309,246 research outputs found
Antisense RNA mediated inhibition of granule - bound starch synthase gene expression in potato
No full textPotato starch and its derivatives are widely used in several fields of application. The manufacturing of most products requires the modification of native starch with respect to, for example, viscosity and physical stability. In addition to the currently used physical, chemical and biochemical derivatization and gelatinization of extracted starch, modification of the starch biosynthetic pathway in planta is regarded as a valuable approach for altering the quality and quantity of potato starch.This thesis describes the application of antisense RNA technology for the modification of the composition of potato tuber starch. Starch consists of amylose and arnylopectin, and is predominantly synthesized in amyloplasts of tubers and seeds, where it is deposited in starch granules. Several enzymes are involved in the biosynthesis of starch, of which granule-bound starch synthase (GBSS) catalyses the formation of amylose. Generally, starch contains 20% of amylose and 80% of arnylopectin. However, mutants are known in which the ratio between amylose and arnylopectin has changed. An example is the amylose-free ( amf ) potato mutant, of which the starch exclusively contains arnylopectin due to a recessive mutation in the GBSS-gene. The suppression of the expression of specific genes can also be achieved by means of antisense inhibition, which is supposed to be based on the formation of an RNA-duplex between the target mRNA and the antisense RNA, thus blocking the transport of the mRNA from the nucleus.To inhibit the (GBSS) gene expression, several antisense genes were introduced into the potato genome via Agrobacterium -mediated transformation. Among transgenic clones in which inhibition of (GBSS) gene expression was observed. two types could be discerned:A. Transgenic clones with completely inhibited (GBSS) gene expression. These clones lacked the (GBSS) protein, (GBSS) activity and amylose. The complete inhibition was demonstrated in microtubers, greenhouse grown tubers and field grown tubers, and was maintained in several tuber generations. The composition of tuber starch from these clones and from the amf -mutant was similar.B. Transgenic clones with incompletely inhibited (GBSS) gene expression. In these clones the (GBSS) protein content, (GBSS) activity and amylose content were reduced as compared to non-transformed clones. With respect to the extent of inhibition, variation was observed between transgenic clones which was supposed to result from position effects. Variation was also observed between tubers of individual plants and within individual tubers. This type of variation was suggested to be caused by factors related to tuber development.Microscopic analysis of iodine stained tuber starch granules from transgenic clones showed that the reduced amount of amylose was not equally distributed throughout the entire granule, but was confined to the central core of the granule. Iodine-staining of starch granules yielded a blue core, in which the amylose content equalled that of wildtype starch, and a red, amylose-free, outer part. The size of the blue core was shown to be positively related to the amylose content, as determined in starch isolated from the transgenic clones. This finding led to the hypothesis that at a certain point in starch granule development the available amount of (GBSS) protein will become insufficient for the formation of starch with a normal amylose content. From this point onwards, amylose-free starch will be produced throughout further starch granule development.With respect to the effectiveness of antisense inhibition, the influence of the composition of the antisense gene on the percentage of transgenic clones with complete or incomplete inhibition was studied. To this end, eleven antisense genes were constructed, based on the full length (GBSS) cDNA, the genomic (GBSS) coding region, and some cDNA- and genomic fragments. Furthermore, a comparison was made between the 35S CaMV promoter and the potato (GBSS) promoter. The extent of inhibition of GBSS gene expression was studied in at least 30 transgenic clones per antisense gene construct. In addition to construct-related differences, the number of T- DNA insertions was found to be positively related to the extent of antisense inhibition. It was concluded that the chance for complete inhibition of (GBSS) gene expression was highest in transgenic clones with three or more copies of the antisense gene based on the full length (GBSS) cDNA driven by the (GBSS) promoter.In order to evaluate the applicability of the antisense (GBSS) system, two antisense genes based on the full length (GBSS) cDNA and driven by the (GBSS) or the 35S CaMV promoter were introduced into several potato cultivars via transformation with A . tumefaciens. The trangenic clones of one of the cultivars were analysed for the extent of antisense inhibition and its stability in a field trial based on in vitro plantlets. Complete inhibiton of (GBSS) gene expression, resulting in the formation of amylose-free starch, was demonstrated in mature tubers of four of these clones. Other characteristics, such as the total starch- and sugar content, the total yield and the dry matter content, did not deviate significantly as compared to the non-transformed cultivar. This led to the conclusion that antisense inhibition has good perspectives for the formation of amylose-free starch in potato tubers. In 1993, three of the transgenic clones with amylose-free tuber starch that are described in this thesis, were submitted to the Board for Plant Breeder's Rights for registration
