The role of plant growth promoting bacteria on arsenic removal: a review of existing perspectives

Phytobial remediation is an innovative tool that uses plants and microbes to mitigate Arsenic (As) contamination of the environment. Recently, plant growth-promoting bacteria (PGPB) that assists phytoremediation has been highly touted for both improving plant metal tolerance and promoting plant growth while achieving the goal of large-scale removal of As. This review focuses on the PGPB characteristics influencing plants and the mechanisms in which they function to overcome/lessen As-induced adversities. Several recent examples of mechanisms responsible for increasing the availability of As to plants and coping with As stresses facilitated by PGPB will be reviewed. Although drawbacks to phytoremediation have been reported, encouraging results have been developed with regular monitoring. Introducing PGPB-assisted phytoremediation of As in a field requires an assessment of the environmental effects of PGPB, especially with respect to the impacts on indigenous bacteria

Traitement d'images et reseaux neuromimetiques appliques a la detection et a la classification des vehicules

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 82646 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Physiological and molecular dissection of phytic acid role in response of plant to environmental stress

La faible disponibilité du phosphore (P) constitue une contrainte majeure à la croissance et au développement des cultures végétales à l’échelle mondiale. En fait, jusqu’à 95% du P total dans les sols agricoles existe sous forme de P organique dont le composant le plus prépondérant est l’acide phytique, qui n’est disponible aux plantes que s’il est hydrolysé par des enzymes spécifiques appelées les phytases. Nous nous sommes intéressés ici à l’étude d’une phytase PHY-US417 de la souche de Bacillus subtilis US417 afin de tester sa capacité à améliorer la mobilisation du P à partir de l’AP chez les plantes d’Arabidopsis thaliana. Nous avons démontré dans un premier temps que la surexpression chez Arabidopsis d'une forme intracellulaire de la phytase PHY-US417 a entrainé une diminution de 40% le taux d’AP dans les graines. Des analyses physiologiques ont révélé que la surexpression de cette phytase améliore la croissance des plantes après un stress par manque de P, grâce à l’augmentation du niveau intracellulaire du Pi et du sulfate. Remarquablement, une plus forte mobilisation du fer a été observée au cours de la germination chez ces lignées transgéniques. En outre, la perception du Pi extérieur suite à des changements dans les profils d'expression de certains gènes induits par la carence en phosphate. Ces résultats indiquent que l’AP constitue non seulement une forme de stockage de P au niveau des graines mais agit aussi comme une molécule de signalisation qui régule l’interaction entre l’homéostasie du phosphore et du sulfate.Ces lignées transgéniques nous ont conduit à conclure aussi que l'AP et ses dérivés en inositol phosphates pourraient être impliqués aussi dans l'interconnexion entre les voies régulant l'homéostasie le P et celle du Zn. Ces mêmes composants semblent également jouer un rôle de régulateur positif dans la réponse des plantes au stress osmotique et ce via une stimulation des activités antioxydantes. Dans un deuxième temps, l'effet de la sécrétion de la phytase PHU-US417 par les racines d'Arabidopsis a été étudié. Les résultats obtenus ont montré que la forme extracellulaire ePHY-US417 a été capable d'hydrolyser l'AP utilisé comme seul source de Pi dans le milieu extérieur. En conséquence, ces lignées surexprimant ePHY-US417 ont une meilleure acquisition du Pi et une meilleure croissance. Enfin cette amélioration de la croissance dans des conditions de carence en Pi a concerné aussi d'autres plantes d'Arabidopsis ou de tabac co-cultivées avec les lignées sécrétant la phytase ePHY-US417. Une telle avancée montre que les phytases secrétées pourraient avoir un fort potentiel de valorisation via le développement de nouvelles pratiques de cultures associées qui favorisent une agriculture durable en limitant l'usage intensif des engrais phosphatés.The low availability of phosphorus (P) is a major constraint to growth and development of vegetable crops worldwide. In fact, up to 95% of total P in agricultural soils exists as organic P where phytic acid is the most dominant component, that is not available to plants unless hydrolyzed by specific enzymes called phytases. We are particularly interested to study a microbial phytase PHYC of Bacillus subtilis US417 strain (Farhat et al., 2008) to test its ability to enhance the mobilization of P from PA in Arabidopsis thaliana plants. Firstly, we have demonstrated in this work that overexpression of an intracellular form of phytase PHY-US417 in Arabidopsis resulted in reduction of PA levels in the grain.Physiological analyzes showed that overexpression of this phytase improves plant growth after P deficiency, by increasing the intracellular level of Pi and sulfate. Remarkably, a stronger mobilization of iron was observed during germination in these transgenic lines. In addition, the perception of the outside Pi result of changes in the expression profiles of genes induced by phosphate deficiency. These results show that the AP is not only a storage form in seeds but also acts as a signaling molecule that regulates the interaction between the phosphorus and sulfate homeostasis.These transgenic lines also led to conclude that the AP and its derivatives inositol phosphates may also be involved in the interconnection between the pathways regulating homeostasis of P and Zn. These components also appear to play a role as a positive regulator in the plant response to osmotic stress and this via stimulation of antioxidant activities.In a second step, the effect of the secretion of the PHY-US417 phytase by Arabidopsis roots was studied. The results showed that the extracellular form ePHY-US417 was able to hydrolyze the PA used as the sole P source of Pi in the external environment. Therefore these lines over ePHY-US417 have a better acquisition of Pi and better growth.Finally, this improved growth in Pi deficiency conditions has also affected other plants Arabidopsis or tobacco co-cultivated with plants secreting phytase. Such a step shows that the secreted phytase could have a significant upside potential through the development of new ways of "intercropping" that support sustainable agriculture by limiting the intensive use of phosphate fertilizers

