1,721,004 research outputs found
Resistance of Fritillaria imperialis to freezing stress through gene expression, osmotic adjustment and antioxidants
Get PDFPlant survival in response to freezing stress depends on the efficient activation of tolerance mechanisms. Fritillaria imperialis exposure to freezing stress enhanced signalling molecules Ca2+ and H2O2 along with overexpression of Ca2+ signalling proteins (Ca2+ dependent protein kinases, CPK), followed by upregulation of NHX1 (Na+/H+ antiporter), LEA (late embryogenesis abundant proteins) and P5CS (1-pyrroline-5-carboxylate synthetase). Overexpression of OsCNGC6 was responsible for high accumulation Ca2+, Na+ and K+. The NHX1 gene product transported Na+ to vacuoles and increased cytosolic K+ content to re-establish ionic homeostasis under stress conditions. The reduced water potential of leaves was due to high accumulation of osmolytes and ions. No changes were observed in relative water content of leaves, which might be correlated with overexpression of the LEA gene, which protects against dehydration. High accumulation of H2O2 under freezing stress was responsible for activation of antioxidant systems involving SOD, phenols, anthocyanins, catalase and ascorbate peroxidase. Photosynthesis, suppressed in freezing-stressed plants, returned to normal levels after termination of freezing stress. Taken together, our findings suggest that Fritillaria efficiently tolerated freezing stress through induction of signalling mechanisms and overexpression of cold stress-responsive genes, and prevention of cold-induced water stress, oxidative stress and photosynthetic damage
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
Exploiting the allelopathic potential of aqueous leaf extracts of artemisia absinthium and psidium guajava against parthenium hysterophorus, a widespread weed in India
Get PDFArtemisia absinthium and Psidium guajava are powerful sources of secondary metabolites, some of them with potential allelopathic activity. Both the species grow together in India with a weed (Parthenium hysterophorus) that is becoming extremely invasive. The aim of the present research was to test the allelopathic effect of A. absinthium and P. guajava aqueous leaf extracts on seed germination, seedling growth (shoot and root length), as well as some biochemical parameters (enzymatic and non-enzymatic antioxidants, photosynthetic pigments, osmolytes, and malondialdehyde by-products) of P. hysterophorus plants. Leaf extracts of both A. absinthium and P. guajava constrained the germination and seedling development (root and shoot length), affected pigment content (chlorophylls, carotenoids), stimulated the activity of antioxidant enzymes, and increased the level of malondialdehyde by-products of P. hysterophorus plants. Non-enzymatic antioxidants (glutathione and ascorbic acid) in P. hysterophorus leaves were, conversely, negatively affected by both leaf extracts tested in the present experiment. Although A. absinthium was more effective than P. guajava in impacting some biochemical parameters of P. hysterophorus leaves (including a higher EC50 for seed germination), P. guajava extract showed a higher EC50 in terms of root inhibition of P. hysterophorus seedlings. The present study provides the evidence that A. absinthium and P. guajava extract could be proficiently exploited as a botanical herbicide against P. hysterophorus
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
Plasticity of photosynthetic processes and the accumulation of secondary metabolites in plants in response to monochromatic light environments: A review
No full textLight spectra significantly influence plant metabolism, growth and development. Here, we review the effects of monochromatic blue, red and green light compared to those of multispectral light sources on the morpho-anatomical, photosynthetic and molecular traits of herbaceous plants. Emphasis is given to the effect of light spectra on the accumulation of secondary metabolites, which are important bioactive phytochemicals that determine the nutritional quality of vegetables. Overall, blue light may promote the accumulation of phenylpropanoid-based compounds without substantially affecting plant morpho-anatomical traits compared to the effects of white light. Red light, conversely, strongly alters plant morphology and physiology compared to that under white light without showing a consistent positive effect on secondary metabolism. Due to species-specific effects and the small shifts in the spectral band within the same color that can substantially affect plant growth and metabolism, it is conceivable that monochromatic light significantly affects not only plant photosynthetic performance but also the “quality” of plants by modulating the biosynthesis of photoprotective compounds
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
Chlorophyll-depleted wheat mutants are disturbed in photosynthetic electron flow regulation but can retain an acclimation ability to a fluctuating light regime
