1,720,963 research outputs found
The polyamines and their catabolic products are significant players in the turnover of nitrogenous molecules in plants
No full text""Polyamines (PAs) are nitrogenous molecules which play a well-established role in most cellular processes during growth and development under physiological or biotic\\\/abiotic stress conditions. The molecular mode(s) of PA action have only recently started to be unveiled, and comprehensive models for their molecular interactions have been proposed. Their multiple roles are exerted, at least partially, through signalling by hydrogen peroxide (H(2)O(2)), which is generated by the oxidation\\\/back-conversion of PAs by copper amine oxidases and PA oxidases. Accumulating evidence suggests that in plants the cellular titres of PAs are affected by other nitrogenous compounds. Here, we discuss the state of the art on the possible nitrogen flow in PAs, their interconnection with nitrogen metabolism, as well as the signalling roles of PA-derived H(2)O(2) during some developmental processes and stress responses.. . "
Nitrogen flow into regulatory molecules: The case of Polyamines and Polyamine oxidases.
No full text""\\"Glutamate plays a central role in the flow of nitrogen to various regulatory molecules, such as Polyamines (PAs). PAs are low MW nitrogenous molecules. The most common PAs are the diamine Putrescine (Put), the triamine Spermidine (Spd) and the tetramine Spermine (Spm). In plants, Put and Spd are the obligatory precursors of Spd and Spm, respectively. PAs have been implicated in plant growth and development, abiotic and biotic stress responses (1,2,3,4,5,6). PA oxidation is catalyzed by Di- and PA oxidases (DAO and PAOs, respectively) in the apoplast [terminal catabolism; (3)],or in the cytoplasm and the peroxisomes [PA back-conversion; (4)]. In both cases, H2O2 is generated. Recently, PA catabolism-derived H2O2 was shown to significantly participate in the physiological functions of PAs. Stress induces PA exodus into the apoplast, where it is oxidized by apoplastic PAO leading to increase of H2O2 load; this in turn participates in signalling events, inducing differential gene expression, which results to either PA homeostatic responses or the execution of programmed cell death [PCD; (4,6)]. Thus, the level of apoplastic H2O2 determines whether stress-tolerant mechanisms or the PCD syndrome will be induced. Engineering the PA catabolic pathway led to increased tolerance to biotic but sensitivity to abiotic stress (5,6). The pathway is partially controlled by the phytohormone abscissic acid (ABA), which is involved in stress-dependent signalling cascades, including those controlling stomatal closure (7). ABA induces expression of AtPAO3, a peroxisomal Arabidopsis PAO and GUS reporter analysis, revealed that cis-regulatory elements in the promoter region control this induction (8,9). Interestingly, GUS activity post-treatment with ABA was specifically localized to guard cells, implying a direct role of PAO-derived H2O2 in stomatal closure. Moreover, the complete identification and analysis of AtPAOs in Arabidopsis revealed that all four PAOs (AtPAO1, AtPAO2, AtPAO3 and AtPAO4) are back-converting Spm to Spd and additionally AtPAO2 and AtPAO3 back-convert Spd to Put (8,9). Thus, Arabidopsis seems to lack PAOs involved in terminal catabolism of PAs in contrast to maize, in which the until now characterized PAOs produce 1,3-diaminopropane and 4-aminobutanal or N-(3-aminopropyl)-4-aminobutanal from Spd or Spm oxidation, respectively. H1-NMR studies revealed that AtPAOs, in addition to H2O2 and Spd or Put, produce 3-aminopropanal, which can be further converted to the osmoprotectant molecule β-alanine and pantothenate in a pairwise reaction. The AtPAOs are differentially