Photomovement in Dunaliella salina: fluence rate-response curves and action spectra.

We determined the action spectra of the photophobic responses as well as the phototactic response in Dunaliella salina (Volvocales) using both single cells and populations. The action spectra of the photophobic responses have maxima at 510 nm, the spectrum for phototaxis has a maximum at 450-460 nm. These action spectra are not compatible with the hypothesis that flavo-proteins are the photoreceptor pigments, and we suggest that carotenoproteins or rhodopsins act as the photoreceptor pigments. We also conclude that the phototactic response in Dunaliella is an elementary response, quite independent of the step-up and step-down photophobic responses. We also determined the action spectra of the photoaccumulation response in populations of cells adapted to two different salt conditions. Both action spectra have a peak at 490 nm. The photoaccumulation response may be a complex response composed of the phototactic and photophobic responses. Blue or blue-green light does not elicit a photokinetic response in Dunaliella.