Allelopathic potential of two invasive alien Ludwigia spp.

The allelopathic potential of two invasive alien Ludwigia [Onagraceae: L. peploides (Kunth) Raven and L. grandiflora (Michaux) Greuter and Burdet], that have developed quasi-monotypic stands in many aquatic ecosystems in France, was investigated. Since allelopathy involves the release of compounds into the environment, the water of monospecific experimental cultures was directly tested against two target species: Lactuca sativa L., the standard cultivar for bioassays, and Nasturtium officinale R. Brown, a resistant and widespread native hydrophyte. The treatment was carried out at the three main phases of development of both Ludwigia in February, May and August. For each experiment, the germination, mortality and culture yield percentages, the seedling growth (radicle and hypocotyl elongation) and the health of 15-day-old-seedlings were measured. The water of each Ludwigia tank induced: (1) a decrease in germination for watercress in August (control: 68.6%, L. peploides: 48.6%, L. grandiflora: 61.1%); (2) an increase in mortality in May only for watercress (control: 3.4%, L. peploides: 13.5%, L. grandiflora: 12%) and in August for both target species (up to 22.3% vs. 3% for lettuce and 27% vs. 12.5% for watercress); (3) a disturbance of seedling elongation for lettuce in all seasons; and (4) a seedling chlorosis of both target species, particularly in May and August. This study showed that L. peploides and L. grandiflora possess an allelopathic activity that influences the water quality throughout the year. Combined with the various competitive attributes, allelopathy may contribute to the great success of these two invasive Ludwigia in Europe. In threatened wetland communities of the Mediterranean area, in particular, allelopathy might have an important impact by diminishing the seedling survival of the most vulnerable species.     

Impact of the carbon chain length of novel platinum complexes derived from N-alkyl-propanediamines on their cytotoxic activity and cellular uptake

This work describes the synthesis and characterization of four new ligands derived from 1,3-propanediamine in addition to the preparation and characterization of their respective platinum(II) complexes by reaction with K₂PtCl₄. These ligands were obtained by the reaction of the corresponding alkyl mesylate with 1,3-propanediamine. We have prepared compounds having different carbon chains lengths in an attempt to correlate this factor, which influences the lipophilicity of the compounds, with cytotoxic activity. Octanol/water partition coefficients, the effect of the four complexes on the growth of two tumoral cell lines, and their cellular uptake were investigated. Increasing lipophilicity enhances the rate of cellular uptake and, consequently, the cytotoxic activity.     

Neuroendocrine disruption without direct endocrine mode of action: Polychloro-biphenyls (PCBs) and bisphenol A (BPA) as case studies

Endocrine disruption is commonly thought to be restricted to a direct endocrine mode of action i.e. the perturbation of the activation of a given type of hormonal receptor by its natural ligand. Consistent with the WHO definition of an endocrine disrupter, a key issue is the “altered function(s) of the endocrine system”. Such altered functions can result from different chemical interactions, beyond agonistic or antagonistic effect at a given receptor. Based on neuroendocrine disruption by polychlorinated biphenyls and bisphenol A, this paper proposes different mechanistic paradigms that can result in adverse health effects. They are a consequence of altered endocrine function(s) secondary to chemical interaction with different steps in the physiological regulatory processes, thus accounting for a possibly indirect endocrine mode of action.     

Spatial distribution patterns of interphase centromeres during retinoic acid-induced differentiation of promyelocytic leukemia cells

BACKGROUND: The pericentromeric heterochromatin is an important element for the regulation of gene silencing. Its spatial distribution during interphase appears to be cell-type specific. This study analyzes three-dimensional (3D) centromere distribution patterns during cellular differentiation along the neutrophil pathway. METHODS: Differentiation of the promyelocytic leukemia cell line NB4 was induced by retinoic acid. Centromeres in interphase nuclei were visualized by immunofluorescence staining of centromere-associated proteins with CREST serum. 3D images of nuclei were obtained by confocal microscopy. Automated methods for the segmentation of point-like objects in 3D images were implemented to detect the position of centromeres. Features of centromere localization patterns were determined by constructing the minimal spanning tree of the centromere distribution. RESULTS: In differentiated NB4 cells, the number of centromere conglomerates (chromocenters) was decreased and the distance between chromocenters was increased as compared with untreated controls. The nuclear volume did not differ between the two groups. CONCLUSIONS: The measured rearrangement of centromeres indicates a progressive clustering of heterochromatin and a global remodeling of interphase chromosome territories during differentiation of NB4 cells. The developed methods for the analysis of 3D centromere distribution patterns provide the opportunity for a fast and objective analysis of heterochromatin remodeling.     

