Etude des modalites de l'implication et de la mobilisation du calcium lors de l'absorption de glycine par les tissus pulvinaires de Mimosa pudica L

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Uptake and translocation of strontium in hydroponically grown maize plants, and subsequent effects on tissue ion content, growth and chlorophyll a/b ratio: comparison with Ca effects

International audienceStrontium is an element which can be found in the environment in a large range of concentrations, as a result of natural mineral degradation or consecutively to polluting anthropic activities. The transfer of such a contaminant from the environment to plants is a first step leading to contamination of the food pathway. Therefore the main objective of our work was to investigate the Sr2+ transfer from the environment to the plants via root uptake, and to characterize some of the physiological effects induced by this element in maize plants. Hydroponically grown plants were exposed to SrCl2 in different experimental conditions. Data reported here show that, depending on the external [Sr2+] tested, the uptake of Sr2+ by Zea mays L. cv. "Liberal" roots resulted from at least two saturating- (in the range 0.04-25 mM), and one non-saturating (for [Sr2+] up to 100 mM) transport components. The Sr2+ uptake by roots and the translocation of Sr2+ from root to shoot were increased when external Sr2+ concentration was increased from 0.1 mM to 10 mM. However the relative efficiency of the "solution-to-plant root" transfer was higher for low external [Sr2+], whereas the relationship between the relative "root-to-shoot" transfer and the external [Sr2+] was more complex as it depended in particular on the incubation duration. Once taken up by the roots, part of the Sr2+ was translocated to the leaves where it affected the chlorophyll a/b ratio mainly by decreasing the chlorophyll a content. Sr2+ was also found to decrease the Mg and Ca contents of plant tissues. Sr2+ effect on plant growth depended on the organ age and Sr2+ concentration. At first sight, both Sr2+ and Ca2+ could be considered to exert quite similar overall effects in maize plants. This was in particular the case on shoot water and Chl b contents, and shoot DW. However, at similar concentration, Sr2+ was generally less efficient at stimulating or more efficient at inhibiting the physiological processes studied, than Ca2+. In particular, both ions induced significantly different effects on seedling radicle elongation, root length, DW and Mg content, and shoot Mg content. Taken together present data evidence that the amount of Sr2+ transferred from environment to plants was sufficient to affect some physiological processes in maize plants. Most of the Sr2+-induced effects were different from those induced by Ca2+ in a similar range of concentration, which suggests that Sr2+ could not simply be considered to mimic Ca2+

Occurrence of interactions between individual Sr2+- and Ca2+-effects on maize root and shoot growth and Sr2+, Ca2+ and Mg2+ contents, and membrane potential: Consequences on predicting Sr2+-impact

International audienceOccurrence of functional interactions between Sr2+ and Ca2+ were investigated on maize plants grown under hydroponic conditions in presence of various mixtures of SrCl2 [0-0.01-1-10 mM] and CaCl2 [0-0.2-2-20 mM]. External [Ca2+] modulated the effect of Sr2+ on the plant dry weight, and on the Sr2+, Ca2+ and Mg2+ contents of roots and shoots. An intermediary functional step between external [Sr2+] and [Ca2+], and organ ion content, occurred at the plasma membrane of cortical root cells where Sr2+ and Ca2+ could influence ion uptake by acting on membrane potential. The decrease of the Sr2+-evoked membrane depolarization induced by Ca2+ could not solely be attributed to the Ca2+-effect on the resting membrane potential. Most of the time the individual effects of Sr2+ and Ca2+ were not additive, as these two ions clearly interacted with each other to jointly affect the plant physiology. In spite of these interactions, both [Sr2+]ext or [Sr2+]ext/[Ca2+]ext ratio values seemed to enable a correct prediction of the Sr2+-effects on the plant. However using the [Sr2+]ext/[Ca2+]ext ratio improved significantly the adequacy of prediction compared to the use of [Sr2+]ext alone, as it increased up to 25% the proportion of variability accounted for by the model

Membrane effects of 2,4-dichlorophenoxyacetic acid in motor cells of Mimosa pudica L.

International audience2,4-dichlorophenoxyacetic acid applied to excised leaves of Mimosa pudica L. inhibited in a dose-dependent manner the shock-induced pulvinar movement. This inhibition was negatively correlated with the amount of [14C] 2,4-dichlorophenoxyacetic acid present in the vicinity of the motor cells. Although 2,4-dichlorophenoxyacetic acid is a weak acid, its greatest physiological efficiency was obtained with pH values close to neutrality. This observation opens the question of its mode of action which may be through external signaling or following internal transport by a specific anionic form transporter. The effect was related to molecular structure since 2,4-dichlorophenoxyacetic acid > 3,4- dichlorophenoxyacetic acid > 2,3-dichlorophenoxyacetic acid. An essential target of 2,4-dichlorophenoxyacetic acid action lies at the plasmalemma as indicated by the induced hyperpolarization of the cell membrane. Compared to indole-3-acetic acid and fusicoccin, it induced a complex effect on Hþ fluxes. Applied to plasma membrane vesicles purified from motor organs, 2,4-dichlorophenoxyacetic acid enhanced proton pumping, but, unlike fusicoccin, it did not increase the Hþ-ATPase catalytic activity in our experimental conditions. Taken together, the data suggest that 2,4-dichlorophenoxyacetic acid acts on cell turgor variation and the concomittant ion migration, in particular Kþ, by a mechanism involving specific steps compared to indole-3-acetic acid and fusicoccin

Early Sr2+-induced effects on membrane potential, proton pumping- and ATP hydrolysis-activities of plasma membrane vesicles from maize root cells