expressed, as revealed by GUS reporter assays, implying functional diversity inside the AtPAOs family (8,9). Furthermore, Spd Oxidase-derived H2O2 regulates pollen plasma membrane hyperpolarization-activated Ca2+-permeable channels, pollen tube growth and number of seeds (10). Also, PAO-derived H2O2 acts as a signal for deposition of secondary wall and as a mediator of developmental PCD in plant tissues resulting to suppressed primary maize root elongation by inhibiting cell growth and altering cell cycle progression (11). To sum up, all these results along with the recent finding of the involvement of AtPAOs in catabolism of thermospermine, a Spm isomer involved in vascular differentiation and stress adaptation, reveal novel aspects of the PA catabolic pathway and its genetic engineering may result to significant phenotypical and stress-tolerant genotypes. . . REFERENCES. 1.Paschalidis KA & KA Roubelakis-Angelakis (2005) Sites and regulation of polyamine catabolism in the tobacco plant. Correlations with cell division\\\\\\\/expansion, cell cycle progression, and vascular development. Plant Physiol 138(4):2174-84. 2.Paschalidis KA, PN Moschou, I Toumi & KA Roubelakis-Angelakis (2009) Polyamine anabolic\\\\\\\/catabolic regulation along the woody grapevine plant axis is linked to vascular differentiation and to stomatal closure. J Plant Physiol 166(14):1508-19. 3.Moschou, PN, ID Delis, KA Paschalidis & KA Roubelakis-Angelakis (2008) Transgenic tobacco plants overexpressing polyamine oxidase are not able to cope with oxidative burst generated by abiotic factors. Physiol Plant 133(2):140-56. 4.Moschou PN, M. Sanmartin, A. H. Andriopoulou, E. Rojo, J. J. Sanchez-Serrano & KA Roubelakis-Angelakis (2008) Bridging the gap between plant and mammalian polyamine catabolism: a novel peroxisomal polyamine oxidase responsible for a full back-conversion pathway in Arabidopsis. Plant Physiol 147(4):1845-57. 5.Moschou, PN, PF Sarris, N Scandalis, AH Andriopoulou, KA Paschalidis, NJ Panopoulos & KA Roubelakis-Angelakis (2009) Engineered polyamine catabolism preinduces tolerance of tobacco to bacteria and oomycetes. Plant Physiol 149(4):1970-81. 6.Moschou, PN, KA Paschalidis, ID Delis, AH Andriopoulou, GD Lagiotis & KA Roubelakis-Angelakis (2008) Spermidine exodus and oxidation in the apoplast induced by abiotic stress is responsible for H2O2 signatures that direct tolerance responses in tobacco. Plant Cell 20(6): 1708-24.. 7.Toumi I, PN Moschou, KA Paschalidis, S Daldoul, B Bouamama, S Chenennaoui, A Ghorbel, A Mliki & KA Roubelakis-Angelakis 2010. Abscisic acid signals reorientation of polyamine metabolism to orchestrate stress responses via the polyamine exodus pathway in grapevine. J Plant Physiol. doi:10.1016\\\\\\\/j.jplph. 2009.10.022.. 8. Fincato P, PN Moschou, V Spedatelli, R Tavazza, R Angelini, R Federico, KA Roubelakis-Angelakis & P Tavladoraki (2011) Functional diversity inside the Arabidopsis polyamine oxidase gene family. J Exp Bot 62:1155-1168 doi: 10.1093\\\\\\\/jxb\\\\\\\/erq341. 9.Fincato P, PN Moschou, A Ahou, KA Roubelakis-Angelakis, R Federico & P Tavladoraki (2011) The members of Arabidopsis thaliana PAO gene family exhibit tissue-organ specific expression pattern during seedling growth and flower development. Amino Acids DOI 10.1007\\\\\\\/s00726-011-0999-7.. 10.Wu J, H Qu, Z Shang, X Jiang, PN Moschou, KA Roubelakis-Angelakis & S Zhang (2010) Spermidine oxidase-derived H2O2 activates downstream Ca2+ channels which signal pollen tube growth in Pyrus pyrifolia. Plant J 63:1042-1053, DOI: 10.1111\\\\\\\/j.1365-313X.2010.04301.x. 11.Tisi A, R Federico, S Moreno, S Lucretti, PN Moschou, KA Roubelakis-Angelakis, R Angelini & A Cona (2011) Perturbation of polyamine catabolism can strongly affect root development and xylem differentiation. Plant Physiol. DOI:10.1104\\\\\\\/pp.111.173153.. . . \\""
