1,720,964 research outputs found
Silencing approach using poly(ADP-ribose) polymerase gene to improve drought stress tolerance in maize
No full textCurrent and predicted climatic conditions, such as prolonged drought and heat episodes affect plant growth and yield, cause annual losses estimated at billions of dollars and pose a serious challenge for agricultural production worldwide, (Boyer 1982, Mittler 2006). Progress in generating transgenic crops with enhanced tolerance to abiotic stress has nevertheless been slow. The complex field environment with its heterogenic conditions, abiotic stress combinations, and global climatic changes are but a few of the challenges of modern agriculture. A combination of approaches has contributed significantly towards improving abiotic stress tolerance in both the greenhouse and the field (Hirayama and Shinozaki 2010). However, the increasing unpredictability and vagaries of rainfall and temperature variations consequent to global climate change, the dwindling availability of irrigation water and phosphate fertilizer, the escalating population in developing countries indicate that new ways of improving maize yield stability and stress tolerance under suboptimal conditions must be found and employed. A novel strategy to improve abiotic stress tolerance in Arabidopsis and Brassica has been reported by De Block et al., (2005). In their study, poly(ADP-ribosyl) ation activity was downregulated and transgenic plants became tolerant to a broad range of abiotic stresses such as drought, high light and heat. The researchers noted that stress tolerance was obtained by maintaining energy homeostasis due to reduced stress-induced energy consumption by prevention of NADP breakdown. Under abiotic stress conditions, plants overexpressing hairpin RNAi against Arabidopsis APP gene preserve their energy homeostasis without an overactivation of the mitochondrial respiration and avoiding the production of reactive oxygen species. Hence, plants with a lowered PARP activity appear tolerant to multiple stresses. Furthermore, a genome-wide transcript analysis of stressed anti PARP2 transgenic Arabidopsis (hpAt-PARP2) plants revealed that the induction of specific ABA signalling pathways steered increased levels of the cyclic nucleotide ADP-ribose (cADPR) thereby contributing towards tolerance to abiotic stresses (Vanderauwera et al., 2007). Indeed, modulation of poly(ADPribosyl) ation (PAR) reaction by an Arabidopsis thaliana ADP-ribose/NADH pyrophosphohydrolase, AtNUDX7 led to plants becoming tolerant to oxidative stress (Ogawa et al., 2009). Under oxidative stress, AtNUDX7 serves to maintain NAD+ levels by supplying ATP via nucleotide recycling from free ADP-ribose molecules and thus regulates the defence mechanisms against oxidative DNA damage via modulation of the PAR reaction. Furthermore, energy use efficiency is characterized by an epigenetic component that can be directed through selection to increase yield on top of heterosis (Hauben et al., 2009). Arabidopsis findings have previously been found to be directly applicable to commercial crop improvement (Nelson et al., 2005). Therefore, engineering crop plants for high NAD+ regeneration by an efficient 8 upregulation of the NAD+ salvage pathway or by a reduced NAD+ consumption under stress conditions, is a valuable approach to enhance overall stress tolerance in crops. The aim of this study was to assess a similar approach in the model species Zea mays through silencing maize PARP1 gene, a homolog of the Arabidopsis APP gene. This was achieved by establishing tropical maize regeneration system from immature embryo through somatic embryogenesis as a prerequisite for effective genetic transformation mediated by Agrobacterium. Our next goal was to engineer two hairpin constructs targeting maize PARP1 gene within the specific region at the 5’-end of the gene because silencing of the Arabidopsis APP gene using hairpin RNA constructs proved to be a valuable approach to obtain drought tolerance in Arabidopsis and canola (De Block et al., 2005). However, hairpin constructs are not so stable in extreme temperatures in the greenhouse which results in problems with stability in subsequent progenies (Szittya et al., 2003). Therefore, we aimed at evaluating the utility of artificial micro- RNAs (amiRNA) to silence the maize PARP1 gene. This technology is expected to be more effective and stable than the hairpin RNA approach because temperature does not affect the accumulation of microRNA (Szittya et al., 2003). Three amiRNAs were designed targeting maize PARP1 gene. As a complementary approach to the amiRNA and RNAi transgene technology we sought for mutants in the maize PARP1 gene in the Uniform Mu collections mutagenized by the transposon Mutator. Transgene technology and efficient transformation are important to fully exploit a species as a model for functional genomics studies. We developed an efficient and standardized maize transformation method based on the following criteria: (1) Agrobacterium tumefaciens co-cultivation was preferred over particle bombardment because usually intact T-DNA’s are transferred at low copy number, (2) a maize inbred line was favoured over a hybrid line because homogeneous progenies allow transgene testing already in T1 or T2, (3) Gateway vectors were optimized for use in monocots and provide a toolbox for rapid gene cloning. And finally, the transgenic maize plants overexpressing amiRNA constructs against maize PARP1 gene were evaluated for drought and Methyl Viologen-induced oxidative stress tolerance
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Agricultural genomics and sustainable development: perspectives and prospects for Africa
Get PDFThe genomes of various organisms have now been fully sequenced, including human and representative microbial, insect, animal and plant genomes. The research challenge in the post-genome era is to establish how genes and proteins function to bring about changes in phenotype. Some of these phenotypes, and products obtainable through modern biotechnology, are of crucial importance within the context of sustainable development of African economies. The greatest ultimate impact will be in agricultural genomics, especially for marker assisted selection and breeding programs in crop and animal agriculture, development of animal disease diagnostics and vaccines, crop genetic engineering to overcome abiotic and biotic stresses and for improvement of the nutritional quality of major food staples. It is imperative that African countries become key players in the “gene revolution” since the cost of leaving them behind may be higher than the cost of empowering them to become players in mastering and benefiting from biotechnology. This paper highlights the potential impact of the latest advances in modern biotechnology, including genomics and bioinformatics, on sustainable development, in line with the goals of the New Partnership for Africa's Development (NEPAD). These include acceleration of economic growth, eradication of widespread and severe poverty and efforts to halt the marginalization of Africa in the globalization process.
Key Words: Genomics, modern biotechnology, agriculture, sustainable development, Africa.
African Journal of Biotechnology Vol.3(2) 2004: 127-13
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