Analysis and speciation of heavy metals in the water, sediments, and drinking water plant sludge of a deep and sulfate-rich Algerian reservoir.

This research work aimed to assess the water quality, speciation of heavy metals in sediments and water, and the drinking water treatment plant in an important Algerian reservoir (Timgad dam, Batna). Algeria has invested billions of dollars in large seawater desalination plants and dams; however, the water quality remains a serious issue, hence this research. The high concentration (≥ 400 mg/l) of sulfate and the depth (44 m) of the studied reservoir leads to sulfate-reducing bacteria (SRB) activity and water stratification, influencing the sulfur S cycle and metal speciation. The total and sequential extractions, using the method of the European Community Bureau of Reference (BCR), were applied to characterize seven metals in sediments and coagulation sludge. It showed the absence of Zn and only trace levels of other metals in the water, whereas the sediment and the decanter sludge were highly contaminated, especially by Fe and Zn (2100 to 2800 mg/kg); the other metal concentrations were much lower. The absence of Zn in aqueous phases and its high concentration in the solid phases turned out to be a serious paradox and issue of this research work. The compositions of the reservoir sediments and coagulation sludge (decanter sludge) were similar, suggesting the metals travel through turbidity, from reservoir to treatment plant and the potential drinking water contamination. This metal characterization, combined with speciation predictive software, will allow a better understanding of heavy metal behavior and fate.

Constitutive expression of clathrin hub hinders elicitor-induced clathrin-mediated endocytosis and defense gene expression in plant cells.

Endocytosis has been recently implicated in the signaling network associated with the recognition of microbes by plants. In a previous study, we showed that the elicitor cryptogein was able to induce clathrin-mediated endocytosis (CME) in tobacco suspension cells. Herein, we investigate further the induced CME by means of a GFP-tagged clathrin light chain and a CME inhibitor, the hub domain of clathrin heavy chain. Hub constitutive expression does affect neither cell growth nor constitutive endocytosis but abolishes cryptogein-induced CME. Such an inhibition has no impact on early events in the cryptogein signaling pathway but reduces the expression of defense-associated genes.

Nuclear localization of the Arabidopsis APETALA3 and PISTILLATA homeotic gene products depends on their simultaneous expression.

The Arabidopsis APETALA3 (AP3) and PISTILLATA (PI) proteins are thought to act as transcription factors and are required for specifying floral organ identities. To define the nuclear localization signals within these proteins, we generated translational fusions of the coding regions of AP3 and PI to the bacterial uidA gene that encodes beta-glucuronidase (GUS). Transient transformation assays of either the AP3-GUS or PI-GUS fusion protein alone resulted in cytoplasmic localization of GUS activity. However, coexpression of AP3-GUS with PI, or PI-GUS with AP3, resulted in nuclear localization of GUS activity. Stable transformation with these fusion proteins in Arabidopsis showed similar results. The nuclear colocalization signals in AP3 and PI were mapped to the amino-terminal regions of each protein. These observations suggest that the interaction of the AP3 and PI gene products results in the formation of a protein complex that generates or exposes a colocalization signal required to translocate the resulting complex into the nucleus. The colocalization phenomenon that we have described represents a novel mechanism to coordinate the functions of transcription factors within the nucleus.

Cellular interactions mediated by the homeotic PISTILLATA gene determine cell fate in the Arabidopsis flower.

Flowers develop from the coordinated division and differentiation of cells derived from the shoot apical meristem. By inducing chromosomal deletions in individual shoot apical meristem cells, we have generated Arabidopsis plants that are genetically mosaic for the homeotic PISTILLATA gene. Flowers bearing wild-type PISTILLATA epidermal tissue and mutant pistillata internal tissues are phenotypically normal. Based on this non-cell-autonomy, we suggest that PISTILLATA controls the production of a substance involved in cell-cell communication between the outer and inner tissue layers of the flower. These mosaic flowers were also used to assess the relative contributions of meristematic cells to the developing floral organs. These observations indicate that meristematic cells have discrete but somewhat variable contributions to the Arabidopsis flower. We have used these results to construct a fate map of the Arabidopsis floral primordium.

The full-length transcript of the I factor, a LINE element of Drosophila melanogaster, is a potential bicistronic RNA messenger.

The I factor of Drosophila melanogaster is a retrotransposon of the LINE superfamily. The I factor displays two non-overlapping open reading frames (ORFs) that have the potential to encode for a nucleic acid-binding protein (ORF1) and a reverse transcriptase (ORF2). Retrotransposition of the I factor has been demonstrated and a putative full-length RNA intermediate has been identified. No other transcript from functional I factor has ever been described, suggesting that the full-length RNA is also used as a messenger. Here we report that a bicistronic RNA which conserves the ORF1-ORF2 organization of the I factor transcript is a template for ORF2 translation in vivo. We further demonstrate that the first AUG of ORF2 initiates translation, but efficiency of this initiation increases approximately 200 fold when ORF1 is deleted. Our results show that the I factor transcript may be used to translate both ORFs from their own initiation codons at different rates. Various mechanisms of translation are proposed.

Spatial and temporal expression of the I factor during oogenesis in Drosophila melanogaster.

The I factor is a functional non-viral retrotransposon, or LINE, from Drosophila melanogaster. Its mobility is associated with the I-R hybrid dysgenesis. In order to study the expression pattern of this LINE in vivo, a translational fusion between the first ORF of the I factor and the lacZ gene of Escherichia coli has been carried out and introduced in the genome of reactive (R) flies. Homozygous transgenic Drosophila lines have been established and analysed. ORF1 expression is limited to germ-line cells (nurse cells and oocyte) between stage 2 and 10 of oogenesis. No somatic expression is found. Position effects may limit the level of expression of a given transgene but do not modify its basic pattern of expression during the development of the fly. This reproducible control demonstrates both that I factor is driven by its own promoter, probably the internal one suggested by Mizrokhi et al. (Mizrokhi, L.J., Georgevia, S.G. and Ilying, Y.V. (1988). Cell 54, 685-691), and that tissue-specific regulatory sequences are present in the 5' untranslated part of the I factor. The nuclear localization of the fusion protein reveals the presence of nuclear localization signals (NLS) in the ORF1-encoded protein correlating with the possible structural and/or regulatory role of this protein. This expression is restricted to dysgenic and reactive females, and is similar in the two conditions. All the results obtained in this work suggest that I factor transposition occurs as a meiotic event, between stage 2 and 10 of the oogenesis and is regulated at the transcriptional level. It also appears that our transgene is an efficient marker to follow I factor expression.