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 accu rately reconstruct whole cell absorption spectra for photosynthetic di noflagellates, were assessed. Measured spectral absorption properties (400 to 700 nm) included signatures from whole cells, dispersed thylak oid fragments (unpacked absorption), isolated chromoproteins and indiv idual 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 mi nimum and Heterocapsa pygmaea grown in continuous light at 15 degrees C. For model verification, we also developed a procedure to measure un packaged cell absorption, free of solvent and light-scattering effects . Maximum measured chl a-specific absorption at 675 nm appears to be c loser to 0.027 than a predicted value of 0.0203 m(2) mg(-1) chl a base d on absorption from chl a in 90 % acetone. The percent fractional abs orption of 'in vivo' weight-specific absorption coefficients of indivi dual pigments relative to total weighted absorption (all pigments) was estimated to indicate the light-harvesting capabilities of the differ ent pigments as a function of photoadaptive status and water color. Co rrespondingly, the weighted absorption of each pigment fraction has be en estimated in theoretical white Light and in 'clearest' green coasta l and blue oceanic waters. Independent of water color, peridinin was b y far the most important light-harvesting pigment, followed by chl c(2 ) and chl a. The photoprotective diadinoxanthin absorbed most efficien tly in the blue part of the visible spectrum. Results indicate that th e chromoprotein model (1) overcame spectral distortions inherent in mo re general pigment-dependent models and, when combined with correction s for pigment packaging effects, (2) provided accurate spectral estima tes of in vivo absorption coefficents and (3) worked equally well for dinoflagellate species with or without the major light-harvesting peri dinin-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 monitorin g of red tides.