Functional diversity inside the Arabidopsis polyamine oxidase gene family
No full text""Polyamine oxidases (PAOs) are FAD-dependent enzymes involved in polyamine catabolism. All so far characterized PAOs from monocotyledonous plants, such as the apoplastic maize PAO, oxidize spermine (Spm) and spermidine (Spd) to produce 1,3-diaminopropane, H(2)O(2), and an aminoaldehyde, and are thus considered to be involved in a terminal catabolic pathway. Mammalian PAOs oxidize Spm or Spd (and\\\/or their acetyl derivatives) differently from monocotyledonous PAOs, producing Spd or putrescine, respectively, in addition to H(2)O(2) and an aminoaldehyde, and are therefore involved in a polyamine back-conversion pathway. In Arabidopsis thaliana, five PAOs (AtPAO1-AtPAO5) are present with cytosolic or peroxisomal localization and three of them (the peroxisomal AtPAO2, AtPAO3, and AtPAO4) form a distinct PAO subfamily. Here, a comparative study of the catalytic properties of recombinant AtPAO1, AtPAO2, AtPAO3, and AtPAO4 is presented, which shows that all four enzymes strongly resemble their mammalian counterparts, being able to oxidize the common polyamines Spd and\\\/or Spm through a polyamine back-conversion pathway. The existence of this pathway in Arabidopsis plants is also evidenced in vivo. These enzymes are also able to oxidize the naturally occurring uncommon polyamines norspermine and thermospermine, the latter being involved in important plant developmental processes. Furthermore, data herein reveal some important differences in substrate specificity among the various AtPAOs, which suggest functional diversity inside the AtPAO gene family. These results represent a new starting point for further understanding of the physiological role(s) of the polyamine catabolic pathways in plants.. . "
Perturbation of polyamine catabolism can strongly affect root development and xylem differentiation
Full text link""Spermidine (Spd) treatment inhibited root cell elongation, promoted deposition of phenolics in cell walls of rhizodermis, xylem elements, and vascular parenchyma, and resulted in a higher number of cells resting in G(1) and G(2) phases in the maize (Zea mays) primary root apex. Furthermore, Spd treatment induced nuclear condensation and DNA fragmentation as well as precocious differentiation and cell death in both early metaxylem and late metaxylem precursors. Treatment with either N-prenylagmatine, a selective inhibitor of polyamine oxidase (PAO) enzyme activity, or N,N(1)-dimethylthiourea, a hydrogen peroxide (H(2)O(2)) scavenger, reverted Spd-induced autofluorescence intensification, DNA fragmentation, inhibition of root cell elongation, as well as reduction of percentage of nuclei in S phase. Transmission electron microscopy showed that N-prenylagmatine inhibited the differentiation of the secondary wall of early and late metaxylem elements, and xylem parenchymal cells. Moreover, although root growth and xylem differentiation in antisense PAO tobacco (Nicotiana tabacum) plants were unaltered, overexpression of maize PAO (S-ZmPAO) as well as down-regulation of the gene encoding S-adenosyl-L-methionine decarboxylase via RNAi in tobacco plants promoted vascular cell differentiation and induced programmed cell death in root cap cells. Furthermore, following Spd treatment in maize and ZmPAO overexpression in tobacco, the in vivo H(2)O(2) production was enhanced in xylem tissues. Overall, our results suggest that, after Spd supply or PAO overexpression, H(2)O(2) derived from polyamine catabolism behaves as a signal for secondary wall deposition and for induction of developmental programmed cell death. "
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
- …
