Nodule Senescence in Medicago truncatula�CSinorhizobium Symbiosis Under Abiotic Constraints: Biochemical and Structural Processes Involved in Maintaining Nitrogen-Fixing Capacity

Nitrogen-fixing capacity (NFC) in nodules of four Medicago truncatula lines inoculated with four strains of Sinorhizobium was assessed, during the plant life cycle, in relation to parameters identified as indices of plant growth, photosynthetic capacity, nodule integrity, and functioning. Differences in duration of the NFC period were observed among symbiotic associations and were correlated with variability on plant biomass production. Senescence appearance and vigor varied in parallel with structural, physiological, and biochemical stability of nodules. Maintenance of a longer high-NFC period was correlated to a higher stimulation of antioxidant enzymes, mainly superoxide dismutase (SOD, EC 1.15.1.1) and guaiacol peroxidase (POX, EC 1.11.1.7), and a consequent longer maintenance of membrane integrity and nodule structure within the first stages of senescence. Salinity and drought stresses interfered with nodule functioning and triggered fast and global nodule senescence, albeit a superiority of nodules having a long high-NFC period. The protective role of POX activity on salt- and drought-stressed nodules was revealed. On the other hand, SOD stimulation was independent of stress application. Another strategy allowing the maintenance of longer NFC in salt-stressed nodules could be the accumulation of starch granules in the senescence-functioning interface of nodules. This finding is currently under investigation. Interestingly, the symbioses with different behaviors of nodule senescence identified in this work would be useful bases for biochemical, genomic, and proteomic studies dissecting nodule senescence.     

The Halophyte Cakile maritima Reduces Phenanthrene Phytotoxicity

In a previous study, we showed that the halophyte plant model Thellungiella salsuginea was more tolerant to phenanthrene (Polycyclic Aromatic Hydrocarbon: PAH) than its relative glycophyte Arabidopsis thaliana. In the present work, we investigated the potential of another halophyte with higher biomass production, Cakile maritma, to reduce phenanthrene phytotoxicity. Sand was used instead of arable soil with the aim to avoid pollutant degradation by microorganisms or their interaction with the plant. After 6 weeks of treatment by 500 ppm phenanthrene (Phe), stressed plants showed a severe reduction (–73%) in their whole biomass, roots being more affected than leaves and stems. In parallel, Guaiacol peroxidase (GPX) activity was increased by 185 and 62% in leaves and roots, respectively. Non-enzymatic antioxidant capacity (assayed by ABTS test) was maintained unchanged in all plant organs. The model halophytic plant Thellungiella salsuginea was used as a biomarker of phenanthrene stress severity and was grown at 0 (control), 125, 250, and 375 ppm. T. salsuginea plants grown on the sand previously contaminated by 500 ppm Phe then treated by C. maritma culture (phytoremediation culture) showed similar biomass production as plants subjected to 125 ppm Phe. This suggests that the phytotoxic effects of phenanthrene were reduced by 75% by the 6-week treatment by C. maritima. Our findings indicate that C. maritima can constitute a potentially good candidate for PAH phytoremediation.     

The Attractive Serratia plymuthica BMA1 Strain With High Rock Phosphate-Solubilizing Activity and Its Effect on the Growth and Phosphorus Uptake by Vicia faba L. Plants

Abstract

The present work aims to investigate the attractive ability of the newly isolated bacterium Serratia plymuthica BMA1, to release phosphorus (P) from rock phosphate (RP) and also to assess its beneficial effect in promoting the growth of Vicia faba. This strain exhibited the highest RP-solubilization activity ever reported, with 450?mg l^?1 of soluble P at 30?°C. At 10 and 20?°C, its RP-solubilization was estimated at 100 and 200?mg l^?1, respectively. HPLC analysis revealed that RP-solubilizing activity was associated with the release of gluconic acid. The hydroxyapatite (HA) solubilization activity concomitantly occurred with the secretion of gluconic acid and lactic acid. Under greenhouse conditions, application of BMA1 strain as an inoculant in presence of RP as the sole P source, considerably increased phosphorus uptake by V. faba L. and upgraded its overall growth in terms of dry weight and length by 76% and 39%, respectively. This growth promoting effect was accompanied by a substantial increase in chlorophyll contents. Additionally, phosphorus levels within roots and shoots of S. plymuthica BMA1-treated plants were approximately three times greater, compared to the non-inoculated control plants. When HA was used instead of RP, bacterization with BMA1 strain also enhanced the plant growth parameters and P contents, but significantly less than RP. These findings revealed that S. plymuthica BMA1 could be a potential candidate to improve the agronomic effectiveness of RP, toward a clean P-nutrition through the formulation of bio-phosphate fertilizers for plant growth promotion.     

Bacterial sucrose isomerases: properties and structural studies

Due to their significant role in food industry, sucrose isomerases are good candidates for rational protein engineering. Hence, specific modifications in order to modify substrate affinity and selectivity, product specificity but also to adapt their catalytic properties to particular industrial process conditions, is interesting. Our work on the structural studies of the sucrose isomerase, MutB, which presents the first structural data available on a trehalulose synthase and the first experimental data on complexed forms of sucrose isomerases represents a significant advance in the understanding of these enzymes. In this review we give an overview of what is known on biochemical properties and structural aspects of different sucrose isomerases in particular those reported from bacteria.     

Identification of genetic defects underlying FVII deficiency in 10 patients belonging to eight unrelated families of the North provinces from Tunisia

ABSTRACT: Inherited factor VII (FVII) deficiency is a rare disorder characterized by a bleeding phenotype varying from mild to severe. To date, more than 200 mutations have been described along the F7 gene encoding for FVII. The aim of this study was the identification of genetic defects underlying FVII deficiency in 10 patients belonging to eight unrelated families of the North provinces from Tunisia. Mutation detection was performed by sequencing the whole F7 gene coding region, exon-intron boundaries and about 400 bp of the promoter region. We identified 5 mutations in five unrelated families; the novel p.F328Y mutation and the reported mutations: p.R304Q, p.M298I, IVS1aG > A and nt1005C > T. For the remaining 5 patients we didn't identified any mutations using PCR/Sequencing protocol. In conclusion, this study represents the first comprehensive molecular series of FVII deficiency affected patients in Tunisia from the North. We will try in the future to continue the molecular study for Tunisian patients from Center and South provinces in order to have a complete idea about the FVII deficiency mutational profile in our country. Virtual slides The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1288044089753085.