International audienceWhen released in plant environment, strontium (Sr2+) can be absorbed predominantly by the plant roots. As the plasma membrane of root cells is amongst the first barriers encountered by Sr2+ during its soil/plant transfer and the main entry point of Sr2+ into the roots, the main objective of this work aimed to enlighten on some of the Sr2+-induced effects at this level in Zea mays L. cv. "Liberal". Thus this study focused on the Sr2+-induced changes on membrane potential of cortical root cells and on proton fluxes in maize roots, in order to determine whether the activity of some of the ion transport systems present in the plasma membrane of maize root cell could be among the first targets of Sr2+. We focused in particular on the plasma membrane H+-ATPase, known to be one of the major transport systems found in the plasmalemma where it generates a proton motive force (contributing to membrane potential maintaining, and providing energy for ion transport through membrane). The data presented here showed that Sr2+ triggered an early and transient membrane depolarisation whose magnitude and duration were dependent on the Sr2+-concentration. The time course pattern of a second longer lasting depolarisation could be examined in perspective with the Sr2+-induced decrease of the spontaneous proton extrusion observed in root tissues, suggesting a relationship between Sr2+- effects on membrane potential and H+ excretion. Furthermore, the inhibitory effect exerted by Sr2+ on the fusicoccin (FC)-enhanced proton extrusion strongly suggested an inhibition of the plasma membrane H+-ATPase. This hypothesis was supported by the inhibition induced by Sr2+ on proton pumping- and ATP hydrolysis-activities measured in plasma membrane vesicles (PMV) prepared from maize roots. Taken together the data reported here evidence that, with however a lower efficiency, Sr2+ behaved in a quite similar way to Ca2+ when inhibiting the H+-ATPase activity, and suggest that Sr2+ could partially mimic Ca2+ onto regulation of the H+-ATPase activity

Characteristic early membrane effects induced by tryptophan in pulvinar motor cells

International audienceTryptophan at concentrations higher than 0.1 mM, triggered characteristic early physiological effects such as rapid (within 5 min) dose-dependent membrane hyperpolarization in Mimosa pudica motor cells and modification of the time course of the spontaneous proton efflux monitored in the incubation medium of pulvinar tissues. The rapid modifications of the leaf turgor-mediated movements seen on the primary pulvini of M. pudica following a shock and on Cassia fasciculata leaflets during a transition from light to darkness indicate that tryptophan disturbed the ionic migrations involved in the electrophysiological events and in the osmocontractile reaction of the motor cells. These reactions were specific to tryptophan compared to those induced by serine and 5-hydroxytryptophan. The tryptophan mode of action cannot be linked to a direct modification of the plasma membrane H+-ATPase activity as monitored on purified pulvinar plasma membrane vesicles. The tryptophan metabolism-linked products tryptamine and indole also inhibited the motile reactions, activated in a continuous manner the H+ secretion of pulvinar tissues and showed properties of a protonophore and an ATPase activity inhibitor on plasma membrane vesicles, respectively. The specific behavior of tryptophan in the reaction studies here is discussed in light of the previously reported action of phytohormones

Chapitre VII. Les larves de Chironomidae dans les approches écotoxicologiques d’évaluation de la qualité des milieux aquatiques

1. Introduction L’industrialisation, l’urbanisation, l’agriculture intensive et leurs cortèges de produits chimiques (éléments traces métalliques, hydrocarbures, pesticides, médicaments, etc.) ont accru la contamination des eaux continentales de surface et souterraines de manière chronique ou aiguë. Aujourd’hui, plus de 67 millions de substances chimiques sont connues dont environ 100 000 sont considérées d’utilisation courante. Véhiculées par les pluies, les eaux de lessivage des sols, rejet..

Increasing the panel of tree species in phytomanagement strategies

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L5P a specific antigen suitable to detect mycobacterium avium spp. paratuberculosis infection by cell mediated immune response

International audienceContext: The livestock management needs an early diagnostic test to prevent dramatic rise of Mycobacterium avium spp paratuberculosis (Map) infection in cattle. Current serology based diagnostic tests available, detect animals in later stages when they are shedding huge amount of bacillus. Cell mediated immune (CMI) responses that can be detected by Interferon Gamma Release Assays, appear before or combined with antibody responses. Therefore, diagnostic tools based on IGRA could help to identify recently infected animals in order to prevent disease transmission. The sensitivity and specificity of these tests need to define Map-specific T-cell antigens. Map produces a specific cell-wall lipopentapeptide called L5P or LP-01. L5P is suitable to detect Map-infected animals by serodiagnostic. Moreover, L5P can be synthetized chemically at high purity, large scale, and low cost. Objectives: The purpose of this work was to assess the potential of L5P to detect Map-specific cell mediated immune responses to develop an IGRA test. Methods: A panel of 36 cows were selected from two naturally infected herds where clinical paratuberculosis had occurred. We performed 1) serology with the commercial IDEXX diagnostic test and a house-made test using L5P antigen 2) IGRA with Purified Protein Derivative avian (PPD-A) or synthetic L5P antigen 3) microbiological analyses including isolation and identification of bacillus from faeces. Results: In this study 47.2 % of cows were scored positive by the commercial IDEXX diagnostic test but only 22% developed anti-L5P antibodies. PPD-A induced CMI responses in 97 % of cows while 22.2% animals were L5P responders. Map was isolated in 25.7% of animals. We provide, for the first time, evidence that Map-specific L5P is a suitable antigen for serologic and IGRA diagnosis. Perspectives: We will now carry out a longitudinal study to investigate the potential of L5P-based IGRA to predict clinical outcome of Map-infected 18-24 months cattle