1,721,013 research outputs found
Investigation on Photosystem II functional antenna size and excitonic connectivity in Selaginella martensii.
No full textIn an ancient vascular plant the intermediate relaxing component of NPQ depends on a reduced stroma: Evidence from dithiothreitol treatment
No full textIn plants, the non-photochemical quenching of chlorophyll fluorescence (NPQ) induced by high light reveals the occurrence of a multiplicity of regulatory processes of photosynthesis, primarily devoted to photoprotection of photosystem I and II (PSI and PSII). The study of NPQ relaxation in darkness allows the separation of three kinetically distinct phases: the fast relaxing high-energy quenching qE, the intermediate relaxing phase and the nearly non-relaxatable photoinhibitory quenching. Several processes can underlie the intermediate phase. In the ancient vascular plant Selaginella martensii (Lycopodiophyta) this component, here termed qX, was previously proposed to reflect mainly a photoprotective energy-spillover from PSII to PSI. It is hypothesized that qX is induced by an over-reduced photosynthetic electron transport chain from PSII to final acceptors. To test this hypothesis the leaves were treated with the reductant dithiothreitol (DTT) and the chlorophyll fluorescence changes were analysed during the induction with high irradiance and the subsequent relaxation in darkness. DTT treatment caused the well-known decrease in NPQ induction and expectedly resulted in a disturbed photosynthetic electron flow. The relaxation curves of Y(NPQ), formally representing the quantum yield of the regulatory thermal dissipation, revealed a DTT dose-dependent decrease in amplitude not only of qE, but also of qX, up to the complete disappearance of the latter. Modelling of the relaxation curves under alternative scenarios led to the conclusion that DTT is permissive with respect to qX induction but suppresses its dark relaxation. The strong dependence of qX on the chloroplast redox state is discussed with respect to its proposed energy-spillover photoprotective significance in a lycophyte
Effects of long-term light acclimation on Photosystem II functional antenna size and excitonic connectivity in Selaginella martensii.
No full textLycophyte division is composed of ancient vascular plants that diverged from euphyllophyte lineage ca. 400 million years ago. Among these, Selaginella martensii Spring has evolved to inhabit shade environments of tropical-equatorial rainforests. However, this plant is also able to acclimate efficiently to light regimes as different as deep shade and full sunlight (Ferroni et al. 2016, 2021). Such characteristic reveals a marked flexibility of the photosynthetic machinery in response to the light availability, but the underlying structural and dynamic acclimation features have been clarified only partially. In fact, differently from most seed plants, S. martensii is unable to modulate the content of Photosystem II antenna complexes (LHCII), which remains constant from deep shade to full sunlight regime, while the ratio between PSII and PSI decreases. In order to clarify the light acclimation features in S. martensii under deep-shade (L), intermediate shade (M) and full sunlight (H), we analyzed some functional aspects of light harvesting and electron transport after the plants' exposure to dark for 20 minutes, far red (FR) light for 20 minutes and moderate light for 1 hour. The analysis was performed using a HandyPEA (Hansatech, UK) fluorometer, which allowed us to calculate the JIP-test parameters. Among these, we particularly focused on ABS/RC, i.e. the functional antenna size of a PSII unit (Stirbet and Govindjee 2011). We also used the fluorescence transients to calculate the PSII excitonic connectivity parameters, which describe the probability of excitation transfer between different PSII units (Stirbet 2013). Our results suggest that the acclimation to different light regimes influences both PSII functional antenna size and PSII connectivity, but the direction of changes apparently contrasted with expectations. On one hand, the PSII antenna size was only slightly variable from L to H plants. On the other hand, PSII connectivity was in general far lower when compared to common values reported for seed plants. Especially H plants reported connectivity values close to 0, suggesting a "puddle" organization of PSII
Photosystem II photoinhibition and photoprotection in a lycophyte, Selaginella martensii
No full textThe Lycophyte Selaginella martensii efficiently acclimates to diverse light environments, from deep shade to full sunlight. The plant does not modulate the abundance of the Light Harvesting Complex II, mostly found as a free trimer, and does not alter the maximum capacity of thermal dissipation (NPQ). Nevertheless, the photoprotection is expected to be modulatable upon long-term light acclimation to preserve the photosystems (PSII, PSI). The effects of long-term light acclimation on PSII photoprotection were investigated using the chlorophyll fluorometric method known as “photochemical quenching measured in the dark” (qPd). Singularly high-qPd values at relatively low irradiance suggest a heterogeneous antenna system (PSII antenna uncoupling). The extent of antenna uncoupling largely depends on the light regime, reaching the highest value in sun-acclimated plants. In parallel, the photoprotective NPQ (pNPQ) increased from deep-shade to high-light grown plants. It is proposed that the differences in the long-term modulation in the photoprotective capacity are proportional to the amount of uncoupled LHCII. In deep-shade plants, the inconsistency between invariable maximum NPQ and lower pNPQ is attributed to the thermal dissipation occurring in the PSII core
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
The mechanisms of rejection in solid organ transplantation
No full textOrgan transplantation represents the preferred treatment option for many patients in terminal organ failure. The half-life of transplanted organs, however, is still far from being satisfactory with the vast majority of the organs failing within the first two decades following transplantation. At this stage, it has become apparent that rejection (prevalently mediated by humoral events) remains the primary cause of graft loss after the first year. In this light, studies are underway to better comprehend the immune events underlying graft rejection and novel immunosuppressive strategies are being explored. In this context, therapeutic apheresis techniques, that include therapeutic plasma exchange (TPE), immunoadsorption (IA) and extracorporeal photochemotherapy (ECP), represent an important adjunct in the current immunosuppressive armamentarium. This article briefly reviews our current understanding of the immune process underlying rejection of a solid organ transplant and describes the principal areas of application of therapeutic apheresis techniques in transplantation
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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