1,721,080 research outputs found
Bacterial endophytes of rice : their diversity, characteristics and perspectives
Get PDFWith their capacity to synthesize a vast range of photoassimilates, plants attract a diverse number of heterotrophic organisms, including bacteria. Specialized bacteria capable to colonize the internal plant tissues are denoted endophytes. Their ecological role is largely unknown. In my studies, I aimed to characterize the bacterial communities that inhabit rice roots and to identify deterministic factors influencing the ecology of bacterial endophytes. We demonstrated that host genotype has major influence on the composition of the bacterial community, whereas relatively few endophytes were found across cultivars. This suggested that both bacterial adaptation and plant genotype contribute to the shaping of the dynamic bacterial communities. Inside rice roots, Gammaproteobacteria was the most dominant class, with Enterobacter being the most commonly isolated genus. Selected Enterobacter strains revealed several plant growth-promoting capacities as well as plant adaptation traits, of which none were common to all of them, suggesting that more than just one single factor might contribute to host adaptation. Under controlled conditions, rice seeds were an important source of bacterial endophytes, which allow the colonization of the internal plant tissues, the rhizosphere and the surrounding soil. This suggested that under natural conditions seed-borne endophytes might also be released by the plant. Metagenome analysis of the bacterial endophytic microbiome revealed the overrepresentation of several genes involved in niche adaptation and host-microbe interactions, while only a limited number of genes potentially involved in beneficial traits were detected. In summary, our studies suggest that the plant endosphere is an exclusive microhabitat requiring numerous bacterial adaptations.
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Normal operating range of the microbial community under potato
Get PDFOm de invloed van verschillende aardappelrassen op de bodem te meten bepaalde promovenda Özgül Inceoglu de variatie in parameters van de totale microbiële populatie in de bodem onder invloed van een aantal verschillende aardappelrassen. Ook woog zij de mogelijke effecten af van het zogeheten GM-ras tegen die van geselecteerde rassen.
Populaties van micro-organismen worden onder andere beïnvloed door plantenwortels. Dit gebeurt via de organische stoffen die in het door de wortels uitgescheiden exudaat zitten. Op deze manier trekken planten micro-organismen aan, die de door de plant uitgescheiden stoffen consumeren. Omdat verschillende plantensoorten en verschillende groeistadia van de plant leiden tot andere samenstellingen van wortelexudaten, is het logisch dat dit verschil ook tot uiting komt in de samenstelling van de microbiële populaties. Het is echter nog niet bekend in hoeverre zulke veranderingen voorkomen, hoe de dynamiek hiervan is en hoe deze veranderingen het functioneren van het systeem beïnvloeden. Als de invloed op de bodem van genetisch gemodificeerde planten bepaald moet worden, is het dus belangrijk om eerst de samenstelling van de microbiële populatie te bepalen, zowel als de individuele microbiële populaties en fluctuaties hierin. Hiervoor is het belangrijk, dat er eenvoudige methoden voorhanden zijn voor het monitoren van microbiële populaties en veranderingen in de tijd. Deze data vormen dan de basis voor de populatie onder landbouwgewassen in een bepaalde bodem, waaraan vervolgens de data van genetisch gemodificeerde planten gerelateerd kunnen worden, in dit geval voor de aardappel.
Soil-borne microbial communities are influenced by plant roots due to, among other factors, the excretion of organic compounds in the exudates. Plants thus selectively attract
microorganisms in their rhizospheres which then consume particular excreted compounds. It clearly follows that microbial communities in the rhizosphere may be differentially influenced by plant genotype as well as developmental stage if these incur different patterns of root
exudation. However, there is a paucity of knowledge on the extent to which such community shifts may occur, on the dynamics of the changes and on the putative effects regarding the functioning of the system. Hence, in order to weigh effects of transgenic plants, it is important to first assess the overall community composition as well as individual microbial populations as these are affected by plants, and study fluctuations therein. Moreover, easy monitoring methods are needed to track the community and diversity changes over time. Such assessments will define the baseline of cropping in a particular soil, against which the effect of genetically modified cultivars can be weighed, in this study tuned to potato as a crop.
