Photosynthesis Research (v.132, #3)

Remembering Navasard V. Karapetyan (1936–2015) by Nadezhda P. Yurina; Vladimir O. Popov; Alexander A. Krasnovsky Jr.; Govindjee (221-226).
Navasard Vaganovich Karapetyan (September 6, 1936—March 6, 2015) began his scientific career at the Bach Institute of Biochemistry of the Russian Academy of Sciences, Moscow, and was associated with this institute for over 56 years. He worked in the area of biochemistry and biophysics of photosynthesis and was especially known for his studies on chlorophyll a fluorescence in higher plants and cyanobacteria, molecular organization of Photosystem I, photoprotective energy dissipation, and dynamics of energy migration in the two photosystems. We present here a brief biography and comments on the work of Navasard Karapetyan. We remember him as an enthusiastic person who had an unflagging curiosity, energy and profound sincere interest in many aspects of photosynthesis research.
Keywords: Biochemistry and biophysics of photosynthesis; Antenna; Long-wavelength absorbing chlorophyll a ; P700; Reaction center; Fluorescence quenching; Photosystem I; Cyanobacteria

Frederick Yi-Tung Cho (1939–2011) by Govindjee; John C. Munday Jr.; George C. Papageorgiou (227-234).
We present here a Tribute to Frederick Yi-Tung Cho (1939–2011), an innovative and ingenious biophysicist and an entrepreneur. He was one of the 4 earliest PhD students [see: Cederstrand (1965)—Carl Nelson Cederstrand; coadvisor: Eugene Rabinowitch; Papageorgiou (1968)—George C. Papageorgiou (coauthor of this paper); and Munday (1968)—John C. Munday Jr. (also a coauthor of this paper)] of one of us (Govindjee) in Biophysics at the University of Illinois at Urbana-Champaign (UIUC) during the late 1960s (1963–1968). Fred was best known, in the photosynthesis circle for his pioneering work on low temperature (down to liquid helium temperature, 4 K) absorption and fluorescence spectroscopy of photosynthetic systems; he showed temperature independence of excitation energy transfer from (i) chlorophyll (Chl) b to Chl a and (ii) from Chl a 670 to Chl a 678; and temperature dependence of energy transfer from the phycobilins to Chl a and from Chl a 678 to its suggested trap. After doing research in biophysics of photosynthesis, Fred shifted to do research in solid-state physics/engineering in the Government Electronics Division (Group) of the Motorola Company, Scottsdale, Arizona, from where he published research papers in that area and had several patents granted. We focus mainly on his days at the UIUC in context of the laboratory in which he worked. We also list some of his papers and most of his patents in engineering physics. His friends and colleagues have correctly described him as an innovator and an ingenious scientist of the highest order. On the personal side, he was a very easy-going and amiable individual.
Keywords: Excitation energy transfer; Liquid helium temperature; Motorola company; Biophysics of photosynthesis; Govindjee Lab; Surface wave devices; Acoustic charge transport

We present here our tribute to an outstanding unique scientist, a pioneer of plant biochemistry, best known for his seminal ground-breaking discoveries related to electron and proton transport, and their intimate relation to ATP synthesis in chloroplasts. His dedication and in-depth understanding of science was matched by his humor. Here, we offer a modest précis of his life and research. We have also included Reminiscences from: Leonard Fish, Eric Larson, Donald Ort, Thomas Owens, and Robert Turgeon.
Keywords: ATP; Chemiosmosis; Proton gradient; Photophosphorylation

Uncertainty in measurements of the photorespiratory CO2 compensation point and its impact on models of leaf photosynthesis by Berkley J. Walker; Douglas J. Orr; Elizabete Carmo-Silva; Martin A. J. Parry; Carl J. Bernacchi; Donald R. Ort (245-255).
Rates of carbon dioxide assimilation through photosynthesis are readily modeled using the Farquhar, von Caemmerer, and Berry (FvCB) model based on the biochemistry of the initial Rubisco-catalyzed reaction of net C3 photosynthesis. As models of CO2 assimilation rate are used more broadly for simulating photosynthesis among species and across scales, it is increasingly important that their temperature dependencies are accurately parameterized. A vital component of the FvCB model, the photorespiratory CO2 compensation point (Γ *), combines the biochemistry of Rubisco with the stoichiometry of photorespiratory release of CO2. This report details a comparison of the temperature response of Γ * measured using different techniques in three important model and crop species (Nicotiana tabacum, Triticum aestivum, and Glycine max). We determined that the different Γ * determination methods produce different temperature responses in the same species that are large enough to impact higher-scale leaf models of CO2 assimilation rate. These differences are largest in N. tabacum and could be the result of temperature-dependent increases in the amount of CO2 lost from photorespiration per Rubisco oxygenation reaction.
Keywords: Rubisco; Photorespiration; Temperature response; Modeling photosynthesis

