Photosynthesis Research (v.110, #1)

A tribute to Thomas Roosevelt Punnett, Jr. (1926–2008) by William Hagar; Hope Punnett; Laura Punnett; Govindjee (1-7).
We honor here Thomas (Tom) Roosevelt Punnett, Jr. (May 25, 1926–July 4, 2008), who was a pioneer of Biology, particularly of biochemistry of plants and algae, having specialized in photosynthesis under Robert Emerson of the University of Illinois at Urbana-Champaign. He did exciting work on regulation and control of various metabolic reactions. He was an innovator and raconteur par excellence, and he prized critical thinking. His enthusiasm for basic science questions was matched by his grasp of their “real-world” implications. His last project was a patent for anaerobic sewage treatment that he hoped would lead to solution of waste disposal and energy creation world wide, including the clean-up of Lake Erie, where he had sailed as a boy. On the personal side, he had a strong sense of morality and a great wit and humor.
Keywords: Chlorella pyrenoidosa ; Elodea ; Robert Emerson; Robin Hill; Leukocyte; Methane production from organic material; Eugene Rabinowitch; Temple University; University of Illinois at Urbana-Champaign; University of Rochester; Yale University

Adventures with Carbons 11, 12, 13 and 14 by Andrew Alm Benson (9-12).
I provide here a glimpse of my involvement with different isotopes of carbon. In my 65 years of synthetic work with C-12, I had experience working with C-11 (one year, 1942–1943), C-13 (one year, 1999) and C-14 (67 years, 1943–2009). I have also included a postscript dealing with my 1951 communication on the 5-carbon intermediate in photosynthesis.
Keywords: Roland Douce; Martin Kamen; Gilbert N. Lewis; Linus Pauling; Sam Ruben; Glenn T. Seaborg; The Rat House

In photosynthetic eukaryotes, the redox state of the plastoquinone (PQ) pool is an important sensor for mechanisms that regulate the photosynthetic electron transport. In higher plants, a multimeric nicotinamide adenine dinucleotide (phosphate) (NAD(P))H dehydrogenase (NDH) complex and a plastid terminal oxidase (PTOX) are involved in PQ redox homeostasis in the dark. We recently demonstrated that in the microalgae Chlamydomonas reinhardtii, which lacks the multimeric NDH complex of higher plants, non-photochemical PQ reduction is mediated by a monomeric type-II NDH (Nda2). In this study, we further explore the nature and the importance of non-photochemical PQ reduction and oxidation in relation to redox homeostasis in this alga by recording the ‘dark’ chlorophyll fluorescence transients of pre-illuminated algal samples. From the observation that this fluorescence transient is modified by addition of propyl gallate, a known inhibitor of PTOX, and in a Nda2-deficient strain we conclude that it reflects post-illumination changes in the redox state of PQ resulting from simultaneous PTOX and Nda2 activity. We show that the post-illumination fluorescence transient can be used to monitor changes in the relative rates of the non-photochemical PQ reduction and reoxidation in response to different physiological situations. We study this fluorescence transient in algae acclimated to high light and in a mutant deficient in mitochondrial respiration. Some of our observations indicate that the chlororespiratory pathway participates in redox homeostasis in C. reinhardtii.
Keywords: Plastid terminal oxidase; Plastoquinone; Propyl gallate; Chlamydomonas reinhardtii ; Chlororespiration; Plastid NAD(P)H dehydrogenase

The absorption and energy transfer properties of photosynthetic pigments are strongly influenced by their local environment or “site.” Local electrostatic fields vary in time with protein and chromophore molecular movement and thus transiently influence the excited state transition properties of individual chromophores. Site-specific information is experimentally inaccessible in many light-harvesting pigment–proteins due to multiple chromophores with overlapping spectra. Full quantum mechanical calculations of each chromophores excited state properties are too computationally demanding to efficiently calculate the changing excitation energies along a molecular dynamics trajectory in a pigment–protein complex. A simplified calculation of electrostatic interactions with each chromophores ground to excited state transition, the so-called charge density coupling (CDC) for site energy, CDC, has previously been developed to address this problem. We compared CDC to more rigorous quantum chemical calculations to determine its accuracy in computing excited state energy shifts and their fluctuations within a molecular dynamics simulation of the bacteriochlorophyll containing light-harvesting Fenna–Mathews–Olson (FMO) protein. In most cases CDC calculations differed from quantum mechanical (QM) calculations in predicting both excited state energy and its fluctuations. The discrepancies arose from the inability of CDC to account for the differing effects of charge on ground and excited state electron orbitals. Results of our study show that QM calculations are indispensible for site energy computations and the quantification of contributions from different parts of the system to the overall site energy shift. We suggest an extension of QM/MM methodology of site energy shift calculations capable of accounting for long-range electrostatic potential contributions from the whole system, including solvent and ions.
Keywords: Bacteriochlorophyll; FMO protein; Excited state energies; Molecular dynamics

