exudation upon wounding that only works in a few plant species, and the popular EDTA-facilitated exudation technique. These approaches have allowed fundamental advances on the understanding of phloem sap composition and sieve tube physiology, which are surveyed in this review. A more complete picture of metabolites, ions, proteins and RNAs present in phloem sap is now available, which has provided large evidence for the phloem role as a signalling network in addition to its primary role in partitioning of photo-assimilates. Thus, phloem sap sampling methods can have remarkable applications to analyse plant nutrition, physiology and defence responses. Since aphid behaviour is suspected to be affected by phloem sap quality, attempts to manipulate phloem sap content were recently undertaken based on deregulation in mutant plants of genes controlling amino acid or sugar content of phloem sap. This opens up new strategies to control aphid settlement on a plant host

Etude et mise au point de transducteurs piézoélectriques ultrasensibles fonctionnant en milieu liquide.

Quartz microbalance is used in liquid media for various investigations, electrochemistry, biology. . . since the early 1980s. Its attraction lies in the fact that the variations in mass, caused by various physico-chemical phenomenes that may occur on the surface of the sensor, generate a lineary variation of the frequency of resonance of the device measured by the intermediary of an oscillator. By determining the latter, this change in mass can be determined with great precision: a few nanograms for a fundamental frequency of 6 mhz. However, and generally speaking, two problems arise: on the one hand, the lack of sensitivity of devices in liquid medium for the detection of small molecule and on the other hand, the interpretation of the answers of the microbalance in the case of thin layers not ideally elastic. The mass sensitivity is proportional to the edge of the resonance frequency. By increasing this sensitivity, this sensitivity can be increased in a significant way: a factor of 20 is obtained. In this work, we propose a study on a transducer operating in liquid medium at 27 mhz in volume waves (thickness shearing mode) and a plate wave device operating at 100 mhz. The second point focuses on the validation of the response of the quartz microbalance. This was undertaken by developing an electroacoustic admittance measure on the resonator. A physico-chemical model, based on the transmission lines, allows to connect the different physico-chemical quantities of a thin layer, thickness, density, complex shear coefficient, to the electroacoustic experimental admittance. This theoretical model has been validated in various environments: water/glycerol mixtures, oils, metals and electrodepose polymers.La microbalance a quartz est utilisee en milieu liquide pour des investigations variees, electrochimie, biologie. . . , depuis le debut des annees 1980. Son attrait reside dans le fait que les variations de masse, occasionnees par differents phenomenes physico-chimiques pouvant survenir a la surface du capteur, engendrent une variation lineaire de la frequence de resonance du dispositif mesuree par l'intermediaire d'un oscillateur. En determinant cette derniere, ce changement de masse peut etre determine avec une grande precision : quelques nanogrammes pour une frequence fondamentale de 6 mhz. Toutefois et d'une maniere generale, deux problemes se posent : d'une part, le manque de sensibilite des dispositifs en milieu liquide pour la detection de petite molecule et d'autre part, l'interpretation des reponses de la microbalance dans le cas de couches minces non idealement elastiques. La sensibilite massique est proportionnelle au carre de la frequence de resonance. En augmentant celle-ci, cette sensibilite peut etre accrue d'une maniere non negligeable : un facteur vingt est obtenu. Dans ce travail, nous proposons une etude sur un transducteur fonctionnant en milieu liquide a 27 mhz en ondes de volume (mode de cisaillement d'epaisseur) et sur un dispositif a ondes de plaques fonctionnant a 100 mhz. Le second point est focalise sur la validation de la reponse de la microbalance a quartz. Celle-ci a ete entreprise en mettant au point une mesure d'admittance electroacoustique sur le resonateur. Un modele physico-chimique, base sur les lignes de transmission, permet de relier les differentes grandeurs physico-chimiques d'une couche mince, epaisseur, densite, coefficient complexe de cisaillement, a l'admittance electroacoustique experimentale. Des milieux etalons ont permis de valider ce modele theorique : melanges eau/glycerol, huiles, metaux et polymeres electrodeposes

Être plante sur les grèves fluviatiles : stratégies de croissance et de reproduction de la végétation d'étiage.

