Geir Johnsen

WAVELENGTH DEPENDENCY OF THE MAXIMUM QUANTUM YIELD OF CARBON FIXATION FOR TWO RED TIDE DINOFLAGELLATES, HETEROCAPSA PYGMAEA AND PROROCENTRUM MINIMUM (PYRROPHYTA): IMPLICATIONS FOR MEASURING PHOTOSYNTHETIC RATES1

The influence of photoadaptive state on the spectral dependency of the maximum quantum yield for carbon fixation was determined for two red tide dinoflagellates, Heterocapsa pygmaea Loeblich, Schmidt, et Sherley and Prorocentrum minimum Pavillard. Cultures were acclimated to green, blue, red, and white light. The spectral dependency in the light‐limited slope of the photosynthesis–irradiance curves (α) was measured with carbon action spectra that, when divided by the spectrally weighted absorption coefficient, provided estimates of the maximum quantum yield (φmax) for carbon fixation. Values of φmax varied with wavelength within each culture condition as well as between different culture conditions. The degree to which the spectral dependency in φmax was influenced by the presence of photoprotective carotenoids and/or energy imbalances between photosystems I and II was assessed for both dinoflagellates. The impact of photoprotective pigmentation on the spectral dependency of φmax was most significant for cells grown under high light conditions reflecting the enrichment of diadinoxanthin. Energy imbalances between the photosystems was assessed by quantifying enhancement effects on spectral φmax in the presence of background illumination. Under our experimental conditions, enhancement effects on carbon action spectra were evident for H. pygmaea under nearly all growth conditions but were not detectable for P. minimum under any growth condition. We hypothesize that sensitivity to enhancement effects reflected differences in the structure of the photosynthetic machinery of these two peridinin‐containing dinoflagellates. While measurements of φmax are sensitive to the color of the light within an incubator, the relative impact on the spectral dependency of a was less than the wavelength dependency associated with the cellular absorption properties. Finally we used our data to validate an approach proposed by others to aid in the correction of photosynthetic measurements where the in situ spectral light field cannot be easily mimicked. The average error using this approach was 8%, which was significantly less than the error associated with ignoring the spectral dependency in α.

Isolation of membrane bound light-harvesting-complexes from the dinoflagellates Heterocapsa pygmaea and Prorocentrum minimum

We have isolated Chl a-Chl c-carotenoid binding proteins from the dinoflagellates Prorocentrum minimum and Heterocapsa pygmaea grown under high (500 μmol m−2 s−1, HL) and low (35 μmol m−2 s−1, LL) light conditions. We compared various isolation procedures of membrane bound light harvesting complexes (LHCs) and assayed the functionality of the solubilized proteins by determining the energy transfer efficiency from the accessory pigments to Chl a by means of fluorescence excitation spectra. The identity of the newly isolated protein-complexes were confirmed by immunological cross-reactions with antibodies raised against the previously described membrane bound Chl a-c proteins (Boczar et al. (1980) FEBS Lett 120: 243–247). Spectroscopic analysis demonstrated the relatedness of these proteins with the recently described Chl-a-c2-peridinin (ACP) binding protein (Hiller et al. (1993) Photochem Photobiol 57: 125–131; Iglesias Prieto et al. (1993) Phil Trans R Soc London B 338: 381–392). The water-soluble peridinin-Chl a binding-protein (PCP) was not detectable in P. minimum. Two functional forms of ACP with different pigmentation were isolated. A variant of ACP which was isolated from high-light grown cells, that specifically binds increased amounts of diadinoxanthin was compared to the previously described ACPs that bind proportionately more peridinin.

Presentation of the optical sensor OPTISENS designed for Eulerian measurements of phytoplankton on a moored buoy

Since 1988 a newly designed transmissometer (OPTISENS) has been used along the southern Norwegian coast to monitor phytoplankton blooms. The instrument has been suspended on a buoy equipped with an ARGOS PTT for satellite transmission of data. The OPTISENS is a light beam transmissometer with 3 different colors of the light, i.e. red, green and blue with peak wavelengths at 650 nm, 555 nm and 470 nm, respectively. Long-term measurements in the sea and laboratory experiments of in vivo absorption- and fluorescence excitation spectra, have demonstrated that it not only can distinguish between different particles but also identify of different groups of bloom-forming phytoplankton, some of which are toxic. The attenuation coefficient ratios between the colors blue, green, yellow and red will be discussed for different phytoplankton groups.