1,720,995 research outputs found
How a liverwort reacts to wounding: tracing the evolution of defence responses in the nonvascular plant Marchantia polymorpha
Full text linkLight intensity activation of alternative electron transport mechanisms in the moss Physcomitrium patens
Full text linkPhotosynthetic organisms exploit sunlight to drive an electron transport chain and obtain the chemical energy supporting their metabolism. In highly dynamic environmental conditions, excitation energy and electron transport need to be continuously modulated to prevent over-reduction and the consequent damage. An essential role in the regulation of electron transport is played by alternative electron transport mechanisms such as cyclic electron transport (CET) facilitated by PGRL1/PGR5 and NDH complex and pseudo-cyclic electron transport (PCET) mediated by the flavodiiron proteins (FLV) and the Mehler reaction. In this work mutant lines of the moss Physcomitrium patens depleted in PCET (flva KO) or CET (pgrl1/ndhm KO) were compared to wild-type plants for their ability to regulate photosynthetic electron transport in response to light fluctuations of different intensities. FLV activity enables a very fast increase in electron transport capacity but its impact is transient and becomes undetectable after 3 min from a light change. The FLV electron transport capacity is saturated at 100 μmol photons m−2 s−1 and does not increase even if exposed to stronger illumination. On the other hand, CET activation after an increase in illumination has a smaller contribution on electron transport capacity, but it provides a steady contribution for several minutes after a change in illumination intensity. Overall, these results demonstrate that light adapted plants CO2 fixation capacity needs approx. 3 min to adjust to different illumination intensities. In this interval CET and PCET enable adjusting temporary unbalances in electron transport, fully responding to 2–4 time increases in illumination. In case of larger increases, these mechanisms still contribute to protection from light damage by reducing the accumulation of electrons at PSI acceptor side. While the two mechanisms play an overlapping function, their activity shows distinctive kinetics and electron transport capacity thus they are complementary in ensuring optimal photoprotection
Role and regulation of class-C flavodiiron proteins in photosynthetic organisms
No full textThe regulation of photosynthesis is crucial to efficiently support the assimilation of carbon dioxide and to prevent photodamage. One key regulatory mechanism is the pseudo-cyclic electron flow (PCEF) mediated by class-C flavodiiron proteins (FLVs). These enzymes use electrons coming from Photosystem I (PSI) to reduce oxygen to water, preventing over-reduction in the acceptor side of PSI. FLVs are widely distributed among organisms performing oxygenic photosynthesis and they have been shown to be fundamental in many different conditions such as fluctuating light, sulfur deprivation and plant submersion. Moreover, since FLVs reduce oxygen they can help controlling the redox status of the cell and maintaining the microoxic environment essential for processes such as nitrogen fixation in cyanobacteria. Despite these important roles identified in various species, the genes encoding for FLV proteins have been lost in angiosperms where their activity could have been at least partially compensated by a more efficient cyclic electron flow (CEF). The present work reviews the information emerged on FLV function, analyzing recent structural data that suggest FLV could be regulated through a conformational change
Flavodiiron proteins in Physcomitrium patens: navigating the edge between photoprotection and efficiency
Full text linkSunlight is the primary energy source for photosynthetic organisms, driving electron transport that supports the synthesis of ATP and NADPH. In dynamic environmental conditions, photosynthetic electron transport requires continuous modulation to prevent over-reduction and safeguard against potential damage. Flavodiiron proteins (FLV) contribute to photoprotection by accepting electrons downstream of Photosystem I, reducing oxygen to water. FLV were shown to have a seminal role in response to abrupt changes in illumination intensity in various photosynthetic organisms, such as cyanobacteria, green algae, mosses, and gymnosperms but were lost during evolution of angiosperms. In this work, Physcomitrium patens plants with strong FLV accumulation, up to 20 times higher than WT, were isolated. Overexpressor plants exhibited faster activation of electron transport but did not gain additional tolerance to light fluctuations, suggesting that the contribution to photoprotection from the FLV was already saturated in WT plants. On the contrary, strong protein overexpression caused a growth penalty under steady low or high light intensity suggesting that FLV overaccumulation can be detrimental, at least in some conditions, opening hypotheses to explain why these proteins were lost during the evolution of angiosperms
Role of heat dissipation mechanisms in Physcomitrella patens acclimation to different light conditions
No full textRegulation of electron transport is essential for photosystem I stability and plant growth
Full text linkPhotosynthetic electron transport is regulated by cyclic and pseudocyclic electron flow (CEF and PCEF) to maintain the balance between light availability and metabolic demands. CEF transfers electrons from photosystem I to the plastoquinone pool with two mechanisms, dependent either on PGR5/PGRL1 or on the type I NADH dehydrogenase-like (NDH) complex. PCEF uses electrons from photosystem I to reduce oxygen and in many groups of photosynthetic organisms, but remarkably not in angiosperms, it is catalyzed by flavodiiron proteins (FLVs). In this study, Physcomitrella patens plants depleted in PGRL1, NDH and FLVs in different combinations were generated and characterized, showing that all these mechanisms are active in this moss. Surprisingly, in contrast to flowering plants, Physcomitrella patens can cope with the simultaneous inactivation of PGR5- and NDH-dependent CEF but, when FLVs are also depleted, plants show strong growth reduction and photosynthetic activity is drastically reduced. The results demonstrate that mechanisms for modulation of photosynthetic electron transport have large functional overlap but are together indispensable to protect photosystem I from damage and they are an essential component for photosynthesis in any light regime
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
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