1,720,963 research outputs found
Use of plasma membrane vesicles for examination of phosphorus deficiency-induced root excretion of citrate in cluster roots of white lupin
No full textUptake of iron (Fe-59) complexed to water-extractable humic substances by sunflower leaves
No full textA research was carried out to evaluate the leaves' ability to utilize Fe supplied as a complex with water-extractable humic substances (WEHS) and the long-distance transport of 59Fe applied to sections of fully expanded leaves of intact sunflower (Helianthus annuus L.) plants. Plants were grown in a nutrient solution containing 10 μM Fe(III)-EDDHA (Fe-sufficient plants), with the addition of 10 mM NaHCO3 to induce iron chlorosis (Fe-deficient plants). Fe(III)-WEHS could be reduced by sunflower leaf discs at levels comparable to those observed using Fe(III)-EDTA, regardless of the Fe status. On the other hand, 59Fe uptake rate by leaf discs of green and chlorotic plants was significantly lower in Fe-WEHS-treated plants, possibly suggesting the effect of light on photochemical reduction of Fe-EDTA. In the experiments with intact plants, 59Fe-labeled Fe-WEHS or Fe-EDTA were applied onto a section of fully expanded leaves. Irrespective of Fe nutritional status, 59Fe uptake was significantly higher when the treatment was carried out with Fe-EDTA. A significant difference was found in the amount of 59Fe translocated from treated leaf area between green and chlorotic plants. However, irrespective of the Fe nutritional status, no significant difference was observed in the absolute amount of 59Fe translocated to other plant parts when the micronutrient was supplied either as Fe-EDTA or Fe-WEHS. Results show that the utilization of Fe complexed to WEHS by sunflower leaves involves an Fe(III) reduction step in the apoplast prior to its uptake by the symplast of leaf cells and that Fe taken up from the Fe-WEHS complexes can be translocated from fully expanded leaves towards the roots and other parts of the shoot
Uptake of 59Fe from soluble 59Fe-humate complexes by cucumber and barley plants
No full textChlorosis-susceptible fruit trees growing on calcareous soils have been observed to recover in the presence of grass cover species. However, the physiological mechanisms behind this phenomenon are only scarcely understood. An investigation was carried out to verify whether citrus plants can use 59Fe solubilized from a sparingly soluble source by the phytosiderophores (PS) released from graminaceous species. Experiments were performed in hydroponics, using two citrus rootstocks differing in their sensitivity to Fe-deficiency in the field (Poncirus trifoliata x Citrus paradisi, citrumelo "Swingle", highly susceptible, and Citrus aurantium L., moderately tolerant). Barley (Hordeum vulgare L., cv Europa) was used as a model species for PS-releasing graminaceous plants. Fe-deficient citrus plants increased 59Fe-uptake from 59Fe-hydroxide supplied inside a dialysis tube, when Fe-deficient barley plants or PS-containing barley root exudates were present in the uptake solution, this effect being particularly evident for the susceptible rootstock. 59Fe-uptake from 59Fe-hydroxide was also enhanced in Fe-deficient citrumelo "Swingle" in the presence of Fe-deficient Poa pratensis L. and Festuca rubra L., two perennial grasses normally grown in association with fruit trees; no effect was found when Fe-sufficient grasses were employed. The uptake of 59Fe by the susceptible citrus rootstock increased in proportion to the amount of 2′-deoxymugineic acid (DMA), the major PS released by Fe-deficient F. rubra, present in the uptake solution. The beneficial effect of F. rubra or P. pratensis was evident from the leaf re-greening observed when Fe-deficient citrumelo "Swingle" plants were grown in association with the grasses in pots filled with a calcareous soil. Leaf re-greening was not observed when citrumelo "Swingle" plants and yellow stripe 3 (ys3) maize (Zea mays L.) mutant plants, unable to release PS, were co-cultivated in pots filled with calcareous soil, unless exogenous PS were added to the soil. Results indicate that graminaceous cover species can improve the Fe-nutrition of fruit trees grown on calcareous soils by enhancing Fe-availabili
The root-hairless barley mutant brb used as model for assessment of role of root hairs in iron accumulation
No full textMain components of Strategy II mechanism for Fe uptake are secretion of chelating compounds, phytosiderophores, and specific uptake of Fe(III)-phytosiderophores complex.Since the amount of phytosiderophores secreted correlates positively with plant ability to cope with Fe shortage, a role of root hairs in enhancing root capability to store phytosiderophores under Fe stress might be envisaged.In this study the root-hairless mutant of barley (Hordeum vulgare L.) brb (bald root barley) and the wild-type genotype (cv. Pallas) were compared with respect to their capacity to respond to Fe shortage in nutrient solution. Plants were grown with FeIII-EDTA at 0, 0.02 and 0.08 mM, in order to reproduce severe or moderate Fe deficiency, and adequate Fe nutritional status, respectively. Analysis was performed after 11 and 14 days considering leaf Fe content, phytosiderophores release and accumulation in root tips, and 59Fe uptake.Biomass accumulation and chlorophyll content were not reduced in mutant plants as compared to wild-type ones; leaf Fe content was similar in both genotypes after 14 days of growth. Accumulation and release of phytosiderophores showed a similar trend in both genotypes when subjected to Fe limitation. Furthermore, no significant difference between the two genotypes was observed when 59Fe uptake was measured.Results seem to support the idea that the presence of root hairs and their increased production in response to low-Fe availability, while causing major modifications of root geometry, did not necessarily lead neither to an effect on growth nor on Fe uptake and accumulation in barley plants. © 2010 Elsevier Masson SAS
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
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