Effect of dibromothymoquinone (DBMIB) on reduction rates of Photosystem I donors in intact chloroplasts

Dual effect of dibromothymoquinone ( DBMIB ), inhibitor and reducing agent at the donor side of Photosystem I, was investigated in isolated intact chloroplasts by flash-induced absorbance changes at 820 and 515 nm. We show that in the absence of other electron donors, rereduction of P700+ by DBMIB proceeds at a very low rate (half-time of approximately 10 s) Dual effect of DBMIB explains that the initial rise of electrochromic absorbance change induced by repetitive flashes is usually not diminished while the slow rise is fully inhibited by this compound.     

An experimental system to study responses of Medicago truncatula roots to chitin oligomers of high degree of polymerization and other microbial elicitors

Key message

A fully acetylated, soluble CO preparation of mean DP of ca. 7 was perceived with high sensitivity by M. truncatula in a newly designed versatile root elicitation assay.

Abstract

The root system of legume plants interacts with a large variety of microorganisms, either pathogenic or symbiotic. Understanding how legumes recognize and respond specifically to pathogen-associated or symbiotic signals requires the development of standardized bioassays using well-defined preparations of the corresponding signals. Here we describe the preparation of chitin oligosaccharide (CO) fractions from commercial chitin and their characterization by a combination of liquid-state and solid-state nuclear magnetic resonance spectroscopy. We show that the CO fraction with highest degree of polymerization (DP) became essentially insoluble after lyophilization. However, a fully soluble, fully acetylated fraction with a mean DP of ca. 7 was recovered and validated by showing its CERK1-dependent activity in Arabidopsis thaliana. In parallel, we developed a versatile root elicitation bioassay in the model legume Medicago truncatula, using a hydroponic culture system and the Phytophthora β-glucan elicitor as a control elicitor. We then showed that M. truncatula responded with high sensitivity to the CO elicitor, which caused the production of extracellular reactive oxygen species and the transient induction of a variety of defense-associated genes. In addition, the bioassay allowed detection of elicitor activity in culture filtrates of the oomycete Aphanomyces euteiches, opening the way to the analysis of recognition of this important legume root pathogen by M. truncatula.     

Molecular,quantitative and abiotic variables for the delineation of evolutionary significant units: case of sandalwood (<Emphasis Type="Italic">Santalum austrocaledonicum</Emphasis> Vieillard) in New Caledonia

Various approaches have been developed to define conservation units for plant and animal species. In this study we combined nuclear microsatellites (from a previous published study) and chloroplast microsatellites (assessed in the present study), leaf and seed morphology traits and abiotic variables (climate and soil) to define evolutionary significant units (ESU) of Santalum austrocaledonicum, a tree species growing in New Caledonia. Results for chloroplast microsatellites showed that the total population heterozygosity was␣high, (H _cp = 0.84) but varied between islands. Differentiation was strong in the total population (F _stcp = 0.66) but also within the main island Grande Terre (F _stcp = 0.73) and within Iles Loyauté (F _stcp = 0.52), highlighting a limited gene flow between populations. These results confirmed those obtained with nuclear microsatellites. The cluster analysis on molecular markers discriminated two main groups constituted by the populations of Grande Terre and the populations of Iles Loyauté. A principal component analysis of leaf and seed morphology traits singled out the populations of Iles Loyauté and the western populations of Grande Terre. Quantitative genetic analyses showed that the variation between populations was under genetic control (broad sense heritability close to 80%). A high correlation between rainfall and morphological traits suggested an impact of climate on this variation. The integration of these results allows to define two ESUs, one corresponding to Grande Terre and Ile des Pins and the other the Iles Loyauté archipelago. This study stresses the need to restore some populations of Grande Terre that are currently threatened by their small size.     

