177,173 research outputs found
Nitrate uptake and reduction in higher and lower plants
No full textThe nitrogen compounds nitrate and ammonium are the minerals that plants need in large quantities and which limit their growth in temperate zones. The nitrate assimilation pathway starts with nitrate uptake followed by nitrate reduction resulting in ammonium which is fixed into the amino acids glutamine and glutamate in most plants. This review concentrates on nitrate uptake and nitrate reduction with respect to higher and lower plants. The physiology and the progress in molecular approaches of both processes are considered. For nitrate uptake the well-established uptake systems are discussed and special attention is drawn to nitrate sensing and the nitrate carrier. Knowledge, particularly on nitrate sensing is rare, but it seems to be the first step in a signal transduction chain triggered by nitrate. Therefore further work should consider this topic more frequently. For nitrate reductase the focus is on the posttranslational modification as a regulatory tool for nitrate assimilation, on the intersections of carbon and nitrogen metabolism and on the molecular approaches. A few remarks on how environmental conditions affect nitrate assimilation are also included. Further progress is needed to understand the transduction of positive and negative signals from the environment affecting the expression of genes coding for the nitrate assimilating pathway
Isolation and characterization of nitrite-reductase-deficient mutants of Chlorella sorokiniana (strain 211-8k)
No full textA method is presented to isolate mutants of Chlorella sorokiniana with defects in NO3- metabolism Three nitrite-reductase (NIR; E.C.1.7.7.1)-deficient mutants were obtained from 500 pinpoint-colony-forming clones. The final screening was performed using NO3-, NO2- or NH4+ as N-source. The mutants isolated absorb NO3- with rates close to those measured for the wild type and they excrete NO2- into the medium. The ratio between NO3- uptake and NO2- excretion was 1:1. The sensitivity of NO3- uptake to NH4+ was reduced in the mutant strains as it was in the N-starved wild type of Chlorella. Nitrate reductase (NR; EC 1.6.6.1) expression and NR activity were slightly reduced compared to the wild type due to feedback regulation in the mutant strains. No NIR protein was found in the three mutants. However, NIR activity was obtained (50% of the wildtype) for one mutant strain. The NIR-deficient mutants and the already available NR-deficient mutants will be promising tools for investigations of the nitrate assimilation pathway on the molecular level and for studies searching for signaling of C and N metabolism by inorganic N-compounds
The Reverend Józef Tischner as a public figure
No full textBadając myśl księdza Józefa Tischnera przez pryzmat prasy, radia i telewizji, należy stwierdzić, że był on postacią medialną, szczególnie w latach dziewięćdziesiątych ubiegłego stulecia. Dla wielu – w tym także dla dziennikarzy – Tischner jawił się jako autorytet potrafiący z jednej strony podejmować różne, często kontrowersyjne tematy, z drugiej zaś – zaciekawiać swoją wypowiedzią słuchacza czy widza. Stawiając pytanie o przyczynę popularności Tischnera można uznać, że ogromne znaczenie miała także forma Tischnerowskiego przekazu. Celem niniejszego artykułu jest pokazanie ks. Tischnera jako osobowości medialnej. Tekst powstał w oparciu o pracę doktorską nt. Ksiądz Józef Tischner w polskich środkach społecznego przekazu (1955–2000). Studium politologiczno-medioznawcze. Praca została wyróżniona w 2012 r. przez Redakcję „Studiów Medioznawczych” w konkursie na pracę doktorską z zakresu nauk o mediach.Studies on the ideas of the Reverend Józef Tischner seen from the angle of the press, radio and television show clearly that he was a public figure, especially in the 1990s. For many people – including journalists – Tischner appeared to be an authority who could raise different subjects, often controversial, and at the same time engage listeners or the audience with his speech. The significant reason for Tischner’s popularity was also the way he communicated. This article aims at showing the rev. Tischner as a public figure. The article has been based on the doctoral dissertation titled The Reverend Józef Tischner in the Polish mass media (1955–2000). Political and media studies. The dissertation was recognized in 2012 by the „Media Studies” Editorial team during the competition in doctoral dissertation on media studie
