PHOTOMOVEMENT RESPONSES OF PORPHYRIDIUM PURPUREUM

The influence of light quality on positive phototopotaxis by the gliding, unicellular red alga Porphyridium purpureum was obtained using interference filters. Cells exposed to 3 × 10⁻⁷ mol · m²· s⁻¹ of various wavelengths for 72 h showed maximum topotaxis at 420 and 440 nm. The lower threshold for positive, movement was approximately 5 × 10⁻⁸ mol · m⁻²· s⁻¹. Random movement occurred at nonactinic wavelengths, and no movement occurred in the dark. Cell motility appeared to be unaffected by light polarity, suggesting that the photoreceptor(s) for topotaxis and photokinesis are randomly oriented.