FLUORESCENCE EXCITATION-SPECTRA AND LIGHT UTILIZATION IN 2 RED TIDE DINOFLAGELLATES

We compared the impact of structural changes in the light-harvesting m achinery of two bloom-forming dinoflagellates (Prorocentrum minimum an d Heterocapsa pygmaea) by quantifying photophysiological changes in or der to define the alternative mechanisms of photoacclimation. There ar e species-specific and photoacclimative differences in the abundance a nd composition of functional light-harvesting complexes (including pho tosystem 1- and 2-enriched bands) which are reflected in spectral chan ges in absorption, and photosystem 2 (PS2) fluorescence excitation spe ctra of whole cells, thylakoid micelles, and discrete photosynthetic p igment-protein complexes. DCMU-induced variations in fluorescence exci tation spectra are evident in whole cells but not in isolated thylakoi d micelles or functional chromoproteins; such variations indicate that intracellular self-shading which causes variable fluorescence is elim inated in subcellular preparations. We developed a scaling procedure o f PS2-related in vivo fluorescence excitation spectra relative to Chi a-specific absorption coefficients and used the chromoprotein differen ces to illustrate how the chromoprotein composition alters cellular fl uorescence properties. We also examined the energy transfer efficiency of photosynthetic pigments and the photoprotective role and location of diadinoxanthin.