Les grèves sableuses et graveleuses qui apparaissent dans le lit mineur des grands fleuves lors des périodes d'étiage sont un type d'habitat naturel devenu rare au cours du dernier siècle. Les végétaux qui s'y installent sont soumis à une série de différents types de stress et de perturbation : (i) une seulement courte période sans inondation (ii) un courant d'eau plus au moins fort le reste de l'année (iii) lors de la période d'étiage des perturbations fréquentes par des oscillations des niveau d'eaux si elles se trouvent près de la ligne d'eau ou alors une disponibilité limitée de nutriments, un manque d'eau et un stress thermique sur des sites pus hauts et abrités.Cet exposé présentera une étude menée sur la végétation pionnière des grèves de la Loire moyenne. Ici se côtoient des espèces patrimoniales et des espèces d'origine exotiques, dont certaines réputées invasives. Une première étude a suivie, sur des placettes permanentes installées de manière semi-aléatoire à trois niveaux de distance du chenal actif, les stratégies de croissance et de reproduction d'un millier d'individus appartenant à 35 espèces. L'objectif de l'étude était de révéler les différentes stratégies de croissance et de reproduction associées aux différents profils stress/perturbation et de déterminer pour chacun la stratégie paraissant la plus efficace.L'étude a fournie des données statistiquement exploitables pour une quinzaine d'espèces, essentiellement herbacées et majoritairement thérophytes. On distingue espèces ubiquistes, espèces des sites humides et perturbés et espèces des sites secs à stress thermique et hydrique. Dans chacun de ces trois groupes existe un panache de stratégies. Les espèces considérées invasives (Paspalum disticum et Ludwigia peploides) se singularisent par une expansion latérale parmi les plus fortes et une reproduction sexuée particulièrement faible. Ceci laisse penser que ces espèces occupent une niche préalablement non occupé dans ce type d'habitat

Growth and Reproduction Strategies of plants in Fluvial Sand and Gravel Habitats during low-water periods

Sandy and gravely shores and banks that appear during low-flow periods of great rivers are a type of marginal habitat that has become rare during the last century. Plants that establish here are submitted to a series of highly growth-constraining conditions: (i) an only short inundation-free period, (ii) scouring water flow the rest of the year, (iii) frequent disturbances during the low-water period by fluctuating water levels if they are situated on low elevations, or nutrient limitation, drought and thermal stress on higher elevations.The present study presents the results of a small-scale monitoring of vegetation during the summer low-water period on the middle reaches of the Loire River (France). This vegetation hosts endangered plant species as well as exotic ones. Survivorship, growth, and phenology of reproduction were monitored throughout low-water season. A total of about 1000 individual plants on three levels of elevation were observed. The results are analysed in terms of plant strategies and confronted with the stress/disturbance profiles of the habitats. The aim of the study is to single out the most efficient strategies per type of stress/disturbance profile. This will allow predicting vegetation dynamics, especially the dynamics of endangered and exotic species

More than weeds Spontaneous vegetation in streets as a neglected element of urban biodiversity

International audienceCompared to green spaces, the ecological value of built elements has been largely ignored despite representing the main land cover in cities. In streets, pavements are linear built elements which are omnipresent in all neighborhood types and which extend over large cumulative areas in cities. We assessed the capacity of pavements to promote spontaneous flora and investigated the drivers of pavement plant assemblages. Based on a plant survey along 48 km of pavements in a French city which no longer uses pesticides, we examined the relative importance of multi-scale factors (i.e. landscape context, pavement characteristics and frequency of manual weeding) on different aspects of pavement plant communities including total plant cover, species richness and beta-diversity. More than 300 species were recorded. Plant assemblages were mainly determined by the pavement type, plant cover and species richness being much higher on sandy than on asphalt pavements. There were marked differences in species composition between pavement types with many more species associated with sandy than with asphalt pavements. We found a higher species richness and plant cover on pavements located in commercial and industrial areas than in residential neighborhoods. The effects of weeding frequency and the presence of green space around pavements were marginally important. We demonstrate that pavements with a high level of permeability play a major role in promoting urban biodiversity which should be taken into account by urban planners. We recommend that ecologists work with civil engineers and landscape architects to develop new urban ecological designs. © 2019 Elsevier B.V

