Effects of light quality on chlorophyll-forms Ca 684, Ca 690 and Ca 699 of the diatom Phaeodactylum tricornutum.

Colored light modifies the relative concentration of chlorophyll-forms of the diatom Phaeodactylum tricornutum compared to white-light control. No change in the ratio carotenoids/chlorophylls was observed after 4 days exposure to green light (max: 530 nm), blue light (max: 470 nm) or red light (λ > 650 nm) of same intensity.However, the absorption spectra were modified, the content in Ca 684, Ca 690, Ca 699 forms increased in red and green light cultures and photosynthetic unit size of PS II decreased by 30% in green and blue light cultures.Fluorescence emission and fluorescence excitation spectra according to the Butler and Kitajima method (1975) were carried out for each culture. Ca 669 form was predominant in the two photosystems. The newly appeared far red forms fluoresce at 715 nm like PS I forms.We conclude that these new forms originated in a rearrangement of PS II forms. They do not transmit excitation energy to reaction center of PS I and are disconnected from the other chlorophyll-forms of the photosynthetic antennae.