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  • chlorophyll fluorescence  (3)
  • carbon fixation  (1)
  • Springer  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Inhibition of PS II photochemistry by PAR and UV radiation in natural phytoplankton communities (1994)
    Springer
    Photosynthesis research 42 (1994), S. 51-64 
    Details
    ISSN: 1573-5079
    Keywords: absorption cross section of PS II ; chlorophyll fluorescence ; photoinhibition ; phytoplankton ; QA ; quantum efficiency of PS II ; UV radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of PAR and UV radiation on PS II photochemistry were examined in natural phytoplankton communities from coastal waters off Rhode Island (USA) and the subtropical Pacific. The photochemical energy conversion efficiency, the functional absorption cross section and the kinetics of electron transfer on the acceptor side of PS II were derived from variable fluorescence parameters using both pump and probe and fast repetition rate techniques. In both environments, the natural phytoplankton communities displayed marked decreases in PS II photochemical energy conversion efficiency that were correlated with increased PAR. In the coastal waters, the changes in photochemical energy conversion efficiency were not statistically different for samples treated with supplementary UV-B radiation or screened to exclude ambient UV-B. Moreover, no significant light-dependent changes in the functional absorption cross section of PS II were observed. The rate of electron transfer between QA - and QB was, however, slightly reduced in photodamaged cells, indicative of damage on the acceptor side. In the subtropical Pacific, the decrease in photochemical energy conversion efficiency was significantly greater for samples exposed to natural levels of UV-A and/or UV-B compared with those exposed to PAR alone. The cells displayed large diurnal changes in the functional absorption cross section of PS II, indicative of non-photochemical quenching in the antenna. The changes in the functional absorption cross section were highly correlated with PAR but independent of UV radiation. The time course of changes in photochemical efficiency reveals that the photoinhibited reaction centers rapidly recover (within an hour or two) to their preillumination values. Thus, while we found definitive evidence for photoinhibition of PS II photochemistry in both coastal and open ocean phytoplankton communities, we did not find any effect of UV-B on the former, but a clear effect on the latter. The results of this study indicate that the effects of UV-B radiation on phytoplankton photosynthesis are as dependent on the radiative transfer properties of the water body and the mixing rate, as on the wavelength and energy distribution of the radiation and the absorption cross sections of the biophysical targets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00019058
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Measuring photosynthetic parameters in individual algal cells by Fast Repetition Rate fluorometry (1999)
    Springer
    Photosynthesis research 62 (1999), S. 141-153 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; electron transport ; phytoplankton ; quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A Single Cell Fast Repetition Rate (SCFRR) fluorometer was developed to measure the quantum yield of photochemistry, the functional absorption cross section of PS II and the kinetics of electron transport on the acceptor side of PS II in individual algal cells. These parameters are used to quantify the cell-specific photosynthetic performance in natural phytoplankton assembledges in aquatic ecosystems. The SCFRR technique measures chlorophyll fluorescence transients induced by a precisely controlled series of excitation flashlets that cumulatively saturate PS II within 120 μs. To meet the requirement in the analysis for single algal cells, the measurements are conducted in micro volumes, such that the probability of probing more than one cell at a time is vanishingly low. We designed a novel, computer-controlled hydromechanical system to deliver a portion of the sample into the measuring chamber and, following measurement, remove it into one of six sorting containers. The fluorescence signal is induced by a series of high frequency flashlets obtained from high luminosity blue light-emitting diodes and is acquired by a novel red-sensitive PMT-based detection system exhibiting both high sensitivity and a very wide dynamic range. The wide dynamic range of the detector allows SCFRR measurements for a wide variety of cell sizes ranging from 1 to 100 μm equivalent spherical diameter. The compact and light-weight design makes the SCFRR Fluorometer applicable for both laboratory and field studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006360005033
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  • 3
    Electronic Resource
    Electronic Resource
    Cyclic electron flow around Photosystem II in vivo (1996)
    Springer
    Photosynthesis research 48 (1996), S. 395-410 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; cyclic electron transport ; oxygen evolution ; Photosystem II ; quantum yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The oxygen flash yield (YO2) and photochemical yield of PS II (ΦPS II) were simultaneously detected in intact Chlorella cells on a bare platinum oxygen rate electrode. The two yields were measured as a function of background irradiance in the steady-state and following a transition from light to darkness. During steady-state illumination at moderate irradiance levels, YO2 and ΦPS II followed each other, suggesting a close coupling between the oxidation of water and QA reduction (Falkowski et al. (1988) Biochim. Biophys. Acta 933: 432–443). Following a light-to-dark transition, however, the relationship between QA reduction and the fraction of PS II reaction centers capable of evolving O2 became temporarily uncoupled. ΦPS II recovered to the preillumination levels within 5–10 s, while the YO2 required up to 60 s to recover under aerobic conditions. The recovery of YO2 was independent of the redox state of QA, but was accompanied by a 30% increase in the functional absorption cross-section of PS II (σPS II). The hysteresis between YO2 and the reduction of QA during the light-to-dark transition was dependent upon the reduction level of the plastoquinone pool and does not appear to be due to a direct radiative charge back-reaction, but rather is a consequence of a transient cyclic electron flow around PS II. The cycle is engaged in vivo only when the plastoquinone pool is reduced. Hence, the plastoquinone pool can act as a clutch that disconnects the oxygen evolution from photochemical charge separation in PS II.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00029472
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  • 4
    Electronic Resource
    Electronic Resource
    Compensatory changes in Photosystem II electron turnover rates protect photosynthesis from photoinhibition (1998)
    Springer
    Photosynthesis research 58 (1998), S. 259-268 
    Details
    ISSN: 1573-5079
    Keywords: carbon fixation ; phytoplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Exposure of algae or higher plants to bright light can result in a photoinhibitory reduction in the number of functional PS II reaction centers (n) and a consequential decrease in the maximum quantum yield of photosynthesis. However, we found that light-saturated photosynthetic rates (Pmax) in natural phytoplankton assemblages sampled from the south Pacific ocean were not reduced despite photoinhibitory decreases in n of up to 52%. This striking insensitivity of Pmax to photoinhibition resulted from reciprocal increases in electron turnover ( $${1 \mathord{\left/ {\vphantom {1 {\tau _{PSII} }}} \right. \kern-\nulldelimiterspace} {\tau _{PSII} }}$$ )through the remaining functional PS II centers. Similar insensitivity of Pmax was also observed in low light adapted cultures of Thalassiosira weissflogii (a marine diatom), but not in high light adapted cells where Pmax decreased in proportion to n. This differential sensitivity to decreases in n occurred because $${1 \mathord{\left/ {\vphantom {1 {\tau _{PSII} }}} \right. \kern-\nulldelimiterspace} {\tau _{PSII} }}$$ was close to the maximum achievable rate in the high light adapted cells, whereas $${1 \mathord{\left/ {\vphantom {1 {\tau _{PSII} }}} \right. \kern-\nulldelimiterspace} {\tau _{PSII} }}$$ was initially low in the low light adapted cells and could thus increase in response to decreases in n. Our results indicate that decreases in plant productivity are not necessarily commensurate with photoinhibition, but rather will only occur if decreases in n are sufficient to maximize $${1 \mathord{\left/ {\vphantom {1 {\tau _{PSII} }}} \right. \kern-\nulldelimiterspace} {\tau _{PSII} }}$$ or incident irradiance becomes subsaturating.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006138630573
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    Paper (German National Licenses)
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