Photosensory transduction in the flagellated alga,Euglena gracilis

Euglena were cultured under 3 W m^-2 constant white light. In culture medium, cells show immediate and long lasting step-down photophobic responses and photoaccumulation behavior to blue light if dim red light-adapted for 30 min. However, if cells are suspended in buffered, saltcontaining solutions (adaptation buffers), strong step-down photobehavior and photoaccumulation responses are not observed for several hours. These behaviors gradually increase in strength to reach a maximum after 6–12 h; after which a stable response is maintained. The relative rates of appearance and the relative strengths of the responses are influenced by the concentrations of Ca²⁺ and K⁺, but not H⁺ or Na⁺ ions, in the adaptation buffers. Expression of the stepdown photobehavior thus requires that the cells adapt to the chemical environment in which they are suspended.Abbreviations Hepes N-2-hydroxypiperazine-N-2-ethanesulfonic acid - Mes 2(N-morpholino)-ethanesulfonic acid - Pipes piperazine-N,N-bis (2-ethanesulfonic acid) - Taps tris(hydroxymethyl) methylaminopropanesulfonic acidThis work was supported, in part, by grant No. PCM-79-05320 from the U.S. National Science Foundation to B.D.