Influence of fine process particles enriched with metals and metalloids on Lactuca sativa L. leaf fatty acid composition following air and/or soil-plant field exposure

We investigate the effect of both foliar and root uptake of a mixture of metal(loid)s on the fatty acid composition of plant leaves. Our objectives are to determine whether both contamination pathways have a similar effect and whether they interact. Lactuca sativa L. were exposed to fine process particles enriched with metal(loid)s in an industrial area. Data from a first experiment were used to conduct an exploratory statistical analysis which findings were successfully cross-validated by using the data from a second one. Both foliar and root pathways impact plant leaf fatty acid composition and do not interact. Z index (dimensionless quantity), weighted product of fatty acid concentration ratios was built up from the statistical analyses. It provides new insights on the mechanisms involved in metal uptake and phytotoxicity. Plant leaf fatty acid composition is a robust and fruitful approach to detect and understand the effects of metal(loid) contamination on plants

Are plants useful as accumulation indicators of metal bioavailability?

International audienceThe use of accumulation bioindicator to assess metal bioavailability has mainly concerned individual species. This work addresses this issue at the plant community level. Metal content within different species from plant communities found at three contaminated and one uncontaminated site was compared. Results showed that for two contaminated sites, leaf metals concentrations were comparable to those in plants from control site, i.e. approx (mg/kg) 0.1 Cd, 0.2 Cr, 9.2 Cu, 1.8 Ni, 0.5 Pb and 42 Zn. Only plants from the third site showed higher metal contents, ranging from 1.5- to 8-fold those of the control community. This contrasted with ammonium acetate-EDTA extractions, which indicated a very high "availability" of metals at the three sites, as compared to the control site. Thus, metal content in plant communities provided accurate information on actual transfer toward the ensemble of vegetation, which could be used to establish site-specific "fingerprints" of metal bioavailability

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Cell polarity is achieved by regulators such as small G proteins, exocyst members and phosphoinositides, with the latter playing a key role when bound to the exocyst proteins Sec3p and Exo70p, and Rho GTPases. This ensures asymmetric growth via the routing of proteins and lipids to the cell surface using actin cables. Previously, using a yeast mutant for a lysophosphatidylinositol acyl transferase encoded by the PSI1 gene, we demonstrated the role of stearic acid in the acyl chain of phosphoinositides in cytoskeletal organization and secretion. Here, we use a genetic approach to characterize the effect on late steps of the secretory pathway. The constitutive overexpression of PSI1 in mutants affecting kinases involved in the phosphoinositide pathway demonstrated the role of molecular species containing stearic acid in bypassing a lack of phosphatidylinositol-4-phosphate (PI(4)P) at the plasma membrane, which is essential for the function of the Cdc42p module. Decreasing the levels of stearic acid-containing phosphoinositides modifies the environment of the actors involved in the control of late steps in the secretory pathway. This leads to decreased interactions between Exo70p and Sec3p, with Cdc42p, Rho1p and Rho3p, because of disruption of the GTP/GDP ratio of at least Rho1p and Rho3p GTPases, thereby preventing activation of the exocyst

Proteomic Analysis of Lipid Droplets from Arabidopsis Aging Leaves Brings New Insight into Their Biogenesis and Functions

Lipid droplets (LDs) are cell compartments specialized for oil storage. Although their role and biogenesis are relatively well documented in seeds, little is known about their composition, structure and function in senescing leaves where they also accumulate. Here, we used a label free quantitative mass spectrometry approach to define the LD proteome of aging Arabidopsis leaves. We found that its composition is highly different from that of seed/cotyledon and identified 28 proteins including 9 enzymes of the secondary metabolism pathways involved in plant defense response. With the exception of the TRIGALACTOSYLDIACYLGLYCEROL2 protein, we did not identify enzymes implicated in lipid metabolism, suggesting that growth of leaf LDs does not occur by local lipid synthesis but rather through contact sites with the endoplasmic reticulum (ER) or other membranes. The two most abundant proteins of the leaf LDs are the CALEOSIN3 and the SMALL RUBBER PARTICLE1 (AtSRP1); both proteins have structural functions and participate in plant response to stress. CALEOSIN3 and AtSRP1 are part of larger protein families, yet no other members were enriched in the LD proteome suggesting a specific role of both proteins in aging leaves. We thus examined the function of AtSRP1 at this developmental stage and found that AtSRP1 modulates the expression of CALEOSIN3 in aging leaves. Furthermore, AtSRP1 overexpression induces the accumulation of triacylglycerol with an unusual composition compared to wild-type. We demonstrate that, although AtSRP1 expression is naturally increased in wild type senescing leaves, its overexpression in senescent transgenic lines induces an over-accumulation of LDs organized in clusters at restricted sites of the ER. Conversely, atsrp1 knock-down mutants displayed fewer but larger LDs. Together our results reveal that the abundancy of AtSRP1 regulates the neo-formation of LDs during senescence. Using electron tomography, we further provide evidence that LDs in leaves share tenuous physical continuity as well as numerous contact sites with the ER membrane. Thus, our data suggest that leaf LDs are functionally distinct from seed LDs and that their biogenesis is strictly controlled by AtSRP1 at restricted sites of the ER