No full textThe search for more productive crops is exploring accessions with reduced chlorophyll accumulation in leaves, which would promote plant growth mainly because of a higher light transmittance throughout the canopy. Under continuous light, chlorophyll-depleted chlorina mutants of wheat can reach yields similar to WT; however, their performance under fluctuating light could possibly be lowered by a disturbed photosynthetic electron transport. Six chlorina mutants of Triticum aestivum (ANBW4A, ANBW4B, ANK32A) or T. durum (ANDW7A, ANDW7B, ANDW8A) were compared to WT genotypes under continuous and fluctuating light regimes, the latter obtained through a randomized pattern of light intensity changes. After two weeks of plant acclimation under either regimes, light energy management was thoroughly analysed for four weeks. All chlorina mutants showed a defective ability to regulate the electron poise during a fast rise in irradiance. Different extent of deregulation depended on mutation and genomic background, durum wheat being more severely impaired than bread wheat. However, a great acclimative capacity to a fluctuating light regime unexpectedly still characterized the chlorina wheat plants, with the only exception of the mutants carrying the cn-B1b mutated locus (ANDW7B and ANBW4B). Under fluctuating light, all other chlorina mutants developed indeed an ability to improve their control of electron transport against the recurrent reducing bursts caused by lightflecks. Compensatory responses included the regulation of energy distribution between photosystems, the use of alternative electron sinks, and a structural reorganization of the thylakoid system. However, in no case a reduced chlorophyll content led to more productive plants. Among 23 measured photosynthetic parameters, especially the non-regulatory energy dissipation in photosystem II - Y(NO) –, when probed during a light rise, can be proposed in automated phenotyping experiments as a straightforward index to be used for chlorina wheat screening with respect to potential productivity
Long-Term Alleviation of the Functional Phenotype in Chlorophyll-Deficient Wheat and Impact on Productivity: A Semi-Field Phenotyping Experiment
No full textWheat mutants with a reduced chlorophyll synthesis are affected by a defective control of the photosynthetic electron flow, but tend to recover a wild-type phenotype. The sensitivity of some mutants to light fluctuations suggested that cultivation outdoors could significantly impact productivity. Six mutant lines of Triticum durum or Triticum aestivum with their respective wild-type cultivars were cultivated with a regular seasonal cycle (October-May) in a semi-field experiment. Leaf chlorophyll content and fluorescence parameters were analysed at the early (November) and late (May) developmental stages, and checked for correlation with morphometric and grain-production parameters. The alleviation of the phenotype severity concerned primarily the recovery of the photosynthetic-membrane functionality, but not the leaf chlorophyll content. Photosystem II (PSII) was less photoprotected in the mutants, but a moderate PSII photoinhibition could help control the electron flow into the chain. The accumulation of interchain electron carriers was a primary acclimative response towards the naturally fluctuating environment, maximally exploited by the mature durum-wheat mutants. The mutation itself and/or the energy-consuming compensatory mechanisms markedly influenced the plant morphogenesis, leading especially to reduced tillering, which in turn resulted in lower grain production per plant. Consistently with the interrelation between early photosynthetic phenotype and grain-yield per plant, chlorophyll-fluorescence indexes related to the level of photoprotective thermal dissipation (pNPQ), photosystem II antenna size (ABS/RC), and pool of electron carriers (Sm) are proposed as good candidates for the in-field phenotyping of chlorophyll-deficient wheat
Pre-Acclimation to Elevated Temperature Stabilizes the Activity of Photosystem I in Wheat Plants Exposed to an Episode of Severe Heat Stress
Get PDFThe importance of high temperature as an environmental factor is growing in proportion to deepening global climate change. The study aims to evaluate the effects of long-term acclimation of plants to elevated temperature on the tolerance of their photosynthetic apparatus to heat stress. Three wheat (Triticum sp. L.) genotypes differing in leaf and photosynthetic traits were analyzed: Thesee, Roter Samtiger Kolbenweizen, and ANK 32A. The pot experiment was established in natural conditions outdoors (non-acclimated variant), from which a part of the plants was placed in foil tunnel with elevated temperature for 14 days (high temperature-acclimated variant). A severe heat stress screening experiment was induced by an exposition of the plans in a growth chamber with artificial light and air temperature up to 45◦C for ~12 h before the measurements. The measurements of leaf photosynthetic CO2 assimilation, stomatal conductance, and rapid kinetics of chlorophyll a fluorescence was performed. The results confirmed that a high temperature drastically reduced the photosynthetic assimilation rate caused by the non-stomatal (biochemical) limitation of photosynthetic processes. On the other hand, the chlorophyll fluorescence indicated only a moderate level of decrease of quantum efficiency of photosystem (PS) II (Fv/Fm parameter), indicating mostly reversible heat stress effects. The heat stress led to a decrease in the number of active PS II reaction centers (RC/ABS) and overall activity o PSII (PIabs ) in all genotypes, whereas the PS I (parameter ψREo) was negatively influenced by heat stress in the non-acclimated variant only. Our results showed that the genotypes differ in acclimation capacity to heat stress, and rapid noninvasive techniques may help screen the stress effects and identify more tolerant crop genotypes. The acclimation was demonstrated more at the PS I level, which may be associated with the upregulation of alternative photosynthetic electron transport pathways with clearly protective functions
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