Patterns of Root Colonization in Epacridaceous Plants Collected from Different Sites

Root colonization was studied in ten species of the Epacridaceaeat three sites in Victoria by morphological and cross-inoculationexperiments. The sites and genera chosen were Cranbourne [Epacrisimpressa Labill. andLeucopogon ericoides(Smith) R. Br.] andRye [L. parviflorus(Andrews) Lindley] on the Mornington Peninsula,and the Grampians[Astroloma conostephioides(Sond.) Benth.,A.humifusum(Cav.) R. Br.,A pinifolium(R. Br.) Benth,Brachylomadaphnoides(Smith) Benth.,E. impressa, E. impressavar.grandifloraBenth.andStyphelia adscendensR. Br.] in western Victoria. For morphologicalstudies, samples of roots from each species at each site werecleared and stained and examined microscopically. For cross-inoculationstudies, cuttings from each site were struck in potting mediuminoculated with soil from the same and other sites. The ericoidmycorrhizae in the roots of plants found at or grown in Cranbourneand Rye soils were similar. Both were significantly differentfrom the internal hyphae found in the roots of plants foundat or grown in Grampians soils, which were three times largerin diameter and formed dense coils which filled the host celland invaded adjacent epidermal cells. This suggests that morethan one fungus is involved in the relationships, that the MorningtonPeninsula sites had a different fungus from the Grampians siteand that host specificity is low. Vesicular structures werealso found commonly on plants at the Grampians site, in contrastwith other sites. Epacridaceae; root; fungus; mycorrhiza; morphology; inoculation     

Green fluorescent protein (GFP) as gene expression reporter and vital marker for studying development and microbe-plant interaction in the tobacco pathogen Phythphthora parasitica var. nicotianae

PEG-mediated transformation of protoplasts in the presence of lipofectin was achieved in Phytophthora parasitica var. nicotianae, an oomycete pathogen of tobacco. Using oomycete promoter and terminator sequences, a plant-adapted green fluorescent protein (GFP) was introduced into the microorganism. The data show for the first time that this eukaryotic gene reporter can be used in an oomycete, both as a quantitative reporter of gene induction and as a vital marker allowing the study of development of Phytophthora in vitro and in the host plant.     

Ultrasound imaging in an experimental model of fatty liver disease and cirrhosis in rats

Background

Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Retrospective studies have identified cases predating the initial identification of this form of scrapie, and epidemiological studies have indicated that it does not conform to the behaviour of an infectious disease, giving rise to the hypothesis that it represents spontaneous disease. However, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation in transgenic mice and sheep. The first successful challenge of a sheep with 'field' atypical scrapie from an homologous donor sheep was reported in 2007.

Results

This study demonstrates that atypical scrapie has distinct clinical, pathological and biochemical characteristics which are maintained on transmission and sub-passage, and which are distinct from other strains of transmissible spongiform encephalopathies in the same host genotype.

Conclusions

Atypical scrapie is consistently transmissible within AHQ homozygous sheep, and the disease phenotype is preserved on sub-passage.     

Mapping of citrullinated fibrinogen B-cell epitopes in rheumatoid arthritis by imaging surface plasmon resonance

Introduction  

Rheumatoid arthritis (RA) frequently involves the loss of tolerance to citrullinated antigens, which may play a role in pathogenicity. Citrullinated fibrinogen is commonly found in inflamed synovial tissue and is a frequent target of autoantibodies in RA patients. To obtain insight into the B-cell response to citrullinated fibrinogen in RA, its autoepitopes were systematically mapped using a new methodology.     

Quantification of global transcription patterns in prokaryotes using spotted microarrays

We describe an analysis, applicable to any spotted microarray dataset produced using genomic DNA as a reference, that quantifies prokaryotic levels of mRNA on a genome-wide scale. Applying this to Mycobacterium tuberculosis, we validate the technique, show a correlation between level of expression and biological importance, define the complement of invariant genes and analyze absolute levels of expression by functional class to develop ways of understanding an organism's biology without comparison to another growth condition.