Photosynthetic Enhancement in the Diatom Phaeodactylum tricornutum

Enhancement phenomena in photosynthesis of the diatom Phaeodactylum tricornutum Lewin were studied by means of a Haxo oxygen electrode and 2 monochromatic light beams. It was necessary to correct for a minor non-linearity in rate oxygen evolution vs. intensity similar to that reported for Chlorella. Action spectra on complementary backgrounds and derived enhancement spectra were compared to in vivo absorption spectra in identifying the character of pigment systems 1 and 2. Fucoxanthin, chlorophyll c, and chlorophyll a-670 are clearly assignable to pigment system 2 which absorbs in excess at wavelengths 400 to 678 mμ. Chlorophyll a-1 (and a portion of the fucoxanthin) are assignable to pigment system 1 which absorbs in excess at wavelengths 678 to 750 mμ. Enhancement values were generally lower than those observed in Chlorella or Anacystis and lead to conclusion that diatom pigmentation provides an effective light harvesting apparatus.