The role of wastelands to enhance biodiversity in cities: a review.

International audienc

How can wastelands promote biodiversity in cities ? A review.

International audienceUrbanisation leads to natural habitats being fragmented with various effects according to the species and their ecological characteristics. Paradoxically, the urbanisation process creates relatively unused environments, wastelands, habitats which could contribute to biodiversity conservation in urban regions. In this review we examined the role of wastelands in maintaining biodiversity in the city and assessed the different factors responsible for wasteland biodiversity. 37 articles were suitable for our aim. Most of the studies have been conducted in large cities in Western and Central Europe. A wasteland is defined as an abandoned site with spontaneous vegetation (i.e. wild grown vegetation). In most cases, wastelands harbour more species than other urban green spaces. The processes which affect the biodiversity of wastelands operate on two different levels. Locally, the area size, age, soil, microclimate and the vegetation structure are the dominant factors. As in other environments, the species richness increases with the size of the wasteland. Wastelands of different ages include different stages of vegetation, ranging from pioneer to pre-forest stages, and consequently harbour different communities of plants and animals. The diversity of anthropogenic soil substrates leads to different plant communities. At the landscape scale, matrix composition and geographic connectivity between wastelands influence the biodiversity of wastelands, although to a lesser extent than the local features. We show that wastelands have a real potential to contribute to biodiversity conservation in urban regions. At the city scale, they represent habitats which urban planners need to take into account and include in dynamic urban planning

Ontologies and Rules for Access Control: a Feature Oriented Survey

"1st workshop on Collaboration in knowledge discovery and decision making: Applications to sustainable agriculture " has been organized by six research teams from France, Argentina, Colombia and ChileInternational audienceAccess-control systems are key components to guarantee the security and confidentiality of resource repositories. Most access-control systems that are today de facto standards were designed before the generalization of cloud services and Internet of Things. Such systems are particularly heavy to maintain in today's context, which gave rise to more flexible approaches based on logical description using semantic web technologies. In this paper, we propose a survey of these semantic approaches. Although this survey does not aim at being exhaustive, it offers the reader an overview of the main trends and their limitations

Éléments d'état de l'art sur l'extraction et la modélisation de règles formelles à partir de textes légaux

International audienceThe extraction of machine-interpretable formal statements from natural language texts is a challenging and widely studied research field today. One of the application frameworks of this research field consists in extracting formal rules from legal texts and regulations. This paper presents a synthesis of different approaches to extracting rules from legal regulations, and then to formally representing these rules. From this survey, we present the draft of a tool to help of a decision support tool for sharing sensitive information between different organizations, with the aim of validating that these shares comply with the applicable regulations (GDPR or European directives on the use of AI)L'extraction d'énoncés formels interprétables par une machine à partir de textes en langage naturel est un champ de recherche largement étudié aujourd'hui. Un des cadres d'application de ce domaine de recherche consiste à extraire des règles formelles à partir de textes de lois et de réglementations. Cet article présente une synthèse de différentes approches d'extraction de règles à partir de réglementations légales, puis de représentation formelle de ces règles. A partir de cette synthèse, nous présentons l'ébauche d'un outil d'aide à la décision de partage d'informations sensibles entre différentes organisations, dans l'optique de valider que ces partages soient conformes aux réglementations applicables (RGPD ou directives européennes sur l'usage de l'IA)