CHROMATIC REGULATION OF QUANTUM YIELDS FOR PHOTOSYSTEM II CHARGE SEPARATION, OXYGEN EVOLUTION, AND CARBON FIXATION IN HETEROCAPSA PYGMAEA (PYRROPHYTA)¹

Abstract

Operational and maximum quantum yields for system (PSII) charge separation, oxygen evolution, and carbon fixation were quantified and compared for Heterocapsa pygmaea Loeblich, Schmidt et Sherley populations chromatically adapted to white, green, blue, and red light. Significant variability in quantum yields was induced by chromatic adaptation alone or when chromatically adapted cells were suddenly exposed to biased light fields (i.e. white light). Results indicated a close coupling between the variability in quantum yields for PSII charge separation and oxygen evolution, but not between quantum yields for oxygen evolution and carbon fixation. But not between quantum yields for oxygen evolution and carbon fixation. The ability to regrlate and optimize light energy distribution between PSII and photosystem I (PSI) appears to be the mechanism underlying chromatic adaptation for PSII charge separation and oxygen evolution. Conceptually, the resulting impacts on PSI cyclic electron transport rates could account for observed variability in quantum yields for oxygen evolution and some variability in quantum yields for carbon fixation. Similarly, enzymatic processes associated with organic carbon synthesis appeared to be variably dependent on spectral growth irradiances and contributing to the observed variability in quantum yields for carbon fixation. The relevance of these findings to the in situ primary production is discussed.

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

“…A theoretical maximum value for φ c of 0.25 at irradiances under E k has generally been used (Kolber & Falkowski 1993, Babin et al 1996, Boyd et al 1997. However, φ c values as low as 0.14 to 0.19 have been observed (Kroon et al 1993). We used a value of 0.18.…”

Photosynthetic activity of natural microphytobenthos populations measured by fluorescence (PAM) and 14C-tracer methods:a comparison

“…Most of these studies have been carried out on higher plant leaves or on isolated chloroplasts; only a few researchers have applied the PAM technique to study unicellular algae and phytoplankton (Kroon et al 1993, Hofstraat et al 1994. As has been pointed out by Ting & Owens (1992) and Buchel & Wilhelm (1993), there have been considerable limitations in the performance of available instrumentation for quenching analysis using dilute samples of unicellular algae with different antenna organization.…”

“…The PAM system has only been used for a few years in phytoplankton research. There are only a limited number of scientific studies concerned with the estimation of the photochemical efficiency of natural phytoplankton or phytoplankton cultures conducted using the PAM technique (Ting & Owens 1992, Kroon et al 1993, Hofstraat et al 1994. So far this method has not been applied to microphytobenthos communities.…”

Coupling between Photosystem II electron transport and carbon fixation in microphytobenthos

“…) was calculated as the product of the measured specific absorption spectrum a*(λ) and the spectrum of the light source Q (λ) for each light treatment (Kroon et al 1993), measured with a MACAM SR9910 spectroradiometer. Thus, ETR was calculated as: where:…”

“…Hypsochromic shifts and weight-specific spectral absorption coefficients (in HPLC solvent) were made according to Bidigare et al (1990). A relative measure of the extent of pigment packaging within the suspensions was derived by comparing the measured and reconstructed specific absorption coefficients at the 680 nm chl a peak (a* 680 ).To correct for the different spectral properties of each of the light sources used to derive photosynthetic parameters, the specific spectral irradiance absorbed by the MPB assemblage (AQ, µmol quanta [mg chl a]) was calculated as the product of the measured specific absorption spectrum a*(λ) and the spectrum of the light source Q (λ) for each light treatment (Kroon et al 1993), measured with a MACAM SR9910 spectroradiometer. Thus, ETR was calculated as: where:…”