1,721,047 research outputs found
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
Allelopathic potential of apple hairy root secondary metabolites - the effect of phloretin and phloridzin in in vitro culture
No full textOgraniĉenja u izuĉavanju potencijala i mehanizama alelopatskog delovanja glavnih sekundarnih metabolita korena jabuke, floretina i florizina, usled kompleksnosti interakcija u rizosferi, mogu biti prevaziĊena upotrebom kulture transformisanih korenova in vitro. Odabranim naĉinom inokulacije regenerisanih izdanaka jabuke sa Agrobacterium rhizogenes 15834, efikasno su indukovani transformisani korenovi kod sorti Melrouz, Zlatni Delińes, Ĉadel i Gloster. Smenom hranljivih podloga sa i bez auksina, po prvi put je uspostavljena permanentna in vitro kultura izolovanih transformisanih korenova jabuke. UHPLC/(+/-)HESI–MS/MS analizom je utvrĊeno da genetiĉka transformacija nije dovela do promena u sadrņaju glavnih sekundarnih metabolita korena jabuke. U eksudatu transformisanih korenova, sadrņanom u teĉnoj podlozi u kojoj su korenovi gajeni, kvantifikovani su iskljuĉivo florizin, floretin, hlorogena i kafeinska kiselina. Tretman ovim eksudatom je prouzrokovao znaĉajnu inhibiciju rastenja i razvića izdanaka i korenova klijanaca Arabidopsis thaliana. Sliĉan inhibitorni efekat ispoljili su ĉist florizin u koncentraciji od 500 μM, kao i floretin u svim testiranim koncentracijama (125-500 μM), izazivajući krupne promene u morfologiji tretiranih klijanaca, posebno korena. Velike sliĉnosti su zapaņene u obrascu promena ekspresije gena ukljuĉenih u polarni transport auksina, kao i biosintezu auksina i giberelina u korenovima klijanaca arabidopsisa tretiranih eksudatom transformisanih korenova jabuke, sa onim detektovanim kod klijanaca tretiranih 500 μM floretinom. To ukazuje na mogućnost da je floretin u eksudatu korena jabuke metabolit koji je odgovoran za alelopatske efekte, a koji bi se mogli zasnivati na promenama nivoa auksina i giberelina, kao i na interakciji ove dve grupe hormona.The investigation of allelopathic potential and mode of action of the main apple root secondary metabolites, phloridzin and phloretin is difficult to perform due to high complexity of rhizosphere interactions. Therefore, the generation of in vitro hairy root cultures could be an alternative system for allelopathic studies of apple. The efficient induction of hairy roots in apple cvs. Melrose, Golden Delicious, Ĉadel and Gloster was obtained using the appropriate mode of inoculation of regenerated shoots by Agrobacterium rhizogenes 15834. Permanent in vitro culture of apple autonomous hairy roots was established for the first time by cultivation on alternating growth media with and without auxins. UHPLC(+/-)HESI-MS/MS analysis confirmed that genetic transformation did not lead to changes in the content of the main secondary metabolites of apple roots. Dihydrochalcones phloridzin and phloretin, chlorogenic and caffeic acids were detected as only putative allelochemicals exuded into the growth medium in which hairy roots were grown. Apple hairy root exudates significantly affected development and growth of Arabidopsis thaliana seedlings. Pure phloridzin at 500 μM and phloretin in all tested concentrations (125-500 μM) had similar effects as apple hairy root exudates inducing significant alterations in morphology of seedlings, expecially roots. High similarities in the expression patterns of genes involved in polar auxin transport and auxin and gibberellin biosynthetic pathways in roots of arabidopsis seedlings treated with either apple hairy root exudates or 500 μM phloretin were observed. This indicates that phloretin in hairy root exudates could be at least partly responsible for the apple root allelopathic properties, that were most likely based on auxin and gibberellin cross-talk and their altered homeostasis in arabidopsis roots.
