Photosynthesis Research (v.129, #2)

Gernot Renger (1937–2013): his life, Max-Volmer Laboratory, and photosynthesis research by Ulrich Siggel; Franz-Josef Schmitt; Johannes Messinger (109-127).
Gernot Renger (October 23, 1937–January 12, 2013), one of the leading biophysicists in the field of photosynthesis research, studied and worked at the Max-Volmer-Institute (MVI) of the Technische Universität Berlin, Germany, for more than 50 years, and thus witnessed the rise and decline of photosynthesis research at this institute, which at its prime was one of the leading centers in this field. We present a tribute to Gernot Renger’s work and life in the context of the history of photosynthesis research of that period, with special focus on the MVI. Gernot will be remembered for his thought-provoking questions and his boundless enthusiasm for science.
Keywords: Max-Volmer-Institute; Horst T. Witt; Photosystem II; Oxygen evolving complex; Water oxidizing complex (WOC); ADRY agent; Mechanism of water splitting

Remembering Joan (Jan) Mary Anderson (1932–2015) by Wah Soon Chow; Peter Horton; Martin Barrett; Charles Barry Osmond (129-146).
Joan Mary Anderson, known to most people as Jan, was born on May 12, 1932 in Dunedin, New Zealand. She died on August 28, 2015 in Canberra, Australia. To celebrate her life, we present here a brief biography, some comments on her discoveries in photosynthesis during a career spanning more than half a century, and reminiscences from family and friends. We remember this wonderful person who had an unflagging curiosity, creative ability to think laterally, enthusiasm, passion, generosity and love of color and culture.
Keywords: Bertil Andersson; Keith Boardman; Lateral heterogeneity; Molecular organization of thylakoids; Photosystems; Stoichiometry of photosystems

Cyanobacterial ultrastructure in light of genomic sequence data by C. R. Gonzalez-Esquer; J. Smarda; R. Rippka; S. D. Axen; G. Guglielmi; M. Gugger; C. A. Kerfeld (147-157).
Cyanobacteria are physiologically and morphologically diverse photosynthetic microbes that play major roles in the carbon and nitrogen cycles of the biosphere. Recently, they have gained attention as potential platforms for the production of biofuels and other renewable chemicals. Many cyanobacteria were characterized morphologically prior to the advent of genome sequencing. Here, we catalog cyanobacterial ultrastructure within the context of genomic sequence information, including high-magnification transmission electron micrographs that represent the diversity in cyanobacterial morphology. We place the image data in the context of tabulated protein domains—which are the structural, functional, and evolutionary units of proteins—from the 126 cyanobacterial genomes comprising the CyanoGEBA dataset. In particular, we identify the correspondence between ultrastructure and the occurrence of genes encoding protein domains related to the formation of cyanobacterial inclusions. This compilation of images and genome-level domain occurrence will prove useful for a variety of analyses of cyanobacterial sequence data and provides a guidebook to morphological features.
Keywords: Ultrastructure; Morphology; Bioinformatics; Cyanobacteria; Transmission electron microscopy; Protein domain; Carboxysome; Cyanophycin; Polyphosphate; PHB; Glycogen; Lipid droplets; Gas vesicles

