PHOTOINDUCED ELECTRIC CURRENTS IN CAROTENOID-DEFICIENT CHLAMYDOMONAS MUTANTS RECONSTITUTED WITH RETINAL AND ITS ANALOGS

Reconstitution of the photoelectric responses involved in photosensory transduction in ''blind'' cells of Chlamydomonas reinhardtii caroteno id-deficient mutants was studied by means of a recently developed popu lation method. Both the photoreceptor current and the regenerative res ponse can be restored by addition of all-trans-retinal, 9-demethyl-ret inal, or dimethyl-octatrienal, while the retinal analogs prevented fro m 13-cis/trans isomerization, 13-demethyl-retinal and citral, are not effective. Fluence dependence, spectral sensitivity, and effect of hyd roxylamine treatment on retinal-induced photoelectric responses are si milar to those found earlier in green strains of Chlamydomonas, althou gh an alternative mechanism of antenna directivity in white cells of r econstituted ''blind'' mutants (likely based on the focusing effect of the transparent cell bodies) leads to the reversed sign of phototaxis in mutant cells under the same conditions. The results obtained indic ate that both photoreceptor current and and regenerative response are initiated by the same or similar rhodopsins with arhaebacterial-like c hromophore(s) and prove directly the earlier suggested identity of the photoreceptor pigment(s) involved in photomotile and photoelectric re sponses in flagellated algae.