Genotypic variation of nodules’ enzymatic activities in symbiotic nitrogen fixation among common bean (Phaseolus vulgaris L.) genotypes grown under salinity constraint

The effect of salt stress, under glasshouse conditions, was studied on plant biomass, nodulation, and activities of acid phosphatases (APase, EC 3.1.3.2) and trehalose 6-phosphate phosphatase (TPP, EC 3.1.3.12) in the symbiosis common bean (Phaseolus vulgaris L.)-rhizobia nodules. Four common bean recombinant inbred lines (147, 115, 104 and 83) were separately inoculated, with CIAT 899 or RhM11 strains and grown in hydroaeroponic culture. Two NaCl levels (0 and 25 mM NaCl plant^?1 week^?1 corresponding, respectively, to the control and the salt treatment) were applied and the culture was assessed during 42 days after their transplantation. The results showed that the nodulation of these lines was not affected by salinity except for the line 83 inoculated with CIAT 899, whose nodule dry weight decreased by 48.24 % compared with the corresponding controls. For the other symbiotic combinations, shoot and root biomasses were not significantly affected by salt constraint. Salinity stress generally reduced acid phosphatise and trehalose phosphate phosphatase activities in nodules that were less affected in plants inoculated with RhM11. Based on our data, it appears that nodule phosphatase activity may be involved in salinity tolerance in common beans and the levels of salt tolerance depend principally on specific combination of the rhizobial strain and the host cultivar.     

Diversity of Halimeda (Bryopsidales,Chlorophyta) in New Caledonia: a Combined Morphological and Molecular Study

Halimeda is a genus of calcified and segmented green macroalgae in the order Bryopsidales. In New Caledonia, the genus is abundant and represents an important part of the reef flora. Previous studies recorded 19 species that were identified using morphological criteria. The aim of this work was to reassess the diversity of the genus in New Caledonia using morpho‐anatomical examinations and molecular analyses of the plastid tufA and rbcL genes. Our results suggest the occurrence of 22 species. Three of these are reported for the first time from New Caledonia: Halimeda kanaloana, H. xishaensis, and an entity resembling H. stuposa. DNA analyses revealed that the species H. fragilis exhibits cryptic or pseudocryptic diversity in New Caledonia. We also show less conclusive evidence for cryptic species within H. taenicola     

Robotized time-lapse imaging to assess in-planta uptake of phenylurea herbicides and their microbial degradation

Two key physiological parameters of plant leaves, photosynthesis and transpiration, can be continuously monitored by, respectively, chlorophyll a fluorescence imaging and thermography. These non-contact techniques immediately visualize any local stress or treatment affecting either photosynthetic efficiency or water status. Photosystem II-inhibiting herbicides, including the phenylurea derivatives diuron and linuron, cause a marked increase in chlorophyll a fluorescence several days before appearance of chlorosis. Here, bioprotection through microbial degradation of linuron in the feeding solution of common bean plants ( Phaseolus vulgaris L.) was monitored by the absence of an increase in chlorophyll a fluorescence in primary leaves. The different treatments and repeats were imaged sequentially at 2 h intervals using a robotized system with thermal, fluorescence and video cameras. Chlorophyll fluorescence imaging visualized the effect of linuron transported by the transpiration stream earlier than thermography. In addition, local effects and transport after topical application of diuron were recorded presymptomatically in tobacco ( Nicotiana tabacum L.) and Arabidopsis thaliana (L.) Heynh. Thermal imaging clearly monitored localized stomatal closure, coinciding with the first increase in chlorophyll fluorescence, at the sites of diuron treatment. In conclusion, the robotized chlorophyll a fluorescence set-up permits fully reliable, early high-contrast visualization for bioremediation purposes.     

Multi-sensor plant imaging: Towards the development of a stress-catalogue

Agricultural production is limited by a wide range of abiotic (e.g. drought, waterlogging) and biotic (pests, diseases and weeds) stresses. The impact of these stresses can be minimized by appropriate management actions such as irrigation or chemical pesticide application. However, further optimization requires the ability to diagnose and quantify the different stresses at an early stage. Particularly valuable information of plant stress responses is provided by plant imaging, i.e. non-contact sensing with spatial resolving power: (i) thermal imaging, detecting changes in transpiration rate and (ii) fluorescence imaging monitoring alterations in photosynthesis and other physiological processes. These can be supplemented by conventional video imagery for study of growth. An efficient early warning system would need to discriminate between different stressors. Given the wide range of sensors, and the association of specific plant physiological responses with changes at particular wavelengths, this goal seems within reach. This is based on the organization of the individual sensor results in a matrix that identifies specific signatures for multiple stress types. In this report, we first review the diagnostic effectiveness of different individual imaging techniques and then extend this to the multi-sensor stress-identification approach.     

The Conserved nhaAR Operon Is Drastically Divergent between B2 and Non-B2 Escherichia coli and Is Involved in Extra-Intestinal Virulence

The Escherichia coli species is divided in phylogenetic groups that differ in their virulence and commensal distribution. Strains belonging to the B2 group are involved in extra-intestinal pathologies but also appear to be more prevalent as commensals among human occidental populations. To investigate the genetic specificities of B2 sub-group, we used 128 sequenced genomes and identified genes of the core genome that showed marked difference between B2 and non-B2 genomes. We focused on the gene and its surrounding region with the strongest divergence between B2 and non-B2, the antiporter gene nhaA. This gene is part of the nhaAR operon, which is in the core genome but flanked by mobile regions, and is involved in growth at high pH and high sodium concentrations. Consistently, we found that a panel of non-B2 strains grew faster than B2 at high pH and high sodium concentrations. However, we could not identify differences in expression of the nhaAR operon using fluorescence reporter plasmids. Furthermore, the operon deletion had no differential impact between B2 and non-B2 strains, and did not result in a fitness modification in a murine model of gut colonization. Nevertheless, sequence analysis and experiments in a murine model of septicemia revealed that recombination in nhaA among B2 strains was observed in strains with low virulence. Finally, nhaA and nhaAR operon deletions drastically decreased virulence in one B2 strain. This effect of nhaAR deletion appeared to be stronger than deletion of all pathogenicity islands. Thus, a population genetic approach allowed us to identify an operon in the core genome without strong effect in commensalism but with an important role in extra-intestinal virulence, a landmark of the B2 strains.