Light dose versus rate of delivery: implications for macroalgal productivity by Matthew J. Desmond; Daniel W. Pritchard; Christopher D. Hepburn (257-264).
The role of how light is delivered over time is an area of macroalgal photosynthesis that has been overlooked but may play a significant role in controlling rates of productivity and the structure and persistence of communities. Here we present data that quantify the relative influence of total quantum dose and delivery rate on the photosynthetic productivity of five ecologically important Phaeophyceae species from southern New Zealand. Results suggested that greater net oxygen production occurs when light is delivered at a lower photon flux density (PFD) over a longer period compared to a greater PFD over a shorter period, given the same total dose. This was due to greater efficiency (α) at a lower PFD which, for some species, meant a compensatory effect can occur. This resulted in equal or greater productivity even when the total quantum dose of the lower PFD was significantly reduced. It was also shown that light limitation at Huriawa Peninsula, where macroaglae were sourced, may be restricting the acclimation potential of species at greater depths, and that even at shallow depth periods of significant light limitation are likely to occur. This research is of particular interest as the variability of light delivery to coastal reef systems increases as a result of anthropogenic disturbances, and as the value of in situ community primary productivity estimates is recognised.
Keywords: Photosynthesis; Photon flux density; Macroalgae; Productivity; Light dose; Light delivery

Light-induced formation of dimeric LHCII by Ewa Janik; Joanna Bednarska; Karol Sowinski; Rafal Luchowski; Monika Zubik; Wojciech Grudzinski; Wieslaw I. Gruszecki (265-276).
It emerges from numerous experiments that LHCII, the major photosynthetic antenna complex of plants, can appear not only in the trimeric or monomeric states but also as a dimer. We address the problem whether the dimeric form of the complex is just a simple intermediate element of the trimer–monomer transformation or if it can also be a physiologically relevant molecular organization form? Dimers of LHCII were analyzed with application of native electrophoresis, time-resolved fluorescence spectroscopy, and fluorescence correlation spectroscopy. The results reveal the appearance of two types of LHCII dimers: one formed by the dissociation of one monomer from the trimeric structure and the other formed by association of monomers into a distinctively different molecular organizational form, characterized by a high rate of chlorophyll excitation quenching. The hypothetical structure of such an energy quencher is proposed. The high light-induced LHCII dimerization is discussed as a potential element of the photoprotective response in plants.
Keywords: LHCII complex; Dimer; Photoprotection; Fluorescence quenching; Spinacia oleracea

Ecosystem CO2 fluxes measured with eddy-covariance techniques provide a new opportunity to retest functional responses of photosynthesis to abiotic factors at the ecosystem level, but examining the effects of one factor (e.g., temperature) on photosynthesis remains a challenge as other factors may confound under circumstances of natural experiments. In this study, we developed a data mining framework to analyze a set of ecosystem CO2 fluxes measured from three eddy-covariance towers, plus a suite of abiotic variables (e.g., temperature, solar radiation, air, and soil moisture) measured simultaneously, in a Californian oak-grass savanna from 2000 to 2015. Natural covariations of temperature and other factors caused remarkable confounding effects in two particular conditions: lower light intensity at lower temperatures and drier air and soil at higher temperatures. But such confounding effects may cancel out. At the ecosystem level, photosynthetic responses to temperature did follow a quadratic function on average. The optimum value of photosynthesis occurred within a narrow temperature range (i.e., optimum temperature, T opt): 20.6 ± 0.6, 18.5 ± 0.7, 19.2 ± 0.5, and 19.0 ± 0.6 °C for the oak canopy, understory grassland, entire savanna, and open grassland, respectively. This paradigm confirms that photosynthesis response to ambient temperature changes is a functional relationship consistent across leaf–canopy–ecosystem scales. Nevertheless, T opt can shift with variations in light intensity, air dryness, or soil moisture. These findings will pave the way to a direct determination of thermal optima and limits of ecosystem photosynthesis, which can in turn provide a rich resource for baseline thresholds and dynamic response functions required for predicting global carbon balance and geographic shifts of vegetative communities in response to climate change.
Keywords: Growth temperature; Temperature dependence; Thermal adaptation; Thermal acclimation; Net ecosystem exchange of CO2 ; Gross primary productivity