The effects of CO2 and nutrient fertilisation on the growth and temperature response of the mangrove Avicennia germinans by Ruth Reef; Martijn Slot; Uzi Motro; Michal Motro; Yoav Motro; Maria F. Adame; Milton Garcia; Jorge Aranda; Catherine E. Lovelock; Klaus Winter (159-170).
In order to understand plant responses to both the widespread phenomenon of increased nutrient inputs to coastal zones and the concurrent rise in atmospheric CO2 concentrations, CO2–nutrient interactions need to be considered. In addition to its potential stimulating effect on photosynthesis and growth, elevated CO2 affects the temperature response of photosynthesis. The scarcity of experiments testing how elevated CO2 affects the temperature response of tropical trees hinders our ability to model future primary productivity. In a glasshouse study, we examined the effects of elevated CO2 (800 ppm) and nutrient availability on seedlings of the widespread mangrove Avicennia germinans. We assessed photosynthetic performance, the temperature response of photosynthesis, seedling growth and biomass allocation. We found large synergistic gains in both growth (42 %) and photosynthesis (115 %) when seedlings grown under elevated CO2 were supplied with elevated nutrient concentrations relative to their ambient growing conditions. Growth was significantly enhanced under elevated CO2 only under high-nutrient conditions, mainly in above-ground tissues. Under low-nutrient conditions and elevated CO2, root volume was more than double that of seedlings grown under ambient CO2 levels. Elevated CO2 significantly increased the temperature optimum for photosynthesis by ca. 4 °C. Rising CO2 concentrations are likely to have a significant positive effect on the growth rate of A. germinans over the next century, especially in areas where nutrient availability is high.
Keywords: Climate change; CO2 ; Eutrophication; Mangrove; Nitrogen; Phosphorus; Photosynthesis; RUBISCO; Temperature response; Tropics

Transcriptomic analysis illuminates genes involved in chlorophyll synthesis after nitrogen starvation in Acaryochloris sp. CCMEE 5410 by Aki Yoneda; Bruce J. Wittmann; Jeremy D. King; Robert E. Blankenship; Gautam Dantas (171-182).
Acaryochloris species are a genus of cyanobacteria that utilize chlorophyll (chl) d as their primary chlorophyll molecule during oxygenic photosynthesis. Chl d allows Acaryochloris to harvest red-shifted light, which gives them the ability to live in filtered light environments that are depleted in visible light. Although genomes of multiple Acaryochloris species have been sequenced, their analysis has not revealed how chl d is synthesized. Here, we demonstrate that Acaryochloris sp. CCMEE 5410 cells undergo chlorosis by nitrogen depletion and exhibit robust regeneration of chl d by nitrogen repletion. We performed a time course RNA-Seq experiment to quantify global transcriptomic changes during chlorophyll recovery. We observed upregulation of numerous known chl biosynthesis genes and also identified an oxygenase gene with a similar transcriptional profile as these chl biosynthesis genes, suggesting its possible involvement in chl d biosynthesis. Moreover, our data suggest that multiple prochlorophyte chlorophyll-binding homologs are important during chlorophyll recovery, and light-independent chl synthesis genes are more dominant than the light-dependent gene at the transcription level. Transcriptomic characterization of this organism provides crucial clues toward mechanistic elucidation of chl d biosynthesis.
Keywords: Acaryochloris; Chlorophyll d ; Nitrogen starvation; Nitrogen recovery; RNA-Seq; Transcriptomics

Mechanisms that increase the growth efficiency of diatoms in low light by Nerissa L. Fisher; Kimberly H. Halsey (183-197).
Photoacclimation was studied in Thalassiosira pseudonana to help understand mechanisms underlying the success of diatoms in low-light environments, such as coastal and deep mixing ecosystems. Light harvesting and other cell characteristics were combined with oxygen and carbon production measurements to assess the water-splitting reaction at PSII ( $${ ext{GPP}}_{{{ ext{O}}_{2} }}$$ GPP O 2 ) and intermediate steps leading to net carbon production (NPPC). These measurements revealed that T. pseudonana is remarkably efficient at converting harvested light energy into biomass, with at least 57 % of $${ ext{GPP}}_{{{ ext{O}}_{2} }}$$ GPP O 2 retained as NPPC across all light-limited growth rates examined. Evidence for upregulation of ATP generation pathways that circumvent carbon fixation indicated that high growth efficiency at low light levels was at least partly due to increases in the efficiency of ATP production. Growth rate-dependent demands for ATP and NADPH were reflected in carbon composition and in unexpected shifts in the light-limited slope (α) of photosynthesis–irradiance relationships generated from chlorophyll-specific 14C-uptake. Overall, these results suggest that pathway gating of carbon and energy flow depends on light availability and is a key factor promoting the efficiency of diatom growth at low light intensities.
Keywords: Photoacclimation; Photosynthetic energy allocation; Photosynthesis; Phytoplankton; Diatoms; Light limitation; Alternative pathways

