Response of mycorrhizal grapevine to Armillaria mellea inoculation: disease development and polyamines

A study was conducted with the vine rootstock Richter 110 (Vitis berlandieri Planch. x Vitis rupestris L.) in order to assess whether the colonisation by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices (BEG 72) can delay the disease development in plants inoculated with the root-rot fungus Armillaria mellea (Vahl:Fr) Kummer, and to elucidate if the levels of polyamines (PAs) are modified in response to G. intraradices, A. mellea or by the dual infection. Four treatments were considered: control and G. intraradices-inoculated plants infected or not with A. mellea. Plant growth, mycorrhizal colonisation and disease development were monitored throughout the experiment. High performance liquid chromatography (HPLC) in combination with fluorescence spectrophotometry was used to separate and quantify free root and leaf polyamines. The slower development of pathogenic symptoms and the higher plant biomass of mycorrhizal plants inoculated with A. mellea indicate an increase of tolerance due to the AMF inoculation. The variations in free PA levels detected at the beginning of the pathogenic infection suggest that PAs may have a potential role in the signalling mechanisms of the tolerance of mycorrhizal plants against A. mellea.     

On the conformation of reconstituted ferredoxin:NADP oxidoreductase in the thylakoid membrane. Studies via triplet lifetime and rotational diffusion with eosin isothiocyanate as label

Eosin isothiocyanate was covalently bound to isolated ferredoxin-NADP⁺ reductase under protection of the NADP-binding domain. The bound label did not impair the functional reconstitution of the enzyme into depleted thylakoid membranes. Laser spectrophotometric experiments were carried out on thylakoids which were reconstituted with labeled ferredoxin-NADP⁺ reductase. Bound eosin isothiocyanate was used as a spectroscopic probe for conformational changes of ferredoxin-NADP⁺ reductase in either of two ways: We studied the rotational diffusion of labeled ferredoxin-NADP⁺ reductase in the membrane by the photoselection technique, and we studied the triplet lifetime of bound eosin, which measures polypeptide chain flexibility (via access of oxygen) around the binding site. The latter technique was complemented by measurements of the librational motion of bound dye. We observed: (1) When ferredoxin is absent, ferredoxin-NADP⁺ reductase undergoes very rapid rotational diffusion in the thylakoid membrane (correlation time less than 1 μs at 10°C). This is drastically slowed down (40 μs) upon addition of water-soluble ferredoxin. We propose that ferredoxin mediates the formation of a ternary complex with ferredoxin-NADP⁺ reductase and the Photosystem I complex. According to our data, this complex would live longer than required for the photoreduction of ferredoxin-NADP⁺ reductase by Photosystem I via ferredoxin. (2) Under the given incubation conditions, the binding sites for eosin isothiocyanate were located in the FAD domain of ferredoxin-NADP⁺ reductase. We found increased chain flexibility in this domain upon addition of NADP. This suggests induced fit for the binding of NADP and allosteric control of the FAD domain by the remote NADP domain. (3) Acidification of the internal phase of thylakoids decreased the chain flexibility in the FAD domain. This is of particular interest, since ferredoxin-NADP⁺ reductase is a peripheral external membrane protein. It suggests the existence of a binding protein for the oxidoreductase which spans the membrane and senses the internal pH     

Does phylogeny matter? Assessing the impact of phylogenetic information in ecological meta‐analysis

Meta-analysis is increasingly used in ecology and evolutionary biology. Yet, in these fields this technique has an important limitation: phylogenetic non-independence exists among taxa, violating the statistical assumptions underlying traditional meta-analytic models. Recently, meta-analytical techniques incorporating phylogenetic information have been developed to address this issue. However, no syntheses have evaluated how often including phylogenetic information changes meta-analytic results. To address this gap, we built phylogenies for and re-analysed 30 published meta-analyses, comparing results for traditional vs. phylogenetic approaches and assessing which characteristics of phylogenies best explained changes in meta-analytic results and relative model fit. Accounting for phylogeny significantly changed estimates of the overall pooled effect size in 47% of datasets for fixed-effects analyses and 7% of datasets for random-effects analyses. Accounting for phylogeny also changed whether those effect sizes were significantly different from zero in 23 and 40% of our datasets (for fixed- and random-effects models, respectively). Across datasets, decreases in pooled effect size magnitudes after incorporating phylogenetic information were associated with larger phylogenies and those with stronger phylogenetic signal. We conclude that incorporating phylogenetic information in ecological meta-analyses is important, and we provide practical recommendations for doing so.     

The single superoxide dismutase of Rhodobacter capsulatus is a cambialistic,manganese-containing enzyme

The phototrophic bacterium Rhodobacter capsulatus contains a single, oxygen-responsive superoxide dismutase (SOD(Rc)) homologous to iron-containing superoxide dismutase enzymes. Recombinant SOD(Rc), however, displayed higher activity after refolding with Mn(2+), especially when the pH of the assay mixture was raised. SOD(Rc) isolated from Rhodobacter cells also preferentially contains manganese, but metal discrimination depends on the culture conditions, with iron fractions increasing from 7% in aerobic cultures up to 40% in photosynthetic cultures. Therefore, SOD(Rc) behaves as a Mn-containing dismutase with cambialistic properties.     

Oxidative stress in primary culture hepatocytes isolated from partially hepatectomized rats

The aim of this study was to evaluate the influence of partial hepatectomy prior to cell isolation on hepatocytes in vitro. We characterized the possible changes of various stress oxidative parameters within the first 24 h after seeding. Male Wistar rats served as donors. Hepatocytes were isolated by collagenase digestion from either liver of simulated surgery (SH) or from liver 1 h after 70% hepatectomy (PH), and the changes in stress parameters were analyzed after 1, 3, 18, and 24 h in culture. At 24 h, only hepatocytes from PH maintained significantly increased reactive oxygen species production, oxidized glutathione percentage, and Cu/Zn superoxide dismutase and catalase activities. Our results show that hepatocytes suffer significant cell injury as a result of the isolation procedure, but primary cultured cells from SH metabolically recover from this stress after 18 h. After this time, primary culture hepatocytes primed by PH maintain their in vivo-like metabolic activities (increase in both oxidative stress and antioxidant status).