Stimulated growth rate by restriction of P availability at moderate salinity but insensitive to P availability at high salinity in Crithmum maritimum

The halophyte Crithmum maritimum thrives in cracks of calcareous rocks or cliffs at seashores, a situation which associates limited phosphorus availability and high salinity. In order to understand the common patterns of colonization and zonation of this species, seedlings were cultivated for 34 d in inert sandy soil irrigated with a nutrient solution containing or not phosphorus at moderate (50 mM) or high (250 mM) NaCl level. Net assimilation rate and consequently relative growth rate increased in response to P deprivation at moderate saline level, but not at high salinity level. Parallelly, CO2 fixation rate, rubisco capacity, transpiration rate and stomatal conductance were diminished by P deprivation at moderate NaCl level. Intercellular CO2 concentration was therefore not affected. Chlororophyll fluorescence analysis revealed that photosynthetic systems were insensitive to change in P availability at moderate salinity level: neither pigment content, nor effective and maximum quantum yield, photochemical and non photochemical quenching, and electron transport rate were affected by P deprivation. On the contrary, at high salinity level when net photosynthesis, rubisco capacity and the quantum yields of PS2 were severely affected, P deprivation strongly augmented electron transport rate. Stomatal aperture and more modest increase in net photosynthesis, rubisco capacity, photosystem II effective quantum yield and photochemical quenching accompanied this response. This study shows the tolerance of C. maritimum to the phosphorus deprivation combined to moderate or to high saline level which may explain the common patterns of colonization and zonation of this species.     

Differential expression of two plant-like enolases with distinct enzymatic and antigenic properties during stage conversion of the protozoan parasite Toxoplasma gondii

The precise molecular mechanisms underlying the switch between the two developmental stages of Toxoplasma gondii, and the metabolic adaptations occurring during this stage conversion are poorly understood. Because inhibitors of mitochondrial respiration are known to trigger differentiation from tachyzoite into bradyzoite stages, we believe that some of the switch components may be sought in the regulation of central carbohydrate metabolism. We have previously described a cDNA encoding a bradyzoite-specific enolase, ENO1. We now report the isolation and characterization of another enolase-encoding cDNA (ENO2) that is expressed preferentially in the tachyzoite stage. The deduced amino acid sequences of ENO1 and ENO2 share 73.65 % identity. They both display significant homologies to plant enolases with the presence of two plant-like peptide insertions, a pentapeptide EWGW(Y)C(S) and a dipeptide EK (or DK). We demonstrate that deletions of the ENO1 pentapeptide motif on its own or together with the dipeptide reduce drastically the affinity for the 2PGA substrate, suggesting that the evolutionary acquisition of these peptides in enolases of land plants and apicomplexan parasites contribute a specific function to their enzymatic activities. T. gondii ENO1 and ENO2 were also expressed as active recombinant enzymes in Escherichia coli. While ENO1 and ENO2 display similar K(m) values, the pure tachyzoite-specific enzyme (ENO2) has a threefold specific activity at V(max) compared with that of the bradyzoite-specific enolase (ENO1). Moreover, immunoblot analyses performed using polyclonal antibodies raised against the recombinant enzymes revealed that the native enolase in tachyzoite and bradyzoite are also antigenically distinct. Taken together, our results indicate that the differences witnessed between the two activities may be instrumental in maintaining glycolysis in pace with the distinct stage-specific requirements of carbohydrate metabolism.     

Effect of dehydration on nitric oxide, corticotropic and vasopressinergic axis in rat

Effect of dehydration on nitric oxide, corticotropic and vasopressinergic axis in rat. The purpose of our work is to study, in the male 'Wistar' rat, the effects of a chronic dehydration, by deprivation of water for three days out of four, during four repeated cycles, on the evolution of certain blood variables, on the activities of both corticotropic and vasopressinergic axis and on the synthesis of nitric oxide. The chronic dehydration causes a considerable reduction of the body weight, an activation of the vasopressinergic axis and an increase in the circulating rates of the nitrates/nitrites, which represent the final metabolites of the reaction of oxidation of nitric oxide. The pituitary-adrenal axis is not statistically affected by the chronic dehydration. This seems to be in favour of a possible adaptation of corticotropic axis to chronic water deprivation. The activation of synthesis of nitric oxide shows its implication in the regulation of the water balance and its buffer effect on vasoconstriction and hypertension induced by water stress.     

