Photosynthesis Research (v.112, #2)

Berger C. Mayne (1920–2011): a friend and his contributions to photosynthesis research by Darrell Fleischman; Gerald E. Edwards; Govindjee; Leland Mayne; Vijai Tyagi; Karen Jacobsen-Mispagel (81-89).
We provide here insights on the life and work of Berger C. Mayne (1920—2011). We remember and honor Berger, whose study of photosynthesis began with the most basic processes of intersystem electron transport and oxygen evolution, continued with application of fluorescence techniques to the study of photophosphorylation and the unique features of photosystems in specialized cells, and concluded with collaborative study of photosynthesis in certain nitrogen fixing symbioses. Berger loved the outdoors and was dedicated to preserving the environment and to social justice, and was a wonderful friend.
Keywords: C4 plants; Chlorophyll; Prompt and delayed fluorescence; Hill reaction; Emerson enhancement effect; Nitrogen fixation; Photophosphorylation; Photosystem I; Photosystem II

David Alan Walker (1928–2012) by Gerald E. Edwards; Ulrich Heber (91-102).
David Alan Walker, Emeritus Professor of Biology, University of Sheffield, UK and Fellow of the Royal Society, died on February 13, 2012. David had a marvelous 60 year career as a scientist, during which he was a researcher, mentor, valued colleague, and a prolific writer in the field of photosynthesis. His career was marked by creative breakthroughs in isolation and analysis of chloroplast metabolism in vitro and simple but valuable technical advances for measurement of photosynthesis in vivo that remain relevant on a global scale to production of crops and biofuels, as well as plant responses to climate change. We include here personal remembrances by the authors (GEE and UH), and by (in alphabetical order): Zoran Cerovic (France), Bob Furbank (Australia), Geoffrey Hind (USA), John Humby (UK), Agu Laisk (Estonia), Peter Lea (UK), Ross Lilley (Australia), Barry Osmond (Australia), Simon Robinson (Australia) and Charles Stirling (UK).
Keywords: Intact chloroplasts; CAM; Robin Hill; Charles Whittingham; C3–C4 photosynthesis; Oxygen electrode; International society of photosynthesis research (ISPR); Meirion Thomas

Photobiology of sea ice algae during initial spring growth in Kangerlussuaq, West Greenland: insights from imaging variable chlorophyll fluorescence of ice cores by Ian Hawes; Lars Chresten Lund-Hansen; Brian K. Sorrell; Morten Holtegaard Nielsen; Réka Borzák; Inge Buss (103-115).
We undertook a series of measurements of photophysiological parameters of sea ice algae over 12 days of early spring growth in a West Greenland Fjord, by variable chlorophyll fluorescence imaging. Imaging of the ice–water interface showed the development of ice algae in 0.3–0.4 mm wide brine channels between laminar ice crystals in the lower 4–6 mm of the ice, with a several-fold spatial variation in inferred biomass on cm scales. The maximum quantum yield of photosynthesis, F v /F m, was initially low (~0.1), though this increased rapidly to ~0.5 by day 6. Day 6 also saw the onset of biomass increase, the cessation of ice growth and the time at which brine had reached <50 psu and >−2 °C. We interpret this as indicating that the establishment of stable brine channels at close to ambient salinity was required to trigger photosynthetically active populations. Maximum relative electron transport rate (rETRmax), saturation irradiance (E k) and photosynthetic efficiency (α) had also stabilised by day 6 at 5–6 relative units, ~30 μmol photons m−2 s−1 and 0.4–0.5 μmol photons m−2 s−1, respectively. E k was consistent with under-ice irradiance, which peaked at a similar value, confirming that daytime irradiance was adequate to facilitate photosynthetic activity throughout the study period. Photosynthetic parameters showed no substantial differences with depth within the ice, nor variation between cores or brine channels suggesting that during this early phase of ice algal growth cells were unaffected by gradients of environmental conditions within the ice. Variable chlorophyll fluorescence imaging offers a tool to determine how this situation may change over time and as brine channels and algal populations evolve.
Keywords: Photosynthesis; Diatoms; Sea ice; Spring bloom; Photophysiology; Fluorescence; Electron transport

