1,720,967 research outputs found
Transcript accumulation of polygalacturonase inhibiting protein (PGIP) following pathogen infections in soybean
No full textProteins inhibiting fungal endo-polygalacturonase (PGIP) are constitutively expressed and localized on cell walls of most plant species. Induction of pgip transcripts following pathogen infection would demonstrate a role of PGIP in active plant defence mechanisms. We investigated pgip expression in hypocotyls of soybean seedlings (cvs 'Sapporo' and 'Kure') infected with the fungal pathogens Diaporthe phaseolorum var. caulivora, Sclerotinia sclerotiorum and an avirulent (race 1) and virulent (race 20) races of Phytophthora sojae. Two pgip transcripts were transiently expressed in all types of interaction with similar timing and maximum accumulation at 16-24 h after infection. However, soybean seedlings of both cvs infected with the virulent race 20 of P. sojae showed higher levels of pgip expression than seedlings infected with the avirulent race 1. A delay of pgip accumulation was observed when plants were inoculated with zoospores in place of mycelium of P. sojae. The presence of endo-polygalacturonase (endo-PG) in infected tissue was monitored both by immunological detection and by determining PG activity. PG was detected only in soybean seedlings infected with S. sclerotiorum and not in those infected with D. phaseolorum var. caulivora or P. sojae. The apparent inability in vivo of the virulent and avirulent races of P. sojae to produce PG suggests that PG-PGIP interaction is not required for the resistance response of soybean against this pathogen
Polygalacturonase inhibiting proteins from Allium porrum L. and their role in plant tissue against fungal endo- polygalacturonases
No full textFive endo-polygalacturonases (PGs), three produced in culture filtrate by Fusarium moniliforme, Sclerotium cepivorum and Botrytis aclada, respectively, and two (one acidic and one basic isoform) obtained from Sclerotinia sclerotiorum soybean infected hypocotyls, were purified in order to characterize the activity of polygalacturonase inhibitor(s) (PGIP(s)) from leek stalk tissue (Allium porrum L.). Three apparently different PGIPs (PGIP-I, PGIP-II and PGIP-III) were purified from the leek tissue. The two more abundant PGIPs (PGIP I and PGIP-III), although possessing similar pIs of about 6.5, differed in chromatographic behaviour, their molecular mass (39 and 42 kDa, respectively), and specific activity when assayed with the fungal endo-PGs. In addition, PGIP-I was solubilized from tissue homogenate with a low-salt buffer whilst PGIP-III needed a high-salt buffer for extraction (behaving as an ionically wall-bound protein). PGIP-II had very similar properties to PGIP-I, but was extracted using the high-salt buffer. The purified PGIPs and the crude leek extract showed similar inhibition activity patterns against the five fungal endo-PGs. The maximum inhibition activity was observed against the basic endo-PG from S. sclerotiorum, followed by the acidic endo-PG of S. sclerotiorum and the endo-PG from B. aclada. In contrast, no inhibition of endo-PGs from S. cepivorum and F. moniliforme was observed. Four different concentrations of the five fungal endo-PGs were incubated separately with slices of leek stalk, and the galacturonides released in the incubation mixture were measured. At every level used the endo-PGs off. moniliforme and S. cepivorum showed the maximum activity in uronide releasing. The endo-PGs of S. sclerotiorum (acidic PG) and B. aclada were active only when high levels were used while the basic endo-PG of S. sclerotiorum was not active in combustion with any level of PGIP. These results indicate that a close relationship exists between PGIP activity in vitro and the ability of PGIP to protect leek tissue from endo-PG degradation
Fungal strategies to elude polygalacturonase inhibition by plant PGIPs
No full textPolygalacturonase inhibiting proteins (PGIPs) are plant defence molecules able to block the polygalacturonase activity of fungal pathogens. However, fungi have evolved strategies to overcome PGIP inhibition. For example, Sclerotinia sclerotiorum in the early stage of soybean infection produces considerable amount of PG activity encoded by a basic pg gene. By quantitative RT-PCR it was shown that initially the transcript of this pg gene overcomes by one hundred fold the transcript of the soybean pgip gene. Thereafter, pgip gene was noticeably induced and a second pg gene was expressed. This gene encodes a PG that, in the acidic pH conditions determined in diseased tissue by fungal secretion of oxalic acid, is less sensitive to PGIP. In other cases, PGIP may fail to recognise specific PGs produced by some fungi. For example, a PG refractory to all PGIPs was isolated from a Fusarium moniliforme strain. The comparison of the amino acidic sequence of this PG with that obtained from a different F. moniliforme isolate susceptible to PGIP inhibition allowed the identification of a few amino acidic substitutions responsible for escaping inhibition. Further studies using overlap extension of the two PG sequences and site-directed mutagenesis will permit to identify specific amino acids responsible for the lack of recognition by plant PGIP
Enhancement of the wheat defence response to fungal pathogens by modifying the pectin component of the cell wall
No full textPURIFICATION AND MOLECULAR CHARACTERIZATION OF A SOYBEAN POLYGALACTURONASE-INHIBITING PROTEIN
No full textA polygalacturonase-inhibiting protein (PGIP) was detected in soybean (Glycine max (L.) Merr.) seedlings. The protein was purified from germinating seeds and appeared to consist of at least three components with very close molecular weights (between 37 and 40 kDa) but each showing a unique N-terminal sequence. Primers specific for N-terminal and C-terminal nucleotide sequences of field bean (Phaseolus vulgaris L.) PGIP were used in a polymerase chain reaction (PCR) on soybean DNA, and only one amplification band was obtained. The amplified product was cloned and one of the PCR clones was sequenced. The nucleotide sequence comprises 942 bp with a single open reading frame which encodes a polypeptide of 313 amino-acid residues with a predicted molecular weight of 33984 Daltons and an isoelectric point of 8.21. Analysis of genome organization showed a single gene copy of PGIP with few related sequences, and wounding of soybean hypocotyls showed a strong induction of expression of the PGIP gene. The PGIP showed different activities toward three purified fungal endo-polygalacturonases (endo-PGs) (two endo-PGs from Sclerotinia sclerotiorum and one endo-PG from Aspergillus niger). A possible involvement of soybean PGIP in plant defence against fungal pathogens is discussed
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
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
- …
