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Honoring two stalwarts of photosynthesis research: Eva-Mari Aro and Govindjee
No full textOn behalf of the entire photosynthesis community, it is an honor, for us, to write about two very eminent scientists who were recently recognised with a Lifetime Achievement Award from the International Society of Photosynthesis Research (ISPR) on August 5, 2022; this prestigious Award was given during the closing ceremony of the 18th International Congress on Photosynthesis Research in Dunedin, New Zealand. The awardees were: Professor Eva-Mari Aro (Finland) and Professor Emeritus Govindjee Govindjee (USA). One of the authors, Anjana Jajoo, is especially delighted to be a part of this tribute to professors Aro and Govindjee as she was lucky enough to have worked with both of them
The Fo and the O-J-I-P fluorescence rise in higher plants and algae
No full textThe variable chlorophyll (Chl) a fluorescence yield is related to the photochemical activity of photosystem II (PS II) of the oxygen evolving organisms. The kinetics of the fluorescence rise from the minimal yield Fo to the maximal yield Fm is a monitor of the accumulation of net reduced Qa with time in both active (Qb-containing) and inactive (non-Qb) PS II centers. The measurements of true Fo and that of the complete fluorescence transient from true Fo to Fm are useful in obtaining a kinetic picture of PS II activity. Using a shutter-less system (Plant Efficiency Analyzer, Hansatech, UK) that is capable of providing the first measured point at about 20 microseconds and that allows data accumulation over several orders of magnitude of time, we have measured the complete fluorescence transient in low and moderate (up to 700 W m-2 ) light intensities in several photosynthetic systems (higher plant leaves and chloroplasts; and the cell suspensions of green alga Chlamydomonas reinhardtii and several of its herbicide-resistant mutants, altered in single amino acids in its Dl protein). In all cases, the fluorescence transient follows a regular pattern of O-J-I-P—T, where two intermediate inflections J (at about 2 ms) and I (at about 20 ms) appear between Fo and Fm levels. Furthermore, the ratio of Fm to Fo is about 5 in all cases and the lowered published ratio in several cases is suggested to be due to the J level being mistaken for Fo. We also present data on the effects of varying the dark times between preillumination and measurements of the transient, on the intensity dependence, and on the effect of the addition of diuron. The relationship of the 0-J rise to the fast fluorescence rise observed by other investigators will also be discussed.
Chlorophyll (Chl) a fluorescence transients provide information on the photochemical efficiency of photosystem I I (PS I I) of the oxygen evolving organisms 1,2,3,4. Fo ( or the 0 level) level is the “Instantaneous” low fluorescence when photochemical efficiency is maximal; here, the concentration of the electron acceptor Qa is maximal. Measurement of true Fo level is not a trivial problem in instruments that use camera shutters. Most mechanical shutters have a full opening time of one or more ms. On the other hand, light emitting diode has the advantage that no shutter is needed and the time resolution can be as short as 500 ns.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
The evolution of photosynthesis and chloroplasts
Get PDFThis review focuses on what has been learned about the evolution of photosynthesis in the past five years, and omits evolution of CO2 assimilation. Oxygenic photosynthesis (using both photosystems I and II) has evolved from anoxygenic photosynthesis. The latter occurs in different variants, using either a type 1 photosystem resembling photosystem I, or a type 2 photosystem resembling photosystem II. Opinions differ as to how two types of photosystem came to be combined in the same organism, whether by gene transfer between bacteria, by fusion of bacteria, or as a result of gene duplication and evolution within one kind of bacterium. There are also different opinions about when oxygenic photosynthesis arose, in conjunction with the Great Oxygenation Event, 2.3 billion years before the present, or more than a billion years before that. Cyanobacteria were the first organisms to carry out oxygenic photosynthesis. Some of them gave rise to chloroplasts, while others continued to evolve as independent organisms, and the review outlines both lines of evolution. At the end we consider the evolution of photosynthesis in relation to the evolution of our planet
Bicarbonate is a key regulator but not a substrate for O2 evolution in Photosystem II
Get PDFPhotosystem II (PSII) uses light energy to oxidize water and to reduce plastoquinone in the photosynthetic electron transport chain. O2 is produced as a byproduct. While most members of the PSII research community agree that O2 originates from water molecules, alternative hypotheses involving bicarbonate persist in the literature. In this perspective, we provide an overview of the important roles of bicarbonate in regulating PSII activity and assembly. Further, we emphasize that biochemistry, spectroscopy, and structural biology experiments have all failed to detect bicarbonate near the active site of O2 evolution. While thermodynamic arguments for oxygen-centered bicarbonate oxidation are valid, the claim that bicarbonate is a substrate for photosynthetic O2 evolution is challenged
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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