So far, such a baseline of soil functioning has not been well-defined, and this is mainly due to the fact that soil ecosystems are dynamic and can be instantly changed due to seasonal influences as well as to different agricultural management practices. Thus, as this represents the normal operating conditions of the system, the seasonal variability of the soil communities under cropping regimes should be used to establish a baseline. The borders of these microbial
aspects will be provided by the extremes of fluctuations and thus determine the normal operating conditions. This will culminate in the provision of a technically-based protocol for
risk assessment of GM crops in terms of effects on soil.
Since less than 1% of soil microorganisms can be cultivated from their natural environments, new and more sensitive approaches are required that provide better measures
of community structure and function. However, biases of other nature are possibly introduced right at the forefront of most of our current soil DNA-based molecular analyses, that is, at the soil DNA extraction stage. Therefore in Chapter 2 of this thesis, four different DNA extraction methods, including two non-commercial ones, the Smalla et al and CIAT methods, and two commercial ones (MoBio Ultraclean and Powersoil), were compared for their efficiencies in
producing DNA from three agricultural soils of contrasting texture and organic matter content.
The analyses performed included assessments of DNA quality and quantity as well as PCRDGGE based analyses of bacterial, archaeal, ß-proteobacterial, ß-proteobacterial ammonium oxidizer, and pseudomonad and actinobacterial communities. Across the target bacterial groups, clear effects of DNA extraction method on the apparent richness and community structures based on DGGE patterns were discernible. Thus, different DNA extraction methods
applied to the same soil sample yield different views of the communities present in that sample. Powersoil was used for the rest of project, because of its efficiency, yield and purity.
In Chapter 3, the effects of plant cultivar, growth stage and soil type on the communities associated with the potato cultivars Aveka, Aventra, Karnico, Modena, Premiere
and Désirée were assessed in two different sandy fields, containing either high or low amounts of organic compounds in the different growth stages (young plant, flowering, senescence).
Bacterie remt phytophthora
No full textBacteriën kunnen aardappelplanten weerbaarder maken tegen phytophthora. Uit kas-experimenten van Plant Research International (PRI) blijkt dat de aanwezigheid van de bacteriePseudomonas putida(isolaat P9) in twee late aardappelrassen leidt tot een vertraging met 45 procent van het ziekteverloop na aantasting doorPhytophthora infestans. Volgens PRI-onderzoeker Leo van Overbeek biedt dit mogelijkheden om deze bacterie in te zetten als extra component inde geïntegreerde bestrijding van de aardappelziekte. Onderzoekers van PRI onderzochten het effect van P9 op de aardappelplant zelf en op de al aanwezige natuurlijke micro-organismen in de plant. P9 blijkt de plant binnen te dringen en vestigt zich daar permanent. De bacterie leeft in de plant en gaat interacties aan met zijn gastheer en de andere aanwezige micro-organismen. De bacteriesamenstelling in de plant veranderde zodra P9 zich daar vestigde. Dit kan betekenen dat P9 de plant weerbaarder kan maken, en dus beter bestand tegen ziekten en plagen. In het kasexperiment werden twee late aardappelrassen inderdaad weerbaarder tegen de aardappelziekte.De onderzoeksresultaten werpen ook een nieuw licht op biologische bestrijding van ziekten en plagen met micro-organismen. De meeste gangbare biologische bestrijders richten zich op de schimmel. De bacteriën pakken indirect ziekteverwekkers aan door verschuiving van de microbiologische leefgemeenschap in de plant. Dit vergroot de weerbaarheid van de plant zelf. Dit kan een duurzamer mechanisme voor onderdrukking van ziekten en plagen opleveren, omdat eenmalige toepassing volstaa
- …
