Retinal identification in Pelvetia fastigiata.

Unidirectional blue light directs the rhizoid-thallus axis in the apolar zygote of the brown alga Pelvetia fastigiata. This effect is mediated by an increase in the intracellular concentration of cGMP. Here, we show the extraction, purification and identification of 1 microgram of all-trans retinal from 1.2 x 10(6) Pelvetia zygotes. The number of retinal molecules per cell was about 4 x 10(9). Since retinal, wherever present, is exclusively associated with an opsin to form a light sensitive complex (rhodopsin-like proteins), and since the physiological response originated by this protein produces a variation of cGMP concentration, this new finding suggests that a rhodopsin-like protein could be the photoreceptor in this brown alga.