Photosynthesis Research (v.97, #2)

The biochemical basis for structural diversity in the carotenoids of chlorophototrophic bacteria by Julia A. Maresca; Joel E. Graham; Donald A. Bryant (121-140).
Ongoing work has led to the identification of most of the biochemical steps in carotenoid biosynthesis in chlorophototrophic bacteria. In carotenogenesis, a relatively small number of modifications leads to a great diversity of carotenoid structures. This review examines the individual steps in the pathway, discusses how each contributes to structural diversity among carotenoids, and summarizes recent progress in elucidating the biosynthetic pathways for carotenoids in chlorophototrophs.
Keywords: Carotenoids; Carotenogenesis; Photosynthesis; Lycopene cyclase; Cyanobacteria; Green sulfur bacteria

Bacteriophytochromes in anoxygenic photosynthetic bacteria by Eric Giraud; André Verméglio (141-153).
Since the first discovery of a bacteriophytochrome in Rhodospirillum centenum, numerous bacteriophytochromes have been identified and characterized in other anoxygenic photosynthetic bacteria. This review is focused on the biochemical and biophysical properties of bacteriophytochromes with a special emphasis on their roles in the synthesis of the photosynthetic apparatus.
Keywords: Bacteriophytochrome; Light-harvesting complexes; Photosynthesis regulation; Photosynthetic apparatus; Photosynthetic bacteria

Increased protein carbonylation in leaves of Arabidopsis and soybean in response to elevated [CO2] by Quan-Sheng Qiu; Joan L. Huber; Fitzgerald L. Booker; Vanita Jain; Andrew D. B. Leakey; Edwin L. Fiscus; Peter M. Yau; Donald R. Ort; Steven C. Huber (155-166).
While exposure of C3 plants to elevated [CO2] would be expected to reduce production of reactive oxygen species (ROS) in leaves because of reduced photorespiratory metabolism, results obtained in the present study suggest that exposure of plants to elevated [CO2] can result in increased oxidative stress. First, in Arabidopsis and soybean, leaf protein carbonylation, a marker of oxidative stress, was often increased when plants were exposed to elevated [CO2]. In soybean, increased carbonyl content was often associated with loss of leaf chlorophyll and reduced enhancement of leaf photosynthetic rate (Pn) by elevated [CO2]. Second, two-dimensional (2-DE) difference gel electrophoresis (DIGE) analysis of proteins extracted from leaves of soybean plants grown at elevated [CO2] or [O3] revealed that both treatments altered the abundance of a similar subset of proteins, consistent with the idea that both conditions may involve an oxidative stress. The 2-DE analysis of leaf proteins was facilitated by a novel and simple procedure to remove ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from soluble soybean leaf extracts. Collectively, these findings add a new dimension to our understanding of global change biology and raise the possibility that oxidative signals can be an unexpected component of plant response to elevated [CO2].
Keywords: Arabidopsis ; Ascorbate peroxidase; 2-Dimensional gel electrophoresis; Protein carbonylation; Soybean

The evolutionary route from anoxygenic photosynthetic bacteria to oxygenic cyanobacteria is discontinuous in terms of photochemical/photophysical reaction systems. It is difficult to describe this transition process simply because there are no recognized intermediary organisms between the two bacterial groups. Gloeobacter violaceus PCC 7421 might be a model organism that is suitable for analysis because it still possesses primordial characteristics such as the absence of thylakoid membranes. Whole genome analysis and biochemical and biophysical surveys of G. violaceus have favored the hypothesis that it is an intermediary organism. On the other hand, species differentiation is an evolutionary process that could be driven by changes in a small number of genes, and this process might give fair information more in details by monitoring of those genes. Comparative studies of genes, including those in Acaryochloris marina MBIC 11017, have provided information relevant to species differentiation; in particular, the acquisition of a new pigment, chlorophyll d, and changes in amino acid sequences have been informative. Here, based on experimental evidence from these two species, we discuss some of the evolutionary pathways for the appearance and differentiation of cyanobacteria.
Keywords: Cyanobacteria; Evolution; Reaction center; Pigment system; Acaryochloris spp.; Gloeobacter violaceus

Elucidating the site of action of oxalate in photosynthetic electron transport chain in spinach thylakoid membranes by Anjana Jajoo; Archna Sahay; Pooja Singh; Sonal Mathur; Sergei K. Zharmukhamedov; Vyacheslav V. Klimov; Suleyman I. Allakhverdiev; Sudhakar Bharti (177-184).
The effects of oxalate on PS II and PS I photochemistry were studied. The results suggested that in chloride-deficient thylakoid membranes, oxalate inhibited activity of PS II as well as PS I. To our knowledge, this is the only anion so far known which inhibits both the photosystems. Measurements of fluorescence induction kinetics, Y Z decay, and S2 state multiline EPR signal suggested that oxalate inhibited PS II at the donor side most likely on the oxygen evolving complex. Measurements of re-reduction of P700+ signal in isolated PS I particles in oxalate-treated samples suggested a binding site of oxalate on the donor, as well as the acceptor side of PS I.
Keywords: Electron transport chain; EPR; Fluorescence; Oxalate anion; Photosystem II; Photosystem I

The chloroplast ATP synthase synthesizes ATP from ADP and free phosphate coupled by the electrochemical potential across the thylakoid membrane in the light. The light-dependent regulation of ATP synthase activity is carried out in part through redox modulation of a cysteine disulfide bridge in CF1 γ-subunit. In order to investigate the function of the redox regulatory domain and the physiological significance of redox modulation for higher plants, we designed four mutations in the redox regulatory domain of the γ-subunit to create functional mimics of the permanently reduced form of the γ-subunit. While the inability to reduce the regulatory disulfide results in lower photosynthesis and growth, unexpectedly, the results reported here show that inability to reoxidize the dithiol may not be of any direct detriment to plant photosynthetic performance or growth.
Keywords: Chloroplast ATP synthase; Disulfide bond; Redox modulation; Thioredoxin