Ksiądz Józef Tischner jako osobowość medialna
No full textStudies on the ideas of the Reverend Józef Tischner seen from the angle of the press, radio and television show clearly that he was a public figure, especially in the 1990s. For many people – including journalists – Tischner appeared to be an authority who could raise different subjects, often controversial, and at the same time engage listeners or the audience with his speech. The significant reason for Tischner’s popularity was also the way he communicated. This article aims at showing the rev. Tischner as a public figure. The article has been based on the doctoral dissertation titled The Reverend Józef Tischner in the Polish mass media (1955–2000). Political and media studies. The dissertation was recognized in 2012 by the „Media Studies” Editorial team during the competition in doctoral dissertation on media studies.Badając myśl księdza Józefa Tischnera przez pryzmat prasy, radia i telewizji, nie ulega wątpliwości, że był on postacią medialna, szczególnie w latach dziewięćdziesiątych ubiegłego stulecia. Dla wielu – w tym także dla dziennikarzy – Tischner jawił się jako autorytet potrafiący, z jednej strony podejmować różne, często kontrowersyjne tematy, z drugiej zaś zaciekawiać swoją wypowiedzią słuchacza czy widza. Stawiając pytanie o przyczynę popularności Tischnera można uznać, że ogromne znaczenie miała także forma Tischnerowskiego przekazu. Celem niniejszego artykułu jest pokazanie ks. Tischnera jako osobowości medialnej. Tekst powstał w oparciu o pracę doktorską nt. Ksiądz Józef Tischner w polskich środkach społecznego przekazu (1955–2000). Studium politologiczno-medioznawcze. Praca została wyróżniona w 2012 r. przez Redakcję „Studiów Medioznawczych” w konkursie na pracę doktorską z zakresu nauk o mediach.4/2013113130"Studia Medioznawcze
Nitrate reductase from winter wheat leaves is activated at low temperature via protein dephosphorylation
No full textThe effect of short-term low temperature treatment on nitrate reductase (NR, EC 1.6.6.1) activity, NR protein and NR transcript levels in excised leaves of winter wheat (Triticum aestivum L. cv. Sadovo-1) was investigated. NR activity, measured in the presence of Mg2+ (NRact), doubled within 2 h at 4degreesC, whereas NR activity, measured in the presence of EDTA (NRmax), did not respond to the cold treatment. Such an activation of NR occurred only if leaves were exposed to low temperature in the light but not in the dark. It was not affected by feeding cytoplasmic protein synthesis inhibitor, cycloheximide, or protein kinase inhibitor, staurosporin, but was completely prevented by okadaic acid, an inhibitor of protein phosphatases of the type 1 and 2 A. This inhibitory effect decreased gradually when okadaic acid-concentration in the nutrient solution was lowered below 1 muM and tended to disappear when leaves were fed with 10 nM okadaic acid. It was demonstrated that the cold-induced NR activation was dependent neither on cold-triggered calcium influx nor on high endogenous abscisic acid levels. The increased NRact in cold-exposed leaves was found to correlate with a higher level of NR transcript but not with an increased NR protein level. Feeding okadaic acid to these leaves prevented the cold-induced accumulation of NR mRNA. These data point to protein phosphatases of the type 2 A being involved in NR protein dephosphorylation and NR transcript accumulation as targets of activation by low temperature treatment
Aldehyde oxidase isoforms and subunit composition in roots of barley as affected by ammonium and nitrate
No full textAldehyde oxidase (AO; EC 1.2.3.1) isoforms in roots of barley plants grown on ammonium or nitrate as nitrogen sources were studied. Roots of ammonium-grown barley plants exhibited considerable levels of AO2, AO3, and AO4 activities after native PAGE. Significantly lower AO2 and AO3 activity bands were observed in roots of plants grown on nitrate. When abscisic aldehyde was used as a substrate a strong response of the AO2 band was observed as well as a faint reaction of the AO3 band, but no activity of AO4 was observed using this substrate. The 160 and 145 kDa polypeptides were detected in ammonium grown plants. Root extracts of nitrate-fed plants revealed only a minor 145 kDa protein band and none of the 160 kDa subunit was detected. The assembly of the AO3 heterodimer requires the simultaneous presence of 160 and 145 kDa subunits. Subunit analysis of AO2 and AO4 revealed homodimeric composition of 160 and 145 kDa, respectively. Western blot analysis revealed changing AO subunits levels during germination and plant development. Differential expression of AO subunits (160 and 145 kDa) and subsequent formation of isoforms, which differ in substrate specificity, distribution and fulfil different enzymatic reactions, may constitute an important regulatory mechanism in the plant
