1,721,022 research outputs found
The Relationship of Nitrate Reductase Activity to Uptake and Assimilation of Atmospheric 15NO2 -Nitrogen in Needles of Norway Spruce (Picea abies [L.] Karst.)
No full textUsing NO2, relations between nitrate reductase activity and stomatal conductance, N-uptake and N-glutamate were studied in the two youngest needles flushes of potted Norway spruce (Picea abies [L.] Karst.). There were linear correlations between the stomatal conductance and the N-uptake and between the N-uptake and nitrate reductase (E.C. 1.6.6.1/1.6.6.2) activity. The N labelling of free glutamate shows the assimilation of NO2 from the atmosphere in addition to the nitrogen from the soil. The portion of glutamate originating from NO2 was linearly related to nitrate reductase activity in spring experiments. This indicates that this enzyme activity reflected the rate of NO2-assimilation
Buthionine Sulfoximine (BSO) Reduces Chilling Tolerance of a Chilling Tolerant Maize Genotype
No full textA new approach was applied to find evidence for the hypothesis that glutathione (GSH) protects plants against low temperature damage. In this approach the GSH content was decreased and cold tolerance of plants was determined. Buthionine sulfoximine (BSO), a substance which selectively inhibits GSH synthesis, was used to decrease GSH. It was found, that GSH and gamma-glutamylcysteine were decreased by BSO exposure, that cold injury correlated to the concentration of BSO and that injury was visible only after recovery and not after chilling
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
Uptake and assimilation of atmospheric NO2 — N by spruce needles (Picea abies): A field study
Full text linkNO2 enters spruce needles by gas exchange through the slomata. Nitrate formed from NO2 is reduced in the cytosol by nitrate reductase (NR), the rate limiting enzyme of the nitrogen assimilatory pathway. A linear relationship was found between the nitrate reductase activity (NRA), NO2 concentration and the amount of N incorporated into amino acids and proteins, so that NRA was suggested as an estimate of NO2-uptake. In the present field study, 50 spruce trees (Picea abies) have been selected, which grow in a natural habitat in a NO2 concentration gradient in a forest crossed by a highway which is a major NO source. At part of the sites, the microclimatic conditions have been recorded, so that common models of local gas exchange of the needles could be used to estimate stomatal uptake of NO2. NRA was investigated as a function of radiation and stomatal uptake on the day before needle sampling. Close to the highway NRA was permanently elevated with a maximum in summer. As with the laboratory results, a linear relationship between stomatal uptake and NRA was found. Total N — content of current year shoots was not affected by the additional N-source provided by airborne NO2. The present study shows that the gas exchange models are consistent with the physiological reactions of spruce needles on a local level and therefore contribute to the validation of calculations of NO2 dry deposition to spruce forests
NO2-induced nitrate reductase activity in needles of Norway spruce (Picea abies) under laboratory and field conditions
No full textThe induction of activity of the enzyme nitrate reductase (NR, EC 1.6.6.1, 1.6.6.2) in needles of Norway spruce (Picea abies[L.] Karst.) by nitrogen dioxide (NO2) was studied under laboratory and field conditions. In fumigation chambers an increase in nitrate reductase activity (NRA) was detected 4 h after the start of the NO2 treatment. During the first 2 days with 100 µg NO2 m−3, NRA reached a constant level and did not change during the following 4 days. At the same level of NO2, NRA was lower in needles from trees grown on NPK-fertilized soil than on non-fertilized soil. After the transfer of spruce trees from fertilized soil to NPK-rich nutrient solution, NRA was transiently increased. This effect was assigned to root injuries causing nitrate transport to the shoot and subsequent induction of NRA. Neither trees on fertilized soil nor trees transferred to NPK-poor nutrient solution had increased NRA unless NO2 was provided. The NO2 gradient in the vicinity of a highway was used to test the long-term effect of elevated levels of NO2 on needle NRA of potted and field-grown spruce trees. Compared with less polluted sites, permanently increased NRAs were detected when NO2 concentrations were above 20 µg m−3. Controls of field measurements some 10 years after the introduction of catalytic converters in cars showed no significant change neither in NO2 levels nor in the decreasing NRA of spruce needles with the distance from the highway
Increasing the Glutathione Content in a Chilling-Sensitive Maize Genotype Using Safeners Increased Protection against Chilling-Induced Injury
No full textWith the aim of analyzing their protective function against chilling-induced injury, the pools of glutathione and its precursors, cysteine (Cys) and gamma -glutamyl-Cys, were increased in the chilling-sensitive maize (Zea mays) inbred line Penjalinan using a combination of two herbicide safeners. Compared with the controls, the greatest increase in the pool size of the three thiols was detected in the shoots and roots when both safeners were applied at a concentration of 5 muM. This combination increased the relative protection from chilling from 50% to 75%. It is interesting that this increase in the total glutathione (TG) level was accompanied by a rise in glutathione reductase (GR; EC 1.6.4.2) activity. When the most effective safener combination was applied simultaneously with increasing concentrations of buthionine sulfoximine, a specific inhibitor of glutathione synthesis, the total gamma -glutamyl-Cys and TG contents and GR activity were decreased to very low levels and relative protection was lowered from 75% to 44%. During chilling, the ratio of reduced to oxidized thiols first decreased independently of the treatments, but increased again to the initial value in safener-treated seedlings after 7 d at 5 degreesC. Taking all results together resulted in a linear relationship between TG and GR and a biphasic relationship between relative protection and GR or TG, thus demonstrating the relevance of the glutathione levels in protecting maize against chilling-induced injury
Variations on the Author
Full text link“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
Full text linkWe 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
Incorporation of atmospheric 15NO2-nitrogen into free amino acids by Norway spruce Picea abies (L.) Karst.
Full text linkDuring spring and autumn 1991, potted 6-yearold spruce trees (Picea abies (L.) Karst.) were fumigated with 60 nl1–1 15NO2 for 4 days under controlled conditions in constant light. Current and previous flush needles, the bark and the fine roots were analysed for total 15N content and incorporation of 15N into the -amino nitrogen of free amino acids. In addition, in vitro nitrate reductase activity and stomatal conductance of the needles were measured. Nitrate reductase activity was significantly higher in the needles of fumigated trees compared to control trees exposed to filtered air. With an average of 9.1% 15N, free glutamate was the pool with the most label. Taking into account the time-course of the labelling of this pool, this figure can be taken as an estimate of the minimum contribution of NO2 to the N nutrition of the needles. 15N-labelled amino acids were also detected in the bark and the roots, indicating export from the needles
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