Raven JA.. Functional evolution of photochemical energy transformations in oxygen-producing organisms. Funct Plant Biol 36: 505-515

Functional Plant Biology (Impact Factor: 3.15). 01/2009; 36(6). DOI: 10.1071/FP09087


Chlorophyll a is the photochemical agent accounting for most oxygenic photosynthesis, that is, over 99.9% of photosynthetic primary activity on Earth. The spectral and energetic properties of chlorophyll a can, at least in part, be rationalised interms of the solar spectral output and the energetics of oxygenproduction and carbon dioxide reduction with twophotochemicalreactions.Thelongwavelengthlimitoninvivochlorophyllaabsorptionisprobablyclosetotheenergetic limit: longer wavelengths could not support a high rate and efficiency of oxygenic photosynthesis. Retinal, a b-carotene derivative that is the chromophore of rhodopsin, acts not only as a sensory pigment, but also as an ion-pumping photochemical transducer. Both sensory and energy-transforming rhodopsins occur in oxygenic phototrophs, although the extent of expression and the function of the latter are not well understood.

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    • "The calculations are made on the assumptions that one mole of glucose generates either 36 mol ATP via glycolysis and oxidative phosphorylation or 24 mol electrons. Some authors suggest a value of 30 mol ATP per mol glucose respired is reasonable (Raven, 2009), others quote 36 mol for mitochondria and heterotrophic bacteria (Martin and Muller, 1998). Figure 6 shows how the carbohydrate demand for N2 fixation and assimilatory nitrate reduction behaves over a range of theoretical ATP per glucose production rates from 30 to 38 (mol mol−1). "
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    ABSTRACT: The recent detection of heterotrophic nitrogen (N(2)) fixation in deep waters of the southern Californian and Peruvian OMZ questions our current understanding of marine N(2) fixation as a process confined to oligotrophic surface waters of the oceans. In experiments with Crocosphaera watsonii WH8501, a marine unicellular diazotrophic (N(2) fixing) cyanobacterium, we demonstrated that the presence of high nitrate concentrations (up to 800 μM) had no inhibitory effect on growth and N(2) fixation over a period of 2 weeks. In contrast, the environmental oxygen concentration significantly influenced rates of N(2) fixation and respiration, as well as carbon and nitrogen cellular content of C. watsonii over a 24-h period. Cells grown under lowered oxygen atmosphere (5%) had a higher nitrogenase activity and respired less carbon during the dark cycle than under normal oxygen atmosphere (20%). Respiratory oxygen drawdown during the dark period could be fully explained (104%) by energetic needs due to basal metabolism and N(2) fixation at low oxygen, while at normal oxygen these two processes could only account for 40% of the measured respiration rate. Our results revealed that under normal oxygen concentration most of the energetic costs during N(2) fixation (∼60%) are not derived from the process of N(2) fixation per se but rather from the indirect costs incurred for the removal of intracellular oxygen or by the reversal of oxidative damage (e.g., nitrogenase de novo synthesis). Theoretical calculations suggest a slight energetic advantage of N(2) fixation relative to assimilatory nitrate uptake, when oxygen supply is in balance with the oxygen requirement for cellular respiration (i.e., energy generation for basal metabolism and N(2) fixation). Taken together our results imply the existence of a niche for diazotrophic organisms inside oxygen minimum zones, which are predicted to further expand in the future ocean.
    Frontiers in Microbiology 07/2012; 3:236. DOI:10.3389/fmicb.2012.00236 · 3.99 Impact Factor
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    • "Gross photosynthesis (GP) is defined as the rate at which reducing power is generated through the conversion of absorbed light energy, with the assumption that most of this energy is used for organic matter production (gross primary productivity (GPP); Begon et al. 2006). For example, Raven (2009) estimated that oxygenic photosynthesis contributes greater than 99% of global GPP. "
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    ABSTRACT: Phytoplankton primary productivity is most commonly measured by C-14 assimilation although less direct methods, such as O-2 exchange, have also been employed. These methods are invasive, requiring bottle incubation for up to 24 h. As an alternative, Fast Repetition Rate fluorometry (FRRf) has been used, on wide temporal and spatial scales within aquatic systems, to estimate photosystem II (PSII) electron flux per unit volume (JV(PSII)), which generally correlates well with photosynthetic O-2 evolution. A major limitation of using FRRf arises from the need to employ an independent method to determine the concentration of functional photosystem II reaction centers ([RCII]); a requirement that has prevented FRR fluorometers being used, as stand-alone instruments, for the estimation of electron transport. Within this study, we have taken a new approach to the analysis of FRRf data, based on a simple hypothesis; that under a given set of environmental conditions, the ratio of rate constants for RCII fluorescence emission and photochemistry falls within a narrow range, for all groups of phytoplankton. We present a simple equation, derived from the established FRRf algorithm, for determining [RCII] from dark FRRf data alone. We also describe an entirely new algorithm for estimating JV(PSII), which does not require determination of [RCII] and is valid for a heterogeneous model of connectivity among RCIIs. Empirical supporting evidence is presented. These data are derived from FRR measurements across a diverse range of microalgae, in parallel with independent measurements of [RCII]. Possible sources of error, particularly under nutrient stress conditions, are discussed.
    Limnology and oceanography, methods 03/2012; 10:142-154. DOI:10.4319/lom.2012.10.142 · 2.25 Impact Factor
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    • "Probably inspired by increasing concern about our future energy supply, this unanswered question is attracting renewed interest (Terashima et al. 2009; Björn et al. 2009; Raven 2009). It is often pointed out that a mature leaf, especially that of a shade plant, does effectively intercept nearly all visible light. "
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    ABSTRACT: The question of why plants are green has been revisited in several articles recently. A common theme in the discussions is to explain why photosynthesis appears to absorb less of the available green sunlight than expected. The expectation is incorrect, however, because it fails to take the energy cost of the photosynthetic apparatus into account. Depending on that cost, the red absorption band of the chlorophylls may be closely optimized to provide maximum growth power. The optimization predicts a strong influence of Fraunhofer lines in the solar irradiance on the spectral shape of the optimized absorption band, which appears to be correct. It does not predict any absorption at other wavelengths. Electronic supplementary material The online version of this article (doi:10.1007/s11120-009-9522-3) contains supplementary material, which is available to authorized users.
    Photosynthesis Research 02/2010; 103(2):105-9. DOI:10.1007/s11120-009-9522-3 · 3.50 Impact Factor
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