Multiple dissipation components of excess light energy in dry lichen revealed by ultrafast fluorescence study at 5 K by Hirohisa Miyake; Masayuki Komura; Shigeru Itoh; Makiko Kosugi; Yasuhiro Kashino; Kazuhiko Satoh; Yutaka Shibata (39-48).
A time-resolved fluorescence study of living lichen thalli at 5 K was conducted to clarify the dynamics and mechanism of the effective dissipation of excess light energy taking place in lichen under extreme drought conditions. The decay-associated spectra obtained from the experiment at 5 K were characterized by a drastically sharpened spectral band which could not be resolved by experiments at higher temperatures. The present results indicated the existence of two distinct dissipation components of excess light energy in desiccated lichen; one is characterized as rapid fluorescence decay with a time constant of 27 ps in the far-red region that was absent in wet lichen thalli, and the other is recognized as accelerated fluorescence decay in the 685–700 nm spectral region. The former energy-dissipation component with extremely high quenching efficiency is most probably ascribed to the emergence of a rapid quenching state in the peripheral-antenna system of photosystem II (PS II) on desiccation. This is an extremely effective protection mechanism of PS II under desiccation, which lichens have developed to survive in the severely desiccated environments. The latter, which is less efficient at 5 K, might have a supplementary role and take place either in the core antenna of PS II or aggregated peripheral antenna of PS II.
Keywords: Photosystem II; LHCII; Non-photochemical quenching; Parmotrema tinctorum

Ultrafast time-resolved spectroscopy of the light-harvesting complex 2 (LH2) from the photosynthetic bacterium Thermochromatium tepidum by Dariusz M. Niedzwiedzki; Marcel Fuciman; Masayuki Kobayashi; Harry A. Frank; Robert E. Blankenship (49-60).
The light-harvesting complex 2 from the thermophilic purple bacterium Thermochromatium tepidum was purified and studied by steady-state absorption and fluorescence, sub-nanosecond-time-resolved fluorescence and femtosecond time-resolved transient absorption spectroscopy. The measurements were performed at room temperature and at 10 K. The combination of both ultrafast and steady-state optical spectroscopy methods at ambient and cryogenic temperatures allowed the detailed study of carotenoid (Car)-to-bacteriochlorophyll (BChl) as well BChl-to-BChl excitation energy transfer in the complex. The studies show that the dominant Cars rhodopin (N = 11) and spirilloxanthin (N = 13) do not play a significant role as supportive energy donors for BChl a. This is related with their photophysical properties regulated by long π-electron conjugation. On the other hand, such properties favor some of the Cars, particularly spirilloxanthin (N = 13) to play the role of the direct quencher of the excited singlet state of BChl.
Keywords: Carotenoids; Light-harvesting complex 2; Transient absorption; Thermochromatium tepidum ; Rhodopin; Rhodovibrin; Spirilloxanthin; Excited state

Cytochrome c 6-like protein as a putative donor of electrons to photosystem I in the cyanobacterium Nostoc sp. PCC 7119 by Francisco M. Reyes-Sosa; Jorge Gil-Martínez; Fernando P. Molina-Heredia (61-72).
Most organisms performing oxygenic photosynthesis contain either cytochrome c 6 or plastocyanin, or both, to transfer electrons from cytochrome b 6-f to photosystem I. Even though plastocyanin has superseded cytochrome c 6 along evolution, plants contain a modified cytochrome c 6, the so called cytochrome c 6A, whose function still remains unknown. In this article, we describe a second cytochrome c 6 (the so called cytochrome c 6-like protein), which is found in some cyanobacteria but is phylogenetically more related to plant cytochrome c 6A than to cyanobacterial cytochrome c 6. In this article, we conclude that the cytochrome c 6-like protein is a putative electron donor to photosystem I, but does play a role different to that of cytochrome c 6 and plastocyanin as it cannot accept electrons from cytochrome f. The existence of this third electron donor to PSI could explain why some cyanobacteria are able to grow photoautotrophically in the absence of both cytochrome c 6 and plastocyanin. In any way, the Cyt c 6-like protein from Nostoc sp. PCC 7119 would be potentially utilized for the biohydrogen production, using cell-free photosystem I catalytic nanoparticles.
Keywords: Cytochrome c 6-like protein; Cytochrome c 6A ; Biohydrogen; Photosystem I; Spectroscopy; Laser flash spectroscopy