Unexpected mosaic distribution of two hybridizing sibling lineages in the teleplanically dispersing snail Stramonita haemastoma suggests unusual postglacial redistribution or cryptic invasion

Molecular approaches have proven efficient to identify cryptic lineages within single taxonomic entities. Sometimes these cryptic lineages maybe previously unreported or unknown invasive taxa. The genetic structure of the marine gastropod Stramonita haemastoma has been examined in the Western Mediterranean and North‐Eastern Atlantic populations with mtDNA COI sequences and three newly developed microsatellite markers. We identified two cryptic lineages, differentially fixed for alternative mtDNA COI haplogroups and significantly differentiated at microsatellite loci. The mosaic distribution of the two lineages is unusual for a warm‐temperate marine invertebrate with a teleplanic larval stage. The Atlantic lineage was unexpectedly observed as a patch enclosed in the north of the Western Mediterranean Sea between eastern Spain and the French Riviera, and the Mediterranean lineage was found in Macronesian Islands. Although cyto‐nuclear disequilibrium is globally maintained, asymmetric introgression occurs in the Spanish region where the two lineages co‐occur in a hybrid zone. A first interpretation of our results is mito‐nuclear discordance in a stable postglacial hybrid zone. Under this hypothesis, though, the location of genetic discontinuities would be unusual among planktonic dispersers. An alternative interpretation is that the Atlantic lineage, also found in Senegal and Venezuela, has been introduced by human activities in the Mediterranean area and is introgressing Mediterranean genes during its propagation, as theoretically expected. This second hypothesis would add an additional example to the growing list of cryptic marine invasions revealed by molecular studies.     

Butyltin compounds in sediment and biota from the lagoon of Bizerte (northern Tunisia): Potential risk for consumers?

Levels of butyltins (BTs) were monitored in sediment samples and in seven fish species (Boops boops, Diplodus sargus, Sarpa salpa, Serranus scriba, Spicara smaris, Trachurus draco, and Trachinus mediterraneus), five bivalve species (Cerastoderma glaucum, Chlamys flexuosa, Mytilus galloprovincialis, Pinna nobilis, and Ruditapes decussatus), two gastropod species (Bolinus brandaris and Hexaplex trunculus), cuttlefish (Sepia officinalis), and shrimp (Penaeus notialis), most of which are commonly consumed in Tunisia. Samples were collected from Bizerte lagoon during March 2012. Average concentrations of total BTs found in sediment and the muscle of fishes, bivalves, gastropods, cuttlefish, and shrimp were 17.7, 11.5, 31.8, 36.9, 8.1, and 9.4 ng Sn g^?1 dw, respectively. The calculation of tolerable average residue levels and non-cancer hazard quotient for tributyltin (TBT) showed that daily exposure of these seafood to TBT is unlikely to cause any deleterious effects to humans, thus indicating that consumers may not be at risk through the inclusion of these species in their regular diet.     

Inhibition of photosynthetic oxygen evolution and electron transfer from the quinone acceptor Q<Subscript>A</Subscript><Superscript>−</Superscript> to Q<Subscript>B</Subscript> by iron deficiency

The effect of iron deficiency on photosynthetic electron transport in Photosystem II (PS II) was studied in leaves and thylakoid membranes of lettuce (Lactuca sativa, Romaine variety) plants. PS II electron transport was characterized by oxygen evolution and chlorophyll fluorescence parameters. Iron deficiency in the culture medium was shown to affect water oxidation and the advancement of the S-states. A decrease of maximal quantum yield of PS II and an increase of fluorescence intensity at step J and I of OJIP kinetics were also observed. Thermoluminescence measurements revealed that charge recombination between the quinone acceptor of PS II, Q_B, and the S₂ state of the Mn-cluster was strongly perturbed. Also the dark decay of Chl fluorescence after a single turnover white flash was greatly retarded indicating a slower rate of Q_A ⁻ reoxidation.     

TRAIL-R4 promotes tumor growth and resistance to apoptosis in cervical carcinoma HeLa cells through AKT

Background

TRAIL/Apo2L is a pro-apoptotic ligand of the TNF family that engages the apoptotic machinery through two pro-apoptotic receptors, TRAIL-R1 and TRAIL-R2. This cell death program is tightly controlled by two antagonistic receptors, TRAIL-R3 and TRAIL-R4, both devoid of a functional death domain, an intracellular region of the receptor, required for the recruitment and the activation of initiator caspases. Upon TRAIL-binding, TRAIL-R4 forms a heteromeric complex with the agonistic receptor TRAIL-R2 leading to reduced caspase-8 activation and apoptosis.

Methodology/Principal Findings

We provide evidence that TRAIL-R4 can also exhibit, in a ligand independent manner, signaling properties in the cervical carcinoma cell line HeLa, through Akt. Ectopic expression of TRAIL-R4 in HeLa cells induced morphological changes, with cell rounding, loss of adherence and markedly enhanced cell proliferation in vitro and tumor growth in vivo. Disruption of the PI3K/Akt pathway using the pharmacological inhibitor {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002, siRNA targeting the p85 regulatory subunit of phosphatidylinositol-3 kinase, or by PTEN over-expression, partially restored TRAIL-mediated apoptosis in these cells. Moreover, the Akt inhibitor, {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002, restituted normal cell proliferation index in HeLa cells expressing TRAIL-R4.