The purple nonsulfur bacterium Rhodopseudomonas palustris grows aerobically using oxidative phosphorylation or anaerobically using photophosphorylation. The oxygen-responsive transcription regulator, PpsR2, regulates the transition to a phototrophic lifestyle by repressing transcription of photosynthesis genes during aerobic growth. Whereas most R. palustris strains have an arginine (Arg) at position 439 in the helix-turn-helix DNA-binding domain of this protein, some strains, including the well-studied strain CGA009, have a cysteine (Cys) at this position. Using allelic exchange, we found that the Cys439 in PpsR2 resulted in increased pigmentation and photosynthetic gene expression under both aerobic and anaerobic conditions. The Cys439 substitution also conferred a growth advantage to R. palustris at low light intensities. This indicates that variation in the PpsR2 protein results in R. palustris strains that have two different thresholds for derepressing photosynthesis genes in response to oxygen and light.
Keywords: Photosynthesis; PpsR2; Rhodopseudomonas ; Bacteriophytochrome; Low light

Bacteriopheophytin triplet state in Rhodobacter sphaeroides reaction centers by Rafał Białek; Gotard Burdziński; Michael R. Jones; Krzysztof Gibasiewicz (205-216).
It is well established that photoexcitation of Rhodobacter sphaeroides reaction centers (RC) with reduced quinone acceptors results in the formation of a triplet state localized on the primary electron donor P with a significant yield. The energy of this long-lived and therefore potentially damaging excited state is then efficiently quenched by energy transfer to the RC spheroidenone carotenoid, with its subsequent decay to the ground state by intersystem crossing. In this contribution, we present a detailed transient absorption study of triplet states in a set of mutated RCs characterized by different efficiencies of triplet formation that correlate with lifetimes of the initial charge-separated state P+H A . On a microsecond time scale, two types of triplet state were detected: in addition to the well-known spheroidenone triplet state with a lifetime of ~4 μs, in some RCs we discovered a bacteriopheophytin triplet state with a lifetime of ~40 μs. As expected, the yield of the carotenoid triplet increased approximately linearly with the lifetime of P+H A , reaching the value of 42 % for one of the mutants. However, surprisingly, the yield of the bacteriopheophytin triplet was the highest in RCs with the shortest P+H A lifetime and the smallest yield of carotenoid triplet. For these the estimated yield of bacteriopheophytin triplet was comparable with the yield of the carotenoid triplet, reaching a value of ~7 %. Possible mechanisms of formation of the bacteriopheophytin triplet state are discussed.
Keywords: Carotenoid; Triplet; Bacteriopheophytin; Rhodobacter sphaeroides ; Spheroidenone

In the context of global climate change, drought is one of the major stress factors with negative effect on photosynthesis and plant productivity. Currently, chlorophyll fluorescence parameters are widely used as indicators of plant stress, mainly owing to the rapid, non-destructive and simple measurements this technique allows. However, these parameters have been shown to have limited sensitivity for the monitoring of water deficit as leaf desiccation has relatively small effect on photosystem II photochemistry. In this study, we found that blue light-induced increase in leaf transmittance reflecting chloroplast avoidance movement was much more sensitive to a decrease in relative water content (RWC) than chlorophyll fluorescence parameters in dark-desiccating leaves of tobacco (Nicotiana tabacum L.) and barley (Hordeum vulgare L.). Whereas the inhibition of chloroplast avoidance movement was detectable in leaves even with a small RWC decrease, the chlorophyll fluorescence parameters (F V/F M, V J, Ф PSII, NPQ) changed markedly only when RWC dropped below 70 %. For this reason, we propose light-induced chloroplast avoidance movement as a sensitive indicator of the decrease in leaf RWC. As our measurement of chloroplast movement using collimated transmittance is simple and non-destructive, it may be more suitable in some cases for the detection of plant stresses including water deficit than the conventionally used chlorophyll fluorescence methods.
Keywords: Chlorophyll fluorescence; Chloroplast avoidance movement; Desiccation; Relative water content; Transmittance