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Ultrastructural features, chromium content and in situ immunodetection of the 5-methylcytosine following Cr (VI) treatment in two strains of Scenedesmus acutus M. (Chlorophyceae) with different chromium sensitivity
No full textTwo strains of the unicellular green alga Scenedesmus acutus (F.J.F. Meyen) with different sensitivity to chromium (VI) were compared to evaluate their ultrastructural morphology in chromium-free and -supplemented medium with a sub-lethal concentration of Cr(VI) for 72 hours. The ultrastructural alteration in different cytological compartments indicated that Cr(VI) induced earlier and stronger alterations in the wild type (wt) compared with the chromium-tolerant strain (Cr-t). After Cr treatments, ICPMS (Inductively Coupled Plasma Mass Spectrometry) showed a higher Cr accumulation in the wild type than in the Cr-tolerant strain, suggesting a more efficient chromium-exclusion mechanism in the latter. The Cr treatment induced an increase in the nuclear area and a rearrangement in the eu-heterochromatic fraction, suggesting that chromatin remodelling could be at the basis of differential gene expression and metal tolerance. To gain additional information on the remodelling of the nuclear chromatin, we analysed DNA methylation by immunolocalization of 5-methyl-cytosine, before and after Cr exposure. Significant differences in the quantification of the immunolabelling of DNA cytosine-rich zones between the two strains were observed. These data suggest that an epigenetic mechanism could be at the basis of the Cr tolerance in S. acutus, as supported by previous data reporting that the acquired tolerance was inherited and maintained through the progeny
Role of DNA methylation in the chromium tolerance of Scenedesmus acutus (Chlorophyceae) and its impact on the sulfate pathway regulation
Full text linkDNA methylation is a very important epigenetic modification that participates in many biological functions. Although many researches on DNA methylation have been reported in various plant species, few studies have assessed the global DNA methylation pattern in algae. Even more the complex mechanisms by which DNA methylation modulates stress in algae are yet largely unresolved, mainly with respect to heavy metal stress, for which in plants, metal- and species- specific responses were instead evidenced. In this work, we performed a comparative Whole-Genome Bisulfite Sequencing (WGBS) on two strains of the green alga Scenedesmus acutus with different Cr(VI) sensitivity. The pattern of distribution of 5-mC showed significant differences between the two strains concerning both differentially methylated local contexts (CG, CHG and CHH) and Differentially Methylated Regions (DMRs) as well. We also demonstrated that DNA methylation plays an important role in modulating some genes for sulfate uptake/assimilation confirming the involvement of the sulfate pathway in the Cr-tolerance. Our results suggest that DNA methylation may be of particular importance in defining signal specificity associated with Cr-tolerance and in establishing new epigenetic marks which contribute to the adaptation to metal stress and also to transmit the epigenomic traits to the progeny
Role of Sulfate Transporters in Chromium Tolerance in <i>Scenedesmus acutus</i> M. (Sphaeropleales)
Full text linkSulfur (S) is essential for the synthesis of important defense compounds and in the scavenging potential of oxidative stress, conferring increased capacity to cope with biotic and abiotic stresses. Chromate can induce a sort of S-starvation by competing for uptake with SO42− and causing a depletion of cellular reduced compounds, thus emphasizing the role of S-transporters in heavy-metal tolerance. In this work we analyzed the sulfate transporter system in the freshwater green algae Scenedesmus acutus, that proved to possess both H+/SO42− (SULTRs) and Na+/SO42− (SLTs) plasma membrane sulfate transporters and a chloroplast-envelope localized ABC-type holocomplex. We discuss the sulfate uptake system of S. acutus in comparison with other taxa, enlightening differences among the clade Sphaeropleales and Volvocales/Chlamydomonadales. To define the role of S transporters in chromium tolerance, we analyzed the expression of SULTRs and SULPs components of the chloroplast ABC transporter in two strains of S. acutus with different Cr(VI) sensitivity. Their differential expression in response to Cr(VI) exposure and S availability seems directly linked to Cr(VI) tolerance, confirming the role of sulfate uptake/assimilation pathways in the metal stress response. The SULTRs up-regulation, observed in both strains after S-starvation, may directly contribute to enhancing Cr-tolerance by limiting Cr(VI) uptake and increasing sulfur availability for the synthesis of sulfur-containing defense molecules
A putative phytochelatin is involved in Cr(VI) tolerance in strict relation with sulphur metabolism in Scenedesmus acutus (Chlorophyceae).
No full textGoing 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
The role of Phytochelatin Synthase in the microalga Scenedesmus acutus M. (Sphaeropleales).
No full textThe role of Phytochelatin Synthase in the microalga Scenedesmus acutus M. (Sphaeropleales)
M. Ferrari, R. Cozza, M. Marieschi, R. Ruotolo, A. Torelli
Phytochelatins (PCs) are small cysteine-rich peptides that are not genetically encoded but are synthesized by Phytochelatin Synthase (PCS) in the presence of glutathione as substrate. The constitutive expression of PCS and the presence of homologues of the PCS gene(s) in plants growing in ecosystems geographically remote from metal-contaminated sites, as well as in representatives of various kingdoms of living organisms, suggest that PCS has a wide range of different functions (Clemens et al. 2009). However, the main function of PCs in plants is to immobilize, sequester, and detoxify metal ions (Shukla et al. 2013). The effect of metals on the activity of PCS can differ not only between species, but also between different isoforms of the enzyme within a species.