The N-terminal 1E−6L domain of the manganese-stabilizing protein (PsbO) from spinach prevents non-specific binding of the subunit to photosystem II (PSII) and deletions of the 1E−7T or 1E−15T sequences from the PsbO N-terminus reduce or impair, respectively, functional binding of PsbO to PSII (Popelkova et al., Biochemistry 42:6193–6200, 2003). The work presented here provides deeper insights into the interaction of PsbO with PSII. The data show that a single mutation, 15T → A in mature PsbO from spinach reduces the stoichiometry of its functional binding from two to one subunit per PSII and decreases reconstitution of activity to about 45 % of the wild-type control. Replacement of the 1E−6L domain with 6M in the T15A PsbO mutant has no additional negative effect on recovery of O2 evolution activity, but it significantly weakens both functional and nonspecific binding of the truncated mutant to PSII. These results suggest that the 15T side-chain by itself is essential for binding of one of two PsbO subunits to eukaryotic PSII and that specific PSII-binding sites for PsbO are distinguishable; one PSII-binding site does not require PsbO–15T and probably interacts with the other N-terminal domain of PsbO. Identity of the latter domain is revealed by a requirement for the presence of the 1E−6L sequence that is shown here to be necessary for high-affinity binding of PsbO to PSII. When combined with previous results, the data presented here lead to a more detailed model for PsbO binding in eukaryotic PSII.
Keywords: Activity assays; Circular dichroism; Manganese-stabilizing protein; Mutation; Photosystem II; Protein binding

The reaction center is the sensitive target of the mercury(II) ion in intact cells of photosynthetic bacteria by Emese Asztalos; Gábor Sipka; Mariann Kis; Massimo Trotta; Péter Maróti (129-140).
The sensitivity of intact cells of purple photosynthetic bacterium Rhodobacter sphaeroides wild type to low level (<100 μM) of mercury (Hg2+) contamination was evaluated by absorption and fluorescence spectroscopies of the bacteriochlorophyll–protein complexes. All assays related to the function of the reaction center (RC) protein (induction of the bacteriochlorophyll fluorescence, delayed fluorescence and light-induced oxidation and reduction of the bacteriochlorophyll dimer and energization of the photosynthetic membrane) showed prompt and later effects of the mercury ions. The damage expressed by decrease of the magnitude and changes of rates of the electron transfer kinetics followed complex (spatial and temporal) pattern according to the different Hg2+ sensitivities of the electron transport (donor/acceptor) sites including the reduced bound and free cytochrome c 2 and the primary reduced quinone. In contrast to the RC, the light harvesting system and the bc1 complex demonstrated much higher resistance against the mercury pollution. The 850 and 875 nm components of the peripheral and core complexes were particularly insensitive to the mercury(II) ions. The concentration of the photoactive RCs and the connectivity of the photosynthetic units decreased upon mercury treatment. The degree of inhibition of the photosynthetic apparatus was always higher when the cells were kept in the light than in the dark indicating the importance of metabolism in active transport of the mercury ions from outside to the intracytoplasmic membrane. Any of the tests applied in this study can be used for detection of changes in photosynthetic bacteria at the early stages of the action of toxicants.
Keywords: Bacterial photosynthesis; Intact cells; Reaction center; Antenna; Mercury contamination; Bacteriochlorophyll spectroscopy

The physiological significance of photosystem II (PSII) core protein phosphorylation has been suggested to facilitate the migration of oxidative damaged D1 and D2 proteins, but meanwhile the phosphorylation seems to be associated with the suppression of reactive oxygen species (ROS) production, and it also relates to the degradation of PSII reaction center proteins. To more clearly elucidate the possible protecting effect of the phosphorylation on oxidative damage of D1 protein, the degradation of oxidized D1 protein and the production of superoxide anion in the non-phosphorylated and phosphorylated PSII membranes were comparatively detected using the Western blotting and electron spin resonance spin-trapping technique, respectively. Obviously, all of three ROS components, including superoxide anion, hydrogen peroxide and hydroxyl radical are responsible for the degradation of oxidized D1 protein, and the protection of the D1 protein degradation by phosphorylation is accompanied by the inhibition of superoxide anion production. Furthermore, the inhibiting effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a competitor to QB, on superoxide anion production and its protecting effect on D1 protein degradation are even more obvious than those of phosphorylation. Both DCMU effects are independent of whether PSII membranes are phosphorylated or not, which reasonably implies that the herbicide DCMU and D1 protein phosphorylation probably share the same target site in D1 protein of PSII. So, altogether it can be concluded that the phosphorylation of D1 protein reduces the oxidative damage of D1 protein by decreasing the production of superoxide anion in PSII membranes under high light.
Keywords: PSII membranes; D1 protein; Protein phosphorylation; High light; Reactive oxygen species