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
Allelopathic potential of apple hairy root secondary metabolites - the effect of phloretin and phloridzin in vitro culture
Get PDFOgraniĉenja u izuĉavanju potencijala i mehanizama alelopatskog delovanja glavnih
sekundarnih metabolita korena jabuke, floretina i florizina, usled kompleksnosti interakcija
u rizosferi, mogu biti prevaziĊena upotrebom kulture transformisanih korenova in vitro.
Odabranim naĉinom inokulacije regenerisanih izdanaka jabuke sa Agrobacterium
rhizogenes 15834, efikasno su indukovani transformisani korenovi kod sorti Melrouz,
Zlatni Delińes, Ĉadel i Gloster. Smenom hranljivih podloga sa i bez auksina, po prvi put je
uspostavljena permanentna in vitro kultura izolovanih transformisanih korenova jabuke.
UHPLC/(+/-)HESI–MS/MS analizom je utvrĊeno da genetiĉka transformacija nije dovela
do promena u sadrņaju glavnih sekundarnih metabolita korena jabuke. U eksudatu
transformisanih korenova, sadrņanom u teĉnoj podlozi u kojoj su korenovi gajeni,
kvantifikovani su iskljuĉivo florizin, floretin, hlorogena i kafeinska kiselina. Tretman ovim
eksudatom je prouzrokovao znaĉajnu inhibiciju rastenja i razvića izdanaka i korenova
klijanaca Arabidopsis thaliana. Sliĉan inhibitorni efekat ispoljili su ĉist florizin u
koncentraciji od 500 μM, kao i floretin u svim testiranim koncentracijama (125-500 μM),
izazivajući krupne promene u morfologiji tretiranih klijanaca, posebno korena. Velike
sliĉnosti su zapaņene u obrascu promena ekspresije gena ukljuĉenih u polarni transport
auksina, kao i biosintezu auksina i giberelina u korenovima klijanaca arabidopsisa tretiranih
eksudatom transformisanih korenova jabuke, sa onim detektovanim kod klijanaca tretiranih
500 μM floretinom. To ukazuje na mogućnost da je floretin u eksudatu korena jabuke
metabolit koji je odgovoran za alelopatske efekte, a koji bi se mogli zasnivati na
promenama nivoa auksina i giberelina, kao i na interakciji ove dve grupe hormona
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
Allelopathic potential of apple hairy root secondary metabolites - the effect of phloretin and phloridzin in vitro culture
No full textOgraniĉenja u izuĉavanju potencijala i mehanizama alelopatskog delovanja glavnih
sekundarnih metabolita korena jabuke, floretina i florizina, usled kompleksnosti interakcija
u rizosferi, mogu biti prevaziĊena upotrebom kulture transformisanih korenova in vitro.
Odabranim naĉinom inokulacije regenerisanih izdanaka jabuke sa Agrobacterium
rhizogenes 15834, efikasno su indukovani transformisani korenovi kod sorti Melrouz,
Zlatni Delińes, Ĉadel i Gloster. Smenom hranljivih podloga sa i bez auksina, po prvi put je
uspostavljena permanentna in vitro kultura izolovanih transformisanih korenova jabuke.
