Structural characteristics and plant-beneficial effects of bacteria colonizing the shoots of field grown conventional and genetically modified T4-lysozyme producing potatoes

Genetically modified potatoes expressing antibacterial protein T4 lysozyme may offer effective control strategies for bacterial pathogens causing severe potato diseases. Apart from this beneficial effect, it is very important to investigate such engineered potatoes carefully for potential adverse effects on potato-associated bacteria which frequently exhibit plant beneficial functions such as plant growth promotion and antagonism towards pathogens invading the plant. Two field experiments were carried out in Spain to analyze the potential effects of conventional and genetically modified T4-lysozyme producing potatoes on shoot-associated bacteria. The first baseline field trial 2002 was performed in Meliana in which three conventional potato lines, Achirana Inta, Desirée, and Merkur, were cultivated and sampled at flowering. The second field trial was conducted in Cella in 2003 in order to compare the effects of a senescent transgenic, T4 lysozyme expressing potato trait, Desirée DL 12, with its isogenic, non-transformed parental line Desirée. Structural characteristics of potato shoot-associated bacteria was assayed by 16S rRNA-based terminal restriction fragment length polymorphism (T-RFLP) analysis and dominant community members within T-RFLP profiles were identified by sequence analysis of generated 16S rRNA gene libraries. Cultivable bacteria isolated from shoots of potatoes grown in the Meliana field trial were monitored for antibiosis against Ralstonia solanacearum, whereas isolates derived from shoots of potatoes cultivated in the Cella trial were screened for antagonism against Ralstonia solanacearum and Rhizoctonia solani, and for 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase production. Determined antagonists were identified by 16S rRNA gene analysis. All potato traits hosted a cultivar-specific community of bacteria with antagonism against the pathogens and/or potential to produce ACC deaminase. Several antagonists obtained from the Cella field potatoes were also observed as ACC deaminase producers. Community profiling revealed a greater diversity differentiation between the senescent T4 lysozyme expressing and parental Desirée lines grown in the Cella field as compared to the variations between the three flowering conventional lines cultivated in the Meliana field trial. Effects of the two varying field sites and different vegetation stages were greater than those of T4 lysozyme when investigating the community composition of bacteria colonizing the shoots of the Desirée line cultivated in both field trials.     

Losing the last feather: feather loss as an antipredator adaptation in birds

Birds often lose feathers during predation attempts, and thisability has evolved as a means of escape. Because predatorsare more likely to grab feathers on the rump and the back thanon the ventral side of an escaping bird, we predicted that theformer feathers would have evolved to be relatively looselyattached as an antipredator strategy in species that frequentlydie from predation. We estimated the force required to removefeathers from the rump, back, and breast by pulling featherswith a spring balance from a range of European bird speciesin an attempt to investigate ecological factors associated withease of feather loss during predation attempts. The force requiredto loosen a feather from the rump was less than that requiredto loosen a feather from back, which in turn was less than thatrequired to loosen a feather from the breast. The relative forceneeded to loosen rump feathers compared with feathers from theback and the breast was smaller for prey species preferred bythe most common predator of small passerine birds, the sparrowhawkAccipiter nisus. Likewise, the relative force was also smallerin species with a high frequency of complete tail loss amongfree-living birds, which we used as an index of the frequencyof failed predation attempts. The relative force required toremove feathers from the rump was smaller in species with ahigh frequency of fear screams, another measure of the relativeimportance of predation as a cause of death. Feather loss requiredparticularly little force among solitarily breeding bird speciesthat suffer the highest degree of predation. Antipredator defensein terms of force required to remove feathers from the rumpwas larger in species with a strong antiparasite defense interms of T-cell–mediated immune response. These findingsare consistent with the hypothesis that different defenses areantagonistic and that they are traded off against each other.     

A Mechanism of Energy Dissipation in Cyanobacteria

When grown under a variety of stress conditions, cyanobacteria express the isiA gene, which encodes the IsiA pigment-protein complex. Overexpression of the isiA gene under iron-depletion stress conditions leads to the formation of large IsiA aggregates, which display remarkably short fluorescence lifetimes and thus a strong capacity to dissipate energy. In this work we investigate the underlying molecular mechanism responsible for chlorophyll fluorescence quenching. Femtosecond transient absorption spectroscopy allowed us to follow the process of energy dissipation in real time. The light energy harvested by chlorophyll pigments migrated within the system and eventually reaches a quenching site where the energy is transferred to a carotenoid-excited state, which dissipates it by decaying to the ground state. We compare these findings with those obtained for the main light-harvesting complex in green plants (light-harvesting complex II) and artificial light-harvesting antennas, and conclude that all of these systems show the same mechanism of energy dissipation, i.e., one or more carotenoids act as energy dissipators by accepting energy via low-lying singlet-excited S₁ states and dissipating it as heat.     

