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

Functional Plant Biology (Impact Factor: 2.57). 01/2009; 36(6). DOI: 10.1071/FP09087

ABSTRACT 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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    • "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 · 1.68 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 · 3.19 Impact Factor
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    ABSTRACT: As photosynthesis on Earth produces the primary signatures of life that can be detected astronomically at the global scale, a strong focus of the search for extrasolar life will be photosynthesis, particularly photosynthesis that has evolved with a different parent star. We take previously simulated planetary atmospheric compositions for Earth-like planets around observed F2V and K2V, modeled M1V and M5V stars, and around the active M4.5V star AD Leo; our scenarios use Earth's atmospheric composition as well as very low O2 content in case anoxygenic photosynthesis dominates. With a line-by-line radiative transfer model, we calculate the incident spectral photon flux densities at the surface of the planet and under water. We identify bands of available photosynthetically relevant radiation and find that photosynthetic pigments on planets around F2V stars may peak in absorbance in the blue, K2V in the red-orange, and M stars in the near-infrared, in bands at 0.93-1.1 microm, 1.1-1.4 microm, 1.5-1.8 microm, and 1.8-2.5 microm. However, underwater organisms will be restricted to wavelengths shorter than 1.4 microm and more likely below 1.1 microm. M star planets without oxygenic photosynthesis will have photon fluxes above 1.6 microm curtailed by methane. Longer-wavelength, multi-photo-system series would reduce the quantum yield but could allow for oxygenic photosystems at longer wavelengths. A wavelength of 1.1 microm is a possible upper cutoff for electronic transitions versus only vibrational energy; however, this cutoff is not strict, since such energetics depend on molecular configuration. M star planets could be a half to a tenth as productive as Earth in the visible, but exceed Earth if useful photons extend to 1.1 microm for anoxygenic photosynthesis. Under water, organisms would still be able to survive ultraviolet flares from young M stars and acquire adequate light for growth.
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