UHPLC/(+/-)HESI–MS/MS analizom je utvrĊeno da genetiĉka transformacija nije dovela
do promena u sadrņaju glavnih sekundarnih metabolita korena jabuke. U eksudatu
transformisanih korenova, sadrņanom u teĉnoj podlozi u kojoj su korenovi gajeni,
kvantifikovani su iskljuĉivo florizin, floretin, hlorogena i kafeinska kiselina. Tretman ovim
eksudatom je prouzrokovao znaĉajnu inhibiciju rastenja i razvića izdanaka i korenova
klijanaca Arabidopsis thaliana. Sliĉan inhibitorni efekat ispoljili su ĉist florizin u
koncentraciji od 500 μM, kao i floretin u svim testiranim koncentracijama (125-500 μM),
izazivajući krupne promene u morfologiji tretiranih klijanaca, posebno korena. Velike
sliĉnosti su zapaņene u obrascu promena ekspresije gena ukljuĉenih u polarni transport
auksina, kao i biosintezu auksina i giberelina u korenovima klijanaca arabidopsisa tretiranih
eksudatom transformisanih korenova jabuke, sa onim detektovanim kod klijanaca tretiranih
500 μM floretinom. To ukazuje na mogućnost da je floretin u eksudatu korena jabuke
metabolit koji je odgovoran za alelopatske efekte, a koji bi se mogli zasnivati na
promenama nivoa auksina i giberelina, kao i na interakciji ove dve grupe hormona
Allelopathic effects of Chenopodium murale L. hairy roots in vitro
No full textKorenov sistem C. murale produkuje i luči hemijske materije koje imaju alelopatsku aktivnost. Proučavanje efekata na druge organizme, kao i izolovanje i karakterizacija metabolita koji su izlučeni iz korenova u zemljište je veoma kompleksan proces. Zbog toga je cilj ovog istraživanja bio uspostavljanje kulture transformisanih korenova C. murale in vitro, kao novog sistema pogodnog za izučavanje alelopatskog efekta.
Transgeni korenovi su indukovani pomoću Agrobacterium rhizogenes A4M70GUS na eksplantatima korenova, kotiledona, listova i internodija klijanaca C. murale. Eksplantati korenova su imali najveću efikasnost transformacije (11,1%). Uspostavljeni su klonovi transformisanih korenova različite morfologije i potencijala rasta koji se gajenjem (subkultivisanjem) u tečnom MS medijumu održavaju više od dve godine. Potvrda transformacije ovih klonova je urađena pomoću PCR, RT–PCR i histohemijske GUS analize. Nije ustanovljena razlika u prisustvu rol gena među klonovima.
Ispitivan je alelopatski efekat tečnih medijuma u kojima su rasli transformisani i netransformisani korenovi C. murale (fitotoksični medijum) na klijanje i rast klijanaca test biljaka arabidopsisa (Arabidopsis thaliana (L.) Heynh), pšenice (Triticum aestivum L.) i salate (Lactuca sativa L.). Kod sve tri test biljke ustanovljen je inhibitorni efekat na klijanje semena i rast klijanaca. Klonovi transformisanih klonova: R1 i R8, imali su najveći alelopatski potencijal.
Kod test biljaka arabidopsisa i pšenice, koje su bile tretirane fitotoksičnim medijumima, praćena je ukupna aktivnost antioksidativnih enzima – katalaza, peroksidaza i superoksid dismutaza (spektrofotometrijski), kao i zastupljenost i aktivnost pojedinih izoformi navedenih enzima (elektroforetski). Aktivnost ovih enzima (izuzev katalaza kod arabidopsisa) bila je povećana kod klijanaca isklijavanih i gajenih na fitotoksičnim medijumima, što je u skladu sa aktiviranjem odbrambenih mehanizama u biljkama kada se
one bile izlažu stresu (fitotoksinima, tj. alelohemikalijama). Fitotoksični medijumi različitih klonova transformisanih korenova dovodili su do različitog nivoa povećanja aktivnosti katalaza, peroksidaza i superoksid dismutaza kod različitih test biljaka.
Pošto su fitotoksični medijumi dovodili do inhibicije rasta i razvoja klijanaca, kod tretiranih test biljaka ispitivana je i ekspresija gena regulatora ćelijskog ciklusa. Metodom qPCR–a je pokazano statistički značajno smanjenje ekspresije gena koji regulišu prelaz iz G1 u S fazu kao i prelaz iz G2 u M fazu, što ukazuje na potencijalnu inhibiciju procesa DNK sinteze, kao i same mitoze. Homologi geni arabidopsisa i pšenice (CDKA;1 / CDC2 kao i CYCD2;1 / CYCD2) su pokazivali sličan profil ekspresije.