Although it is evident that chromium (Cr) ions can stimulate the formation of PCs in plants (Yu et al. 2018), there is no information on their presence in algae in response to Cr exposure.
In this study, two strains of the green alga Scenedesmus acutus with different Cr(VI) sensitivity, namely the wild type (wt) and the chromium-tolerant strain (Cr-t), were selected as a model algal species to increase the knowledge on the role of PCs in Cr responses in microalgae.
We previously reported the first evidence for a PCS gene (SaPCS) from the microalga S. acutus. More recently, we have also identified two SaPCS isoforms due to a putative alternative splicing.
To define the role of PCS in Cr detoxification, we analyzed the levels of SaPCS transcription, and the abundance of PCS by using RT-qPCR and Western blot, respectively, in both strains of S. acutus after 24h culture in standard and in Cr supplemented medium (1 and 2 mg Cr (VI)/l).
Given the relationship between sulfur (S) metabolism and Cr(VI) tolerance in S. acutus (Sardella et al. 2019), we also performed the same analyses in S-replete cells of both strains after medium renewal following S-starvation.
The results showed a different behavior between strains in the stress response. RT-qPCR analysis revealed an increase in SaPCS transcription after Cr(VI) stress and after medium renewal following S-starvation in wt cells. Instead, the Cr-t strain induced SaPCS transcription only under S-replete conditions.
Western blot analysis, performed with a polyclonal antibody raised against PCS of Arabidopsis thaliana, revealed an immunoreaction signal on two proteins with molecular weights of approximately 73 and 37 kDa. While the abundance of the 73 kDa protein did not change after the stresses studied in the two strains, the 37 kDa protein increased after S-starvation in both strains but in a significant manner only in wt.
Finally, a preliminary quantification of PC production was performed, through LC Mass analysis in the two strains in preculture with or without S and under 1 mg Cr(VI)/l, which showed no modulation of PC abundance in response to Cr(VI) stress and/or S deprivation. Nevertheless, the Cr-t strain maintained PCs level significantly higher than the wt at the end of S-starvation.
These observations suggest that PCS in S. acutus may not be involved in Cr(VI) detoxification, but may play a role in intracellular sulfur balance or in the cell homeostasis during stress.
The PC production in the other experimental conditions (i.e. exposures longer than those studied and different Cr(VI) concentrations) should be investigated to better clarify the role of the enzyme in Cr(VI) detoxification.
Letteratura citata
Shukla D., Tiwari M., Tripathi E.D., Nath P., Trivedi P.K. (2013). Synthetic phytochelatins complement a phytochelatin-deficient Arabidopsis mutant and enhance the accumulation of heavy metal(loid)s. Biochem Biophy Res Commun 434:664–669
Clemens S., Peršoh D. (2009). Multi-tasking phytochelatin synthases. Plant Sci., 177, 266–271.
Yu, X.Z., Ling, Q.L., Li, Y.H., Lin Y.J. (2018) mRNA Analysis of Genes Encoded with Phytochelatin Synthase (PCS) in Rice Seedlings Exposed to Chromium: The Role of Phytochelatins in Cr Detoxification. Bull Environ Contam Toxicol 101, 257–261.
Sardella A., Marieschi M., Mercatali I., Zanni C., Gorbi G., Torelli A. (2019). The relationship between sulfur metabolism and tolerance of hexavalent chromium in Scenedesmus acutus (Spheropleales): Role of ATP sulfurylase. Aquatic Toxicology, 216:105320.
AUTORI
Michele Ferrari ([email protected]), Radiana Cozza, Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci, 87036 Rende (CS).
Matteo Marieschi, Roberta Ruotolo, Anna Torelli, Department of Life Sciences, University of Parma, Parco Area delle Scienze 11/A, 43124 Parm
Phytochelatin Synthase: An In Silico Comparative Analysis in Cyanobacteria and Eukaryotic Microalgae
No full textPhytochelatins (PCs) are small cysteine-rich peptides involved in metal detoxification, not
genetically encoded but enzymatically synthesized by phytochelatin synthases (PCSs) starting from
glutathione. The constitutive PCS expression even in the absence of metal contamination, the wide
phylogenetic distribution and the similarity between PCSs and the papain-type cysteine protease
catalytic domain suggest a wide range of functions for PCSs. These proteins, widely studied in land
plants, have not been fully analyzed in algae and cyanobacteria, although these organisms are the first
to cope with heavy-metal stress in aquatic environments and can be exploited for phytoremediation.
To fill this gap, we compared the features of the PCS proteins of different cyanobacterial and algal
taxa by phylogenetic linkage. The analyzed sequences fall into two main, already known groups
of PCS-like proteins. Contrary to previous assumptions, they are not classed as prokaryotic and
eukaryotic sequences, but rather as sequences characterized by the alternative presence of asparagine
and aspartic/glutamic acid residues in proximity of the catalytic cysteine. The presence of these
enzymes with peculiar features suggests differences in their post-translational regulation related to
cell/environmental requirements or different cell functions rather than to differences due to their
belonging to different phylogenetic tax
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
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