BiGG: a Biochemical Genetic and Genomic knowledgebase of large scale metabolic reconstructions

Background  

Genome-scale metabolic reconstructions under the Constraint Based Reconstruction and Analysis (COBRA) framework are valuable tools for analyzing the metabolic capabilities of organisms and interpreting experimental data. As the number of such reconstructions and analysis methods increases, there is a greater need for data uniformity and ease of distribution and use.     

Immunogold localisation of endogenous immunoglobulin-G in ultrathin frozen sections of the human placenta

Summary Endogenous immunoglobulin-G was localised in ultrathin frozen sections of human term placenta by use of an indirect immuno electron-histochemical methodology. Immunoreactivity of endogenous IgG to rabbit anti-human immunoglobulin-G antibody was visualised by use of protein-A — colloidal gold complex. Gold marked the syncytiotrophoblast in both coated and uncoated regions of the apical plasmalemma, in vesicles and multivesicular bodies, and in vesicles near the basal plasmalemma. Immunoreactivity was also seen in the interstitial space between the trophoblast and the fetal endothelial layer as well as in various types of vesicles within the endothelial cells. No immunoreactivity was seen in the intercellular clefts of the endothelium. The pattern of localisation observed is consistent with receptor-mediated uptake of immunoglobulin-G into the syncytiotrophoblast of the human placenta followed by release into the interstitial space and then vesciular transport through the endothelium.     

Demographic incidence rates

Demographers commonly interpret incidence rates (for first marriages, say, or for births of a given order), cumulated over age for a closed cohort, as prevalences of corresponding demographic statuses. Since one is hard put to find an explicit justification for this interpretation in the literature, this note offers a mathematical proof that it is correct if and only if there is nondifferential mortality, as well as an extension to incidences for events which can happen more than once to an individual. Mortality incidence rates are discussed as well, and some of the evidence that cumulative incidence rates may get absurd values when computed from period data is reviewed.     

Lateral diffusion of gramicidin S,M-13 coat protein and glycophorin in bilayers of saturated phospholipids: Mean field and Monte Carlo studies

We have developed a general model that relates the lateral diffusion coefficient of one isolated large intrinsic molecule (mol. wt. ?1000) in a phosphatidylcholine bilayer to the static lipid hydrocarbon chain order. We have studied how protein lateral diffusion can depend upon protein-lipid interactions but have not investigated possible non-specific contributions from gel-state lattice defects. The model has been used in Monte Carlo simulations or in mean-field approximations to study the lateral diffusion coefficients of Gramicidin S, the M-13 coat protein and glycophorin in dimyristoyl- and dipalmitoylphosphatidylcholine (DMPC and DPPC) bilayers as functions of temperature. Our calculated lateral diffusion coefficients for Gramicidin S and the M-13 coat protein are in good agreement with what has been observed and suggest that Gramicidin S is in a dimeric form in DMPC bilayers. In the case of glycophorin we find that the ‘ice breaker’ effect can be understood as a consequence of perturbation of the lipid polar region around the protein. In order to understand this effect is is necessary that the protein hydrophilic section perturb the polar regions of at least approx. 24 lipid molecules, in good agreement with the numbers of 29–30 measured using ³¹P-NMR. Because of lipid-lipid interactions this effect extends itself out to four or five lipid layers away from the protein so that the hydrocarbon chains of between approx. 74 and approx. 108 lipid molecules are more disordered in the gel phase, so contributing less to the transition enthalpy, in agreement with the numbers of 80–100 deduced from differential scanning calorimetry (DSC). An understanding of the abrupt change in the diffusion coefficient at a temperature below the main bilayer transition temperature requires an additional mechanism. We propose that this change may be a consequence of a ‘coupling-uncoupling’ transition involving the protein hydrophilic section and the lipid polar regions, which may be triggered by the lipid bilayer pretransition. Our calculation of the average number of gauche bonds per lipid chain as a function of temperature and distance away from an isolated polypeptide or integral protein shows the extent of statically disordered lipid around such molecules. The range of this disorder depends upon temperature, particularly near the main transition.