Dissection moléculaire et physiologique du rôle de l'acide phytique dans la réponse des plantes aux stress de l'environnement

The low availability of phosphorus (P) is a major constraint to growth and development of vegetable crops worldwide. In fact, up to 95% of total P in agricultural soils exists as organic P where phytic acid is the most dominant component, that is not available to plants unless hydrolyzed by specific enzymes called phytases. We are particularly interested to study a microbial phytase PHYC of Bacillus subtilis US417 strain (Farhat et al., 2008) to test its ability to enhance the mobilization of P from PA in Arabidopsis thaliana plants. Firstly, we have demonstrated in this work that overexpression of an intracellular form of phytase PHY-US417 in Arabidopsis resulted in reduction of PA levels in the grain.Physiological analyzes showed that overexpression of this phytase improves plant growth after P deficiency, by increasing the intracellular level of Pi and sulfate. Remarkably, a stronger mobilization of iron was observed during germination in these transgenic lines. In addition, the perception of the outside Pi result of changes in the expression profiles of genes induced by phosphate deficiency. These results show that the AP is not only a storage form in seeds but also acts as a signaling molecule that regulates the interaction between the phosphorus and sulfate homeostasis.These transgenic lines also led to conclude that the AP and its derivatives inositol phosphates may also be involved in the interconnection between the pathways regulating homeostasis of P and Zn. These components also appear to play a role as a positive regulator in the plant response to osmotic stress and this via stimulation of antioxidant activities.In a second step, the effect of the secretion of the PHY-US417 phytase by Arabidopsis roots was studied. The results showed that the extracellular form ePHY-US417 was able to hydrolyze the PA used as the sole P source of Pi in the external environment. Therefore these lines over ePHY-US417 have a better acquisition of Pi and better growth.Finally, this improved growth in Pi deficiency conditions has also affected other plants Arabidopsis or tobacco co-cultivated with plants secreting phytase. Such a step shows that the secreted phytase could have a significant upside potential through the development of new ways of "intercropping" that support sustainable agriculture by limiting the intensive use of phosphate fertilizers.La faible disponibilité du phosphore (P) constitue une contrainte majeure à la croissance et au développement des cultures végétales à l’échelle mondiale. En fait, jusqu’à 95% du P total dans les sols agricoles existe sous forme de P organique dont le composant le plus prépondérant est l’acide phytique, qui n’est disponible aux plantes que s’il est hydrolysé par des enzymes spécifiques appelées les phytases. Nous nous sommes intéressés ici à l’étude d’une phytase PHY-US417 de la souche de Bacillus subtilis US417 afin de tester sa capacité à améliorer la mobilisation du P à partir de l’AP chez les plantes d’Arabidopsis thaliana. Nous avons démontré dans un premier temps que la surexpression chez Arabidopsis d'une forme intracellulaire de la phytase PHY-US417 a entrainé une diminution de 40% le taux d’AP dans les graines. Des analyses physiologiques ont révélé que la surexpression de cette phytase améliore la croissance des plantes après un stress par manque de P, grâce à l’augmentation du niveau intracellulaire du Pi et du sulfate. Remarquablement, une plus forte mobilisation du fer a été observée au cours de la germination chez ces lignées transgéniques. En outre, la perception du Pi extérieur suite à des changements dans les profils d'expression de certains gènes induits par la carence en phosphate. Ces résultats indiquent que l’AP constitue non seulement une forme de stockage de P au niveau des graines mais agit aussi comme une molécule de signalisation qui régule l’interaction entre l’homéostasie du phosphore et du sulfate.Ces lignées transgéniques nous ont conduit à conclure aussi que l'AP et ses dérivés en inositol phosphates pourraient être impliqués aussi dans l'interconnexion entre les voies régulant l'homéostasie le P et celle du Zn. Ces mêmes composants semblent également jouer un rôle de régulateur positif dans la réponse des plantes au stress osmotique et ce via une stimulation des activités antioxydantes. Dans un deuxième temps, l'effet de la sécrétion de la phytase PHU-US417 par les racines d'Arabidopsis a été étudié. Les résultats obtenus ont montré que la forme extracellulaire ePHY-US417 a été capable d'hydrolyser l'AP utilisé comme seul source de Pi dans le milieu extérieur. En conséquence, ces lignées surexprimant ePHY-US417 ont une meilleure acquisition du Pi et une meilleure croissance. Enfin cette amélioration de la croissance dans des conditions de carence en Pi a concerné aussi d'autres plantes d'Arabidopsis ou de tabac co-cultivées avec les lignées sécrétant la phytase ePHY-US417. Une telle avancée montre que les phytases secrétées pourraient avoir un fort potentiel de valorisation via le développement de nouvelles pratiques de cultures associées qui favorisent une agriculture durable en limitant l'usage intensif des engrais phosphatés

Components of variability in bituminous concrete pavement construction

Civil Engineerin

A new calculation approach for dielectric space charge characterization from nano to macro-scales by the thermal step method

In this paper, a new calculation approach is developed and applied, for the first time, to different dielectric scales using the thermal step method (TSM). The thermal aspect of the approach concerns insulating materials from nano to macro-scales. The theoretical approach is based on the ballistic-diffuse transport taking into account the relaxation time of heat phonons and their effects on the trapped space charges. These effects are revealed on the temporal evolution of the induced image charges that constitute the electrical signal of the thermal step method. The temperature distributions and the TSM induced image charges are obtained by applying the numerical finite element method, the Newmark direct integration, the mean value theorem and the composite Simpson approximation. In a first step, the results of the temperature distributions are validated with those obtained by Boltzmann and Chen models for nano-polyethylene sample. In a second step, our approach is validated with TSM previous works using the Fourier's model for space charge characterizations in the micro and macro-dielectrics. The validated results of the TSM induced image charges for micro and macro-scales show good agreements, and prove that our approach is a consistent tool to be applied in space charge characterizations for different dielectric scales

Transient and steady-state currents in polyethylene film under low and high dc voltages

Transient and steady state currents in polyethylene, under low and high dc voltages, are studied. In fact, a bipolar transport physical model is developed in order to characterize the space charge dynamics within an additive-free polyethylene film, under trapping and recombination mechanisms. The numerical computational models, used for the bipolar transport of carriers, are applied to the Poisson's, the continuity and the transport equations with the appropriate physical conditions. The principal and the new numerical results are calculated especially when high dc voltages are applied. Indeed, the net charge density numerical profiles show the appearance of the space charge packets that are revealed for the first time in numerical modelling although they have long been reported in experimental works. These space charge packets induce some new aspects on the external transient current evolutions, produce the oscillations of the conduction and the displacement current before the steady state, and generate a conduction regime that is dominated by the interface electrode-insulator. These numerical results are consistent with those reported in some experimental works. However, under low dc voltage the space charge packets disappear and the space charge limited current aspect appears on the external current profile

Phytase overexpression in Arabidopsis improves plant growth under osmotic stress and in combination with phosphate deficiency

Engineering osmotolerant plants is a challenge for modern agriculture. An interaction between osmotic stress response and phosphate homeostasis has been reported in plants, but the identity of molecules involved in this interaction remains unknown. In this study we assessed the role of phytic acid (PA) in response to osmotic stress and/or phosphate deficiency in Arabidopsis thaliana. For this purpose, we used Arabidopsis lines (L7 and L9) expressing a bacterial beta-propeller phytase PHY-US417, and a mutant in inositol polyphosphate kinase 1 gene (ipk1-1), which were characterized by low PA content, 40% (L7 and L9) and 83% (ipk1-1) of the wild-type (WT) plants level. We show that the PHYoverexpressor lines have higher osmotolerance and lower sensitivity to abscisic acid than ipk1-1 and WT. Furthermore, PHY-overexpressors showed an increase by more than 50% in foliar ascorbic acid levels and antioxidant enzyme activities compared to ipk1-1 and WT plants. Finally, PHY-overexpressors are more tolerant to combined mannitol stresses and phosphate deficiency than WT plants. Overall, our results demonstrate that the modulation of PA improves plant growth under osmotic stress, likely via stimulation of enzymatic and non-enzymatic antioxidant systems, and that beside its regulatory role in phosphate homeostasis, PA may be also involved in fine tuning osmotic stress response in plants

Post breakdown and lifetime of low density polyethylene film under generated transient charge packets

It is well known that space charge accumulation in insulating materials constitutes the principal cause of dielectric breakdown. Though space charge measurements in polymeric materials have been extensively developed over the last two decades, modeling and simulation works have progressed slowly in this respect. In the present study, a model for bipolar charge transport, as a basis for studying breakdown phenomenon in low density polyethylene (LDPE), is presented. Indeed, we are especially interested in external current dynamic which is the witness of the sample post breakdown. Our results show the effect of the high dc applied voltage and the generation of the space charge packets on the apparition of the post breakdown of the insulator. In order for this effect to be revealed, the external current evolutions under low and high dc applied voltages before and at the breakdown are determined. Indeed, these evolutions show an abrupt increase that is observed when the charge packet aspect occurred in the sample under high dc applied voltage. This observed abrupt increase of the external current is attributed to post breakdown phenomenon. These results are obtained for the first time in modeling and show some aspects similar to those observed in some experimental works