1,720,962 research outputs found
Activities of sucrose and sorbitol metabolizing enzymes in vegetative sinks of peach and correlation with sink growth rate
No full textTerminal portions of ‘Flordaguard’ peach roots [Prunus persica (L.), Batsch] were divided into six segments and the activities of NAD+-dependent sorbitol dehydrogenase (SDH), sorbitol oxidase (SOX), sucrose synthase (SS), soluble acid invertase (AI), and soluble neutral invertase (NI) were measured in each segment 10, 15, and 20 ds after seed germination. The same type of experiment was conducted with terminal portions of ‘Flordaguard’ and ‘Nemaguard’ peach shoots except that one of the six segments consisted of the leaflets surrounding the apex. Independent of the age of individual roots, activities of SDH and AI were consistently highest in the meristematic portion and decreased with tissue maturation. In shoots, AI was the most active enzyme in the elongating portion subtending the apex, whereas SDH was primarily associated with meristematic tissues. A positive correlation between SDH and AI activities was found in various developmental zones of roots (r = 0.96) and shoots (r = 0.90). Sorbitol and sucrose contents were low in roots regardless of distance from tip, while sucrose showed a decreasing trend with distance and sorbitol, fructose, and glucose increased with distance from the meristem in shoots. Activity of SDH in internodes, but not apices, correlated with shoot elongation rate of both cultivars, whereas activities of other enzymes did not correlate with shoot elongation rate. We conclude that AI and SDH are the predominant enzymes of carbohydrate catabolism and the best indicators of sink growth and development in vegetative sinks of peach
Effect of drought on sorbitol and sucrose metabolism in sinks and sources of peach
No full textIn peach (Prunus persica [L.] Batsch.), sorbitol and sucrose are the two main forms of photosynthetic and translocated carbon and may have different functions depending on the organ of utilization and its developmental stage. The role and interaction of sorbitol and sucrose metabolism was studied in mature leaves (source) and shoot tips (sinks) of ‘Nemaguard’ peach under drought stress. Plants were irrigated daily at rates of 100, 67, and 33% of evapotranspiration (ET). The relative elongation rate (RER) of growing shoots was measured daily. In mature leaves, water potential (Pw), osmotic potential (Ps), sorbitol-6-phosphate dehydrogenase (S6PDH, EC 1.1.1.200), and sucrose-phosphate synthase (SPS, EC 2.4.1.14) activities were measured weekly. Measurements of Ps, sorbitol dehydrogenase (SDH, 1.1.1.14), sucrose synthase (SS, EC 2.4.1.13), acid invertase (AI, EC 3.2.1.26), and neutral invertase (NI, EC 3.2.1.27) activities were taken weekly in shoot tips. Drought stress reduced RER and Pw of plants in proportion to water supply. Osmotic adjustment was detected by the second week of treatment in mature leaves and by the third week in shoot tips. Both SDH and S6PDH activities were reduced by drought stress within 4 days of treatment and positively correlated with overall Pw levels. However, only SDH activity was correlated with Ps. Among the sucrose enzymes, only SS was affected by drought, being reduced after 3 weeks. Sorbitol accumulation in both mature leaves and shoot tips of stressed plants was observed starting from the second week of treatment and reached up to 80% of total solutes involved in osmotic adjustment. Sucrose content was up to 8-fold lower than sorbitol content and accumulated only occasionally. We conclude that a loss of SDH activity in sinks leads to osmotic adjustment via sorbitol accumulation in peach. We propose an adaptive role of sorbitol metabolism versus a maintenance role of sucrose metabolism in peach under drought stress
Carbohydrate metabolism of vegetative and reproductive sinks in the late-maturing peach cultivar ‘Encore’
No full textActivities of NAD+-dependent sorbitol dehydrogenase (SDH), sucrose synthase (SS), acid invertase (AI), and neutral invertase (NI) in ‘Encore’ peach (Prunus persica L.) fruits and developing shoot tips were followed during the growth season to see whether they could serve as indicators of sink strength. In fruit flesh, SS was active during stage I of growth, when cells were actively dividing, and SDH activity was detected during stage III, when cells were actively enlarging. Acid invertase was active in stage I and showed the best correlation with the relative increase in fruit weight during the season. During seed filling and pit hardening (stage II), when relative fruit growth rate was slowest, activities of carbohydrate metabolizing enzymes in fruit flesh were not detectable. No sorbitol oxidase (SOX) activity was detected during stages I and II. The highest sucrose content occurred when sucrose metabolizing enzyme activities were low, near the end of fruit development. In developing shoot tips, SDH activity was low at the beginning and end of the season when vegetative growth was slowest. Also, shoot tips exhibited a 2 : 1 sorbitol : sucrose (w : w) ratio during these periods. A 1 : 1 sorbitol : sucrose (w : w) ratio along with an increase in SDH activity was present in shoot tips during mid-growing season. In root tips of ‘Nemaguard’ peach, SDH exhibited its highest activity compared to that in other organs. When sorbitol and sucrose metabolizing enzyme activities were correlated with shoot growth of ‘Nemaguard’ plants, only SDH activity showed a positive response
A simple, rapid extraction and assay procedure for the NAD+-dependent sorbitol dehydrogenase (SDH) in peach
No full textSorbitol is the major photosynthetic product in peach. In sink tissues, sorbitol is converted to fructose via the NAD+-dependent sorbitol dehydrogenase (SDH). A new procedure is described that allows rapid, simple quantification of SDH activity in growing tissues. The procedure uses only 0.01 to 2.5 grams of fresh tissue per sample, such that a single shoot tip, a single root tip, or about 5 g of fruit flesh can be assayed for SDH activity. Storage of samples at 4 or -20 C° over night resulted in significant loss of enzyme activity. Thus, freshly harvested tissues were ground with sand in buffer at 2°C in a mortar and pestle, and the homogenate centrifuged @ 3000 ́ g to remove particulate matter and sand. The supernatant was desalted on a Sephadex G-25 column, and the eluent assayed for SDH activity immediately. Activity was determined by measuring the production of NADH per min in the assay mixture using a spectrophotometer (@340 nm). Tris buffer at pH 9.0 was the best for extraction of peach SDH. Activity of SDH was strongly inhibited by dithiothreitol (DTT) in the extraction mixture and by DTT, L-cystein, or SDI-158 in the assay mixture, similar to results reported for SDH from mammalian tissues. Peach SDH has a Km of 37.7 mm for sorbitol and a pH optimum of 9.5, similar to those reported for apple SDH. Unlike older protocols for SDH activity in plant tissues, the new procedure features reduced sample size (1/10 to 1/100th that previously used), smaller volumes of buffer, fewer buffer ingredients, greatly reduced time for sample preparation, yet comparable or higher values of SDH specific activity. Following the same procedure SDH activity was also measured in Prunus fremontii, Prunus ilicifolia, and Marianna 2624 plum (P. munsoniana × P. cerasifera)
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
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