Les acyl-CoA elongases d'allium porrum : solubilisation, purification partielle essais de reconstitution et analyse theorique de leur fonctionnement

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Etude de la lyso-PC acyltransférase de l'enveloppe des chloroplastes (interaction avec les métaux, solubilisation et purification partielle)

Il a été mis l'hypothèse que l'import de lipides dans les chloroplastes implique une déacylation de la PC (phosphatidylcholine) dans les membranes du RE, menant à la formation de la lyso-PC (lysophosphatidylcholine). Par la suite ces molécules de lyso-PC transféreraient vers les membranes plastidiales où elles seraient acylées par une lyso-PC acyltransférase localisée dans l'enveloppe des plastes. Cette hypothèse a été confortée par plusieurs résultats obtenus in vitro et in vivo. Pour tester plus avant l'implication de la lyso-PC acyltransférase plastidiale dans l'import de lipides, nous envisageons d'obtenir des plantes surexprimant ou dépourvues de cette activité. Puisqu'aucune séquence de lyso-PC acyltransférase n'est connue à ce jour, et ce dans aucun organisme, la solubilisation et la purification partielle de cette enzyme ont été réalisées, ainsi qu'une étude de l'interaction de la lyso-PC acyltransférase avec les sels de métaux.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

De l'implication des radeaux membranaires du plasmalemme dans les phénomènes de signalisation chez les végétaux

De nombreuses évidences montrent que les membranes plasmiques sont organisées en domaines. Nous avons isolé des microdomaines plasmalemmiques appelés DIM (Détergent Insoluble Membranes) par solubilisation différentielle par les détergents non ioniques à froid. L'hypothèse de travail selon laquelle les acteurs de la signalisation lipidique pourraient être recrutés/exclus de façon dynamique dans les DIM, a été testée par des approches complémentaires. L'analyse globale par spectrométrie de masse du contenu protéique des DIM de cellules BY2 et de racines de Medicago truncatula a montré que la majorité des protéines présentes sont impliquées dans les voies de signalisation, parmi lesquelles des enzymes liées au métabolisme des phospholipides de signalisation (phospholipases Dð et C). Nous avons aussi mis en évidence un enrchissement en phosphoinositides (PIP et PIP2) dans ces DIM végétaux. Nous proposons que "les DIM sont des structures appauvries en phospholipides "de structure" et enrichies en stérols, sphingolipides et phospholipides" de signalisation". L'ensemble des enzymes intervenant dans le métabolisme du PIP et du PIP2 est également présent dans les DIM. A l'inverse les phospholipases D (PLD) qui synthétisent l'acide phosphatidique y sont peu présentes. De plus, les résultats préliminaires montrent que l'activité de certaines enzymes (PLD, PA kinase) présentes dans les DIM fluctue après un traitement hormonal. Ces données suggèrent que les DIM des membranes plasmiques végétales pourraient être impliqués dans les mécanismes de transduction des signaux en compartimentant les voies de synthèse/dégradation des phospholipides "de signalisation".A large body of evidence supports the existence of microdomains in plant plasma membrane. We used differential cold solubilization by nonionic detergents to isolate these plasma membrane microdomains, called Detergent Insoluble Membranes (DIM). We hypothesized that DIM are able to selectively and dynamically recruit or exclude lipids and lipid-utilising enzymes involved in signalling pathways. Several approaches were undertaken to test this hypothesis. First, mass spectrometric analyses show that both tobacco leaf and Medicago truncatula root plasma membrane DIM are enriched in proteins involved in many signaling pathways, like phospholipases Dơ and C. The data clearly indicate that polyphosphoinositides (PIP, PIP2) are also enriched in tobacco DIM. We propose that DIM are membrane domains depleted in "structural phodpholipids" and largely enriched in sterols, sphingolipids and "signalling phospholipids" (PIP, PIP2). Moreover, enzymes involved in polyphosphoinositides metabolism are found in DIM whereas phospholipases D -which synthesize phosphophatidic acid (PA)- seem to be depleted. First results show that both PLD and PA kinase activities fluctuate in DIM after Abscisic Acid Treatment. Taken together these data suggest the involvement of plant plasma membrane DIM in signal transduction by partitioning synthesis and hydrolysis pathways of "signalling phospholipids".BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF