Light dependence of quantum yields for PSII charge separation and oxygen evolution in eucaryotic algae

Abstract

Quantum yields of photosystcm I1 (PSII) charge separation (@& and oxygen production ((I) (,,) were determined by simultaneous measurements of oxygen production and variable fluorescence in four different aquatic microalgae representing three different taxonomic groups: the freshwater alga Scenedesmus protuberans (Chlorophyceae) and the marine algae Phneorystis globosa (Prymnesiophyceae), Emiliania huxleyi (Prymnesiophyceae), and Phaeodactylum tricornutum (Bacillariophyceae). In S. protuberans, P. tricornutum, and E. huxleyi, light-dependent variability was observed in the ratio of a(,,, to a,,, i.c. in the number of oxygen molecules produced per electron generated by PSII. The ratio ao,:@,, was highly variable at low light intensities (E < OSE,), and at higher light intensities (E > OSE,) @(,, : @,, showed a nonlinear decrease with increasing light intensity. In contrast, in P. globosa. a trend in a<,, : @,, could not be distinguished, and this species showed a decrease in @'o, : $ during the day, indicating a dependency of a(,, : a,, on light history. Additionally, considerable interspecific quantitative differences in a(,, : a,, were observed. Two possible interpretations to explain the variability in '.I+)! : a, are discussed. Assuming that 0, is a reliable measure of the quantum yield for charge separation at PSII, one interpretation is that net oxygen production is influenced by processes that consume oxygen or affect linear electron transport (e.g. cyclic electron transport around PSII, pseudocyclic electron transport in the Mehler reaction, Rubisco oxygenase activity, and lightdependent mitochondrial respiration). A second interpretation, however, suggests that at saturating light, changes in photosynthesis turnover time occur, such that $ does not predict the steady-state O2 yield.Quantum yields of phytoplankton photosynthesis are usually defined as the quantum yields for O? production (CacjL) or C fixation (@c,,,) (Kok 1948;Myers 1980;Babin et al. 1996). Because measurements of @oz and @'co, are laborious and time-consuming, much attention has been focused lately on the use of variable chlorophyll fluorescence as a tool to measure the quantum yield of charge separation in photosystem II (PSIl) reaction centers (Genty et al. 1989). This technique is rapid and noninvasive and may offer high temporal and spatial resolution when used in field measurements (Schreiber et al. 1986). Theoretically, the rate of noncyclic photosynthetic electron transport of a PSI1 (J) can be calculated from the quantum yield of PSI1 charge separation (a,,) according to J = @,J%s,,rwhere E is the incident light intensity and cr,,,, is the absorption cross section of PSII, which determines the fraction of the incident light intensity that is actually used by PSI1 (e.g. Kolber and Falkowski 1993; Kroon 1991; Hofstraat et al. 1994, Biehler andFock 1995). In order to use J as a measure for photosynthesis, the relationships between @,,, @coL, and @coz have to be well established. According to the stoichiometry of the Z-schem...

Coupling between Photosystem II electron transport and carbon fixation in microphytobenthos

“…Values of the QR calculated in this study ranged from a maximum of 18.2 quanta (C) -1 to a minimum of 13.8 quanta (C) -1 , which is very close to the theoretical minimum of between 10.1 and 14.1 (depending on the photosynthetic quotient used) derived by Ley & Mauzerall (1982). This suggests that over the range of growth conditions examined, the use of variable fluorescence as an alternative method for estimating the photosynthetic parameters of MPB algal suspensions seems to offer considerable promise, a conclusion previously reached by a number of other authors (Flameling & Kromkamp 1998, Gilbert et al 2000, Morris & Kromkamp 2003.However, significant differences were observed between photosynthetic parameters measured in situ and on suspensions (Figs. 3 & 5).…”

“…According to theory, using either 'multiple' or 'single' turnover saturation kinetics (see Kromkamp & Forster 2003) the effective quantum efficiency of Photosystem II (PSII) (ΔF/F m '), which generally represents the effective quantum efficiency of photosynthesis (Φ P ) (Genty et al 1989), can be derived at a range of irradiances. If ΔF/F m ' is then multiplied by the irradiance absorbed by PSII, the rate of non-cyclic electron transport (ETR) can be calculated (Hofstraat et al 1994, Kromkamp & Forster 2003, which can be converted to a photosynthetic rate by multiplying by the electron use efficiency (Φ e , mol C fixed per mol electrons produced by PSII) (Gilbert et al 2000).ETR of algal suspensions is often linearly correlated to O 2 -production or C-fixation at limiting irradiances; however, sometimes at saturating irradiance, ETR can under-or overestimate the maximum rate of photosynthesis (Flameling & Kromkamp 1998, Hartig et al 1998, Masojídek et al 2001. Comparisons of ETR and standard measures for the quantification of undisturbed MPB biofilm photosynthetic rates are rare, and the published results are often contradictory (Barranguet & Kromkamp 2000, Perkins et al 2002, Serôdio 2003.…”

Effects of temperature on photosynthetic parameters and TEP production in eight species of marine microalgae

“…The rate of photosynthesis estimated by PAM fluorometry and oxygen evolution or carbon fixation have been compared in several phytoplankton species (Flameling & Kromkamp 1998, Morris & Kromkamp 2003, Lefebvre et al 2007), which allows estimation of the number of mol of C fixed per mol of electrons. Morris & Kromkamp (2003) found a value of 0.114 mol C (mol electron) -1 .…”

Bio-optical modelling of primary production in the SW Finnish coastal zone, Baltic Sea: fast repetition rate fluorometry in Case 2 waters

“…We used a value of 0.18. Flameling & Kronkamp (1998) measured the ratio of the quantum yields of O 2 production to the charge separation for 4 microalgae, and a value of 0.18 equals an average value below E k , interpreted from the graphical presentation by Flameling & Kronkamp, multiplied by 2, since 1 quantum is needed for both of the RCs to transfer 1 electron from the water-splitting complex to the terminal electron acceptors. Values of n PSII from 1/800 to 1/500 have been used for eucaryotic microalgae (Kolber & Falkowski 1993, Falkowski & Kolber 1995, Boyd et al 1997.…”

“…Utilisation of FRRF metrics as the sole source for estimates of PP is, however, hindered by deviation observed between the photosynthetic electron flow and the fixation of C at high irradiance levels (Flameling & Kronkamp 1998), and by the factors reflecting natural variability that are at present set as constants in the variable fluorescence theory (Kolber & Falkowski 1993, Raateoja & Seppälä 2001. Most research programmes (e.g.…”