Our previous studies indicated that high light induced significant photoinhibition of photosystem I (PSI) in the shade-establishing tree species Psychotria henryi. However, the underlying mechanism has not been fully clarified. In the present study, in order to investigate the mechanism of PSI photoinhibition in P. henryi, we treated detached leaves with constant high light in the presence of methyl viologen (MV) or a soluble α-tocopherol analog, 2,2,5,7,8-pentamethyl-6-chromanol (PMC). We found that MV significantly depressed photochemical quantum yields in PSI and PSII when compared to PMC. On condition that no PSI photoinhibition happened, although cyclic electron flow (CEF) was abolished in the MV-treated samples, P700 oxidation ratio was maintain at higher levels than the PMC-treated samples. In the presence of PMC, PSI photoinhibition little changed but PSII photoinhibition was significantly alleviated. Importantly, PSI photoinhibition was largely accelerated in the presence of MV, which stimulates the production of superoxide and subsequently other reactive oxygen species at the chloroplast stroma by accepting electrons from PSI. Furthermore, MV largely aggravated PSII photoinhibition when compared to control. These results suggest that high P700 oxidation ratio cannot prevent PSI photoinhibition in P. henryi. Furthermore, the superoxide produced in the chloroplast stroma is critical for PSI photoinhibition in the higher plant P. henryi, which is opposite to the mechanism underlying PSI photoinhibition in Arabidopsis thaliana and spinach. These findings highlight a new mechanism of PSI photoinhibition in higher plants.
Keywords: Chlorophyll fluorescence; Methyl viologen; P700 oxidation; Photosystem I; Photoinhibition; Superoxide

A simple and efficient method to prepare pure dimers and monomers of the cytochrome b 6 f complex from spinach by María A. Luján; Patricia Lorente; Valter Zazubovich; Rafael Picorel (305-309).
Using a single size-exclusion chromatography we were able to isolate highly pure dimers and monomers of the Cyt b 6 f complex from spinach from a bulk preparation of that protein complex obtained with a standard procedure. At higher protein/detergent ratio during the chromatography most of the Cyt b 6 f complex remained as dimers. In contrast, at lower protein/detergent ratio (around 15 times lower), most dimers became monomerized. As a bonus, this chromatography also allowed the elimination of potential Chl a contaminant to the Cyt b 6 f preparations. SDS-PAGE protein analysis with 18% (w/v) acrylamide revealed the loss of the ISP subunit in our monomeric preparation. However, it fully retained the content of Chl a, a prerequisite to perform any spectroscopic study involving this unique pigment.
Keywords: Cytochrome b 6 f ; Photosynthesis; Plant; Protein; Purification; SDS-PAGE

Absorptance determinations on multicellular tissues by Román Manuel Vásquez-Elizondo; Lyz Legaria-Moreno; Miguel Ángel Pérez-Castro; Wiebke E. Krämer; Tim Scheufen; Roberto Iglesias-Prieto; Susana Enríquez (311-324).
The analysis of the variation of the capacity and efficiency of photosynthetic tissues to collect solar energy is fundamental to understand the differences among species in their ability to transform this energy into organic molecules. This analysis may also help to understand natural changes in species distribution and/or abundance, and differences in species ability to colonize contrasting light environments or respond to environmental changes. Unfortunately, the challenge that optical determinations on highly dispersive samples represent has strongly limited the progression of this analysis on multicellular tissues, limiting our knowledge of the role that optical properties of photosynthetic tissues may play in the optimization of photosynthesis and growth of benthonic primary producers. The aim of this study is to stimulate the use of optical tools in marine eco-physiology, offering a succinct description of the more convenient tools and also solutions to resolve the more common technical difficulties that arise while performing optical determinations on highly dispersive samples. Our study focuses on two-dimensional (2D-) parameters: absorptance, transmittance, and reflectance, and illustrates with correct and incorrect examples, specific problems and their respective solutions. We also offer a general view of the broad variation in light absorption shown by photosynthetic structures of marine primary producers, and its low association with pigment content. The ecological and evolutionary functional implications of this variability deserve to be investigated across different taxa, populations, and marine environments.
Keywords: Light absorption; Scattering; Absorptance; Reflectance; Transmittance; Macrophytes; Corals