PHOTOTACTIC AND PHOTOKINETIC ACTION SPECTRA OF THE DIATOM NITZSCHIA COMMUNIS

Abstract— Three different types of photomotion reactions, photokinesis, photo-topotaxis and photo-phobotaxis, have been investigated in the diatom Nitzschia communis . In photokinesis the active light appears to be absorbed by the photosynthetic pigments. Apparently, the acceleration of movement by light is due to an additional ATP supply from photosynthetic phosphorylation, as it is the case in the blue-green algae of the genus Phormidium . On the other hand, no correlations exist between photo-phobotaxis and photosynthesis, because red light does not induce photo-phobotactic responses in N. communis . The phobotactic action spectrum resembles that one of photo-topotaxis. In the visible region only violet, blue and blue-green light is active in both the reactions. However, it is not yet clear whether or not the stimuli are mediated by the same photoreceptor, mainly because of the different sensitivity of both the reactions to u.v.