HPLC analizom fitotoksičnih medijuma utvrđeno je prisustvo fenolnih kiselina, kafeinske, ferulinske i p–kumarinske kiseline u koncentraciji od 0,07 – 2,85 μmol/l. Sve tri fenolne kiseline, komercijalno proizvedene, primenjene pojedinačno ili u binarnim ili tercijarnim smešama, u koncentraciji od 5 mmol/l za pšenicu i salatu i 0,5 mmol/l za arabidopsis, pokazale su sličan inhibitorni efekat na klijanje semena i rast klijanaca test biljaka, kao i u slučaju primene fitotoksičnih medijuma. Međutim, pošto su koncentracije čistih supstanci fenolnih kiselina koje izazivaju inhibitorni efekat bile znatno veće od koncentracija ovih fenolnih kiselina određenih u fitotoksičnim medijumima, pretpostavljamo da alelopatsko svojstvo fitotoksičnih medijuma potiče od nekih drugih hemijskih jedinjenja ili njihovih interakcija, što će biti predmet daljih istraživanja.
Rezultati ovog istraživanja predstavljaju osnovu za rasvetljavanje hemijske prirode i mehanizma alelopatske interferencije biljaka C. murale.Root system produces and releases chemical compounds with allelopathic activity. Isolation and characterization of these metabolites, as well as investigation of their effects on other organisms, are very complicated processes. The aim of the present study was to initiate and establish Chenopodium murale L. transgenic hairy root in vitro culture system, as a new tool for allelopathic assays.
Transgenic hairy roots were induced by Agrobacterium rhizogenes A4M70GUS from roots, cotyledons, leaves and internodes of C. murale seedlings. Roots were found to be the best target explants, providing transformation efficiency of up to 11.1%. Established 13 hairy root clones differed in their morphology and growth potential. The liquid culture system of characterized hairy root clones was maintained for over two years. Molecular characterization of these clones was carried out by PCR, RT-PCR and histochemical GUS analyses. No differences in rol gene presence were observed.
We investigated allelopathic effect of wild-type and hairy root growth media (phytotoxic media) against germination and seedling development of Arabidopsis thaliana (L.) Heynh, wheat (Triticum aestivum L.) and lettuce (Lactuca sativa L.) test plants. The inhibitory potential varied depending on the test plant and hairy root clone. R1 and R8 clones had strong allelopathic effects. These results revealed that hairy roots as an independent system synthesize some bioactive substances with allelopathic activity and exude them into the growth medium.
In test plants A. thaliana and wheat, after treatment with phytotoxic media, activity of different antioxidative enzymes (catalase, peroxidase and superoxide dismutase) were analyzed spectrophotometrically and electrophoretically. Activities of these antioxidative enzymes were higher in comparison to the control, except the catalase activity in A. thaliana, which was the same or lower. Phytotoxic media from different hairy root clones cause different changes in activities of catalases, peroxidases and superoxide dismutases in test plants.
Allelopathic interactions implicate the inhibition of cell division by allelochemicals. We investigated expression of cell cycle-related genes (CDK and CYC) in test plant A. thaliana and wheat, after phytotoxic medium treatment of clone R8. We demonstrated, by q-PCR method, that expression of genes involved in G1-to-S and G2-to-M transition were significantly down-regulated by phytotoxic medium of clone R8 in root and shoot apexes of test plants, indicating inhibition of DNK synthesis and mitosis. Homologous genes of A. thaliana and wheat (CDKA;1/CDC2 and CYCD2;1/CYCD2) had similar expression profiles, after the treatment with phytotoxic medium.
Concentrations of caffeic, ferulic and p-coumaric acids (0.07 – 2.85 μmol/l) identified and quantified by HPLC analyses in the growth media, were significantly lower than the inhibitory active concentration of pure grade phenolic acids when applied to A. thaliana (0.5 mmol/l) or wheat and lettuce (5.0 mmol/l, both), suggesting that phenolic acids have a limited role in the allelopathic phenomena of C. murale. The presented hairy root system appears to be a suitable tool for further investigation of the potential and nature of root-mediated allelopathic interference of C. murale
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