Purification and Partial Identification of Novel Antimicrobial Protein from Marine Bacterium <Emphasis Type="Italic">Pseudoalteromonas</Emphasis> Species Strain X153

A marine bacterium, X153, was isolated from a pebble collected at St. Anne du Portzic (France). By 16S ribosomal DNA gene sequence analysis, X153 strain was identified as a Pseudoalteromonas sp. close to P. piscicida. The crude culture of X153 was highly active against human pathogenic strains involved in dermatologic diseases, and marine bacteria including various ichthyopathogenic Vibrio strains. The active substance occurred both in bacterial cells and in culture supernatant. An antimicrobial protein was purified to homogeneity by a 4-step procedure using size-exclusion and ion-exchange chromatography. The highly purified P-153 protein is anionic, and sodium dodecylsulfate polyacrylamide gel electrophoresis gives an apparent molecular mass of 87 kDa. The X153 bacterium protected bivalve larvae against mortality, following experimental challenges with ichthyopathogenic Vibrio. Pseudoalteromonas sp. X153 may be useful in aquaculture as a probiotic bacterium.     

Evidence for non-random spatial distribution of meiotic exchanges in Podospora anserina: comparison between linkage groups 1 and 6.

Summary In Podospora anserina, positive and very efficient chiasma interference is observed. However, its modalities are different for the two linkage groups 1 (LG1) and 6 (LG6) studied here.In the right arm of LG1, two zones exist in which always occurs only one crossing-over. They are formed independently each other. Moreover, the genetic map consists of clusters of genes located near the centromere and at the limit between the two interference zones. It is postulated that this structure of the map results from the localization of crossing-over in the middle of each zone. We suppose that the type of chiasma interference, in Podospora, is a typical one as it is in Drosophila. It seems that both these phenomena are under common genetical control.In the LG6, we observe a weaker positive chiasma interference without crossing-over localization.Laboratoire associé au C.N.R.S.n^o 086     

Co-assembly properties of higher plant microtubule-associated proteins with purified brain and plant tubulins

The knowledge of higher plant microtubule-associated proteins (MAPs) remains limited to a few examples that illustrate essentially their binding properties to preformed microtubules as described in carrots. Using taxol-stabilized microtubules a putative MAP-enriched fraction has been isolated in maize cultured cell extracts, one of these polypeptides is immunologically related to neural tau. At present, these proteins are being characterized by co-assembly assays that were not possible before. Similar experiments were done also in a heterologous system using brain tubulin. Three polypeptides out of seven that constituted the MAP fraction were found to co-assemble specifically with tubulin subunits of both origins. Their apparent molecular weights are 67, 83 and 125 kDa. A two-dimensional gel immunoblot of the 83 kDa polypeptide with tau antibodies revealed one major spot. Polypeptides were quantiated by scanning the gels. These results shed light on the present debate on higher plant MAPs and their potential activity in the regulation of microtubule assembly and function in the higher plant cell.     

Modification of subunit interaction in membrane-bound acid β-glucosidase from Gaucher disease

The radiation inactivation method has been used to determine the molecular mass of membrane-bound acid β-glucosidase (EC 3.2.1.21) in situ, in normal human spleen and in that of two patients with type I Gaucher disease: the molecular mass in Gaucher spleen is about double (125 000 ± 8900) of that found in the normal spleen (67 000 ± 7700) which is compatible with the existence of subunit coupling in the muted acid β-glucosidase. From the results, we conclude that subunit interaction is altered in mutant acid β-glucosidase and that this may be due to a direct effect of the mutation.