Cytosolic and chloroplastic glutamine synthetase of sugarbeet (Beta vulgaris) respond differently to organ ontogeny and nitrogen source
No full textChanges in the activity and subunit composition of cytosolic glutamine synthetase (GS 1; EC 6.3.1.2) and chloroplastic GS (GS 2) were studied in response to an internal (organ ontogeny) and external signal (N source: NO3- or NH4+). Maximum GS 1 activity of all organs examined was measured in the fibre roots, irrespective of the N source. The response of GS 1 to the N source was, however, organ specific. In the fibre roots, NH4+ nutrition resulted in a 2- to 7-fold (based on protein or freshweight, respectively) increase of CS 1 activity compared to NO3--grown plants. In contrast to the roots, GS I activity in the leaf blades was 2-fold lower with NH4+ nutrition, whereas only minor changes occurred in the petioles. CS 2 activity was highest in the mature and senescing leaf blade; activity was 2-fold higher with NH4+ than with NO3- nutrition, Not only activity, but also subunit composition of GS 1 changed during organ ontogeny as well as in response to the N source. In contrast to GS 1, only minor changes were evident in GS 2 subunit composition, despite significant changes in GS 2 activity. Up to 5 different GS 1 subunits of approximate to 41-43 kDa were separated; they were identical in all organs examined. GS 2 was composed of 4 different subunits of similar to 48 kDa
Cloning, functional expression and expression studies of the nitrate transporter gene from Chlorella sorokiniana (strain 211-8k)
No full textThe nitrate transporter from Chlorella sorokiniana (accession number AY026523) has been cloned by screening a cDNA library based on mRNA isolated after 30 min treatment of Chlorella with 5 mM nitrate and with a RT-PCR product (730 bp) as a probe. The Chlorella sequence has similarity to known nitrate transporters of the NRT2 family (high-affinity nitrate transporters). The cDNA clone was used for functional expression in Xenopus oocytes and a nitrate-dependent current was measured at pH 5.5 but not at pH 7.4. A second algal gene or a second gene product was not needed for functional expression in Xenopus. Inhibitor studies in Chlorella indicated that protein phosphorylation/dephosphorylation is involved in nitrate induction of ChNRT2.1. In addition to nitrate, ChNRT2.1 expression is induced by nitroprusside, a NO donor, and is affected by glucose
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Interference with the citrulline-based nitric oxide synthase assay by argininosuccinate lyase activity in Arabidopsis extracts
No full textThere are many reports of an arginine-dependent nitric oxide synthase activity in plants; however, the gene(s) or protein(s) responsible for this activity have yet to be convincingly identified. To measure nitric oxide synthase activity, many studies have relied on a citrulline-based assay that measures the formation of L-citrulline from L-arginine using ion exchange chromatography. In this article, we report that when such assays are used with protein extracts from Arabidopsis, an arginine-dependent activity was observed, but it produced a product other than citrulline. TLC analysis identified the product as argininosuccinate. The reaction was stimulated by fumarate (> 500 microM), implicating the urea cycle enzyme argininosuccinate lyase (EC 4.3.2.1), which reversibly converts arginine and fumarate to argininosuccinate. These results indicate that caution is needed when using standard citrulline-based assays to measure nitric oxide synthase activity in plant extracts, and highlight the importance of verifying the identity of the product as citrulline.Rudolf Tischner, Mary Galli, Yair M. Heimer, Sarah Bielefeld, Mamoru Okamoto, Alyson Mack and Nigel M. Crawfor
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