CHROMOPROTEIN-DEPENDENT AND PIGMENT-DEPENDENT MODELING OF SPECTRAL LIGHT-ABSORPTION IN 2 DINOFLAGELLATES, PROROCENTRUM-MINIMUM AND HETEROCAPSA-PYGMAEA

Pigment- and chromoprotein-dependent spectral models, designed to accurately reconstruct whole cell absorption spectra for photosynthetic dinoflagellates, were assessed. Measured spectral absorption properties (400 to 700 nm) included signatures from whole cells, dispersed thylakoid fragments (unpacked absorption), isolated chromoproteins and individual pigments from high (500 mu mol m(-2) s(-1)) and low (35 mu mol m(-2) s(-1)) light-adapted cells of the dinoflagellates Prorocentrum minimum and Heterocapsa pygmaea grown in continuous light at 15 degrees C. For model verification, we also developed a procedure to measure unpackaged cell absorption, free of solvent and light-scattering effects. Maximum measured chl a-specific absorption at 675 nm appears to be closer to 0.027 than a predicted value of 0.0203 m(2) mg(-1) chl a based on absorption from chl a in 90 % acetone. The percent fractional absorption of 'in vivo' weight-specific absorption coefficients of individual pigments relative to total weighted absorption (all pigments) was estimated to indicate the light-harvesting capabilities of the different pigments as a function of photoadaptive status and water color. Correspondingly, the weighted absorption of each pigment fraction has been estimated in theoretical white Light and in 'clearest' green coastal and blue oceanic waters. Independent of water color, peridinin was by far the most important light-harvesting pigment, followed by chl c(2) and chl a. The photoprotective diadinoxanthin absorbed most efficiently in the blue part of the visible spectrum. Results indicate that the chromoprotein model (1) overcame spectral distortions inherent in more general pigment-dependent models and, when combined with corrections for pigment packaging effects, (2) provided accurate spectral estimates of in vivo absorption coefficents and (3) worked equally well for dinoflagellate species with or without the major light-harvesting peridinin-chlorophyll-protein complex, PCP. Findings are discussed in the context of modeling of bio-optical characteristics in dinoflagellates, their photoecology and implications for the in situ optical monitoring of red tides.