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Topological Protection in Radiative Photonic Crystal Cavities
No full textWe study the signatures of topological light confinement in the leakage radiation of two-dimensional topological photonic crystal cavities that feature the quantum spin Hall effect at telecom wavelengths. The mode profiles in real and momentum space are retrieved using far field imaging and Fourier spectropolarimetry. We examine the scaling behavior of mode spectra, observe band-inversion-induced confinement, and demonstrate hallmarks of topological protection in the loss rates, which are largely unaffected by cavity shape and size. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.QN/Kuipers LabQN/Quantum Nanoscienc
A validation of a new measure of activity in psychosis
No full textDespite demonstrated relationships between activity and clinical change, we lack effective measures of time use in psychosis. Existing time budget measures of activity are demanding to complete, and thus unsuited to routine clinical use as measures of change. Less burdensome 'check-box' measures are prone to bias and omission in the activities selected. We recently devised a simplified time budget measure of activity in psychosis which was piloted on a small sample [Jolly, S., Garely, P., Dunn, G., White, J., Aitken, M., Challocombe, F., Griggs, M., Wallace, M., Craig, T. 2005. A pilot validation study of a new measure of activity in psychosis. Soc. Psychiatry Psychiatr. Epidemiol. 40, 905-911]. This study is a larger scale validation. 276 participants with a recent relapse of non-affective psychosis completed the new time budget, together with an established measure of global social functioning, measures of positive and negative psychotic symptoms, positive symptom distress and affect. The time budget measure showed a correlation of 0.5 with both the SOFAS and the SANS avolition/apathy subscale. Activity levels were related to psychotic symptomatology, both positive and negative. Positive symptom distress was more strongly associated with activity levels than symptom severity and affective disturbance. We conclude that the time budget measure can be used as an indicator of social functioning, with potential as a measure of therapeutic change. We are currently investigating its sensitivity in this context. (c) 2006 Elsevier B.V. All rights reserved
Author, publisher and bookseller : a tripartite synergy in Nigerian book industry
Full text linkThis work is about the roles of Author, Publisher and Bookseller in Book development in
Nigeria. The paper started by delving into the history of Book Publishing in Nigeria after
which it proceeded by defining who an author, a publisher, and a bookseller is and
expatiated on the indispensable roles of these key actors in Nigerian Book Industry and in
the emerging Information Society. Furthermore, the various constraints to book
development were identified while the paper advised on how the Book Industry can be
further promoted in Nigeria. However, the paper concluded and made recommendations
on how the Book sector can help in enhancing scholarship in the country
Emotion and psychosis: Links between depression, self-esteem, negative schematic beliefs and delusions and hallucinations
No full textBackground: The role of emotion in psychosis is being increasingly recognised. Cognitive conceptualisations of psychosis (e.g. [Garety, P.A., Kuipers, E.K., Fowler, D., Freeman, D., Bebbington, P.E., 2001. A cognitive model of the positive symptoms of psychosis. Psychological Medicine, 31, 189-195]) emphasise a central, normal, direct and non-defensive role for negative emotion in the development and maintenance of psychosis. This study tests specific predictions made by Garety et al. [Garety, P.A., Kuipers, E.K., Fowler, D., Freeman, D., Bebbington, P.E., 2001. A cognitive model of the positive symptoms of psychosis. Psychological Medicine, 31, 189-195] about the role of emotion and negative evaluative beliefs in psychosis.Methods: 100 participants who had suffered a recent relapse in psychosis were recruited at baseline for the Prevention of Relapse in Psychosis (PRP) trial. In a cross-sectional analysis, we examined the role of depression, self-esteem and negative evaluative beliefs in relation to specific positive symptoms (persecutory delusions, auditory hallucinations and grandiose delusions) and symptom dimensions (e.g. distress, negative content, pre-occupation and conviction).Results: Analysis indicated that individuals with more depression and lower self-esteem had auditory hallucinations of greater severity and more intensely negative content, and were more distressed by them. In addition, individuals with more depression, lower self-esteem and more negative evaluations about themselves and others had persecutory delusions of greater severity and were more pre-occupied and distressed by them. The severity of grandiose delusions was related inversely to depression scores and negative evaluations about self, and directly to higher self-esteem.Conclusions: This study provides evidence for the role of emotion in schizophrenia spectrum-disorders. Mood, self-esteem and negative evaluative beliefs should be considered when conceptualising psychosis and designing interventions. (c) 2006 Elsevier B.V. All rights reserved
- …