Conclusions/Significance

Altogether, these results indicate that, besides its ability to directly inhibit TRAIL-induced cell death at the membrane, TRAIL-R4 can also trigger the activation of signaling pathways leading to cell survival and proliferation in HeLa cells. Our findings raise the possibility that TRAIL-R4 may contribute to cervical carcinogenesis.     

Imposex and butyltin burden in Bolinus brandaris (Mollusca, Gastropoda) and sediment from the Tunisian coast

The present study aimed at analyzing the imposex incidence and the presence of butyltins namely tributyltin (TBT) with its di- and mono-substituted metabolites in Bolinus brandaris whole tissues and in surface sediments at seven sites from the Tunisian coast during one campaign in May 2010. Butyltin levels were evaluated using isotope dilution GC–MS. Except the population collected from Zarat site, imposex was found in snails from the remained six sites with a maximal incidence and sterility (closure of the vaginal opening) registered in Carrier bay. Both imposex indices VDSI and RPLI showed a positive correlation with tissue concentrations of TBT. Total butyltin concentrations in sediments were higher in sites located in the vicinity of shipping areas with levels of TBT high enough to cause environmental concern if there is no legislative restriction and enforcement for the sale and use of these chemicals in Tunisia. These results further confirmed that B. brandaris is a good bioindicator of butyltin pollution in the studied areas. In addition, this study provided recent and new data on sediment butyltin concentrations that could serve for long-term monitoring of TBT pollution in Tunisia and the Mediterranean Sea.     

Distribution of phenolic compounds and antioxidant activity between young and old leaves of Carthamus tinctorius L. and their induction by salt stress

In the present work, we investigated the effect of salt stress on the distribution of safflower (Carthamus tinctorius L.) antioxidant system in relation to leaf age. The study was carried out under growth chamber conditions using seedlings of three cultivars which were subjected to 0 and 50 mM NaCl for 3 weeks. Leaf growth, water content, lipid peroxidation, and phenolic compound (total polyphenols, total flavonoids, and proanthocyanidins) concentration were measured at two leaf stages (young and old leaves). Leaf growth was affected by salinity only in Kairouan cultivar that also showed a significant decrease in old leaf water content. By contrast, Gabes and Tazarka cultivars maintained their old leaf water content constant and showed a reduction in that of young leaves. This could be attributed to a higher aptitude of the latter two cultivars to use absorbed sodium and chloride for osmotic adjustment in old leaves, keeping potassium for specific functions. Salt-induced lipid peroxidation was observed only in old leaves, whereas the accumulation of the major phenolic compounds under saline conditions was higher in young leaves, except in Gabes cultivar where no significant difference was found between the two leaf stages. A significant variability was also found between the three cultivars. The better behavior of salt-challenged leaves of Gabes and Tazarka cultivars compared to that of Kairouan cultivar may be related to their higher water content and the accumulation of polyphenols, in particular flavonoids that were shown to be efficiently involved in the restriction of salt-induced oxidative damages.     

Salt stress (NaCl) affects plant growth and branch pathways of carotenoid and flavonoid biosyntheses in <Emphasis Type="Italic">Solanum nigrum</Emphasis>

In this study, we set out to investigate the effect of sodium chloride (NaCl) on carotenoid and flavonoid production by the black nightshade (Solanum nigrum L.). The study was carried out under green chamber conditions using seedlings subjected to 0, 50, 100 and 150 mM NaCl for 3 weeks. The negative effect of NaCl on dry biomass production of roots and leaves were accompanied by a significant restriction in K⁺, Ca²⁺ and Mg²⁺ ion uptake and by an increase in Na⁺ ion concentrations, the effects of which were most pronounced at the highest NaCl level. Salt stress also induced oxidative stress, according to the amplified levels of thiobarbituric acid reactive substances and relative ion leakage ratio. Expression of some related carotenoid (phytoene synthase 2 and β-lycopene cyclase) and flavonoids genes (phenylalanine ammonialyase, chalcone synthase and flavonol synthase) were induced by NaCl, followed enhanced production of β-carotene, lutein, and quercetin 3-β-d-glucoside. At the highest NaCl level (150 mM NaCl), quercetin 3-β-d-glucoside synthesis came at the expense of reduced β-carotene and lutein, while salt stress treatment affected leaf antioxidant activities to a great extent relative to the control. Our data suggest that the potential antioxidant properties of carotenoids and flavonoids and their related key genes may be efficiently involved in the restriction of salt-induced oxidative damages.