Organisation in vivo des diverses voies de métabolisation de l'atrazine chez le maïs

Three pathways of atrazine detoxication, producing non-phytotoxic products, were previously described : 1 - the chemical conversion of atrazine into its hydroxylated derivative ; 2 - the enzymatic N-dealkylation leading to the formation of deethyl-, deisopropyl- and didealkyl-atrazine ; 3 - the enzymatic glutathione conjugation. The work presented here shows the relative importance of these three pathways of detoxication in living maize seedlings. The non-enzymatic hydroxylation pathway, associated with the presence of benzoxazinones in corn (var. Furio) was shown to be the major detoxication mechanism. In association with the N-dealkylation pathway, it leeds to the formation of hydroxy-dealkylated derivatives accumulated in high amounts, which may reach 80 % of the total metabolites. The distribution of these metabolites inside the seedlings is quite different from that of atrazine. / Troies voies de transformation de l'atrazine, conduisant à des dérivés non phytotoxiques, ont été décrites dans la littérature : 1 - l'hydroxylation chimique conduisant à l'hydroxyatrazine, 2 - la N-déalkylation enzymatique produisant des dérivés déisopropylés, dééthylés ou didéalkylés et enfin, 3 - une voie de conjugaison enzymatique avec le glutathion. Nous avons étudié, in vivo, l'importance comparée de ces différentes voies de transformation de l'atrazine. La voie d'hydroxylation chimique, en présence des benzoxazinones, est très intense dès le stade plantule. Associée à la voie de N-déalkylation, les dérivés hydroxylés-déalkylés représentent, dans les conditions agronomiques, plus de 80 % des métabolites produits par le maïs. Cela explique que la distribution de la radioactivité, issue de l'emploi d'atrazine U 14C au sein de la plantule de maïs, soit totalement différente de celle de l'atrazine elle-même

Ecoremediation : cooperation between plants and soil microorganisms. Molecular aspects and limits

International audienceIn terrestrial ecosystems, higher plants are organized in two quite different spatial parts: a) a photosynthetic compartment, developed in the atmosphere, under light, and b) a soil compartment, specialized in the absorption of water and mineral salts, in the dark

Bases théoriques des traitements herbicides de pré-levée : vers la réduction de la charge polluante

The process of pre-emergence herbicide treatment requires that the active ingredient sprayed on the soil be sufficiently available in space and time to kill plantlets of weeds during the period when they may hindercrop development. Three important concepts concerning the effectiveness of a pre-emergence herbicide are developed : the critical concentration corresponding to the active ingredient concentration which must be maintained in surface soil water, in order to kill plantlets, the critical period, which represents the period of time during which this concentration must be maintained to ensure the crop protection, the critical depth reprensenting the layer of soil where weeds are able to germinate. A last concept is presented : the critical depth of metabolization corresponding to the layer of soil able to metabolize the active ingredient, and which plays a major role in defining the pollutant load associated with pre-emergence treatments. New approaches of the formulation of pre-emergence herbicides, particularly micro-encapsulation with controlled release, should allow to maintain a critical concentration within the critical depth with the use of lower amounts of active ingredient in comparison with classical treatments resorting to wettable powder or flow. This approach, which does not alter the agronomical efficiency, appears as an interesting way of research for reducing atmosphere and underground contamination. / La réussite d'un traitement herbicide de pré-levée nécessite que la matière active déversée sur le sol soit suffisamment disponible dans le temps et dans l'espace afin d'éradiquer les plantules des adventices durant la période où celles-ci peuvent nuire à la culture. Trois concepts importants relatifs à l'efficacité d'un herbicide de pré-levée sont développés : la concentration critique qui correspond à la concentration en matière active qu'il est nécessaire d'obtenir dans l'eau du sol de surface pour détruire les advendices au stade plantule, la durée critique, période durant laquelle cette concentration doit être maintenue pour supprimer la concurrence des advendices liés à cette culture, la profondeur critique de métabolisation qui joue un rôle primordial dans la définition de la charge polluante liée aux traitements de pré-levée. De nouvelles approches de la formulation des herbicides de pré-levée, en particulier la micro-encapsulation à relargage contrôle, devrait permettre le maintien de la concentration critique dans la profondeur critique avec beaucoup moins de matière active que celle nécessaire lors de traitements de réduction de la contamination environnementale tant atmosphérique que souterraine, tout en gardant l'efficacité agronomique

Exploiting plant metabolism for the phytoremediation of persistent herbicides.

Weed control by herbicides has helped us to create the green revolution and to provide food for at least the majority of human beings living today. However, some herbicides remain in the environment and pose an ecological problem. The present review describes the properties and fate of four representative herbicides known to be presistent in ecosystems. Metabolic networks are depiced and it is concluded that removal of these comopounds by the ecologically friendly technique of phytoremediation is possible. The largest problem is seen in the uptake of the compounds into suitable plants and the time needed for such an approach

Biodisponibilité du fipronil au sein de la plantule de maïs

Fipronil is an insecticide authorized in France for soil treatment granulars to fight against wireworms in maize crop. From granulars, the active ingredient diffuses into soil water and is subjected to a complex process of distribution between the clay-humic complex, the microbial population and the maize plants. In the plant, a fast loading of growing parts, in contact with soil water occurs. A slower subconcentration is seen in tegument and in seed reserves. The apparent subconcentration in plant material is related with the lipid content of each plant organ. Taking into account the wireworm feeding habits, it is the concentration in newly formed ground parts which seems to play an important part in the determinism of insecticidal action. / Le fipronil est un insecticide homologué en France en traitement de sol par granulés en vue de lutter contre les taupins (Agriotes sp) en culture de maïs. A partir des granulés, la matière active diffuse dans l'eau du sol et est soumise à un processus complexe de distribution entre le complexe argilo-humique, la biomasse microbienne et la plante de maïs. Au sein de celle-ci, on assiste à un chargement rapide des parties en croissance, en contact avec l'eau du sol, et à une surconcentration plus lente dans le tégument et les réserves de la graine. La surconcentration apparente dans le matériel végétal est en relation avec la teneur en lipides de chacun des organes de la plantule. Eu égard aux habitudes alimentaires du taupin, c'est la concentration dans les parties souterraines néoformées qui sembleraient jouer en rôle important dans le déterminisme de l'action insecticide

Uptake and xylem transport of fipronil in sunflower

International audienceThe phenylpyrazole insecticide, fipronil, is used in seed coating against Agriotes larvae, which infest mainly corn and sunflower. Coating the seeds of the cultivated plants with fipronil has proven its effectiveness against Agriotes populations. In the case of sunflower or even corn, the possible root uptake of this insecticide may lead to a toxic effect against pollinators such as honeybees. In the present report, the uptake and transport of fipronil inside the sunflower seedling was studied in the laboratory. In a first study, sunflower was cultivated on an aqueous medium containing fipronil. An intense root uptake of fipronil occurred, leading to a transport into leaves depending upon transpiration. In a second study, plants were cultivated on a soil in which fipronil was uniformly distributed. Under our soil conditions (20% organic carbon), the partition coefficient between soil and water (K-d) was found to be equal to 386 +/- 30. The average rate of fipronil transfer from soil water to seedlings was from 2 to 2.6 times lower than water transfer. During the 3 week experiment, 55% of recovered labeled compounds was in the parent form and 35% had been converted to lipophilic metabolites, with either a 4-CF3-SO2 or 4-CF3-S substituant, which are also very potent lipophilic insecticides. This paper suggests that the possible uptake of fipronil by sunflower seedlings under agronomic conditions is mainly controlled by the physicochemical characteristics of the seed-coating mixture

Complementarity of analytical tools in biomonitoring studies

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