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

Operational and maximum quantum yields for photosystem II (PSII) charg e separation, oxygen evolution, and carbon fixation were quantified an d compared for Heterocapsa pygmaea Loeblich, Schmidt et Sherley popula tions chromatically adapted to white, green, blue, and red light. Sign ificant variability in quantum yields was induced by chromatic adaptat ion alone or when chromatically adapted cells were suddenly exposed to biased light fields (i.e. white light). Results indicated a close cou pling between the variability in quantum yields for PSII charge separa tion and oxygen evolution, but not between quantum yields for oxygen e volution and carbon fixation. The ability to regulate and optimize lig ht energy distribution between PSII and photosystem I (PSI) appears to be the mechanism underlying chromatic adaptation for PSII charge sepa ration and oxygen evolution. Conceptually, the resulting impacts on PS I cyclic electron transport rates could account for observed variabili ty in quantum yields for oxygen evolution and some variability in quan tum yields for carbon fixation. Similarly, enzymatic processes associa ted with organic carbon synthesis appeared to be variably dependent on spectral growth irradiances and contributing to the observed variabil ity in quantum yields for carbon fixation. The relevance of these find ings to the bio-optical modeling of light-saturation constants (I(k)) and in situ primary production is discussed.